Perspective Chapter: Titanium – A Versatile Metal in Modern Applications

Abstract

Titanium, a considerable metal renowned for its exceptional properties, has found its way into numerous industrial, medical, and aerospace applications. This chapter provides an overview of titanium’s unique characteristics, which include high strength-to-weight ratio, excellent corrosion resistance, and biocompatibility, making it an ideal choice for diverse engineering and medical purposes. In the aerospace industry, titanium’s low density and remarkable strength make it an essential material for aircraft components, from engine components to structural parts. Its resistance to corrosion in aggressive environments also renders it invaluable for marine applications. Medical fields have accepted titanium for orthopedic implants, dental fixtures, and surgical instruments due to its biocompatibility and ability to integrate seamlessly with living tissues. In addition to its medical and aerospace applications, titanium is used in the automotive industry for lightweight components that enhance fuel efficiency and reduce emissions.

1. Introduction

In recent decades, titanium has become one of the most valued and utilized materials across various technological and medical domains, owing to its exceptional properties. Initially discovered as dioxide in the year 1788 and extracted in its pure metallic form only by 1925, titanium has traveled a significant journey to become recognized as a revolutionary metal [1, 2, 3]. This chapter seeks to delve into the complexity and versatility of titanium, an element placed in the fourth subgroup of Mendeleev’s system, alongside thorium, hafnium, and zirconium, highlighting its indispensable role in contemporary innovations.

Titanium, with atomic number 22 and an atomic weight of 47.90, is distinguished by its white-silver color, remarkable tensile strength, impressive melting and boiling points, and superior mechanical and corrosion resistance properties compared to other metals. These features render titanium and its alloys as ideal materials for a broad spectrum of applications, ranging from aerospace to medical fields, where its biocompatibility is of significant importance [4, 5, 6].

The history of titanium alloys (Figure 1) begins within the context of titanium’s discovery and its evolving use as a metal in engineering and technology. Although pure titanium was initially isolated in its metallic form in the early nineteenth century, the development of titanium alloys truly commenced in the 1950s [7], when the demand for materials with enhanced performance in advanced applications became evident [5, 8].

Figure 1.

Timeline of the discovery and use of titanium.

Initially, titanium was considered a rare metal with limited uses due to the difficulties in extraction and processing. However, the discovery of its unique properties, such as exceptional corrosion resistance, an optimal strength-to-weight ratio, and biocompatibility, sparked interest in the development of alloys to optimize and extend these characteristics for specific applications [9, 10, 11].

In the 1950s and 1960s, with the development of the aerospace industry and space race, the demand for lightweight and strong materials increased significantly. Titanium alloys met this demand, providing ideal solutions for components of aircraft, rockets, and satellites, thanks to their resistance to extremely high temperatures and corrosion. For example, Ti-6Al-4 V, a titanium alloy with aluminum and vanadium, became one of the most utilized alloys due to its optimal balance between ductility, strength, and corrosion resistance [11].

As the processing technology for titanium evolved, other alloys were developed to meet the specific needs of various industries. In medicine, titanium alloys were adapted to maximize biocompatibility and fatigue resistance, essential for orthopedic and dental implants. In the chemical industry and marine applications, titanium alloys were optimized for maximum corrosion resistance.

Alloying elements play an important role in modifying and improving the properties of titanium alloys, allowing them to be adapted for a wide range of industrial and medical applications. By adding different elements to the chemical composition of titanium, the mechanical properties, corrosion resistance, ductility, and machinability of the alloys can be specifically adjusted. An example is the alloy Ti-6Al-4 V, valued in the aerospace and medical industry for its balance between strength and ductility. Another alloy, Ti-6Al-7Nb, is specifically used in medical implants, providing a biocompatible alternative to traditional alloys. Alongside the well-established and widely used titanium alloy systems in industry and medicine, there is ongoing research for the development of new alloy systems that offer improved properties for specific applications. Among these, also, new titanium alloy systems are under research: Ti-Mo-Si, Ti-Mo-Zr-Mn, Ti-Mo-Zr-Ta, and Ti-Mo-Zr-Ta-Si. These alloy systems demonstrate the versatility of titanium and its capacity to be customized for specific needs (Figure 2) [4, 12, 13, 14].

Figure 2.

Development trends of titanium alloys.

Thus, the development of titanium alloys has been strongly associated with both industry-specific requirements and advances in technology. The defining characteristic of this process has been the ongoing collaboration of scientists, engineers, and technicians who have investigated and expanded the possibilities of this adaptable metal. With new studies focusing on enhancing mechanical qualities, creating shape memory alloys, and investigating potential in cutting-edge biomedical applications and green technology, titanium alloys continue to play a vital role in innovation today [1, 2, 9, 15, 16].

The classical methods of elaboration of Ti-based alloys for aerospace, biomedical implants, and military applications are arc remelting (VAR and EBM), selective laser melting (SLM), atomization, cold hearth melting, plasma arc welding, hot isostatic pressing (HIP), rotary forging, centrifugal casting, and sheet metal forming.

This chapter will explore the evolution of titanium’s application in technology and medicine, highlighting its pivotal role in engineering innovation. It will also provide an in-depth analysis of titanium’s distinctive features that contribute to its high value. In addition, we will investigate titanium alloys, the manufacturing techniques that enable its full utilization, and analyze specific applications that gain from the benefits provided by this metal [17].

Hence, this chapter will not only demonstrate the significance of titanium in the contemporary world but also emphasize its untapped capacity, opening up possibilities for novel findings and uses that have the potential to revolutionize the existing technical and medical domain.

2. The unique properties of titanium

Titanium, first identified in 1791 by William Gregor, is a metallic element with a silver-gray appearance and is relatively abundant in the Earth’s crust. It holds the 22nd position on the periodic table, under Group 4, and is the seventh most common element in nature (0.63%), following Al (8.8%), Fe (5.1%), Ca (3.6%), Na (2.64%), K (2.6%), and Mg (2.1%). It is part of around 100 minerals, with the most important being:

• Rutile, TiO₂

• Ilmenite, FeTiO₃ or FeO.TiO₂

• Titanomagnetite, Fe₃TiO₆ or Fe₃O₄.TiO₂

• Perovskite, CaTiO₃ or CaO.TiO₂

• Titanite (sphene), CaTiSiO₅ or CaO.TiO₂.SiO₂.

Ilmenite is the primary titanium mineral due to its high titanium content and ease of decomposition. Rutile, the richest titanium mineral, has been less important historically, but recent methods have made it possible to convert rutile into a very pure intermediate liquid product. Titanium production is costly due to its strong chemical bonds in existing compounds, its reactivity with many chemical elements, its absorption of gases, and the high costs associated with the metallothermic reduction of TiCl₄ using magnesium and sodium, as well as the purification and high-purity titanium production processes such as electrolysis or the iodide method. Despite its high cost compared to other metals, the benefits of using titanium are considerable.

Key physical properties of pure titanium are detailed in Table 1 [18, 19].

Property	Characteristic/Value
Color in solid state	Silver-white
Density at 25°C (α-Ti)	4.51 g/cm^3
Density at 900°C (β-Ti)	4.33 g/cm^3
Melting temperature	1668°C
Thermal expansion coefficient	9.1x10^−6/K
Specific heat at 25°C	0.523 J/g.K
Thermal conductivity at 25°C	17–22 W/mK
Surface tension at 1600°C	1.7 N/m
Elastic modulus at 25°C	108 GN/m^2
Tensile strength	450 MPa before casting and 850 MPa after casting
Yield strength	100–200 N/m^2; 15–20%
Hardness	160–190 HB, 80–105 HV

Table 1.

Physical properties of titanium.

Titanium is a refractory metal with a melting point of 1725°C and undergoes a polymorphic transformation at 882°C, from alpha titanium with a hexagonal close-packed structure to beta titanium with a body-centered cubic structure.

When it comes to mechanical properties, titanium and its alloys have very high specific strengths. These are higher than those of steels or precipitation-hardened aluminum alloys (compare to steels in terms of strength, but with a density over 45% lower; more than twice that of aluminum alloys, with only 60% higher density). Some titanium alloys, such as Beta C, exceed, after heat treatment, a tensile strength of 1400 MPa under conditions where the density does not exceed 4.5 kg/m³. However, very high strengths are found when alloying with a large amount of alloying elements, some of which have increased cytotoxic potential [20].

The mechanical properties of titanium distinguish it as a high-performance material, favored in many engineering and technological applications. These properties, which include tensile strength, ductility, fatigue resistance, and elastic modulus, contribute to its remarkable versatility and durability [21, 22].

The tensile strength of commercially pure titanium (with a minimum titanium content of 99%), which is characterized by excellent biocompatibility, does not exceed 550 MPa, even when it contains dissolved oxygen and nitrogen at the upper limit of the standardized range. For higher purity levels (over 99.5% Ti), the strength does not surpass 330 MPa. The hardness of pure commercial titanium does not exceed 265 HB (120 HB for grade 1 purity), and even high-strength alloys do not exceed 400 HB in the annealed state. This represents a disadvantage of titanium, which does not perform well in wear situations. Indeed, in the case of large joint prostheses (knee or hip), wear particles are responsible for many post-operative complications that can lead to implant failure.

The ductility of commercially pure titanium is good, especially in the annealed state, although its crystal structure is α in a compact hexagonal system. This phenomenon is due to the c/a ratio being close to the theoretical value of 1.633, which ensures a greater number of slip planes. The ductility of titanium is largely dependent on the dissolved amount of hydrogen, as well as oxygen and nitrogen. For the highest standardized purity for medical use (class 1, minimum 99.5% Ti), the elongation at break reaches 30%, and the reduction at break exceeds 35% at room temperature. A typical application benefiting from this ductility is surgical staples, used for viscerosynthesis or tissue clips. Regarding chemical properties, titanium is a highly reactive metal (immediately following aluminum in the activity series of metals). It reacts intensely in contact with gases, especially at high temperatures. It burns when heated in the atmosphere at temperatures above 610–650°C and even burns in pure nitrogen above 800°C, being one of the only elements to exhibit such behavior. This requires that the machining of precision parts that need an impurity-free surface, such as medical titanium accessories, is performed only in vacuums more advanced than 10–5 torr or in argon.

The excellent corrosion resistance of titanium is the property that determines its extensive medical use. It withstands all types of water, acid, or salt solutions, exhibiting behavior comparable to platinum in chemical corrosion. It presents some issues in contact with the ClO3 ion and cannot be heated in contact with halogens at temperatures above 550°C due to the so-called salt corrosion.

By combining these excellent properties, titanium proves to be an extremely valuable material for a wide range of applications, offering efficient and durable solutions that surpass the performance of traditional materials.

3. Titanium alloys

Titanium alloys represent a class of advanced materials that enhance and diversify the already remarkable properties of pure titanium, thus expanding the range of applications in which this metal can be used. By alloying titanium with other elements, such as aluminum, vanadium, molybdenum, zirconium, and others, alloys with specific mechanical, thermal, and chemical characteristics can be obtained, tailored to the particular needs of various industries.

Titanium alloys are generally classified into three main categories, based on the crystal structure and alloy composition (Figure 3).

• Alpha (α) alloys, these alloys contain alpha stabilizers, such as aluminum and oxygen, which improve high-temperature strength and corrosion resistance. They are characterized by good weldability and toughness at low temperatures.

• Beta (β) alloys contain beta stabilizers, such as molybdenum, vanadium, and niobium, which lower the beta-alpha transformation temperature, thereby improving ductility and workability. These alloys can be heat-treated to enhance strength.

• Alpha-Beta (α-β) alloys, the combination of alpha and beta stabilizers provides a balance between ductility and strength, making these alloys versatile and widely used, especially in the aerospace industry [23, 24].

Figure 3.

Titanium alloys classified by metallurgical structure.

Alloying elements can significantly influence the properties of titanium, transforming it for specific applications in various industries [25]. Titanium is known for its good properties, but adding alloying elements can improve other characteristics as well. In Table 2, some of the most common alloying elements and their effects on titanium are highlighted.

Element	Influence on titanium
Aluminum	the most common alloying element for titanium; it improves tensile strength and increases the ability to withstand high temperatures; most titanium alloys contain between 2.5 and 6.5% aluminum.
Vanadium	usually between 2% and 4%, increases the mechanical strength of titanium without greatly compromising ductility; titanium alloys containing vanadium are commonly used in the aeronautical industry and in orthopedic implants.
Molybdenum	added in percentages up to 3%, increases resistance to high temperatures and corrosion; it also helps maintain strength and ductility at low temperatures.
Zirconium	is added to improve corrosion resistance, especially in chemically aggressive environments; it can also be useful in improving the processability of alloys.
Tin	is used to improve corrosion resistance and increase the strength and hardness of titanium alloys.
Nickel	improve corrosion resistance in reducing environments and to increase mechanical strength.
Palladium and platinum	are used in small amounts to improve corrosion resistance in highly corrosive environments such as those in the chemical and petrochemical industries.

Table 2.

Influence of alloying elements on the properties of titanium.

Beta titanium alloys are highly significant in the medical domain owing to their distinctive characteristics:

• the biocompatibility of beta titanium alloys renders them exceptionally suitable for implants and medical devices, as they are well received by the human body and do not elicit unpleasant reactions. It is important for any material that is inserted into the body, as it decreases the likelihood of post-operative problems and rejection of the implant;

• beta titanium alloys provide exceptional corrosion resistance in biological settings, such as bodily fluids. Implants composed of these alloys exhibit long-term stability and resistance to degradation, guaranteeing both durability and lifespan. Corrosion resistance has an important role for durable implants like hip and knee replacements;

• as they possess excellent mechanical strength and changeable hardness that can be enhanced with heat treatments. As a result, they are capable of enduring significant amounts of pressure and operating effectively when subjected to physical strain. This quality makes them well-suited for use in orthopedic and dental implants, which must endure the forces generated during movement and chewing.

• they are utilized in a diverse range of medical applications: orthopedic implants include prostheses for the hip and knee, as well as plates and screws used for bone stabilization; dental implants consist of root implants and other prosthetic components; surgical instruments refer to equipment that are both lightweight and resistant to corrosion; vascular stents, on the other hand, include coronary stents and other devices used in cardiovascular procedures.

The development and use of titanium alloys continue to evolve, with ongoing research aimed at creating new compositions that offer enhanced performance for specific applications, opening new horizons in engineering and technology.

4. Applications of titanium alloys in the aerospace and maritime industries

In the aerospace industry, materials must meet rigorous criteria for performance and safety. Titanium alloy has been extensively utilized in various industries, including aerospace, military, chemical, medical, and offshore oil, due to its exceptional performance benefits. Often referred to as “space metal” “marine metal” and “smart metal”, titanium alloy is a new type of structural metal material pivotal in developing high-tech defense weapons and equipments. Many global powers recognize it as a strategic structural metal for the twenty-first century, essential to their military development. With the rapid and sustainable growth of national economies, the demand for titanium alloys in the aerospace and armament sectors in China has been increasing annually by 20 to 30%.

The United States developed the first titanium alloy (Ti-13 V-11Cr-3Al) in the 1950s that was truly used for flight, particularly in high-speed early warning aircraft. By the 1960s, titanium alloys had become widespread in military aeroengines and large-body jets like the Boeing 747. In the 1970s, titanium alloys accounted for about 80% of the total U.S. titanium alloy market. The 1980s and 1990s saw significant growth in the use of titanium and its alloys in aircraft in Europe and Russia, with Japan also showing a yearly increase in its use in aircraft.

Examples of titanium alloys used in the aerospace industry:

• Ti-6Al-4 V (Grade 5) is the most widely used titanium alloy in the aerospace industry due to its excellent combination of strength, ductility, and corrosion resistance. It is used in manufacturing aircraft structures, engine components, survival systems, and landing gear.

• Ti-6Al-2Sn-4Zr-2Mo, this alloy is valued for its high resistance to elevated temperatures and is used in aircraft engine components such as turbine disks and casings.

• Ti-3Al-2.5 V (Grade 9), this alloy is lighter and has better corrosion resistance compared to Ti-6Al-4 V. It is used in manufacturing tubes for hydraulic systems and other structural applications of aircraft that require good strength and reduced weight.

• Ti-5Al-2Sn-2Zr-4Mo-4Cr (Beta C), this beta alloy is known for its exceptional strength and ability to resist stress cracking. It is used in manufacturing aircraft structural components and in applications requiring high corrosion and cracking resistance.

• Ti-15 V-3Cr-3Al-3Sn (Grade 38) is a beta metastable titanium alloy, valued for its excellent formability at low temperatures and corrosion resistance. It is used in the production of cold-formed parts and in applications where good corrosion resistance and ease of fabrication are required.

In the fabrication of aircraft and spacecraft, particularly in situations where weight is a critical factor, titanium alloys are utilized to production of jet engine parts, including as compressors, turbines, and casings, because of their outstanding ability to withstand high temperatures and resist corrosion. Titanium alloys offer both strength and lightweight, making them advantageous for many aircraft components such as skeletons, fuselage panels, and fasteners. Within the space sector, these components are utilized to endure and tolerate drastic fluctuations in temperature and pressure. They provide exceptional performance and reliability even in the most challenging operational circumstances. Titanium plays an important role in the construction of an aviation engine by providing essential components such as fan blades, fan case, fan disk, and low-pressure compressor blade/stator vane/disk [26, 27].

Titanium and its alloys are extensively used in marine industries due to their distinctive characteristics, such as superior strength, low weight, and extraordinary resistance to corrosion caused by seawater. These materials have a higher level of resistance to corrosion compared to various metals, including aluminum and stainless steels. As a result, they are often selected in harsh settings where they are exposed to salt water and significant temperature fluctuations. Titanium alloys exhibit exceptional mechanical strength even at elevated temperatures, making them highly desirable for use in engine components.

But the use of titanium is valuable in the marine industry not only for their resistance to corrosion, but also for other properties that make them ideal, such as:

• Corrosion resistance, one of the most outstanding advantages of titanium alloys is their superior corrosion resistance, especially in environments exposed to chlorides such as seawater. It resists erosion, pitting corrosion and stress cracking, common problems in marine metal construction.

• Strength-to-weight ratio, these alloys offer one of the highest strength-to-weight ratios of all metals, making them extremely effective for lightweight structures and components, such as ship superstructures, that require materials that does not add significant extra weight.

• High-temperature resistance, titanium alloys maintain their strength and structural integrity at much higher temperatures. This property is useful for marine applications that may be exposed to intense heat sources or temperature variations.

• Biocompatibility, titanium is highly resistant to corrosion by marine microorganisms. This feature reduces the need for maintenance and cleaning, extending the life of marine structures.

Among the main applications of titanium in the maritime sector are [28]: in shipbuilding, titanium is used in parts of ships exposed to corrosive environments, such as propellers, propeller shafts, and the hull material of certain specialized ships. Its resistance to saltwater corrosion makes it an ideal material for these applications, extending the life of these parts and reducing maintenance costs; boat hulls and components are found in the construction of yachts, speedboats and other watercraft, and titanium can be used for structural parts, including the keel and mooring components, to increase strength and reduce maintenance; desalination plants, titanium is used in the construction of desalination plants, which turn seawater into drinking water. Its components, especially those involved in heat exchange processes, benefit from titanium’s corrosion resistance; underwater applications, because of its outstanding corrosion resistance and structural integrity, titanium is often used in underwater equipment and vehicles, including submarines, remotely operated underwater vehicles (ROVs) and underwater instrument housings.

Despite the significant advantages, titanium alloys also have some disadvantages. The high cost is one of their main disadvantages, given the price of the raw material and the complexity of the production process. Machining titanium alloys can also be difficult and expensive, as they require special tools and advanced machining techniques. In addition, titanium can suffer from embrittlement at cryogenic temperatures, limiting its use in space applications that require exposure to extremely cold conditions.

5. Applications of titanium alloys in the medical field

Titanium enjoys remarkable success in medical applications, owing to its exceptional biocompatibility, superior mechanical properties, and high resistance to corrosion. These characteristics make it ideal for various medical devices, including joint implants, bone screws, dental implants, and spinal fixation devices. The adaptability of titanium alloys to the human body minimizes the risk of rejection and increases the durability and success rate of medical implants, thus contributing to improved patient outcomes.

Titanium and its alloys are widely used in the medical field (Figure 4), primarily for manufacturing orthopedic implants, such as artificial knee and hip joints, plates, and screws for bone fracture fixation. Titanium is also chosen for dental implants due to its excellent biocompatibility and osseointegration capacity. In cardiology, titanium is used in stents and heart valves. Due to its corrosion resistance and anti-allergic properties, titanium is ideal for long-term applications within the human body [29].

Figure 4.

Titanium alloys used in medical devices throughout the entire human body.

Titanium began to be used in medical applications in the 1950s, owing to its exceptional properties of biocompatibility and corrosion resistance. Initially, it was used in dental prostheses, and its use gradually expanded to other types of implants, such as orthopedic and cardiac implants. Due to its ability to integrate well with human bone (osseointegration), titanium has become the preferred material for many types of medical implants, significantly improving the quality of life for patients.

Titanium exhibits exceptional biological compatibility, contributing to the process of osseointegration, where bone tissue adheres directly to the implant surface without causing chronic inflammation. This is due to the formation of a layer of titanium oxide on the metal surface, which not only provides corrosion resistance but also promotes bone adhesion [1].

For medical applications, some of the most common titanium alloys are as follows:

• Ti-6Al-4 V (Titanium Grade 5), probably the most widely used titanium alloy in the medical field. It contains 6% aluminum and 4% vanadium and offers good mechanical strength and corrosion resistance. It is used for orthopedic implants such as hip or knee prostheses.

• Pure titanium (Titanium Grade 1 and Grade 2) is used especially for surgical implants, such as plates or screws used in reconstructive or maxillofacial surgery. It is preferred because it is biocompatible and corrosion-resistant.

• Ti-6Al-7Nb (Titanium Grade 7), this alloy contains niobium and is used especially for implants that require superior corrosion resistance. It is also biocompatible and has elasticity similar to bones, making it suitable for certain surgical applications.

• A fascinating aspect of titanium is its alloys with nickel, such as Nitinol-55, which exhibits shape memory; these can regain their original shape when heated above a certain temperature. This property is leveraged in various medical applications, including dentistry, cardiac surgery, and orthopedics, due to their excellent ductility at low temperatures, biocompatibility, and corrosion resistance [30, 31].

Biologically, titanium is non-magnetic, does not interfere with magnetic fields, and promotes regenerative processes, attracting calcium ions and favoring the formation of hydroxyapatite around the implant. Osseointegration represents another major advantage, with titanium establishing a strong bond with the surrounding bone.

However, titanium also has disadvantages, including a relatively low shear and wear resistance, as well as difficulties in the manufacturing process. Despite these challenges, the positive qualities of titanium, including its corrosion resistance, biocompatibility, and osseointegration capacity, make it the preferred material for numerous medical applications, from dental and orthopedic implants to artificial hearts and other surgical devices.

It is interesting to note that although titanium is widely used in medicine, the amount of titanium released into the body from an implant is thousands of times less than what is naturally metabolized by the human body daily, underscoring its safety and biological irrelevance in the context of implants [32, 33].

Therefore, the exceptional qualities of titanium, both in terms of its physical–mechanical and biological aspects, make it an essential material in the medical field, significantly contributing to the success of surgical interventions and improving the quality of life for patients.

New alloys from the TiMoZrTaSi system, such as Ti20Mo7Zr15TaxSi (where x = 0.5, 0.75, 1%) [4, 18], show significant potential for medical applications. These alloys are carefully engineered to possess essential properties for medical devices, including biocompatibility, low toxicity, and mechanical attributes similar to those of bone. Through experimental production, these alloys have demonstrated changes in mechanical properties with the addition of silicon, resulting in reduced hardness and a slight increase in the modulus of elasticity as silicon content increases.

Cytocompatibility assessments conducted on fibroblasts and osteoblasts revealed no adverse effects on cell proliferation or morphology after incubation with these alloys. In vivo studies confirmed their excellent biocompatibility and ability to facilitate bone remodeling without impeding new bone formation.

Similarly, alloys from the Ti15Mo7Zr15TaxSi system were developed, with a focus on their chemical and mechanical properties, as well as biocompatibility. These alloys showed high production efficiency and maintained the desired chemical composition. The addition of silicon improved mechanical properties, leading to increased hardness and modulus of elasticity.

In vitro cytocompatibility tests showed no cytotoxic effects, with a slight increase in cell viability at higher silicon concentrations. Further in vivo studies demonstrated enhanced osseointegration after implantation, along with significant bone remodeling activity in the peri-implant areas.

Additionally, biocompatible Ti-based alloys from the Ti20MoxSi system were developed by adjusting the silicon content while keeping molybdenum levels constant. These alloys exhibited improved mechanical properties with the incorporation of silicon, as evidenced by a decrease in modulus of elasticity and hardness.

Cytocompatibility tests confirmed positive interactions with both fibroblasts and osteosarcoma cells, without affecting cell growth or morphology. In vivo evaluations supported their compatibility with surrounding tissue and successful osseointegration, accompanied by notable bone remodeling near implant sites. This research highlights the potential of newly engineered titanium alloys for medical applications, demonstrating excellent biocompatibility, mechanical properties, and the ability to support bone integration and remodeling.

Furthermore, Ti-based alloys are attractive for biomedical applications due to their superior mechanical properties, corrosion resistance, and biocompatibility. Another study provides a comparative analysis of four novel Ti-based alloys designed for various biomedical implant applications: Ti15Mo7Zr5Ta, Ti15Mo7Zr15Ta, Ti15Mo0.5Si, and Ti15Mo1Si, alloys that incorporate non-toxic elements. The research included microstructural examinations, indentation tests, Vickers hardness assessments, X-ray diffraction (XRD) analysis, and evaluations of corrosion resistance. These analyses revealed attributes superior to those of many commercial implant materials, with Young’s modulus closely matching that of human bone.

There is a continuous global interest in advancing alloy research for medical and biomedical applications, aiming to improve traditional implant manufacturing technologies and biomaterial synthesis. This pursuit strives to introduce a new generation of multifunctional implants with long-lasting performance.

Biomaterials are intended to mimic or closely interact with living tissues, necessitating properties similar to human bone. The Young’s modulus of Ti-based alloys, ranging from 19.82 to 69.02 GPa, suits them well for implantology applications.

Surface analyses have revealed titanium oxidation, which forms an adherent oxide layer that passivates the alloy, leading to relatively low corrosion rates across alloys with uniform compositions. The inclusion of tantalum has been found to reduce both the modulus of elasticity and the corrosion rate, while silicon has shown beneficial effects at low percentages (below 0.5%) [34].

In conclusion, the characteristics of titanium alloys depend on the alloying elements, influencing their mechanical properties and biocompatibility. Elements such as molybdenum, zirconium, tantalum, and silicon, when combined with titanium, confer advantageous properties, promising a wide range of medical applications, including for dental and orthopedic implants.

Advancements in titanium alloys have been marked by innovative treatments and coatings, aiming to optimize their application in the medical field, particularly for implants. Among these, the application of zirconia coatings and hydroxyapatite/tricalcium phosphate via biomimetic methods have demonstrated promising enhancements in biocompatibility and mechanical properties [35].

Zirconia coatings on substrates such as Ti15Mo, Ti15Mo0.5Si, Ti15Mo0.75Si, and Ti15Mo1.0Si showcased uniform morphologies without microcracks, highlighting the presence of β-Ti and ZrO2 phases with a tetragonal crystalline structure. These coatings, notably devoid of un-melted zirconia compounds, exhibited an improved modulus of elasticity, significantly enhancing the alloys’ suitability for orthopedic implants by mimicking the mechanical properties of human bone more closely.

Furthermore, the impact of heat treatments on Ti-Mo-Zr-Ta alloys revealed important insights into microstructural optimization and mechanical property enhancement. Focusing on superficial hardening, these treatments have led to better wear behavior, fatigue, and corrosion resistance. The formation of β-type structures, aided by the precise inclusion of β stabilizing elements like molybdenum, tantalum, and silicon, results in a refined and evenly distributed microstructure, improving both hardness and elasticity modulus [36].

Additionally, the coating of HA/tricalcium phosphate on titanium surfaces using the biomimetic method has emerged as a groundbreaking advancement. This technique facilitates the formation of a bone-like apatite layer in simulated physiological conditions, enhancing the bioactivity and bacteriostatic properties of the implants. These coatings, characterized by nanometric crystals similar to natural bone, promise a leap forward in the biocompatibility and integration of titanium-based implants [37].

Surface wettability analysis further underscores the biocompatible potential of these treated alloys, with specific compositions exhibiting hydrophilic characteristics conducive to better interaction with living tissues.

These advancements underscore a multidirectional approach to enhancing titanium alloys for medical applications. By focusing on coatings that improve biocompatibility and mechanical properties, alongside heat treatments that optimize microstructure and wear resistance, the field is moving toward the development of more durable, reliable, and biologically harmonious implants.

Current trends in the development of alloys for medical applications focus on enhancing biocompatibility and reducing adverse effects in the body. Alloys with elements such as zirconium and tantalum, known for their reduced corrosion and minimal reactions with tissues, are being explored. Additionally, shape memory alloys are being developed for specific applications that require adaptability to the conditions of the human body. Another area of interest is the creation of nano-modified alloy surfaces to improve osseointegration and reduce the risk of infections.

6. Applications of titanium alloys in the automotive industry

Titanium, owing to its distinctive characteristics, has been utilized in significant capacities not only in the medical domain but also in the automotive sector. The utilization of this material in these industries is grounded on its remarkable resistance to corrosion, exceptional ratio of strength to weight, and resilience to high temperatures.

Titanium is highly prized in the automotive sector for its capacity to decrease the weight of vehicles, hence enhancing fuel efficiency and dynamic performance. Despite the expensive nature of titanium, it is frequently employed in the parts of high-performance automobiles, supercars and in the realm of auto racing, where its benefits outweigh the expense. Some specific applications of this material include manufacturing important engine components such as valves, valve springs, valve spring retainer seats, and connecting rods. The lower weight and high strength of titanium contribute to enhanced engine performance and efficiency, benefiting these components.

Chassis components are utilized in various applications such as springs, exhaust systems, axle shafts, and fasteners. These applications utilize titanium’s corrosion resistance, fatigue resistance, and strength.

Other applications include suspension springs, piston bolts, turbocharger rotors, fasteners, wheel nuts, bumper brackets, door beams, brake caliper pistons, bolts, clutch discs, pressure plates, and gear shift knobs. These components have the potential to greatly decrease the total weight of the vehicle, hence enhancing its performance and fuel efficiency.

Two major obstacles in utilizing titanium in the automobile sector are its exorbitant price and the complexities associated with the material and manufacturing processes. The primary obstacle impeding the extensive utilization of titanium in the automobile industry has been its high price. The process of titanium processing entails the melting, manufacturing, and utilization of various materials. The exorbitant expense of alloying elements also adds to the overall costs. The extraction and processing of titanium are challenging due to its high melting point and its reactivity with elements such as oxygen, hydrogen, nitrogen, and carbon. The conventional Kroll process utilized for manufacturing sponge titanium is characterized by high energy consumption, a lengthy production cycle, and the utilization of costly magnesium as a reducing agent.

In order to decrease manufacturing expenses, contemporary methods such as the utilization of titanium scrap and swarf for repetitive production have been implemented. These methods have been identified as efficient means to decrease the expenses associated with acquiring raw materials. Each incremental 1% rise in the utilization of titanium scrap results in a corresponding reduction of 0.8% in the manufacturing expenses associated with ingots.

7. Challenges and limitations

Although titanium is a material with many advantages, there are also challenges and limitations in its use, both in the previously mentioned industries and in general applications. These limitations are often related to its cost, processing difficulties, and performance considerations under certain conditions (Figure 5).

Figure 5.

Limitations of Ti alloys.

Despite these challenges and limitations, continuous innovations in technology and manufacturing processes contribute to cost reduction and improved efficiency in titanium processing. Additionally, the development of new alloys and surface treatments expands the scope of titanium applications, overcoming some of its initial limitations and paving the way for innovative and high-performance uses in various industries.

8. Future trends and innovations

Advancements in technology and ongoing research in materials science have paved the way for new trends and innovations in titanium usage. These developments promise to overcome some of the current limitations and expand the applicability of titanium across various industries.

Researchers are working on the development of new titanium alloys that offer an improved balance of strength, ductility, and corrosion resistance at varying temperatures. These new alloys are designed to outperform in specific applications, such as highly corrosive environments or high-temperature settings, thereby extending the use of titanium into new domains like advanced aerospace industry and renewable energy applications.

Innovations in materials processing, such as additive manufacturing (3D printing) and superplastic forming, are transforming how titanium can be utilized. 3D printing enables the creation of complex titanium components with minimal material waste and at reduced costs compared to traditional methods. This opens up new possibilities in the design of customized products, ranging from medical implants to specific parts for vehicles and aircraft.

Characteristics of 3D printed titanium alloys can exhibit exceptional mechanical strength, characterized by high tensile strength and favorable fatigue resistance. However, the specific properties may be subject to variation depending on the printing conditions and post-processing procedures employed. The microstructure of titanium alloys produced using 3D printing can exhibit greater complexity compared to alloys manufactured using traditional methods. The high-speed cooling rates and step-by-step manufacturing can lead to intricate microstructures and distinctive grain formations. A notable benefit of 3D printing is its capacity to create intricate geometries that are challenging or unattainable using traditional techniques. This encompasses lattice structures as well as interior channels. Generally, post-processing is necessary for 3D printed components to attain the intended surface finish and dimensional tolerances. This can encompass processes such as machining, polishing, or other forms of treatment [35, 36, 37, 38, 39].

There is a strong push toward improving titanium extraction and processing processes to make them more environmentally friendly. Titanium recycling is becoming a priority, with the development of technologies that enable efficient recovery and reuse of titanium waste. These innovations reduce environmental impact and make titanium more accessible and sustainable.

Titanium holds significant potential in the field of renewable energy, particularly in wind turbines and marine applications, due to its corrosion resistance in saline environments and material fatigue resistance. Developing titanium components for these systems can enhance their efficiency and durability, contributing to a more sustainable energy transition.

Innovations in the field of biomedicine are exploring the use of titanium in smart implants, which can monitor healing and release drugs at the implant site. These technologies promise to improve treatment outcomes and provide personalized solutions to patients.

The development of composite and hybrid materials that integrate titanium with other materials, such as carbon fibers or advanced ceramics, offers new perspectives for creating ultra-lightweight and high-performance components. These combine the superior properties of titanium with those of other materials to achieve improved performance in specific applications.

These trends and innovations underscore the titanium’s potential to play an even more significant role in future technology. By overcoming current challenges and exploiting new possibilities, titanium remains at the forefront of advanced materials development, offering innovative solutions for a wide range of industrial and technological applications.

Ongoing research in titanium alloys aims to overcome existing limitations by developing new compositions and processing techniques to reduce costs and improve material properties. Innovations in additive manufacturing (3D printing) promise to revolutionize how titanium components are produced, offering the ability to create complex shapes with material efficiency and reduced costs. Additionally, research in surface treatments and intermetallic alloys opens up new possibilities for the use of titanium in even more demanding conditions.

9. Conclusions

Titanium, owing to its unique combination of remarkable physical and chemical properties, has revolutionized many fields, from medicine and aerospace industry to automotive and maritime applications. However, its use comes with specific challenges, including high production costs, processing difficulties, and limitations in certain applications due to material properties. Despite these obstacles, continuous innovations in alloys, processing techniques, and recycling promise to further expand the uses of titanium, surpassing current limitations and opening new horizons for this versatile material.

Advancements in additive manufacturing, the development of new alloys, and advanced processing techniques, as well as the focus on sustainability and recycling, have the potential to reduce costs and make titanium more accessible for a wider range of applications. Additionally, exploring titanium’s potential in emerging fields such as renewable energy and biomedicine highlights its role in addressing some of the most pressing challenges of modern society.

In conclusion, titanium continues to be a frontier material, with significant potential to contribute to innovations in design, engineering, and technology. As research progresses and technologies develop, titanium is expected to maintain its position as an essential material, opening up new possibilities for the future of technological and industrial development.

Acknowledgments

“This work was supported by a grant of from the Ministry of Research, Innovation and Digitization, CNCS/CCCDI—UEFISCDI, project number ERA-NET-ERAMIN-3-Cool&SmartTit-1, contract no. 8/2024 within PNCDI IV.”

Conflict of interest

The authors declare no conflict of interest.