Titanium-Based Alloys: Classification and Diverse Applications

Abstract

Titanium-based alloys have emerged as pivotal materials across numerous industries due to their exceptional properties, including high strength-to-weight ratios, corrosion resistance, and biocompatibility. This chapter provides a comprehensive overview of the classification and diverse applications of titanium-based alloys, spanning aerospace, medical implants, automotive engineering, and beyond. Through case studies and technological advancements, the chapter elucidates the remarkable history of titanium alloys and their contributions to innovation, sustainability, and enhanced performance in various sectors. Special attention is given to Ti-6Al-4V, a widely utilized alloy renowned for its unique properties. Overall, this chapter offers insights into the widespread influence and promising future prospects of titanium-based alloys in shaping modern technological landscapes.

1. Introduction

Titanium, a versatile and robust metal, has been a cornerstone in various industries for over two centuries since its discovery by British mineralogist William Gregor in 1791. The development of Ti-6Al-4V, one of its most popular alloys, occurred successfully in the 1940s. Renowned for its exceptional properties such as high corrosion resistance, remarkable strength-to-weight ratio, and biocompatibility, titanium, and its alloys have found widespread applications across sectors ranging from aerospace to medical, chemical processing, offshore and marine engineering, power generation, medicine, transportation, architecture, and consumer goods [1, 2, 3, 4]. With a density approximately 60% lower than that of steel and superalloys, titanium exhibits remarkable lightweight properties. In addition to their remarkable resistance to corrosion, titanium and its alloys exhibit exceptional properties such as high fracture toughness, high-temperature strength, and an impressive strength-to-weight ratio [1]. Titanium alloys, despite being 45% lighter than standard low-carbon steels, surpass them in strength. They are only 60% heavier but twice as strong as soft aluminum alloys. Moreover, through alloying and deformation processing of Ti-alloys, substantial enhancements in strength can be achieved [1]. In this chapter, we will delve into the classification of titanium-based alloys, which is determined by both chemical composition and thermomechanical processing [2].

In addition, we will explore their diverse applications in detail, highlighting key examples and considerations.

2. Classification of titanium-based alloys

Titanium is available as commercially pure and as alloys. Pure titanium, in its elemental form, exhibits characteristics such as low thermal conductivity, relatively low density and elastic modulus, moderate strength, excellent corrosion resistance in diverse environments, and high reactivity with various elements. Table 1 provides a comparison of selected properties [2] of titanium with those of competing metals, where titanium shows outstanding properties among others. The microstructure and properties of these alloys are influenced by factors such as chemical composition and thermomechanical processing. At low temperatures, pure titanium adopts a hexagonal close-packed structure (hcp), known as α-titanium. However, at elevated temperatures, it transitions to a body-centered cubic (bcc) structure, referred to as β-titanium. Figure 1 shows the atomic unit cells of these structures. The β-transus temperature for pure titanium is approximately 882°C [5], which can vary with the presence of incorporated impurities [6]. The coexistence of these two crystal structures forms the basis for the diverse range of properties observed in titanium alloys. The alloying elements utilized in titanium alloys are categorized as neutral, α-stabilizers, or β-stabilizers [5, 6, 7] based on their impact on stabilizing α or β phases (as shown in Table 2). This table also delineates the position of the alloying element within the lattice crystal, which can be either interstitial or substitutional. α-stabilizers elevate the β-transus temperature, whereas β-stabilizers decrease it. Neutral elements exert minimal influence on the β-transus temperature. β-Stabilizers are further classified into β-isomorphous and β-eutectoid elements. The former promotes β phase stability across all alloy compositions, while the latter induces eutectoid transformations of the β phase [2]. Notably, aluminum serves as the primary α-stabilizer, while molybdenum ranks among the principal β-stabilizers. The α-stabilizers and their relative efficacy in stabilizing the α phase are quantified in terms of aluminum equivalence, with molybdenum holding similar significance for the β phase [8].

	Ti	Al	Ni	Fe
Density, g/cm^3	4.5	2.7	8.9	7.9
Melting point, °C	1670	660	1455	1538
Thermal conductivity, W/mK	15–22	221–247	72–92	68–80
Elastic modulus, GPa	115	72	200	215
Reactivity with oxygen	High+	High	Low	Low
Corrosion resistance	High+	High	Medium	Low
Cost	High+	High	High	Low

Table 1.

Physical properties of titanium and other selected contestant materials.

Figure 1.

The crystalline structure and phase transformation of elemental titanium.

	α-Stabilizer						β-Stabilizer					Neutral
					β-Eutectoid			β-Isomorphous
	Al	O	N	C	Mo	V	Fe	Cr	Mn	H	Ni	Sn	Zr
Substitutional	ο				ο	ο						ο	ο
Interstitial		ο	ο	ο			ο	ο	ο	ο	ο

Table 2.

Alloying elements used in titanium-based alloys.

According to their metallurgical structure, titanium-based alloys can be categorized into three main groups: alpha (α), alpha-beta (α-β), and beta (β). In addition, titanium-based alloys are subdivided into near alpha and metastable beta alloys (see Table 3) [1, 2]. Alpha alloys are primarily composed of α-phase structures, which include both pure titanium and alloys infused with α-stabilizers like aluminum and tin. These alloys are frequently utilized in aerospace applications due to their distinct characteristics, which balance strength and formability [9]. Notable examples of alpha alloys include ASTM Grades 1–4 and Ti/Pd alloys (ASTM Grades 7 and 11). Near alpha alloys exhibit a predominant α-phase with limited β-stabilizers, striking a balance between strength and formability, making them adaptable for various applications [10].

Category	Examples
Alpha alloys	Commercially pure titanium—ASTM Grades 1, 2, 3, and 4; Ti/Pd alloys—ASTM Grades 7 and 11; Ti-2Cu
Near alpha alloys	Ti-8Al-1Mo-1V; Ti-6Al-5Zr-0.5Mo-0.2Si-IMI 685; Ti-6Al-4Zr-3Sn-2Mo-0.08Si; Ti-5.5Al-3Zr-3.5Sn-0.3Mo-1Nb-0.3Si-IMI 829
Alpha-Beta alloys	Ti-6Al-4V; Ti-6Al-6V-2Sn; Ti-4Al-4Mo-4Sn-0.5Si; Ti-6Al-2Sn-4Zr-6Mo
Beta alloys	Ti-13V-11Cr-3Al; T-13V-11Cr-3Al; Ti-11.5Mo-6Zr-4.5Sn
Metastable beta alloys	Ti-3Al-8V-6Cr-4Mo-4Zr-Beta C; Ti-6V-6Mo-5.7Fe-2.7Al-TIMETAL 125; Ti-15V-3Cr-3Sn-3Al

Table 3.

Classification of titanium-based alloys with examples.

Alpha-beta alloys maintain an equilibrium between α and β phases, offering a blend of strength, ductility, and heat resistance that finds extensive usage across diverse industries [9]. Examples of alpha-beta alloys include the popular Ti-6Al-4V and Ti-6Al-6V-2Sn, known for their exceptional properties and widespread availability. Beta alloys are primarily composed of the β phase and are characterized by elements such as vanadium and molybdenum [11]. These alloys prioritize ductility over mechanical strength compared to alpha-beta alloys and find applications in specialized industries. Notable examples include Ti-13V-11Cr-3Al and Ti-11.5Mo-6Zr-4.5Sn. Beta metastable alloys, or near beta alloys, are chiefly composed of β phases with restricted α-stabilizers, prioritizing ductility over mechanical strength compared to α-beta alloys [12]. Moreover, Nitinol, although technically classified as a nickel-titanium intermetallic, is included among titanium alloys due to its widespread application in biomedical fields despite its high nickel content [13]. However, as it is an intermetallic rather than a traditional alloy, it will not be extensively discussed in this chapter. Additionally, Table 3 presents examples of alloys with varying chemical compositions, highlighting both underutilized and highly sought-after alloys like Ti-6Al-4V, renowned for its unique properties and significant demand across numerous industries. Understanding the classification and characteristics of these alloys is essential for selecting the appropriate material for specific industrial needs.

3. Applications of titanium-based alloys

Among the categories of titanium-based alloys, the α + β alloys hold the largest share at 70% in the US market. Globally, Ti-6Al-4V constitutes over 50% of titanium alloy consumption, while commercially pure titanium accounts for approximately 20–30% [5]. Although there are more than 100 known titanium alloys, only 20–30 have attained commercial status. Recently, there has been growing interest in titanium aluminides, particularly γ(TiAl)-based alloys, for aerospace and automotive applications.

Titanium and its alloys find extensive use across various industries, with selection criteria often based on corrosion resistance or strength requirements. Biocompatibility is also a critical consideration for biomedical implant applications. Commercially pure Ti (ASTM Grades 1–4) is commonly employed for corrosion-resistant applications due to its good corrosion resistance but relatively low strength. Grades 7, 8, and 11 are utilized for specific corrosion resistance needs. In the medical field, Grade 2 is preferred for low-strength applications, while Grade 5 (Ti-6Al-4V) is chosen for higher strength requirements [14]. For applications demanding high strength, titanium alloys like Ti-6Al-4V, Ti-8Al-1Mo-1V, Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-6V-2Sn, and Ti-10V-2Fe-3Al are utilized. Among these, Ti-6Al-4V stands out due to its unique combination of properties, workability, widespread production experience, and commercial availability. Consequently, it has become the benchmark against which other titanium alloys are compared when selecting for specific applications [14]. Let us explore some of the key applications of titanium-based alloys in detail:

3.1 Applications of titanium-based alloys in aerospace Industry

Titanium-based alloys have garnered significant attention and application in the major field of aerospace industry due to their exceptional properties, where their lightweight yet strong characteristics are highly valued, making them a preferred choice for various critical components. From structural components to jet engine parts and spacecraft components, these alloys contribute to enhanced performance, efficiency, and reliability in aerospace applications. This section explores the diverse applications of titanium alloys within aerospace, focusing on their structural, engine, fastener, and spacecraft applications [15, 16].

3.1.1 Structural components

Titanium alloys, notably Ti-6Al-4V, are extensively used in aerospace for structural components. Their high strength-to-weight ratio and corrosion resistance make them ideal for airframe structures, landing gear components, and other critical load-bearing parts in aircraft [17].

3.1.2 Jet engine components

In the realm of jet engines, titanium-based alloys find indispensable use. Their ability to withstand high temperatures and aggressive environments makes them suitable for turbine blades, discs, and casings, contributing to increased efficiency and reliability of jet engines [18].

3.1.3 Aerospace fasteners

Titanium alloys are extensively employed in aerospace fasteners due to their high strength, low weight, and excellent corrosion resistance. These alloys play a crucial role in securing critical components while minimizing overall weight, enhancing fuel efficiency, and ensuring structural integrity [19].

3.1.4 Spacecraft and satellite components

The lightweight nature and durability of titanium-based alloys make them indispensable in spacecraft and satellite construction. From structural components to thermal shields and satellite frames, these alloys ensure reliability and endurance in the harsh conditions of space [20].

The unique combination of properties possessed by titanium-based alloys has positioned them as vital materials in the aerospace industry. Their contributions to structural integrity, engine efficiency, fastening systems, and space exploration continue to drive advancements in aerospace technology [21].

Table 4 outlines various applications of titanium materials in aerospace, highlighting their advantages over aluminum alloys in terms of higher strength leading to weight savings. Titanium alloys are often substituted for aluminum alloys in areas where operational temperatures exceed the limits of aluminum. These areas include nacelles, auxiliary power units, and wing anti-icing systems. For instance, landing gear beams on aircraft like the Boeing 747 and 757 demonstrate the challenge of volume constraints, which can be addressed by utilizing titanium alloys despite their higher cost compared to aluminum. Titanium’s corrosion resistance obviates the need for painting in most cases, except when galvanic corrosion risk arises from contact with aluminum or low alloy steel components. For structures exposed to highly corrosive environments, such as the floor support under kitchens and lavatories, titanium ensures better structural durability. Some examples of commonly used titanium-based alloys in airframe structure such as floors, windows frames, landing gears and springs are: commercially pure titanium, Ti-6Al-4V, Ti-10V-2Fe-3Al, Ti-6-6-2, and Ti-15V-3Cr-3Sn-3Al. On the other hand, Ti-6Al-4V, Ti-6-2-4-2S, Ti-35V-15Cr, and TIMETAL21S are commonly used in parts of gas turbine engines such as compressor discs, compressor blades, fan discs and blades, compressor stators, and nozzle assembly. Moreover, Table 5 provides further details on the application of titanium materials in aerospace, categorized by alloy type, reinforcing the versatility and importance of titanium in this industry.

Material	Application
Commercially pure titanium	Airframe structure	Floors
Ti-6Al-4V		Windows frames
Ti-10V-2Fe-3Al; Ti-6-6-2		Landing gear
Ti-3Al-2.5V		Hydraulic tubing
Ti-15V-3Cr-3Sn-3Al		Springs
Ti-6Al-4V; Ti-6-2-4-2S	Gas turbine engines	Compressor disc
		Compressor blades
		Fan discs and blades
Ti-35V-15Cr		Compressor stators
TIMETAL21S		Nozzle assembly

Table 4.

Applications of selected titanium-based alloys in the aerospace industry.

Alloy type		Application
α Alloy	Commercially pure titanium	The annealed conditions for floor support structure in the areas of galley and lavatories.; Brackets and clips.; Pipes/tubes in the lavatory system.; Ducting for the anti-icing.; Environmental control systems at temperatures up to 230°C.
	Ti-5-2.5	The hydrogen side of the high-pressure fuel turbo-pump of the space shuttle.; The annealed condition for cryogenic applications.
	Ti-6-2-4-2S	Parts of gas turbine engine at temperatures up to 540°C.
	Timetal-II00 (Ti-6Al-2.8Sr-4Zr-0.4Mo-0.4Si)	Allison gas turbine engines, at temperatures up to 600°C.
	Ti-3Al-2.5V	High pressure hydraulic lines.; Fabrication of honeycomb core.
	Ti-8-1-1	Fan blades for military engines.; Tear straps on commercial airframes.
α + β Alloy	Ti-6Al-4V	Static and rotating components of gas turbine engines covering all sections of aircraft.; The floor support structure in galleys and lavatory areas.
	Ti-6-2-4-6	Moderate temperatures applications up to 315°C.; Military engines, for example F-119 and F-100.
	Ti-5Al-2Sn-2Zr-4Mo-4Cr	Fan and compressor discs below 400°C.
β Alloy	Ti-6Al-2Sn-2Zr-2Mo-2Cr + Si (Ti-6-22-22)	The Lockheed/Boeing F-22 program is as moderate strength-damage tolerant alloy.
	Ti-13V-11Cr-3Al (Ti-13-11-3)	Wing and body skins, bulkheads, rivets, frames, ribs, and landing gears of SR-71 airplane.
	Ti-10-2-3	The entire main landing gear of the 777.
	Ti-15-3	Springs from flat products, such as clock-type springs.; Strip is its primary product form.
	Alloy C	Exhaust structure and cast compressor components of F-119 engine that powers the Lockheed/Boeing F-22.

Table 5.

Applications of selected titanium-based alloys in the aerospace industry based on alloy type.

3.2 Applications of titanium-based alloys in medical devices and implants

In comparison to conventional stainless steel and Co-Cr alloys, the biocompatibility and corrosion resistance of titanium alloys make them ideal for medical implants and devices. Orthopedic implants like joint replacements, bone plates, and dental implants often use titanium alloys due to their ability to integrate well with human tissues and withstand the body’s harsh physiological environment [22, 23]. Utilizing a broad spectrum of available alloys, the biomedical industry predominantly relies on commercially pure titanium Grade 2 and Ti-6Al-4V Grade 5 for over 95% of titanium biomedical devices. Additionally, ELI (extra-low interstitials) alloys are prevalent in biomedical applications, boasting a chemical composition akin to the aforementioned alloys but with significantly reduced interstitial element levels. The diminished presence of interstitial elements, namely oxygen, nitrogen, hydrogen, and boron, within the alloy confers advantageous enhancements in material ductility and fracture toughness [24]. Various titanium alloys are employed in biomedical devices based on their specific function, size, shape, and anatomical location. This section will delve into the diverse biomedical applications, with a comprehensive list provided in Table 6 [25, 26, 27, 28, 29, 30, 31].

Material	Application
Commercially pure titanium, Ti-6Al-4V, Ti-6Al-7Nb, Ti-15Mo, Nitinol	Cardiovascular devices (heart connectors, valves, catheters, implantable defibrillators, ventricular assist devices)
Commercially pure titanium, Ti-6Al-4V, Ti-6Al-7Nb, Ti-15Mo, Ti-13Nb-13Zr, Nitinol	Orthopedic implants (hip and knee joints, meshes, bone substitute, fixation devices)
Commercially pure titanium (grades 1, 2, 3, and 4), Ti-6Al-4V, −titanium, Ti, Nitinol	Dental implants (braces, bridges, fixation devices, abutments)
Commercially pure titanium, Ti-6Al-4V, Ti-6Al-7Nb	trauma devices (screws, plates, nails, nodes)
	Soft tissue implants (breast reconstruction meshes, hernia meshes, fixation devices)

Table 6.

Medical applications of some titanium-based alloys.

3.2.1 Cardiovascular devices

Titanium alloys are also employed in cardiovascular devices such as stents, pacemaker cases, and heart valve components. Their biocompatibility and resistance to corrosion in bodily fluids make them suitable for these critical applications within the cardiovascular system [32]. Titanium and its alloys are integral to the advancement of cardiovascular devices, playing a pivotal role in enhancing patient outcomes for heart and vascular conditions. These alloys exhibit properties that make them highly suitable for devices aimed at restoring normal blood flow, improving cardiac function, and providing structural support [9].

In cardiovascular applications, titanium alloys are utilized in various devices, including coronary and peripheral vascular stents, which are employed to open narrowed or blocked arteries, thus restoring blood flow and preventing complications like heart attacks. Additionally, titanium alloys are used in artificial mechanical heart valves, replacing damaged tissue to ensure proper blood flow through the heart chambers.

The biocompatibility and corrosion resistance of titanium makes it an ideal material for enclosures housing pacemakers and implantable cardioverter-defibrillators (ICDs), safeguarding sensitive electronics from the harsh biological environment and external electromagnetic interferences. Unlike materials used in other medical devices, the choice of titanium for pacemakers and defibrillators is primarily driven by its chemical resistance and insulation capabilities rather than mechanical strength. Titanium can also be employed for electrode tips in these devices [33].

The mechanical properties of titanium alloys are crucial for cardiovascular applications, particularly in stents and mechanical heart valves. Stents, which maintain the openness of narrowed or blocked blood vessels, are typically made from metals such as titanium, stainless steel, platinum-iridium alloys, tantalum, and cobalt-chromium alloys. To prevent restenosis, stents are often coated with hard and anti-adhesive layers like titanium oxide and titanium nitride [9, 34].

Similarly, heart valves, subjected to mechanical loads, are coated with anti-adherent layers to prevent cellular adhesion and obstruction. Titanium alloys like Ti-6Al-4V, commercially pure titanium (Grade 2), and Nitinol find application in cardiovascular devices due to their mechanical strength, corrosion resistance, biocompatibility, and unique properties such as shape memory and super elasticity [9, 35, 36].

3.2.2 Orthopedic implants

Titanium and its alloys are instrumental in addressing the intricate requirements of musculoskeletal devices, ranging from joint replacements to fixation components [9, 37]. These materials have revolutionized the development of implants, seamlessly integrating with bone and significantly enhancing mobility, function, and overall quality of life for countless patients [28, 38]. Notably, titanium’s remarkable strength enables the fabrication of durable implants capable of withstanding physiological loads, ensuring stability and longevity in orthopedic settings.

While cobalt-chromium alloys have historically achieved similar outcomes in orthopedics, titanium offers two critical advantages: easier osseointegration and a higher strength-to-weight ratio, resulting in lighter implants [9]. Although titanium is utilized in various joint implants, it is never used as an articulating component due to limitations in wear and tribo-corrosion resistance. Instead, titanium excels as a material for load-bearing components, such as femoral stems and acetabular cups in hip replacements, providing essential stability and support to transfer mechanical loads to surrounding bone [9].

Beyond joint prostheses, titanium finds application in nonarticulating bone implants like ribcages, skull implants, spinal cages, and bone scaffolds, where minimal risk of tribological damage exists [39, 40]. These fixed devices benefit from titanium’s longevity and reliability, as they lack moving parts or surfaces in contact, reducing wear, friction-induced debris, and corrosion.

Several titanium alloys are approved for orthopedic use, including Ti-6Al-4V, Ti-6Al-7Nb, Ti-15Mo, Ti-13Nb-13Zr, and commercially pure titanium [9]. Each alloy offers unique properties suited for specific applications, such as load-bearing implants, spinal implants, bone screws, and fixation devices. Despite concerns like ion release and stress shielding, titanium alloys have demonstrated remarkable clinical success, with some implants lasting over three decades in challenging environments.

3.2.3 Dental prosthetics

The biocompatibility and corrosion resistance of titanium-based alloys makes them ideal for dental implants and prosthetics. These alloys are used in dental implants, crowns, bridges, and orthodontic appliances, offering durability and compatibility with oral tissues [41]. The utilization of titanium has brought about a transformative impact on both dental implants and orthodontic braces, leading to significant enhancements in patient outcomes and comfort [42]. Dr. Per-Ingvar Brånemark’s discovery of osseointegration, the direct bonding between bone and titanium surfaces, laid the foundation for titanium’s widespread use in dentistry and orthodontics [9].

Dental implants, particularly titanium posts, have become the preferred method for replacing missing teeth. Surgically placed into the jawbone, these posts gradually integrate with surrounding bone tissue, providing a stable foundation for prosthetic teeth. Dental implants not only restore chewing and speech functions but also prevent bone loss, preserving facial structure and overall oral health [43].

In orthodontics, titanium alloys are instrumental in creating braces, wires, and other devices due to their exceptional strength-to-weight ratio and corrosion resistance. These properties enable the application of controlled forces to move teeth into proper alignment, leading to effective and predictable outcomes [25].

The oral environment poses unique challenges for dental implants and orthodontic devices, including pH fluctuations and bacterial colonization. Titanium’s corrosion resistance and biocompatibility are critical in combating these challenges, ensuring the longevity and stability of dental devices.

Long-term clinical studies affirm the success of titanium-based dental devices, with impressive survival rates exceeding 95% over 10 years [26, 27]. The most common titanium alloys in dentistry include β-titanium alloys, Ti-6Al-4V, commercially pure titanium, and Nitinol, each catering to specific dental applications ranging from wires and brackets to bone plates and orthodontic archwires [9].

3.2.4 Surgical and trauma instruments

The strength, durability, and corrosion resistance of titanium alloys make them ideal for surgical instruments. These instruments include forceps, retractors, and scalpels, benefiting from the lightweight yet robust nature of titanium-based materials [44].

The most used titanium materials in surgical devices are mainly Ti-6Al-4V and commercially pure titanium, where the latter was considered to be the best biocompatible metallic material due to its surface properties enabling the spontaneous build-up of stable and inert oxide layer [45, 46]. Trauma devices, including bone plates, screws, and intramedullary nails, necessitate materials capable of withstanding significant mechanical stresses within the human body, often surpassing those experienced by orthopedic implants. Titanium, alongside cobalt-chromium and stainless steel, is commonly used in trauma devices despite being less mechanically robust, particularly under cyclic fatigue conditions [9]. Research suggests that titanium implants may have higher failure rates due to fracture compared to stainless steel alternatives, but they offer superior biological properties and lower infection risks [47]. However, the design of titanium implants must carefully consider anatomical location, as titanium’s softness can lead to the production of cytotoxic particulates through abrasive wear [9, 48, 49].

In screw designs, while thread fractures are rare, shaft fractures are relatively common, indicating weaker forces at the thread-bone interface compared to bending stresses on the shaft [50]. Additionally, the stress distribution differs significantly between locking and conventional plates. Locking plates, which anchor screws directly to the plate, offer enhanced stability but may increase mechanical stress on both bone and device, potentially leading to tissue damage [51, 52]. Despite these considerations, titanium alloys such as Ti-6Al-4V, Ti-6Al-7Nb, and commercially pure titanium remain the primary choices for trauma devices.

3.2.5 Challenges and considerations

However, Ti-6Al-4V offers excellent properties for many applications. Its relatively poor wear resistance makes it unsuitable for bearing surface applications without surface treatments [45].

Recent research has indicated that the elastic behavior of α + β titanium alloys like Ti-6Al-4V may not be ideal for orthopedic applications due to their mismatch with the elastic modulus of cortical bone [2]. This can lead to inadequate load transfer to the adjacent bone and subsequent degradation [53]. Furthermore, the presence of toxic elements like vanadium (V) and aluminum (Al) in Ti-6Al-4V alloy has raised concerns about biocompatibility. As a result, vanadium-free alloys such as Ti-6Al-7Nb and Ti-5Al-2.5Fe have been developed, offering improved biocompatibility, higher fatigue strength, and lower elastic modulus [45].

Efforts to develop alloys completely free of toxic elements have led to the creation of alloys like Ti-13Nb-13Zr, Ti-12Mo-6Zr-2Fe, and Ti-29Nb-13Ta-4.6Zr [54]. Authors suggest that suitable heat treatment and the addition of biocompatible alloying elements such as niobium (Nb), tantalum (Ta), and zirconium (Zr) to titanium are essential for achieving titanium alloys with optimal mechanical properties, including low elastic modulus and excellent biocompatibility [53, 55].

The versatility and biocompatibility of titanium-based alloys continue to drive innovation in medical device manufacturing. Ongoing research focuses on enhancing surface modifications and biodegradability and integrating advanced technologies to further improve the performance of these materials in medical applications [56]. To address certain challenges associated with conventional titanium alloys, Haase et al. [57] have developed two novel alloys, Ti-0.44O-0.5Fe-0.08C-0.4Si-0.1Au and Ti-0.44O-0.5Fe-0.08C-2.0Mo, characterized by medium to high strength. Notably, these alloys exclusively incorporate elements either found naturally in the human body or known to be biocompatible. Their study demonstrated exceptional mechanical properties, suggesting their potential as viable alternatives to Ti-6Al-4V for medical applications.

Titanium-based alloys have revolutionized the medical field, offering a unique combination of biocompatibility, strength, and corrosion resistance. Their applications in orthopedic implants, dental prosthetics, cardiovascular devices, and surgical instruments continue to improve patient outcomes and drive advancements in medical technology [23].

3.3 Applications of titanium-based alloys in automotive and marine applications

In the automotive industry, titanium alloys are used in exhaust systems, engine components, and other parts where high-temperature resistance, strength, and corrosion resistance are crucial. Similarly, in marine applications, titanium alloys’ resistance to corrosion in saltwater environments makes them suitable for components such as propeller shafts and hulls [58, 59].

3.3.1 Lightweight components

Titanium-based alloys contribute to reducing vehicle weight in both automotive and marine applications. Components such as valves, connecting rods, and exhaust systems benefit from the high strength-to-weight ratio of titanium alloys, enhancing performance and fuel efficiency [60].

3.3.2 Engine systems

In high-performance engines, titanium alloys are used in valve systems due to their excellent heat resistance, corrosion resistance, and strength at elevated temperatures. Titanium valves offer improved engine performance, reliability, and durability, especially in racing and high-end automotive and marine engines [61]. Ti-6Al-4V, γ(TiAl), Grade 2, and Ti-6Al-2S-4Zr-2Mo-0.1Si are commonly used alloys in parts of the engine [2, 61].

3.3.3 Corrosion-resistant parts

Titanium-based alloys are employed in marine environments for their exceptional corrosion resistance. Components exposed to saltwater, such as propeller shafts, hulls, and fasteners, benefit from the anti-corrosive properties of titanium alloys, extending their lifespan in marine applications [62].

3.3.4 Suspension systems

In automotive applications, titanium alloys such as Ti-6Al-4V, and Ti-6.8Mo-4.5Fe-1.5Al are utilized in suspension systems due to their high strength and corrosion resistance. Suspension components made from these alloys offer durability and enhanced performance under various road conditions [63].

3.3.5 Challenges and considerations

Titanium-based alloys play a pivotal role in automotive and marine applications, offering a balance of strength, corrosion resistance, and lightweight properties. Their use in lightweight components, engine systems, corrosion-resistant parts, and suspension systems contributes to improved performance, efficiency, and durability in vehicles and marine vessels [60]. However, the high cost of titanium alloys has historically limited their use in automobiles to racing and specialized vehicles, despite the automotive industry’s interest in their lightweight properties, fuel efficiency, and performance benefits. On the other hand, in recent years, there has been a growing adoption of titanium and its alloys for various automobile components (see Table 7) [2, 64]. A significant number of titanium intake valves, primarily made of Ti-6Al-4V alloy, have been installed in many cars and motorcycles [64]. Surface treatment has been a key challenge, with efforts focused on improving wear resistance through methods such as TiN coating, Mo thermal spray coating, and Cr plating [2]. These treatments, however, are costly and not always effective for prolonged wear resistance. As an alternative, an oxidizing treatment has been developed to enhance hardness by forming a thick, hardened layer through the diffusion of concentrated oxygen into the titanium surface layer.

Material	Application
Ti-6Al-4V	Engine	Intake valve; Connecting rods; Outlet valves
γ(TiAl)		Turbocharger rotors; Outlet valve
Grade 2		Exhaust system; Outlet valve
Ti-6Al-2S-4Zr-2Mo-0.1Si		Outlet valve
Ti-6Al-4V	Frame structure	Body; Armor; Suspension springs
Commercially pure titanium (Grade 4)		Body
Ti-6.8Mo-4.5Fe-1.5Al		Suspension springs

Table 7.

Automotive applications of some titanium-based alloys.

For exhaust valves, which endure high temperatures, the heat-resistant alloy Ti-6Al-2Sn-4Zr-2Mo-0.1Si (6242S) is commonly used. However, for mass-produced motorcycles subjected to even higher temperatures for extended periods, research has explored the application of TIMETAL@1100 (Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si), one of the most heat-resistant titanium alloys available. It was found that this alloy’s service temperature aligns with the requirements for motorcycle exhaust valves [2].

Table 8 outlines the adoption of titanium alloys by automakers in their industries, with weight reduction being a primary focus and benefit. Automobile manufacturers like Mitsubishi, Honda Motors, Toyota, and Nissan Motors adapted titanium alloys such as Ti-22V-4Al, Ti-6Al-4V, Ti-6Al-2S-4Zr-2Mo-Si, Ti-3Al-2.5V+REM, Ti-Al-Zr-Sn-Nb-Mo-Si/TiB, Ti-6Al-4V/TiB, and Ti-4.5Fe-6.8Mo-1.5Al that were introduced beginning in 1989 [64]. Ongoing research is also investigating new alloys for automobile parts, including Super-TIX, Super-TIX51AF (Ti-5%Al-1%Fe), Super-TIX800 (Ti-1%Fe-0.35%O-0.01%N), and TIMETAL@LCB (Ti-4.5Fe-6.8Mo-1.5Al), among others [64].

Material	Producer	Application
Ti-22V-4Al	Mitsubishi	AMG engine retainers of the Gallant 1
Ti-6Al-4V; Ti-6Al-2S-4Zr-2Mo-Si	Nissan Motors	Engine inlet and exhaust valves for the CIMA
Ti-3Al-2.5V + REM	Honda Motors	Connecting rods of sport car NSX
Ti-Al-Zr-Sn-Nb-Mo-Si/TiB; Ti-6Al-4V/TiB	Toyota	Intake and exhaust engine valves in the Altezza
Ti-4.5Fe-6.8Mo-1.5Al	Volkswagen	Suspension spring of Lupo FS
Titanium alloys	Kawasaki; General Motors	Muffler of the large sports-type motorcycle ZX-9; Dual mufflers of the Corvette Z06

Table 8.

Automotive applications and producers of some titanium-based alloys.

3.4 Applications of titanium-based alloys in sports equipment and consumer goods

The high strength-to-weight ratio of titanium alloys makes them attractive for sporting equipment like bicycle frames, golf clubs, and tennis rackets. Additionally, due to their esthetic appeal, corrosion resistance, and durability, titanium alloys are utilized in luxury goods such as watches, jewelry, and eyewear [65, 66].

3.4.1 Sports equipment

Titanium-based alloys offer a unique combination of strength and lightness, improving performance and endurance in sports gear. Titanium frames in bicycles, for example, provide high strength while maintaining a lightweight structure, enhancing maneuverability and speed [67]. The utilization of titanium in sports equipment has advanced significantly, ranging from early tennis and badminton rackets to modern golf heads, handles, racing bicycles, and even racing cars, marking a notable progression in the comprehension of titanium’s capabilities [67].

In golf, titanium’s lightweight and high strength properties have allowed for the creation of larger club heads without increasing overall weight, resulting in improved performance and distance for golfers. Innovative titanium alloys, such as those developed by Nippon Kokan KK, offer enhanced durability for golf head surfaces, contributing to their popularity in the market.

In tennis and badminton, the incorporation of titanium components, such as pure titanium nets and super-elastic titanium-nickel alloy handles, has bolstered racket performance, leading to increased hitting power and user satisfaction. Additionally, ongoing research into titanium fiber materials aims to leverage titanium’s rebound force to further enhance racket effectiveness [68].

Racing bicycles benefit from titanium’s lightness and strength, with titanium components reducing weight and wind resistance. Titanium bicycle frames, composed of industrial pure titanium tubes and sport-grade titanium alloys, have gained popularity among cyclists worldwide, especially in high-end bicycle sports [68].

In the realm of racing cars, titanium’s exceptional physical and mechanical properties have led to its widespread use in various components, including bolts, connecting rods, exhaust pipes, and brakes. The application of titanium contributes to reduced vehicle weight, lower fuel consumption, and improved environmental impact, showcasing titanium’s versatility and effectiveness in automotive engineering [68].

Furthermore, titanium finds applications in mountaineering and skiing equipment, where its lightweight and robust characteristics make it ideal for items such as mountaineering sticks, spikes, ski poles, and ice skates. Titanium’s use extends to fencing gear, fishing equipment, rowing parts, and track and field athletics spikes, highlighting its versatility across a diverse range of sporting goods [67, 68].

3.4.2 Watches and jewelry

Titanium-based alloys are increasingly popular in watchmaking and jewelry due to their durability, corrosion resistance, and hypoallergenic properties. Watches made from titanium alloys are lightweight, scratch-resistant, and highly robust. In jewelry, titanium alloys offer a modern esthetic, durability, and resistance to tarnishing, appealing to consumers seeking high-quality and long-lasting pieces [69].

3.4.3 Eyewear and fashion accessories

In the realm of fashion accessories, titanium-based alloys find application in eyewear frames and fashion accessories like wallets, belt buckles, and phone cases. The strength and lightweight nature of these alloys contribute to comfortable and durable products, appealing to consumers looking for stylish yet functional accessories [70].

3.4.4 Consumer goods

Titanium-based alloys are also employed in various consumer goods, including camping equipment, cookware, and electronic devices. The corrosion resistance, heat resistance, and lightweight properties of these alloys contribute to durable and high-performance consumer products [71].

Titanium-based alloys have found diverse applications in sports equipment and consumer goods, offering a balance of strength, durability, and lightweight properties. Their use in sports gear, watches, jewelry, fashion accessories, and various consumer products continues to drive innovation and cater to consumer demands for high-performance and long-lasting products [67].

3.5 Applications of titanium-based alloys in construction

Titanium-based alloys have emerged as innovative materials in the construction industry due to their unique properties, offering durability, corrosion resistance, and strength. This chapter explores the diverse applications of titanium alloys in construction, focusing on architectural structures, infrastructure, and specialty applications.

3.5.1 Architectural structures

Titanium-based alloys find application in architectural structures due to their esthetic appeal, durability, and corrosion resistance. The lightweight nature of these alloys allows for innovative and unique designs in buildings, facades, and artistic installations [72].

3.5.2 Infrastructure

In infrastructure projects, titanium-based alloys are utilized in bridge components, reinforcing bars, and cladding due to their corrosion resistance and long-term durability. These alloys contribute to extending the lifespan of structures exposed to harsh environmental conditions [73].

3.5.3 Specialty applications

Titanium alloys are used in specialty construction applications such as roofing materials, high-performance coatings, and seismic reinforcement due to their strength, lightness, and corrosion resistance. These applications contribute to enhanced structural integrity and longevity [74].

3.5.4 Sustainable construction

The use of titanium-based alloys in construction aligns with sustainability goals due to their recyclability, longevity, and resistance to corrosion. Their contribution to reducing maintenance and replacement needs aligns with sustainable construction practices [75].

Titanium-based alloys offer unique advantages in the construction industry, contributing to innovative architectural designs, resilient infrastructure, and specialty applications. Their properties of strength, corrosion resistance, and sustainability continue to drive their adoption in various construction projects [72].

4. Conclusion

Titanium-based alloys offer a wide range of applications across industries, driven by their unique combination of properties such as strength, lightweight, corrosion resistance, and biocompatibility. This chapter has provided a thorough examination of titanium-based alloys, showcasing their classification and extensive applications. The chapter contains collected and organized information from the most recent studies. By categorizing these alloys based on their metallurgical structure and alloying elements into three main groups (alpha, beta, and alpha-beta alloys) and two subcategories (near alpha and meta-stable beta alloys), engineers and researchers have unlocked a multitude of possibilities for their utilization across diverse industries. From aerospace to medical, automotive, sports, and construction, titanium alloys continue to revolutionize various sectors, contributing to advancements in technology, healthcare, and infrastructure. As research and development efforts continue to advance, titanium-based alloys are expected to play an increasingly significant role in shaping the future of engineering and materials science. With ongoing optimization of their properties and exploration of new applications, these alloys hold immense promise for driving innovation and revolutionizing industries worldwide.