High-Temperature Titanium Alloys and Their Classification and Properties

The world's first successful high-temperature titanium alloy was Ti-6Al-4V, with a service temperature of 300-350°C. Subsequent developments led to alloys like IMI550 and BT3-1, with service temperatures of up to 400°C, and IMI679, IMI685, Ti-6246, and Ti-6242, with service temperatures of 450-500°C. New high-temperature titanium alloys currently used in aircraft engines include the UK's IMI829 and IMI834 alloys, the US's Ti-1100 alloy, and Russia's BT18Y and BT36 alloys. In recent years, the development direction for high-temperature titanium alloys has focused on using rapid solidification/powder metallurgy technology and fiber or particle reinforced composites, which can increase the service temperature of titanium alloys to above 650°C. McDonnell Douglas in the US has successfully developed a high-purity, high-density titanium alloy using rapid solidification/powder metallurgy technology, with strength at 760°C comparable to that of titanium alloys used at room temperature.

Titanium-Aluminum Compound-Based Titanium Alloys

Compared with general titanium alloys, titanium-aluminum compound-based intermetallics Ti3Al (α2) and TiAl (γ) have advantages such as good high-temperature performance (service temperatures of 816 and 982°C, respectively), strong oxidation resistance, good creep resistance, and light weight (density is only half that of nickel-based superalloys). These advantages make them competitive materials for future aircraft engines and structural components. Currently, two Ti3Al-based titanium alloys, Ti-21Nb-14Al and Ti-24Al-14Nb-0.5Mo, have begun mass production in the US. Other recently developed Ti3Al-based titanium alloys include Ti-24Al-11Nb, Ti-25Al-17Nb-1Mo, and Ti-25Al-10Nb-3V-1Mo. TiAl (γ)-based titanium alloys are being studied for compositions ranging from TAl-(1-10)M (at.%), where M is at least one element from V, Cr, Mn, Nb, Mo, and W. Recently, TiAl3-based titanium alloys such as Ti-65Al-10Ni have started to attract attention.

High-Strength and High-Toughness β-Type Titanium Alloys

The first β-type titanium alloy was B120VCA (Ti-13V-11Cr-3Al), developed by Crucible in the mid-1950s. β-type titanium alloys have good hot and cold processing performance, are easy to forge, can be rolled and welded, and achieve high mechanical properties, good environmental resistance, and a good combination of strength and fracture toughness through solution and aging treatment. Representative new high-strength and high-toughness β-type titanium alloys include:

• Ti1023 (Ti-10V-2Fe-3Al): This alloy has performance comparable to the commonly used 30CrMnSiA high-strength structural steel in aircraft structural components and has excellent forging performance.
• Ti153 (Ti-15V-3Cr-3Al-3Sn): This alloy has better cold processing performance than industrial pure titanium, with a room temperature tensile strength of over 1000 MPa after aging.
• β21S (Ti-15Mo-3Al-2.7Nb-0.2Si): Developed by Timet, this alloy has excellent oxidation resistance and hot and cold processing performance and can be made into foil with a thickness of 0.064mm.
• SP-700 (Ti-4.5Al-3V-2Mo-2Fe): Developed by Japan Steel Pipe Company (NKK), this alloy has high strength and superplastic elongation of up to 2000%, with a superplastic forming temperature 140°C lower than Ti-6Al-4V, making it suitable for manufacturing various aerospace components using superplastic forming-diffusion bonding (SPF/DB) technology.
• BT-22 (Ti-5V-5Mo-1Cr-5Al): Developed in Russia, this alloy has a tensile strength of over 1105 MPa.

Flame-Resistant Titanium Alloys

Conventional titanium alloys have a tendency to ignite under specific conditions, significantly limiting their application. To address this, countries have conducted research on flame-resistant titanium alloys and made certain breakthroughs. Alloy C (also known as Alloy T), developed in China, with a nominal composition of 50Ti-35V-15Cr (mass fraction), is a flame-resistant titanium alloy insensitive to continuous burning and has been used in the F119 engine. BTT-1 and BTT-3, developed in Russia, are Ti-Cu-Al-based flame-resistant titanium alloys with good hot deformation processing performance, suitable for making complex parts.

Medical Titanium Alloys

Titanium is non-toxic, lightweight, high-strength, and has excellent biocompatibility, making it an ideal material for Medical Grade Titanium applications such as implants. Currently, Ti-6Al-4V ELI alloy is widely used in the medical field. However, the release of trace amounts of vanadium and aluminum ions reduces its cell compatibility and may harm the human body, which has long been a concern in the medical community. Since the mid-1980s, the US has been developing aluminum- and vanadium-free titanium alloys with biocompatibility for orthopedic applications. Japan, the UK, and other countries have also conducted extensive research and achieved new progress. For example, Japan has developed a series of α+β titanium alloys with excellent biocompatibility, including Ti-15Zr-4Nb-4Ta-0.2Pd, Ti-15Zr-4Nb-4Ta-0.2Pd-0.2-0.05N, Ti-15Sn-4Nb-2Ta-0.2Pd, and Ti-15Sn-4Nb-2Ta-0.2Pd-0.2. These alloys have better corrosion resistance, fatigue strength, and corrosion resistance than Ti-6Al-4V ELI. Compared to α+β titanium alloys, β titanium alloys have higher strength, better notch performance, and toughness, making them more suitable for implants. In the US, five β titanium alloys have been recommended for medical use: TMZFTM (Ti-12Mo-6Zr-2Fe), Ti-13Nb-13Zr, Timetal 21SRx (Ti-15Mo-2.5Nb-0.2Si), Tiadyne 1610 (Ti-16Nb-9.5Hf), and Ti-15Mo. It is expected that in the near future, these high-strength, low-modulus, and excellent formability and corrosion resistance β titanium alloys may replace the widely used Titanium 6AL4V ELI alloy in the medical field.