Ti-6Al-4V (UNS designation R56400), also sometimes called TC4, Ti64,[1] or ASTM Grade 5, is an alpha-beta titanium alloy with a high specific strength and excellent corrosion resistance. It is one of the most commonly used titanium alloys and is applied in a wide range of applications where low density and excellent corrosion resistance are necessary such as e.g. aerospace industry and biomechanical applications (implants and prostheses).
Studies of titanium alloys used in armors began in the 1950s at the Watertown Arsenal, which later became a part of the Army Research Laboratory.[2][3]
A 1948 graduate of MIT, Stanley Abkowitz (1927-2017) was a pioneer in the titanium industry and is credited for the invention of the Ti-6Al-4V during his time at the US Army’s Watertown Arsenal Laboratory in the early 1950s.[4]
Titanium/Aluminum/Vanadium alloy was hailed as a major breakthrough with strategic military significance. It is the most commercially successful titanium alloy and is still in use today, having shaped numerous industrial and commercial applications.[5]
Increased use of titanium alloys as biomaterials is occurring due to their lower modulus, superior biocompatibility and enhanced corrosion resistance when compared to more conventional stainless steels and cobalt-based alloys.[6] These attractive properties were a driving force for the early introduction of α (cpTi) and α+β (Ti—6Al—4V) alloys as well as for the more recent development of new Ti-alloy compositions and orthopaedic metastable b titanium alloys. The latter possess enhanced biocompatibility, reduced elastic modulus, and superior strain-controlled and notch fatigue resistance.[7] However, the poor shear strength and wear resistance of titanium alloys have nevertheless limited their biomedical use. Although the wear resistance of b-Ti alloys has shown some improvement when compared to a#b alloys, the ultimate utility of orthopaedic titanium alloys as wear components will require a more complete fundamental understanding of the wear mechanisms involved.
Chemistry
(in wt. %)[8]
| V | Al | Fe | O | C | N | H | Y | Ti | Remainder Each | Remainder Total | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | 3.5 | 5.5 | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| Max | 4.5 | 6.75 | .3 | .2 | .08 | .05 | .015 | .005 | Balance | .1 | .3 |
Physical and mechanical properties
Ti-6Al-4V titanium alloy commonly exists in alpha, with hcp crystal structure, (SG : P63/mmc) and beta, with bcc crystal structure, (SG : Im-3m) phases. While mechanical properties are a function of the heat treatment condition of the alloy and can vary based upon properties, typical property ranges for well-processed Ti-6Al-4V are shown below.[9][10][11] Aluminum stabilizes the alpha phase, while vanadium stabilizes the beta phase.[12][13]
| Density | Young's Modulus | Shear Modulus | Bulk Modulus | Poisson's Ratio | Tensile Yield Stress | Tensile Ultimate Stress | Hardness | Uniform Elongation | |
|---|---|---|---|---|---|---|---|---|---|
| Min | 4.429 g/cm3 (0.160 lb/cu in) | 104 GPa (15.1×106 psi) | 40 GPa (5.8×106 psi) | 96.8 GPa (14.0×106 psi) | 0.31 | 880 MPa (128,000 psi) | 900 MPa (130,000 psi) | 36 Rockwell C (Typical) | 5% |
| Max | 4.512 g/cm3 (0.163 lb/cu in) | 113 GPa (16.4×106 psi) | 45 GPa (6.5×106 psi) | 153 GPa (22.2×106 psi) | 0.37 | 920 MPa (133,000 psi) | 950 MPa (138,000 psi) | -- | 18% |
Ti-6Al-4V has a very low thermal conductivity at room temperature of 6.7 to 7.5 W/m·K,[14][15] which contributes to its relatively poor machinability.[15]
Heat treatment of Ti-6Al-4V
Ti-6Al-4V is heat treated to vary the amounts of and microstructure of 
Applications
- Aerospace structures. The Boeing 787 is 15% titanium by weight,[19] and the Airbus A350 is 14%.[20]
- Biomedical implants and prostheses[21]
- High-performance race cars
- High-end bicycles
- Additive manufacturing[22]
- Apple iPhone 15 Pro (Max) case