Ti-6Al-4V

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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).

Contents

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]

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. [4] These attractive properties were a driving force for the early introduction of a (cpTi) and a#b (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. [5] 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. %) [6]

V Al Fe O C N H Y Ti Remainder EachRemainder Total
Min3.55.5------------------
Max4.56.75.3.2.08.05.015.005Balance.1.3

Physical and Mechanical Properties

One possible microstructure of Ti-6Al-4V alloy with equiaxed alpha grains and discontinuous beta phase Ti64 20s rub krolls rod crossection.png
One possible microstructure of Ti-6Al-4V alloy with equiaxed alpha grains and discontinuous beta phase

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. [7] [8] [9] Aluminum stabilizes the alpha phase, while vanadium stabilizes the beta phase. [10] [11]

Density, g/cm3Young's Modulus, GPaShear Modulus, GPaBulk Modulus,GPaPoisson's RatioYield Stress, MPa (Tensile)Ultimate Stress, MPa (Tensile)Hardness, Rockwell CUniform Elongation, %
Min4.4291044096.80.3188090036 (Typical)5
Max4.512113451530.37920950--18

Ti-6Al-4V has a very low thermal conductivity at room temperature, 6.7 - 7.5 W/m·K, [12] [13] which contributes to its relatively poor machinability. [13]

The alloy is vulnerable to cold dwell fatigue. [14]

Heat Treatment of Ti-6Al-4V

Mill anneal, duplex anneal, and solution treatment and aging heat treatment processes for Ti-6Al-4V. Exact times and temperatures will vary by manufacturer. Common Ti-6Al-4V Heat Treatment Processes.svg
Mill anneal, duplex anneal, and solution treatment and aging heat treatment processes for Ti-6Al-4V. Exact times and temperatures will vary by manufacturer.

Ti-6Al-4V is heat treated to vary the amounts of and microstructure of and phases in the alloy. The microstructure will vary significantly depending on the exact heat treatment and method of processing. Three common heat treatment processes are mill annealing, duplex annealing, and solution treating and aging. [15]

Applications

Specifications

Related Research Articles

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References

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