Microstructure and Mechanical Properties of As-Cast Ti-Al-V Alloys with Different Proportion of α/β Clusters
The dual-cluster composition formula of the widely-used α + β Ti-6Al-4V and α-{[Al-Ti12](AlTi2)}12 + β-{[Al-Ti14](V2Ti)}5,reported in our previous work,indicates that all Ti alloys are com-posed of α and β units.In this study,Ti-(3.19-7.45)Al-(0-12.03)V(mass fraction,%)alloys are designed following composition formula of[Al-Ti12](AlTi2)}17-n + β-{[Al-Ti14](V2Ti)}n by changing n value(number of β cluster units).The alloys as prepared by copper mould suction-casting cover microstructures ranging from pure α to pure β.In the as-cast state,as the n value increases,the microstructure changes from sin-gle α phase(α'martensite),via α + β dual-phase,and finally to single β phase.The morphology of α'mar-tensite gradually changes from plate-like to lamellar and needle-like.Ti-6Al-4V alloy corresponds to n = 5,where β phase begins to appear.When n = 8,needle-like α'martensite shows the highest content.When n = 12,α phase disappears completely and is replaced by β phase.Correspondingly,the strength of the alloys increases first and then decreases,while the plasticity changes inversely,due to the pres-ence of fine-needle α'martensite.Among all the compositions,Ti-5.28Al-6.14V alloy(n = 8)shows the highest strength(about 90 MPa higher than Ti-6Al-4V),with tensile strength of 1019 MPa,yield strength of 867 MPa.Its specific strength and hardness of 230 kN·m/kg and 0.76 GPa·cm3/g increased by 9%and 5%,respectively,are both superior to Ti-6Al-4V.
titanium alloyTi-Al-Vcluster-plus-glue atom modelcomposition formulacomposition designmicrostructuremechanical property
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