Influence of Si on precipitation phenomena and age hardening of beta Ti alloy

The phase transformations occurring in a quenched and aged β-phase (bcc) Ti-40 at. pct V + 1 at. pct Si alloy have been investigated using transmission electron microscopy. Upon aging at 5700C, the most probable precipitation sequence is the following: bcc supersaturated solid solution → bcc zones → (Ti,V)/sub x/Si/sub y/ (hexagonal) → (Ti,V)3Si (tetragonal). The bcc precipitates may be considered Si-rich GP zones which are homogeneously nucleated and coherent with the matrix. The (Ti,V)/sub x/Si/sub y/ particles are a rod-shaped transition phase aligned along the (100) matrix directions. The precipitation reaction causes two peaks in the dependence of the yield stress or hardness upon aging time. The particle diameter and interparticle spacings of the hexagonal silicides indicate that these precipitates are responsible for the second hardness peak. The bcc zones evidently cause the first hardness peak at short aging times at 5700C