Effect of microstructure on the strength, toughness, and stress-corrosion cracking susceptibility of a metastable beta titanium alloy (Ti−11.5Mo−6Zr−4.5Sn)

This paper describes the influence of mictrostructure on the mechanical properties of the alloy Ti−11.5Mo−6Zr−4.5Sn. The phase transformations are similar to those that occur in binary Ti−Mo alloys containing 10 to 12 pct Mo. Thus, the β phase can be retained by quenching from above 1400°F. The β phase deforms in a complex manner, including mechanical twinning, and is characterized by low strength, high ductility, and high toughness. The ω phase, which also forms on quenching, is stable at temperatures up to 800°F. Yield strengths of up to 220 ksi have been measured in (β+ω) structures, the strength level being dependent on the size and volume fraction of the ω phase. In contrast, fracture toughness reaches a minimum value of }20 ksi\(\sqrt {in} \) when the ω particle size ≥100A. (β+α) structures show good combinations of yield strength and fracture toughness. Unfortunately, the best combinations are susceptible to stress-corrosion cracking in aqueous solutions containing halide ions.