Abstract:

Two near α titanium alloys Ti-5.6Al-4.8Sn-2.0Zr-1Mo-0.35Si (1#) and Ti-6.0Al-4.8Sn-2.0Zr-1Mo-0.35Si (2#) were solution-treated in the upper α+β phase fields and the duplex mixture microstructures consisting of the less volume fraction primary phase ( α_p) and the transformed phase (β_t) were obtained. The aging treatments were carried out at 700℃ for 1# alloy and 760℃ for 2# alloy under varied terms, respectively. It guaranteed 2 ordered phase to precipitate only in p but not in t for the two alloys. The slower precipitation and growth of the α₂ ordered phase and silicide was observed in 1# alloy in comparison with that in 2# alloy. The mechanical properties including tensile strength and ductility, the creep and lasting properties at the temperature of 600℃ were investigated. Prolonging aging time did not predominantly change the tensile strength and ductility for the two alloys. The 600℃/100h thermal exposure caused a notable decrease of tensile ductility in 2# alloy though no distinct decrease could be observed in 1# alloy after the thermal exposure. The lasting property of 1# alloy was increased with prolonging aging time and finally equal to or even better than that of 2# alloy. Nevertheless, No evident increase emerged in 2# alloy with prolonging aging time. Similarly, the creep property of 1 # alloy monotonously increased with increasing aging time and finally equal to or even better than that of 2# alloy. No evident increase could be observed for 2# alloy. It can be deduced that the overgrowth of α₂ ordered phase and silicide is unable to enhance hot strength properties but causes an unacceptable damage to tensile ductility. The optimum equilibrium of the comprehensive properties depending on the proper control of α₂ ordered phase and silicide can be achieved by selecting aging temperature and time.

Key words: Titanium alloy, Mechanical property, Aging treatment