Creep-fatigue interaction of a high temperature (α+β) titanium alloy at room temperature

TI-6Al-1.6Zr-3.3Mo-0.3Si (VT 9) is an (alpha+beta) titanium alloy of Russian origin designed for applications as compressor disc and blade ill jet engines for use upto the temperatures of 773K. These alloys are known to exhibit an appreciable amount of creep even at ambient temperatures. Thus creep and low cycle fatigue (LCF) interaction at room temperature is an important phenomenon during service. The beta transus temperature of this alloy is approximate to 1233K. The alloy was beta solution treated at 1293K for 0.5 hours and air cooled (AC). The AC material when aged at 973K for 12 hours is designated as ACA. The Coffin-Manson (C-M) plots for AC and ACA conditions showed dual slopes. These plots were placed correspondingly lower when compared to those of oil quenched (OQ) and oil quenched and aged (OQA) conditions reported in the literature. Thc hold period during LCF testing in OQ condition has caused higher percentage of reduction in fatigue life as compared to that in AC condition. While aging of the AC condition showed marginal effect on the fatigue life due to hold I,period. it is significant in OQ condition. The reduction in fatigue life in OQA condition due to hold period is comparable to that ii? AC condition. The behavior of the material under these thermally treated conditions can be explained based on the microstructural changes namely the clustering of silicide forming elements, formation of silicides on aging and enriching of alpha in alpha alloying elements.