Effects of purity on high temperature mechanical properties of vanadium alloys

Creep tests of highly purified V–4Cr–4Ti alloy (NIFS-Heat) and V–10Cr–5Ti were examined using a purification technique of Zr heat treatment. The creep strain rate for highly purified specimens from the Zr-treatment was higher than for the original specimens. The effect of dynamic strain aging almost disappeared in the highly purified NIFS-Heat alloy containing less than 10 wppm oxygen. The result of the dissolution of precipitate bands and precipitates and removal of interstitial impurities was a decrease in the flow stress and ultimate tensile stress and a decrease of creep strength. These occurred at temperatures where the effect of dynamic strain aging can be seen in specimens containing above 170 wppm oxygen. The strain rate sensitivity parameters at a flow stress at 8% were negative even in highly purified NIFS-heat alloys, however their values were smaller than for specimens containing 150 wppm oxygen, and for data from previous work.