TYPES OF SUPERPLASTIC M-DELTA CURVES OF TI-6AL-4V ALLOY AND THEIR INTERTRANSFORMATION

The superplastic m-delta curves of Ti-6Al-4 alloy have been determined at different temperatures and strain rates; all were of the m(L)=m(max) type, and were of either fundamental, descending or ascending types. The latter two types were transformed from the former through the processes of M(L) --> M(o), delta(L) --> delta(o) and M(L) --> delta(F), respectively. The highest total elongation, delta(F), was 1150% obtained at 950-degrees-C and 1.55 x 10(-3) s-1. The Chin Liu equation has been applied to all types of m-6 curves. The parameters characteristic of all types of m-delta curves have been obtained and were found to vary with temperature and strain rate. The total elongation, delta(F), is determined by the resultant effects of all other parameters, not by a single m value, theoretically considered to be constant and determined practically by a tensile strain of about 30%-50% (m30%-50%) as usual.