Deformation of CoTi polycrystals

Deformation behaviour of polycrystalline B2-type CoTi intermetallic compounds was investigated in relation to testing temperature (77 to 1073 K), alloy composition (50 to 48 at.% Ti) and strain rate (4.2 x 10^–4 to 4.2 x 10^–3 sec^–1). Four distinct temperature regions were distinguished. A low-temperature region where the yield stress rapidly decreased with temperature; an intermediate temperature region where the yield stress increased with temperature, accompanied by very high strain-hardening rate, serration on the stress-strain curves and kink deformation; a high temperature region where the yield stress again rapidly decreased with temperature, and a very high temperature region where the yield stress slowly decreased with temperature. Deviation from stoichiometry resulted in increased yield stresses over whole temperature regions. Positive strain-rate dependence of the yield stress was regarded in the two higher temperature regions. Slip traces were observed at all temperatures. Possible explanations are given in comparison with other B2-type intermetallic compounds.