EFFECT OF IRON ADDITIONS ON MECHANICAL-PROPERTIES OF CO3TI ALLOY

High temperature tensile tests were carried out on Ll(2), type Co, Ti alloys, both undoped and doped with 1-4 at.-%Fe. There were anomalous increases of the 0.2% yield stress (yield strength) with increasing te st temperature from 473 to 1073 K (or 1173 K, depending on the composi tion). The elongation and ultimate tensile stress (UTS) monotonically decreased with increasing temperature. The fracture surfaces of specim ens showed a variety of fracture modes which were dependent on the tes t temperature and composition. There was a correlation between the duc tility and the fracture mode: the more transgranular the fracture mode , the higher the ductility. It was found that Co, Ti with 2 at.-%Fe ex hibited improved ductility and it exhibited the highest peak value of yield strength and peak temperature. The alloys were also hydrogen cha rged to investigate their hydrogen embrittlement behaviour. Room tempe rature tests indicated that the addition of 2 at.-%Fe decreased the hy drogen related embrittlement.