On the Formation of Stress-Induced Martensite in Ti-Al-Co Alloys

Abstract

The phenomenon of decrease of yield strength in Ti-4∼8%Al-2∼6%Co alloys quenched from β or α+β fields was investigated by tensile test, hardness measurement, microscopic observation and X-ray diffraction techniques. The remarkable decrease of yield strength in alloys containing 2∼4%Co is due to the deformation caused by martensite formation. The stress required to form martensite has relation with the stability of retained β phase,and the stability of retained β depends principally on the content of Co. The reason why the formation of stress-induced martensite takes place in Ti-Al-Co ternary alloys and not in Ti-Co binary alloys is that in the ternary alloys aluminium inhibits the formation of ω phase.