THE EFFECT OF HAFNIUM CONTENT ON THE TRANSFORMATION TEMPERATURES OF NI49TIS1-XHFX SHAPE-MEMORY ALLOYS

Ternary alloys of NiTiHf, having higher transformation temperatures th an binary NiTi shape memory alloys, have been produced and analyzed. B eginning with a base composition of Ni49Ti51, Hf was substituted for T i up to 30 atomic percent. Differential scanning calorimetry was used to determine the transformation temperatures of the as-cast alloys. Th e peak martensite temperature of the Ni49Ti51 alloy was 69 degrees C a nd increased to 525 degrees C for the Ni49Ti21Hf30 alloy. The peak aus tenite temperature of the Ni49Ti51 alloy was 114 degrees C and increas ed to 622 degrees C for the Ni49Ti21Hf30 alloy. An apparent minimum in the peak transformation temperatures occurred between 0 and 3 atomic percent Kf. Preliminary experiments were also conducted to determine t he effect of thermomechanical processing on the shape memory propertie s of the Ni49Ti41Hf10. Data are presented on the effect of cold work a nd heat treatment on the transformation temperatures of this alloy.