The Effect of Hafnium Content on the Transformation Temperatures of Ni49Ti51-xHfx. Shape Memory Alloys
Johnson Controls, Inc., Central Research Laboratory, 1701 W. Civic Dr. MS A-37, Milwaukee, WI 53209, U.S.A.
Ternary alloys of NiTiHf, having higher transformation temperatures than binary NiTi shape memory alloys, have been produced and analyzed. Beginning with a base composition of Ni49Ti51’, Hf was substituted for Ti up to 30 atomic percent. Differential scanning calorimetry was used to determine the transformation temperatures of the as-cast alloys. The peak martensite temperature of the Ni49Ti51alloy was 69°C and increased to 525°C for the Ni49Ti21Hf30 alloy. The peak austenite temperature of the Ni49Ti51alloy was 114°C and increased to 622°C for the Ni49Ti21Hf30 alloy. An apparent minimum in the peak transformation temperatures occurred between 0 and 3 atomic percent Hf. Preliminary experiments were also conducted to determine the effect of thermomechanical processing on the shape memory properties of the Ni49Ti41Hf10. Data are presented on the effect of cold work and heat treatment on the transformation temperatures of this alloy.
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