Invar-type effect induced by cold-rolling deformation in shape memory alloys

Since the discovery of Fe-Ni alloys showing low thermal expansion (LTE) in 1896, many Invar alloys have been developed based on magnetovolume effect where negative thermal expansion is induced by magnetic transformation. Herein, we show that the control of stress-induced martensitic transformation due to cold working of the Cu-Zn-Al polycrystalline alloy results in the LTE. This type of LTE material is easily fabricated by conventional cold rolling, and the coefficient of thermal expansion in the range from about 0 to 32x10(-6) K-1 can be obtained by controlling the reduction ratio. The LTE effect due to the present method can also be obtained for other shape memory (SM) alloys such as Ni-Ti, Cu-Mn-Al and Ni-Al base alloys, which have high potential for various practical applications. (C) 2002 American Institute of Physics.