2-WAY SHAPE-MEMORY PROPERTIES OF A NI-RICH TI-NI ALLOY AGED UNDER TENSILE-STRESS

The strength of the ''all-round (two-way) shape memory effect'' and th e work we can gain by using this effect were investigated. The alloy u sed was a Ti-51 (at%)Ni alloy. In order to align particles of Ti3Ni4 p recipitate, plate-shaped specimens were aged at 773 K for 6 ks under s everal different tensile-stresses. Thermal cycling tests under several different tensile-stresses (sigma(Test)) were made on these aged spec imens. Specimens aged under an appropriate tensile-stress shrink in as sociation with the B2-->23R transformation and the total shrinkage dec reases with increasing sigma(Test). Due to this shrinkage, the specime ns do work on the outside: this work is the largest when sigma(Test) i s between 50 and 100 MPa. The B2--B19' transformation start temperatur e of these specimens decreases as sigma(Test) increases. In associatio n with the later R-->Br19' transformation, the aged specimens shrink w hen sigma(Test) is below 50 MPa, and elongate when it is above. Unreco verable strain does not remain in the specimen as long as the B2<->R t ransformation is repeated, but it does when the B2<->R<->B19' transfor mations are repeated.