T. Fukuda et al., MARTENSITIC-TRANSFORMATION BEHAVIOR OF A SHAPE-MEMORY TI-40.5NI-10CU ALLOY AFFECTED BY THE C11(B)-TYPE PRECIPITATES, Materials transactions, JIM, 37(10), 1996, pp. 1540-1546
Effect of aging at 873 K on the two-step B2-->B19-->B19' transformatio
n of a shape memory Ti-40.5Ni-10Cu alloy was studied. It was found tha
t the start temperature of the B2-->B19 transformation and that of the
B19-->B19' transformation increase with increasing aging time. The st
art temperatures of the reverse transformations also increase. The tem
perature range of the two-step transformation decreases with increasin
g aging time. The aged Ti-40.5Ni-1OCu alloy is composed of the matrix
with B2-type structure (a(c)=0.3029 nm) and precipitates with C11(b)-t
ype structure (a(t)=0.3132 nm, c(t)=0.7991 nm). The precipitates are p
artly coherent with the matrix and are plate-like in shape having a or
ientation relationship [100](c)//[100](t) and [001](c)//[001](t), and
a habit plane {001}(c). The increase of transformation temperature is
caused by the precipitation through aging. The precipitation increases
the Ti content of the matrix, and the precipitates act as a nucleatio
n sites of B19 martensite due to strain field around them preferable f
or the B19 martensite.