In-(13−<I>X</I>) at%Pb-<I>X</I> at%Sn擬2元系合金のマルテンサイト変態

Abstract

Changes in both crystal structure and surface relief during the phase transformation in Indium-(13−X) at%Pb-X at%Sn pseudobinary alloys have been studied by means of metallurgical techniques. Lattice parameters at each temperature during the phase transformation show that the alloys undergo two kinds of phase transformation: fct(c⁄a<1)↔fco phase transformation in the alloys containing (0-9) at%Sn and fct(c⁄a<1)↔fct(c⁄a>1) one in the alloys containing (11-13) at%Sn. The characteristic feature of phase transformation becomes more recognizable first-order gradually with increasing tin content. The appearance of a banded surface relief in a low-temperature phase concludes that these phase transformations are martensitic ones taking place by the cooperative movement of atoms. The change in surface relief is reversible in the alloys containing (0-7) at%Sn, but not in others. Corresponding to this, the amount of shape recovery in the former alloys is nearly constant, and the latter alloys show a decrease in shape recovery with increasing tin content. The characteristic features of shape recovery associated with phase transformation on heating is discussed in terms of the crystallographic reversibility in each phase transformation. Furthermore, the fct(c⁄a<1)↔fco phase transformation is analyzed phenomenologically on the basis of the Landau theory, and some physical quantities such as the change in entropy and the elastic constant C′ are calculated. The temperature dependence of the stress-strain relation is also discussed in terms of ferro- and super-elasticity. The analyzed results suggest that the characteristic behavior of the fct(c⁄a<1)↔fco phase transformation depends upon the average atomic size as well as the valence electron concentration.