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Elastic constants of single crystals of the three phases of InPb alloys

1979; Elsevier BV; Volume: 40; Issue: 12 Linguagem: Inglês

10.1016/0022-3697(79)90120-3

1879-2553

M. R. Madhava, G. A. Saunders,

Non-Destructive Testing Techniques

Abstract In a study of the elastic behaviour of the InPb alloys, the elastic stiffness tensor components of crystals of each of the three phases (fct, c a > 1 ; fct, c a > 1 ; fcc) have been obtained as a function of temperature from pulse superposition measurements of ultrasonic wave velocities. Comparison of the elastic stiffness constants obtained for a fct ( c a > 1 ) 5 atm.% Pb alloy with those of In itself and those of InTl and InCd alloys, establishes for this phase that alloying with Pb, as with TI and Cd, enhances the softening of the acoustic [110] phonon mode, polarization [1 1 0] near the Brillouin zone centre. The elastic properties of a 17 atm.% Pb crystal, which is in the fct ( c a > 1 ) phase, are quite different from those shown by In alloys in the fct ( c a > 1 phase; in particular the response to a shear stress is remarkably isotropie: there is no phonon mode softening in this alloy. Neither is there softening of this mode (which corresponds at the zone centre to the shear stiffness 1 2 (C 11 ;C 12 )) in crystals of the fee phase — in complete contrast to the dominating influence of the softening of 1 2 (C 11 ;C 12 ) in the InTl and InCd fee alloys. In fact for a fcc In-75 atm.% Pb alloy the anistropy ratio for shear 2C 44 (C 11 C 12 ) is close to unity. The transitions between the three phases of the InPb alloys are markedly first order and acoustic mode softening has a much smaller influence on the elastic behaviour of the fct ( c a ) and fcc InPb alloys than it has on the fct ( c a ) InPb, InCd and InTl alloys.