MECHANICAL PROPERTIES OF SOME TANTALUM ALLOYS

Abstract

The mechanical properties of a series of Ta–Re alloys and some Ta–Mo and Ta–W alloys have been investigated by deforming single crystals in compression. Experimental results on slip-line observations, stress–strain curves, yield stresses and anisotropic elastic constants are presented. Slip occurs on the {110} planes; twinning is never observed and the alloys become increasingly brittle as the solute concentration is increased or the temperature is decreased. Yield stress versus composition curves show a minimum at low temperatures. It is suggested that this is due to a reduction in the intrinsic lattice friction stress of the pure metal by alloying, before alloy hardening is able to increase the yield stress again. The alloy hardening has been analyzed and the yield stress τ, the solute concentration c, and the temperature T are related by an expression [Formula: see text], where k and T0 are constants and μ is the shear modulus. Such a relationship has been derived by Fleischer for interactions of dislocations with tetragonal distortions. It is unlikely that this implies that tetragonal defects (for example, solute pairs) are important in tantalum alloys; presumably elastic interactions with single solute atoms can also give such a temperature and concentration dependence of the yield stress. Comparisons with other b.c.c. alloys have been made and it is found that the rate of alloy hardening is directly proportional to the atomic size misfit in most of the alloys where data are available for single crystals.