INTERNAL FRICTION DUE TO DOMAIN-WALL MOTION IN MARTENSITICALLY TRANSFORMED A15 COMPOUNDS

Abstract
A lattice instability in A15 materials in some cases leads to a cubic- to-tetragonal martensitic transformation at low temperatures. The transformed material orients in lamellae with c axes alternately aligned along the <100> directions producing domain walls between the lamellae. An internal-friction (δ) feature below T_m is attributed to stress-induced domain-wall motion. The magnitude of the friction increases as temperature is lowered below T_m as (1-c/a) increases, and behaves as (1-c/a)² from T_m down to the superconducting critical temperature where the increasing tetragonality is inhibited. The effect of strain in the lattice is to decrease the domain-wall internal friction, but not affect T_m. Neutron-induced disorder and the addition of some third-elements in alloying decrease both δ and T_m, with some elements reducing only the former. Less than 1 at . % H is seen to completely suppress both δ and T_m. Martensitically transformed V₂Zr demonstrates lowtemperature internal-friction and modulus behavior consistent with easy β/m wall motion relative to the easy m/m motion of the A15's. For the V₂Zr , a peak in δ is observed, qualitatively in agreement with expected β/m wall motion.