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

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 directions producing domain walls between the lamellae. An internal-friction (δ) feature below Tm is attributed to stress-induced domain-wall motion. The magnitude of the friction increases as temperature is lowered below Tm as (1-c/a) increases, and behaves as (1-c/a)2 from Tm 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 Tm. Neutron-induced disorder and the addition of some third-elements in alloying decrease both δ and Tm, with some elements reducing only the former. Less than 1 at . % H is seen to completely suppress both δ and Tm. 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