A possible role for hydrogen-induced lattice migration in alloy materials processing

Abstract

Evidence for hydrogen-induced lattice migration leading to rearranged lattices is given based on recent studies of palladium-rich alloys. In f.c.c. initially homogeneous PdRh, PdNi and PdPt alloys, hydrogen heat treatment (HHT) causes segregation. In PdRh alloys the segregation is clearly due to the miscibility gap which exists in this system; it takes place at both low hydrogen contents and high temperatures, approximately 873 K, and at moderate temperatures, approximately 473 K, and relatively high hydrogen contents. In the PdNi and PdPt alloys, however, segregation from HHT takes place only at moderate temperatures and relatively high hydrogen contents. In PdNi alloys it is shown that HHT at elevated temperatures promotes metal atom diffusion leading to the elimination of compositional variations in an initially inhomogeneous alloy. Dissolved hydrogen plays a dual role in some of these alloys, i.e. it catalyzes metal atom diffusion and also affects the equilibrium state.