The formation of denuded zones at grain boundaries, normal to the tensile stress, during deformation of magnesium-zirconium hydride materials, has been cited as direct evidence for the occurrence of Nabarro-Herring (N-H) diffusional creep. Recently, the present authors refuted this evidence and instead concluded that the deformation process in these materials was one of diffusion-controlled dislocation creep. It was further postulated that the experimentally-observed denuded zones developed as a result of tensile-stress-directed grain boundary migration during creep; a process which dissolves hydride precipitates as the boundary moves. The evidence and conclusions regarding denuded zones given in reference [4]have been challenged by Burton and Reynolds [5], by Greenwood [6], by Bilde-Sorensen and Smith [7], and by Langdon [8]. A response to Burton and Reynolds and to Greenwood has been given by Ruano et al [9]. In that paper, additional evidence was presented supporting our view that diffusional-controlled dislocation creep or grain boundary sliding accommodated by slip (GBS), rather than diffusional creep, was considered to be the dominant deformation process. Bilde-Sorensen and Smith [7]agreed with our conclusion that denuded zones may occur from mechanisms other than diffusional creep, but disagreed with our statement that in “the diffusional creep model denuded zones of equal size are required on both sides of transverse boundaries.” They point out that not all grain boundaries in tension are good sources of vacancy generation and that such boundaries would not be expected to show denuded zones.

Peer reviewed