Experimental deformation of chalcopyrite single crystals at 200°C

Abstract

Abstract Prismatic specimens of chalcopyrite, CuFeS 2 , cut from a large natural crystal were experimentally deformed at 200°C, 300 MPa confining pressure and a strain rate of approximately 4·10 −6 s −1 . Orientation determinations discriminating [001] and [100] within the pseudocubic crystal structure, were carried out by X-ray texture goniometry using 103-reflections. Eight different orientations—[001], [100], [110], [111], [021], [221], [421], [821]—were tested by compression. The specimens were subjected to permanent axial shortenings of between 0.7% and 2.3%. After deformation, pre-polished specimen surfaces were inspected by means of interference contrast methods. Two-surface analysis of glide line orientations and of the sense of glide steps allows determination of the glide plane and assignment of the glide direction to a specific quadrant within a stereographic projection that is drawn from the top surface of the crystal. The height of slip steps further confines the glide directions which are assumed to be along low index lattice lines. The main deformation mechanism in all specimens, except the [001]-sample, was by slip on {112}. Coarse slip bands and fine slip lines of remarkably straight character often extend throughout the crystal indicating a planar slip behaviour. They all agree with {112}〈311〉 slip and {112}〈311〉 slip, respectively. The two slip modes are not crystallographically equivalent but the critical resolved shear stresses are similar, about 80 MPa. The Burgers vector 1 2〈311〉 = 0.986 nm is large and it is expected that the dislocations would undergo a complex dissociation into partials. The formerly predicted, “sphalerite-like”, slip directions 〈110〉, 〈021〉 are not consistent with the recent observations. In the [001]-specimen {112}〈111〉 twinning was the main glide mode. The twins exhibit a pronounced wavy character in sections across n 1 and are straight in sections along n 1 . The twinning shear stress was 115 MPa.