Dislocation configurations developed during carburization of nickel

Abstract

Dislocation configurations are shown to develop in nickel single crystals as a result of diffusion of carbon from a vapor source. Since carbon is dissolved interstitially in nickel, the presence of such dislocation configurations demonstrates that lattice parameter changes suffice for generating dislocation arrays and that the vacancy requirements involved in diffusion of substitutionally dissolved atoms are nonessential. In particular, carbon was diffused for 30 min at 1000°C into the (111) surfaces of thick nickel crystals, and the resulting dislocation arrangements in the diffusion zone were examined by etch pitting (111) sections. The dislocation density increases from the “grown-in” 1.5 x 10⁶ per cm² so that in some regions near that surface it is about 107 per cm². At least half of all the dislocations appear to be arrayed in subgrain boundaries in these sections. The dislocation density decreases towards the interior until at about 3.5√Dt_e (√Dt _e= 210 μm) it approximates the “grown-in” dislocation density, but even at distances exceeding 0.7√Dt_e there still exist locally high density regions. These have a regular geometry in which dislocations appear to be on (•111), (1•11) or (11•1) slip planes. The subgrain size is 36 μm near the as-diffused surface and increases, until at 3.5√Dt_e, it is 160 μm, which is the average subgrain size in the undiffused crystal.