DIFFUSION INDUCED GRAIN BOUNDARY MIGRATION IN Ni(Zn) POLYCRYSTALS

Diffusion induced grain boundary migration (DIGM) has been investigated in the Ni(Zn) system for the first time by zincification of pure Ni polycrystals. The morphology of the reaction has been studied on sections parallel and perpendicular to the specimen surface. In addition to DIGM, diffusion induced recrystallization (DIR) has also been observed. The experimental results show that the boundary migration velocity during DIGM is strongly dependent on the annealing temperature. Also, the velocity depends on the depth below the nickel surface. The greater the depth, the smaller the velocity. Concentration profiles have been measured by energy dispersive X-ray analysis (EDX). The Zn concentration depends on both the annealing conditions and the depth below the surface. The concentration profiles were used as the basis for calculating the driving force, the grain boundary diffusivity and the grain boundary mobility

MISORIENTATION DEPENDENCE OF DIFFUSION INDUCED GRAIN BOUNDARY MIGRATION (DIGM) IN ORIENTED Cu (Zn) BICRYSTALS

Diffusion induced grain boundary migration (DIGM) has been studied in the Cu(Zn) system using Cu bicrystals with initially symmetrical tilt grain boundaries (GBs) of the {011} type produced by diffusion bonding. The misorientation has been varied systematically over the range from 10.1 to 171.9°. Measurements of the GB velocity showed it to have a strong dependence on the misorientation angle. The morphology of DIGM has been studied by optical microscopy. As a special morphological phenomenon, faceting has been investigated at a symmetrical Σ 19a/26.52° {011} GB

Effect of Nd:YAG laser parameters on the penetration depth of a representative Ni–Cr dental casting alloy

The effects of voltage and laser beam (spot) diameter on the penetration depth during laser beam welding in a representative nickel–chromium (Ni–Cr) dental alloy were the subject of this study. The cast alloy specimens were butted against each other and laser welded at their interface using various voltages (160–390 V) and spot diameters (0.2–1.8 mm) and a constant pulse duration of 10 ms. After welding, the laser beam penetration depths in the alloy were measured. The results were plotted and were statistically analyzed with a two-way ANOVA, employing voltage and spot diameter as the discriminating variables and using Holm–Sidak post hoc method (a = 0.05). The maximum penetration depth was 4.7 mm. The penetration depth increased as the spot diameter decreased at a fixed voltage and increased as the voltage increased at a fixed spot diameter. Varying the parameters of voltage and laser spot diameter significantly affected the depth of penetration of the dental cast Ni–Cr alloy. The penetration depth of laser-welded Ni–Cr dental alloys can be accurately adjusted based on the aforementioned results, leading to successfully joined/repaired dental restorations, saving manufacturing time, reducing final cost, and enhancing the longevity of dental prostheses. © 2013, Springer-Verlag London