Electrical discharge surface alloying

This paper details the electrical discharge surface alloying/modification of γ-TiAl (Ti–46.5Al–4(Cr, Nb, Ta, B)) and α/β Ti alloy (Ti–6Al–4V) sheet (1 mm thick) during wire cutting using deionised water dielectric with nickel and copper wires. In addition, topography, microstructure and wear test data are given for a 2% Cr steel mill roll material textured/alloyed using partially sintered powder metallurgy (PM) hardmetal tool electrodes. Wire cutting produced surfaces with porous discontinuous recast layers up to 136 μm thick and in some cases, a surface hardness lower than the bulk was obtained. In contrast, some textured and alloyed layers on the roll material were over 900 HK0.025 when using WC/Co electrodes as compared to surfaces produced with standard Cu/graphite tools of 500–740 HK0.025. Scratch wear test data on the alloyed 2% Cr steel surfaces showed that a significantly reduced coefficient of friction (∼50%) was obtained when using the carbide electrodes as compared with similar surfaces machined with standard tools. Chromium-plated surfaces however gave a 30% reduction in friction force over the hardmetal alloyed surface.