Electric-spark alloying of steels with TiN-Cr materials

Abstract

A single spark discharge produces on the anode a conical crater whose depth, shape, and mean diameter depend on the phase composition of the anode material. The total anode erosion is sharply reduced by the addition of 10% Cr to titanium nitride, and becomes stabilized at a chromium concentration in the anode of 40%, which is due to a decrease in the extent of brittle disintegration of the anode. The process of formation of the reinforced layer is affected by the phase composition of the anode material and by the particle size and phase composition of the erosion products. The presence of intermetallic compounds and solid solutions in the anode material improves the conditions of formation of the layer, while a eutectic component in the anode material and oxides in the erosion products have a deleterious effect on them. The highest coefficient of transfer (K = 0.25) is attained in ESA with electrodes containing more than 40% Cr. The microhardness of the reinforced layer falls (from 17,000 to 8230 MPa) and its thickness and continuity grow (from 5 to 50 μm and from 30 to 100%, respectively) with increasing volume fraction of chromium in the anode material. A TiN + (40–60%) Cr composite may be recommended as an electrode material for the electric-spark alloying of steels, to which, however, additions must be made capable of raising the coefficient of transfer without adversely affecting the key characteristics of the alloyed layer.