Textures induced by the roller burnishing process

The roller burnishing of machine elements improves considerably their smoothness and resistance to corrosion and wear. This process delays an initiation and propagation of microcracks in the surface layer of the burnished elements. It is due to induced high compressive residual stresses and increased yield stresses of the layer. The plastic anisotropy that appears in the layer is caused by texture development during the plastic yield of the material. However, the opposite effect is frequently observed in the engineering practice (Pahlitzsch and Krohn, 1966): too many cycles of the burnishing process may cause a softening and finally a peeling and cracking of the surface layer. A description of the above ''seizing effect'' has been given recently by Gambin (1996a,b). To find the reason for softening of the burnished surface, the textures induced in metal surface layers after successive cycles of the process are analysed in the paper. On the basis of the classical solution to rolling of rigid-perfectly plastic half-space (Collins, 1972), velocity gradients in the plastic zone are determined. Next, a previously proposed model of crystal plastic behaviour (Gambin, 1991a,b) enables one to calculate crystallographic lattice reorientations, and to predict a texture development in the burnished surface layer. The texture obtained after the first pass of the roller is different from those observed after rolling of thin metal sheets. Successive passes of the roller gradually destroy the first pass texture. It confirms practical observations; i.e., the burnishing of machine elements through a few passes under a higher load gives better results than the burnishing through many powerless passes.