Dynamics of Screw Dislocations Piled Up against the Surface Hardened Layer of Nitrided Titanium

Abstract

Computer simulations of the dynamics of screw dislocations are performed, using the model in which screw dislocations are piled up against a hard thin layer after their slip movement in a region possessing the distribution of friction stress. The calculation of stress field in the compound layer is performed for various values of slip length and thickness of a thin surface layer in order to discuss the effect of these factors on the fatigue strength of nitrided titanium. The results show that the well-known Hall-Petch-type relation between the fatigue strength and the grain size can be predicted for nitrided titanium through analysis of the proposed model. And the results exhibit that further consideration concerning the role of crack initiation resistance of the compound layer is essential for a better understanding of the influence of the thickness of the surface-hardened layer on the fatigue strength of nitrided titanium.