Influence of Nd: YAG Laser Parameters on Tensile Behaviour, Microhardness and Surface Roughness of Ni-Cr Alloy for Dental Prostheses

Abstract

The paper presents the results of tensile behaviour, microhardness, surface roughness and microstructure of Ni-Cr alloy surface treated using high power Q-switched Nd: YAG laser has been studied. The major clinical disadvantage of the Ni – Cr is their lack of adequate ductility and yield strength. These properties combined made finishing, polishing and burnishing of conventional base metal alloys rather difficult. The dumbbell shaped tensile and cylindrical specimens of Ni-Cr were cast with a phosphate bonded investment material, using an induction melting centrifugal casting machine. The microhardness values of the surface melted layers increased as compared with Ni-Cr as - cast condition. The results of experiment showed that the surface treatment process has improved the % elongation, and surface roughness and microhardness as compared with as-cast. The improvement of the mechanical properties may be attributed due to grain refinement imparted by laser shock peening. The microstructure and changes in crystal orientation presented in the surface layer of the laser treated material were analyzed by optical, SEM as well as XRD. The chemical composition of laser treated surface was determined by EDAX attached along with SEM. Vickers microhardness was measured as per ASTM E384 11el standard test method. The data were compared using ANOVA and post hoc –Tukey test. In our present study, the laser shock peening process shows, a substantial increase in surface roughness from Ra = 0.440 μm before LSP treatment to 1.781 μm and surface hardness of Ni-Cr was achieved by 53.5% the base material hardness (i.e. from284 HV to 436 HV) and the mean values of % elongation of Ni-Cr alloy was higher (double) than that of after laser shock peening. The mean values of UTS, YS, modulus of elasticity of Ni-Cr were significantly lower after LSP. The experimental results showed that the mean values of percentage elongation of Ni-Cr increased by 200 % after LSP. It is evident from the above experimentation, increase of ductility of Ni-Cr alloy facilities workability which could produce a reliable removable partial denture (RPD) metal framework for dental prostheses.