Laser surface treatment to improve mechanical properties of cast titanium

Abstract

Objective The aim of this study was to investigate the effect of laser surface treatment on the mechanical properties of cast titanium and to compare with those of the Co–Cr alloy. Methods Dumbbell-shaped cast specimens were prepared for commercially pure titanium (grade 2) and Co–Cr alloy. The cast titanium specimens were laser-treated on the surface using a dental Nd:YAG laser machine at 240 V and 300 V. After laser treatment, tensile testing was conducted to obtain the tensile strength, percent elongation and modulus of elasticity. The hardness depth profile was made from the cast subsurface (25 μm) to 1500 μm in depth using the cross-sections of the cast rods with the same diameter as the dumbbell. The data were statistically analyzed by ANOVA/post hoc tests ( p < 0.05). Results The highest tensile strength was obtained for the titanium specimens laser-treated with 300 V followed by the 240 V and the control specimens. The laser-treated titanium specimens with 300 V showed a tensile strength equivalent to the Co–Cr alloy. Although the highest modulus of elasticity was found for the specimens laser-treated with 240 V, there were no significant differences in elastic modulus among 240 V, 300 V and Co–Cr. The laser-treated groups showed significantly lower hardness at the subsurface of 25 μm and maintained their hardness until the depth of 400 μm. The hardness of the control group was very high at 25 μm depth, and dramatically decreased until the 200 μm depth. Conclusion The results of tensile testing and hardness depth-profiling indicated that the laser treatment significantly improved the mechanical properties of cast titanium by improving the surface integrity of the cast surface contamination.