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 240V and 300V. 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 (25μm) to 1500μm 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 300V followed by the 240V and the control specimens. The laser-treated titanium specimens with 300V showed a tensile strength equivalent to the Co–Cr alloy. Although the highest modulus of elasticity was found for the specimens laser-treated with 240V, there were no significant differences in elastic modulus among 240V, 300V and Co–Cr. The laser-treated groups showed significantly lower hardness at the subsurface of 25μm and maintained their hardness until the depth of 400μm. The hardness of the control group was very high at 25μm depth, and dramatically decreased until the 200μm 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.

Keywords: Laser treatment, Cast titanium, Strength, Hardness profile