Laser Welding between Cast Pure Titanium and Titanium Alloy

Objectives: To investigate the joint properties between commercially pure titanium and titanium alloy laser welded by Nd:YAG laser.  Materials and Methods: Cast plates (0.5x3.0x10mm) were fabricated from commercially pure titanium (CP-Ti) and Ti-6Al-7Nb alloy (Ti67).  The CP-Ti plates were then mounted in a jig, abutted to Ti67 plates, and welded at two different voltages (180V and 210 V: pulse duration = 10 ms, spot diameter = 1.0 mm) using a dental Nd:YAG laser welding machine.  Homogenously welded specimens and non-welded control specimens were also prepared.  Tensile testing revealed failure load (N) and elongation (%) values.  The data was statistically analyzed using ANOVA and Tukey's HSD test (p<0.05).  SEM photographs of the fracture site were examined to determine the type of fracture and the penetration of the weld.  Results: The failure loads of heterogeneous groups (180V: 869±53N, 220V: 889N±50N) at both voltages was found to be similar to those of control (911±56N) and homogenously (896±45N) welded CP-Ti groups.  Increasing the voltage from 180V (956±135N) to 220V (1278±134N) with homogenous Ti67 significantly (p<0.05) increased the failure loads to a level similar to that of Ti67 control (1471±145N). Although the results of elongation showed a trend similar to those of failure load, the heterogeneous CP-Ti/Ti67 specimens had elongation values significantly higher than the other groups (except for Ti67/Ti67 homo 220V). SEM photograph analysis revealed that all specimens in the homogenous Ti67 180V group had broken at the weld due to poor laser penetration and an un-welded center area.  All other groups containing a CP-Ti portion broke predominantly within this section.  Conclusion: The results of this study indicated that the CP-Ti laser-welded to Ti-6Al-7Nb alloy could have weld strength similar to those of homogeneously welded and non-welded CP-Ti. Supported by the Baylor Oral Health Foundation.