Laser welding of titanium and dental precious alloys

The performance of laser welding of Ti and two dental precious alloys (Ag-Pd-Au, Au-Pt-Ag) was investigated by mechanical testing and microscopic observation, using butt joint as design. The laser irradiation was done using a commercial Nd:YAG dental laser-welding device in a single pulse mode with output currents 150, 200, 250, 300 A, spot diameters 0.6, 0.9, 1.2 mm, and pulse duration 10 ms. The average welding fracture strength of the dissimilar metals were 108.9 and 137.2 MPa for Ti and Ag-Pd-Au alloy, and Au-Pt-Ag alloy, respectively. The average welding fracture strength of the same metals were 594.9. 648.8 and 312.9 MPa for Ti, Ag-Pd-Au alloy and Au-Pt-Ag alloy. The hardness increased in weld zone, compared with the base metals. Penetration depths were affected by the welding conditions such as the output currents and spot diameters. The welding cracks and porosity were observed in microstructures of the welds. Mapping by EPMA showed the remarkable heterogeneity of the component metals concerned. The welding cracks, porosities and granular precipitates similar to metallic compounds in the weld zones were suggested as the cause for lower welding fracture strength in the dissimilar welds, compared with the similar metals.