Laser Welding of Titanium and Dental Precious Alloys

Abstract

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.

Laser Welding and Syncristallization Techniques Comparison:In VitroStudy

“…The cracks are generated during or after welding, and they are determined by the laser output, spot diameter, and laser beam diameter, [14]. This might explain the difference in the fissures numbers observed between group A and B samples.…”

“…Hot cracking susceptibility during welding is usually evaluated when the strain or stress is changed during the process, but the use of a pulsed Nd : YAG laser, where power is continuously decreased with time, may control the rate of solidification and can effectively reduce hot cracking in alloys [ 13 ]. The cracks are generated during or after welding, and they are determined by the laser output, spot diameter, and laser beam diameter, [ 14 ]. This might explain the difference in the fissures numbers observed between group A and B samples.…”

Applications of Laser Welding in Dentistry: A State-of-the-Art Review

“…Reduction in fracture toughness is due to the cracks and pores formed in the weld zones and this is the result of insufficient melting and mixture between components with different properties. Resulting low strength weld joint are considered to be the consequences of cracks, porosity and precipitates generated in the welded region [ 90 ]. Nishio et al also investigated several dental alloys for evaluating the performance of the butt joint.…”

Fracture Resistance of Nd:YAG Laser-welded Cast Titanium Joints with Various Clinical Thicknesses and Welding Pulse Energies

“…Berg et al 5) found that the presence of large pores (a few hundreds of m in diameter) in the weld metal appeared to be the most important factor in influencing the strength of laser-welded Ti joints. Similarly, in a study by Iwasaki et al 14) on the performance of laser-welded Ti and dental precious alloys by mechanical testing, they arrived at the same conclusion. The authors found that porosity in the weld zone was the cause for lower welding fracture strength of dissimilar metals as compared with similar metals 14) .…”

“…Similarly, in a study by Iwasaki et al 14) on the performance of laser-welded Ti and dental precious alloys by mechanical testing, they arrived at the same conclusion. The authors found that porosity in the weld zone was the cause for lower welding fracture strength of dissimilar metals as compared with similar metals 14) . In this study, however, the four-point bending test results showed that the presence of voids (from a few tens to hundreds of m in diameter) in the weld metal with various welding pulse energies (11 24 J) had no detrimental influence on the fracture resistance of cast Ti plate joints (thickness: 1 3 mm).…”