Prevention method of crack generation in laser weld of dental cobalt-chromium alloy casting

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Cracking is more likely to occur in castings than in ingots in dental cobalt-chromium alloy. We investigated a casting method that prevents cracking of laser-welded regions. For the experimental material, we used cobalt-chromium alloys for denture bases and porcelain fused-to-metal crowns. Ingots and castings were analyzed. Castings were prepared employing two methods : the conventional method and a method using a sintered mold. Welding was performed using a laser for dental use. The occurrence and cause of cracking were investigated by metal microstructure observation under a light microscope, fracture surface observation under a scanning electron microscope, and element concentration analysis using an energy-dispersive X-ray spectrometer. The occurrence of cracking was reduced in castings prepared using a sintered mold. Solidification cracks were widely present on the fracture surface in the welded region of the castings prepared by the conventional method, whereas the dimple pattern was widely noted on the fracture surface in the welded region of the castings prepared using a sintered mold. On quantitative analysis, the phosphorus content was high in the fracture surface with solidification cracks. We concluded that cracking sensitivity can be reduced in dental cobalt-chromium alloy by using a sintered mold.
2013-04-00