Laser Weldability of Cobalt-Chromium Alloy for Dental Use

对7种市售铸造用钴铬合金和1种加工用钴铬合金进行了脉冲激光辐照焊接性试验。结果表明：铸造钴铬合金的激光焊接均出现裂纹。铸造钴铬合金焊接断口为脆性断口，有凝固断口，而激光焊接钴铬合金加工断口不产生裂纹。断口为韧性断口。铸造用钴铬合金经激光焊接后硬化，加工用合金软化。母材晶界含有大量的钼、硅、硫和碳，通过对三种铸造合金的化学分析，发现激光焊接裂纹产生最多的合金含有大量的硅、碳、磷。X-射线衍射仪分析表明，铸造合金的焊缝为面心立方(FCC)组织，母材为密排六方(HCP)组织。另一方面，加工用合金母材和焊缝均为面心立方组织。铸造合金焊缝中含有大量的共晶组织，似为氧化硅。此外，还观察到了铝或氧化铬和硫化钙。因此，碳、硅和硫的存在被认为是焊缝裂纹产生的原因。当考察低碳合金的激光焊接性时，发现碳控制的焊缝裂纹产生减少，铝的参与导致了裂纹的产生。此外，还可以通过在合金中重叠点焊来控制裂纹，而且产生的裂纹很少。此外，通过控制脉冲形状可以控制焊接缺陷的产生。

For seven kinds of marketing cobalt-chromium alloy for casting and one alloy for processing, weldability by the pulsed YAG laser irradiation was examined. The following results were obtained.The crack occurred in the laser weld of any cobalt chrome alloy for casting. The fracture surface of weled cobalt-chromium alloy for casting was brittle fracture surface which had fracture surface of solidification, On the other hand, no crack generated in the laser weld of the cobalt-chromium alloy for processing. The fracture surface was ductile fracture surface. The cobalt-chromium alloys for casting were hardened by laser welding, but alloy for processing was softened. There were a lot of molybdenum, silicon, sulfur, and carbon in the grain boundary of the base metal.It turned out for the alloy with the largest crack generation in laser weld to contain a lot of silicon, carbon, and phosphorus by chemical analyze of three kinds of alloy for casting. The weld of the alloy for the casting was a face-centered cubic (fcc) structure though the base metal was a closed-packed hexagonal (hcp) structure according to the X-ray diffractometer analyze. On the other hand, both base metal and weld for the alloy for processing were fcc structures. There were many eutectics which seemed to be silicon oxide in the weld of the alloy for casting. Moreover, aluminum, or chromium oxide, and calcium sulfide were observed. Therefore, the existence of the carbon, silicon, and sulfur was thought as a cause of the crack generation of the weld.When the laser weldability of the alloy with little carbon was examined, it turned out the reduce of carbon controlled crack generation in weld, and involvement of aluminum generated the crack. Moreover, it turned out to be able to control the crack by overlapping the spot weld in the alloy with a little crack generation. In addition, it turned out to be able to control the generation of the welding defect by controlling the pulse shape.