Laser Weldability of Cobalt-Chromium Alloy for Dental Use

对7种市售的铸造用钴铬合金和1种加工用钴铬合金进行了脉冲YAG激光辐照焊接性能的研究。得到了以下结果：任何铸造用钴铬合金的激光焊接都存在裂纹。铸造用钴铬合金焊接断口为脆性断口，具有凝固断口，而加工用钴铬合金激光焊接时不产生裂纹。断口为韧性断口。铸造用钴铬合金采用激光焊接硬化，加工用钴铬合金采用激光焊接软化。在母材的晶界中有大量的钼、硅、硫和碳。通过对三种铸造用合金的化学分析，发现激光焊接中产生裂纹最大的合金含有大量的硅、碳和磷。x射线衍射分析表明，铸造用合金焊缝为面心立方（fcc）结构，而母材为密装六方（hcp）结构。另一方面，用于加工的合金的母材和焊缝都是fcc结构。铸造用合金焊缝中存在大量类似氧化硅的共晶。此外，还观察到铝或氧化铬和硫化钙。因此，碳、硅和硫的存在被认为是焊缝产生裂纹的原因。对低碳合金的激光可焊性进行了测试，发现焊缝中碳控制裂纹的产生减少，铝的参与使裂纹产生。此外，通过在合金中重叠点焊，可以有效地控制裂纹的产生，并且裂纹的产生很少。此外，还可以通过控制脉冲形状来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.