The purpose of this study was to investigate the effect of output energy and welding method on joint strength of laser-welded cobalt-chromium alloy (Cobaltan, Shofu Inc., Japan). Plastic patterns (1.0 ´ 3.0 ´ 40 mm³ ) were invested with a phosphate-bonded investment (Snow White, Shofu Inc., Japan) and cast using a vaccum induction casting machine (Argon Caster, Shofu Inc., Japan). Transverse sections of the plate were made at mid-span. After polishing the cut surfaces with 600 SiC paper, the two surfaces were butted against one another, and the joint was welded using a laser-welding machine (Tanaka TLL7000, Japan). The pulse duration and the spot diameter fixed were 10 ms and 1.0 mm, respectively. The output energy ranged from 180 to 300 A in increments of 30 A. Three laser pulses were applied from one side (single-welded) or both sides (double-welded) to cover the joint width of the specimens. The joint strength were determined in tensile mode on a universal testing machine with a crosshead speed of 2.0 mm/min and a gauge length of 20 mm. Data were analyzed using ANOVA and Turky HSD test (n=5, P<0.05).

	Control	180A	210A	240A	270A	300A
single-welded	1733(153)	224(45)a	266(73)a	420(158)ab	622(107)b	557(199)b
double-welded	1733(153)	252(106)a	284(102)a	569(177)ab	1292(338)c	841(125)b

Identical letter indicate that mean values are not statistically different (p<0.05)

The mean fracture force ranged from 224 N to 622 N (single-welded) and from 252 N to 1292 N (double-welded). The maximum fracture force was found for double-side laser application at a current of 270 A. The result suggested that laser-welding under the appropriate condition improved the joint strength of cobalt-chromium alloy. Partially supported by NIH grant DE11787.

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