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Laser welding of cast titanium and dental alloys using argon shielding.

PURPOSE
This study investigated the effect of argon gas shielding on the strengths of laser-welded cast Ti and Ti-6Al-7Nb and compared the results to those of two dental casting alloys.


MATERIALS AND METHODS
Cast plates of Ti, Ti-6Al-7Nb, gold, and Co-Cr alloy were prepared. After polishing the surfaces to be welded, two plates were abutted and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each metal by bilaterally welding them with three or five spots either with or without argon shielding. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min.


RESULTS
The factor of argon shielding significantly affected the failure load and elongation of the laser-welded specimens. The failure loads of argon-shielded laser-welded CP Ti and Ti-6Al-7Nb were greater compared with the failure loads of specimens welded without argon shielding for both three- and five-spot welding. Regardless of argon shielding, the failure loads of the laser-welded gold alloy were approximately half that of the control specimens. In contrast, the failure loads of the nonshielded laser-welded Co-Cr alloy were greater. The percent elongations positively correlated with the failure loads.


CONCLUSIONS
The use of argon shielding is necessary for effective laser-welding of CP Ti and Ti-6Al-7Nb but not for gold and Co-Cr alloy.