engleski

Analysis of Base Alloys Joints made ba Soldering and Laser Welding

Due to some technological failures or prosthetic reconstructions, functional and/or technical durabillity of prosthetic appliances there is a need for joining parts of metallic construction together, of same or different compositions. Joining means includes metals heating at high temperature in various atmospheric conditions with or without additional material. The aim of this study was the analysis of microstructure and microhardness of the soldered or laser welded joints of six base as-cast alloys ; two Ni-Cr alloys, two Co-Cr alloys for prosthesis and two Co-Cr alloys for metaloceramic system. Speciments (32 x 10 x 1, 5 mm) were cut in the middle, and the parts were joined together using the procedures of soldering and laser welding. Soldering was performed by Burner Oksy adding Wiron sold for Ni-Cr alloys and Wirobond sold for Co-Cr alloys. Flame had been achived by burnout of oxygen + prophane/butan. For welding neodymium YAG laser (Nd:YAG- yttrium aluminium garnet), had been used. As additional material were Wiroweld NC wire for Ni-Cr alloys and Wiroweld wire for Co-Cr alloys. The quality of joints and heat affected zone(HAZ) were analyzed by optical microscopy and SEM. Microhardness was measured by Vickers method, with loading of 1, 96 N (HV 0.2). Microstructures of all cast specimens were dendritic. All joints showed specific concentration of porosity and inclusions. As-casts of Co-Cr alloys (340 HV0.2) are significantly harder than as-casts of Ni-Cr alloy (230 HV0.2). Laser joints have approximately equal microhardness values as well as parent material casts. Soldered joints with main microhardness (360 HV0.2) imply a potential precipitation hardening. The fusion line is most frequently irregular. The obtained results indicates that microstructure of the joints depends on the handling materials and on the method of joining. The oral cavity as an agressive and changeable corosion medium could cause different electrochemical behavior of analyzed joints.

soldering; laser welding

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