| The conventional brazing is not suitable for dissimilar metals welding. This subject apply laser-welding technique into prosthdontics, used for dissimilar metal and evaluating the effects. This will enlarge the prosthdontics range of denture, and improve the accuracy and strengthen of denture. The results were proved by the clinical performance.Methods: Under a suitable laser-welding setting parameters, cast AuPt, cast CoCr, cast NiCr and pure cast Ti are welded each other and the metallographic changes and heat-affected zones of the welding areas were examined. Then the fusion and distribution characters after welding wasscan-ned and analyzed by the X-ray analyzer. We tested the mechanical properties and micro-hardness of welding zone and investigated the fractured surfaces using scanning electron microscopy (SEM). The experimental results were applied into clinical practices of dental restoration.Results: 1. NiCr-CoCr, NiCr-AuPt, CoCr-AuPt groups: After laser-welding, the welded areas were well intergradation, show a phenomenon of metallurgic style. The metal elements of two pairs of alloys equably distributed, presented an excellent weldability. 2. AuPt-Ti, NiCr-Ti, CoCr-Ti groups: The welded area nearby Ti interface show uncontinuous intergradation, There was an apparent interface and has some micro-gaps. Evenmore, the elements didn't well fused and mixed and a lot of piles of Ti element were found in the welded zone. 3. Two pairs of alloys in the welded area were fused and mixed, the metal element percentage was determined by the amount of alloy of each part. At the parts far from the welded area, the elements were majorly from the parent metal. 4. The three pairs of alloys (NiCr-CoCr, NiCr-AuPt, CoCr-AuPt) which have good weldabilities were tested of their mechanical properties. The results show: except each group's tensile strength, 0.2% yield strength were lower than AuPt alloy and CoCr-AuPt group's yield strength-was lower than CoCr alloy, all the other properties had no statistic differences with the NiCr or CoCr alloys, and NiCr-CoCr group's percentage elongation was much higher than their parent elements. 5. Micro-hardness testing show that the parts closer to the welded area, higher of the micro-hardness. The laser-welding might can make the welded area has more strengthen and change themetal's microstructure. 6. Scanning electron microscopy (SEM) shows the interface of NiCr-AuPt was composed of porcelain-like material majority and a little of tenacious fossa conformation. The interface of CoCr-AuPt was major composed of dendritic conformation, and a little of tenacious fossa conformation. The interface of NiCr-CoCr was majority composed of tenacious fossa conformation and a little of dendrite conformation, this kind of interface has a good plasticity. 7. After 15 cases of clinical performance of prostheses and 3 month's follow-up study, the prostheses were well located. The false tooth's functions were satisfactory. And there were no joint fractures and no apparent corrosion and color changes.Conclusion: 1. After Ti and other metal elements were welded, brittle phase was likely to occur. Under the conditions of this experiment, all the dissimilar alloys has very good effects by laser welding except Ti. 2. The weldings of NiCr-AuPt, NiCr-CoCr, CoCr-AuPt can receive a very good effect. Their mechanical properties can meet the requirements of chemical performances. And the NiCr-CoCr group's effect was the best which can obtain high level percentage elongation and malleabilities. 3. It's proved by clinical practices that the prostheses maded by laser-welding of dissimilar metals has very well denseness, and has normal functions. There was no joint fractures and corrosions and color changes. |
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