Castability And Elemental Analysis Of The Reused Ni-Cr-Ti Alloy

Tilite V Ni-Cr-Ti alloy was a kind of new alloy used to fabricate fixed prosthesis because of its high quality, performance, and safety standards. But it was quit expensive. On the other hand, casting procedures required more metal to be fused than is needed to fill the mold. The surplus, known as a button, was separated from the casting. Thus, the possibility that the button may be reused to produce an acceptable casting was a matter of economy. The purpose of this study was to investigate the effects of different methods of surface treatment as well as different weight ratios of reused alloys on the castability and to analyze the metallography and elemental composition of casting surfaces, giving proof to the reuse of TILITE V Ni-Cr-Ti alloy.This study includes three parts. Part 1, Castability of reusedNi-Cr-Ti alloys: 3 groups of Ni-Cr-Ti alloys containing 50% reused materials, one treated by sandblasting with the other two pickled with acid combinations for Inconel alloy and Nimonic alloy respectively, were cast into sieve patterns to calculate the castability value (CV). Then the castability of alloys containing 0%, 50%, 62.5%, 75%, 87.5%, 100% reused materials was evaluated with the same method. Metallographies of tcastings were observed with reversed type of metallosocope. And elemental analyses and of castings and the new alloys were performed with x-ray energy-dispersive spectroscopy (EDS) attached to a scanning electron microscope (SEM).In this research, we found that with proper treatment of sandblasting or pickling with the acid combination for Inconel alloy, the Ni-Cr-Ti alloys containing 50% reused materials had a CV value of 100% , which were significantly higher than the CV of alloy picked with acid combination for Nimonic alloy (p<0. 05). And with the same treatment of sandblasting, the CVs of alloys containing reused materials less than 75% were 100%, which were significantly higher than alloys containing 75% or more reused materials . Metallographies of castings made from reused alloyswere looser than that of castings made of new alloys. And there were non-maetal impurities and shrinkage porosities in the castings made from reused alloys. But no indistinction of grain boundaries was observed. With the growth of reused alloys weight ratio, the amounts of Ti> Al> Si decreased while the amount of S and other minor elements increased. But the changes were generally minimal.Based on these findings, it was concluded that the proper treatment for casted Ni-Cr-Ti alloys was sandblasting or pickling with right acid combinations. To get satisfactory castability, the weight ratio of reused alloys should be not higher than 75%. Castings made from new alloys and that made from reused alloys had similar metallography and elemental composition.