Effects of recasting on the composition and microstructure of Ni-Cr ceramic alloy / 中国组织工程研究

ABSTRACT

BACKGROUND: Whether ceramic alloy can be reused after casting depends on its chemical composition, microstructure, castability, as well as mechanical property. However, the effects of recasting on the composition and microstructure of Ni-Cr ceramic alloys are poorly understood. OBJECTIVE: To investigate the effects of recasting on the composition and microstructure of Ni-Cr ceramic alloys. DESIGN, TIME AND SETTING: In vitro materials observation. The experiment was performed at the Department of Prosthodontics, Affiliated Stomatological Hospital, Fujian Medical University, Instrumentation Analysis and Measurement Center, Fuzhou University, from June to August 2007. MATERIALS The Ni-Cr ceramic alloys were recast 6 times in argon protection to obtain testing sample with diameter of 30.0 mm, thickness of 1.0 mm and side length of 10.0 mm, thickness of 1.0 mm, namely generation I VI. Simultaneously, the sample produced by initial alloy was called generation 0. METHODS: The original alloy and each generation square plates were analyzed by X-ray fluorescence spectrometry (XRF) for qualitative and semi-quantitative analysis. The microstructure and the phase structure of original alloy and each generation castings which had been polished by buffing machine were observed and analyzed by metallographic microscope and X-ray diffractometer (XRD). MAIN OUTCOME MEASURES: Contents of chemical composition, shrinkage cavity, porosity and inclusion, and distribution of XRD patterns. RESULTS: The results of XRF indicated that there were no significant difference on the main composition (Ni, Cr, Mo, Al, Be) among the Ni-Cr ceramic alloys multiple recast 0-6 times in argon protection and accorded with the demands. The metallographic structure of Ni-Cr ceramic alloys were dendritic eutectic structure, but the size of dendritic crystal grain in the casting coarsening, shrinkage cavity, porosity and inclusion gradually increased, with the increase of multiple recast times. The phase structure of Ni-Cr ceramic alloys were Ni-base solid solution (face-centered cubic lattice structure) and the chromium was widely distributed in the nickel base. There were neither significant difference of phase structure nor the new phase structure appeared among the Ni-Cr ceramic alloys multiple recast 0-6 times. CONCLUSION: There is no significant difference of main composition and phase structure between original alloy and each generation castings in argon protection. With the increase of recast times, the size of dendritic crystal coarsening, shrinkage cavity, porosity and inclusion gradually increased.