反复熔铸对镍铬烤瓷合金化学成分和微观组织结构的影响

背景:熔铸后烤瓷合金能否回收再利用取决于熔铸后烤瓷合金的化学成分、微观组织结构、铸流率、力学性能、金瓷结合性能等因素的变化情况,但目前研究反复熔铸后镍铬烤瓷合金化学成分及微观组织结构的报道较少.目的:分析反复熔铸对镍铬烤瓷合金化学成分、微观组织结构变化的影响.设计、时间及地点:医学材料学体外观察实验,于2007-06/08在福建医科大学附属口腔医院技工室、福州大学材料测试中心进行.材料:以经0～5次熔铸后的镍铬烤瓷合金为原料在真空加压氩气保护铸造机铸造,即获得分别经1～6次熔铸后直径为30.0 mm、厚度为1.0 mm和边长为10.0 mm、厚度为1.0 mm的试样,依次称为Ⅰ～Ⅵ代试样,同时将厂家提供的原始合金加工成相同的形状称为0代试样.方法:应用X射线荧光光谱仪对镍铬烤瓷合金原始合金和反复熔铸后铸成的各代试样进行定性半定量分析.应用正置式反射金相显微镜对经过表面抛光后的镍铬烤瓷合金原始合金和反复熔铸后铸成的各代试样的金相显微结构进行观察;应用X射线粉末衍射仪对镍铬烤瓷合金原始合金和反复熔铸后铸成的各代试样进行物相分析.主要观察指标:各代试件中各化学成分的含量;金相显微镜下观察各代试件有无夹杂物,有无缩松、缩孔等现象;各代试件X射线峰分布情况.结果:在真空加压氩气保护的铸造环境下,经反复熔铸后,镍铬烤瓷合金的主要组分Ni、Cr、Mo、Al、Be等元素所占的质量百分数没有显著性变化,且符合相关标准要求;其金相结构为树枝状共晶结构,随着反复熔铸次数的增加,出现枝晶粗化、枝晶排列稍显紊乱、晶间相(基质)增多现象,且合金内部夹杂物的含量以及缩孔、缩松的数量分布随着反复熔铸次数的增加而逐渐增多、增广;其相结构为镍基固溶体、面心立方(FCC)晶格结构,铬元素广泛分布于镍基质中,经1～6次反复熔铸后的镍铬烤瓷合金的物相结构没有发生变化,未出现新相.结论:在真空加压氩气保护的铸造环境下,镍铬烤瓷合金各主要元素组分的质量百分数和物相结构随着反复熔铸次数的增多没有发生显著变化,随着熔铸次数的增多其枝晶粗化,合金内部夹杂物和铸造缺陷增多.

Effects of recasting on the composition and microstructure of Ni-Cr ceramic alloy

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.