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首页> 外文学位 >Development, processing and fabrication of a nickel based nickel-chromium-iron alloy.
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Development, processing and fabrication of a nickel based nickel-chromium-iron alloy.

机译：镍基镍铬铁合金的开发，加工和制造。

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An optimal powder metallurgy (P/M) approach to produce a nickel base Superalloy similar in composition to INCONEL(TM) 600 was carried out utilising a simple uniaxial pressing process. The efficiencies of a lubricant addition, binder, sintering times and temperatures were measured in terms of green and sintered densities as well as microstructural changes that occurred during processing. It was observed that with increasing % polyvinyl alcohol (PVA), an overall decrease in density of compact was obtained and that using 0.75wt % of lubricant (microwax) green densities in excess of 70% can be obtained.;The samples were subsequently sintered in air at 1270°C for times ranging from 0.5h to 5h and also in vacuum (6 millitorr) with temperatures ranging from 1260 through to 1400°C. The air sintering was carried out to optimize sintering time, whereas the vacuum sintering was employed to optimize sintering temperature. On sintering for 5h in air, chromium enrichment occurred at the grain boundaries with subsequent depletion of nickel and iron; this was not noted for 2h sintering or for sintering under vacuum. The optimum sintering conditions were determined to be at 1300°C sintering for 2h in vacuum. The samples processed under the optimum conditions were successfully cold rolled to 40% of the original thickness without cracking.;An investigation was also undertaken to determine the effect of Al concentration (1-12w/o) on the microstructure of the powder metallurgically (P/M) processed Ni-Cr-Fe ternary alloy, with a view to determine the concentration of aluminium that would yield a homogenously distributed and optimum volume fraction of the intermetallic-gamma'(Ni3Al) phase without the formation of topologically closed packed phases in the ternary alloy.;The phases that were likely to form with the variation in concentration of Al were first simulated by JMatPro(TM) thermodynamic software package, and then Ni-Cr-Fe alloys with varying concentration of aluminum were produced by P/M processing. The microstructure of the alloys was characterized by X-ray diffractometer (XRD), optical microscope (OM) and scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and then compared with the thermodynamic predictions. It was observed that the experimental results matched reasonably closely with the thermodynamic predictions in terms of the phases present when Al was added to the ternary alloy, but not the volume fraction of the phases present in the microstructure. It was also observed by SEM image and quantitative EDS analysis that the optimum amount of well distributed Ni3Al phase formed when the concentration of aluminium was 6w/o. These results suggest that despite potential problems encountered in high temperature powder processing of Superalloys that often tend to influence the feasibility of using thermodynamic predictions to model such alloy systems, the software and predictions used in this study offer a way to simulate both design and characterisation of the experimental alloy.;To characterize the phases that formed in the 6w/o Al modified ternary Ni-Cr-Fe alloy during heating to the sintering temperature, a differential scanning calorimetric study was carried out to study sequence of phase transformations, their reaction modes and products on heating a green compact from room temperature to the sintering temperature of 1300°C. Two different heating rates were employed for the DSC study, 2.5°C/min and 10°C/min. Transformation reactions were also studied by heating the samples in a DSC to the points of exo/endothermicity and quenching in argon followed by phase identification by X-ray diffraction, and microstructural analysis by SEM equipped with EDS capability. A series of AlxNiy and AlxFe y type intermetallics were observed to form by phase transformation at temperatures from 540°C to 1120°C.;The sequence of the formation of intermetallics by these phase transformations closely replicated the intermetallics that were predicted by the binary Ni-Al and the Fe-Al equilibrium phase diagrams, with the final microstructure being Ni3Al (gamma'), AlNi, AlFe in a Ni-Cr-Fe (gamma) matrix. Most of these phase transformations were diffusion controlled, but at 640°C AlNi formed by combustion synthesis. Selected mechanical property of the alloy at 1120°C which corresponds to the completion of transformations was estimated in terms of micro-hardness and compared to the as-sintered Ni-Cr-Fe ternary.
机译：利用简单的单轴压制工艺进行了最佳粉末冶金（P / M）方法，以生产组成类似于INCONEL™600的镍基高温合金。根据生坯和烧结的密度以及加工过程中发生的微观结构变化来测量润滑剂的添加效率，粘合剂，烧结时间和温度。观察到，随着聚乙烯醇（PVA）含量的增加，压坯的密度总体下降，使用0.75wt％的润滑剂（微蜡）可得到超过70％的生坯密度;随后将样品烧结在1270°C的空气中放置0.5h至5h，在真空（6毫托）中，温度在1260至1400°C之间。进行空气烧结以优化烧结时间，而采用真空烧结以优化烧结温度。在空气中烧结5h后，在晶界处发生了铬富集，随后镍和铁被耗尽。对于2h烧结或在真空下烧结没有注意到。确定最佳烧结条件为在1300°C下真空烧结2h。在最佳条件下处理的样品已成功冷轧至原始厚度的40％而没有开裂。;还进行了一项研究，以确定铝浓度（1-12w / o）对粉末冶金（P的）组织的影响/ M）处理的Ni-Cr-Fe三元合金，以确定铝的浓度，该浓度将产生金属间γ'（Ni3Al）相的均匀分布和最佳体积分数，而不会在其中形成拓扑封闭的填充相首先通过JMatPro（TM）热力学软件包模拟了随Al浓度变化而可能形成的相，然后通过P / M生产了具有不同铝浓度的Ni-Cr-Fe合金。处理。用X射线衍射仪（XRD），光学显微镜（OM）和装有能谱仪（EDS）的扫描电子显微镜（SEM）对合金的微观结构进行了表征，然后与热力学预测结果进行了比较。观察到，在将铝添加到三元合金中时，存在的相方面的实验结果与热力学预测合理地匹配，但是在微观结构中存在的相的体积分数却没有。通过SEM图像和定量EDS分析还观察到，当铝的浓度为6w / o时，形成最佳分布的Ni 3 Al相的最佳量。这些结果表明，尽管在高温合金的高温粉末加工过程中遇到了潜在的问题，这些问题通常会影响使用热力学预测对此类合金系统进行建模的可行性，但本研究中使用的软件和预测提供了一种方法来模拟合金的设计和表征为了表征在加热到烧结温度期间6w / o Al改性的三元Ni-Cr-Fe合金中形成的相，进行了差示扫描量热研究，研究了相变的顺序及其反应模式。以及将生坯从室温加热到1300°C的烧结温度的产品。 DSC研究采用两种不同的加热速率：2.5°C / min和10°C / min。还通过将DSC中的样品加热到放热/吸热点并在氩气中淬灭，然后通过X射线衍射进行相鉴定，并通过配备EDS功能的SEM进行显微结构分析，研究了转化反应。在540°C至1120°C的温度下观察到一系列AlxNiy和AlxFe y型金属间化合物的形成;通过这些相变形成金属间化合物的顺序紧密地复制了由二元Ni预测的金属间化合物-Al和Fe-Al平衡相图，最终的微观结构是Ni-Cr-Fe（γ）基质中的Ni3Al（γ'），AlNi，AlFe。这些相变大多数是受扩散控制的，但在640°C下通过燃烧合成形成AlNi。根据显微硬度，估算了在1120°C下合金的选定机械性能，该性能对应于相变的完成，并与烧结后的Ni-Cr-Fe三元相比较。

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