Rempel S V, Gusev A I
Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990, Russia.
Phys Chem Chem Phys. 2020 Jul 8;22(26):14918-14931. doi: 10.1039/d0cp02074e.
The crystal structure and microstructure of pseudobinary (ZrC0.96)1-x(NbC0.97)x carbide solid solutions has been studied. It was found that monocrystalline grains of zirconium carbide are spontaneously isolated on the surface of diluted solid solutions of the pseudobinary system ZrCy-NbCy' containing less than 2.0 mol% of zirconium carbide. It is shown that the appearance of zirconium carbide is a consequence of the solid-phase decomposition of these solid solutions and anisotropy of elastic properties of monocrystalline ZrC carbide grains. The model of subregular solutions was used in the temperature interval from 300 to 3900 K to calculate and plot an equilibrium phase diagram of the ternary Zr-Nb-C system. It is shown that at temperatures above 1210 K in the Zr-Nb-C ternary system, nonstoichiometric carbides ZrCy and NbCy' have unlimited mutual solubility and form a continuous series of (ZrCy)1-x(NbCy')x solid solutions with 0.6 ≤ y ≤ 0.98, 0.7 ≤ y' ≤ 1.0, and 0 ≤ x ≤ 1.0. At temperatures below 1200 K, under equilibrium conditions, a discontinuity of the miscibility of the solid solutions ZrCy-NbCy' is observed and there appears a region of solid phase decomposition. The anisotropy of elastic properties of monocrystalline grains of ZrC was considered. It is predicted that solid-phase decomposition and surface segregation can be observed in such related carbide systems as HfCy-NbCy', HfCy-TaCy', ZrCy-TaCy', VCy-TaCy' and VCy-NbCy'.
对伪二元(ZrC0.96)1-x(NbC0.97)x碳化物固溶体的晶体结构和微观结构进行了研究。发现在含碳化锆小于2.0摩尔%的ZrCy-NbCy'伪二元体系稀释固溶体表面，碳化锆单晶颗粒会自发分离。结果表明，碳化锆的出现是这些固溶体固相分解以及单晶ZrC碳化物颗粒弹性性能各向异性的结果。在300至3900K的温度区间内，使用亚规则溶液模型计算并绘制了三元Zr-Nb-C体系的平衡相图。结果表明，在Zr-Nb-C三元体系中，温度高于1210K时，非化学计量碳化物ZrCy和NbCy'具有无限互溶性，并形成一系列连续的(ZrCy)1-x(NbCy')x固溶体，其中0.6≤y≤0.98，0.7≤y'≤1.0，且0≤x≤1.0。在温度低于1200K时，在平衡条件下，观察到固溶体ZrCy-NbCy'混溶间断，并出现固相分解区域。考虑了ZrC单晶颗粒弹性性能的各向异性。预计在HfCy-NbCy'、HfCy-TaCy'、ZrCy-TaCy'、VCy-TaCy'和VCy-NbCy'等相关碳化物体系中可观察到固相分解和表面偏析现象。
