Experimental investigation and thermodynamic assessment of phase equilibria in the Nb-Si-Zr ternary

• 作 者: J.Li Y.H.Guo S.Y.Yang Z.Shi C.P.Wang X.J.Liu
• 机 构: Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361
• 出 处: 第十七届全国相图学术会议暨相图与材料设计国际研讨会
• 发表日期: 2015年12期

The intermetallic compounds of Nb-Si based refractory alloys have been investigated extensively for potential candidates in the fields of aircraft engines and gas turbines.However,the poor oxidation resistance at high temperature and low fracture toughness at room temperature prevent the practical applications of Nb-Si based alloys.According to previous results, adding proper content of Zr into Nb-Si based alloys can bring some visible microstructural change and improvement of mechanical properties of the alloys.In order to well understand the effects of Zr on the microstructurc and properties of Nb-Si based alloys,the knowledge of phase equilibrium in the Nb-Si-Zr system is a prerequisite.However, the phase equilibrium about Nb-Si-Zr system were rare.It is not beneficial to materials design in Nb-Si based alloys for aircraft engines.In this study, the phase equilibria of Nb-Si-Zr at 1373 K, 1473 K and 1573 K were experimentally determined by means of back-scattered electron (BSE), electron probe microanalysis (EPMA) and X-ray diffraction (XRD).The results show that there were five three-phase regions and sixteen two-phase regions in the studied isothermal sections, and no any ternary compounds were found.The solubility of Si in the Nb-Zr side is very small.Large solubilities of Nb in αZ-rsSi4, Zr3Si2 and Zr2Si phases were observed, otherwise the solubilities of Nb in ZrSi2, αZrSi and Zr3Si phases are relatively small.Based on the present experimental results, the thermodynamic assessment of Nb-Si-Zr system was carried out using the CALPHAD (Calculation of Phase Diagrams) method.The current calculated phase diagrams are in reasonable agreement with the present experimental data.