Ab initio-aided CALPHAD thermodynamic modeling for the Mo-V and Mo-Zr binary systems

摘要

Superalloys are current used materials for high temperature application Recently a new type of alloy called high entropy alloys are found to have a great potential to replace superalloys as material for high temperature application Investigation on high entropy alloys are mostly done by experiment which is time consuming and costly In the future computational method to design High Entropy alloys (HEAs) will be very useful Computational method need to be done accurately for lower order system before going into high-order alloy system A well-known computational method to predict materials properties ab initio calculation based on Density Functional Theory (DFT) has been proven to be a great tool for predicting various material properties This thesis contains ab initio calculation to predict thermodynamic properties Ab initio thermodynamic properties calculation is applied into Mo-V and Mo-Zr CALPHAD modeling to improve their thermodynamic description Mo V and Zr are common added element in refractory-HEAs The thermodynamic description has been assessed in literature However experimental phase diagram data and thermochemical data are rarely available Therefore ab initio-aided CALPHAD modeling is employed to reassess the Mo-V and Mo-Zr binary systems Thermodynamic reassessment of Mo-V and Mo-Zr binary systems has been done and the results are closely agreed to the experimental phase diagram in the literature The assessed parameters are proposed into high-order alloy systems such as HEAs Furthermore Mo-V-Zr ternary systems can be developed by assessing V-Zr binary system Ab initio calculation for V-Zr binary system is presented in the appendix B for the possibility of integrated Mo-V Mo-Zr and V-Zr binary systems into Mo-V-Zr ternary systems Additionally ab initio elastic properties calculations of pure elements and binary constituents from MoNbHfTiZr HEA are presented in the appendix C The elastic properties calculations are performed to get some insights into practical application of HEAs Ab initio calculation successfully predict elastic properties of pure Mo Nb Hf Ti and Zr In bcc and hcp structure compared with experimental and calculated data from the literature Furthermore elastic properties of ten binary alloys from Mo Nb Hf Ti and Zr in bcc-SQS were calculated

獎項日期	2015 6月 25
原文	English
監督員	Shih-kang Lin (Supervisor)