合金化Mo-3Nb单晶力学性能及微观组织分析/Mechanical Properties and Microstructure Analyze of Alloy
Refractory metal materials can be served as high temperature components and elements because they have high melting point, advantageous high temperature mechanical properties and some specific properties. They are used widely in electron and electric、aviation and spaceflight、nuclear-powered fields and so on. It restricts their long-life performance that crystal grains of refractory metal polycrystalline materials grow up in high temperature. So the refractory alloying single crystal materials(such as Mo-3Nb、W-3Nb single crystal materials) were developed in world. Alloying Mo-3Nb single crystal material was prepared by electron beam zone melting method, in which Nb as strengthen element was added in Mo matrix. The properties of this kind of material have close relationship with microscopic structure, composition profiles and operating environments. Therefore it is very important to investigate the microscopic structure, composition profiles and annealing practice effect on mechanical properties of alloying Mo-3Nb single crystal material, which can help to realize the strengthen mechanism of Mo-3Nb single crystal, improve on its preparation technique and appraise its service performance.
In this thesis, the mechanical properties of Mo-3Nb single crystal specimens which include original state and 900℃～1800℃ annealing state supplied by Russian and home-made were tested by miniature disk testing method; By means of optical microscope, scanning electron microscope and transmission electron microscope, the microscopic structure, alloying elements distributing and the phase structure of educts were investigated; According to the different phase structure of educts of the two kinds of crystal specimens and the data of mechanical properties of original state and annealing state, the strengthen mechanism of Mo-3Nb single crystal was analyzed. The main results are followed:
Alloying Mo-3Nb single crystal material was prepared by electron beam zone melting processing in Northwest Institute for Nonferrous Metal Research. The components and the angle of alternation between  crystallographic direction and axial direction of Mo-3Nb single crystal material are controlled very well.
Comparing to these datas of mechanical properties, the testing values of the Russian single crystal specimens are in good agreement with literature data; In addition, the dispersion degree of testing data is rather small. Therefore we can believe that the data of mechanical properties of Mo-3Nb single crystal specimens that were tested by the miniature disk testing method is dependable.
Comparing the testing data of original specimens supplied by Russian with that of home-made original specimens, we known that the yield strengthσ0.2 of home-made Mo-3Nb single crystal is less seven percent than that of Russian single crystal, tensile strength is less two percent, microhardness is less thirteen percent, and specific elongation is more nine percent. After vacuum annealing in different temperature from 900℃ to 1800℃, the intension of the two kinds of single crystal specimens decreases with the increasing annealing temperature; elongation is increasing with annealing temperature. The yield strength and tensile strength of Russian Mo-3Nb single crystal after annealing in more than 1600℃decrease 20% than that of original state , while that of home-made decrease 15%. The elongation of them increases respectively 28% and 22%.
The Nb component in Russian Mo-3Nb single crystal is a little more than that in home-made single crystal. There are bar shape precipitate phases with high Nb assay in Russian single crystal. By gauging these phases, the main components of them are NbC and Nb2C. There is only a little ball shape matter with high Nb assay in home-made single crystal. In conclusion, the main reason of the Russian single crystal room temperature strength more than that of the home-made is the double strengthening effect of higher Nb component and carbide precipitate phases.
In this thesis, there are only preliminary analyze and investigation on the mechanical properties testing and microscopy structure of Russian and home-made alloying Mo-3Nb single crystal. The high temperature mechanical properties investigation and strengthening mechanism should be done. According to these investigation results, we can make improving suggestion to the preparing units of alloying Mo-3Nb single crystal.