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

2018-08-29 00:49:46

single Mo Nb crystal 单晶



难熔金属材料由于其高的熔点、优良的高温力学性能及某些特殊的性能用作高温部件和元件,被广泛的应用于电子电气、航空航天、核动力等高技术领域。由于难熔金属多晶材料在高温使用工况下存在晶粒长大等问题,限制了难熔金属多晶材料的长期使用性能。因此,国际上开发出性能更为优越的难熔金属合金化单晶材料(Mo-3Nb、W-3Nb等单晶材料)。合金化Mo-3Nb单晶材料是在Mo基体中添加合金元素Nb作为强化元素通过电子束区熔方法制备而成。合金化Mo-3Nb单晶的性能同材料制备工艺、微观组织和使用环境密切相关,因此,研究合金化Mo-3Nb单晶的微观组织结构、成分分布、室温力学性能和退火工艺对力学性能的影响,对了解合金化Mo-3Nb单晶的强化机理、改进单晶制备工艺、进行使用性能的评估具有重要意义。
本文介绍了利用微型样品力学测试方法,研究了俄罗斯提供和国内研制的在原始状态和经900℃~1800℃不同高真空退火工艺处理后合金化Mo-3Nb单晶样品的力学性能;采用光学显微镜、扫描电镜、透射电镜分析了俄罗斯提供和国内研制的合金化Mo-3Nb单晶的微观组织结构、合金元素成分分布、析出物的相结构。结合两种单晶样品的不同的析出物相组成和原始及退火后单晶样品的力学性能的数据变化趋势,分析合金化Mo-3Nb单晶的强化机理。
通过研究表明:
西北有色金属研究院采用电子束区熔工艺实现了合金化Mo-3Nb单晶制备。拉制的Mo-3Nb单晶的成分、[111]晶向与轴向的偏离角得到了很好地控制。
数据对比表明,俄罗斯单晶的测试数据与文献数据一致,且测试数据的离散度较小,证明采用微型试样方法测定Mo-3Nb单晶力学性能数据具有很高的可靠性。
对比俄罗斯和国内研制合金化单晶的原始样品测试数据可以看出,国内研制的Mo-3Nb单晶的屈服强度σ0.2比俄罗斯提供Mo-3Nb单晶低7%左右,拉伸断裂强度σb低2%,维氏显微硬度低13%,延伸率高9%左右。两种单晶经900℃~1800℃不同温度真空退火后,强度随退火温度的上升而降低,延伸率随退火温度上升而升高。经1600℃以上温度退火后,俄罗斯Mo-3Nb单晶的屈服强度和断裂强度与室温相比下降近20%,而国内研制单晶强度下降在15%以内,延伸率分别上升28%和22%。对比退火后样品的测试数据,合金化Mo-3Nb单晶经1600℃以上退火处理的力学性能均不会有明显变化。
俄罗斯Mo-3Nb单晶基体Nb含量略高于国内研制单晶,且俄罗斯单晶中存在Nb含量很高的棒状结构的析出相,棒状物结构具有良好的一致性,经分析标定主要成分为NbC和Nb2C;而国内研制的Mo-3Nb单晶基体中只有少量的球状高Nb含量组织。分析认为,正是由于俄罗斯单晶的Nb含量偏高和碳化物析出相的双重强化作用,导致俄罗斯单晶室温强度高于国内研制的单晶材料。
本文仅对俄罗斯和国内研制合金化Mo-3Nb单晶的力学性能测试和显微组织结构进行了初步的分析和研究,还应进一步开展单晶的高温力学性能研究和强化机理研究,并根据研究结果对国内合金化Mo-3Nb单晶研制单位提出制备工艺改进建议。


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 [111] 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.