Mo-Nb-Hf-Zr-Ti难熔高熵合金组织与力学性能

发布时间：2018-05-28 18:39

本文选题：难熔合金 + 高熵合金　；参考：《哈尔滨工业大学》2016年博士论文

【摘要】：高熵合金打破传统合金以一种或两种元素为主元的合金设计思路,以五种及五种以上元素为主元,具有热力学上的高熵效应、动力学上的缓慢扩散效应、结构上的严重晶格畸变效应及性能上的鸡尾酒效应等特性,合金具有简单的组织结构及优异的综合性能。为开发新型高温结构材料,本文根据高熵合金的设计理念,采用真空电弧熔炼技术制备以难熔金属元素为主元的Mo-Nb-Hf-Zr-Ti难熔高熵合金体系,并分别添加金属元素Al、Cr或非金属元素Si、B、C调整合金性能,研究添加元素对合金组织和性能的影响规律及机制。首先采用Thermo-calc软件结合TCNI-5数据库相图计算预测MoNbHf ZrTi合金相组成,试验研究等摩尔MoNbHfZrTi合金的相组成、显微组织、相稳定性、力学性能及热变形行为,并研究了MoNbHfZr Ti合金中五种组成元素含量变化对合金组织和性能的影响规律。研究发现:相图计算与试验结果一致,MoNbHfZrTi合金由单相体心立方(BCC)固溶体相组成,热分析(DSC)和热处理结果表明该BCC相具有极高的结构稳定性,在1450 oC以下没有发生任何相变。铸态合金和均匀化态合金室温下的屈服强度分别为1719 MPa和1575 MPa,合金压缩断口属于典型的脆性断裂。在ε?=0.1 s-1及T=1200 oC下,合金屈服强度仍能达到750 MPa。MoNbHfZrTi合金在900 oC及以上温度热变形时,应力-应变曲线呈现典型的动态再结晶特征,连续动态再结晶和不连续动态再结晶同时发生,其中不连续动态再结晶占主导地位,变形温度的升高和应变速率的增加将弱化连续动态再结晶机制。MoNbHf ZrTi合金中各组元含量在11.11~27.27at.%之间时,合金仍由单相BCC固溶体相组成,与等摩尔MoNbHfZrTi合金相比,合金强度和硬度均降低,但在非等摩尔Mo-Nb-Hf-Zr-Ti合金中,Mo含量增加合金强度提高,Hf、Zr和Ti含量增加合金强度降低,Nb含量变化对合金强度影响不大。综合考虑强度、塑性、密度及成本等方面的因素,选取综合性能较好的Mo0.5NbHf0.5ZrTi(Mo0.5Hf0.5)合金作为基体合金,分别添加Al或Cr元素研究合金组织和性能的变化规律。研究发现少量的Al或Cr元素可以固溶入基体相BCC1中,较多Al元素的添加合金将形成与BCC1晶格常数相近的新的固溶相BCC2相,基体相BCC1富集Mo和Nb元素,BCC2相富集Zr和Hf元素;Cr元素添加后合金中形成MgCu2型Laves相(Nb,Hf,Zr,Ti)-(Mo,Cr)2。Mo0.5NbHf0.5ZrTiAl0.3(Al0.3)和Mo0.5NbHf0.5ZrTiCr0.3(Cr0.3)合金热处理后分别析出更多的BCC2相和Laves相。少量Al或Cr元素的添加可以提高合金强度同时改善合金塑性。随Al元素含量增加合金强度有少量提高塑性降低,随Cr元素含量增加合金强度逐渐提高,强度的提高主要归因于Laves相的形成。非金属元素B、Si或C元素添加到Mo0.5NbHf0.5ZrTi合金中形成了硼化物、硅化物或碳化物增强的Mo0.5NbHf0.5ZrTi难熔高熵合金。研究发现:合金基体相仍为BCC固溶相,硼化物增强相为MB2相,其中M为Mo、Nb、Hf、Zr、Ti元素,硅化物增强相为M5Si3相,其中M为Mo、Nb、Hf、Zr、Ti元素,碳化物增强相为MC,其中M为Hf、Nb、Zr、Ti元素。B、Si或C与金属元素之间的二元合金混合焓值越负即结合能越强所形成的硼化物、硅化物或碳化物中金属元素的含量越高。少量B、Si或C元素的添加,合金的强度提高同时塑性也得到改善,塑性的提高主要归因于细晶强化及基体相固溶强化度的降低,而较多B、Si或C元素的添加提高合金强度的同时降低了合金的塑韧性。研究同时添加Al、Cr、B、Si或C其中几种元素后Mo-Nb-Hf-Zr-Ti合金的组织结构发现:同时添加多种合金化元素后Mo-Nb-Hf-Zr-Ti合金仍由BCC固溶相作为基体相,而其它相的形成种类和数量与加入的合金化元素的含量及合金化元素与基体合金组成元素的结合能有紧密的联系。如在合金MoNb1.5Hf0.3Zr0.5Ti1.5Al0.2Cr0.2C0.05B0.05Si0.05中尽管Si、C、B三种元素的含量是相同的,但是C元素与Mo、Nb、Hf、Zr、Ti的结合能最强,因此合金中形成的第二相主要为碳化物相。
[Abstract]:High entropy alloy has broken the design idea of alloy with one or two elements as the main element, with five and more than five elements as the main element. The alloy has the characteristics of high entropy effect in thermodynamics, slow diffusion effect in kinetics, serious lattice distortion effect in structure and the effect of chicken tail wine on performance, and the alloy has simple tissue junction. In order to develop new high temperature structural materials, based on the design concept of high entropy alloy, this paper uses vacuum arc smelting technology to prepare Mo-Nb-Hf-Zr-Ti refractory high entropy alloy system with refractory metal elements as the main element, and to add metal elements Al, Cr or non-metallic element Si, B, C to adjust the alloy properties, and to study the addition of the alloy. The influence law and mechanism of elements on Microstructure and properties of alloy. First, the phase composition of MoNbHf ZrTi alloy was calculated and predicted by Thermo-calc software combined with TCNI-5 database phase diagram. The phase composition, microstructure, phase stability, mechanical properties and thermal deformation behavior of MoNbHf ZrTi alloy were tested and studied, and five groups of MoNbHfZr Ti alloys were studied. The effect of the change of the content of the elements on the microstructure and properties of the alloy. It is found that the calculation of the phase diagram is in agreement with the experimental results. The MoNbHfZrTi alloy is composed of the solid solution phase of the single phase body center cubic (BCC). The thermal analysis (DSC) and heat treatment results show that the BCC phase has a very high structural stability, and there is no phase transition below 1450 oC. The yield strength of gold and homogenized alloys at room temperature is 1719 MPa and 1575 MPa respectively. The alloy compression fracture belongs to typical brittle fracture. Under the epsilon =0.1 S-1 and T=1200 oC, the yield strength of the alloy can still reach the typical dynamic recrystallization characteristic of the stress strain curve when the temperature of 750 MPa.MoNbHfZrTi alloy is 900 oC and above the thermal deformation. Continuous dynamic recrystallization and discontinuous dynamic recrystallization occur simultaneously, in which the discontinuous dynamic recrystallization takes the dominant position. The increase of the deformation temperature and the increase of the strain rate will weaken the continuous dynamic recrystallization mechanism of the.MoNbHf ZrTi alloy. The alloy is still composed of the single-phase BCC solid solution phase. Compared to the mole MoNbHfZrTi alloy, the strength and hardness of the alloy decreased, but in the non equimormole Mo-Nb-Hf-Zr-Ti alloy, the Mo content increased the alloy strength, the Hf, Zr and Ti content increased the alloy strength, and the change of Nb content had little effect on the strength of the alloy. The comprehensive performance was selected by considering the factors such as strength, plasticity, density and cost. A good Mo0.5NbHf0.5ZrTi (Mo0.5Hf0.5) alloy is used as a matrix alloy, adding Al or Cr elements to study the change law of the microstructure and properties of the alloy respectively. It is found that a small amount of Al or Cr elements can be dissolved into the matrix phase BCC1, and the addition of Al elements will form a new solid solution phase BCC2 phase similar to the normal number of the BCC1 lattice, and the matrix phase is BCC1 rich. The concentration of Mo and Nb elements, BCC2 phase enrichment of Zr and Hf elements, and the addition of Cr elements to the formation of MgCu2 type Laves phase (Nb, Hf, Zr, Ti). Gold plasticity. With the increase of the content of Al elements, the strength of the alloy decreases slightly, and the strength of the alloy increases gradually with the increase of the content of the Cr element. The increase of the strength is mainly attributed to the formation of the Laves phase. The addition of the non metal elements B, Si or C elements to the Mo0.5NbHf0.5ZrTi alloy has formed a boron carbide, silicide or carbide enhanced Mo0.5NbHf0.5ZrTi. It is found that the matrix phase of the alloy is still BCC solid solution phase and the reinforced phase of boride is MB2 phase, in which M is Mo, Nb, Hf, Zr, Ti, and the silicide phase is M5Si3 phase, and M is Mo. The higher the binding energy, the higher the content of the metal elements in the borides, silicides or carbides. A small amount of B, Si or C elements are added, the strength of the alloy is improved and the plasticity is improved. The increase of the plasticity is mainly due to the refinement of the fine crystal and the decrease of the solid solution intensity of the matrix phase, and the addition of more B, Si or C elements to improve the alloy. The strength of the alloy reduces the ductility of the alloy at the same time. The structure of the Mo-Nb-Hf-Zr-Ti alloy after adding several elements of Al, Cr, B, Si or C is found. After adding a variety of alloying elements, the Mo-Nb-Hf-Zr-Ti alloy is still composed of the solid solution phase of BCC as the matrix phase, and the formation and quantity of other phases and the content of the alloying elements are added. The binding energy of the amount and alloying element to the matrix alloy is closely related. In the alloy MoNb1.5Hf0.3Zr0.5Ti1.5Al0.2Cr0.2C0.05B0.05Si0.05, although the content of the three elements of Si, C, and B is the same, the binding energy of C elements to Mo, Nb, Hf, Zr and Ti is the strongest, so the secondary phase formed in the alloy is mainly carbide phase.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.412

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