激光熔覆难熔多组元高熵合金涂层设计与制备
发布时间：2018-10-05 11:25
【摘要】：高熵合金的混合熵高于合金整体的熔化熵,一般会形成简单固溶体相,显微组织简单化、一般不倾向于生成金属间化合物等复杂相、具有纳米级析出物或非晶结构等特征,具有高硬度、高强度、高耐蚀、高耐磨、高电阻、高热阻等特性。目前对于快速凝固高熵合金熔覆涂层的精细结构的深入研究较少。高熵合金熔覆涂层的不断发展是熔覆涂层领域向高功能,高附加值迅猛发展的良好契机。本文首先通过经验参数计算和第一性原理计算方法,选定实验所用合金组元体系。通过第一性原理计算了合金的X射线衍射图谱、结合能、形成焓、弹性常数与模量、各向异性参数以及态密度分布等参数。并研究了混合熵对以上计算结果的影响。并选用计算结果优异的合金组元组合进行激光熔覆涂层的制备,应用OM、SEM、EDS以及XRD等测试手段分析涂层宏观形貌与微观组织形态。并借助显微硬度计对涂层各区域进行测试,电化学工作站测试涂层以及基体材料的抗腐蚀性能。实验结果表明,计算与实验所得XRD图谱主峰吻合度较高,并通过晶格常数的对比,可以确定本计算方法具有较大的可靠性。计算所得每个合金的晶格参数存在微弱的差异,结合能与形成焓皆小于0。本文所计算的难熔高熵合金体系同样具有较好的机械稳定性。随着熵的增加,体弹性模量、剪切模量与杨氏模量均呈上升趋势。所有的合金体系皆为韧性材料。高熵合金的体弹性模量的各向异性是不强的。所有合金在费米能级处的态密度值DOS值皆大于零。每个组元的分态密度曲线具有较低的重叠度,证明合金并未有形成金属间化合物等复杂相结构。本文选择TiZrVMoTa、TiZrVMoNb与TiZrVMoTaNb三种组元进行激光熔覆实验。工艺参数:光斑直径3.0mm、扫描速度为300mm/s、激光熔覆功率为4000W。TiZrVMoTaNb高熵合金涂层的相组成为BCC相与少量HCP相;TiZrVMoNb高熵合金涂层的相组成为BCC相与HCP相;TiZrVMoTa高熵合金涂层的相组成为BCC相、HCP相与少量未知相。TiZrVMoTa、TiZrVMoNb与TiZrVMoTaNb高熵合金涂层组织皆以树枝晶为主。TiZrVMoTaNb相比其两类合金涂层的组织存在较大变化,生成较多细小“雪花状”晶粒,排列散乱,形成致密晶粒组织。各高熵合金涂层组织中高熔点元素富集于枝晶内,而低熔点元素富集于枝晶间。熔覆层硬度从底部、中部到顶部依次递增。TiZrVMoNb高熵合金涂层出现了较明显的钝化,腐蚀性能优于基材与其他两类合金。
[Abstract]:The mixing entropy of the high entropy alloy is higher than the melting entropy of the whole alloy, and the simple solid solution phase is formed, the microstructure is simplified, the complex phase such as intermetallic compound is not formed, and it has the characteristics of nanoscale precipitates or amorphous structure, etc. With high hardness, high strength, high corrosion resistance, high wear resistance, high thermal resistance and other characteristics. At present, there is little research on the fine structure of rapid solidification high entropy alloy cladding coating. The continuous development of high entropy alloy cladding coatings is a good opportunity for the rapid development of high function and high added value in the field of cladding coatings. In this paper, the experimental alloy component system is first selected by means of empirical parameter calculation and first-principle calculation method. The X-ray diffraction patterns of the alloy were calculated by first principle. The binding energy, formation enthalpy, elastic constant and modulus, anisotropic parameters and density of state distribution were calculated. The effect of mixed entropy on the above results is studied. The laser cladding coating was prepared by the combination of alloy components with excellent calculation results. The macroscopic morphology and microstructure of the coating were analyzed by means of OM,SEM,EDS and XRD. The corrosion resistance of the coating and the substrate were tested by means of microhardness tester and electrochemical workstation. The experimental results show that the main peak of the XRD spectra obtained by the calculation is in good agreement with that of the experimental ones, and the calculation method can be confirmed to be reliable by comparing the lattice constants. The lattice parameters of each alloy are slightly different, and the binding energy and formation enthalpy are less than 0. The refractory high entropy alloy system calculated in this paper also has good mechanical stability. With the increase of entropy, the bulk elastic modulus, shear modulus and Young's modulus all show an upward trend. All alloy systems are ductile materials. The anisotropy of bulk elastic modulus of high entropy alloy is not strong. The density of states (DOS) of all alloys at Fermi level is greater than zero. The partial density curve of each component has a low degree of overlap, which indicates that the alloy does not form complex phase structures such as intermetallic compounds. In this paper, TiZrVMoTa,TiZrVMoNb and TiZrVMoTaNb components are selected for laser cladding experiments. Process parameters: spot diameter 3.0 mm, scanning speed 300mm / s, laser cladding power 4000W.TiZrVMoTaNb high entropy alloy coating phase composition: BCC phase and a small amount of HCP phase TiZrVMoNb high entropy alloy coating phase composition: BCC phase and HCP phase TiZrVMoTa high entropy alloy coating phase composition The microstructures of BCC phase and a few unknown phase. TiZrVMoTaPTiZrVMoNb and TiZrVMoTaNb high entropy alloy coating are mainly dendrite. TiZrVMoTaNb has a great change in microstructure compared with its two kinds of alloy coatings. A large number of fine "snowflake" grains are formed, which are arranged and scattered to form dense grain structure. The high melting point elements in the microstructure of each high entropy alloy coating are enriched in the branch crystals, while the low melting point elements are enriched in the branch crystals. The hardness of the cladding layer increases from bottom to top. TiZrVMoNb high entropy alloy coating shows obvious passivation and its corrosion resistance is better than that of substrate and other two kinds of alloys.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4
[Abstract]:The mixing entropy of the high entropy alloy is higher than the melting entropy of the whole alloy, and the simple solid solution phase is formed, the microstructure is simplified, the complex phase such as intermetallic compound is not formed, and it has the characteristics of nanoscale precipitates or amorphous structure, etc. With high hardness, high strength, high corrosion resistance, high wear resistance, high thermal resistance and other characteristics. At present, there is little research on the fine structure of rapid solidification high entropy alloy cladding coating. The continuous development of high entropy alloy cladding coatings is a good opportunity for the rapid development of high function and high added value in the field of cladding coatings. In this paper, the experimental alloy component system is first selected by means of empirical parameter calculation and first-principle calculation method. The X-ray diffraction patterns of the alloy were calculated by first principle. The binding energy, formation enthalpy, elastic constant and modulus, anisotropic parameters and density of state distribution were calculated. The effect of mixed entropy on the above results is studied. The laser cladding coating was prepared by the combination of alloy components with excellent calculation results. The macroscopic morphology and microstructure of the coating were analyzed by means of OM,SEM,EDS and XRD. The corrosion resistance of the coating and the substrate were tested by means of microhardness tester and electrochemical workstation. The experimental results show that the main peak of the XRD spectra obtained by the calculation is in good agreement with that of the experimental ones, and the calculation method can be confirmed to be reliable by comparing the lattice constants. The lattice parameters of each alloy are slightly different, and the binding energy and formation enthalpy are less than 0. The refractory high entropy alloy system calculated in this paper also has good mechanical stability. With the increase of entropy, the bulk elastic modulus, shear modulus and Young's modulus all show an upward trend. All alloy systems are ductile materials. The anisotropy of bulk elastic modulus of high entropy alloy is not strong. The density of states (DOS) of all alloys at Fermi level is greater than zero. The partial density curve of each component has a low degree of overlap, which indicates that the alloy does not form complex phase structures such as intermetallic compounds. In this paper, TiZrVMoTa,TiZrVMoNb and TiZrVMoTaNb components are selected for laser cladding experiments. Process parameters: spot diameter 3.0 mm, scanning speed 300mm / s, laser cladding power 4000W.TiZrVMoTaNb high entropy alloy coating phase composition: BCC phase and a small amount of HCP phase TiZrVMoNb high entropy alloy coating phase composition: BCC phase and HCP phase TiZrVMoTa high entropy alloy coating phase composition The microstructures of BCC phase and a few unknown phase. TiZrVMoTaPTiZrVMoNb and TiZrVMoTaNb high entropy alloy coating are mainly dendrite. TiZrVMoTaNb has a great change in microstructure compared with its two kinds of alloy coatings. A large number of fine "snowflake" grains are formed, which are arranged and scattered to form dense grain structure. The high melting point elements in the microstructure of each high entropy alloy coating are enriched in the branch crystals, while the low melting point elements are enriched in the branch crystals. The hardness of the cladding layer increases from bottom to top. TiZrVMoNb high entropy alloy coating shows obvious passivation and its corrosion resistance is better than that of substrate and other two kinds of alloys.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4
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