【摘要】：高熵合金的混合熵高于合金整體的熔化熵,一般會形成簡單固溶體相,顯微組織簡單化、一般不傾向于生成金屬間化合物等復(fù)雜相、具有納米級析出物或非晶結(jié)構(gòu)等特征,具有高硬度、高強(qiáng)度、高耐蝕、高耐磨、高電阻、高熱阻等特性。目前對于快速凝固高熵合金熔覆涂層的精細(xì)結(jié)構(gòu)的深入研究較少。高熵合金熔覆涂層的不斷發(fā)展是熔覆涂層領(lǐng)域向高功能,高附加值迅猛發(fā)展的良好契機(jī)。本文首先通過經(jīng)驗(yàn)參數(shù)計算和第一性原理計算方法,選定實(shí)驗(yàn)所用合金組元體系。通過第一性原理計算了合金的X射線衍射圖譜、結(jié)合能、形成焓、彈性常數(shù)與模量、各向異性參數(shù)以及態(tài)密度分布等參數(shù)。并研究了混合熵對以上計算結(jié)果的影響。并選用計算結(jié)果優(yōu)異的合金組元組合進(jìn)行激光熔覆涂層的制備,應(yīng)用OM、SEM、EDS以及XRD等測試手段分析涂層宏觀形貌與微觀組織形態(tài)。并借助顯微硬度計對涂層各區(qū)域進(jìn)行測試,電化學(xué)工作站測試涂層以及基體材料的抗腐蝕性能。實(shí)驗(yàn)結(jié)果表明,計算與實(shí)驗(yàn)所得XRD圖譜主峰吻合度較高,并通過晶格常數(shù)的對比,可以確定本計算方法具有較大的可靠性。計算所得每個合金的晶格參數(shù)存在微弱的差異,結(jié)合能與形成焓皆小于0。本文所計算的難熔高熵合金體系同樣具有較好的機(jī)械穩(wěn)定性。隨著熵的增加,體彈性模量、剪切模量與楊氏模量均呈上升趨勢。所有的合金體系皆為韌性材料。高熵合金的體彈性模量的各向異性是不強(qiáng)的。所有合金在費(fèi)米能級處的態(tài)密度值DOS值皆大于零。每個組元的分態(tài)密度曲線具有較低的重疊度,證明合金并未有形成金屬間化合物等復(fù)雜相結(jié)構(gòu)。本文選擇TiZrVMoTa、TiZrVMoNb與TiZrVMoTaNb三種組元進(jìn)行激光熔覆實(shí)驗(yàn)。工藝參數(shù):光斑直徑3.0mm、掃描速度為300mm/s、激光熔覆功率為4000W。TiZrVMoTaNb高熵合金涂層的相組成為BCC相與少量HCP相;TiZrVMoNb高熵合金涂層的相組成為BCC相與HCP相;TiZrVMoTa高熵合金涂層的相組成為BCC相、HCP相與少量未知相。TiZrVMoTa、TiZrVMoNb與TiZrVMoTaNb高熵合金涂層組織皆以樹枝晶為主。TiZrVMoTaNb相比其兩類合金涂層的組織存在較大變化,生成較多細(xì)小“雪花狀”晶粒,排列散亂,形成致密晶粒組織。各高熵合金涂層組織中高熔點(diǎn)元素富集于枝晶內(nèi),而低熔點(diǎn)元素富集于枝晶間。熔覆層硬度從底部、中部到頂部依次遞增。TiZrVMoNb高熵合金涂層出現(xiàn)了較明顯的鈍化,腐蝕性能優(yōu)于基材與其他兩類合金。
[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.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG174.4

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本文編號：2253197