本文選題：等離子熔覆　切入點(diǎn)：Fe-Cr-C系合金　出處：《中國礦業(yè)大學(xué)》2017年碩士論文

【摘要】：等離子熔覆技術(shù)具有高精度、機(jī)械化等優(yōu)點(diǎn),是機(jī)械類零部件表面強(qiáng)化的核心技術(shù)之一。Fe-Cr-C系合金熔覆層內(nèi)含有大量的碳化物強(qiáng)化相,硬度及耐磨性均較高,但高C與Cr含量的過共晶Fe-Cr-C系合金熔覆層內(nèi)碳化物粗大且分布不均勻,內(nèi)部切削作用強(qiáng),脆性較大,在使用過程中易發(fā)生裂紋擴(kuò)展及脆性斷裂造成熔覆層失效,限制著該合金在表面強(qiáng)化領(lǐng)域的使用。本文通過等離子熔覆工藝制備不同C與Cr含量的Fe-Cr-C系合金熔覆層,對比分析其性能的差異,通過加入純Ti粉原位生成TiC對過共晶Fe-Cr-C系合金熔覆層進(jìn)行改性研究,探索不同Ti含量對于該合金體系性能的影響,結(jié)合第一性原理對熔覆層內(nèi)碳化物硬質(zhì)相進(jìn)行彈性常數(shù)理論計(jì)算,根據(jù)Voigt-Reuss-Hill近似計(jì)算碳化物彈性模量及泊松比,參考半經(jīng)驗(yàn)公式對碳化物的微觀力學(xué)性能進(jìn)行理論計(jì)算分析,為設(shè)計(jì)合金體系提供理論基礎(chǔ)。亞共晶Fe-Cr-C系熔覆層組織以胞狀晶為主,表面平均硬度值為42.6HRC,磨損過程中以黏著磨損為主,耐磨性較差;近共晶熔覆層表面平均硬度值為52HRC,熔覆層開始出現(xiàn)長條狀亞共晶碳化物,耐磨性有一定的提升;過共晶Fe-Cr-C熔覆層內(nèi)彌散的分布著六邊形及粗條狀碳化物硬質(zhì)相,表面平均硬度值達(dá)到62HRC,以磨粒磨損為主,耐磨性最強(qiáng),但內(nèi)部存在應(yīng)力裂紋,需要進(jìn)一步研究改良。過共晶Fe-Cr-C系熔覆層硬質(zhì)相主要為正交結(jié)構(gòu)六棱柱形Cr7C3(PNMA),通過對熔覆層冷卻過程相變及熱力學(xué)分析,在1000℃以上時含Ti熔覆層冷卻過程中優(yōu)先生成TiC,降低熔覆層過共晶程度的同時在熔覆層內(nèi)形成局部成分過冷,碳化物生長具有一定的方向性,且優(yōu)先形成的TiC作為Cr7C3的異質(zhì)形核核心,起到細(xì)晶強(qiáng)化作用。Cr7C3的均勻分布降低熔覆層內(nèi)部的微觀切削作用及殘余應(yīng)力,減小熔覆層的裂紋產(chǎn)生傾向。過量的Ti導(dǎo)致熔覆層內(nèi)部出現(xiàn)氣孔,Ti含量為0.5%-1.0%時的過共晶Fe-Cr-C系熔覆層呈現(xiàn)出最佳的微觀力學(xué)性能。結(jié)合第一性原理對熔覆層硬質(zhì)相微觀力學(xué)性能研究,熔覆層硬質(zhì)相Cr7C3(PNMA)呈現(xiàn)出金屬鍵特性,而TiC則以共價鍵為主,價鍵較強(qiáng)。通過Voigt-Reuss-Hill近似計(jì)算,正交結(jié)構(gòu)PNMA型Cr7C3及立方結(jié)構(gòu)TiC晶體均滿足結(jié)構(gòu)穩(wěn)定性,且正交結(jié)構(gòu)PNMA型Cr7C3呈現(xiàn)出一定的塑性,與納米探針及顯微硬度實(shí)驗(yàn)結(jié)果相一致。結(jié)合高硬度材料理論微觀硬度值半經(jīng)驗(yàn)公式計(jì)算,PNMA型Cr7C3理論硬度值為13.13GPa,TiC的理論硬度值則為19.73GPa,兩種硬質(zhì)相理論硬度的比值為0.67,與實(shí)驗(yàn)中測得兩種強(qiáng)化相的比例相對應(yīng),說明模擬計(jì)算結(jié)果的可靠性,此計(jì)算方法可以為高硬度材料的開發(fā)提供一定的理論參考基礎(chǔ)。
[Abstract]:Plasma cladding technology has the advantages of high precision and mechanization. It is one of the core technologies for surface strengthening of mechanical parts. Fe-Cr-C alloy cladding contains a large number of carbide strengthening phases, and its hardness and wear resistance are high. However, Hypereutectic Fe-Cr-C alloy with high C and Cr content is characterized by large and uneven distribution of carbides in the cladding layer, strong internal cutting and high brittleness. Crack propagation and brittle fracture are easy to occur in the process of application, which results in the failure of the cladding layer. The application of the alloy in the field of surface strengthening is limited. In this paper, Fe-Cr-C alloy cladding with different content of C and Cr was prepared by plasma cladding, and the difference of its properties was compared and analyzed. The effect of Ti content on the properties of hypereutectic Fe-Cr-C alloy cladding was studied by adding pure Ti powder to form TiC in situ. In combination with the first principle, the elastic constants of the hard phase in the cladding are calculated, the elastic modulus and Poisson's ratio of the carbide are calculated according to the Voigt-Reuss-Hill approximation, and the microscopic mechanical properties of the carbides are calculated and analyzed with reference to the semi-empirical formula. In order to provide the theoretical basis for the design of alloy system, the microstructure of hypoeutectic Fe-Cr-C cladding layer is mainly cellular crystal, the average surface hardness is 42.6 HRC, the adhesion wear is dominant in the wear process, and the wear resistance is poor. The average surface hardness of near-eutectic cladding is 52HRC, and long stripe hypoeutectic carbides begin to appear in the cladding layer, the wear resistance is improved to some extent, and the hard phases of hexagonal and coarse carbides are distributed in the hypereutectic Fe-Cr-C cladding layer. The average hardness value of the surface is 62 HRC, the abrasive wear is the main, the wear resistance is the strongest, but there are stress cracks in the surface. The hypereutectic Fe-Cr-C cladding is mainly composed of hexagonal hexagonal Cr7C3PNMAs. The phase transition and thermodynamics of the cladding layer are analyzed. During cooling process of the cladding layer containing Ti at above 1000 鈩，

本文編號：1681943