【作者】 屈平；

【导师】 马跃进； 孙维连；

【作者基本信息】 河北农业大学 ， 农业机械化工程， 2015， 博士

【摘要】 针对农业机械化作业的特点,为解决旋耕刀、犁铧等触土刀具制造成本高、易磨损、失效频繁和寿命低等现状,研究开发了金属表面熔覆陶瓷新工艺。采用等离子弧(PTA)熔覆技术在Q235钢表面原位合成Ti(C,N)-WC、Al2O3-Ti(C,N)等硬质相颗粒的金属陶瓷复合材料涂层,通过调节和控制工艺参数及改变原料粉末添加量、配方,研究了复合涂层的组织结构及耐磨耐蚀性,分析了涂层形成机理,并采用正交试验法优化了熔覆工艺参数,为Ti(C,N)/金属复合涂层应用于农机材料表面强化提供参考。研究表明,采用Ti N粉末为固体氮源原位合成了Ti(C,N)-WC/Ni60A基金属陶瓷复合涂层,该涂层与基体呈冶金结合,其表层中多角片状WC较多,次表层由呈芯-环结构的硬质相埋置于粘结相之中构成。随着Ni60A含量的增加,涂层中硬质相晶粒减少,包覆相不完整,芯壳结构逐渐消失,涂层硬度降低;随着Ti N含量的增加,硬质相晶粒细化,包覆相厚度减小或不完整,孔隙相、裂缝增多,并出现脆生相Ni3Ti,涂层硬度降低;随着WC含量的增加,改善了硬质相与粘结相之间的润湿性,抑制了硬质相晶粒长大,涂层硬度提高,当WC含量为12Wt%时涂层硬度最高。对Ti-C-N-W-Fe-Ni体系进行了热力学分析,生成的Ti(C,N)颗粒自由能最低,生成物最稳定,生成含Ti(C,N)硬质相颗粒是可行的;对体系进行了反应动力学分析,建立了反应动力学模型及特征方程,通过减少Ni60A含量、提高温度、减小中间层厚度、细化碳颗粒等方法可提高生成Ti C、Ti(C,N)的反应速率;硬质相颗粒扩散距离与体系的绝对温度、熔覆时长、颗粒直径及金属液体粘度系数有关。涂层硬度最高HV0.52040,平均硬度HV0.51750,约为基体硬度的7.2倍;涂层干滑动摩擦系数平均值为0.38,其耐磨性比65Mn钢及Q235基体分别提高6倍及16倍;以磨损量为考察指标对熔覆工艺参数进行优化,最佳水平组合为A3B2C3D3E2;WC含量为12Wt%的涂层在酸性及氯化钠溶液环境中腐蚀速率分别为基体的1/9和1/4,涂层耐腐蚀性能优于基体。采用Ti N粉末为固体氮源,以铝热剂的放热反应提供内在热源、等离子弧柱为外在热源,原位合成了Al2O3-Ti(C,N)基复合材料涂层,涂层与基体呈冶金结合,涂层由网状、嵌套、球状等三种结构组成,硬质相Al2O3、Ti(C,N)与粘结相Fe-Ni之间相互包裹、互相嵌套,构形成空间网状骨架结构。涂层硬度最高可达HV0.52160,平均硬度HV0.51870,约为基体Q235钢的7.7倍;涂层摩擦系数约为0.372,其耐磨性比65Mn钢及Q235钢分别提高7倍多及17倍多;在酸性和氯化钠盐溶液环境中,涂层腐蚀速率分别为Q235钢的1/10和1/5,涂层耐腐蚀性能优于基体。采用三聚氰胺为碳氮前驱体预先制备g-C3N4粉末并以其为碳氮源,原位合成了Ti(C,N)基复合涂层,涂层与基体呈现冶金结合,涂层主要由芯-壳结构和多角片状WC硬质相弥散于Fe-Ni粘结相之中构成;涂层硬度最高HV0.51830,平均硬度HV0.51700,约为基体材料的7倍;涂层摩擦系数约为0.42,其耐磨性比65Mn钢和Q235钢分别提高4.7倍及11.6倍;在酸性及氯化钠溶液环境中,涂层腐蚀速率分别为Q235钢的1/7倍和2/7,以三聚氰胺为前驱体的复合涂层耐蚀性优于基体。更多还原

【Abstract】 In order to improve the agricultural touching soil cutter and ploughshare which tend to wear out easily, break down frequently, have high costs and short service scope, the paper has taken a process of cladding ceramic coating on the metal surface as its object.The method adopted is as following: a kind of PTA(Plasma Transferred Arc) cladding technology with the use of atmospheric pressure reactive to synthesize in-situ hard phase Ti(C,N)-WC, Al2O3-Ti(C,N) particles to form metal ceramic composite coating on Q235 A plain carbon steel surface. Under the conditions of regulating and controlling the process parameters, raw powder of mass ratio and different formulations are tested to study the organization structure, wear resistance and corrosion resistance of the Ti(C,N)/metal composite coating. This paper studies the formation mechanism, applying orthogonal test method to optimize plasma cladding process parameters, with the intention of providing reference for the surface strengthening of agricultural materials with applying composite coating containing Ti(C,N).The results demonstrate that the Ti(C,N)-WC/Ni60 A based metal ceramic composite coating with Ti N powder as solid nitrogen source and through the reactive plasma cladding technology, was synthesized in-situ. The Ti(C,N)-WC/Ni60 A composite coating metallurgical combined with the substrate. Polygonal flake WC distributed in the cladding coating surface and the core-ring structure dispersed among the adhesive phase of the subsurface. The raw material powder composition and its content had such influences on coating quality and organizational structure as the followings. With the increase of Ni60 A, the number of the hard phase particles decreased; the core-ring structure was not complete; the distribution of the hard phase particles tended to be uneven and disappeared and the hardness of the coating decreased. Besides, the ring thickness of Surrounding Structure phase reduced or ring was not complete; the hard phase grain was refined gradually; the core-ring structure became incomplete and porosity and cracks in coating increased. Consequently, the coating produces crisp phase Ni3 Ti, leading to the hardness decrease. In a certain range when WC content was 12%, the micro-hardness, degree of wearing out and corrosion resistance of coating were optimal, the increase of WC content effectively improved the wettability of the hard phase and binder phase, inhibited the hard phase grain growth and improved the micro-hardness.The Ti-C-N-W-Fe-Ni system has been analyzed by thermodynamics with the result that under the condition that the free energy Ti(C,N) particles is the minimum, and the reaction products are the most stable it is feasible to form Ti(C,N)-WC hard phase particles.The kinetics having been analyzed with the metallurgy reaction kinetics model and thecharacteristic equation, was found the reaction rate of Ti C、Ti(C,N) by reducing the content of Ni60 A, improving the cladding temperature, decreasing the Ti-rich intermediate layer thickness, and refining the carbon particle size. Distribution and diffusion distance of the hard phase particles are related to the system absolute temperature, cladding time, the particle diameter and the metal liquid viscosity coefficient.The highest hardness value of the coatings was up to HV0.52040, and the average hardness was HV0.51750, about 7.2 times of the substrate. When the coatings was in wear stable period, the mean dry sliding friction coefficient was 0.38, and the wear resistance of the composite coating was 6 times higher than 65 Mn steel, and 16 times higher than Q235 A substrate. The plasma cladding process parameters were optimized by wear loss as the investigation target, and the best combination of the process parameters was A3B2C3D3E2,coatings had better corrosion resistance behavior than the substrate. In 5% H2SO4 solution,the corrosion rate of the coating with WC content of 12% was 1/9 of Q235 A, while in3.5% Na Cl solution was 1/4 of Q235 A.Using Ti N powder as solid nitrogen source, the heat released from the exothermic reaction of termite as an internal heat source, and plasma arc column as an external heat source, Al2O3-Ti(C,N)(AT composite materials) was synthesized in-situ, and the coating and the substrate was metallurgical combined. The coating was composed of reticular structure, nested structure and spherical structure. The hard phase Al2O3 and Ti(C,N) and Fe-Ni binding phase were mutual inclusion between themselves body, nested within each other, constituting the spatial reticulate structure. The highest hardness value of the coatings was up to HV0.52160, and the average hardness was HV0.51870, and about 7.7times of Q235 A steel substrate. The friction coefficient of AT composite coating was about0.372, and the wear resistance of the AT composite coating was 7 times higher than 65 Mn steel, and 17 times higher than Q235 A substrate surface. In acid and sodium chloride salt solution environment, the corrosion rates of AT coating were respectively 1/10 and 1/5 of Q235 A. The corrosion resistance of the AT composite coating was better than Q235 A.Using the low cost carbon nitrogen compounds as the precursor of carbon and nitrogen and pre-preparing high nitrogen content of carbon nitride powder, with g-C3N4 powder as carbon and nitrogen source, the Ti(C,N) was synthesized in-situ, and the coating and the substrate was metallurgical combined. The coating zone was mainly composed of spherical core-ring structure including Ti(C,N) and white edges flake WC as hard phase,and Fe-Ni alloy as the binding phase. The highest hardness value of the coatings was up to HV0.51830, and the average hardness of the coating was HV0.51700, and about 7 times of the Q235 A. The friction coefficient of the composite coating was about 0.42, the wear resistance was 4.7 times higher than 65 Mn steel, and was 11.6 times higher than Q235A;In acid and sodium chloride salt solution environment, the corrosion rates of composite coating were respectively 1/7 and 2/7 of Q235 A. The melamine as the precursor of carbon and nitrogen prepared the composite coating which had better corrosion resistance than the Q235 A substrate.更多还原