【作者】 王昕；

【导师】 许云华； 钟黎声；

【作者基本信息】 西安理工大学 ， 材料加工工程， 2017， 硕士

【摘要】 在均质基体材料表面制备一层梯度增强层,即获得表面梯度复合材料实现成分和组织的梯度分布,可以使表面增强层与基体材料结合更好,提高材料的综合使用性能。表面梯度复合材料结构和性能的可控性使其广泛应用于航空航天、切割工具、冶金、矿山等领域,是一类非常有前景的新型复合材料。本文以纯钒和灰口铸铁为原料,利用金属钒的强碳化物形成特性,通过固相原位反应方法制备VCp/Fe表面梯度复合材料,对其原位反应过程、组织演变规律、各反应层的生长动力学和耐磨性等进行研究。主要研究结果包括:(1)采用固相原位反应方法可以实现VCp/Fe表面梯度复合材料的制备。随着保温温度的升高(950℃、1000℃和1050℃)和保温时间(0.5h,1h,2h,4h)的延长,原有物相(具体:V2C、V8C7)含量逐渐增大,没有新的物相生成。通过对比950℃保温不同时间的试样组织,当保温0.5h时反应层总厚度为55μm,当保温4h时,反应层总厚度达到168μm左右;说明随着保温时间的增加,反应层的厚度逐渐增大,同时V8C7致密层组织的致密度有所减小,组织中开始出现基体成分的夹杂,同时扩散区的碳化物分布更加均匀。(2)对VCp/Fe表面梯度复合材料V2C和V8C7致密反应层厚度随保温温度和保温时间的变化规律进行研究。结果表明,随着保温温度的升高,V2C和V8C7致密反应层的厚度呈指数关系逐渐增大;同时,随着保温时间的延长,V2C和V8C7致密反应层的厚度呈抛物线关系增长。计算得出,V2C和V8C7致密反应层的生长激活能分别为53.92kJ/mol和42.39kJ/mol。推导得出V2C致密反应层或V8C7致密层厚度(d)与反应温度(T)和时间(t)之间的关系分别为:a=d0+kt1/n=3.52 ×10-4+1.38 × 10-3 exp(-6485.33/T)t-1/2 d=d0+kt1/n=8.10×10-4+2.44×10-3 exp(-5098.13/T)t1/2(3)VCp/Fe表面梯度复合材料的显微硬度从表面至基体呈梯度分布。V2C致密反应层的平均硬度为1963HV0.1,是灰口铸铁显微硬度(235HV0.1)的8倍,V8C7致密反应层的平均显微硬度也达到1707HV0.1。纳米压痕试验测定V8C7致密反应层的弹性模量为431.98GPa。计算得出所制备V8C7致密反应层的断裂韧性为3.73 MPa·m1/2。磨粒磨损条件下,V2C和V8C7致密反应层的相对耐磨性为23.41。V2C层的磨损表面只有少量的刮擦和较浅犁沟,而在V8C7致密组织中还存在碳化物颗粒的破碎和剥落。摩擦磨损条件下,V8C7致密反应层的相对耐磨性分别为基体的4倍(室温)、9倍(400℃)和3倍(800℃)。室温下,V8C7致密反应层磨损机理以磨粒磨损和轻微的粘着磨损为主,而高温(400℃和800℃)下,磨损机理主要以粘着磨损和氧化磨损为主。更多还原

【Abstract】 The usability of material can be improved by realizing compoment and microstructure gradient distribution on the surface of a homogeneous material,which due to better bonding strength between enhancement layer and matrix.The controllability of the surface gradient composite make it widely used in aviation aerospace,cutting tools,metallurgy,mine and other fields.The VCp/Fe surface gradient composite was prepared by using vanadium plate(99.90%)and grey cast iron as raw materials,which make use of the better carbide formation characteristics of metal vanadium.And the in situ reaction process,microstructure evolution,growth dynamics of the reaction layers and wear resistance of the composite were sutdied.The main research results include:(1)The VCp/Fe surface gradient composite can be prepared by solid phase reaction method.With the increase of heat preservation temperature(950℃,1000℃ and 1050℃)and the holding time(0.5h,1h,2h,4h),the original phase(V2C and V8C7)increased gradually,and no new phase was formed.The thickness of the layer is 55 μm when the holding temperature and time are 950℃ and 0.5h,respectively,while 168 μm for 4h.With the increase of the holding time,the thickness of the reaction layer increased gradually,while the density of the dense layer of VSC7 decreased.(2)The relationship among the thickness of reinforcement layer,the temperature and holding time of the VCp/Fe gradient composites was studied.The results showed that with the increase of temperature,the thickness of V2C and V8C7 dense layer exponentially increase gradually;at the same time,with the prolonging of holding time,the thickness of V2C and V8C7 dense layer is parabola growth.Calculation shows that the V2C and V8C7 dense layer growth activation energy were 53.92kJ/mol and 42.39kJ/mol,respectively.It is deduced that the relationship between the thickness of V2C or V8C7 dense layer(d)and reaction temperature(T)and time(t):For V2C dense layer,d=d0+kt1/n=3.52×10-4+2.10×10-8 exp(6063.94/T)t 1/2 For V8C7 dense layer,d=d0+kt1/n=8.10 × 10-4+1.810-6 exp(8114.28/T)t1/2(3)The microhardness of the VCp/Fe surface gradient composites showed a gradient distribution from the surface to the matrix.The microhardness of the V2C dense layer is the highest and the average hardness is 1963 HV0.1,which is six times higher than that of the matrix(235 HV0.1).The average hardness of V8C7 dense reaction layer reach to 1707 HV0.1.The elastic modulus of V8C7 dense layer is 431.98 GPa by nanoindentation.The fracture toughness of the V8C7 dense layer is 3.73 MPa·m1/2.Under abrasive wear conditions,the relative wear resistance of V2C and V8C7 dense layer is 23.41.V2C layer on the worn surface of only a small amount of scratching and shallow furrows,and V8C7 in dense tissue also exist in the carbide grain crushing and spalling.Under friction wear conditions,V8C7 dense layer on the wear resistance were 4 times(room temperature),9 times(400℃)and 3 times(800℃)of the matrix.At room temperature,the wear mechanism of V8C7 dense layer is mainly abrasive wear and slight adhesive wear,and the wear mechanism is mainly adhesive wear and oxidation wear at high temperature(400℃ and 800℃).更多还原