【作者】 高凡；

【导师】 蒋业华；

【作者基本信息】 昆明理工大学 ， 材料加工工程， 2009， 硕士

【摘要】 近年来,陶瓷颗粒增强钢铁基表面复合材料研究得到了较好的发展,但由于基体和增强颗粒、基材与复合层之间热物理性能的不匹配问题使得其热震性能不高,限制了该类复合材料在激冷激热等特定工况下的应用。针对于此,论文研究了WC颗粒增强高铬钢基表层复合材料的制备工艺和抗热震性能,重点考察了加热温度、陶瓷WC颗粒体积分数等参数对其抗热震性能的影响,并对裂纹的萌生和扩展进行了初步研究。论文采用真空实型负压(V-EPC)铸渗工艺,成功制备了不同WC颗粒体积分数的高铬高铬钢基表层复合材料,碳化钨颗粒与基体的界面结合为冶金结合,过渡区过渡平缓,复合效果较好。热震实验结果表明：随着温度的升高,裂纹萌生扩展速度增大,在700℃与800℃的热震实验中,WC颗粒发生完全氧化,在金相制备过程中即发生粉化,于复合层表面形成孔洞；随着WC颗粒体积分数的变化,基体组织与基体体积分数均随之改变,从而影响了裂纹的萌生扩展速度与走向。为了研究复合材料的热疲劳失效机理,论文研究了复合材料的高温氧化行为,结果表明：高温氧化削弱了复合层的抗疲劳破坏能力,且随着温度的升高,氧化反应速度加快。另外,WC颗粒在高于600℃时氧化速度明显增大,易氧化为结构疏松的W03,对裂纹的扩展及材料的失效速度均产生影响。结合复合材料的高温氧化行为和热疲劳裂纹萌生、扩展的形貌观察指出,陶瓷颗粒增强高铬钢基表层复合材料的热疲劳失效是高温氧化和材料热应力两者共同作用的结果,在复合层自身的缺陷处及WC颗粒与基体的结合界面处裂纹开始萌生、扩展。因此,为提高陶瓷颗粒增强金属基表层复合材料的抗热震性能,应选择高温下抗氧化性能较好的陶瓷颗粒作为增强体,同时,易将陶瓷颗粒与金属的热膨胀系数、弹性模量等失配程度控制在较小的范围内。更多还原

【Abstract】 Recently, steel-based surface composites reinforced with hard ceramic particles become a new class of advanced materials, but the application in thermal shock specific conditions was limited because the thermal physical properties did not match between substrate and composite layer, matrix and reinforcing particulate in the composite layer, which led to of their thermal shock performance is low. In this paper, the preparation process and thermal shock resistance of WC particles reinforced steel substrate surface composites were studied, and effects of heating temperature and WC particles volume fraction on their thermal shock resistance, crack initiation and expansion were focused on.In the paper, the high-carbon chromium steel substrate surface composites containing different volume fractions of WC particles were fabricated successfully by V-EPC infiltrating casting process. In the surface composites, interface between particles and matrix is metallurgical bonding and the transitional zone is gentle.The thermal shock experiment results showed that, with the increase in temperature, the velocity of crack initiation and expansion increased. During 700℃to 800℃temperature, WC particles were completely oxidized and changed into powder during the preparation of metallographic, so that some pinholes were found in the surface of the composite layer. When the volume fraction of WC particles is changed, the metallographic of matrix and the volume fraction of the matrix are changed, thus affecting the rate of crack initiation and direction of expansion.In order to study thermal fatigue failure mechanism, high-temperature oxidation behavior of the composite were studied, the results showed that, high-temperature oxidation behavior of the composite layer could decrease their ability of anti-fatigue damage, and with the increase in the temperature the oxidation rate become faster. When the test temperature was above 650℃, oxidation rate of WC particles was increased obviously, and oxidation product was WO3, which was osteoporosis structure and harmful to the thermal shock resistance of the composites.According to high-temperature oxidation behavior and the crack initiation and expansion patterns after thermal fatigue, the thermal fatigue failure mechanism of the surface composites was discussed. The results showed that, the thermal fatigue failure of the surface composites was the result of harmonious effects of the high-temperature oxidation and thermal stress, and crack initiation and expansion occured in the interface of WC particles and matrices and the defects of the composite layer.In order to enhance the thermal shock resistance of ceramic particles reinforced metal substrate surface composites, ceramic particles should have good anti-oxidant capacity at high temperature, and compared with metal sustrate, the thermal expansion coefficient and elastic modulus of the ceramic particles should be controlled in little difference.更多还原