【作者】 王晓东；

【导师】 胡平；

【作者基本信息】 哈尔滨工业大学 ， 材料工程（专业学位）， 2017， 硕士

【摘要】 ZrB₂基超高温陶瓷高温综合性能优异,在高温结构材料方面具有很大的应用前景。但其较差的抗热冲击性能和较低的损伤容限在一定程度上制约了其工程应用。针对这一问题,研究人员也通过多种方法完善该类材料的抗热冲击性能,并取得了一定研究成果。考核材料抗热冲击性能的传统方法多采用方形试样件（高×宽×长=3mm×4mm×36mm）为研究对象,但这类形状的试样在热冲击过程中棱角处容易产生较为明显的应力集中,影响材料的真实抗热冲击性能的评价。采用圆棒状试样替代方形试样考核超高温陶瓷的抗热冲击性能可以降低应力集中对该类材料抗热冲击性能评价的影响。因此本文采用圆棒状试样（Φ4¹0mm×34mm）与方形试样在同一条件下对ZrB₂-SiC基超高温陶瓷材料进行了淬火-强度实验,研究了形状、尺寸等因素对此类材料抗热冲击性能的影响。研究了形状（方形、圆棒）和尺寸（直径4mm、6mm、10mm）对ZrB₂-20vol.%SiC（ZS）陶瓷抗热冲击性能的影响。圆棒状试样显著提高了材料热冲击断裂抗性,并改善了材料的热冲击损伤抗性;而且,随着试样直径的增大,ZS陶瓷抗热冲击性能下降。初步研究了预氧化温度对ZS陶瓷材料抗热冲击性能影响。预氧化后试样初始强度和抗热冲击性能皆得以大幅提高,且从微观角度对试样表面和内部变化进行了分析。研究了形状、尺寸对ZrB₂-20vol.%SiC-15vol.%G（ZS15G）陶瓷以及形状对ZrB₂-20vol.%SiC-20vol.%G（ZS20G）抗热冲击性能的影响。圆棒试样减少了棱角应力集中的影响,提高了材料热冲击临界温差等相关宏观表征参数;而且ZS15G陶瓷的抗热冲击性能同样存在尺寸效应。此外,受热压方向影响,ZS15G陶瓷试样的力学性能和一些热物理性能存在各向异性,导致其抗热冲击性能也存在一定方向性。还探究了预氧化对ZS15G陶瓷和ZS20G陶瓷抗热冲击性能的影响。随着氧化温度的升高,材料的初始强度和抗热冲击性能均得以提升,且在1400℃时,随着氧化时间的增加（30⁶0min）,ZS20G陶瓷的力学性能和抗热冲击性能也均得到提高。利用有限元计算,分析了不同形状和尺寸ZS、ZS15G、ZS20G陶瓷材料热冲击过程中温度场和应力场。比较了不同形状和尺寸试样应力分布和大小,同时分析了热压方向对ZS15G陶瓷抗热冲击性能的影响。模拟结果都较好的反映了形状、尺寸以及热压方向对材料抗热冲击性能的影响,和实验结果相对吻合。更多还原

【Abstract】 ZrB₂-based ultra-high-temperature ceramics are a great potential material in high-temperature structure areas due to their excellent properties.Howerer,the relatively poor thermal shock resistance and damage tolerance of these materials limit their application for engineering.To overcome the issues mentioned above,the researchers have contributed to much attention for improving the thermal shock resistance,and have achieved a certain amount of research results.The traditional methods of assessing the thermal shock resistance of materials are based on rectangular samples（3mm×4mm×36mm in high,width and length,respectively）.However,this kind of shape specimens are easily produce stress concentration at edage of the specimens,which effects the result of the thermal shock resistance.To minimize the effects of stress concentration on the material,cylindrical specimen（4 mm in diameter,length of 34 mm）is a good choice.Besides,the effects of shape and size of the speciments on thermal shock resistance were also investigated.Firstly,the effects of shape,i.e,cylindrical and rectangular speciment,and size（4mm,6mm,10 mm in diameter）on thermal shock resistance for Zr B 2-20 vol.% SiC（ZS）ceramics were investigated.Using cylindrical speciments not only the thermal shock fracture resistance was significantly improved,but also the thermal shock damage resisitance.Moreover,the thermal shock risistance of ZS ceramic was decreased with the increase diameter of the speciments.In addition,the effect of pre-oxidation temperature on the mechanical and thermal sh ock resistance was also conducted.The results point that the initial strength and thermal shock resistance are greatly increased after pre-oxidation.The surface of specimen were analyzed by Scanning Electronic Microscopy（SEM）.Secondly,the effects of shape and size on thermal shock resistance for ZrB₂-20 vol.%SiC-15 vol.%G（ZS15G）and ZrB₂-20 vol.%SiC-20 vol.%G（ZS20G）ceramics were also investigated.The critical themperature of thermal shock was increased due to the cylindrical speciments reduced the stress concentration.Besides,the size effect has also have a great influence on the thermal shock for the ZS15 G ceramic.In addition,the directions of hot pressing also have effect on the thermal shock resistance of ZS15 G ceramicsdue to the anisotropic of mec hanical properties and thermal physical properties.In this paper,the effects of pre-oxidation temperature on thermal shock resistance of ZS15 G and ZS20 G ceramics were studied.Increasing the pre-oxidation temperature,the initial strength and thermal shock resistance are improved.Specifically,the mechanical properties and thermal shock resistance of ZS20 G ceramics increased when the pre-oxidation time ranged from 30 to 60 min at 1400℃.Finally,the distribution of thermal field and stress field which ca used by the shape or size of ZS and ZSG ceramics during the process of thermal shock was calculated by finite element methods.Not only the distribution and the value of sress of the different shape and size were conducted,but also the effect of the directions of hot pressing on thermal shock resistance.The calculated values are consistent with the experimental results.更多还原