MoSi2的强韧化及氧化烧蚀性能研究

工学硕士学位论文MoSi2的强韧化及氧化烧蚀性能研究THE RESEARCH OF STRENGTHENING, TOUGHENING, ABLATION AND OXIDATION OF MOLYBDENUM DISILICIDE BASED COMPOSITE徐东明哈尔滨工业大学2007年7月国内图书分类号：TB332国际图书分类号：620工学硕士学位论文MoSi2的强韧化及氧化烧蚀性能研究硕 士 研究生：徐东明导 师：张幸红教授申 请 学 位：工学硕士学 科、专 业：材料学所 在 单 位：复合材料与结构研究所答 辩 日 期：2007年7月授予学位单位：哈尔滨工业大学Classified Index: TB332U.D.C: 620Dissertation for the Master Degree in EngineeringTHE RESEARCH OF STRENGTHENING, TOUGHENING, ABLATION ANDOXIDATION OF MOLYBDENUMDISILICIDE BASED COMPOSITECandidate:Supervisor:Academic Degree Applied for: Speciality:Affiliation：Date of Defence:Degree-Conferring-Institution:Xu DongmingProf. Zhang Xinghong Master of Engineering Materials ScienceSchool of Astronautics July, 2007Harbin Institute of Technology哈尔滨工业大学硕士学位论文摘要金属间化合物MoSi2由于具有优异的高温抗氧化能力，而成为新一代航空发动机热端部件的热门候选材料。

但MoSi2的室温断裂韧性低，高温强度不足使其还不能立即应用于该领域。

并且航空发动机热端部件的服役环境非常恶劣，需经受温度的急剧变化和高温燃气流的冲刷。

所以MoSi2的抗热震性和抗动态氧化能力也是必须考察的重点。

碳化硅晶须（SiC w）是缺陷很少的陶瓷单晶体，它具有很大的长径比。

因此碳化硅晶须具有优异的力学性能，其拉伸强度达到14GPa，弹性模量能够达到700GPa，是一种很理想的陶瓷增韧体。

采用SiC w增韧MoSi2，改善MoSi2的本征脆性，并提高其抗热震性具有重大的实用价值。

为提高MoSi2粉体烧结的本征驱动力，采用湿法球磨的方法将MoSi2粉体的中位粒径降低到 1.80μm。

选用非离子型分散剂聚乙二醇和无机电解质类分散剂焦磷酸钠做为SiC w的分散剂，选用无水乙醇做为SiC w的分散介质。

采用超声振动加球磨混合的方法对SiC w进行分散。

实验结果表明SiC w 在基体MoSi2中的分散效果良好。

在1600℃的烧结温度和 30MPa的烧结压力下，保温时间1h热压烧结制备了MoSi2\SiC w和MoSi2\SiC p复合材料。

通过对体系的烧结动力学研究，发现SiC w含量为30vol%的试样的致密化速率曲线明显不同于SiC w含量为20vol%和10vol%的试样。

晶须含量对烧结致密化影响明显，而晶须的形状对烧结的影响不明显。

通过力学性能的测试发现SiC w的加入明显改善了MoSi2的力学性能。

复合材料的断裂韧性随SiC w含量的提高而上升。

由于SiC w竹节状的外形和热膨胀失配引起的残余压应力，SiC w和MoSi2界面解离困难，限制了晶须桥联和晶须拔出等重要韧化机制作用的发挥。

主要的韧化机制是裂纹偏转、晶粒细化和残余应力韧化。

使用氧-乙炔烧蚀实验装置考察材料的抗热震能力和动态氧化能力。

理论计算表明：强度的提高是MoSi2\SiC w复合材料抗热冲击断裂性提高的主要原因，而热膨胀系数降低则是MoSi2抗热震损伤性提高的主要原因。

尽管理论计算表明SiC w的加入能提高MoSi2的抗热震性，但在实际的热震测试中，试样均发生了热震破坏。

即使是SiC w含量高达30vol%的MoSi2\SiC w复合材料也还是不能有效地抵抗热冲击破坏。

1710℃动态氧化条件下MoSi2\SiC w表面生成致密的SiO2保护层，4min内- I -哈尔滨工业大学硕士学位论文没有烧蚀。

1817℃，表面的SiO2氧化层发生了严重退化。

关键词二硅化钼；碳化硅晶须；烧结动力学；韧化；热震；动态氧化- II -哈尔滨工业大学硕士学位论文AbstractIntermetallic compounds MoSi2 is a hot candidate material for next generation of aero-engine because of its excellent oxidation resistance at high temperature. However, MoSi2 use is limited by the brittleness at room temperature and the low strength at high temperature. The components of aero-engine need to withstand the dramatic changes in temperature and the high-temperature gas flow erosion. So the thermal shock resistance and dynamic oxidation resistance of MoSi2 must to be researched.SiC whiskers (SiC w) has excellent mechanical properties for its little defects and high aspect ratio. Its tensile strength can be up to 14 GPa and elastic modulus can reach to 700 GPa. Therefore using the SiC w as the toughening agent to improve the intrinsic brittleness of MoSi2 and enhance its thermal shock resistance is of great practical significance.MoSi2 powder was wet milled to 1.80 μm for enhancing the intrinsic driving force of sintering. Polyethylene glycol and sodium pyrophosphate were used as the dispersant of SiC w. And ethanol was choosed as the dispersion medium. Ultrasonic vibration and milling mixed approach were used to scatter the SiC w. Experimental results showed that SiC w were well dispersed in MoSi2 matrix. MoSi2\SiC w and MoSi2\SiC p composites material were prepared by the hot pressing sintering. The sintering temperature was 1600℃ and the holding pressure was 30 MPa. Densification rate curve of MoSi2\30vol% SiC w is significantly different from MoSi2\20vol%SiC w and MoSi2\10vol%SiC w by studying the sintering kinetics of the system. The content of the SiC w affected on the densification significantly. And the shape of whisker is not the main factor affecting sintering.The mechanical properties improvement of MoSi2 by the adding of SiC w was significant.The fracture toughness of the composite materials rose with the increasing of SiC w content.As the bamboo-shaped outer surface of SiC w and the residual compressive stress results from thermal expansion mismatch between SiC w and MoSi2, interface debonding is very difficult. Two important whisker toughening mechanisms of whisker bridging and pullout were both limited to- III -哈尔滨工业大学硕士学位论文playing their roles.The main toughening mechanisms are crack deflection, grain refinement and residual stress toughening.The oxygen-acetylene device was set up for the thermal shock and oxidation dynamic testing. Calculations shows the rise of strength is the key factor for the increasing of thermal shock fracture resistance in MoSi2\SiC w composite. And lower thermal expansion coefficient was account for the rising of thermal shock damage resistance in MoSi2\SiC w. Although theoretical calculations indicated that the SiC w was able to improve the material thermal shock resistance, all of the samples were damaged in the actual thermal shock tests. It was infered that MoSi2\30vol%SiC w has a higher thermal shock resistance than MoSi2\20vol%SiC w and MoSi2\10vol%SiC w by studying the surface and the fracture macrograph of the thermal shocked samples with different content of SiC w.MoSi2\SiC w generated compact surface SiO2 protection layer at 1710℃dynamic oxidation conditions. So there was no ablation in 4 min.And the silica oxide layer began to severely degrade up to 1817℃.Keywords MoSi2, SiC w, toughening mechanism, thermal shock, dynamic oxidation- IV -哈尔滨工业大学硕士学位论文目录摘要 (I)Abstract (III)第1章绪论 (1)1.1 课题背景 (1)1.2 MoSi2的晶体结构、微观组织及性能 (2)1.2.1 MoSi2的组成及晶体结构 (2)1.2.2 MoSi2的微观组织 (3)1.2.3 MoSi2的性能 (4)1.3 MoSi2的复合化 (7)1.4 SiC w的结构、性能及对MoSi2性能的影响 (9)1.4.1 SiC w的结构及性能 (9)1.4.2 SiC w对MoSi2性能的影响 (10)1.4.3 SiC w\MoSi2复合材料性能的影响因素 (11)1.5 国内外关于MoSi2及MoSi2\SiC w的研究进展 (13)1.6 研究的主要内容 (15)第2章材料与试验方法 (17)2.1 材料体系及成分设计 (17)2.1.1 原料分析 (17)2.1.2 成分设计 (19)2.2 试验及表征方法 (20)2.2.1 密度及相对密度测试 (20)2.2.2 粉体粒度测试 (21)2.2.3 力学性能测试 (21)2.2.4 成分及组织结构分析 (22)2.2.5 热震 (22)2.2.6 动态氧化 (23)第3章制备工艺及烧结动力学分析 (24)3.1 制备工艺 (24)3.1.1 MoSi2粉体细磨工艺 (24)- V -哈尔滨工业大学硕士学位论文3.1.2 晶须的酸洗工艺 (26)3.1.3 分散工艺 (27)3.1.4 烧结工艺 (28)3.2 烧结动力学分析 (28)3.2.1 扩散蠕变理论模型 (28)3.2.2 实际烧结曲线 (31)3.2.3 第二相对烧结的影响 (34)3.3 本章小结 (37)第4章力学性能及韧化机制 (38)4.1 微观组织分析 (38)4.1.1 MoSi2的微观组织分析 (38)4.1.2 MoSi2\SiC w的微观组织 (39)4.1.3 MoSi2\SiC p的微观组织 (40)4.2 力学性能 (40)4.3 MoSi2的断裂模式及本征脆性 (42)4.4 界面解离条件 (43)4.5 残余应力大小计算 (44)4.6 MoSi2\SiC w增韧机制探讨 (47)4.6.1 裂纹偏转机制 (48)4.6.2 晶须拔出机制 (49)4.6.3 晶须对裂纹的桥联 (50)4.6.4 晶粒细化 (50)4.6.5 晶须断裂 (52)4.6.6 残余应力增韧 (53)4.7 以减弱残余应力为目的的界面设计 (54)4.7.1 改性剂的选择 (55)4.7.2 增韧效果 (55)4.7.3 结果分析 (56)4.8 本章小结 (58)第5章热震及动态氧化 (59)5.1 热震性能研究 (59)5.1.1 SiC w对MoSi2抗热震性的影响 (59)5.1.2 热震性能分析 (65)- VI -哈尔滨工业大学硕士学位论文5.1.3 C的加入对抗热震性的影响 (68)5.2 动态氧化 (70)5.2.1 氧化机制 (70)5.2.2 氧化结果 (72)5.2.3 氧化结果分析 (74)5.3 本章小结 (74)结论 (76)参考文献 (77)哈尔滨工业大学硕士学位论文原创性声明 (80)哈尔滨工业大学硕士学位论文使用授权书 (80)致谢 (81)- VII -哈尔滨工业大学硕士学位论文第1章绪论1.1课题背景随着航空航天高技术的飞速发展，对材料性能提出了越来越高的要求。