【作者】 黄太文；

【导师】 刘林；

【作者基本信息】 西北工业大学 ， 凝聚态物理， 2002， 硕士

【摘要】 本文在课题前期工作的基础上，采用新型细化剂在不同条件下细化镍基高温合金K4169，得到细化良好的铸造试样；分析了晶粒细化后的一些组织的变化；测试了不同晶粒组织的室温和中温条件下的拉伸性能和低周疲劳性能，并用扫描电镜观察性能试样的断口及进行断口分析。 实验结果表明： 新型细化剂对高温合金具有优良的细化作用。在1400℃时浇注试样，晶粒可细化至ASTM1.7级，断面等轴晶比例达到96％。同时，发现晶粒细化后出现球化现象。铸件成型良好，金相观察和探针分析表明，细晶试样的显微缩孔、微观偏析情况都所改善。 细晶试样在室温试的拉伸性能有明显的提高。但在中温的条件下(700℃)，抗拉强度和屈服强度提高的同时，塑性有所降低。研究表明，细晶材料性能的提高除了由于晶界对位错的阻碍作用外，还由于细化后组织均匀、偏析减轻和第二相得到细化。 在室温下，细晶组织比粗晶有得更长的疲劳寿命。显微分析表明，寿命的提高是因为晶粒细化后疲劳裂纹的扩展受到阻碍作用，速度较慢。但在中温时，应变幅对疲劳寿命有较大的影响。在应变幅较小时，细晶有更长的寿命；应变幅较大时，粗晶相反表现出更好的性能。研究表明，中温时，在应变较大时，很多相界、晶界、第二相质点等不稳定的地方成为内裂纹源。 实验表明，晶粒细化对循环应力响应有一定的影响，比如硬化指数的提高。同时疲劳过渡寿命降低。更多还原

【Abstract】 On the basis of the previous work, a new refiner is developed to refine a Fe-Ni based superalloy K4169 under different casting parameters in this thesis. By this way, the grain size was obviously refined. We have analyzed the changes of the microstructure, measured tensile and low cyclic fatigue properties at room temperature and at 700 D, observed the fracture of the test bars by SEM and analyzed the fracture mechanism.The results are as follows:Trace addition of the new refiner to the melt can obviously refine the grains of the alloy. At a conventional pouring temperature of 1400D, the grains could be refined to the order of ASTM1.7, the proportion of equiaxed grains at traverse cross-section could be improved to 96%. Under this process, the granulation phenomenon was found and the cast have much less casting defects. The size of porosity and the interdendritic segregation level of main elements was reduced with grain refinement.The yield and tensile strength of the test bars of fine grains is higher than that of the coarse ones at room temperature and at 700 D, and the plasticity is also superior for fine grains at room temperature, but debase at 70011. The improvement of strength of fine ones can be attributed not only to the retardation of dislocation by grain interface, but also to the uniformity of microstructure, the reduction of segregation and the refinement of the secondary phase after grain refinement.The fatigue lives of the test bar of fine grains are longer than that of coarse ones at room temperature. The results reveal that the improvement of the fatigue lives of fine grained ones was attributed to that the extend of fatigue crack had been decelerated. Whereas at moderate-high temperature, the strain amplitude has great effect on the fatigue life. Only at a lower strain amplitude the disposal of grain refinement improve the mechanical of LCF. The study also reveals that some unstable place such as phase interface and grain interface and grain interface can be provenance ofinside fatigue cracks at this temperature and at high strain.The results show that the fine grain process of casting has some effects on the behavior of response to cyclic stress, such as the increase in rigidification exponential of fine grains.更多还原