氧化物夹杂与Ni-Cr-Mo-V钢多层焊缝低温冲击韧性变化规律的关系

测试了反应堆压力容器用Ni-Cr-Mo-V钢焊缝的冲击韧性,实验结果表明,当实验温度较低时,同一实验温度下沿盖面焊到焊根方向不同层焊缝样品的冲击吸收能呈下降趋势。通过低温实验样品断口观察到韧窝底部、起裂源、解离断刻面裂纹源存在直径为0.3~2.0μm的球形氧化物夹杂,导致试样在变形过程中氧化物夹杂与基体分离形成微裂纹,并发展为试样的韧窝、起裂源和解离断刻面裂纹源,由此推断氧化物夹杂是造成焊缝低温失效的主要原因。同时氧化物夹杂的数量沿盖面焊到焊根方向逐渐增多,使得微裂纹形核率逐渐增加,造成焊缝低温冲击韧性沿盖面焊到焊根方向逐渐变差。

Failure mechanism and forming limit of tube axial compressive process

Based on minimum energy principle for plastic forming, tearing and buckling failures mechanisms are explored and criteria for them are developed by theoretical analysis and experiment. Combined with finite element software developed forming limit and effects of process parameters on failures are investigated and proper parameters for stable forming are determined. The results show that: 1) The failures and forming limit are mainly determined by geometry and materials parameters of tube blank, fillet radius or half conical angle of die. For the process under fillet die, there exists a maximum fillet radius within which no tearing failure happens, and a maximum radius and a minimum radius range within which no buckling failure happens. For the process under conical die, there exists a maximum and minimum half conical angle range within which no tearing and buckling failures occur. 2) For both forming processes, the higher the value of material strain hardening exponent or the lower the value of relative thickness, the more impossible for tearing and buckling failures to occur, and the larger the ranges of fillet radius and half conical angle. The experiment results verify the reliability and practicability of this research.

热处理及SiC颗粒尺寸对15%SiC_p/6061Al复合材料性能的影响

采用粉末冶金法制备了体积分数15%的、不同粒度SiC颗粒增强的6061Al基复合材料,研究了固溶-时效热处理工艺对复合材料屈服强度、抗拉强度、延伸率的影响规律,确定了最佳热处理工艺参数,揭示了Si C颗粒(SiC_p)粒度变化对复合材料力学性能的影响规律,研究表明:随SiC_p粒度的增加,SiC_p/6061Al基复合材料的弹性模量基本不受影响;但复合材料的屈服强度、抗拉强度逐渐降低,延伸率、断面收缩率先增大后减小。当SiC_p粒度增加到10μm时,复合材料屈服强度、抗拉强度出现明显下降,同时复合材料延伸率和断面收缩率由提高变为降低,其原因是复合材料断裂失效机制由基体撕裂控制转变为增强颗粒开裂与基体撕裂共同控制。拉伸断口扫描电镜(SEM)分析表明,随着SiC_p粒度的增加,SiC_p/6061Al复合材料中出现颗粒开裂并且数量逐渐增加。