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Failure mechanisms in cobalt welded with a silver-copper filler

机译：用银铜填料焊接钴的失效机理

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摘要

Cobalt silver-copper (Co-AgCu) weldments approximate the stresses and failure mechanisms of beryllium aluminum-silicon (Be-AlSi) welds, which have strategic importance but are hazardous to study. Failure tests of these surrogate Co-AgCu welds, examined in tension and four-point bending, show that residual stresses and post-welding heat treatment have little or no effect on strength, whereas weld quality and geometry are extremely important. Scanning electron microscopy images reveal abundant defects in poor welds, which usually fail through propagation of preexisting cracks. Fracture surfaces show a variety of morphologies, ranging from dimples in the AgCu filler, to cleavage steps in the CoCu peritectic, and suspected intergranular fracture in the cobalt base. Spatially resolved acoustic spectro-scopy reveals significant changes in microstructure near the base-filler interface, whereas wavelength dispersive analysis shows high Cu concentrations in this area.. Contrary to finite element predictions, these welds were found to be stronger during face bending than root bending, likely resulting from the increased number of cracks and imperfections in the Co base. These computations correctly predict that weld strength depends on geometry and that welds fail either in the cobalt base, or along the base-filler interface. Crack compliance measurements show that the largest residual stresses are located along this interface. However, these stresses are unlikely to influence failure due to their direction, whereas stresses in the weld root are too small to have observable effects on failure. The strength of Co-AgCu welds depends strongly on geometry, penetration, and weld quality, but little on residual stresses, and this conclusion is tentatively extended to Be-AlSi welds.
机译：钴-银-铜（Co-AgCu）焊件近似于铍铝硅（Be-AlSi）焊缝的应力和破坏机理，这虽然具有战略重要性，但研究起来很危险。在拉伸和四点弯曲中对这些替代的Co-AgCu焊缝进行的失效测试表明，残余应力和焊后热处理对强度几乎没有影响，而焊接质量和几何形状则极为重要。扫描电子显微镜图像显示出不良焊缝中的大量缺陷，这些缺陷通常由于先前存在的裂纹扩展而失效。断裂表面表现出多种形态，从AgCu填料中的凹痕到CoCu包晶中的裂解步骤，以及钴基中的可能的晶间断裂。空间分辨声学光谱显示，底部填充物界面附近的微观结构发生了显着变化，而波长色散分析显示该区域中的铜浓度很高。与有限元预测相反，发现这些焊缝在面弯曲过程中比根部弯曲更牢固，可能是由于钴基中裂纹和缺陷的数量增加所致。这些计算正确地预测了焊接强度取决于几何形状，并且焊缝在钴基中或沿基体-填料界面失效。裂纹顺应性测量表明，最大残余应力位于该界面上。但是，这些应力由于其方向而不太可能影响失效，而焊缝根部的应力太小而无法对失效产生明显影响。 Co-AgCu焊缝的强度在很大程度上取决于几何形状，熔深和焊缝质量，而在很大程度上取决于残余应力，并且该结论暂时扩展到了Be-AlSi焊缝。

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  • 来源
    《Materials Science and Engineering》 |2015年第1期|369-382|共14页
  • 作者

    Everett M. Criss; Richard J. Smith; Marc A. Meyers;

  • 作者单位

    Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, USA;

    Electrical Systems and Optics Research Division, Faculty of Engineering, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom;

    Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, USA,Materials Science and Engineering Program, University of California, San Diego, La Jolla, USA,Department of Nanoengineering, University of California, San Diego, La Jolla, USA;

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  • 正文语种 eng
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  • 关键词

    Cobalt; Silver-copper; Welding surrogacy; Tungsten inert gas welding; Residual stress; Weld fracture;

    机译：钴;银铜焊接代孕;钨极惰性气体保护焊;残余应力;焊缝断裂;

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