This study was to characterize the microstructure of Alloy 690-SUS 304L stainless steel dissimilar weldments with Inconel 52 and 82 filler metals (I-52 and I-82). The weldments were butt-welded with gas tungsten arc welding. Microstructural analyses were conducted on the samples prepared from the middle of each fusion zone. Precipitates observed in the interdendritic region and along the grain boundary of the I-52 fusion zone were TiNs, while Ti-Nb-rich phases were detected in the I-82 fusion zone. In the root regions, Cr-carbides precipitated abundantly in the I-52, whereas few Cr-carbides were found in the I-82. The Cr content of the grain boundary was higher than 9 mass% in the root regions of both I-52 and I-82 welds. Owing to the dilution with base metal Alloy 690, the average Cr content was higher in the I-82 root region than in the cap region.
Effects of Ag content (0 ~ 3 wt.%) in Sn-xAgCu0.7 solders on microstructure characteristics and low cycling fatigue at different temperature conditions are overall investigated. To increase Ag content, the solidus point 228.8 ? of Sn-Cu0.7 gradually decreases to 218.5 ? and temperature range of solid-liquid coexistence phase is also decrease. The Sn-Cu0.7 matrix consisted of small particles of Cu6Sn5 within ß-Sn equiaxial grains and did not significantly influence solder hardness. Moreover, much intermetallic compound of plate-like Ag3Sn and rod-like Cu6Sn5 existed in Sn-xAgCu0.7 solders enables to enhance the hardness due to dense network of Ag3Sn precipitation and near eutectic point. As a result of plastic displacement decreases with higher Ag additions, better fatigue lifetime could be achieved at Ag content to 1.5 wt.%. Besides, crack stemmed from thicker IMC layer in Sn-3.0Ag-Cu0.7 solder interface will decrease fatigue performance especially for 80 ? and 120 ?.
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