保护气流量对纯镍等离子弧焊接头微观组织的影响

对N6纯镍采用不填丝穿孔等离子弧焊方法研究了保护气流量对焊缝微观组织的影响.结果表明，随着保护气流量不断增大，焊缝宏观形貌中的表面缺陷逐渐消失，开始产生明显的金属光泽；焊缝背面的热影响区宽度随保护气流量增加而逐渐增加，并趋近于正面焊缝热影响区宽度.通过对焊缝横截面的微观组织进行观察，发现从母材到焊缝中心晶粒逐渐变大.随着保护气流量的增加，热影响区晶粒尺寸并没有发生明显变化，而焊缝中心处晶粒则是逐渐变大.当保护气不足时，焊缝中出现大量气孔，通过SEM+EDS分析发现，气孔内壁含有大量Ni，C，N，Mg元素为主要成分的氧化物；同时焊缝中发现大量“大脑皮层花纹状”富氧杂质集团.

Effects of shielding gas flow on microstructure of PAW welded joints of pure Nickel N6

The effect of shielding gas flow (SGF) on weld microstructure was investigated in the plasma arc welding (PAW) of pure N6 Ni without filler wire. The results show that weld appearance has an obvious metallic luster and no surface defects with the increase of the SGF. The HAZ width on the back side of weld seam increases with the SGF rate being increased, and reaches gradually up to that on the front of weld seam. The grains size increase from the base metal to the center of weld. The grain size in HAZ has no few variations with the increase of the SGF, while the grains in the weld center become gradually coarser. Meanwhile, a large number of pores appear when the shielding gas is not enough. From analysis of SEM and EDS results, there are a large number of oxides with Ni, C, N, and Mg as main components in the inner wall of the porosities in weld, and oxygen-riched impurities groups have a texture of cerebral cortex like.