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Effect of the Surface States of 1Cr18Ni9Ti Stainless Steel on Mn-Based Brazing Alloy Wetting

The wetting properties of the brazing filler on the substrates play an important role in achieving a reliable joint. In this work, the wetting behaviour of the Mn-based brazing alloy on the surface of 1Cr18Ni9Ti stainless steel is investigated. First, surface treatment was adopted to prepare four different surface states on the stainless steel, including polished, acid treatment, nickel coating, and sandblasting. The surface morphology with nickel coating shows micro-and nano-scale protrusions, forming a uniform 3D Ni layer. The surface roughness of substrates increases after sandblasting treatment. It is found that the wetting angle of brazing alloy on the Ni coated substrates decreases noticeably. After sandblasting, the high roughness speeds up the wetting spread of the brazing alloy at the initial stage. The effect of heating temperature and holding time is also studied systematically. With the increase in holding time, the height of the melting brazing alloy decreases slightly on the sample surfaces. Based on the characterization of the joint section, the Ni layer dissolves into the melting brazing alloy. The diffusion and dissolving are indicated between the brazing alloy and substrates, forming a reliable bond.