Liu Shubin, Luan Yuqi, Shohji Ikuo
Provincial Key Lab of Advanced Welding Technology, School of Materials Science and Engineering, Jiangsu University of Science and Technology, 666 Changhui Road, Zhenjiang 212100, China.
Graduate School of Science and Technology, Gunma University, 1-5-1, Tenjin-cho, Kiryu 376-8515, Japan.
Materials (Basel). 2025 May 21;18(10):2406. doi: 10.3390/ma18102406.
A new brazing process for thin-walled stainless steel was proposed by combining green and efficient Ni-Cr-P electrodeposition with brazing technology. Novel information was attained by analyzing the electrodeposited Ni-Cr-P interlayers and the brazed joints and characterizing them using a combination of advanced techniques. The incorporation mechanisms of impurities (i.e., oxygen and carbon) in the Ni-Cr-P interlayers electrodeposited from a Cr(III)-glycine solution were revealed. The oxygen mainly came from the Cr(III)-hydroxy complexes formed by the hydrolysis and olation between Cr(III) complexes and OH ions near the cathode. Glycine did not directly participate in the cathode reactions but decomposed on the anode surface. These byproducts (carbonyl compounds) were directly incorporated into the interlayers in a molecular pattern, forming a weak link to the metallic chromium. Brazing test results showed that a certain amount of CrO powder, formed by the decomposition of chromium hydroxides in the interlayers under high-temperature catalysis, would cause the degradation of the brazed joints. Using the step-wise brazing method, the brazing sheets were first annealed to eliminate the impurities by utilizing the strong reducing effect of hydrogen and the weak link characteristics between carbonyl compounds and metallic chromium atoms. An excellent joint with a shear strength of 63.0 MPa was obtained by subsequent brazing. The microstructural analysis showed that the brazed seam was mainly composed of a Ni-Fe-Cr solid solution, the NiP eutectic phase, and small quantities of the NiP phase scattered in the NiP eutectic phase. Fracture mode observations showed that the cracks extended along the interface between the brittle P-containing phase and the primary phase, resulting in fracture.
通过将绿色高效的镍铬磷电沉积与钎焊技术相结合，提出了一种用于薄壁不锈钢的新型钎焊工艺。通过分析电沉积的镍铬磷中间层和钎焊接头，并结合先进技术对其进行表征，获得了新的信息。揭示了从Cr(III)-甘氨酸溶液中电沉积的镍铬磷中间层中杂质（即氧和碳）的掺入机制。氧主要来自阴极附近Cr(III)配合物与OH离子水解和配位形成的Cr(III)-羟基配合物。甘氨酸不直接参与阴极反应，而是在阳极表面分解。这些副产物（羰基化合物）以分子形式直接掺入中间层，与金属铬形成薄弱连接。钎焊试验结果表明，中间层中的氢氧化铬在高温催化下分解形成的一定量的CrO粉末会导致钎焊接头性能下降。采用分步钎焊方法，首先对钎焊片进行退火，利用氢气的强还原作用和羰基化合物与金属铬原子之间的薄弱连接特性去除杂质。随后进行钎焊，获得了剪切强度为63.0 MPa的优良接头。微观结构分析表明，钎焊缝主要由Ni-Fe-Cr固溶体、NiP共晶相以及少量分散在NiP共晶相中的NiP相组成。断口模式观察表明，裂纹沿脆性含磷相和初生相之间的界面扩展，导致断裂。
