Liu Xuesong, Su Guokang, Fan Qingming, Zhang Yongjun, Chen Hua, Zhang Chuanyun
School of Mechatronic Engineering, Xi'an Technological University, Xi'an 710021, China.
Shaanxi Engineering Research Center of Digital Precision Electrochemical Machining, Xi'an 710021, China.
Micromachines (Basel). 2024 Aug 23;15(9):1062. doi: 10.3390/mi15091062.
Bearing steel (GCr15) is widely used in key parts of mechanical transmission for its excellent mechanical properties. Electrochemical machining (ECM) is a potential method for machining GCr15, as the machining process is the electrochemical dissolution of GCr15 regardless of its high hardness (>50 HRC). In ECM, NaNO solution is a popular electrolyte, as it has the ability to help in the nonlinear dissolution of many metallic alloy materials, making it useful for precision machining. However, due to high carbon content of GCr15, the electrochemical dissolution of GCr15 is unique, and there is always a black layer with high roughness on the machined surface, reducing the surface quality. In order to improve the electrochemical machining of GCr15 with a high surface quality, the surface characteristics of GCr15 in ECM were investigated. The anodic polarisation curve in the NaNO electrolyte was measured and electrochemical dissolution experiments were conducted with different current densities. SEM, XRD, and XPS were employed to analyse the surface morphology and composition formed on the machined surface at different current densities. The initial results showed that there were two parts (black part and bright part) formed on the machined surface when a short circuit occurred, and the test results suggested that the black part contained a mass of FeO while the bright part was composed of mainly Fe and FeC. Further investigation uncovered that a black flocculent layer (FeO) always formed in a low current density (32 A/cm) with high roughness. With the current density increased, the amount of black flocculent layer was reduced, and FeC particles appeared on the machined surface. When the current density reached 81 A/cm, the entire flocculent oxide layer was removed, only some spherical FeC particles were inserted on the machined surface, and the roughness was reduced from Ra7.743 μm to Ra1.783 μm. In addition, due to exposed FeC particles on the machined surface, the corrosion resistance of the machined surface was significantly improved. Finally, circular arc grooves of high quality were well manufactured with current density of 81 A/cm in NaNO electrolyte.
轴承钢（GCr15）因其优异的机械性能而广泛应用于机械传动的关键部件。电化学加工（ECM）是加工GCr15的一种潜在方法，因为加工过程是GCr15的电化学溶解，而不考虑其高硬度（>50 HRC）。在ECM中，NaNO溶液是一种常用的电解液，因为它能够帮助许多金属合金材料进行非线性溶解，使其适用于精密加工。然而，由于GCr15的碳含量高，其电化学溶解具有独特性，加工表面总会出现粗糙度高的黑色层，降低了表面质量。为了提高具有高表面质量的GCr15的电化学加工性能，研究了GCr15在ECM中的表面特性。测量了在NaNO电解液中的阳极极化曲线，并进行了不同电流密度的电化学溶解实验。采用扫描电子显微镜（SEM）、X射线衍射（XRD）和X射线光电子能谱（XPS）分析了不同电流密度下加工表面形成的表面形貌和成分。初步结果表明，短路时加工表面形成了两部分（黑色部分和光亮部分），测试结果表明黑色部分含有大量的FeO，而光亮部分主要由Fe和FeC组成。进一步研究发现，在低电流密度（32 A/cm²）下总会形成粗糙度高的黑色絮凝层（FeO）。随着电流密度的增加，黑色絮凝层的数量减少，加工表面出现FeC颗粒。当电流密度达到81 A/cm²时，整个絮凝氧化层被去除，加工表面仅插入一些球形FeC颗粒，粗糙度从Ra7.743μm降至Ra1.783μm。此外，由于加工表面暴露的FeC颗粒，加工表面的耐腐蚀性显著提高。最后，在NaNO电解液中以81 A/cm²的电流密度成功加工出了高质量的圆弧槽。
