The machined surface geometric quality including surface roughness, surface morphology and surface defects can significantly influence the wear and fatigue resistance of components, and this problem is garnering increasing attention. However, for heterogeneous materials such as cast irons, the systematic investigation of the machined surface geometric quality and the role of secondary phase particles in the surface formation process remains unclear. The present study investigated the effects of cutting speed, feed per tooth, cutting depth and flank wear of the cutting tool on the machined surface geometric quality during face milling the compacted graphite iron (CGI), an ideal material for engine cylinder blocks. The results revealed that the surface roughness at high cutting speeds was significantly lower than that at low cutting speeds, primarily attributed to the reduction in the matrix exfoliation resulting from elevated cutting temperatures at high speeds. The predominant surface defects included feed marks, ploughing grooves, cavities, cracks, and matrix exfoliation at the low speed. While at high speeds, matrix exfoliation was reduced, and material adhesion, side flow, and plastic smearing occurred on the surfaces. Interestingly, the surfaces machined with a worn tool exhibited lower roughness than those machined with an unworn tool at the low speeds, and this interesting result was related to the diminished matrix exfoliation defects. Whereas at high speed, the surface roughness increased with tool wear due to the enhanced cutting forces and temperatures, resulting from more burr defects. Plastic smearing at high speeds or under tool wear conditions led to carbon diffusion from the graphite particles into the matrix, combined with factors such as high temperature and plastic deformation, resulting in partial phase transformation from pearlite to austenite. The role of graphite in the machined surface geometric quality formation of CGI can be attributed to two aspects such as the contribution of graphite to the formation of defects including cavities, cracks, matrix exfoliation and plastic smearing and the influence of graphite on the depth and degree of plastic deformation of the machined surface along the gradient direction. These findings contribute to the optimization of cutting conditions of CGI to mitigate specific defects and enhance surface quality and provide new insights into the surface formation mechanism of heterogeneous materials.

中文翻译：

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压实石墨铁加工表面几何质量形成机制的几点新发现


加工表面的几何质量（包括表面粗糙度、表面形貌和表面缺陷）会显著影响部件的耐磨性和抗疲劳性，这一问题越来越受到关注。然而，对于铸铁等非均质材料，对加工表面几何质量和第二相颗粒在表面形成过程中的作用的系统研究仍不清楚。本研究调查了切削速度、每齿进给量、切削深度和切削刀具的后刀面磨损对压实石墨铁 （CGI） 进行面铣时加工表面几何质量的影响，CGI 是发动机气缸体的理想材料。结果表明，高切削速度下的表面粗糙度明显低于低切削速度下的表面粗糙度，这主要是由于高速切削温度升高导致基体剥落减少。主要的表面缺陷包括进料痕迹、犁槽、空腔、裂纹和低速时基质剥落。在高速下，基质剥落减少，表面出现材料粘附、侧流和塑料污迹。有趣的是，在低速下，用磨损工具加工的表面比用未磨损的工具加工的表面表现出更低的粗糙度，这个有趣的结果与基体剥落缺陷的减少有关。而在高速下，由于切削力和温度的增加，表面粗糙度随着刀具磨损而增加，而毛刺缺陷更多。 高速或工具磨损条件下的塑料涂抹导致碳从石墨颗粒扩散到基体中，再加上高温和塑性变形等因素，导致从珠光体到奥氏体的部分相变。石墨在 CGI 加工表面几何质量形成中的作用可归因于两个方面，例如石墨对缺陷形成的贡献，包括空腔、裂纹、基体剥落和塑性涂抹，以及石墨对加工表面沿梯度方向塑性变形的深度和程度的影响。这些发现有助于优化 CGI 的切割条件，以减少特定缺陷并提高表面质量，并为异质材料的表面形成机制提供新的见解。