Compacted graphite iron (CGI), a prototypical heterogeneous material, potentially demonstrates distinctive cutting deformation behaviours attributed to the random distribution of graphite and performance differences between graphite and the matrix, which have not yet received adequate attention. This study focuses on the influence of the microstructure characteristics of CGI on the formation of serrated chips. The morphology of the serrated chip segments during the orthogonal turning of CGI was observed in detail, the microstructures of the chip roots were characterised and analysed using various techniques, and a finite-element cutting simulation model considering the microstructural characteristics of CGI was developed. Results suggest that the formation of serrated chips in CGI is influenced by periodic and aperiodic brittle fractures, referred to as quasi-periodic brittle fractures, which are controlled by the distribution of graphite in CGI. This results in variations in the morphology and dimensions of the serrated chips in CGI. Plastic deformation is concentrated in a triangular deformation zone (TDZ) near the tool-chip interface, which is broader than the conventional secondary deformation zone. The experimental and simulation results revealed the reasons for the formation of the TDZ and emphasized the critical role of graphite in the formation of serrated chips in CGI. The graphite particles near the tool-chip interface promoted plastic deformation along the interface owing to the principle of minimum energy and restricted deformation perpendicular to the interface due to its structure, leading to the formation of the TDZ. The influence of graphite on material flow and the formation of the TDZ during the formation of serrated chips in CGI is a novel discovery. The microstructure evolution of the pearlite matrix in CGI caused by cutting deformation was analysed. The results demonstrate that the distinctive deformation behaviour of CGI contributes to the fragmentation of the pearlite structure, grain refinement, and increased dislocation density in the TDZ. Finally, the influence of the serrated chip formation mechanism on chip morphology and cutting force in CGI was discussed. These findings offer significant scientific insights and contribute to the fundamental understanding of the chip formation process in CGI.

中文翻译：

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考虑切削过程中微观结构演变的切屑形成机制：以蠕墨铸铁加工为例

蠕墨铸铁（CGI）是一种典型的异质材料，由于石墨的随机分布以及石墨与基体之间的性能差异，可能表现出独特的切削变形行为，但尚未得到足够的关注。本研究重点研究CGI微观结构特征对锯齿状切屑形成的影响。详细观察了CGI正交车削过程中锯齿状切屑段的形貌，利用多种技术对切屑根部的微观结构进行了表征和分析，建立了考虑CGI微观结构特征的有限元切削仿真模型。结果表明，CGI 中锯齿状切屑的形成受到周期性和非周期性脆性断裂（称为准周期性脆性断裂）的影响，其受 CGI 中石墨分布的控制。这导致 CGI 中锯齿状切屑的形态和尺寸发生变化。塑性变形集中在刀具-切屑界面附近的三角形变形区（TDZ），该区域比传统的二次变形区更宽。实验和模拟结果揭示了TDZ形成的原因，并强调了石墨在CGI锯齿状切屑形成中的关键作用。刀具-切屑界面附近的石墨颗粒由于最小能量原理而促进沿界面的塑性变形，并因其结构而限制垂直于界面的变形，从而形成TDZ。在 CGI 中锯齿状切屑形成过程中石墨对材料流动和 TDZ 形成的影响是一个新颖的发现。分析了CGI中由切削变形引起的珠光体基体的显微组织演变。结果表明，CGI 独特的变形行为有助于珠光体结构的破碎、晶粒细化以及 TDZ 中位错密度的增加。最后讨论了CGI中锯齿状切屑形成机制对切屑形态和切削力的影响。这些发现提供了重要的科学见解，有助于对 CGI 芯片形成过程的基本理解。