Crack Evolution and Multiaxial Stress Regulation in High-Carbon Steel Fabricated by Direct Laser Deposition
摘要
High-carbon steels fabricated by Direct Laser Deposition (DLD) are prone to cracking due to the complex thermal cycles and multiaxial stress states. To mitigate cracking issues in high-performance 70Cr8Ni2Y high-carbon steel coatings prepared by DLD, this study combines numerical simulation with experimental validation to investigate crack evolution and stress field regulation under varying scanning speeds. A thermo-mechanical coupled multi-physics model is established using finite element software to explore the dynamic evolution of temperature and stress fields during DLD process. The crack morphology, microstructure, and properties of DLD 70Cr8Ni2Y coatings at different scanning speeds was analyzed. Moreover, this work revealed the stress distribution and crack evolution, elucidating the multiaxial stress interplay and crack regulation mechanism. Results show that low scanning speeds lead to excessive heat accumulation and significant von Mises stress, inducing macroscopic cracks. Conversely, high scanning speeds cause rapid cooling and localized shear stress, promoting microscopic cracks. Localized plastic strain and dislocation accumulation induced by thermal stress are the fundamental causes of crack initiation. The essence of optimizing scanning speed lies in balancing the suppression of macroscopic cracks driven by global von Mises stress and microscopic cracks induced by localized shear stress. A scanning speed of 20 mm/s represents the optimal parameter for achieving effective crack suppression and obtaining dense, crack-free coating. Simultaneously, the coating exhibits the highest microhardness (726 ± 14 HV0.2) and superior wear resistance (wear rate of 0.850%). This research provides theoretical basis and process guidance for crack-free laser additive manufacturing of high-performance high-carbon steel.