Efficient post-processing of additive manufactured maraging steel enhanced by the mechanochemical effect

Abstract

Additive manufacturing technologies are beginning to shift toward hybridization with subtractive processes and it is vital to identify techniques that can enhance the machinability of the difficult-to-cut additively manufactured metals and offer easy integration. The mechanochemical effect, which can be induced by surfactant, is a feasible solution for hybrid integration due to the beneficial enhancements to the cutting performance, online integrability, and negligible impact on the AM process as compared to cutting fluids, cryogenic cutting, etc. To realize the successful integration of the mechanochemical effect and hybrid additive/subtractive manufacturing, micro-cutting of AMed high-strength maraging steel was performed to study the relationship between microstructural features, mechanical properties, cutting performance and effectiveness of the mechanochemical effect. The results show that the mechanochemical effect was successfully induced in the as-built and solution-treated steels by inhibiting dislocation movement to induce the embrittlement of chip surface and strain localization within the chip, thereby leading to substantial reductions in cutting forces of up to 35.24 % and 53.09 %, respectively, with significant improvement in the machined surface quality. However, the presence of 7.7 nm nanoparticles in the age-treated steels renders the mechanochemical effect ineffective in improving machinability. The nanoparticles sharply increased the strength, hardness, and brittleness of the AMed maraging steel where the brittleness replaced the role of surfactant that suppressed plasticity in the chip free surface. The notion was affirmed by the similarities between the cutting chips of the brittle aged steel without surfactant and the as-built steel with surfactant. This study systematically revealed the underlying mechanism of inducing the mechanochemical effect during the micro-cutting of AMed high-strength materials with different microstructures and mechanical properties. More importantly, it is evident that the mechanochemical effect is a highly feasible solution for enhanced hybrid manufacturing, especially for robot-based fabrication works that involve high degrees of freedom and large working ranges but are limited by low mechanical stiffness.