Microstructure investigation of dynamic recrystallization in hard machining: From thermodynamic irreversibility perspective

Abstract

The drastically changed thermal, mechanical, and chemical energies within the machined surface layer during hard machining tend to initiate microstructural alteration. In this paper, attention is paid to the introduction of thermodynamic potential to unravel the mechanism of microstructure evolution. First, the thermodynamic potential-based model expressed by the Helmholtz free energy was proposed for predicting the microstructure changes of serrated chip and the machined surface layer. Second, the proposed model was implemented into a validated finite element simulation model for cutting operation as a user-defined subroutine. In addition, the predicted irreversible thermodynamic state change in the deformation zones associated with grain size, which was reduced to less than 1 mm from the initial size of 1.5 mm on the machined surface, was provided for an in-depth explanation. The good consistency between the simulated results and experimental data validated the efficacy of the developed model. This research helps to provide further insight into the microstructure alteration during metal cutting.

Key words： thermodynamic irreversibility; Helmholtz free energy; microstructure evolution; dynamic recrystallization; hard milling

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grants Nos. 51975333 and 51575321), the Major Science and Technology Innovation Project of Shandong Province, China (Grant No. 2019JZZY010437), and the Taishan Scholar Project of Shandong Province, China (Grant No. ts201712002).

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