Journal of South China University of Technology(Natural Science Edition) ›› 2023, Vol. 51 ›› Issue (2): 35-46.doi: 10.12141/j.issn.1000-565X.220181

Special Issue: 2023年机械工程

• Mechanical Engineering • Previous Articles     Next Articles

Hardness Prediction of TC4 Machined Surface Based on the Evolution of Multi-scale Grain Refinement

WANG Qingqing1,2 LIU Zhanqiang3 CHENG Yanhai1,2 TIAN Xianhua1,2   

  1. 1.School Mechatronic Engineering,China University of Mining and Technology,Xuzhou 221116,Jiangsu,China
    2.Jiangsu Collaborative Innovation Center of Intelligent Mining Equipment,Xuzhou 221116,Jiangsu,China
    3.School of Mechanical Engineering,Shandong University,Jinan 250061,Shandong,China
  • Received:2022-04-05 Online:2023-02-25 Published:2023-02-01
  • Contact: 刘战强(1969-),男,博士,教授,主要从事切削加工理论与刀具技术研究。 E-mail:melius@sdu.edu.cn
  • About author:王情情(1990-),女,博士,讲师,主要从事高效加工及表面强化技术研究。E-mail:wangqingqing@cumt.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(52105494);the Natural Science Foundation of Jiangsu Province for Youths(BK20200640);the Program of Chinese Postdoctoral Science Foundation(2019M661976);the Priority Academic Program Development of Jiangsu Higher Education Institution (PAPD)

Abstract:

The microstructure variations of machined surface determine the performance of machined components. Accurately predicting the microstructure evolution of machined surface and thus enhancing surface hardness of machined components is an effective way to improve the service performance and realize the controllable machining of components. Machining is one the fundamental manufacturing techniques of TC4 components and the severe plastic deformation during machining process induces the complex evolutions of microstructure for TC4 machined surface. For the grain refinement phenomenon during TC4 cutting, this paper studied the multi-scale distribution characteristics of microstructure, evolution mechanisms of grain refinement and its effect on the material hardness under different cutting speeds (100 ~ 500 m/min). The results show that grain refinement degree at meso-scale (10-6 ~ 10-5 m) increases first and then decreases with the increasing of cutting speed. At cutting speed of 300 m/min, grain refinement degree of machined surface is 69.7% and the grains in the shear bands of chips are refined to 2 ~ 6 μm. Complex dislocation patterns and nano twining are the features of microstructure at micro-scale (10-8 ~ 10-7 m). The deformation twinning type is mainly characterized as {101ˉ1} compression twinning and it is generated at higher cutting speed (> 200 m/min). Grain refinement during machining of TC4 was predicted based on the modified Z-H grain refinement model and nano twining volume fraction prediction model. The hardening effect of grain refinement was also considered in the prediction model. The evolution of grain sizes and the work hardening was predicted. The relation between grain refinement and material hardness was established, and the hardness of TC4 machined surface was predicted with directional controlling the grain refinement degree and formation of nano twinning. And the hardening mechanism in micro-scale of TC4 machined surface was revealed.

Key words: machining, grain refinement, evolution prediction, surface hardness, titanium alloy

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