The influence of cutting parameters on the defect structure of subsurface in orthogonal cutting of titanium alloy
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Zhen Tong Centre for Precision Technologies, University of Huddersfield, Huddersfield HD1 3DH, U.K.
Guoda Chen Key Laboratory of E & M, Ministry of Education & Zhejiang Province, Zhejiang University of Technology, Hangzhou 310032, People’s Republic of China (Received 17 July 2017; accepted 19 September 2017)
Subsurface microstructure alteration has been a major concern to implement micromachining of titanium alloy in the high-tech industry. To quantitatively promulgate the underlying mechanisms of this alteration, a discrete dislocation dynamics-based model is proposed and used to simulate the subsurface defects and their evolution under different cutting conditions. The model considers the subsurface dislocation configuration and inner stress distribution during the orthogonal cutting of titanium alloy. The results show that subsurface defect structure consists of plenty of dislocation dipoles, twining dislocation bands, and refined grains after cutting. In the primary shear zone, two different characteristics of subsurface damage layers can be found, the nearsurface damage layer and deep-surface damage layer, which have different structural natures and distribution features. Moreover, it is found that high cutting speed and small depth of the cut can suppress the formation and propagation of subsurface defects. A powerful inner stress state would promote the distortion of the lattice and result in a microcrack within the subsurface matrix. The simulation results have been compared with experimental findings on the machined surface and subsurface of similar materials, and strong similarities were revealed and discussed.
I. INTRODUCTION
Titanium and its alloys have become key supporting materials in biomedical and aerospace industry due to their excellent comprehensive mechanical properties and the improvements made on machining these alloys.1,2 According to Ulutan and Tan,3,4 a typical characteristic of the titanium alloy-machined surface consists mainly of three parts: the surface white layer, the subsurface plastic deformation zone, and bulk material. In previous studies, the surface white layer states that processed components have attracted substantial efforts in academic and in the application field.5,6 However, with the increasing demands for machined precision and surface quality in the micro-machining process, it is important to recognize that the mechanical properties and lifetime of the workpiece are determined by no means only on the shape or on precision of the machined surface, and the characteristics of the subsurface microstructure may dominate the
Contributing Editor: Jürgen Eckert Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.397
component’s service performance and reliability, as well.7 Specially, the change of the subsurface microstructure and the release of residual stress caused by powerful shearing action would result in inherent deformation and form the subsurface damage (SSD) layer underneath the surface. The p
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