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research-article

Chip Morphology and Chip Formation Mechanisms during Machining of ECAE-Processed Titanium

[+] Author and Article Information
Brian Davis

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
bdavis.18.bd@gmail.com

David Dabrow

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
daviddabrow@ufl.edu

Ryan Newell

Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
ryan.newell@knights.ucf.edu

Andrew Miller

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
andrewjmiller@ufl.edu

John Schueller

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
schuejk@ufl.edu

Guoxian Xiao

General Motors Global R&D, Warren, MI 48090, USA
guoxian.xiao@gm.com

Steven Y. Liang

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
steven.liang@me.gatech.edu

Karl T. Hartwig

Materials Science and Engineering Department, Texas A&M University, College Station, TX 77843-3003, USA
kthartwig@suddenlinkmail.com

Nancy Jean Ruzycki

Department of Material Science and Engineering, University of Florida, Gainesville, FL 32611, USA
nruzycki@mse.ufl.edu

Yongho Sohn

Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
Yongho.Sohn@ucf.edu

Yong Huang

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA; Department of Material Science and Engineering, University of Florida, Gainesville, FL 32611, USA
yongh@ufl.edu

1Corresponding author.

ASME doi:10.1115/1.4038442 History: Received June 03, 2017; Revised October 30, 2017

Abstract

Severe plastic deformation (SPD) processing such as equal channel angular extrusion (ECAE) has been pioneered to produce ultra-fine grained (UFG) metals for improved mechanical and physical properties. However, understanding the machining of SPD-processed metals is still limited. This study aims to investigate the differences in chip morphology when machining ECAE-processed UFG and coarse-grained (CG) titanium (Ti) and understand the chip formation mechanism using metallographic analysis, digital imaging correlation, and nano-indentation. The chip morphology is classified as aperiodic saw-tooth, continuous, or periodic saw-tooth, and changes with the cutting speed. The chip formation mechanism of the ECAE-processed Ti transitions from cyclic shear localization within the low cutting speed regime (such as 0.1 m/s or higher) to uniform shear localization within the moderately high cutting speed regime (such as from 0.5 to 1.0 m/s) and to cyclic shear localization (1.0 m/s). The shear band spacing increases with the cutting speed and is always lower than that of the CG counterpart. If the shear strain rate distribution contains a shift in the chip flow direction, the chip morphology appears saw-tooth, and cyclic shear localization is the chip formation mechanism. If no such shift occurs, the chip formation is considered continuous, and uniform shear localization is the chip formation mechanism. Hardness measurements show that cyclic shear localization is the chip formation mechanism when localized hardness peaks occur, whereas uniform shear localization is operative when the hardness is relatively constant.

Copyright (c) 2017 by ASME
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