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Research Papers

Effect of Severe Plastic Deformation in Machining Elucidated via Rate-Strain-Microstructure Mappings

[+] Author and Article Information
S. Shekhar

Department of Materials Science and Engineering, Indian Institute of Technology—Kanpur, Uttar Pradesh 208016, Indiashashank@iitk.ac.in

S. Abolghasem

Department of Industrial Engineering, Swanson School of Engineering, 3700 O’Hara Street,  University of Pittsburgh, Pittsburgh, PA 15261sea40@pitt.edu

S. Basu

Department of Industrial Engineering, Swanson School of Engineering, 3700 O’Hara Street,  University of Pittsburgh, Pittsburgh, PA 15261sab115@pitt.edu

J. Cai

Department of Industrial Engineering, Swanson School of Engineering, 3700 O’Hara Street,  University of Pittsburgh, Pittsburgh, PA 15261jic32@pitt.edu

M. R. Shankar1

Department of Industrial Engineering, Swanson School of Engineering, 3700 O’Hara Street,  University of Pittsburgh, Pittsburgh, PA 15261ravishm@pitt.edu

1

Corresponding author.

J. Manuf. Sci. Eng 134(3), 031008 (May 07, 2012) (11 pages) doi:10.1115/1.4006549 History: Received November 29, 2010; Revised March 27, 2012; Published May 07, 2012; Online May 07, 2012

Machining induces severe plastic deformation (SPD) in the chip and on the surface to stimulate dramatic microstructural transformations which can often result in a manufactured component with a fine-grained surface. The aim of this paper is to study the one-to-one mappings between the thermomechanics of deformation during chip formation and an array of resulting microstructural characteristics in terms of central deformation parameters–strain, strain-rate, temperature, and the corresponding Zener–Hollomon (ZH) parameter. Here, we propose a generalizable rate-strain-microstructure (RSM) framework for relating the deformation parameters to the resulting deformed grain size and interface characteristics. We utilize Oxley’s model to calculate the strain and strain-rate for a given orthogonal machining condition which was also validated using digital imaging correlation-based deformation field characterization. Complementary infrared thermography in combination with a modified-Oxley’s analysis was utilized to characterize the temperature in the deformation zone where the SPD at high strain-rates is imposed. These characterizations were utilized to delineate a suitable RSM phase-space composed of the strain as one axis and the ZH parameter as the other. Distinctive one-to-one mappings of various microstructures corresponding to an array of grain sizes and grain boundary distributions onto unique subspaces of this RSM space are shown. Building on the realization that the microstructure on machined surfaces is closely related to the chip microstructure derived from the primary deformation zone, this elucidation is expected to offer a reliable approach for controlling surface microstructures from orthogonal machining.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Linear test bed used for orthogonal machining

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Figure 2

Comparison of OIM micrographs of chip (machined at 20M condition) with that near the machined surface (machined at 20M condition), where the machined surface is ∼30 μm away from the top edge of the micrograph. The lines surrounding the grains in the OIM micrograph depict boundaries with grain misorientations greater than 5 deg. Optical micrograph of bulk copper showing large grains (∼200 μm) in the undeformed region is superimposed on the workpiece region (Note: The subsurface OIM micrograph on the bottom right is approximately ∼100 μm below the freshly cut surface).

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Figure 3

Infrared thermograph for a sample which was strained to ɛ = 1.2 at a strain-rate of ɛ̇ = 3040 s− 1 . The calculated temperature for this orthogonal machining condition was 342 K and the measured value was 336 K.

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Figure 4

Strain-rate field obtained using DIC for copper machined using 40 deg rake angle tool at a cutting speed of 25 mm/s and doc = 0.15 mm

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Figure 5

Inverse pole figure obtained using EBSD based OIM for various sample conditions: (a) 0L; (b) 0M; (c) 0H; (d) 20L; (e) 20M; (f) 20H; (g) 30M; and (h) 30H (scale markers are each 5 μm in length). Inset in (c) displays the triangle orientation scale of the images.

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Figure 6

Misorientation distribution plots for various sample conditions: (a) 0L; (b) 0M; (c) 0H; (d) 20L; (e) 20M; (f) 20H; (g) 30M; and (h) 30H. 0L is strongly high angle boundary dominated. 0H is strongly twin-dominated. 0M and 20L have even distribution of low angle boundaries and high angle boundaries. 20M, 20H, 30M, and 30H are strongly low angle boundary dominated (Note: Total misorientation is 62.8 deg, hence each block represents 62.8/19 = ∼3.3 deg).

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Figure 7

Grain size distribution plot for various sample conditions: (a) 0L; (b) 0M; (c) 0H; (d) 20L; (e) 20M; (f) 20H; (g) 30M; and (h) 30H. The dashed-dotted line show the general trend of the distribution and illustrates the unimodal distribution in 0L, 0H, and 20L, small fraction of multimodal grain distribution in 0M and strong multimodality in 20M, 20H, 30M, and 30H.

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Figure 8

Temperature contours showing the expected temperature at plane EF of the deformation zone as a function of strain and strain-rate

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Figure 9

Temperature contours showing the expected temperature at plane EF of the deformation zone as a function of strain and natural logarithm of ZH parameter (lnZ). Experimental sample conditions are marked on the plot.

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Figure 10

Average grain size as a function of strain and Zener–Hollomon parameter. Contours show equigrainsize plots. Fine-grained microstructures are obtained toward to upper right side of the map and coarse grained microstructures are obtained toward to bottom left side of the map. Hatched region represents the condition which is expected to result in recrystallization.

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Figure 11

LAGB as a function of strain and Zener–Hollomon parameter. Contours are equi-LAGB fraction plots. LAGB dominated microstructures are obtained toward lower-left corner of the map while HAGB dominated microstructures are obtained toward the top-right corner of the map. Hatched region represents the condition which is expected to result in recrystallization.

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Figure 12

RSM map for copper as a function of strain and Zener–Hollomon parameter demarcating various regions of recrystallization, HAGB dominated region, LAGB dominated region, and mixed regions. Our experimental sample conditions are also overlaid on the map.

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