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Research Papers

Microstructure and Thermal Stress Distributions in Laser Carbonitriding Treatment of Ti–6Al–4V Alloy

[+] Author and Article Information
B. S. Yilbas, S. S. Akhtar

Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia

A. Matthews

Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia; Department of Engineering Materials, Sheffield University, Sheffield, S1 3JD UK

C. Karatas

Engineering Faculty, Hacettepe University, Turkey

A. Leyland

Department of Engineering Materials, Sheffield University, Sheffield, S1 3JD UK

J. Manuf. Sci. Eng 133(2), 021013 (Mar 23, 2011) (8 pages) doi:10.1115/1.4003523 History: Received April 26, 2010; Revised January 11, 2011; Published March 23, 2011; Online March 23, 2011

The results of experiments into laser assisted gas carbonitriding of a Ti–6Al–4V alloy are reported. The temperature and thermal stress fields were simulated using finite element analysis. Microstructural changes in the laser treated region were examined using scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction. In the process, a carbon film was formed at the workpiece surface prior to laser processing and the laser scanning speed was kept constant during the process. It was found that the laser treated layer extended uniformly along the surface; the depth of the layer was about 55μm. The formation of TiCxN1x, TiN, and TiC in the surface region enhances the hardness significantly.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Laser heating situation and the coordinate system

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Figure 2

XRD measurement of d sin2 Ψ for TiN

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Figure 3

Temporal variation of surface temperatures obtained from the predictions and the experiment. Thermocouple locations are x=1.5 mm and x=4 mm away from the initiation of scanning point (0,0,0). Two thermocouples are located 0.5 mm away from the laser scanning line to avoid the melting of the thermocouple tips.

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Figure 4

Temperature distribution along the x-axis for different cooling periods

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Figure 5

Temperature contours at time t=0.05 s (initiation of cooling cycle)

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Figure 6

von Mises stress distribution along the x-axis for different cooling periods.

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Figure 7

von Mises Stress contours at time t=0.05 s (initiation of cooling cycle).

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Figure 8

Temperature distribution along the y-axis for different cooling periods.

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Figure 9

von Mises stress distribution along the y-axis for different cooling periods.

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Figure 10

Temperature distribution along the z-axis for different cooling periods.

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Figure 11

von Mises stress distribution along the z-axis for different cooling periods.

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Figure 12

Stress (σz) distribution inside the substrate material along the z-axis. The stress becomes the residual stress once the cooling period ends (t=260 s). It should be noted that there is no significant contribution of the shear stress to the residual stress as observed from the XRD data (Fig. 2).

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Figure 13

SEM micrographs of the top views of the carbon film and the laser treated surfaces

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Figure 14

SEM micrographs of cross section of laser treated surface

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Figure 15

XRD diffractogram for as received and laser treated workpieces

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