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Technical Briefs

Characterization of Zinc Powder Compactions: Factors Affecting Mechanical Properties and Analytical Powder Metallurgy Models

[+] Author and Article Information
Ben J. Rael

Mechanical Engineering Department, MSC01-1150 University of New Mexico, Albuquerque , NM 87131

Casey L. Dyck

Mechanical Engineering and Sciences Department, University of Illinois at Urbana-Champaign, Champaign, IL 61820

Tariq A. Khraishi

Mechanical Engineering Department, MSC01-1150 University of New Mexico, Albuquerque, NM 87131

Mehran Tehrani, Marwan S. Al Haik

Virginia Tech. Engineering Science and Mechanics, MC 0219 223 Norris Hall, Blacksburg, VA 24061

J. Eng. Mater. Technol 134(4), 044502 (Aug 24, 2012) (5 pages) doi:10.1115/1.4005404 History: Received April 06, 2010; Revised October 26, 2011; Published August 24, 2012; Online August 24, 2012

In this study, the effectiveness of analytical models which attempt to predict the density of unsintered powder metallurgy (PM) compacts as a function of consolidation pressure is investigated. These models do not incorporate the nonuniform densification of powder compacts and may insufficiently describe the pressure/densification process. Fabrication of uniform and nonuniform Zinc (Zn) tablets is conducted to assess the validity of the pressure/density model developed by Quadrini (Quadrini and Squeo, 2008, “Density Measurement of Powder Metallurgy Compacts by Means of Small Indentation,” J. Manuf. Sci. Eng., 130 (3), pp. 0345031–0345034). Different tablet properties were obtained by varying the compaction pressure and fabrication protocol. Density gradients within Zn tablets result in a spatial dependence of Vickers microhardness (HV) throughout the fabricated specimen. As a result, micro-indentation testing is used extensively in this study as a characterization tool to evaluate the degree of nonuniformity in fabricated Zn tablets. Scanning electron microscopy (SEM) is also employed to verify tablet density by visual examination of surface porosity as compaction pressure is varied and sintering is applied.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Particle size distribution for zinc powder (median 6–9 μm) used in this study, (inset) SEM micrograph of zinc powder

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Figure 2

Experimental setup

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Figure 3

Scanning electron micrograph of Vickers indent of sample consolidated at 300 MPa

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Figure 4

Superposed loading and unloading curves for a specimen consolidated at 450 MPa. Two grams of Zn powder was used for the tablet here.

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Figure 5

Microhardness as a function of specimen/tablet depth. Indent load = 300 g. Each data point represents the average of three specimens tested. Eight grams of Zn powder was used for each tablet.

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Figure 6

Hardness as a function of radial distance. Tablets consolidated at 400 MPa in the green state, 300 g load. Two grams Zinc powder was used for each tablet here.

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Figure 7

Numerical optimization of Eq. 1 superposed on experimental data. Each data point represents the average of three specimens tested. Five grams of Zn powder was used for each tablet.

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Figure 8

Hardness comparison for green and sintered tablets. All hardness indents were performed close to the center of the tablet using a 50 g load. Each data point represents the average of five hardness measurements. Two grams of Zinc powder was used for each tablet here.

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Figure 9

SEM image of zinc powder compacted at 200 MPa in green state

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Figure 10

SEM image of zinc powder compacted at 400 MPa in green state

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Figure 11

SEM image of zinc powder compacted at 400 MPa after sintering at 378 °C for 45 min with 60 sccm nitrogen flow

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