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Research Papers

# Densification and Properties of 420 Stainless Steel Produced by Three-Dimensional Printing With Addition of $Si3N4$ Powder

[+] Author and Article Information
Li Sun, Patrick Kwon

Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824

Yong-Ha Kim

Department of Mechanical Engineering, University of Washington, Seattle, WA 98195

Dave (Dae-Wook) Kim1

School of Engineering and Computer Science, Washington State University, Vancouver, WA 98685kimd@vancouver.wsu.edu

1

Corresponding author.

J. Manuf. Sci. Eng 131(6), 061001 (Oct 26, 2009) (7 pages) doi:10.1115/1.4000335 History: Received May 27, 2009; Revised September 17, 2009; Published October 26, 2009

## Abstract

This study is aimed to investigate the effect of adding $Si3N4$ on the three-dimensional printing (3DP) processed 420 stainless steel (SS). The final density, dimensional changes, and mechanical properties have been studied for the samples prepared under a series of sintering conditions. The contents of $Si3N4$ powder ranging between $0 wt %$ and $15 wt %$ and the sintering temperature were varied in the experiments in order to understand the dependence of densification kinetics and changes in properties on these process parameters. The experiments provide the evidence that the addition of $Si3N4$ can improve the densification kinetics of 420 SS significantly. The 420 SS samples produced by 3DP with $12.5 wt %$$Si3N4$ sintered at $1225°C$ for 6 h yielded 95% relative density, 190 GPa Young’s modulus, and 500 Knoop microhardness without any major sample shape distortion. The results are promising in that the 3DP process can be used to yield the prototype almost equivalent to a real part with a full mechanical capacity.

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## Figures

Figure 3

Ramp/soak profile for the sintering process

Figure 6

The temperature dependent sintering kinetics curves for the representative samples. The small figure shows the presintering curve of 0 wt %Si3N4 sample sintered at 1225°C (the soak duration is 6 h for all three curves).

Figure 7

The dependence of height shrinkage ratio on the proportion of Si3N4 and sintering temperature

Figure 10

Angle variation in the insider corners for the various L-shaped samples (soak duration: 6 h)

Figure 11

The Young’s moduli of various samples (the 12.5 wt %Si3N4 samples sintered at 1300°C, and most 15 wt %Si3N4 samples are with smaller length than the supporter distance of three-point bending test supporters, so the corresponding result was not measured)

Figure 12

The hardness of various samples (samples with liquid sintering were not tested)

Figure 4

Micrographs of representative green parts with (a) 0 wt %Si3N4 and (b) 12.5 wt %Si3N4

Figure 5

Volume ratio of each component in various green parts

Figure 1

Appearance and particle size distribution profile of (a) 420 SS powder, and (b) Si3N4 powder

Figure 2

Schematics of 3DP procedures

Figure 8

The dependence of relative densities of the sintered samples with varied proportions of Si3N4 and sintering temperature (values of pure Si3N4 were acquired from sintered cold pressed samples under 80 MPa)

Figure 9

The micrographs of etched representative 420 SS/Si3N4 samples and their EDX analysis results: (a) 420 SS with Si3N4 of 7.5 wt % sintered at 1225°C, (b) with Si3N4 of 12.5 wt % sintered at 1225°C, (c) with Si3N4 of 12.5 wt % sintered at 1300°C (etchant composition: HCl of 5 ml, ethanol of 95 ml, picric acid of 1 g)

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