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Powder metallurgy methods and compositions

Inactive Publication Date: 2007-04-05
APEX ADVANCED TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0013] Metal parts formed using the metal powder compositions and methods according to the invention exhibit a substantially higher sintered density than metal parts formed from metal powder compositions that do not comprise an organic acid, and such higher densities can be reached in less time and at lower energy costs. For example, it is possible to form carbon steel or low alloy steel metal parts that have a sintered density that approaches 100% of theoretical density. Subsequent heat treatment of metal parts formed from the metal powder compositions and methods of the invention substantially improve the mechanical properties of the parts, which in some cases are better than can be achieved using non-powder metallurgical processes such as forging and casting.

Problems solved by technology

However, the sintered density of parts formed from most metal powder compositions does not approach 100% of theoretical density.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0035] A Stock Powder Metallurgy Composition (“Stock P / M”) was prepared by dry mixing the components set forth in Table 1 below:

TABLE 1ComponentWeight PercentANCORSTEEL 85 HP*97.00% UT-3PM**2.00%Graphite Powder0.65%SUPERLUBE PS1000-B***0.35%

*ANCORSTEEL 85 HP is a water atomized, pre-alloyed steel powder (approximate chemical composition in weight percent: ˜98.93% Fe; 0.86% Mo; 0.12% Mn; 0.08% O; and <0.1% C)available from Hoeganeaes Corporation of Cinnaminson, New Jersey.

**UT-3PM is a high-purity nickel powder for pressed powder metallurgy applications available from Norilsk of Moscow, Russia.

***SUPERLUBE PS1000-B is a pressed powder metallurgy lubricant capable of transforming from a solid to a liquid due to shear from Apex Advanced Technologies of Cleveland, Ohio.

example 2

[0036] Test bars were formed using the Stock P / M formed in Example 1. In Sample 1, the test bar was formed solely out of the Stock P / M formed in Example 1. In Samples 2 and 3, the test bars were formed by blending the Stock P / M with citric acid at a 0.2% by weight loading and a 0.4% by weight loading, respectively. Each test bar was formed using a 50 tsi (tons per square inch) Tinius Olsen hydraulic press. Each test bar had the following dimensions: ½″ wide×1¼″ long×¼″ thick.

[0037] The green density of the pressed test bars was measured in accordance with the procedures set forth in MPIF Standard 45 and ASTM B331-95 (2002). The green test bars were delubed at normal conditions and were sintered in a continuous furnace at a heat up rate of 133° F. / min in the hot zone to a temperature of 2,480° F. in an atmosphere consisting of 25% H2 and 75% N2. The density of the green and sintered test bars is reported in Table 2 below:

TABLE 2SampleStock P / MCitric AcidGreen DensitySintered Densi...

example 3

[0039] The test bars were formed using the same Stock P / M formed in Example 1 using the same procedures as set forth in Example 2. The green test bars were delubed at normal conditions, sintered in a continuous furnace at a heat up rate of 50° F. / min in the hot zone to a temperature of 2,480° F. in an atmosphere consisting of 25% H2 and 75% N2. The density of the green and sintered test bars is reported in Table 3 below:

TABLE 3SampleStock P / MCitric AcidGreen DensitySintered Density4 100% 0%7.29 g / cm37.42 g / cm3599.6%0.4%7.21 g / cm37.35 g / cm3699.2%0.8%7.10 g / cm37.23 g / cm3

[0040] The data reported in Table 3 shows that the presence of small amounts of citric acid in the Stock P / M blend does not result in any improvement in sintered density when the heat up rate is below 60° F. / min. Specifically, the sintered density of the test bars decreased with the addition of citric acid at a heat up rate of 50° F. / min due to lower green density to start. Typically there is a direct correlation bet...

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Abstract

The present invention provides metal powder compositions for pressed powder metallurgy and methods of forming metal parts using the metal powder compositions. In one embodiment, the metal powder composition according to the invention includes a blend of primary metal particles, one or more liquid phase forming materials or precursors thereof, a lubricant and an organic acid that is capable of reacting with an oxide of a metal in the primary metal particles to form an organic metal salt that decomposes when the metal powder composition is sintered under reducing or non-oxidizing conditions. During a “delubing” step, the organic acid reacts with an oxide of a metal in the primary metal particles to form an organic metal salt that decomposes into a base metal or a metal-carbide during sintering.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of Invention [0002] The present invention relates to methods and compositions for use in pressed powder metallurgy. [0003] 2. Description of Related Art [0004] In pressed powder metallurgy, a substantially dry metal powder composition is charged into a die cavity of a die press and compressed to form a green compact. Pressing causes the metal powder particles in the metal powder composition to mechanically interlock and form cold-weld bonds that are strong enough to allow the green compact to be further processed. After pressing, the green compact is removed from the die cavity and sintered at a temperature that is below the melting point of the major metallic constituent of the metal powder composition, but sufficiently high enough to strengthen the bond between the metal powder particles, principally through solid-state diffusion. Some metal powder compositions include minor amounts of other metals and / or alloying elements that melt duri...

Claims

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Application Information

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IPC IPC(8): B22F3/12
CPCB22F3/1039B22F2998/00B22F2998/10B22F3/1021B22F2201/01B22F2201/02B22F2201/20B22F1/007B22F3/02B22F1/02B22F1/0062B22F1/105B22F1/102B22F1/16
Inventor HAMMOND, DENNIS L.PHILLIPS, RICHARD R.
Owner APEX ADVANCED TECH
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