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Chagnon F.,Rio Tinto Metal Powders
Proceedings of the World Powder Metallurgy Congress and Exhibition, World PM 2010 | Year: 2010

Although most of the new PM applications require high density to withstand demanding loads, many parts are still produced in a density range of 6.0 to 6.6 g/cm3. For such applications, high green strength is a key factor to avoid green cracks during compaction and handling before sintering. These parts must also show good dimensional stability during sintering. A study has been carried out to evaluate the behaviour of various powder grades during sintering. F-0005 and FC-0205 mixes were prepared and pressed to a green density of 6.4 g/cm3. Sintered properties were evaluated and dimensional behaviour characterized by dilatometry. Also, compressibility and green strength were determined at 275, 480 and 690 MPa using a mix with 0.75% EBS wax. Results showed that with proper modification of particle morphology and particle size distribution, the dimensional change can be modified and the green strength improved.

Lemieux P.,IMFINE Corporation | Gelinas C.,Rio Tinto Metal Powders
Advances in Powder Metallurgy and Particulate Materials - Proceedings of the 2015 International Conference on Powder Metallurgy and Particulate Materials, PowderMet 2015 | Year: 2015

A new approach in the method of depositing an external lubricant on the die walls of a powder metallurgy press has been developed which allows the compaction of parts from mixes with no or minimal lubricant content. By heating the die to moderate temperatures (70°C - 100°C) and using new composite lubricants, optimum thickness lubricant layers can be deposited allowing the compaction-ejection of difficult parts. Trials were carried out on an industrial press with measurement of the compaction and ejection forces for different parts and powder mixes. In particular, an iron-resin powder mix with no internal lubricant was pressed into rectangular shapes of different thicknesses and punch profiles. Mixes for high density applications were also pressed into rectangular shapes using die wall lubrication (DWL). The results are compared to those obtained with regular mixes containing 0.75% wax and special mixes intended for high density applications (low internal lubricant) pressed without the DWL.

Chagnon F.,Rio Tinto Metal Powders
International Journal of Powder Metallurgy (Princeton, New Jersey) | Year: 2010

The effect of sintering temperature and mix composition on the static and dynamic properties of sinter-hardened steels was evaluated in relation to the level of retained austenite. Using a low-alloy steel-base powder, mixes were prepared with 2 w/o Cu and two levels of graphite to attain -0.7and 0.5 w/o carbon after sintering, with or without admixed 1 w/o Ni, followed by temperating. Transverse rupture (TR) strength, tensile properties, and plane bending fatigue strength were evaluated. The highest tensile properties are attained at a retained austenite: martensite ratio (γR:M) <0.15. Plane-bending fatigue strength is maximized at a (γR: M) ratio of 0.25 with attendant crack growth primarily through interparticle crack necks. Under cyclic loading, a microstructure consisting of high-carbon plate martensite, compared with low-carbon lath martensite, is preferred.

Tougas B.,Laval University | Blais C.,Laval University | Chagnon F.,Rio Tinto Metal Powders | Pelletier S.,National Research Council Canada
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

Admixing pure elements to powder mixes can cause the formation of heterogeneous microstructures in sintered parts. For instance, nickel is renowned for forming nickel-rich areas (NRA) in powder metallurgy (PM) nickel steels due to its poor diffusivity in iron matrix (or lattice). The present work is aimed at characterizing the principal diffusion mechanisms of nickel and their influence on microstructures and properties of PM nickel steels. A new wavelength dispersive X-ray spectrometry (WDS) approach linking line scans and X-ray maps to concentration maps is proposed. Grain boundary and volume diffusion coefficients of admixed nickel have been determined in PM nickel steels using Suzuoka's equation. Results also show that nickel distributes itself in the iron matrix mainly by surface and grain boundary diffusion. © 2012 The Minerals, Metals & Materials Society and ASM International.

Desbiens J.,CEGEP de Thetford Mines | Robert-Perron E.,Rio Tinto Alcan | Blais C.,Laval University | Chagnon F.,Rio Tinto Metal Powders
Materials Science and Engineering A | Year: 2012

A study was carried out to determine if green machining of powder metallurgy sinter-hardenable steel components had detrimental effect on their tensile properties as well as their fatigue resistance. Results show that tensile properties and axial fatigue resistance of green machined specimens and specimens machined after sintering are statistically identical. © 2012 Elsevier B.V.

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