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Brunico - Bruneck, Italy

Muterlle P.V.,University of Trento | Straffelini G.,University of Trento | Molinari A.,University of Trento | Pahl W.,GKN SinterMetals
Powder Metallurgy

The influence of the microstructure on the wear behaviour of some hardened sintered steels produced with diffusion bonded powders and subjected to through hardening, carburising and sinterhardening was investigated. In dry sliding, wear was oxidative in nature and the localised surface deformation caused delamination, which further reduce the wear resistance. In these conditions, the harder the microstructure, the better the resistance to plastic strain. In lubricated rolling-sliding, wear occurs by rolling contact fatigue. Cracks nucleation was caused by the stress localisation at the pores edges. In this case, a brittle virgin martensite has a negative effect. Tempering reduces martensite brittleness, and makes its resistance to nucleation and propagation of the rolling contact fatigue comparable to that of Fe-Ni austenite. © 2010 Maney Publishing. Source

Cristofolini I.,University of Trento | Molinari A.,University of Trento | Tesfaye S.,University of Trento | Federici M.,Sacmi | And 4 more authors.
Advances in Powder Metallurgy and Particulate Materials - 2014, Proceedings of the 2014 World Congress on Powder Metallurgy and Particulate Materials, PM 2014

The effect of high temperature on dimensional change, porosity, microstructure, dimensional and geometrical characteristics of parts is analyzed. On increasing the sintering temperature shrinkage increases and anisotropy of dimensional change gets progressively attenuated. The fraction of the load bearing section increases and the microstructure of the ferrous matrix may result unmodified, hardened (enhanced diffusion of alloying elements), softened (decarburizing). Sintering temperature may be increased up to 1350°C without affecting dimensional and geometrical precision of steel parts. Source

Muterlle P.V.,University of Brasilia | Cristofolini I.,University of Trento | Pilla M.,University of Trento | Pahl W.,GKN SinterMetals | Molinari A.,GKN SinterMetals
Materials and Design

Sintered bronze with the addition of graphite as self lubricant is widely used in sliding bearings and bushes applications, especially where grease and oil lubricant cannot be considered. Aim of this work is to study the dry sliding wear behavior of a porous sintered bronze-graphite composite, which is characterized by a transition from solid lubrication to adhesive wear. In this last condition graphite loses its efficiency as solid lubricant due to the frictional heat. The efficiency of the solid lubrication was examined at different loads and sliding velocities; it decreases on increasing both load and velocity. The behavior in the different dry sliding conditions was investigated and the corresponding flash temperature was calculated. Results indicate that transition occurs when the flash temperature reaches at least 360K. Some design guidelines were then proposed, based on a P0 vs. v map, which defines the parameters ensuring both that no plastic deformation occurs and that solid lubrication is efficient during dry sliding. The relative design scheme gives a tool to verify if the dimensional and geometrical characteristics of the part are guaranteed during its expected life. © 2011 Elsevier Ltd. Source

Metinoz I.,University of Trento | Cristofolini I.,University of Trento | Pahl W.,GKN SinterMetals | DeNicolo A.,GKN SinterMetals | And 2 more authors.
Materials Science and Engineering A

A conservative approach to predict the contact fatigue behavior of a Powder Metallurgy steel, in the sinter-hardened condition and after shot peening, was proposed. It is based on the assumption that the contact fatigue crack nucleation is anticipated by the local plastic deformation of the material, which occurs when the maximum local stress exceeds the yield strength of the matrix. A model to predict contact fatigue crack nucleation has been proposed and validated by experiments. A local approach is used, based on the characteristics of the largest pores, which promote fatigue crack nucleation, and on the microhardness of the microstructural constituents where they are localized. Shot peening improves the contact fatigue resistance of the sinterhardened steel by 30%. © 2014 Elsevier B.V. Source

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