Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Method to determine shrinkage and viscosity during sintering by IET

During the first two years of the project, the overall shrinkage of warm-pressed Astaloy CrM and Distaloy AE test-bars after dewaxing and sintering has been investigated. Additionally, various in situ high temperature techniques (dilatometry, bending, DSC, high temperature impulse excitated resonant frequency analysis and microtomography) together with computer aided thermodynamic calculations have been used in order to obtain additional data for the modelling and a better understanding of the physical and chemical phenomena occurring during sintering.

The results of the characterisarion of shrinkage obtained showed for both laboratory and industrial conditions, a very limited but clearly anisotropic shrinkage for Distaloy AE with higher values in the axial direction (0.2%) than in both transversal directions (less than 0.1%). The results obtained for Astaloy CrM showed slight shrinkage or swelling lower than 0.1%.

During dewaxing, a significant swelling was observed in the denser A+ and D+ specimens in good agreement with the overall shrinkage data measured. Viscosity (characterised through in-situ bending tests) has shown to increase linearly with the sintering time during isothermal sintering.

HT-IET and DSC results were correlated with equilibrium thermodynamics by means of multicomponent phase diagrams calculated by the Thermo-Calc software and the SSOL database. The temperatures for aèg transformation, magnetic transition, M23C6 precipitation in Astaloy CrM and copper melting in Distaloy AE were identified and correlated by both experimental techniques. In spite of the rather poor correlation with calculated equilibrium temperatures (especially during the heating segment of the thermal cycle), good agreement between DSC and HT-IET was achieved. The correlation during heating was notably improved when the Fe-C binary phase diagram was considered.

The non-destructive in-situ microstructural characterisation by synchrotron tomography has showed evidence of predominant disappearing of contact interfaces in the direction perpendicular to the pressing direction. This phenomenon should be correlated with the macroscopic anisotropic deformations measured.

Reported by

K.U.Leuven - Dept. of Metallurgy and Materials Engineering
Kasteelpark Arenberg 44
BE-3001 Leuven
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