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The Co-MIM Preparation of Gradient Cemented Carbide and Research of Sintering Densification

Author: PanWenQiang
Tutor: LiYiMin
School: Central South University
Course: Materials Science and Engineering
Keywords: powder co-injection molding skin-core thickness uniformity interface stress capillary force liquid phase co-sintering densificationtheory the mechanism of Co phases migration Co mean free path (λ)
CLC: TF124
Type: Master's thesis
Year: 2013
Downloads: 6
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Abstract


Powder Co-injection Molding is a near net shape technology, which combines plastic co-injection molding process and convention powder metallurgy. It offers the ability to integrate two dissimilar materials with different properties in a single production route. This article studied the co-injection process, densification behavior and mechanism of Co phase migration during the period of sintering of (0.8μm) WC-8Co/(3μm) WC-8Co samples. The methods and results of this study are as follows:In this study loading of58%YG8hard feedstock, WC particle sizes were0.8μm (skin layer) and3μm (core layer), were used for co-injection process study. Skin-core thickness uniformity is an indicator which is selected to evaluate the most suitable co-injection process. Research shows that when the core and skin layer injection temperature was175℃and the skin pre-filled amount was30%, it is possible to obtain a good interface morphology and favorable uniformity of the skin-core carbide ball tooth.Experiments on densification behavior of co-sintered alloy in different temperature were studied. Research showed that it lead to a density gradient and co-sintered density deviation from the free sintering average density with the effect of interfacial stress and elements diffusion in interface of the co-sintered alloy.This paper deduced the densification equations during liquid phase co-sintering process based on viscosity sintering theory and assumption that the tangential strain rate of co-sintering materials at interface are equal and capillary are the main sintering stress. In the model, the relative parameters were obtained from experiments. The study showed that there are some deviations between experimental results and liquid co-sintering densification modeling results. The reason is that Co phase migrates from coarse particle side to the fine particle side. This article studied the distribution of Co phase between coarse particle side and the fine particle side. And the results showed that when λ is proportional to d0.4the modeling results were good agreement with experimental results.

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CLC: > Industrial Technology > Metallurgical Industry > Metallurgical Technology > Powder metallurgy (metal ceramic technology ) > Powder molding, sintering and post-processing
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