Abstract
Present paper deals with the mathematical simulation of the heat transfer between a WC-Co coating and a copper substrate during HVOF spraying. This modelling includes the investigation of temperature variation, coating solidification, melting and subsequent solidification in the substrate interfacial region and specific features of the substrate-coating thermal interaction. The results obtained are used for modelling of the development of the coating structure and adhesion during HVOF spraying of the WC-Co powder on a copper substrate. Two types of substrate were considered: smooth (polished) and rough. Variations of solidification times, solidification velocity, thermal gradient and cooling velocity in the coating and substrate interfacial region are studied. Development of the amorphous and crystalline structures in the coating and of the crystalline structure in the substrate interfacial region is discussed. Behaviour of the crystal size and intercrystalline distance with respect to the thermal spray parameters and morphology of the substrate surface is analyzed. Optimal conditions for the formation of fine and dense crystalline structure are determined. Structural changes in the solid state of the substrate occurring because of heating and rapid cooling are considered. Mechanical and thermal mechanisms of development of the substrate-coating adhesion are discussed. Results obtained agree well with experimental data.
Highlights
Present paper deals with the mathematical simulation of the heat transfer between a WC-Co coating and a copper substrate during HVOF spraying
El valor medio de £ para el caso de superficie pulida del sustrato varía de forma no uniforme con el aumento de TlQ y dismuye con el aumento de r20 (Fig. 6)
33 [5], 1997 2 9 7 http://revistademetalurgia.revistas.csic.es
Summary
El desarrollo de la estructura del recubrimiento, y con ello de las propiedades, depende esencialmente de la transferencia de calor entre el sustrato y. Para un determinado tipo de recubrimiento, la dinámica de la transferencia de calor depende significativamente del material que forma el sustrato y de la morfología de la superficie del sustrato. Se han establecido diferencias muy marcadas entre la cinética de solidificación y fusión del recubrimiento y la de solidificación de la región interfacial del sustrato debido a las propiedades termofísicas diferentes de los materiales que constituyen el sustrato. El flujo térmico de la lámina delgada formada en la superficie pulida del sustrato, se dispersa rápidamente hacia el interior del mismo; por ello, el grosor de la capa fundida en la región interfacial del sustrato resulta ser pequeño. Esto conduce a la disminución de la transferencia de calor entre el recubrimiento y el sustrato y, por tanto, al aumento de la temperatura en el sustrato y al aumento de la profundidad de la zona fundida en la región interfacial del mismo
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