J. A. Calero

Modelling of particle movement and thermal behaviour during high velocity oxy-fuel spraying

Abstract A theoretical model is presented to investigate the particle mechanical and thermal behaviour in the process of high velocity oxy-fuel (HVOF) spraying. The model accounts for the various phenomena which influence the momentum and heat transfer during particle movement and heating. The mathematical formulation takes into account the fluid velocity dependence on the particle density, internal heat conduction in particles and their composite structure, steep temperature gradients near the particle surface and fluid parameter variations. Comparison with experimental data shows that the present model enables accurate predictions to be made and optimal conditions of HVOF spraying to be established.

Influence of thermal processes on coating formation during high velocity oxy-fuel (HVOF) spraying of WC-Ni powder particles

Mathematical simulation of the thermal processes occurring during the formation of a WC-Ni coating on a low alloy steel by high velocity oxy-fuel (HVOF) spraying was carried out. The factors assessed during the simulation include the overall temperature changes, the solidification of the coating, the melting and subsequent solidification of the interface regions of the substrate and the thermal interactions between the different layers of the coating. The optimum conditions for the formation of good structures in the coating and the adjacent substrate are estimated.

Formation of structure of WC-Co coatings on aluminum alloy substrate during high-velocity oxygen-fuel (HVOF) spraying

This paper is based on Ref 1 and concerns the mathematical simulation of the structure formation of the WC-Co coating on aluminum alloy (Al-4% Cu) substrate during high-velocity oxygen-fuel (HVOF) spraying. Variations of the solidification velocity, thermal gradient, and cooling velocity in the coating and substrate interfacial region are studied. Formation of the amorphous and crystalline structures in the coating and of the crystalline structure in the substrate interfacial region is discussed. Behavior of the crystal size and intercrystalline distance with respect to the thermal spray parameters is analyzed. Opti-mal conditions for the development of fine and dense crystalline structure are established. Results agree well with experimental data.

Prediction of powder particle behavior during high-velocity oxyfuel spraying

A mathematical model is developed to predict particle velocity and temperature during high-velocity oxyfuel (HVOF) spraying. This model accounts for internal heat conduction in powder particles; particle heating, fusion, cooling, and solidification; the influence of particle morphology on thermal behavior; and the composite structure of the particles. Analytical results are obtained that describe particle velocity and temperature variations. The dependence of fluid velocity on particle density and volume fraction is shown. The results agree with empirically established HVOF spraying practice.

Thermal interaction between WC-Co coating and steel substrate in process of HVOF spraying

The WC-Co powders can be used to produce good adhesive and wear resistant HVOF thermal spray coatings on steel and light alloys substrates. In order to understand the properties of this kind of coating, the phases which are present in the coatings and structure changes during post heat treatments have been investigated. Although the coating properties depend very much on the structure developed in the substrate-coating interfacial region it has not been yet investigated in detail. The present study is devoted to the experimental and theoretical analysis of this interfacial region. The structure characterization has been performed mainly through the use of transmission electron microscopy. To provide a theoretical investigation a realistic prediction model of the process has been developed and on its base the mathematical simulation of the substrate-coating thermal interaction has been undertaken.

Heat transfer during the formation of an HVOF sprayed WC–Co coating on a copper substrate

Abstract Mathematical modelling of the heat transfer between a WC–Co coating and a copper substrate during HVOF spraying is undertaken. This modelling includes the investigation of temperature variation, coating solidification, melting and solidification in the substrate interfacial region, and specific features of the substrate–coating thermal interaction. The results obtained agree well with experimental data.

Heat transfer between WC-Co coating and aluminum alloy substrate during high-velocity oxygen-fuel (HVOF) spraying

Mathematical simulation of the heat transfer between a WC-Co coating and an aluminum alloy (Al-4%Cu) substrate during HVOF spraying is provided. This simulation includes the investigation of tem-perature evolution, coating solidification, fusion and solidification in the substrate interfacial region, and particular features of the substrate-coating thermal interaction. Optimal thermal conditions for forming the coating structure are estimated. The results obtained are used in another paper (Ref 15), “Formation of Structure of WC-Co Coating on Aluminum Alloy Substrate During High-Velocity Oxygen-Fuel (HVOF) Spraying,” to predict the structural parameters, which agree well with the experimental data.

Influence of in-flight dissolution process on composite powder particle (WCNi) behaviour during high velocity oxy-fuel spraying

Abstract The in-flight dissolution of composite powder particles consisting of WC with a coating of Ni during high velocity oxy-fuel spraying has been investigated using mathematical modelling techniques. The model has been used to assess the variations with time in the volume of the coating metal as dissolution of the carbide occurs using two basic particle shapes: spheres and cylinders. The changes occurring in the velocities and temperatures of the composite particles as a function of their size, shape and initial temperature during spraying have also been investigated. Possible variations in the dissolution parameters have also been considered. The results obtained were consistent with experimental data and enable the optimum spraying conditions for the powder to be determined.

Development of coating structure and adhesion during high velocity oxygen-fuel spraying of WC-Co powder on a copper substrate

This paper deals with the mathematical modeling of the development of the WC-Co coating structure and adhesion on a copper substrate during high velocity oxygen-fuel (HVOF) spraying. Two types of substrates are considered: smooth (polished) and rough (grit blasted). Variations of solidification time, 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. Behavior 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.

Modelling of the in-flight behaviour of stainless steel powder particles in high velocity oxy-fuel spraying

Abstract Modelling of the mechanical and thermal behaviour of stainless steel 316L powder particles during high velocity oxy-fuel (HVOF) spraying is presented. This modelling accounts for the combustion process, the gas dynamics inside and outside of the spray gun, gas-particle interactions, acceleration and deceleration of the gas flow, internal heat conduction in the powder particles and particle heating, melting, cooling and solidification. Variations of the times of flight and melting of the particles are studied. Optimal conditions of spraying are predicted. The results agree with experimentally-established HVOF spraying practice.