Abstract
When a complex geometry is rotated in front of the thermal spray gun, the following kinematic parameters vary in a coupled fashion dictated by the geometry: Stand-off distance, spray angle and gun traverse speed. These fluctuations affect the conditions of particle impact with major implications on the coating's properties. This work aims to probe into the interplay and isolated effect of these parameters on vital coating characteristics in applications requiring variable stand-off distance and spray angles. WC-17Co powders are sprayed via HVOF on steel substrates in a set of experiments that simulates the spray process of a non-circular cross section, while it allows for individual control of the kinematic parameters. Comprehensive investigation of their influence is made on deposition rate, residual stresses, porosity and microhardness of the final coating. It was determined that oblique spray angles and long stand-off distances compromise the coating properties but in some cases, the interplay of the kinematic parameters produced non-linear behaviours. Microhardness is related negatively with oblique spray angles at short distances while a positive correlation emerges as the stand-off distance is increased. Porosity and residual stresses are sensitive to the spray angle only in relatively short stand-off distances.
Highlights
The past decades, hardmetals or cermet coatings have been successfully applied to protect parts that experience intense mechanical wear, erosion and corrosion in their working life
It is generally accepted that the decline in coating thickness with decreasing angle is associated with the incremental division of the particle velocity vector to its normal (Vn) and tangential (Vt) components in respect of the substrate plane, as the spray angle is reduced [4,9,10,11]
This work probes into the interplay and isolated effect of the kinematic spray parameters playing a vital role in the coating characteristics of applications requiring variable stand-off distance and spray angles
Summary
The past decades, hardmetals or cermet coatings have been successfully applied to protect parts that experience intense mechanical wear, erosion and corrosion in their working life. These coatings can be deposited via various thermal spray methods, of which, combustion methods such as HVOF and HVAF are preferred due to their high velocity gas streams at low deposition temperatures. There is an increasingly pressing demand to coat complex parts, either externally or internally. These parts are typically, non-symmetric and may possess edges, corners and curvature.
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