Experimental study of high velocity oxy-fuel sprayed WC-17Co coatings applied on complex geometries. Part A: Influence of kinematic spray parameters on thickness, porosity, residual stresses and microhardness

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

Prediction of Coating Properties of Thermally Sprayed WC–Co on Complex Geometries

“…As discussed in previous work (Ref 17,18), the significant role of spray distance and spray angle in determining the particle impingement conditions does not allow for the isolated study of either one without considering the interplay between them. The same is not true for the effect of gun traverse speed since it does not influence the particle impingement conditions, rather it affects the coating via post-impingement mechanisms (Ref 18).…”

“…Although the method of the kinematic calculator can be generalized to model any coating material or thermal spray method, in this work, the application of WC-17Co with HVOF is examined due to the availability of experimental results from previous work (Ref 17,18). It was shown that there is significant interplay between the spray distance and spray angle in determining the coating properties since both determine the impingement conditions of the particles.…”

“…The limits of the prediction space are dictated by the extreme values of the input experimental results. In the case study presented here, the experimental results from previous work (Ref 17,18) were used as input for constructing the prediction space for the coating thickness, WC vol.% and microhardness. Additionally, the sliding wear resistance was included in the study herein, though detailed analysis and discussion of the tribology of the coatings will be presented in a future publication.…”

FIB-SEM Sectioning Study of Decarburization Products in the Microstructure of HVOF-Sprayed WC-Co Coatings

“…Previous work on the effects of the spray kinematic parameters on various coating properties (Ref 3,19) demonstrated that the increased spray distance resulted in coatings with significant decarburization of WC, which was attributed to the respective longer dwell time of the particles in-flight. Moreover, oblique spray angles proved to promote the preferential rebounding of particles that did not meet the critical impact parameters (temperature and normal component of velocity).…”

Structural and Mechanical Properties of Arc-Sprayed Ni–Cr Coating Post-Treated by Surface Mechanical Attrition Treatment (SMAT)

“…Previous studies have been performed to explore the effect of different spraying conditions on the structural and mechanical properties of thermally sprayed coatings [11,[18][19][20][21]. It has been 2 of 13 demonstrated that porosity and defects contents in the thermally sprayed coatings can be controlled by changing several process parameters, such as spraying angle, particle velocity, temperature at impact, and spray distance.…”