On the investigation of coating characteristics within the experimental domain imposed by inner-diameter HVOF process

Abstract

Widely used in multiple industries, hard chrome plated coatings are proven to exhibit good properties. Yet, the process of hard chrome plating is extremely toxic. Therefore, High Velocity Oxyfuel (HVOF) spraying is gradually replacing hard chrome plating in many industries. Yet, HVOF is not adapted for complex geometries and inner diameters smaller than six inches due to the size of the spraying apparatus. The aim of this project is to establish process-properties relations between the spraying parameters inherent to ID-HVOF (inner diameter high velocity oxyfuel) and the resulting WCCoCr coating characteristics. For this project, two WCCoCr powder compositions were used. To highlight any possible differences, powder characterization tests included phase composition analysis by X-Ray Diffraction (XRD), morphology analysis and granulometry. It was found that the particle size distribution has an effect on the decarburization phenomena within the coating during the deposition process. For each produced set of samples, the goal was to establish relations between the highest temperature reached during the deposition process and the sample’s properties. Coating characterization tests included morphology analysis, porosity quantification, phase composition analysis by X-Ray Diffraction (XRD), microhardness measurements and abrasion tests. A first set of flat samples of 4340 AISI steel and a WCCoCr coating were produced. By imposing a shorter spraying distance, it was possible to simulate ID-HVOF conditions. After rectification of the decarburization zone on the 4340 AISI steel substrates, a second set of WCCoCr coatings was produced. The third set of WCCoCr coatings was deposited onto mild steel substrates, in order to extend the characterization tests led on set 2. For the last set of WCCoCr coatings, two types of 4340 AISI steel coupons were employed. Each substrate type received two different surface treatments. For these experiments, the goal was to compare the effect of substrate surface treatment on the overall performance of the samples. In summary, the influence of the maximum temperature on the coating’s properties and behavior was studied. It was found that the spraying parameters affected the deposited thickness per pass. Porosity and abrasion were nonetheless not correlated to temperature variation. In addition, a close correlation between temperature, hardness loss and decarburization was established.

Date	14 Dec 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Lucas Hof (Supervisor) & Philippe Bocher (Co-supervisor)