Optimization of HVOF Cr3C2NiCr coating for increased fatigue performance

• By using the CJS high kinetic thermal spray process, compressive residual stress onto the Cr3C2NiCr coating was produced.
• It was shown that axial fatigue performance of the steel could be improved by applying such coating.
• Good fatigue performance comparing to other treatments was mainly related to the compressive stress state of the substrate.
• Well adhered, low defect, structurally dense coating on the fatigue performance was also of importance.

Thermally sprayed coatings are strong candidates to be used for replacement of hard chromium – process which is regarded as an environmental risk – in many sliding surfaces for engineering applications such as hydraulic cylinders and aircraft landing gears. Recent advance in thermal spraying technology, based on the increase of the spray particle velocity, has led to improved coating quality. This study focuses on the fatigue performance of structural steel coated with Cr3C2NiCr coating. Coating has been produced by using high kinetic HVOF thermal spray process. First, the coating was optimized for fatigue purposes by studying the residual stress generation. The optimized coating was selected for deposition of axial fatigue tests specimens, whose fatigue performance was compared to the uncoated steel specimens having different surface treatments (turning, polishing, and shot blasting) relevant for the target applications. The results showed that by using a high kinetic energy coating, the fatigue performance of Cr3C2NiCr coated structural steel was clearly improved compared to uncoated steel of similar surface quality. Increased fatigue resistance of the coated material was attributed to the substantial compressive residual stresses that hindered crack initiation and that was caused by the high velocity spray particles during the coating process.