Effects of HVOF Process Parameters on the Properties of Ni-Cr Coatings

Abstract

This research examined the influence of processing parameters on the structure of a Ni-50Cr coating applied by high-velocity oxy-fuel spraying onto stainless steel specimens. This type of coating is normally used as protection against heat and corrosion encountered in power plant and marine boilers, and oil refinery heaters. A statistical design of experiments identified fuel and oxygen flow rates and spraying distance as the most influential parameters controlling the in-flight characteristics of the powder particles prior to impact. The effects of these parameters on the porosity level, oxide content, and microhardness of the coatings were then investigated in more detail. These results indicated that the oxide content and hardness of the coatings were dependent on the gas combustion ratio but not on spraying distance. The porosity level and amount of unmelted particles were reduced at the longest spraying distance.

Corrosion and erosion–corrosion behaviour of activated combustion high-velocity air fuel sprayed Fe-based amorphous coatings in chloride-containing solutions

“…However, the oxide content could not be decreased for the HVOF process because the molten particles were always in the oxygen containing environment during the spraying process [38]. Hence, the AMC with relatively low-melting temperature of AC-HVAF exhibits superiority because the porosity and oxidation can be considerably reduced.…”

Corrosion resistance of Ni‐50Cr HVOF coatings on 310S alloy substrates in a metal dusting atmosphere

“…There are a large number of processing variables in HVOF spraying, and the present samples were selected from the previously described [16] matrix of experiments, designed to identify the influence of process variables on the structure of the coatings. Two sets of HVOF process parameters were employed, selected to produce coatings with porosity levels and oxide contents of 2.5 vol% and 0.6 wt% for coating 1 and 0.8 vol% and 4.8 wt% for coating 2 ( Table 2).…”

Ni‐Ti Shape Memory Alloy Coatings for Structural Applications: Optimization of HVOF Spraying Parameters

“…Combustion produces a flow of hot gas at supersonic or hypersonic velocity of approximately 2000 m/s [19,[22][23][24]. e flame achieves supersonic velocities in the process of expansion at the exit of the convergent-divergent nozzle with a diameter size from 8 to 9 mm [13,22] and temperatures in the range of 2500-3200°C, depending on the type of the fuel, the fuel-to-oxygen ratio, and the combustion pressure [13,25,26].…”

“…Spray distance acts on velocity and temperature of the in-flight particles and influences porosity, hardness of the coating [31], and oxide content of the sprayed powders [23]; powder feed rate and melting degree of powders affect the coating hardness and corrosion resistance, respectively [30,32]; the fuel-to-oxygen mixing ratio influences the flame temperature and velocity [33] and particle velocity [21] and affects oxide content and density of coating [23]. On the basis of these findings, to obtain the best properties of the coating, it is necessary to define the optimal spraying and coating parameters.…”