Statistical comparison of processing different powder feedstock in an HVOF thermal spray process

Abstract

Cermet coatings such as WC-Co and Cr3C2-NiCr are frequently applied by means of thermal spray processes to protect highly stressed surfaces against wear. The investigation of the respective spray materials and their coating properties and in-flight particle properties are often carried out in separate experiments. In this study, the coating characteristics (hardness, deposition rate, porosity, thickness) and in-flight particle properties (particle velocity and temperature) of three different WC-based powders and a Cr3C2-NiCr powder processed by means of an HVOF process are investigated as a function of some key process parameters such as kerosene flow rate, lambda, spray distance and feeder disc velocity. These parameters were varied within a design of experiments, whilst all other parameters were fixed. Both the design of experiments plan and the settings of the fixed parameters were defined identically. The in-flight particle properties and coating characteristics are statistically modeled as a function of the process parameters and their influences are compared. A well-selected, limited number of experimental runs using statistical design of experiment (DoE) enable this comparison. The deployed statistical models are generalized linear models with Gamma-distributed responses. The models show that particle velocity and particle temperature mainly depend on kerosene flow rate and spray distance. However, in the case of particle temperature, the model coefficients for Cr3C2-NiCr and WC powders have different signs, reflecting different qualitative behavior.