Slurry and Dry Erosion of High Velocity Oxy-Fuel Thermal Sprayed Coatings

Abstract

Abstract Improvement of the high velocity oxy-fuel deposition (HVOF) process in the last decade has led to coatings with significant improved microstructures for better protection against wear and corrosion. HVOF coatings of cermet and metallic materials provide protection against erosion and are therefore good alternatives to the use of high-priced material. This paper presents the results of a study undertaken within the core research program of the National Research Council of Canada technology group in surface engineering, "SURFTEC", in which the performance of ten HVOF erosion-resistant coatings were evaluated under both dry and slurry erosion. Ten different types of HVOF coatings were studied including: six grades of WC with either Co or a Ni based matrix, one grade of Cr3C2 in a Ni-Cr matrix, and three grades of metallic alloy: Ni alloy, Co alloy and a SS 316-L. Coatings performance was evaluated with respect to the volume ratio and composition of metallic binder in carbide coatings, type of carbide, coating microstructure, impinging angle and the size of the erodent particles. All coatings were produced using the HVOF IP5000 system controlled by the Hawcs-II controller. Slurry jet erosion tests were conducted using a 10 %w/w alumina particle/water slurry. Two alumina particle sizes, 320 and 80 grit (nominal grain diameters 35 μm and 200 μm, respectively) were used. The nominal impact velocity of the slurry was 15 m/s and the nozzle-specimen distance 100 mm. Dry erosion tests were conducted using 50 μm diameter alumina particles projected onto coated flat test coupons through a carbide nozzle of diameter 1.14mm with a particle velocity of 84 m/s at a feed rate of 2 ±1 g/min. let impingement angles of 90° and 20° were used for both dry and slurry erosion tests. The volume loss of material under various erosion conditions was related to the coating properties and microstructure. Results indicate that the coating behavior is dependent on the erodent particle size, the erosion impinging angle to some extent and for slurry erosion, to the corrosion resistance of the cermet matrix.