Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2–NiCr hardmetal coatings

Abstract

This paper provides a comprehensive characterisation of HVOF-and HVAF-sprayed Cr 3 C 2-25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr 3 C 2 than the feedstock powder, possibly due to the rebound of some Cr 3 C 2rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter-and intra-lamellar cohesion, being higher (Z 70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (E5x10 À 6 mm 3 /(Nm)). At 400°C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from E0.7 to E 0.5. The thermal expansion coefficient of the coatings (11.08x10 À 6°C À 1 in the 30-400°C range) is sufficiently close to that of the steel substrate (14.23x 10 À 6°C À 1) to avoid macro-cracking.

Microstructure, Mechanical Properties and Wear Behavior of High-Velocity Oxygen-Fuel (HVOF) Sprayed (Cr3C2-NiCr+Al) Composite Coating on Ductile Cast Iron

“…Mechanisms responsible for the degradation of the coating under erosive wear can be divided into two types: plastic and brittle. Elements such as cutting and craters surrounded by lips indicate the plastic nature of wear, while cracks and chipping indicate the fragile nature of wear [19][20][21]. Based on the above results, it can be suggested and emphasized, that on the interface of coating/substrate there were found no defects that could reduce wear resistance or that could cause poor adhesion of the coating to the substrate.…”

Nanocrystalline Cermet Coatings for Erosion–Corrosion Protection

“…In the case of nanocrystalline grain size, more than 50% of atoms are associated with grain boundaries due to small grain size resulting in more contribution towards physical properties of material [25]. Nanocrystalline coatings can be deposited using several techniques, yet thermal spraying has been reported by several researchers as one of the best techniques available [46][47][48][49][50][51][52][53][54][55]. Thermal spraying with nanostructured feedstock powders has resulted in higher hardness, strength, and corrosion resistance compared to conventional powders.…”

“…Mechanical and wear behavior of the reported coatings are summarized in Table 1. In Cr 3 C 2 -NiCr and WC-based coatings using the HVOF thermal spray technique, low porosity of cermet coatings can be achieved due to fast deposition rates, which results in good wear resistance, oxidation resistance, and adhesion properties [8,17,21,22,41,47,[80][81][82][83][84][85][86]. Note: HVOF-high-velocity oxy-fuel; HVAF-high-velocity air-fuel; CAPS-controlled atmospheric plasma spray; APS-atmospheric plasma spray.…”

“…WC-based coatings exhibited high hardness and wear resistance as compared to Cr 3 C 2 -NiCr coatings due to the presence of hard WC particles embedded in the matrix or binder phase. Although WC-based coatings are harder and more wear resistant than Cr 3 C 2 -based coatings, their operating temperature is limited to less than 450 • C; however, Cr 3 C 2 -based coatings are utilized in corrosive and moderate wear environment at the temperature up to 850 • C. During abrasion, the formation of the tribo oxide film with low shear strength, which became stable and resistant against delamination up to 850 • C was responsible for the reduction in friction coefficient of Cr 3 C 2 -NiCr coating and also their greater fracture toughness reduces cracking during surface grinding and tribocorrosion tests [41,47,82,83,87,89,92]. The volume fraction of Cr 3 C 2 /Ni-Cr matrix has an influence on the surface roughness of the coating and when its volume fraction increases from 0.24 to 2.14, average roughness value is reported to increase by~42% [88].…”

“…Meanwhile, the fine feedstock powder provides slightly more wear-resistant coatings than the coarse one, due to a stronger matrix-carbide cohesion inside the lamellae after spraying. Although the numerous carbide grains are responsible for sliding wear, the amount of defects in the carbide grains and their cohesion to the matrix controls the sliding wear, too [47].…”