Effect of WC morphology on dry sliding wear behavior of cold-sprayed Ni-WC composite coatings

Abstract

Cold spray is a relatively new method used to deposit WC reinforced composite coatings, where its low temperature is advantageous for avoiding oxidation and carbide decomposition.Previous studies demonstrated that using agglomerated WC resulted in higher WC retention within the Ni matrix, as compared to that of cast WC. However, the influence of the morphology of the starting powders on the coating's microstructure, properties, and wear performance is not well understood. Here we report cold spray deposition of Ni with two types of WC particles, i.e. cast and agglomerated. In both cases, ~30vol.% WC was retained in coatings, allowing for a side-byside comparison. Coatings with cast WC featured a multi-modal distribution of WC particles ranging from 0.2 to 20 µm with a mean free path (MFP) between particles of 8.5 ± 0.7 µm. In comparison, coatings with agglomerated WC had WC size range of 0.3 to 1.3 µm and a MFP of 31 ± 4 µm. The sliding wear behavior of coatings was studied with a sliding speed of 3 mm/s under normal loads of 5 and 12 N. Coatings with cast WC were found to be more wear resistant than coatings with agglomerated WC. The multi-modal size distribution of cast WC with significantly lower MFP minimized adhesive wear and helped to develop a higher coverage of protective mechanically mixed layers (MMLs) that typically formed near WC particles. For coatings with cast WC, subsurface microstructure and chemical analysis suggested higher oxidation for MMLs with lower depths of deformation zones extended beneath MMLs compared to coatings with agglomerated powder. The two main factors for improved wear resistance of cast WC coatings compared to agglomerated WC coatings were the stability of the MMLs, and the wider size distribution and lower MFP, which offered better load supporting properties.

Effects of WC Particle Types on the Microstructures and Properties of WC-Reinforced Ni60 Composite Coatings Produced by Laser Cladding

“…However, owing to the obvious interface, and to factors including the large performance difference between the Ni-based alloy and the WC hard phase, the phenomenon of WC particles falling off, melting, burning, and sinking easily occurs during laser cladding. The WC particles deposited at the bottom of the cladding coating are not conducive to the wear resistance of the cladding coating surface, and instead they can also cause abrupt changes in the properties of the matrix that are related to the cladding coating, which easily lead to cracks and fatigue damage, and these are some of the biggest obstacles to their engineering applications [10,11].…”

Microstructure and Mechanical Properties of Ni-WC Thermal Sprayed Composite Coatings

“…These effects increase the wear resistance of the material: the presence and the rate of fracture of MML have a greater impact onto it than the bulk properties of the coating material. The wear behaviour of CCs depends on the carbides amount, their size and distribution, as it was evidenced for cold sprayed and flame sprayed Ni base -WC CCs [11,13,15]. Nickel alloys with cast WC particles are more wear resistant than agglomerated ones due to their multimodal size distribution and lower so called mean free path between particles [11].…”

“…The wear behaviour of CCs depends on the carbides amount, their size and distribution, as it was evidenced for cold sprayed and flame sprayed Ni base -WC CCs [11,13,15]. Nickel alloys with cast WC particles are more wear resistant than agglomerated ones due to their multimodal size distribution and lower so called mean free path between particles [11]. CCs designed for the service at elevated temperatures are based mainly on Ni-Cr-B-Si matrix [6,[16][17][18].…”

“…The matrix materials of sprayed coatings are generally based on iron, nickel or cobalt. The presence of hard carbide particles in the matrix results in faster appearance of mechanically mixed layers (MML), containing in-situ formed complexive oxides in dry sliding wear conditions with further stabilization of these MMLs [6,[11][12][13][14]. These effects increase the wear resistance of the material: the presence and the rate of fracture of MML have a greater impact onto it than the bulk properties of the coating material.…”

Cold Sprayed Tungsten Armor for Tokamak First Wall

“…Even then, the studies employing such concept are limited in the literature and involve successful depositions of W-Cu by Kang and Kang [10] and Deng et al [11], W-Ni-Fe by Xia et al [12], and low tungsten content in W-90Ta coatings by Barnett et al [13] only. Considering their excellent wear properties, a significantly broader series of studies involved the research of cemented carbides in a form of WC-Co [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], WC-Ni [32][33][34][35][36][37][38][39][40][41], WC-Co-Ni [42], WC-Co-Cr [31,[43][44][45], or WC-Cu-MoS 2 [46,47]. Unfortunately, the carbides could not be used for PFCs and so we could not built on these results.…”