Investigation on Elevated Temperature Adhesive Wear Behavior of Microwave Fused Thermal Spray Tribaloy Composite Coatings

Abstract

Metallic materials that operate under high speed, high temperature and harsh chemical environments are prone to wear and corrosion degradation. This leads to the failure of metallic components and results in huge economic loss to industries. The amorphous alloy or metallic glasses exhibit superior properties like high hardness, good wear, and corrosion resistance. Metallic glasses eliminate an ordered crystalline structure, hinders plastic deformation. The Co-based amorphous alloy is the best example of bulk metallic glassy structure alloy and presence of primary intermetallic laves phase’s exhibits good mechanical as well as chemical properties. This is mostly employed as coatings because they are too brittle to be used in bulk form. Co-based metallic glass coating depositing on metallic materials could positively eliminate the failure of the working component caused by serious wear and erosion issues. In the present study, CoMoCrSi superalloy powder (Tribaloy-T400) comprising of a primary intermetallic laves phase of Co-rich solid solution has shown better mechanical and tribological properties. Processing of CoMoCrSi feedstock powder is carried out through a high-energy ball milling (HEBM) technique to obtain a higher volume fraction of intermetallic laves phases. The hard phases of 30% Cr3C2, WC-CrC-Ni and WC-12Co are reinforced into milled CoMoCrSi feedstock. The four different feedstock powders CoMoCrSi, CoMoCrSi+30%Cr3C2, CoMoCrSi+30%WC-CrC-Ni and CoMoCrSi+30%WC- 12Co are sprayed on pure titanium grade-15 substrate using High-Velocity-Oxy-Fuel (HVOF) and flame spray methods. The as-sprayed coatings are subjected to post heat treatment to refine their metallurgical and mechanical properties using microwave hybrid heating technique. Characterization of feedstock, as-sprayed and microwave fused coatings is done by using Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray Diffraction (XRD). Porosity, surface roughness, microhardness, and adhesion strength of as-sprayed and fused coatings are evaluated. The substrate, as-sprayed and microwave fused coatings are subjected to elevated temperature sliding wear test against alumina disc under dry conditions. The test is carried out at 200°C, 400°C, and 600°C temperatures for 10 N and 20 N normal loads. Microwave fused coatings exhibit higher wear resistance than the as-sprayed coatings and substrate. The hard intermetalliclaves phases which are amorphous (bulk metallic glass) in nature strengthen the coatings at high temperatures. Co3Mo2Si, Co7Mo6, Mo3Si, Co3Mo, and Co2Mo3 are the intermetallic laves phases generated in CoMoCrSi feedstock during HEBM process. The coatings produced from HVOF and flame spray process exhibits heterogeneous structure by showing cracks and pores, also cohesive strength between splats is low. The microhardness and adhesion strength of as-sprayed coatings is lower than fused coatings. Microwave fused coatings exhibit homogeneous structure with less porosity, and surface roughness. The posttreated coatings reveals the inter-diffusion of atoms near substrate-coating interface region, these results in formation of metallurgical bonding leads to increase in microhardness and adhesion strength. The as-sprayed coatings exhibits higher wear rate and coefficient of friction due to lower microhardness. The worn surface of as-sprayed coatings reveals detachment of splats with severe deformation results in adhesive wear mechanism. Microwave fused coatings exhibits lower wear rate and coefficient of friction due to higher microhardness obtained from intermetallic laves phases and also formation of homogeneous structure. The fused coatings exhibits tribo-oxide layers during sliding action which is the main phenomenon for improving the wear resistance of the fused composite coatings. CoMoCrSi+WC-12Co composite coating showed better mechanical and tribological properties compared to other types of coatings.