Novel suspension route to incorporate graphene nano-platelets in HVAF-sprayed Cr3C2–NiCr coatings for superior wear performance

Satyapal Mahade,Uta Klement,Stefan Björklund,Shrikant Joshi,Antonio Mulone

doi:10.1016/j.jmrt.2021.04.096

Satyapal Mahade, Uta Klement + Show 3 more

Open Access

https://doi.org/10.1016/j.jmrt.2021.04.096

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Abstract

Graphene nano platelets (GNP) have several attractive properties, including excellent lubricity that can be used to develop wear-resistant coatings. Thermally sprayed chromium carbideenickel chromium (Cr3C2eNiCr) coatings are widely employed to impart wear resistance to engineering components. This work attempts to improve the wear resistance of high velocity air fuel (HVAF) sprayed Cr3C2eNiCr coatings by incorporating GNP using a hybrid approach in which Cr3C2eNiCr (powder) and GNP (suspension) are co-axially injected. Two different powder-to-suspension delivery ratios were employed in this study that utilizes a liquid feedstock in tandem with a HVAF system. Furthermore, for comparison, a pure (without graphene) Cr3C2eNiCr reference coating was deposited by the HVAF process using identical spray parameters. The as-sprayed coatings were characterized for their microstructure and phase constitution by SEM/EDS and X-Ray Diffraction. Mechanical properties such as hardness and fracture toughness were evaluated using micro-indentation technique. The hybrid coatings were subjected to dry sliding wear tests and wear performance was compared with reference Cr3C2eNiCr. The GNP incorporated hybrid coatings exhibited lower CoF and lower wear rates than the reference Cr3C2eNiCr coating. Post wear SEM/EDS analysis revealed different wear mechanisms predominant in the investigated coatings. Utilizing the above as a case study, this work provides key insights into a new approach to produce GNP incorporated coatings for mitigating wear.

Highlights

Wear contributes to inferior performance of engineering components and often results in economic losses due to premature component failure and unscheduled maintenance related halts
The motivation to opt for high velocity air fuel (HVAF) process was to utilize its capability to deposit coatings with minimal defects whereas Graphene nano platelets (GNP) were chosen as a reinforcement to exploit their excellent mechanical properties for imparting wear resistance
GNP were devoid of agglomeration, which is desirable to exploit the merits of GNP in the form of a reinforcement as agglomeration could lead to uneven distribution of GNP in the microstructure

Summary

Introduction

Wear contributes to inferior performance of engineering components and often results in economic losses due to premature component failure and unscheduled maintenance related halts. Among the existing thermal spray processes, atmospheric plasma spray (APS) is used to deposit ceramics such as alumina, chromia based coatings to improve wear resistance [11e13] whereas, high velocity oxy fuel (HVOF) and high velocity air fuel (HVAF) are used to deposit metallic and cermet coatings such as WC-CoCr, Cr3C2eNiCr etc. Murray et al employed suspension-HVOF (SHVOF) process to deposit GNP incorporated alumina coatings and reported ultra-low coefficient of friction, which aided in improving the wear performance [27]. The motivation to opt for HVAF process was to utilize its capability to deposit coatings with minimal defects whereas GNP were chosen as a reinforcement to exploit their excellent mechanical properties for imparting wear resistance. Post wear analysis was performed using SEM/EDS and Profilometry analysis to evaluate and understand the wear performance and wear mechanisms of investigated coatings with and without incorporated GNP

Experimental method

Microstructural analysis

Mechanical properties determined using microindentation

Sliding wear test

Post- sliding wear test analysis

Conclusion