Zhuojin Pipe Fitting Co., LtdPlasma Arc Surfacing Nickel-Based Spherical Tungsten Carbide Composite Coatings Friction and Wear Study
Literature Overview
This paper, published in Surface Technology (2018, Vol. 47, No. 2, pp. 103-110), investigates the tribological performance of plasma transferred arc (PTA) surfacing nickel-based composite coatings reinforced with spherical tungsten carbide (WC) particles. The study was conducted by researchers from CNOOC Energy Development Equipment Technology Co., Ltd. and Shanghai Maritime University, funded under the Marine Public Welfare Industry Scientific Research Special Fund Project (No. 201405013-3). The work addresses a critical need in marine and offshore engineering where severe abrasive and adhesive wear conditions demand advanced surface protection strategies.
Core Technical Approach and Methodology
The experimental design employs a systematic variation of WC content in the nickel-based matrix powder, with mass fractions of 20%, 30%, 50%, and 60% tested. The PTA process parameters were carefully controlled to ensure adequate dilution management and bonding quality between the base metal and the deposited overlay. Characterization methods include surface morphology examination, coefficient of friction measurement, groove cross-sectional area analysis, and microstructural observation of wear tracks.
| Parameter | Tested Values | Purpose |
|---|---|---|
| WC mass fraction | 20%, 30%, 50%, 60% | Evaluate reinforcement effect |
| Base powder | Nickel-based alloy | Matrix binder |
| Deposition method | PTA | Low dilution, good bonding |
| Test equipment | Bruker universal tribometer | Standardized wear testing |
| Wear track location | Coating side surface | Representative wear condition |
Key Findings and Technical Interpretation
The primary conclusion is that wear resistance increases monotonically with increasing WC content, and the near-heat-affected-zone (HAZ) base metal also benefits from the thermal cycling effect of multi-pass deposition. The wear mechanism transitions at a critical WC content threshold:
| WC Content | Dominant Wear Mechanisms | Microstructural Feature |
|---|---|---|
| < 50% | Adhesive wear + Oxidative wear | Matrix-dominated, WC particles act as secondary hard phases |
| > 50% | Adhesive wear + Abrasive wear | WC-rich microstructure, particle-particle contact and fracture |
The transition from oxidative to abrasive wear dominance at 50% WC is technically significant because it indicates a shift in the load-bearing mechanism of the coating. Below 50%, the nickel matrix accommodates deformation and oxidation, while above this threshold, the hard WC phase network directly resists material removal through its high hardness and fracture toughness.
Engineering Practice Implications
The recommendation of 50% WC as the optimal composition for practical applications reflects a balanced engineering judgment between performance and cost. In offshore drilling equipment, subsea connectors, and marine structural components, this composition provides sufficient wear resistance while maintaining manageable deposition costs and acceptable welding processability. The spherical morphology of WC particles is particularly advantageous over irregular shapes because it promotes uniform distribution and reduces stress concentration at particle-matrix interfaces.
From a metallurgical perspective, the PTA process is preferred over conventional arc surfacing because it offers lower dilution rates (typically 5-15% versus 30-50% for SMAW), preserving the integrity of the composite coating microstructure. The spherical WC particles also reduce porosity formation during deposition because their uniform shape allows better packing and reduces gas entrapment.
Critical Reflection and Technical Insights
One noteworthy observation is that the improvement in HAZ base metal wear resistance suggests a secondary benefit of the surfacing process: the thermal input from multi-pass PTA deposition may induce a beneficial tempering or refinement effect in the near-surface base metal. This phenomenon warrants further investigation because it implies that PTA surfacing may not only protect the surface but also enhance the subsurface material properties through controlled thermal cycling.
The selection of 50% WC as optimal should be validated against specific service conditions. In highly abrasive environments such as sand-laden slurry pipelines or subsea wellhead components, higher WC content (60%) might be justified despite the increased cost. Conversely, in environments where thermal cycling and corrosion resistance are equally important, lower WC content with better ductility might be preferable.
Summary
This study provides valuable guidance for selecting WC content in nickel-based PTA composite coatings for wear-critical marine applications. The identification of the 50% WC threshold as both a wear mechanism transition point and a cost-performance optimum represents a practically useful engineering criterion. The findings support the development of standardized PTA surfacing procedures for offshore equipment protection, particularly for components exposed to severe sliding and abrasive wear conditions in marine environments.