CLADDING TECHNOLOGY SHANXI CO., LTDWear Resistance of Ni60-Cr3C2-WC/TiC Composite Plasma Arc Cladding Layer
Literature Overview and Research Background
This study published in the Powder Metallurgy Industry journal in 2019 by researchers from the School of Mechanical Engineering at North University of China investigates the tribological performance of a composite plasma transferred arc (PTA) cladding layer. The base material is the well-known Stellite-type Ni60 alloy (UNS N06600 equivalent), which is reinforced with three distinct ceramic phases: chromium carbide (Cr3C2), tungsten carbide (WC), and titanium carbide (TiC). The research addresses a critical engineering challenge — how to enhance the already excellent wear resistance of Ni60 through strategic ceramic reinforcement while maintaining adequate metallurgical bonding with the substrate.
The motivation for this research is clear in industrial contexts where components face severe sliding wear, abrasion, and erosive-corrosive environments simultaneously. Conventional Ni60 cladding, while offering good corrosion resistance and moderate wear resistance, often falls short in high-abrasion scenarios such as mining equipment, cement mill liners, and slurry pump impellers. The incorporation of hard ceramic carbides is a well-established strategy, but the challenge lies in balancing hardness, toughness, and bond strength within a single overlay layer.
Core Technical Approach and Process Parameters
The plasma arc cladding process was employed for depositing the composite layer. PTA offers several advantages over other overlay methods for this application: precise thermal control, low dilution with the substrate, high deposition efficiency, and the ability to handle composite powders with varying melting points. The plasma arc provides a stable, high-temperature heat source that can melt both the metallic Ni60 matrix and the ceramic carbide particles without excessive substrate penetration.
| Parameter | Typical Range | Notes |
|---|---|---|
| Plasma current | 80–160 A | Higher current increases deposition rate but risks dilution |
| Arc voltage | 18–25 V | Controls arc length and heat input |
| Powder feed rate | 0.5–1.5 g/s | Must balance with arc power for complete melting |
| Travel speed | 100–300 mm/min | Affects layer thickness and dilution |
| Shielding gas | Argon | Inert atmosphere to prevent oxidation |
| Substrate preheat | 100–200°C | Reduces residual stress and cracking risk |
| Interpass temperature | <300°C | Prevents softening of previous pass |
The composite powder formulation typically involves blending Ni60 alloy powder with Cr3C2, WC, and TiC particles at specific weight percentages. The particle size distribution is critical — generally in the range of 15–45 micrometers — to ensure uniform feeding and complete melting in the plasma arc. Cr3C2 particles, with a melting point around 2180°C, tend to remain partially intact in the matrix, providing a hard phase while the WC and TiC particles, with even higher melting points (2870°C and 3140°C respectively), act as refractory reinforcement.
Microstructural Analysis and Phase Composition
The resulting cladding layer microstructure exhibits a dendritic cellular morphology characteristic of rapid solidification in PTA processing. The Ni60 matrix solidifies in a dendritic pattern, with the ceramic carbide particles distributed at dendrite boundaries and within the interdendritic regions. The Cr3C2 particles tend to dissolve partially during the plasma arc melting process, releasing chromium into the matrix and forming secondary carbide phases such as M7C3-type chromium carbides. This partial dissolution is actually beneficial as it creates a gradient in hardness and improves the metallurgical compatibility of the layer.
The WC particles are particularly interesting from a metallurgical perspective. During the high-temperature exposure in the PTA process, the carbon in WC can react with chromium in the Ni60 matrix to form chromium carbides, while the tungsten dissolves into the nickel matrix, forming tungsten-nickel solid solution. This reaction partially depletes the WC but creates a network of fine carbide phases that contribute to wear resistance. TiC, being extremely stable and refractory, remains largely intact throughout the process, providing discrete hard points that resist abrasive wear.
Wear Performance Evaluation
The wear resistance evaluation typically employs pin-on-disk or block-on-ring tribometer testing under dry sliding conditions. The results consistently show that the composite-reinforced Ni60 layer significantly outperforms the unreinforced Ni60 baseline. The hardness of the composite layer typically reaches HV 800–1000, compared to HV 400–500 for conventional Ni60 cladding. The wear rate reduction can be as high as 60–80% depending on the ceramic content and distribution.
The wear mechanism transitions from adhesive wear in pure Ni60 to a combination of abrasive and micro-ploughing mechanisms in the composite layer. The hard ceramic particles resist ploughing by abrasive asperities, and the matrix binds them effectively, preventing particle pullout. The Cr3C2 contributes to both hardness and some degree of corrosion resistance due to chromium enrichment at the particle-matrix interface.
Engineering Practice Implications and Process Considerations
From an engineering practice standpoint, several critical issues must be addressed when implementing this technology:
- Powder feed consistency: The composite powder blend must be thoroughly mixed to prevent segregation of ceramic particles, which can cause localized porosity or incomplete melting.
- Dilution control: The dilution rate with the substrate must be kept below 10% to maintain the intended alloy composition and wear properties. Excessive dilution reduces hardness and introduces unwanted carbon and iron into the overlay.
- Cracking susceptibility: The combination of high thermal mismatch and the presence of hard ceramic particles increases the risk of micro-cracking. Preheating and controlled interpass temperatures are essential.
- Surface finish: PTA layers typically exhibit a rough surface with visible track boundaries. Post-cladding machining is often required for functional applications.
Key Questions and Reflective Insights
The most significant question raised by this research is the optimal balance between ceramic content and mechanical integrity. Increasing the ceramic fraction improves hardness and wear resistance but simultaneously increases brittleness and reduces the layer's ability to accommodate thermal and mechanical stresses. In practical applications, a ceramic content of 15–25% by weight typically provides the best compromise, though this varies with the specific service conditions.
Another important consideration is the long-term stability of the ceramic phases under operating conditions. In high-temperature environments, the Cr3C2 may undergo further dissolution or reaction, potentially altering the wear characteristics over time. The WC may experience carbon depletion through carbide decomposition, while TiC remains the most thermally stable component. Understanding these time-dependent changes is crucial for predicting service life.
The research also highlights the importance of substrate preparation. Surface roughness, contamination, and residual stress in the base material all influence the quality of the plasma arc cladding layer. Proper surface treatment, including machining to remove scale and oxide, is a prerequisite for achieving full metallurgical bonding and optimal wear performance.
This work represents a valuable contribution to the field of composite overlay design, demonstrating that the strategic combination of multiple ceramic reinforcements with a nickel-based matrix can yield synergistic improvements in wear resistance. The findings are directly applicable to the design of wear-critical components in mining, cement, and power generation industries where PTA cladding is a cost-effective repair and protection strategy.