Microstructure and Tribological Performance of WC-Reinforced Iron-Based Composite Plasma Cladding Layer

Literature Overview and Research Background

The application of tungsten carbide (WC) particles as reinforcement in iron-based matrix composite cladding layers represents a promising approach to achieving superior wear resistance in components subjected to severe abrasive and erosive conditions. Plasma transferred arc (PTA) cladding is a well-established process for depositing thick, dense, and metallurgically bonded overlay layers with minimal dilution. The study investigates the microstructure evolution and tribological behavior of spherical WC particle-reinforced iron-based composite cladding layers deposited by PTA, with particular attention to the interaction between the WC reinforcement and the iron-based matrix, the formation of interfacial phases, and the resulting wear mechanisms under dry sliding conditions.

Core Technical Points on Microstructural Characteristics

The PTA cladding process deposits the composite layer with a typical powder feed rate of 200–400 g/min, arc current of 300–450 A, and travel speed of 300–600 mm/min. The spherical WC particles, typically in the size range of 15–45 µm, are fed as a blend with the iron-based matrix powder (containing Fe, Cr, Mo, and binder phases). The resulting cladding layer exhibits a microstructure consisting of retained austenite, martensite, carbides (Cr₇C₃, Mo₂C, Fe₃C), and the WC reinforcement particles embedded within the matrix.

A critical finding of the study is that the PTA thermal cycle causes partial transformation of WC to W₂C at the particle-matrix interface due to the high local temperatures exceeding the WC decomposition temperature of approximately 1500 °C. The extent of this transformation depends on the arc power density and travel speed; higher power density with slower travel leads to greater WC decomposition and reduced effective reinforcement content. The study recommends using a travel speed of at least 400 mm/min with an arc current of 350–400 A to maintain WC integrity while achieving adequate melting and bonding.

Tribological Performance Analysis

The wear behavior is evaluated through pin-on-disk dry sliding tests at loads of 5 N, 10 N, and 20 N with a sliding distance of 1000 m against a Si₃N₄ counterface. The wear rate of the WC-reinforced composite cladding layer is significantly lower than that of the un-reinforced iron-based matrix under all test conditions, with a reduction of 60–80 % at 10 N load. The wear mechanism transitions from abrasive wear at low loads to a combination of abrasive and adhesive wear at higher loads.

The excellent wear resistance is attributed to the synergistic effect of hard WC particles providing primary abrasion resistance, the tough austenitic-martensitic matrix accommodating plastic deformation, and the secondary carbide network distributing stress. The retained austenite contributes to strain-induced transformation hardening during sliding, which helps to maintain surface integrity over extended wear cycles.

Process Optimization and Defect Prevention

The PTA cladding process for WC-reinforced composites requires careful control of several parameters to avoid defects that compromise tribological performance. Key process considerations include:

1. Powder blend homogeneity: The WC particles must be uniformly distributed in the powder feed to avoid localized regions of high or low reinforcement concentration, which can cause uneven wear and stress concentration.
2. Arc stability: Pulsed plasma mode is preferred over continuous mode to reduce thermal input and minimize WC decomposition. A pulse frequency of 50–100 Hz with a duty cycle of 60–70 % provides optimal thermal management.
3. Layer thickness control: Each pass should deposit a thickness of 0.5–1.0 mm to maintain adequate cooling between passes and prevent excessive heat accumulation.
4. Interpass temperature: Must be maintained below 150 °C to prevent softening of previously deposited layers and to avoid additional WC decomposition.
5. Shielding gas: Argon is the preferred shielding gas at a flow rate of 15–25 L/min to prevent oxidation of the molten pool and to protect the WC particles from forming WO₃ during the melting process.

Common defects include porosity caused by hydrogen absorption from contaminated powder, cracking in the matrix due to high carbon equivalent and rapid cooling, and incomplete bonding at the interface due to insufficient heat input. The FMEA analysis identifies porosity as the highest-risk defect with a severity rating of 8, occurrence of 5, and detection difficulty of 6, yielding a risk priority number of 240. Mitigation measures include powder drying at 200 °C for 2 hours prior to use and ensuring clean gas supply with dew point below -40 °C.

Engineering Applications and Practice Integration

The WC-reinforced iron-based PTA cladding is particularly suitable for components in mining, cement, and power generation industries where severe abrasion is the dominant failure mode. Applications include pump impellers, valve seats, crusher liners, and wear plates in material handling systems. The study's findings directly inform the specification of cladding parameters for production-scale components, where the balance between wear resistance and toughness must be optimized based on the specific service conditions. For components subjected to impact loading in addition to abrasion, a higher retained austenite content (achieved by lower cooling rates) is preferred to provide additional toughness, whereas for pure abrasion service, a higher martensite fraction with maximum WC retention provides the best wear resistance.

Summary

The study demonstrates that spherical WC particle-reinforced iron-based PTA cladding layers offer a compelling combination of high hardness, excellent wear resistance, and adequate toughness for demanding tribological applications. The key to achieving optimal performance lies in controlling the PTA process parameters to minimize WC decomposition while maintaining metallurgical bonding and microstructural homogeneity. Engineers selecting this technology for production applications should specify the powder blend composition, particle size distribution, and PTA parameters as tightly controlled quality characteristics, with regular verification through metallographic examination and tribological testing to ensure consistent performance throughout the production run.