Microstructure Evolution and Tribological Properties of WC-Reinforced Nickel-Based Alloy Cladding Layer at Different Preheating Temperatures

Literature Overview

This 2024 study by Zhang Chunlin and colleagues from Liaoning University of Science and Technology, supported by the National Key R&D Program of China (2021YFB3702003), examines the microstructure evolution and tribological performance of a tungsten carbide (WC)-reinforced nickel-based alloy cladding layer deposited at various preheating temperatures. The research addresses a critical gap in understanding how preheat temperature influences the thermal stability of WC particles during the cladding process, which directly determines the wear resistance of the final overlay. The study was published in Surface Technology and represents a current and highly relevant investigation into advanced surface engineering for severe wear applications.

Core Technical Findings

The study systematically varied the preheating temperature of the substrate from 100°C to 500°C in increments of 100°C, while maintaining consistent welding parameters for each condition. The cladding alloy was a nickel-based matrix reinforced with 15–20 wt% WC particles, a composition commonly used in applications requiring high wear resistance and corrosion resistance, such as mining equipment, chemical processing components, and aerospace structural parts.

Microstructure Evolution with Preheat Temperature

The most critical finding is the progressive decomposition of WC particles as preheat temperature increases. At temperatures below 300°C, the WC particles remain largely intact, providing excellent wear resistance through the formation of hard carbide phases. However, above 300°C, the WC particles begin to decompose into W₂C and free carbon, and at 500°C, the decomposition becomes nearly complete, significantly reducing the hardness and wear resistance of the overlay.

Tribological Performance

The tribological tests were conducted using a pin-on-disk apparatus under dry sliding conditions against a Si₃N₄ counterface. The results clearly demonstrated the direct relationship between WC retention and wear resistance:

• At 100°C preheat, the wear rate was approximately 8.5 × 10⁻⁷ mm³/(N·m), with the dominant wear mechanism being micro-ploughing of the matrix around intact WC particles.
• At 300°C preheat, the wear rate increased to approximately 1.8 × 10⁻⁶ mm³/(N·m), with adhesive wear becoming more prominent due to the reduced WC particle density.
• At 500°C preheat, the wear rate reached approximately 3.2 × 10⁻⁶ mm³/(N·m), with severe adhesive and abrasive wear mechanisms dominating.

Process Analysis and Optimization

Preheat Temperature Selection Criteria

The selection of preheat temperature involves a fundamental trade-off between crack resistance and WC retention. Higher preheat temperatures reduce the cooling rate and minimize the risk of cracking in the nickel-based matrix, particularly in thick deposits or on high-carbon substrates. However, excessively high preheat temperatures promote the decomposition of WC particles, which undermines the primary purpose of the reinforcement.

Based on the study results, an optimal preheat temperature window of 200–300°C is recommended for WC-reinforced nickel-based alloy cladding. Within this range:

1. The cooling rate is sufficiently reduced to prevent cracking in the nickel-based matrix.
2. The WC particle retention remains above 60%, maintaining acceptable hardness levels above 700 HV30.
3. The residual stress in the overlay is within acceptable limits for most engineering applications.

Welding Parameter Interactions

The study also examined the interaction between preheat temperature and other welding parameters:

• Heat input: Lower heat input (achieved through reduced current or increased travel speed) helps preserve WC particles but must be balanced against the risk of incomplete melting and poor bond strength.
• Powder feed rate: A higher feed rate increases the dilution rate and may dilute the WC particles more uniformly, but excessive feed rates can lead to porosity and incomplete melting.
• Arc voltage: Higher arc voltage increases the arc length and may lead to greater spatter and reduced deposition efficiency, which can indirectly affect the thermal cycle experienced by the WC particles.

Engineering Practice Implications

For engineers designing cladding processes for WC-reinforced nickel-based alloys, the following practical guidelines emerge:

• Preheat the substrate to 200–300°C, avoiding temperatures above 350°C to minimize WC decomposition.
• Use low to moderate heat input to reduce the thermal exposure of WC particles while maintaining adequate melting of the base metal.
• Perform metallographic examination of the overlay to verify WC particle retention; a minimum retention rate of 60% should be targeted.
• Conduct microhardness profiling across the overlay thickness to ensure uniform hardness distribution; a hardness variation of more than 100 HV30 across the overlay thickness indicates non-uniform WC distribution.
• Perform tribological testing on representative samples before production to validate that the wear rate meets the design requirements for the specific application.

Key Questions and Reflections

The study raises several important questions for future research and engineering practice. First, the long-term stability of the WC particles under thermal cycling conditions (such as those experienced in chemical processing or energy applications) requires further investigation. Second, the effect of post-weld heat treatment on WC particle retention and overall overlay performance should be systematically studied, as PWHT is commonly employed to relieve residual stresses but may further promote WC decomposition. Third, the development of alternative carbide reinforcements, such as TaC or NbC, which may exhibit greater thermal stability at elevated temperatures, warrants exploration.

Study Insights and Implications

The work by Zhang et al. provides critical data for the rational design of cladding processes involving WC-reinforced nickel-based alloys. The systematic investigation of preheat temperature effects fills an important gap in the literature and provides engineers with quantitative guidance for process optimization. The clear correlation between WC particle retention, microstructure, and tribological performance establishes a robust framework for quality control and process development. For industries relying on hardfacing for severe wear protection, this study underscores the importance of thermal cycle management as a primary factor in achieving the desired surface properties. The findings also highlight the need for application-specific process development, as the optimal preheat temperature may vary depending on the substrate material, overlay thickness, and service conditions.