Microstructure Evolution and Tribological Performance of WC-Reinforced Nickel-Based Cladding Layers under Different Preheating Temperatures

Literature Overview

This paper by Zhang Chunlin and colleagues from Liaoning University of Science and Technology, published in Surface Technology (2024, Vol. 53, No. 9, pp. 127-136), addresses a critical yet underexplored variable in plasma arc cladding of hardmetal-reinforced nickel-based alloys: the role of substrate preheating temperature. The study investigates how preheating at 200°C versus 400°C influences the microstructural evolution, mechanical properties, and wear resistance of WC particle-reinforced nickel-based alloy cladding layers deposited on 42CrMo steel substrates. The research is supported by the National Key R&D Program (2021YFB3702003), reflecting its significance in advanced surface engineering for demanding industrial applications.

Core Technical Findings

The authors systematically established a strong mapping relationship between process parameters, microstructure, mechanical properties, and tribological performance. The cladding layers were characterized using XRD, SEM, microhardness testing, and pin-on-disk wear testing. The following key results were obtained:

Phase Composition and Microstructural Features

The cladding layers were found to consist of multiple phases including γ-Ni/Fe solid solution, intact WC particles, W₂C, M₇C₃, M₂₃C₆, Ni₂W₄C, and Cr₃C₂. The critical difference between the two preheating conditions lies in the extent of secondary carbide precipitation and WC particle distribution:

Mechanism Interpretation

At 200°C preheating, the relatively low thermal energy available during solidification results in insufficient interfacial reaction between WC particles and the molten pool. This leads to two detrimental effects: first, limited dissolution and subsequent precipitation of secondary carbides (W₂C, M₇C₃, Ni₂W₄C) that would otherwise strengthen the matrix; second, severe gravitational sedimentation of unreacted WC particles toward the bottom of the weld pool, creating a heterogeneous distribution with particle-rich zones at the fusion line and particle-depleted zones near the surface.

At 400°C preheating, the elevated thermal input promotes extensive interfacial chemical reactions between WC and the Ni/Fe melt. The higher temperature facilitates the decomposition of WC into W and C, followed by the formation of multiple secondary carbide phases. This mechanism effectively "consumes" the excess WC particles that would otherwise sediment, distributing their strengthening contribution throughout the entire cladding cross-section rather than concentrating it at the bottom. The result is a more uniform microstructure with enhanced hardness and significantly improved wear resistance.

Process-Structure-Property Relationship Analysis

The study demonstrates that preheating temperature is not merely a thermal management parameter to prevent cracking, but a fundamental microstructural control variable. The engineering implication is profound: for WC-reinforced nickel-based cladding systems, preheating above 400°C should be considered standard practice rather than optional. However, this recommendation must be balanced against the risk of excessive dilution, substrate softening, and residual stress accumulation in thick-section components.

Practical Considerations for 42CrMo Substrate

42CrMo is a medium-carbon alloy steel with moderate hardenability. Preheating at 400°C reduces the cooling rate during cladding, which decreases the hardness gradient at the fusion zone. This is generally beneficial for preventing cold cracking but may slightly reduce the hardness of the heat-affected zone. In engineering practice, a post-cladding tempering treatment at 550-600°C is recommended to equilibrate the hardness profile and relieve residual stresses.

Engineering Practice Integration

From a quality control perspective, the following recommendations emerge:

• Preheating should be verified using calibrated infrared pyrometers or contact thermocouples at multiple points across the substrate surface, with temperature uniformity maintained within ±20°C.
• Interpass temperature monitoring is essential; maintaining interpass temperatures above 350°C prevents localized cooling that would negate the benefits of initial preheating.
• Microstructural verification through metallographic examination of cross-sections is recommended for production qualification, with particular attention to WC particle distribution uniformity and secondary carbide morphology.
• Wear testing should be conducted under conditions representative of the intended service environment, as the tribological response of WC-reinforced cladding layers is highly dependent on the counterface material and lubrication regime.

Study Insights and Reflections

This work contributes significantly to the understanding of thermal management in hardmetal-reinforced cladding systems. The finding that approximately 52% improvement in wear resistance can be achieved simply by increasing preheating from 200°C to 400°C is practically remarkable. It suggests that many existing industrial cladding processes may be underperforming due to conservative preheating practices. However, I note that the study does not address preheating temperatures above 400°C, and there may be an optimal window beyond which substrate degradation becomes unacceptable. Future work should explore a wider temperature range and include long-term thermal cycling tests to assess the stability of the secondary carbide phases under service conditions.

The methodology of establishing a complete process-microstructure-property mapping is exemplary and should be adopted as a standard approach in surface engineering research. The practical value of this work extends to any application requiring hardfacing of alloy steels with WC-based consumables, including oil and gas equipment, mining machinery, and power generation components.