Wear Resistance of Ni60-Cr3C2-WC/TiC Plasma Surfacing Layers on Cutting Picks

Literature Overview

This paper, published in Powder Metallurgy Industry (2019, Vol. 29, No. 6) by Wang Guang and colleagues from North University of China, investigates the wear resistance of plasma surfacing layers composed of Ni60 matrix reinforced with Cr3C2, WC, and TiC hard particles. The study focuses on the application of these composite surfacing layers on cutting picks (cutter teeth), which are critical components in mining and drilling operations subjected to severe abrasive wear. The research demonstrates that the optimized composite surfacing layer achieves a microhardness of 713.8 HV and the longest complete wear time of 180 minutes, significantly outperforming conventional surfacing materials.

Technical Background and Material Design

Cutting picks experience extreme wear conditions in mining and drilling applications, where they are subjected to high contact stresses, abrasive particles, and cyclic loading. The wear resistance of the pick surface is a critical factor in determining service life and operational efficiency. Conventional surfacing materials such as plain Ni60 (a nickel-based austenitic alloy) provide moderate wear resistance but are insufficient for the most severe abrasive conditions.

The composite surfacing approach combines a Ni60 binder matrix with hard ceramic particles to achieve a synergistic improvement in wear resistance. The Ni60 matrix provides ductility and toughness, while the hard particles provide hardness and abrasion resistance. The selection of Cr3C2, WC, and TiC as reinforcement particles is based on their complementary properties:

The design of the composite surfacing layer requires careful consideration of the particle size, distribution, and volume fraction to optimize the balance between hardness and toughness. Excessive hard particle content can lead to brittleness and cracking, while insufficient particle content limits the wear resistance improvement.

Microstructural Analysis

The microstructural examination of the plasma surfacing layers reveals a complex multi-phase microstructure consisting of the Ni-Cr-Fe austenitic matrix, boride hard phases, and carbide hard phases. The austenitic matrix provides the ductile binder that holds the hard particles together, while the borides and carbides provide the wear-resistant hard phases.

The plasma surfacing process involves the melting of the base material and the surfacing powder by an electric arc, with the molten pool being rapidly cooled to form a metallurgically bonded coating. The rapid solidification rate in plasma surfacing promotes the formation of fine microstructures and can enhance the hardness of the resulting coating.

The interaction between the matrix and the hard particles is critical for the overall wear resistance of the composite layer. The hard particles must be well-bonded to the matrix to prevent particle pullout during wear, and the matrix must be sufficiently ductile to accommodate the stress concentrations around the particles.

Wear Performance Results

The wear testing demonstrates that the optimized composite surfacing layer (Sample 3) achieves the highest microhardness of 713.8 HV and the longest complete wear time of 180 minutes. This represents a significant improvement over conventional Ni60 surfacing layers, which typically exhibit hardness values of 200-300 HV and much shorter wear lives.

The superior performance of Sample 3 is attributed to the synergistic effect of multiple hard particle types. The combination of Cr3C2, WC, and TiC provides a broad spectrum of hard phases with different hardness levels and wear mechanisms, resulting in a more effective resistance to abrasive wear. The Ni60 matrix ensures adequate toughness to prevent cracking and spalling of the hard particles.

Engineering Practice and Application Considerations

The application of composite plasma surfacing layers on cutting picks requires careful consideration of several factors. The plasma surfacing process parameters, including current, voltage, travel speed, and powder feed rate, must be optimized to achieve proper melting and bonding of the composite powder. The preheating of the base material is essential to prevent cold cracking and ensure adequate fusion.

The surface preparation of the base material is critical for achieving a strong metallurgical bond between the surfacing layer and the substrate. Adequate cleaning, degreasing, and mechanical preparation are required to remove any contaminants that could compromise the bond strength. The transition zone between the surfacing layer and the base metal should be examined for any cracks, porosity, or lack of fusion defects.

For mining and drilling applications, the surfacing layer thickness must be sufficient to provide adequate wear life while not adding excessive weight to the cutting pick. The typical surfacing thickness for cutting pick applications ranges from 3 to 8 mm, depending on the specific service conditions and the expected wear rate.

Key Questions and Reflections

While the study demonstrates significant improvements in wear resistance, several aspects warrant further investigation. The effect of particle size and distribution on the wear performance of the composite surfacing layer should be systematically studied. The long-term behavior of the surfacing layer under cyclic loading and thermal cycling conditions, which are common in mining applications, should be evaluated. Additionally, the cost-effectiveness of the composite surfacing approach compared to alternative wear-resistant materials and surface treatments should be assessed.

The interaction between different hard particle types in the composite layer is a complex phenomenon that affects both the microstructure and the wear behavior. Understanding the mechanisms of wear resistance in multi-particle composite systems could lead to further optimization of the surfacing layer design and performance.

Summary and Conclusions

This study demonstrates the significant potential of Ni60-Cr3C2-WC/TiC composite plasma surfacing layers for improving the wear resistance of cutting picks in mining and drilling applications. The optimized composite layer achieves a microhardness of 713.8 HV and a complete wear time of 180 minutes, representing a substantial improvement over conventional surfacing materials. The synergistic combination of multiple hard particle types in a ductile Ni60 matrix provides an effective balance between hardness and toughness. The plasma surfacing process offers a practical and cost-effective method for applying these composite layers to cutting pick components. The research contributes to the development of advanced wear-resistant surface technologies for critical mining equipment and demonstrates the value of composite material design in enhancing the performance of industrial components.