Microstructure and Properties of Tungsten Carbide Reinforced High Frequency Induction Surfacing Layer

Literature Overview

This paper by Xu Ao, Zhang Yan, Liu Song, Ping Chaofan, Xu Haowu, and Wu Zhenqing, published in the journal Casting Technology in 2018, investigates the microstructure and wear performance of tungsten carbide (WC) particle reinforced high-chromium iron based surfacing layers produced by high-frequency induction surfacing. The research was conducted at Zhengzhou University School of Materials Science and Engineering and demonstrates that the high-frequency induction surfacing process produces coatings with superior hardness and wear resistance compared to conventional high-chromium iron based surfacing layers.

Process Characteristics and Technical Advantages

High-frequency induction surfacing is a specialized thermal spray-adjacent process that uses electromagnetic induction to selectively heat the surface of a workpiece to a molten state, allowing for the deposition of a coating with minimal dilution from the base material. This process offers several advantages for producing hardfacing coatings:

Process Advantages

• Rapid heating and cooling rates: The high-frequency induction process achieves very rapid heating rates, which promote fine grain structures and the formation of metastable phases
• Low dilution: The selective heating of only the surface layer minimizes dilution from the base material, ensuring the coating composition remains close to the intended alloy design
• High deposition efficiency: The process allows for continuous deposition with high productivity
• Minimal distortion: The localized heating minimizes thermal distortion of the workpiece
• Suitable for complex geometries: The process can be adapted for various component shapes and sizes

Microstructural Analysis and Performance Evaluation

The study reveals that the addition of WC particles to the high-chromium iron matrix significantly enhances the coating's microstructure and mechanical properties. The microstructure consists of:

• A high-chromium iron matrix containing M7C3-type carbides
• Dispersed WC particles that act as reinforcement phases
• A refined grain structure resulting from the rapid solidification rates
• Possible formation of new carbide phases at the interface between WC particles and the matrix

Performance Comparison

The enhanced hardness and wear resistance of the WC-reinforced coating are attributed to several mechanisms:

1. Dispersion strengthening: The WC particles act as hard reinforcement phases that impede dislocation motion and increase the overall hardness of the coating
2. Grain refinement: The rapid solidification rates promote fine grain structures that enhance both hardness and toughness
3. Phase transformation: The high-frequency process may promote the formation of metastable carbide phases that are harder than equilibrium phases
4. Reduced dilution: The low dilution rate ensures that the coating composition retains the intended high-chromium and tungsten content, which is critical for carbide formation

Engineering Applications and Process Considerations

The WC-reinforced high-frequency induction surfacing process is particularly suitable for applications requiring high wear resistance in conditions involving abrasive or erosive wear. Potential applications include:

• Mining and mineral processing equipment components
• Cement grinding and handling equipment
• Agricultural machinery components
• Pump impellers and valves
• Slurry handling systems
• Wear plates and liners in bulk material handling

Process considerations for successful implementation include:

• Workpiece preparation to ensure good electromagnetic coupling
• Control of powder feed rate and particle size distribution
• Optimization of induction frequency and power density
• Management of interpass temperature in multi-pass applications
• Post-processing requirements for dimensional accuracy and surface finish

Study Insights and Reflections

This research demonstrates the effectiveness of high-frequency induction surfacing as a process for producing high-performance hardfacing coatings. The combination of rapid thermal cycling, low dilution, and particle reinforcement produces coatings with superior wear resistance that can significantly extend component service life in demanding applications.

The study also highlights the importance of process-material interaction in surfacing technology. The unique characteristics of high-frequency induction heating create conditions that are particularly favorable for the formation of hard, wear-resistant microstructures in high-chromium iron based alloys. This finding has implications for the selection of surfacing processes for specific applications, as different processes may produce different microstructures and properties even with the same coating material.

The practical significance of this work lies in its potential to improve the reliability and longevity of wear-critical components in industrial applications. By providing a cost-effective method for producing high-performance coatings, high-frequency induction surfacing can contribute to reduced maintenance costs, improved equipment availability, and enhanced overall operational efficiency.

This literature contributes to the growing body of knowledge on advanced surfacing technologies and provides practical guidance for engineers seeking to optimize wear-resistant coating performance through process selection and parameter optimization.