Microstructure and Properties of Tungsten Carbide Cladding Layer Prepared by TIG Arc Welding

Literature Overview

This paper, published in Journal of Tianjin University (Natural Science and Engineering) (2019, Vol. 52, No. 8, pp. 829–835) by Yang Lijun, Sun Tao, Wang Yaowei, and Huang Yiming from Tianjin University, investigates the microstructure and mechanical properties of tungsten carbide (WC) cladding layers fabricated via TIG arc welding using a self-developed flux-cored wire. The research was funded by the National Natural Science Foundation of China (Project No. 51875403). The study addresses the wear resistance challenge of iron-based materials used in offshore oil extraction and advanced weapon manufacturing, providing a solution through WC particle-reinforced cladding.

Core Technical Findings

WC Particle States and Hardness

The study identifies three distinct states of WC particles in the cladding layer, each with different hardness values:

Element Diffusion and Metallurgical Bonding

Undissolved and partially dissolved WC particles undergo element diffusion with the matrix:

• Carbon and tungsten diffuse from WC particles into the matrix.
• Iron diffuses from the matrix into WC particles.
• This diffusion creates metallurgical bonding between WC particles and the matrix.

Wear Performance

Under sliding wear conditions against a GCr15 steel wheel:

• Applied load: 50 N
• Test duration: 1 h
• Wear track width: 2.5 mm
• Wear volume: 0.4 mm³
• Wear volume ratio: 1/50 of the base material

Technical Interpretation and Engineering Relevance

Wear Mechanism Analysis

The wear resistance improvement mechanism involves two synergistic effects:

1. Undissolved and partially dissolved WC particles: These particles act as hard phases that resist abrasive wear. The metallurgical bonding ensures that the particles remain anchored in the matrix, preventing debonding during wear. The matrix provides support to the WC particles, while the WC particles protect the matrix from direct contact with the counterface.
2. Completely dissolved WC: The dissolved tungsten and carbon atoms form high-hardness cast microstructures during solidification, enhancing the matrix hardness and contributing to overall wear resistance.

Cladding Process Advantages

The TIG arc welding process with flux-cored wire offers several advantages for WC cladding:

• Uniform distribution of WC particles throughout the cladding layer.
• Good metallurgical bonding between WC particles and the matrix.
• Controllable dilution rate, allowing optimization of the balance between hard phase retention and matrix hardness.

Engineering Applications

The study is particularly relevant for applications requiring enhanced wear resistance:

• Offshore oil extraction: Drill bits, valve components, and subsea equipment subjected to abrasive slurries.
• Advanced weapon manufacturing: Gun barrels, armor components, and other wear-critical parts.
• Industrial machinery: Pump impellers, valve seats, and other components exposed to erosive environments.

Engineering Practice Considerations

1. Flux-cored wire design: The self-developed flux-cored wire is critical for achieving uniform WC particle distribution. The flux composition and particle size distribution should be optimized to minimize excessive dissolution while maintaining good metallurgical bonding.
2. Welding parameter control: TIG welding parameters (current, voltage, travel speed, shielding gas flow) must be carefully controlled to achieve the desired dilution rate. Excessive heat input leads to complete WC dissolution, reducing wear resistance, while insufficient heat input may result in poor metallurgical bonding.
3. Quality control: Non-destructive testing (NDT) methods such as ultrasonic testing (UT) and magnetic particle testing (MT) should be employed to detect porosity, cracks, and lack of fusion in the cladding layer. Hardness mapping and metallographic examination are essential for verifying WC particle distribution and dissolution state.
4. Wear testing protocols: Standardized wear testing (e.g., ASTM G99, ISO 20627) should be conducted to validate the wear performance of the cladding layer under specific operating conditions.

Key Questions and Reflections

A significant question is the optimal balance between WC particle retention and matrix hardness. Complete dissolution maximizes matrix hardness but eliminates the hard phase reinforcement, while excessive retention may compromise metallurgical bonding. The study suggests that a combination of undissolved, partially dissolved, and completely dissolved particles provides the best overall wear performance, indicating that a controlled dilution rate is essential.

Another reflection concerns the scalability of the TIG cladding process for large industrial components. TIG welding is relatively slow compared to other cladding processes (e.g., HVOF, plasma arc surfacing), which may limit its application to smaller or more critical components. However, the superior metallurgical bonding achieved with TIG welding may justify the slower process for high-value applications.

Study Insights and Implications

The study demonstrates that TIG arc welding with flux-cored wire is an effective method for fabricating WC-reinforced cladding layers with excellent wear resistance. The three-state WC particle distribution and the associated metallurgical bonding mechanism provide a robust wear protection strategy.

For engineering practice, the key recommendations are:

• Optimize flux-cored wire composition and WC particle size distribution to achieve the desired three-state distribution.
• Control TIG welding parameters to maintain a dilution rate that preserves sufficient WC particles while ensuring good metallurgical bonding.
• Implement rigorous quality control procedures, including NDT, hardness mapping, and metallographic examination.
• Validate wear performance through standardized testing under representative operating conditions.

The study provides a solid technical foundation for the application of WC cladding in wear-critical industries, and the insights gained can guide process optimization and quality assurance for industrial implementation.