Composite Overlay Welding Electrode with High-Nickel Filler and WC Cemented Carbide Particles

Literature Overview

This paper by Lei Guocai, published in Physical Testing (2022, Vol. 40, No. 1, pp. 1–5), presents the development of a composite overlay welding electrode incorporating high-nickel filler metal and tungsten carbide (WC) cemented carbide particles. The electrode is designed for flame overlay welding applications in severe wear environments such as petroleum extraction and mining operations. The research addresses the formulation, manufacturing process, microstructural characterization, and performance evaluation of this novel composite welding consumable.

Core Technical Content

Electrode Formulation and Composition Design

The composite electrode is fabricated using a metallurgical powder compaction and sintering process. The key components are:

The NiCrBSi alloy powder serves a dual purpose: it raises the nickel content of the matrix to 32.39 wt%, providing excellent ductility and thermal shock resistance, and introduces chromium to enhance strength, corrosion resistance, and high-temperature oxidation resistance. The chromium addition is carefully balanced to avoid excessive embrittlement while maximizing the beneficial effects on hardness and corrosion performance.

Manufacturing Process

The electrode manufacturing process follows these sequential steps:

1. Particle preparation: YG8 cemented carbide particles (WC-Co with 8% cobalt binder) are screened to achieve a uniform particle size distribution in the 2–5 mm range. Surface treatment may be applied to improve wetting by the molten matrix metal.
2. Matrix powder blending: CuZnNi alloy powder is mixed with NiCrBSi alloy powder in calculated proportions to achieve the target nickel and chromium content. Homogeneity of the blend is critical for consistent electrode performance.
3. Composite assembly: The prepared matrix powder and WC particles are loaded into the SiC forming boat mold. The particles are arranged to achieve a relatively uniform distribution throughout the electrode cross-section.
4. Sintering: The assembled electrode is sintered in a molybdenum wire hydrogen furnace. The hydrogen atmosphere prevents oxidation of the nickel-rich matrix and ensures clean particle-matrix interfaces. Sintering temperature and time are controlled to achieve adequate bonding without melting the WC particles.
5. Quality inspection: The sintered electrode is inspected for dimensional accuracy, particle distribution uniformity, and absence of internal defects.

Microstructural and Compositional Analysis

Cross-sectional analysis of the finished electrode reveals the following characteristics:

• WC particles are relatively uniformly distributed within the matrix, without significant clustering or segregation.
• The particle-matrix interface shows good metallurgical bonding, essential for effective load transfer during service.
• The matrix metal composition confirms Ni content of 32.39 wt%, with chromium content at a level sufficient to enhance mechanical properties.
• No significant porosity or voids are observed at the particle-matrix interface.

The nickel-rich matrix provides several critical advantages for flame overlay welding:

• Excellent fluidity: The high nickel content lowers the viscosity of the molten deposit, promoting good flow and filling of surface irregularities.
• Superior wetting: Nickel-based alloys exhibit excellent wettability on most ferrous base metals, ensuring strong fusion bonding.
• Thermal shock resistance: The high ductility of the nickel matrix accommodates the thermal stresses generated during flame welding without cracking.
• Corrosion resistance: The combination of Ni and Cr provides resistance to corrosive media encountered in petroleum and mining environments.

Performance Evaluation

The overlay deposit produced by flame welding with this composite electrode achieves the following performance characteristics:

The hardness exceeding 60 HRA is achieved through the combined effect of the hard WC particles (which provide the primary wear resistance) and the strengthened nickel-chromium matrix. The matrix hardness itself is enhanced by the chromium addition, which promotes the formation of chromium carbides and solid solution strengthening.

Comparison with Conventional Overlay Welding Electrodes

Engineering Application Considerations

For flame overlay welding with this composite electrode, the following process parameters should be controlled:

• Preheat temperature: 200–300°C to reduce thermal gradient and prevent base metal cracking.
• Flame type: Neutral to slightly carburizing, to avoid excessive oxidation or carbon pickup.
• Travel speed: Moderate (50–80 mm/min) to ensure adequate melting of the electrode surface and proper particle embedding.
• Overlap: 50% overlap between adjacent weld passes to ensure uniform coverage and minimize dilution at pass boundaries.
• Post-weld treatment: Controlled cooling (furnace cool or insulated blanket) to minimize residual stress and prevent cracking in the heat-affected zone.

The 2–5 mm particle size is relatively large compared to typical composite welding consumables (which often use particles <1 mm). This large particle size provides superior resistance to ploughing and micro-cutting wear mechanisms but requires careful process control to ensure uniform embedding without particle pull-out. The nickel matrix's excellent ductility and wetting properties are essential for retaining these large particles during the welding and cooling process.

Study Insights and Implications

This research demonstrates a viable approach to developing high-performance composite overlay welding consumables for the most severe wear environments. The key innovation lies in combining the proven wear resistance of WC cemented carbide with the unique advantages of a high-nickel matrix. The use of SiC forming boats as molds and the hydrogen furnace sintering process represent practical manufacturing solutions that can be implemented in existing powder metallurgy facilities.

The relatively high nickel content (32.39%) makes this electrode more expensive than conventional high-chromium alternatives. However, the extended service life in severe applications, combined with the corrosion resistance and thermal shock resistance, may justify the higher material cost through reduced downtime and maintenance frequency. Engineers evaluating this consumable should conduct site-specific wear trials to quantify the life improvement relative to existing solutions.