Research and Application of Metal-Ceramic Electrode Cladding Process

Literature Overview and Technical Background

Metal-ceramic electrode cladding represents a specialized weld overlay technique that deposits composite materials consisting of a metallic matrix reinforced with ceramic particles or phases. This approach combines the toughness and ductility of metallic alloys with the exceptional hardness, wear resistance, and thermal stability of ceramic materials, producing overlay layers that outperform either pure metal or pure ceramic coatings in combined service environments. The referenced study investigates the cladding process parameters, microstructural development, mechanical performance, and industrial applications of metal-ceramic electrode cladding, with particular focus on electrodes containing Cr3C2, TiC, or SiC ceramic reinforcements in a nickel- or iron-based metallic matrix.

The motivation for metal-ceramic electrode cladding lies in the limitations of conventional hardfacing materials. Pure metallic overlays, such as H13 or Stellite, achieve hardness levels of 50–65 HRC but suffer from abrasive wear under severe conditions. Pure ceramic coatings, such as alumina or silicon carbide thermal spray coatings, achieve extreme hardness (>1500 HV) but are brittle and susceptible to chipping and spallation under impact loading. Metal-ceramic composites bridge this gap by providing hardness levels of 800–1200 HV with acceptable toughness and impact resistance.

Electrode Design and Composition

Electrode Composition Matrix

The electrode design philosophy follows a dilution-compensated approach similar to pre-alloyed powder systems. Since the metallic matrix undergoes dilution with the substrate during arc welding (typically 20–35% for stick electrode cladding), the ceramic content in the electrode must be adjusted upward to ensure sufficient ceramic reinforcement in the final overlay. For example, an electrode with 20 wt% Cr3C2 may result in an overlay with 12–15 wt% Cr3C2 after 25–30% dilution, which is the minimum required for the target hardness level.

Electrode Manufacturing Considerations

The study addresses the manufacturing challenges of metal-ceramic electrodes, which are more complex than conventional hardfacing electrodes:

1. Powder mixing: Ceramic particles (typically 10–50 μm for stick electrodes, 5–30 μm for wire electrodes) must be uniformly dispersed in the metallic powder without agglomeration.
2. Flux coating: The flux composition must be compatible with both the metallic matrix and the ceramic reinforcement, avoiding reactions that degrade ceramic particle integrity.
3. Drying and curing: Metal-ceramic electrode coatings require controlled drying (150°C for 2–4 hours) to prevent moisture-related defects while avoiding thermal degradation of the ceramic particles.
4. Storage: Electrodes must be stored at controlled humidity (<60% RH) to prevent flux moisture absorption, which can cause hydrogen porosity and ceramic particle hydrolysis.

Process Parameters and Deposition Behavior

Optimal Parameter Window

The use of direct current electrode negative (DCEN) for nickel-based metal-ceramic electrodes provides deeper penetration and better ceramic particle retention in the overlay, while direct current electrode positive (DCEP) for iron-based electrodes provides shallower penetration and better surface wetting, which is beneficial for ceramic particle distribution near the surface.

Microstructural Development

Metallographic analysis of MC-Ni-1 overlays revealed a dendritic austenitic matrix with Cr3C2 ceramic particles distributed both at interdendritic regions and within the dendrite arms. The ceramic particles retained their original morphology (irregular, angular) in approximately 70% of cases, with the remaining 30% showing partial melting or reaction with the metallic matrix to form Cr7C3 and Cr23C6 carbides. This partial reaction is beneficial as it creates a metallurgical bond between the ceramic and matrix, improving toughness without significantly reducing hardness.

The MC-Fe-1 overlay exhibited a martensitic matrix with tempered carbides after post-weld tempering at 550°C. The Cr3C2 particles acted as nucleation sites for carbide precipitation, resulting in a finer and more uniformly distributed carbide structure compared to conventional H13 hardfacing. This refined carbide distribution contributes to the improved wear resistance observed in tribological testing.

Mechanical Performance and Wear Testing

The metal-ceramic overlays demonstrate an optimal balance between hardness and toughness. While their hardness is lower than pure ceramic coatings, their fracture toughness is 3–5 times higher, making them suitable for applications involving impact loading combined with abrasive wear. The abrasive wear rate of MC-Ni-1 is approximately 3 times better than H13 hardfacing, while maintaining acceptable impact resistance.

Industrial Applications

Application Case 1: Coal Mill Roller Bushings

In a coal-fired power plant, the roller bushings of a vertical roller mill were clad with MC-Fe-1 electrode overlay. The bushings are subjected to severe abrasive wear from coal particles and moisture, with a previous service life of 6 months using H13 hardfacing. After MC-Fe-1 cladding with 3 passes (total overlay thickness 4 mm), the service life extended to 18 months — a 3-fold improvement. The overlay showed no cracking or spallation after the extended service period, confirming the toughness advantage of the metal-ceramic composite.

Application Case 2: Cement Kiln Refractory Wear Parts

In a cement plant, the kiln shell wear plates were clad with MC-Ni-1 electrode overlay. The plates are exposed to abrasive cement clinker particles at temperatures of 200–400°C. The MC-Ni-1 overlay achieved a service life of 24 months compared to 8 months for conventional cast iron wear plates, representing a 3-fold improvement. The nickel-based matrix provided excellent thermal stability and oxidation resistance at elevated temperatures.

Application Case 3: Mining Shovel Bucket Teeth

In a mining operation, the bucket teeth of an electric shovel were repaired using MC-Fe-2 electrode cladding. The teeth are subjected to combined impact loading from rock impact and abrasive wear from sandy soil. The MC-Fe-2 overlay with mixed TiC + Cr3C2 reinforcement achieved a service life of 12,000 hours compared to 4,000 hours for solid carbide tips, with the added benefit of being repairable in the field.

Quality Control and Defect Analysis