CLADDING TECHNOLOGY SHANXI CO., LTDStructure and Friction Wear Analysis of Cr3C2-Ni3Al Composite Overlay Layer
Literature Overview
This 2012 study by An Tongbang, Gong Karin, Luo Heli, Peng Yun, Zhu Xiaoyun, and Tian Zhiling, conducted jointly by the China Iron and Steel Research Institute, Chalmers University of Technology, and Kunming University of Science and Technology, investigates the microstructure and friction wear behavior of a Cr₃C₂/Ni₃Al composite overlay layer. Published in The International Journal of Welding, this research addresses the challenge of developing overlay materials that simultaneously resist abrasive wear and high-temperature oxidation — a requirement common in cement kiln linings, coal mill components, and hot gas duct applications.
Alloy System Rationale
The selection of the Cr₃C₂/Ni₃Al system is based on a synergistic design philosophy:
- Cr₃C₂ serves as the primary wear-resistant hard phase, providing high hardness (approximately 2500 HV) and excellent thermal stability up to 1000°C
- Ni₃Al serves as the matrix phase, offering excellent oxidation resistance due to its ordered intermetallic structure and the ability to form a protective alumina (Al₂O₃) scale at elevated temperatures
- The composite combination aims to achieve wear resistance from the carbide phase and oxidation resistance from the intermetallic matrix, with the metallic Ni addition providing additional toughness
| Component | Composition | Function |
|---|---|---|
| Hard phase | Cr₃C₂ (40–50 vol%) | Abrasion resistance, thermal stability |
| Matrix phase | Ni₃Al + Ni (50–60 vol%) | Oxidation resistance, toughness, bonding |
| Binder element | Ni (10–20 wt%) | Solid solution strengthening, ductility |
| Additional elements | Mo, W (trace) | Matrix strengthening, refine microstructure |
Deposition Process and Microstructure
The overlay layer was deposited using plasma transferred arc (PTA) cladding onto 45 steel substrates. The powder was a pre-blended composite of Cr₃C₂ particles (10–45 μm) and Ni-based intermetallic powder. The PTA parameters were optimized to achieve minimal dilution (<3%) and uniform powder melting.
The resulting microstructure consisted of:
- Cr₃C₂ particles: Retained their original morphology after PTA deposition, appearing as angular to sub-angular particles (10–40 μm) embedded in the matrix. The particles showed minimal dissolution during the rapid solidification process, confirming the high melting point (approximately 2200°C) and chemical stability of chromium carbide.
- Ni₃Al matrix: The matrix solidified as a dendritic structure with Ni₃Al (γ') as the primary phase and a Ni-rich interdendritic region. The γ' phase exhibited a B2 ordered structure with Al concentration in the range of 45–55 at%, confirming the intermetallic character.
- Interface region: The Cr₃C₂/Ni₃Al interface showed good metallurgical bonding with a thin reaction layer (0.5–2 μm) consisting of mixed Ni-Cr carbides and intermetallic compounds. No microcracks or debonding were observed at the particle-matrix interface, indicating good thermal compatibility.
- Fusion boundary: The overlay/base metal interface showed a fully fused bond with a transition zone of approximately 50–100 μm containing a gradient of chromium and nickel content.
Friction and Wear Testing Results
Friction and wear testing was conducted using a pin-on-disk tribometer with a Si₃N₄ ceramic counterface at room temperature, 400°C, and 600°C. The normal load was varied from 5 N to 30 N, and the sliding distance was 1000 m for each test condition.
| Test Condition | Coefficient of Friction | Specific Wear Rate (×10⁻⁶ mm³/N·m) |
|---|---|---|
| Room temperature, 10 N | 0.35–0.42 | 8.5–12.0 |
| Room temperature, 20 N | 0.38–0.45 | 15.0–22.0 |
| 400°C, 10 N | 0.40–0.48 | 12.0–18.0 |
| 400°C, 20 N | 0.45–0.55 | 25.0–35.0 |
| 600°C, 10 N | 0.52–0.60 | 35.0–50.0 |
| 600°C, 20 N | 0.58–0.68 | 60.0–85.0 |
The wear mechanism analysis revealed three distinct regimes:
- Adhesive-abrasive mixed wear (low load, room temperature): The Cr₃C₂ particles resist penetration by the counterface, while the Ni₃Al matrix undergoes mild adhesive transfer. The hard carbide particles act as ploughing obstacles, and the matrix material is removed by micro-ploughing.
- Oxidative wear dominance (400°C): At elevated temperatures, a thin oxide layer forms on the wear surface, consisting primarily of Cr₂O₃ and Al₂O₃. This oxide film provides a protective barrier that reduces adhesive wear but is periodically broken by abrasive action.
- Matrix softening and particle pull-out (600°C): At 600°C, the Ni₃Al matrix undergoes significant softening (yield strength reduction of approximately 40%), leading to matrix flow and eventual pull-out of Cr₃C₂ particles. The wear rate increases dramatically as the protective carbide network is disrupted.
Engineering Implications and Recommendations
The study provides several important engineering insights:
- The Cr₃C₂/Ni₃Al composite overlay is suitable for service temperatures up to approximately 500°C, beyond which matrix softening becomes critical.
- The optimal Cr₃C₂ volume fraction is in the range of 40–50%; higher fractions improve wear resistance but reduce toughness and increase the risk of particle cracking.
- Post-deposition annealing at 900°C for 1 hour improves the matrix toughness without significantly degrading the carbide hardness, making it a recommended heat treatment for engineering applications.
- The overlay shows excellent potential for cement kiln applications where the service temperature is typically 400–600°C and the wear mechanism is a combination of abrasion and oxidation.
This research demonstrates that the strategic combination of hard ceramic particles with an ordered intermetallic matrix can produce composite overlays with complementary wear and oxidation resistance properties that are not achievable with either component alone.