CLADDING TECHNOLOGY SHANXI CO., LTDTungsten Carbide Metal Ceramic Overlay Materials for Extreme Abrasive Wear
Technical Overview and Material System
Tungsten carbide-based metal ceramic overlay materials represent the most extreme end of the wear-resistant overlay spectrum, achieving surface hardness levels of HRC 65-72 (approximately 1500-1800 HV), which exceeds the hardness of any pure metal or conventional alloy. These materials combine the extraordinary hardness of tungsten carbide (WC) particles with a ductile metallic binder (nickel or cobalt), creating a composite structure that provides unmatched resistance to abrasive wear while maintaining sufficient toughness to resist spalling and catastrophic failure. The two primary binder systems are WC/Ni (tungsten carbide in nickel matrix) and WC/Co (tungsten carbide in cobalt matrix), each with distinct property profiles and application domains.
| Property | WC/Ni System | WC/Co System |
|---|---|---|
| Hardness (HRC) | 65-72 | 68-75 |
| Binder Composition | Ni-based (Ni + Fe + Cr + Mo) | Co-based (Co + Cr + W + C) |
| WC Content (wt%) | 60-70% | 60-70% |
| WC Particle Size | 5-25 μm (fine) to 50-150 μm (coarse) | 5-25 μm (fine) to 50-150 μm (coarse) |
| Thermal Conductivity | Moderate | Lower |
| Oxidation Resistance | Good (Ni-Cr matrix) | Moderate (Co matrix) |
| Typical Application | Mining, cement, slurry pumps | High-temperature wear, extrusion |
| Application Process | PTA, FCAW, brazing | PTA, FCAW, plasma spraying |
Microstructural Analysis and Wear Mechanism
The exceptional hardness of WC-based overlays is derived from the tungsten carbide particles, which have a Vickers hardness exceeding 2800 HV. These particles are distributed throughout the metallic binder matrix in a discontinuous, dispersed pattern. The key to the material's wear resistance lies in the interaction between the hard WC particles and the metallic binder:
- The WC particles provide the primary wear resistance through their extreme hardness, which resists micro-ploughing and micro-cutting by abrasive particles.
- The metallic binder provides toughness and ductility, allowing the overlay to absorb impact energy without cracking or spalling.
- The bond between WC particles and the binder matrix is critical; a weak bond leads to particle pull-out, which initiates abrasive wear through a three-body abrasion mechanism.
The particle size distribution is a critical design parameter. Coarse WC particles (50-150 μm) provide superior resistance to severe abrasive wear (such as sand and gravel in mining applications) because they are more resistant to fracture and pull-out. Fine WC particles (5-25 μm) provide a smoother surface finish and are preferred for applications where surface quality is important (such as hydraulic cylinder barrels or pump impellers).
Application Process Comparison
| Process | Deposition Rate | Dilution | Surface Quality | Equipment Cost | Typical Application |
|---|---|---|---|---|---|
| PTA (Plasma Transfer Arc) | High (500-2000 g/h) | Low (5-15%) | Excellent (smooth, uniform) | High | Pumps, valves, large components |
| FCAW (Flux-cored) | Very High (2000-5000 g/h) | Moderate (10-25%) | Good (slightly rough) | Moderate | Mining buckets, cement mill liners |
| GTAW (TIG) | Low (50-200 g/h) | Low (5-10%) | Excellent (precise) | Low | Precision components, small parts |
| Laser Cladding | High (300-800 g/h) | Very Low (2-8%) | Excellent (smooth, dense) | Very High | High-value components, repair |
| Plasma Spraying | Very High (1000-3000 g/h) | None (thermal spray) | Good (porous) | High | Large-area coating, thermal barrier |
PTA (Plasma Transfer Arc) is the preferred process for WC/Ni and WC/Co powder overlay because it provides excellent control over dilution, microstructure, and surface quality. The plasma arc provides a stable, high-temperature heat source that melts the powder and a controlled amount of base metal, producing a dense, well-bonded overlay with minimal dilution. The powder feed rate, arc current, travel speed, and powder-to-base metal ratio can all be precisely controlled to optimize the overlay properties.
Process Parameters for PTA Application
| Parameter | Typical Range | Effect on Properties |
|---|---|---|
| Arc Current (A) | 250-450 | Higher current = more dilution, thicker bead |
| Powder Feed Rate (g/min) | 300-800 | Higher rate = more alloy, less dilution |
| Travel Speed (mm/min) | 100-300 | Higher speed = less dilution, thinner bead |
| Powder-to-Melt Ratio | 2:1 to 5:1 | Higher ratio = less dilution, more alloy |
| Bead Overlap | 30-50% | Adequate overlap for uniform coverage |
| Interpass Temperature | ≤200°C | Prevent cracking, maintain hardness |
The powder-to-melt ratio is the single most important parameter for controlling dilution in PTA overlay. A ratio of 3:1 or higher is typically required to achieve dilution below 15%, which is necessary for maintaining the full hardness and wear resistance of the WC/Ni or WC/Co overlay. Lower ratios result in excessive base metal dilution, which reduces hardness and may compromise the carbide-binder bond.
Common Defects and Quality Control
| Defect | Root Cause | Impact on Performance | Countermeasure |
|---|---|---|---|
| WC particle pull-out | Weak carbide-binder bond |