CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure Evolution and Tribological Properties of WC-Reinforced Nickel-Based Alloy Cladding Layers at Different Preheating Temperatures
Literature Overview
This study examines the effect of substrate preheating temperature on the microstructure evolution and tribological properties of tungsten carbide (WC)-reinforced nickel-based alloy cladding layers. Nickel-based alloys are widely used in high-temperature and corrosive environments due to their excellent oxidation resistance, thermal stability, and corrosion resistance. The addition of WC particles provides significant wear resistance enhancement through dispersion strengthening and composite hardening effects. However, the interaction between WC particles and the nickel-based matrix during welding is complex and highly dependent on thermal processing parameters, particularly the preheating temperature. This study investigates how varying the preheating temperature affects WC particle dissolution, carbide formation, and ultimately the wear performance of the cladding layer.
Core Technical Points
Experimental Design and Process Parameters
The study fabricated WC-reinforced nickel-based alloy cladding layers on steel substrates using plasma transferred arc (PTA) cladding. The preheating temperature was varied to investigate its effect on the thermal cycle and solidification behavior:
| Parameter | Value |
|---|---|
| Cladding powder | 70% Ni-based alloy + 30% WC (by weight) |
| Powder size | 45–75 μm |
| Substrate | Q345R low-carbon steel |
| Cladding thickness | 4–6 mm |
| PTA current | 280–320 A |
| Travel speed | 150–200 mm/min |
| Shielding gas | 100% Ar |
| Preheating Temperature | Heat Input per Pass | Number of Passes |
|---|---|---|
| 100 °C | 8.5 kJ/mm | 3 |
| 200 °C | 8.5 kJ/mm | 3 |
| 300 °C | 8.5 kJ/mm | 3 |
| 400 °C | 8.5 kJ/mm | 3 |
| 500 °C | 8.5 kJ/mm | 3 |
The constant heat input per pass ensures that the primary variable is the initial substrate temperature, which affects the overall thermal cycle, cooling rate, and solidification behavior of the cladding layer.
Microstructural Evolution with Preheating Temperature
The microstructure of the WC-reinforced nickel-based cladding layers shows significant variation with preheating temperature:
| Preheat (°C) | WC Dissolution (%) | New Carbides Formed | Matrix Structure | Microhardness (HV) |
|---|---|---|---|---|
| 100 | 15–20% | Ni3W, Ni4W | Fine dendritic + eutectic | 750–800 |
| 200 | 20–25% | Ni3W, Ni4W, Ni3WC | Dendritic + eutectic | 720–770 |
| 300 | 30–35% | Ni3WC, Ni4W, Ni3W | Coarse dendritic | 680–730 |
| 400 | 40–45% | Ni3WC dominant, Ni4W | Coarse dendritic + intergranular | 650–700 |
| 500 | 50–55% | Ni3WC, Ni4W, Ni2W | Coarse dendritic + extensive intergranular | 620–670 |
At low preheating temperatures (100–200 °C), the rapid cooling rate limits WC dissolution, preserving a higher fraction of intact WC particles. These undissolved WC particles (hardness ~1500–2000 HV) provide excellent dispersion strengthening. At higher preheating temperatures (400–500 °C), the increased thermal energy and slower cooling rate promote significant WC dissolution, leading to the formation of new nickel-tungsten carbides such as Ni3WC and Ni4W. While these new carbides are also hard, they are generally less effective than intact WC particles in resisting abrasive wear.
Tribological Performance
The wear testing results reveal a clear trend with preheating temperature:
| Preheat (°C) | Wear Rate (mg/N·m) | Wear Volume (mm³) | Surface Hardness (HV) |
|---|---|---|---|
| 100 | 2.5 | 0.85 | 780 |
| 200 | 3.0 | 1.02 | 750 |
| 300 | 4.2 | 1.45 | 700 |
| 400 | 5.5 | 1.90 | 670 |
| 500 | 6.8 | 2.35 | 640 |
The wear rate increases monotonically with preheating temperature, indicating that lower preheating temperatures are beneficial for wear resistance. The primary wear mechanism transitions from abrasive wear (dominant at low preheat) to a combination of abrasive and adhesive wear (dominant at high preheat). This is attributed to the reduced WC particle content and the formation of softer nickel-tungsten intermetallics at higher preheating temperatures.
Key Technical Insights
WC Dissolution Mechanism and Its Consequences
The dissolution of WC particles during welding is governed by the thermodynamic stability of WC in the molten nickel-based matrix. The dissolution reaction can be represented as:
WC → W (in solution) + C (in solution)
The dissolution rate depends on temperature, holding time, and the composition of the surrounding matrix. At higher preheating temperatures, the initial temperature of the substrate is elevated, which increases the overall temperature of the weld pool and extends the time spent above the WC dissolution temperature. This results in more complete dissolution of WC particles and the formation of new carbides upon solidification.
The consequences of WC dissolution are significant:
- Loss of dispersion strengthening: Intact WC particles provide the highest hardness and are most effective against abrasive wear.
- Formation of new carbides: Ni3WC and Ni4W carbides are harder than the matrix but softer than WC, and they may have different crystallographic orientations that affect wear behavior.
- Matrix composition change: The dissolved W and C atoms alter the matrix composition, potentially affecting the matrix hardness and toughness.
The Role of Cooling Rate in Microstructure Refinement
At lower preheating temperatures, the cooling rate is higher, which promotes finer dendritic structures and smaller carbide particles. This refined microstructure contributes to higher hardness and better wear resistance through Hall-Petch strengthening and more effective dispersion hardening. At higher preheating temperatures, the slower cooling rate allows for coarser dendritic growth and larger carbide particles, which reduces the overall hardness and wear resistance.
Preheating Temperature Selection Guidelines
Based on the study results, the following guidelines for preheating temperature selection are recommended:
| Application Requirement | Recommended Preheat (°C) | Rationale |
|---|---|---|
| Maximum wear resistance | 100–200 | Maximum WC retention, finest microstructure |
| Balanced wear and toughness | 200–300 | Moderate WC dissolution, acceptable toughness |
| High-temperature service | 300–400 | Reduced residual stress, moderate wear resistance |
| Crack-sensitive substrate | 400–500 | Minimum cracking risk, acceptable wear performance |
Defect Analysis and Countermeasures
Defects Related to Preheating Temperature
| Defect | Low Preheat (100–200 °C) | High Preheat (400–500 °C) | Countermeasures |
|---|---|---|---|
| Cracking | Higher risk | Lower risk | Increase preheat, reduce heat input |
| Porosity | Moderate risk | Moderate risk | Ensure proper powder feeding, adequate shielding |
| Dilution | Lower | Higher | Control heat input, use multi-pass technique |
| Residual stress | Higher | Lower | Post-weld stress relief if needed |
The trade-off between wear resistance and cracking susceptibility is a critical consideration in preheating temperature selection. For applications where wear resistance is paramount and the substrate is not crack-sensitive, lower preheating temperatures are preferred. For applications involving thick sections or crack-sensitive substrates, higher preheating temperatures may be necessary to prevent cracking, even at the expense of some wear resistance.
Integration with Engineering Practice
In industrial applications, WC-reinforced nickel-based alloy cladding is commonly used for components subjected to severe abrasive wear in corrosive environments, such as:
- Pump impellers and wear rings
- Valve seats and stems
- Heat exchanger tubes
- Hydraulic cylinder liners
- Mining and quarry equipment
The preheating temperature selection must be integrated with the overall fabrication process. For example, if the component requires subsequent machining, the residual stresses from welding must be considered. If the component will be subjected to thermal cycling in service, the thermal expansion mismatch between the cladding layer and substrate must be evaluated.
For quality control, the following inspections are recommended:
- Metallographic examination of the cladding cross-section to assess WC particle retention and carbide distribution.
- Microhardness traverse across the cladding thickness to verify the hardness profile.
- Wear testing on coupon samples fabricated under the same process parameters as the production component.
- Non-destructive testing (NDT) for cracks and porosity, especially at the fusion line.
Key Questions and Reflections
One important question is whether alternative processing methods could achieve better WC retention than conventional PTA cladding. For example, laser cladding with its much higher cooling rates might preserve more WC particles. However, laser cladding has limitations in terms of deposition rate and maximum cladding thickness. Another approach could be to use WC particles with a protective coating that delays dissolution during welding.
Another reflection is the need to consider the service environment more comprehensively. The wear behavior of WC-reinforced nickel-based alloys in corrosive-abrasive environments may differ significantly from dry sliding wear. The corrosion products may alter the wear mechanism, and the protective passive film of the nickel-based matrix may be compromised by the presence of hard carbide particles.
Study Insights and Implications
This study demonstrates that preheating temperature is a critical process parameter for WC-reinforced nickel-based alloy cladding, with a direct and significant impact on microstructure and wear performance. The key insight is that lower preheating temperatures (100–200 °C) maximize WC particle retention and produce the finest microstructure, resulting in the best wear resistance. However, this must be balanced against the increased risk of cracking and higher residual stresses at lower preheating temperatures.
For engineers designing cladding processes for WC-reinforced nickel-based alloys, this study provides a clear framework for preheating temperature selection based on the specific application requirements. It also highlights the importance of understanding the fundamental mechanisms of WC dissolution and carbide formation during welding, which can guide the development of improved process parameters and powder compositions. The practical implication is that careful process optimization, rather than simply maximizing preheating temperature to prevent cracking, can significantly improve the service life of cladded components.