CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Welding Process Parameters and Tungsten Carbide Content on Nickel-Based Tungsten Carbide Coating Performance
Literature Overview
This study systematically investigates the influence of welding process parameters and tungsten carbide (WC) particle content on the mechanical and tribological performance of nickel-based WC coatings produced by weld overlay techniques. Nickel-based WC hardfacing coatings are extensively used in applications requiring extreme wear resistance, such as mining equipment, cement mill liners, hydraulic cylinder barrels, and chemical pump impellers. The performance of these coatings is governed by a complex interplay between the binder phase (nickel matrix), the hard phase (WC particles), and the microstructural features introduced by the welding process.
Systematic Investigation of Process Parameters
The study examines the effects of multiple welding process parameters on coating performance, including arc current, voltage, travel speed, wire/feed rate, and gas flow rate. Each parameter influences the heat input, which in turn affects the dissolution behavior of WC particles, the microstructure of the nickel matrix, and the residual stress state of the coating.
| Parameter | Low Value | High Value | Effect on WC Dissolution | Effect on Hardness |
|---|---|---|---|---|
| Arc current (A) | 100 | 250 | Low dissolution | Decreases |
| Voltage (V) | 18 | 32 | Moderate dissolution | Decreases |
| Travel speed (mm/min) | 50 | 300 | High dissolution | Increases |
| Wire/feed rate (kg/h) | 0.3 | 1.5 | Low dissolution | Increases |
| Gas flow rate (L/min) | 5 | 25 | No significant effect | No significant effect |
The heat input (Q), calculated as Q = (U × I × η) / v, where U is voltage, I is current, η is efficiency, and v is travel speed, emerges as the most critical parameter governing WC dissolution. At high heat inputs (Q > 4.5 kJ/mm), significant dissolution of WC particles occurs, leading to the formation of metallic carbides (Fe₃W₃C, Ni₃W) and a substantial reduction in coating hardness. Conversely, at low heat inputs (Q < 2.0 kJ/mm), insufficient melting of the powder can lead to poor bonding and porosity defects.
Effect of Tungsten Carbide Content
The WC particle content is varied from 20% to 60% by weight in the coating alloy. The study demonstrates that WC content has a direct but non-linear relationship with coating hardness and wear resistance:
- 20–30% WC: Hardness increases from 350 to 550 HV due to increasing hard phase volume fraction. The nickel matrix remains ductile enough to provide good bonding and resistance to spalling.
- 30–50% WC: Hardness continues to increase to 700–850 HV. However, the ductility of the coating decreases significantly, and the risk of cracking during cooling increases.
- 50–60% WC: Hardness reaches 900–1000 HV, but the coating becomes brittle and prone to cracking. The WC particles may not be fully wetted by the nickel matrix, leading to poor interfacial bonding and potential delamination under impact loading.
The optimal WC content for most industrial applications is in the range of 35–50%, which provides a good balance between hardness, wear resistance, and toughness. This range also ensures that the WC particles are sufficiently wetted by the molten nickel matrix to maintain good interfacial adhesion.
Defect Analysis and Countermeasures
The study identifies several common defects in nickel-based WC coatings and their root causes:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking | High residual stress, excessive WC content, rapid cooling | Reduce heat input, add preheating, use multi-pass deposition |
| Porosity | Incomplete melting of powder, gas entrapment, insufficient shielding | Increase arc power, optimize gas flow, use vacuum or inert atmosphere |
| Poor bonding | Insufficient penetration, oxide contamination, incompatible materials | Clean substrate thoroughly, increase current, use compatible filler |
| WC dissolution | Excessive heat input, slow travel speed | Increase travel speed, reduce current, use cold wire TIG (CMT) |
| Spalling | Brittle coating, poor interfacial toughness, thermal cycling | Reduce WC content, use gradient composition, apply multi-layer structure |
Engineering Practice Integration
In practical manufacturing of nickel-based WC coatings for critical components such as hydraulic cylinder barrels, the following process optimization strategies are recommended:
- Use a multi-layer deposition strategy. The first layer (transition layer) should have lower WC content (25–30%) to ensure good bonding with the substrate. Subsequent layers can have progressively higher WC content (40–50%) to achieve the desired surface hardness.
- Implement interpass temperature control. Maintaining the interpass temperature below 150°C minimizes the cumulative heat input and reduces the risk of WC dissolution in previously deposited layers.
- Employ post-weld stress relief. A low-temperature stress relief treatment (350–450°C for 2 hours) can reduce residual stresses by 50–70% without significantly affecting the hardness of the coating.
- Conduct comprehensive qualification testing. The qualification should include hardness profiling across the coating thickness, microstructural examination to assess WC dissolution, and wear testing under representative service conditions.
Study Insights and Implications
This study provides a comprehensive understanding of the parameter-performance relationships in nickel-based WC coatings. The key insight is that coating performance is not determined by any single parameter in isolation but by the synergistic interaction of process parameters, composition, and microstructural features. Engineers must adopt a holistic approach to coating design, considering the full process window and its interaction with the intended service environment. The systematic data presented in this study can serve as a basis for developing process maps and design guidelines for nickel-based WC coating applications, enabling more rational and efficient coating specification in industrial practice.