CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Plasma Cladding Nickel-Based Alloy with Spherical Tungsten Carbide Particles
Background and Motivation
The plasma transferred arc (PTA) cladding process is widely used for depositing wear-resistant and corrosion-resistant overlay layers on critical components. The addition of hard particles such as tungsten carbide (WC) to the cladding powder can significantly enhance the wear resistance of the overlay layer. However, the morphology, size distribution, and dispersion uniformity of the hard particles directly influence the microstructure, mechanical properties, and service performance of the cladded layer. This study investigates the effects of spherical WC particles on the microstructure and properties of PTA-clad nickel-based alloy overlay layers, providing insights for optimizing the composite cladding process.
Core Technical Content
Experimental Design
The study employs PTA cladding to deposit nickel-based alloy (Ni-Cr-Mo type, similar to Inconel 625) overlay layers reinforced with spherical WC particles on a stainless steel substrate. The spherical WC particles are obtained through a sphericalization process that converts the irregular angular WC grains into near-spherical morphology, which improves flowability and dispersion in the powder blend.
| Parameter | Condition 1 | Condition 2 | Condition 3 |
|---|---|---|---|
| WC content (wt%) | 10 | 20 | 30 |
| WC particle size (μm) | 15-25 | 15-25 | 15-25 |
| Powder morphology | Spherical WC + spherical Ni-alloy | Spherical WC + spherical Ni-alloy | Spherical WC + spherical Ni-alloy |
| Plasma power (kW) | 12 | 12 | 12 |
| Travel speed (mm/min) | 200 | 200 | 200 |
| Powder feed rate (g/min) | 120 | 130 | 140 |
| Shielding gas | Ar + 5% H2 | Ar + 5% H2 | Ar + 5% H2 |
Microstructural Analysis
The metallographic analysis reveals that the spherical WC particles are well-dispersed in the nickel-based alloy matrix, with minimal agglomeration compared to angular WC particles. The spherical morphology promotes better wetting and bonding between the WC particles and the Ni-alloy matrix, reducing the risk of particle pull-out during wear. The microstructure of the overlay layer consists of a dendritic Ni-alloy matrix with WC particles located primarily at the interdendritic regions and grain boundaries.
At 10 wt% WC, the microstructure is characterized by a fine dendritic Ni-alloy matrix with isolated WC particles. At 20 wt% WC, the dendrite spacing decreases due to the increased nucleation sites provided by the WC particles, resulting in a finer microstructure. At 30 wt% WC, particle agglomeration begins to occur, leading to localized regions of high WC concentration and potential weakness in the overlay layer.
Mechanical Properties
| Property | Substrate | 10% WC | 20% WC | 30% WC |
|---|---|---|---|---|
| Hardness (HV0.3) | 200 | 420 | 510 | 480 |
| Wear volume loss (mm³) | 85 | 12 | 5 | 8 |
| Bond strength (MPa) | - | 295 | 278 | 245 |
| Tensile strength (MPa) | - | 680 | 620 | 550 |
| Elongation (%) | - | 12 | 9 | 6 |
The results demonstrate that 20 wt% WC content provides the optimal balance between hardness, wear resistance, and mechanical integrity. Beyond 20 wt%, the increasing WC content leads to particle agglomeration, reduced ductility, and decreased bond strength due to the formation of brittle phases at the particle-matrix interface.
Wear Mechanism Analysis
The wear test results indicate that the wear mechanism transitions from adhesive wear in the substrate to abrasive wear in the WC-reinforced overlay layers. At 20 wt% WC, the wear resistance is improved by approximately 17 times compared to the unclad substrate. The spherical WC particles contribute to wear resistance through two mechanisms: (1) direct load-bearing capacity due to their high hardness (HV3000), and (2) promotion of a finer Ni-alloy matrix microstructure that resists matrix deformation.
Engineering Practice Integration
The PTA cladding of WC-reinforced nickel-based alloys is applicable to components requiring extreme wear resistance in aggressive environments, such as valve seats, pump impellers, and mining equipment. The study's findings provide clear guidelines for optimizing the WC content and particle morphology in composite cladding applications.
Process Optimization Recommendations
- The WC particle size should be selected in the range of 15-25 μm to balance dispersion uniformity and load-bearing capacity.
- The WC content should be limited to 20 wt% to avoid particle agglomeration and excessive brittleness.
- The plasma power and travel speed should be optimized to ensure complete melting of the Ni-alloy powder while minimizing the dissolution of WC particles.
- A preheating temperature of 200-300°C is recommended to reduce thermal stress and prevent cracking in the overlay layer.
- The overlay layer thickness should be controlled to 1.0-3.0 mm to ensure adequate wear life without excessive material usage.
Reflections and Study Insights
This study provides valuable insights into the design of composite cladding systems where hard particles are used to enhance wear resistance. The key finding that spherical WC particles outperform angular WC particles in terms of dispersion and bonding is a significant contribution to the field of composite cladding. The optimal WC content of 20 wt% identified in this study is consistent with previous research on angular WC particles but highlights the importance of particle morphology in determining the optimal reinforcement fraction. Engineers designing composite cladding systems should carefully consider the particle morphology, size distribution, and content in conjunction with the process parameters to achieve the desired balance between wear resistance and mechanical integrity. The study also emphasizes the importance of bond strength testing, as the addition of hard particles can compromise the metallurgical bonding between the overlay layer and the substrate if not properly controlled.