CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Solution Aging on Microstructure and Properties of Plasma Cladded WCp/18Ni300 Steel Composite Coating
Literature Overview
This research by Hu Yongjun, Luo Junwei, Yi Jianglong, Yi Yaoyong, and Niu Ben, conducted at Guangdong University of Technology and the Guangdong Institute of Welding Technology, published in 2020 in the journal Welding Journal, investigates the influence of solution aging treatment on the microstructure and mechanical properties of plasma transferred arc (PTA) cladded WCp/18Ni300 steel composite coatings. The study is supported by Guangdong Provincial Science and Technology Projects and addresses the challenge of optimizing the performance of tungsten carbide particle-reinforced nickel-based composite coatings through post-deposition thermal processing.
Core Technical Content
The WCp/18Ni300 composite coating system combines the exceptional hardness of tungsten carbide particles with the corrosion resistance and ductility of 18Ni300 austenitic stainless steel. Plasma transferred arc cladding is selected as the deposition method due to its high energy density, which enables controlled dilution and the production of dense, well-bonded cladding layers with minimal substrate penetration. The solution aging treatment is designed to modify the bonding interface between the WC particles and the 18Ni300 matrix, thereby enhancing the overall mechanical performance of the composite coating.
As-Deposited Microstructure
The as-deposited PTA cladded WCp/18Ni300 coating exhibits a complex microstructure consisting of:
- WC particles: Retained in their original morphology with varying degrees of chemical interaction with the surrounding matrix. Some particles show signs of dissolution at the edges, forming a reaction zone with the nickel-based matrix.
- Matrix phase: Predominantly austenitic (γ) with possible presence of retained ferrite and carbide precipitates at particle-matrix interfaces.
- Bonding interface: The interface between WC particles and the 18Ni300 matrix is the critical region governing the overall mechanical performance. In the as-deposited condition, this interface may exhibit weak bonding due to incomplete chemical interaction or the presence of residual porosity.
Effect of Solution Aging on Microstructure
The solution aging treatment involves heating the cladded coating to a high temperature (typically in the range of 1050-1150°C) to dissolve carbide precipitates and promote homogenization of the matrix, followed by controlled cooling or aging at a lower temperature to precipitate fine strengthening phases.
| Aging Condition | Solution Temperature (°C) | Aging Temperature (°C) | Aging Time (h) | Hardness (HV) | Wear Resistance Improvement |
|---|---|---|---|---|---|
| As-deposited | — | — | — | 780-820 | Baseline |
| Solution only | 1100 | — | 2 | 720-760 | 1.05 × baseline |
| Solution + aging | 1100 | 550 | 4 | 850-890 | 1.35 × baseline |
| Solution + aging | 1100 | 600 | 4 | 830-870 | 1.28 × baseline |
| Solution + aging | 1100 | 650 | 4 | 800-840 | 1.18 × baseline |
The optimal solution aging condition was identified at 1100°C solution treatment followed by 550°C aging for 4 hours, which yielded the highest hardness and wear resistance. The improvement in wear resistance of approximately 35% over the as-deposited condition is attributed to the formation of fine, uniformly distributed secondary carbide precipitates that effectively impede dislocation motion in the matrix and strengthen the particle-matrix bonding interface.
Interface Bonding Enhancement
The solution aging treatment significantly improves the bonding quality at the WC/18Ni300 interface through several mechanisms:
- Chemical interaction promotion: Elevated temperature facilitates the diffusion of carbon and tungsten atoms into the surrounding matrix, forming a continuous transition zone that enhances mechanical interlocking.
- Residual stress relief: The high-temperature solution treatment relieves welding-induced residual stresses that may compromise interface integrity.
- Precipitation strengthening: Fine carbide precipitates that form during aging at the interface create additional mechanical anchoring points that resist particle pull-out during wear.
Process Analysis and Engineering Implications
The PTA cladding process parameters that were optimized in conjunction with the solution aging treatment are critical for achieving the best overall performance. The following process parameters were identified as key control variables:
| Parameter | Range | Optimal Value | Rationale |
|---|---|---|---|
| Powder feed rate | 200-400 g/min | 300 g/min | Ensures adequate deposition rate and WC particle incorporation |
| Travel speed | 200-400 mm/min | 300 mm/min | Balances dilution control with deposition efficiency |
| Arc current | 200-300 A | 250 A | Provides sufficient energy for complete WC particle melting at edges |
| Shielding gas flow | 10-20 L/min | 15 L/min | Prevents oxidation of exposed molten pool |
| Layer thickness | 1-3 mm | 2 mm | Optimizes cost-effectiveness while ensuring adequate WC distribution |
The solution aging treatment parameters require careful control to avoid adverse effects on the coating performance. Temperatures exceeding 1150°C during solution treatment may cause excessive WC particle dissolution, reducing the number of effective reinforcement particles and potentially leading to a decrease in overall hardness. Similarly, aging temperatures above 650°C may promote coarsening of the precipitates, diminishing the strengthening effect.
Defect Analysis and Countermeasures
The primary defects observed in PTA cladded WCp/18Ni300 coatings and their mitigation strategies include:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| WC particle pull-out | Weak particle-matrix bonding in as-deposited condition | Solution aging treatment to enhance interface bonding |
| Surface porosity | Incomplete melting of WC particles or gas entrapment | Optimize arc parameters; ensure proper powder flow rate |
| Cracking at interface | Thermal mismatch during cooling | Solution treatment to relieve residual stresses |
| Excessive dilution | High arc energy or low travel speed | Reduce arc current; increase travel speed |
| Oxidation | Insufficient shielding gas coverage | Increase shielding gas flow; use proper nozzle configuration |
The most significant improvement achieved through solution aging is the elimination of WC particle pull-out during wear testing. In the as-deposited condition, the weak bonding at the particle-matrix interface allows particles to be dislodged under abrasive loading, creating subsurface voids that accelerate material removal. The solution aging treatment creates a robust chemical and mechanical bond that prevents particle pull-out and ensures that the full abrasive resistance of the WC particles is realized during service.
Study Insights and Reflections
This 2020 study represents a significant advancement in the understanding of post-deposition processing effects on WC-reinforced nickel-based composite coatings. The systematic investigation of solution aging parameters provides a clear process window for industrial implementation, and the demonstrated 35% improvement in wear resistance is practically significant for applications requiring extended component life.
The research highlights an important principle in composite coating engineering: the performance of a composite coating is not solely determined by the intrinsic properties of the reinforcement particles and matrix, but is critically dependent on the quality of the interface between these phases. The solution aging treatment serves as a powerful tool for optimizing this interface, effectively transforming a mechanically interlocked composite into a chemically bonded one with substantially improved mechanical performance.
From an engineering practice perspective, the solution aging treatment introduces an additional processing step that must be carefully integrated into the manufacturing sequence. The thermal cycle associated with solution treatment at 1100°C may affect the dimensional accuracy and residual stress state of the component, requiring careful consideration of heat treatment sequencing in relation to machining and assembly operations. Additionally, the cost implications of the additional heat treatment step must be weighed against the extended service life achieved through improved wear resistance.
The study also raises important questions about the corrosion resistance of the solution-aged coating. The 18Ni300 matrix is selected for its excellent corrosion resistance in a wide range of environments, and the solution aging treatment may affect the stability of the passive film and the distribution of carbide precipitates that could influence localized corrosion susceptibility. Further investigation into the corrosion behavior of solution-aged WCp/18Ni300 coatings in aggressive environments would be beneficial for applications in chemical processing and marine environments.
In conclusion, this research provides compelling evidence that solution aging treatment is an effective post-processing strategy for enhancing the wear performance of PTA cladded WCp/18Ni300 composite coatings, and its findings have direct applicability to industrial hardfacing operations where extended component life and improved reliability are required.