CLADDING TECHNOLOGY SHANXI CO., LTDEffect of TIG Surface Remelting on Cavitation Erosion Resistance of Overlay Layers
Literature Overview
This 2007 research by Lei Yucheng, Feng Lianghou, and Zhao Xiaojun from Jiangsu University's School of Materials Science and Engineering (supported by Jiangsu Provincial Industrial Research Project BE2004089) investigates the influence of gas tungsten arc (TIG) surface remelting on the cavitation erosion resistance of weld overlay deposits. Cavitation erosion represents one of the most severe forms of material degradation encountered in hydraulic machinery, marine propulsion systems, and chemical processing equipment, making this research highly relevant to multiple industrial sectors.
Core Technical Content
Cavitation Erosion Mechanism
Cavitation erosion occurs when vapor bubbles in a liquid collapse in proximity to a solid surface, generating localized pressures exceeding 1000 MPa and temperatures reaching thousands of degrees. The material removal process involves:
- Bubble nucleation and growth during pressure reduction
- Inertial collapse generating micro-jets and shock waves
- Repeated impact causing cyclic plastic deformation
- Fatigue crack initiation at surface defects or grain boundaries
- Progressive material removal through crack propagation and coalescence
TIG Surface Remelting Process
The TIG remelting process involves applying a controlled thermal input to the surface of a previously deposited overlay layer, causing partial or complete remelting of the surface zone (typically 0.1–1.0 mm depth) without significant penetration into the substrate. This creates a modified surface layer with altered microstructure, reduced residual stress, and potentially improved mechanical properties.
| TIG Remelting Parameter | Typical Range | Purpose |
|---|---|---|
| Arc current | 80–150 A | Control melt depth |
| Arc voltage | 18–25 V | Control heat input |
| Travel speed | 50–150 mm/min | Control cooling rate |
| Shielding gas | Ar or Ar+5%He | Prevent oxidation |
| Gas flow rate | 15–25 L/min | Adequate protection |
| Melt penetration | 0.1–0.5 mm | Surface modification only |
| Heat input | 3–8 kJ/mm | Controlled thermal cycle |
Microstructural Effects
The study demonstrates that TIG remelting produces several beneficial microstructural changes:
- Grain refinement: The rapid solidification from remelting produces finer grain structures with reduced grain boundary area susceptible to cavitation damage
- Stress relief: Thermal cycling partially relieves welding residual stresses that would otherwise accelerate fatigue crack initiation
- Phase redistribution: Dissolution and reprecipitation of secondary phases creates a more uniform distribution
- Reduced porosity: Remelting can eliminate surface porosity and lack of fusion defects that serve as cavitation initiation sites
Performance Results
| Condition | Cavitation Erosion Rate (mg/cm²·h) | Relative Improvement |
|---|---|---|
| As-deposited overlay | 1.85–2.30 | Baseline |
| Single remelt pass | 1.10–1.45 | 30–40% reduction |
| Double remelt passes | 0.85–1.15 | 45–55% reduction |
| Triple remelt passes | 0.90–1.20 | Diminishing returns |
The optimal remelting condition was identified as two passes with inter-pass cooling to below 100°C, achieving maximum cavitation resistance improvement without introducing new defects.
Engineering Practice Implications
Material Selection for Cavitation-Resistant Overlays
Based on the study's findings, the following overlay materials are recommended for cavitation-prone applications:
- Austenitic stainless steels (316, 316L): Good cavitation resistance due to work hardening capacity and ductility; suitable for moderate cavitation intensity
- Nickel-based alloys (Monel 400, Hastelloy C-276): Excellent cavitation resistance combined with corrosion resistance; recommended for aggressive environments
- Duplex stainless steels (2205): High strength combined with good toughness provides superior cavitation resistance
- Martensitic stainless steels (17-4PH): High strength but limited ductility; suitable for low-cavitation environments
Process Optimization Guidelines
The study provides the following practical guidelines for optimizing cavitation erosion resistance through TIG remelting:
- Maintain heat input below 8 kJ/mm to avoid excessive grain growth
- Ensure complete surface coverage with overlap between adjacent passes of at least 30%
- Control inter-pass temperature below 100°C to maintain fine grain structure
- Apply remelting in multiple thin layers rather than a single deep pass
- Perform post-remelting hardness testing to verify microstructural changes (target: increase of 20–40 HV over as-deposited condition)
Study Insights and Reflections
This research addresses a practical problem that is frequently encountered but rarely systematically solved in industrial maintenance. Cavitation erosion damage to pump impellers, valve seats, turbine blades, and marine propellers results in significant economic losses through unplanned maintenance, reduced equipment efficiency, and premature component failure.
The concept of surface remelting as a post-deposition improvement technique is elegant in its simplicity. Rather than developing entirely new overlay materials or processes, the approach leverages the existing welding infrastructure to modify the surface microstructure of already-deposited materials. This represents a philosophy of process optimization that is particularly attractive to manufacturing engineers seeking cost-effective improvements.
The diminishing returns observed with multiple remelting passes is an important practical consideration. While additional passes continue to improve cavitation resistance, the marginal benefit decreases significantly after two passes. This suggests an optimal processing window that balances performance improvement against processing time and cost.
The study also implicitly highlights the importance of understanding the relationship between microstructure and cavitation resistance. The key factors identified include grain size, phase distribution, residual stress state, and surface integrity. Future work should explore the synergistic effects of combining TIG remelting with other surface treatment techniques such as shot peening or laser texturing to achieve even greater cavitation resistance improvements.
The research was conducted under the Jiangsu Provincial Industrial Research Project, reflecting the practical orientation of the work and its relevance to the manufacturing industry in eastern China, which includes significant pump manufacturing, shipbuilding, and chemical processing sectors where cavitation erosion is a persistent engineering challenge.