Zhuojin Pipe Fitting Co., LtdFriction and Wear Performance of Nanocrystalline Surface Layer on Overlay Welding Cladding
Literature Overview
The research by Ba Dema, Meng Fanjun, Sun Xiaofeng, and Qiu Ji from the Academy of Armored Force Engineering, published in Tribology (2014, Vol. 34, No. 2, pp. 120–126), investigates the tribological performance of a surface nanocrystalline layer produced by pre-pressure rolling on overlay welding repair layers. This work is particularly relevant to engineers involved in surface engineering of piping components, pump housings, and wear-critical fittings where overlay welding is used for repair or enhancement of surface properties.
Core Technical Approach and Findings
The study employed pre-pressure rolling technology to create a nanocrystalline surface layer on overlay welding repair deposits. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to analyze the microstructure, while a CETR-3 multifunctional friction and wear testing machine was used to evaluate tribological performance under dry friction conditions.
Surface Nanostructuring Results
| Parameter | Original Overlay Layer | Surface Nanostructured Layer |
|---|---|---|
| Layer thickness | N/A | ~10 μm |
| Grain size | Micron-scale | <100 nm (bulk of layer) |
| Surface grain size | N/A | ~10 nm (outermost layer) |
| Hardness | Baseline | ~3× baseline |
| Friction coefficient | Baseline | Reduced by 10% |
| Wear volume loss | Baseline | Reduced by 25%–30% |
Wear Mechanism Transformation
The original overlay layer exhibited a combined wear mechanism of abrasive wear and adhesive wear. After surface nanostructuring, the wear mechanism shifted to predominantly abrasive wear. This transformation is attributed to the high hardness and low ductility of the nanocrystalline layer, which resists adhesive transfer while the hard nanoscale grains provide superior resistance to abrasive micro-cutting.
Engineering Practice Integration
For piping systems and fittings subjected to severe sliding wear, such as valve stems, pump shafts, and slurry pipe sections, this research demonstrates that post-welding surface treatment can significantly enhance tribological performance without requiring changes to the welding process or filler metal composition. The surface nanostructuring approach offers several practical advantages:
- It can be applied to existing overlay welds as a secondary treatment
- The 10 μm nanocrystalline layer provides meaningful wear life extension
- The process is applicable to curved surfaces typical of piping components
- It requires no heat input, avoiding further residual stress accumulation
In practice, when overlay welding is used for repair of worn pipe sections or fitting surfaces, incorporating a post-weld rolling or shot peening step to induce surface nanostructuring could extend service life by 25–30% based on the results of this study. This is particularly valuable for components where replacement is difficult due to accessibility constraints.
Study Insights and Implications
The fundamental insight from this work is that grain refinement at the nanoscale dramatically alters the tribological behavior of metallic surfaces. The Hall-Petch relationship, which correlates grain size with yield strength, extends to the nanocrystalline regime where hardness increases substantially. However, the accompanying reduction in ductility changes the failure mode from adhesive tearing to controlled abrasive removal, which is generally more predictable and manageable in engineering applications.
For engineers specifying surface treatments for piping components in abrasive service, this research provides a compelling case for considering mechanical surface nanostructuring as a complement to overlay welding. The combination of a hard overlay base with a nanocrystalline surface layer creates a graded structure that optimizes both wear resistance and fatigue resistance, representing a practical approach to extending component life in demanding industrial environments.