CLADDING TECHNOLOGY SHANXI CO., LTDFretting Wear Properties of Deposited Metal in Different Weld Overlay Layers Within Slip Zones
Literature Overview and Research Background
This study investigates the fretting wear behavior of deposited metal in weld overlay layers within slip zones, which are regions of constrained relative motion between contacting surfaces. Fretting wear is a significant degradation mechanism in mechanical systems where components experience small-amplitude oscillatory motion under load, such as in bolted joints, gear contacts, rail-wheel interfaces, and pressure vessel flange connections. The study focuses on how the microstructure, composition, and mechanical properties of different weld overlay layers influence their resistance to fretting wear within slip zones.
The research addresses a critical gap in the understanding of fretting wear mechanisms in weld overlay applications. Conventional wear testing methods (e.g., pin-on-disk, block-on-ring) do not adequately simulate the fretting conditions experienced in slip zones, where the wear mechanism is dominated by oxide formation, material transfer, and subsurface crack initiation. The study develops a fretting wear testing protocol that replicates the slip zone conditions and systematically evaluates the fretting wear resistance of various weld overlay materials.
Core Technical Findings
Fretting Wear Testing Protocol
The study employs a reciprocating fretting wear tester with the following parameters:
| Parameter | Value |
|---|---|
| Contact geometry | Flat-on-flat |
| Normal load | 50–200 N |
| Amplitude | 50–200 μm |
| Frequency | 1–5 Hz |
| Duration | 10,000–100,000 cycles |
| Environment | Ambient air / controlled humidity |
| Counterface material | 52100 bearing steel |
The fretting wear volume is measured using profilometry, and the wear mechanisms are analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The fretting regime is determined from the Amplitude-Load diagram, with the study focusing on the slip zone (partial slip regime) where the most damaging fretting conditions occur.
Microstructure Effects on Fretting Wear
The study evaluates four different weld overlay materials with distinct microstructures:
| Overlay Material | Microstructure | Hardness (HV) | Fretting Wear Volume (mm³) | Fretting Damage Factor (FDF) |
|---|---|---|---|---|
| 304L stainless steel | Austenitic | 180 | 0.045 | 0.85 |
| 316L stainless steel | Austenitic | 190 | 0.038 | 0.78 |
| Inconel 625 | γ + γ' + Laves | 320 | 0.015 | 0.42 |
| Stellite 6 | Austenitic + carbides | 450 | 0.008 | 0.25 |
The data clearly demonstrates that harder overlay materials exhibit lower fretting wear volumes. The Stellite 6 overlay, with its high hardness and carbide reinforcement, shows the best fretting wear resistance, with a wear volume only 18% of the 304L overlay. The Fretting Damage Factor (FDF), which normalizes the wear volume by the applied energy, confirms that Stellite 6 has the best fretting damage resistance.
Oxide Layer Formation and Stability
A critical finding of the study is the role of oxide layer formation in fretting wear resistance. During fretting, a protective oxide layer forms on the contact surface, and the stability of this layer determines the wear rate. The study analyzes the oxide layer composition and thickness for each overlay material:
| Overlay Material | Oxide Layer Thickness (nm) | Primary Oxide Phases | Oxide Stability Index |
|---|---|---|---|
| 304L | 150–200 | Cr₂O₃, Fe₂O₃ | Moderate |
| 316L | 180–250 | Cr₂O₃, MoO₃, Fe₂O₃ | Good |
| Inconel 625 | 200–300 | Cr₂O₃, NiO, Nb₂O₅ | Very Good |
| Stellite 6 | 250–350 | Cr₂O₃, MoO₃, CoO | Excellent |
The oxide stability index is determined by the adhesion strength of the oxide layer to the underlying metal. The Stellite 6 overlay forms the most stable oxide layer, which protects the underlying metal from further wear. The 304L overlay forms a less stable oxide layer, which is easily removed during fretting, exposing fresh metal to further oxidation and wear.
Subsurface Crack Initiation and Propagation
The study also investigates the subsurface crack initiation and propagation behavior in the overlay layers during fretting. Using cross-sectional SEM analysis, the following findings are observed:
| Overlay Material | Crack Initiation Depth (μm) | Crack Length (μm) | Crack Density (cracks/mm²) |
|---|---|---|---|
| 304L | 50–80 | 200–400 | 15–25 |
| 316L | 60–100 | 150–300 | 10–18 |
| Inconel 625 | 100–150 | 100–200 | 5–10 |
| Stellite 6 | 150–200 | 50–100 | 2–5 |
The harder overlay materials (Inconel 625, Stellite 6) show deeper crack initiation depths and lower crack densities, indicating better resistance to subsurface crack formation. This is attributed to the higher yield strength of these materials, which requires higher contact stresses to initiate plastic deformation and crack nucleation.
Engineering Practice Integration
Application to Pressure Vessel Flange Connections
Weld overlay layers are commonly applied to pressure vessel flange faces to improve corrosion resistance and reduce gasket wear. In these applications, the flange bolts experience fretting during thermal cycling and pressure fluctuations, which can lead to fretting wear at the bolt-to-flange contact interface. The study's findings inform the selection of overlay materials for flange applications, with Stellite 6 or Inconel 625 recommended for critical applications where fretting wear is a concern.