Abrasive wear damages observation in engineering ceramics using micro-Raman tomography
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-12-31 |
| Journal | Journal of Advanced Mechanical Design Systems and Manufacturing |
| Authors | Teppei Onuki, Kazuki Kaneko, Hirotaka Ojima, Jun Shimizu, Libo ZHOU |
| Institutions | Ibaraki University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research evaluates the applicability and limitations of micro-Raman Tomographic Imaging (mRTI) for non-destructive observation of subsurface abrasive wear damage in polycrystalline industrial ceramics.
- Core Challenge: Polycrystalline alumina ceramics are optically diffusive, causing severe light scattering that limits the effective measurement depth of mRTI to only 4-8 ”m on the initial surface.
- Mitigation Strategy: Surface polishing was employed to reduce surface roughness (Ra) and minimize optical diffusion, thereby extending the measurable depth range.
- Key Achievement: Polishing with #800 diamond abrasive film (Ra 200 nm) successfully extended the effective measurement depth to the full 17 ”m scan range, allowing clear visualization of subsurface damage.
- Damage Visualization: mRTI successfully mapped wear damage by observing changes in Raman peak width (indicating crystal lattice disorder) and peak shift (indicating residual compressive/tensile strain).
- Process Sensitivity: The study confirmed that surface preparation is highly sensitive; inadequate (#400 polish) or excessive polishing can induce new damage or overwrite the original wear damage, masking the true material state.
- Conclusion: mRTI is a viable technique for ceramic wear analysis, provided that surface polishing conditions are carefully optimized to reduce light diffusion without introducing or masking the damage state.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Type | Alumina (α-Al2O3) | - | Polycrystalline industrial ceramic plate |
| Material Purity | 96 | % | - |
| Laser Wavelength | 532 | nm | Raman excitation source |
| Laser Power | 10 | mW | Power used during measurement |
| Confocal Aperture | 25 | ”m | Pin hole size |
| Grating Density | 1800 | lines/mm | Spectrometer resolution |
| Objective Lens NA | 0.9 | - | Magnification x100 |
| Exposure Time | 16 | sec | Per measurement point |
| Alumina Refractive Index (n) | 1.76 | - | Used for depth correction |
| Initial Surface Roughness (Ra) | 600 | nm | Arithmetic average roughness |
| #400 Polished Roughness (Ra) | 300 | nm | After #400 lapping film treatment |
| #800 Polished Roughness (Ra) | 200 | nm | After #800 lapping film treatment |
| Effective Depth (Initial Surface) | 4 to 8 | ”m | Limited by light diffusion |
| Effective Depth (#800 Polished) | 17 | ”m | Effective over entire scan range |
| Raman Peak Measured | 417 | cm-1 | Corresponds to A1g vibration mode |
| Induced Damage (Peak Width) | up to 2.6 | cm-1 | Broadening observed after #400 polishing |
| Induced Strain (Peak Shift) | +0.5 | cm-1 | Shift observed after #400 polishing (compressive strain) |
| Stress Sensitivity (Estimated) | ±2 ± 0.3 | cm-1/GPa | Peak shift sensitivity for alumina |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Preparation: Alumina ceramic plates (MISUMI CEA-20-20-1) were used. Three surface conditions were prepared: the initial surface, and surfaces polished by hand for 15 minutes using #400 and #800 diamond abrasive lapping films.
- Surface Characterization: Surface topography and roughness (Ry and Ra) were measured using an optical surface profiler (Zygo New View 2000) to quantify the effect of polishing.
- mRTI Setup: Measurements were conducted using a DXR Raman microscope (Thermo Fisher Scientific) with a 532 nm laser (10 mW power) and a 0.9 NA objective lens.
- Data Acquisition: Depth-slice 2D scanning was performed using confocal laser Raman microscopy. The scan range was 24 ”m horizontally (1 ”m pitch) and 17 ”m in depth (0.85 ”m pitch), corrected using the alumina refractive index (n = 1.76).
- Spectral Analysis: Raman spectra were acquired with a 16-second exposure time per point. The spectra were fitted using the Lorentzian function to extract three key features of the 417 cm-1 peak:
- Peak Intensity (related to signal strength/diffusion).
- Peak Width (w, related to crystal lattice disorder/damage).
- Peak Position (Ὴ, related to residual elastic strain/stress).
- Tomographic Imaging: The extracted feature values were mapped as color gradations in 2D depth-slice (y-z plane) tomographic images to visualize the distribution of wear damage and strain fields.
Commercial Applications
Section titled âCommercial Applicationsâ- Precision Mechanical Components: Quality assurance and failure analysis for high-performance ceramic parts (e.g., bearings, seals, piston rings) where subsurface damage dictates component lifespan and reliability.
- Semiconductor Wafer Processing: Non-destructive assessment of subsurface damage and residual stress induced during grinding, lapping, and polishing of wide bandgap semiconductor materials (e.g., sapphire, SiC, GaN).
- Advanced Tribology and Wear Studies: Fundamental research into wear mechanisms in ceramics, allowing visualization of the transition from surface damage to deep subsurface strain fields without cross-sectioning.
- Coating and Barrier Layer Integrity: Depth profiling of stress and degradation in ceramic environmental barrier coatings (EBCs) or multilayer photovoltaic backsheets.
- Manufacturing Process Control: Optimization of precision machining and finishing processes for ceramics by providing quantitative feedback on the depth and severity of induced lattice damage, ensuring processing conditions do not overwrite critical wear data.
View Original Abstract
Micro Raman tomographic imaging (mRTI) is an excellent measurement technique that can nondestructively measure and image the fracture state of the crystal lattice inside materials with a high spatial resolution. mRTI has been successfully used for translucent materials such as wide bandgap semiconductor wafers. The applicability of this measurement method was evaluated by observing the wear damage in polycrystalline industrial ceramics materials. The influence of optical diffusion on the surface and inside of polycrystalline materials is a concern for the internal measurements by the optical beam. The quality degradation of spectral signals due to disturbances in the optical beam was confirmed by mRTI measurements on a commercial alumina plate. The application of surface polishing treatment was attempted to reduce the influence of surface optical diffusion. Three kinds of the surfaces were observed by mRTI, as the initial surface of the alumina plate, polished with #400 and #800 diamond abrasive lapping film, respectively. It was confirmed that the effective measurement depth range can be extended by reducing the surface roughness. However, we confirmed that excessive surface polishing may overwrite the damage on the measurement surface, making it difficult to observe the original damage.