Raman Imaging for Local Analysis of Ceramic Materials, Interfaces, and Metastable Phases

Raman imaging enables non-destructive, microscopically resolved determination of composition, phases, and local residual stresses in ceramic materials. So-called Raman images are generated by using area mappings of Raman spectra. Depending on the segmented information, these images provide phase-sensitive data such as phase distributions, bonding states, defects and interfaces, as well as the distribution of residual stresses. The resulting distribution maps provide valuable insights into the microstructure of ceramic phases, and they can optionally be supplemented with correlative techniques such as SEM/EDS, EBSD, and XRD. Due to its high sensitivity, Raman imaging is a valuable tool for the development of superhard composite materials, particularly in the presence of polytypism, i.e. the occurrence of different crystal structures or the metastability of a compound, such as silicon carbide (SiC), boron nitride (BN), and diamond.

One application example of Raman imaging is the local detection of SiC as a particle coating on cubic boron nitride (cBN). In this case, it was possible to show clear evidence of the thin SiC coating as a cubic phase at the interfaces. Area mappings reveal the degree of coverage, homogeneity, and layer continuity, as well as island formation or agglomeration of such coating morphologies. The detection of metastable transformations under thermal or chemical loading is also of great interest: in such cases, diamond may transform into graphite, or cubic boron nitride (cBN) into hexagonal boron nitride (hBN). Raman imaging identifies these transformations via characteristic bands and maps their spatial distribution down to the micrometer scale (Fig. 1). This enables the optimization of critical process steps such as sintering, joining, or grinding with respect to temperature time regimes and cooling conditions in order to preserve the hardness, incorporation, and functionality of these metastable phases.

In hard-particle-reinforced ceramics or ceramic matrix composites, residual stresses arise from differences in the thermal expansion behavior of the matrix and the hard particles. These stresses are locally detected via minute Raman peak shifts and visualized as maps, ranging from tensile and compressive stress fields at particle edges to gradients across layers and interfaces. The results reveal potential crack initiation zones and provide reliable input parameters for fracture-mechanics-based design, finite element models, and optimized heat treatment strategies.

Services offered
 

• Artifact-free ceramic sample preparation using mechanical and ion-beam-based methods
• Analysis of local interfacial phenomena using Raman spectroscopy and Raman imaging
• Application of complementary methods for identifying the composition of local phases