What testing methods are used to detect sliver defects in single crystal castings?

NDT Surface Inspection

Sliver defects typically form as thin, plate-like, near-surface misoriented grains. Non-destructive testing (NDT) methods such as dye penetrant testing (PT) and visual inspection are often the first steps in identifying these defects. PT is especially effective because slivers frequently occur close to the casting surface and create fine, crack-like indications that trap penetrant. While PT cannot quantify internal crystallographic misorientation, it provides early detection for surface-breaking slivers in components produced through single-crystal casting.

CT and Radiographic Methods

Computed tomography (CT) scanning is one of the most effective NDT tools for detecting subsurface or partially buried sliver defects. Slivers produce density or orientation-related discontinuities that CT can resolve as thin, irregular features near the mold-wall boundary. Compared with conventional radiography, CT offers three-dimensional visualization, enabling engineers to determine the sliver’s distribution, extent, and depth. Radiographic inspection may also detect pronounced slivers, but CT provides significantly higher contrast and spatial resolution.

EBSD for Microstructural Verification

Electron Backscatter Diffraction (EBSD) is essential for confirming sliver defects because it directly maps crystallographic orientation. When a sliver is suspected, EBSD reveals sharp orientation discontinuities between the parent single crystal and the misoriented grain. This method is particularly useful for validating doubtful NDT indications and for distinguishing slivers from harmless surface features. EBSD is typically performed after sample sectioning, making it a destructive but definitive form of microstructural analysis.

Material Testing Integration

Advanced characterization services—such as material testing and analysis—support sliver detection through metallography, SEM imaging, and microhardness mapping. These methods help quantify sliver thickness, growth direction, and associated dendritic disruptions. Although destructive, they provide indispensable data for root-cause analysis and process optimization.