X Ray Diffraction
X-ray diffraction (XRD) is a non-destructive analytical technique that measures how X-rays scatter from crystalline materials to identify phase composition, crystal structure, preferred orientation, lattice strain, crystallite size, and residual stress. By analyzing diffraction peak positions and intensities, XRD provides quantitative surface and near-surface stress information, making it a key quality control tool for machined metal parts.
On a CNC shop floor, XRD is typically used after finish turning, milling, grinding, or hard machining to verify whether the process left compressive or tensile residual stress that could affect fatigue life, distortion, or crack initiation. A part is moved to an inspection area or portable XRD setup, where diffraction peaks are measured at defined orientations. The technician calculates stress from lattice strain and compares results against process acceptance limits. This non-destructive feedback helps determine whether stress relief is needed, whether a toolpath induces harmful stress, or whether a process change improved the residual-stress state. In millwork and edgebanding, XRD applies mainly to metallized hardware, coated tooling, fasteners, or plated components rather than wood, because the method requires crystalline materials. The real value is verifying surface integrity without cutting or sectioning the workpiece.
What physical quantity does XRD actually measure first?
XRD measures diffraction angles and peak shifts from crystal lattice planes; residual stress is then inferred from lattice strain using Bragg-based calculations.
Why is XRD preferred over destructive stress-relief methods in production?
It is non-destructive, can be performed directly on finished parts, and provides a quantitative surface-stress assessment without cutting, sectioning, or otherwise altering the component.
What is the main limitation for machined parts?
The method is most sensitive to surface and near-surface stress, so it does not fully characterize bulk stress through the entire cross-section unless additional depth-removal or complementary methods are used.