At Proto®, we use x-ray diffraction (XRD) to measure properties of materials. When an x-ray beam is scattered off of a material, information about the material can be obtained, such as residual stress, crystal orientation, and material structure. XRD has many application areas, each with specialized equipment.
Powder diffraction is most commonly applied for phase analysis and structure determination of polycrystalline samples. Powder samples are exposed to a beam of monochromatic x-rays to generate an x-ray diffraction pattern. This pattern is a unique fingerprint of the material and gives structural information about the material. These patterns can be compared to known patterns in databases such as the ICDD PDF 4+ to identify the exact material. Applications range from determining the composition of ore from a mine to quality control of pharmaceuticals.
X-ray diffraction can be used to measure the residual stress in a material by determining the distance between crystallographic planes (d-spacings). When the material is in tension, the d-spacing increases, and when under compression, the d-spacing decreases.
The d-spacings are calculated using Bragg's Law: nλ = 2dsinθ.
If a monochromatic (λ) x-ray beam impinges upon a crystalline sample, then constructive interference will occur at an angle θ. By measuring the angle θ with an x-ray detector, we can calculate the d-spacing, which can then be converted into a strain value. Finally, stress is determined using Hooke's law (stress = strain x elastic modulus). The non-destructive and very accurate nature of the x-ray diffraction technique has made residual stress characterization a useful tool for process optimization, design improvements, and failure analysis in metals and ceramics.
Laue diffraction is most commonly used to quantify the orientation of single-crystal materials. It can also be used to assess a crystal’s perfection and disorder. The Laue technique works by exposing a crystal to a collimated beam of polychromatic x-rays and collecting the diffracted image onto a 2D x-ray detector. The image is made up of a number of spots in a pattern that correspond to the orientation and structure of the crystal. One advantage of the Laue method is that it is fast and non-destructive. A common industrial application is checking the orientation of single-crystal turbine blades for use in gas turbine engines.
