At PROTO we use x-ray diffraction to measure properties of materials. In general when an x-ray beam is scattered (reflected) off of a material, information can be obtained about the material such as residual stress, crystal orientation and material structure. XRD has many application areas each with specialized equipment. Our areas of specialty are powder diffraction, residual stress measurement and Laue orientation.
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 uniquely identify the 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 residual stress using the distance between crystallographic planes (d-spacings) as a strain gage. 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: λ = 2dsinθ.
If a monochromatic (λ) x-ray beam impinges upon a sample with an ordered lattice spacing (d), constructive interference will occur at an angle θ. Changes in strain and thus the d-spacing translate into changes in the diffraction angle θ measured by the x-ray detectors. Stresses can be determined from the measured d-spacings. The nondestructive nature of the x-ray diffraction technique has made residual stress characterization a useful tool for process optimization, design improvements and failure analysis. X-ray diffraction is presently the only portable nondestructive method that can quantitatively measure residual stress in crystalline and semi-crystalline materials. Our high speed x-ray detector technology enables measurements to be performed easily on metals and ceramics; including traditionally difficult materials such as shot peened titanium.
Laue diffraction is most commonly used to find and adjust the orientation of a crystal. It can also be used to assess a crystal’s perfection and disorder. The Laue techniques 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. Laue diffraction is widely used in the single crystal industry as a quality measure, as well as academic labs worldwide. A common industrial application is checking the orientation of single crystal turbine blades for use in gas turbine engines.