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X-ray diffraction (XRD)

The facility and software package

X-ray diffraction equipment

The principles of XRD

The fundamental of X-ray diffraction (XRD) is the Bragg equation (2d×sinq= l). This equation defines the diffraction angle of an X-ray beam (having wavelength l) on a crystalline lattice plane, where d stands for its d-spacing. The principal function of XRD is to measure the diffraction beam intensity and the d-spacings of crystalline materials, which however has been developed to determine many structural properties, such as identification of unknown crystalline phases, preferred crystalline orientation (texture), grain size or micro-strain, surface stresses, etc.

Materials capabilities

Lattice constant: XRD provides the most precise measurement of lattice parameters of polycrystallines, including the multilayer period of superlattice coatings, lattice mismatches of coherent intermetallic precipitates (e.g. nickel superalloys);

Phase identification: By identifying a series of diffraction peaks in a detected XRD curve (intensity of diffraction beam plotted vs diffraction angle) and subsequently calculating the related d-spacings, XRD can be used to determine the crystalline structure of un-known phase(s);

Phase quantification: If the intensity of each diffraction peak is quantitatively measured in above experiment, the quantity of phases in a multi-phase material can be determined provided calibration samples are available;

Texture measurement: Measuring the intensity of diffraction peaks and comparing to those data of randomly oriented samples, one can determine the preferred crystalline orientation of polycrystalline materials;

Residual stresses: Using the well-established sin2ymethod, XRD can measure quantitatively the in-plane residual stresses of polycrystalline materials.

Micro-straining and grain size: By quantifying the line broadening of diffraction peaks, XRD can characterize the micro-straining arising mainly from grain boundaries of polycrystalline materials and thereafter estimate the grain sizes.

R&D and industrial

  • Advanced high performance PVD coatings and plasma surface engineering materials
  • R&D of ultrahigh strength steels
  • Long-term aged Nimonic alloys for thermal power generation
  • Ceramics: a wide range of oxides, carbides, nitrides, either powder or bulk solids

Sample requirement

XRD works on polycrystalline materials, either powders or block samples.

Example: stress measurement of residual stresses on a shot-peened superalloy surface as compared to an as-manufactured surface of the same alloy.

2-theta measurement

Residual stress measurement of blast shot-peened superalloy

Shot-peened As-manufactured
Residual Stress -951 MPa -336 MPa
Stress-free d-spacing of the {331} plane 0.1076 nm 0.1076 nm

Selected publications

For more information please contact Dr Anthony Bell

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