Surface Engineering by Expanded Austenite
X-Ray Diffraction (XRD) Machine
The analysis technique of X-ray diffraction (XRD) uses the interference patterns caused by x-ray beams incident upon a crystalline planes to determine features of a materials microstructure such as atomic spacings, grain orientation and phase constitution.
For the purpose of this investigation, the process was used to calculate the expansion of the crystal lattice and to determine the phase of the microstructure.
The X-ray diffraction machine rotates round a flat surface sample while sending out a monochromatic beam of x-rays. On the other side there is a detector which picks up the diffracted x-ray beams; the position of this detector is recorded as a function of 2θ. When the x-ray beams reach the sample, they are scattered by the atoms creating interference patterns where the x-rays react constructively and destructively. The sample under scrutiny is rotated on a perpendicular plane at the same time to keep it focused as the atoms it is diffracting upon oscillate. The detector then measures the intensity at each 2θ angle as a measure of “counts”. A graph of intensity versus position (2θ) is produced simultaneously. The array of waves that interact constructively can be defined by using Bragg’s equation;
2*d*sinθ = n*λ
d is the distance between diffraction planes (pm),
θ is the angle of incidence of the x-ray beam,
n is an integer,
λ is the wavelength
The calculation of d, the spacing between atoms, allows a 3D map of the crystal structure to be built. Analysis of the change in the atomics spacings (d value), between both carburised and non-carburised samples and between the different materials allows for the determination of how much carbon has diffused with the lattice matrix of each sample.
The graphs produced can then be analysed quantitatively or qualitatively; however for this investigation only qualitative analysis is performed. The qualitative measurement which one would be looking to extract from the graphs are; the crystalline phases that are present in the sample, an insight into how much of each crystalline phase is in the sample and also any amorphous materials within the sample
