Single crystal Elastic Constants (SECs) are fundamental to the understanding of the deformation behaviour of materials. SECs define the elastic resistance of single crystals to external forces. Estimation of SECs is particularly important as single crystals find applications in semiconductors, sensors and turbine blades. Also, SECs directly relate to the bonding between the atoms and are most often used for the validation of interatomic potentials. SECs are also essential for micromechanical modelling of various properties, for residual stress measurements using diffraction techniques and for interpretation of seismic data in the field of geological sciences. Though the necessity for estimating SECs is well established, standard methodologies for the estimation are limited and accompanied by complexities. The most common techniques used to measure SECs are resonant acoustic spectroscopy (RUS) and the Brillouin scattering and in both these techniques sufficiently large single crystals are required. But for many of the inorganic compounds and engineering alloys, it is difficult to grow a single crystal of sufficiently large length and also of the same composition as a polycrystalline counterpart. This led to the use of computational techniques and in particular first principle Density Functional Theory (DFT) simulations. Though DFT simulations are successful in estimating SECs for several inorganic compounds, the method fails for several new engineering alloys and also the SECs estimated using computational techniques require experimental validation. One alternate approach to estimate SECs is by in situ loading of polycrystalline samples in a diffractometer. Such experiments are usually carried out in synchrotron and neutron diffraction facilities. However, it takes a while before beamtime is allotted in such facilities.
Therefore in this thesis, we intend to develop an elegant and easy to access methodology wherein SECs could be determined from the polycrystalline samples using a commercial laboratory X-ray diffractometer. For this purpose, a universal miniature multiaxial loading fixture was custom-built that is capable of performing in-situ experiments by integrating it with a commercial laboratory X-ray diffractometer. Proof-of-concept experiments were carried out and the results were discussed in the 1st seminar.
In this seminar, the methodology that was developed to estimate SECs from a polycrystalline material will be discussed. Also, the material system for which we intended to estimate SECs is an entropy stabilized oxide of composition (MgCuNiZnCo)O. The scientific rationale for the obtained SECs for this material system will also be discussed in this seminar.