Characterization of microstructural, electrical and mechanical properties of MgB2 superconductor fabricated by different argon pressure and different annealing time

MgB2 superconductors were produced in a vacuum ambient, in Ar atmosphere, under 10 Bar and 20 Bar Ar pressure by ex-situ reaction method and annealed at 850 oC for 0,5 and 1 hour. XRD, SEM, EDS, Magnetoresistivity, Vickers microhardness measurements were performed in order to investigate the effects of pressure and different annealing times on microstructural, electrical and mechanical properties of bulk samples produced. a and c lattice parameters of the samples that annealed in vacuum ambient have the maximum values and both of them decreased with increasing applied pressure. The grain size of the samples decreased owing to decreasing bond distance between the atoms with pressure. Smaller grain size caused high Jc values in the samples by providing strong grain connectivity. SEM images show that the samples produced have the characteristic morphology of granular MgB2. It is also confirmed decreasing grain size and so that enhanced grain connectivity between grains by SEM images. T_c of the samples produced in vacuum ambient have the maximum values and they decreased with increasing pressure. In this study, particularly, the mechanical properties of MgB2 samples produced were examined in detail. Vickers Microhardness values of all the samples were calculated and it is seen that these values are load dependent. Microhardness values of the samples decreased with increasing pressure. The sample that produced under 20 Bar for 0,5 hour shows ISE behavior while rest of them show RISE behavior. All the samples were analyzed by using the some models such as the Meyer?s law, EPD Model, PSR Model, HK approach and IIC model. HK approach best explains the ISE behavior of sample produced under 20 Bar for 0,5 hour and IIC model best explains the RISE behavior of rest of them.