The effect of in-situ formed layered hBN on the machinability and mechanical properties of SPS sintered SiC

In this study, the relationship between machinability, mechanical properties and microstructure of hBN-SiC composites was investigated. Manufacturing of the composites started with the calcination of raw materials at 850 degrees C for 16 h under a nitrogen atmosphere prior to mixing with 5 wt% of Al2O3:Y2O3 sintering additives and then powder mixtures were spark plasma sintered at 1850 degrees C for 17 min by applying 50 MPa pressure. Char-acterizations of the samples were carried out with FTIR, XRD, SEM and TEM methods. The physical and me-chanical properties of the samples were determined with density measurement, Vickers hardness, Young's modulus, three-point bending, fracture toughness and drill test methods. The amount of in-situ formed hBN phase within the sintered composites was calculated by using the Rietveld method. The physical, mechanical and machinability properties of the composite were evaluated according to the calculated amount of hBN. The highest drilling speed during the test was obtained as 34.24 mm/min for the sample containing 29 wt% of hBN. Increasing the drill load from 19.61 N to 49.03 N resulted in 4.33 times increase in the drilling rate. TEM and STEM studies which were carried out for the microstructural investigations showed the internal defects as delamination bands within hBN phase formed during sintering. In addition to these analyses, novel precession electron diffraction method in TEM was utilized for orientation mapping to investigate any possible orientation relationship between SiC and in-situ synthesized hBN phase.