Intrinsic hardness of the individual constitutive phases (carbides and binder) of cemented carbides

Hardmetals are heterogeneous materials at microstructural scale, i.e. they are conformed by different phases defined by their chemical nature or their crystallographic orientation. In the present Master thesis, a WC-(Ta-Ti)C-Co hardmetal grade with five phases (WC basal, WC prismatic, (010) plane oriented (Ti-Ta)C, (111) plane oriented (Ti-Ta)C and metallic Co binder) has been investigated in order to determine the intrinsic hardness of the constitutive phases, by means of statistical analysis of data from massive nanoindentation technique. Nanoindentation tests were carried out with a Berkovich diamond tip and using the continuous stiffness measurement module, with maximum penetration depth of 2000 nm to determine the hardness value at micrometric length and with maximum penetration depth of 200 nm to determine values of intrinsic hardness for the individual carbides and binder phases. As outcome, consistent values of intrinsic hardness for the defined phases were determined. Electron backscattered diffraction, allowed determining the influence of the crystallographic orientation in the values of intrinsic hardness for the (Ti-Ta)C phase. Findings indicated that (Ti-Ta)C grains oriented near the (010) plane showed higher values of intrinsic hardness than (Ti-Ta)C grains oriented near the (111) plane. Besides the study of crystal anisotropy, uniaxial compression of micro-pillars milled by means of focused ion beam, FIB, allowed determining the yielding point of the hardmetal, ranging from 0.2 GPa to 1.8 GPa. Finally by means of field emission scanning electron microscopy it was possible to detect deformation/failure mechanisms mainly in the WC/(Ta-Ti)C and WC/Co interfaces that appear to act as stress concentrators