Investigation On The Microstructure And Properties Of WC-Ni₃Al-（Co） Cemented Carbides

Abstract:Two types of cemented carbides, WC-40vol.%Ni3Al and WC-40vol.%(N13AI+Co), were studied in the present work and the traditional WC-40vol.%Co composites were examined for comparison. Experimental methods including X-ray diffraction (XRD), electron probe microanalysis, selected area electron diffraction (SAED) its simulation, high resolution transmission electron microscopy (HRTEM), and matrix calculation of interfacial orientations were employed to investigate the microstructures of the two metals containing Ni3Al. The possible reasons for the difference in the mechanical properties between the two composites were discussed based on the microstructural results. The conclusions are listed below:The binder phase in the WC-40vol.%Ni3Al composites is the Ni3Al compound with slight solution of W and C. Although WC grains and Ni3Al match each other mainly in random relationships, a preferential orientation relationship between them was repetitively found by SEAD and HRTEM observations. This orientation relation can be descripted as:[100]WC//[110]Ni3Al,(001)wc//(001)Ni3Al, under which, the derived relations (100)WC//(110) Ni3Al consists well with a set of probably coherent planes that were detected from XRD measurements.The binder phase in the WC-40vol.%(Ni3Al+Co) composites was found to be the mixture of y1((Ni1-xCox)3Al) and y ((Co1-xNix)). The ordered γ’ with cubic morphology was dispersed in the disordered y phase, the size of γ’ is about100nm. A set of orientation relationship between WC grains and the binder phase, which can be described as [011]WC//[112]binder,(122)wc//(220)binder, was found via SAED.The edge of WC grains in the WC-40vol.%Ni3Al alloy was found to be round and blunt, which is quite different from those sharp edges found in the WC-40vol.%Co composites; the WC grains in the alloys containing Ni3Al were found to be finer compared with those that only consist of Co; WC grains are more uniformly distributed in the Co binder phases than in the other two. Both round and sharp edges of the WC grains can be observed in the WC-40vol.%(Ni3Al+Co) alloys, and the size of these grains fall in between of the other two alloys. The compositional gradient at the WC/Ni3Al interfaces were larger and resultant transition layers are thinner than those at the WC/Co interfaces, and those of the WC-40vol.%(Ni3Al+Co) alloy again fall in between of the two alloy above.The hardness of the WC-40vol.%Ni3Al composites is higher but its transverse rupture strength and fracture toughness are lower compared to the WC-40vol.%Co alloy. The transverse rupture strength and fracture toughness of the WC-40vol.%(Ni3Al+Co) alloy are the highest among the three alloys.