In-situ ZrB2-hBN ceramics with high strength and low elasticity

ZrB2 ceramics with various hexagonal BN(hBN)additions up to 37 vol%were reactively densified by spark plasma sintering using powder mixtures containing ZrB2,ZrN and boron.ZrN-boron based additives effectively promoted the densification process,ZrB2 ceramics reached>99%relative density at 2000℃and an applied pressure of 60 MPa with only 5 vol%in-situ formed hBN,whereas the relative density of pure ZrB2 was only 91.2%at the same conditions.Increasing thehBN contents,the morphology of hBN grains gradually changed from quasi-spherical to flake dominated,which has substantial influence on their mechanical properties.In-situ ZrB2-10 vol%hBN ceramics demonstrated high flexural strength of 597±22 MPa,relatively low Young’s modulus of 406 GPa and good machinability,especially for the impressively large strain to failure(1.47×10^-3)which is superior to most of their counterparts in the ZrB2 based particulate reinforced ceramics.