Fig. 2. SEM micrographs SU11274 polished surfaces of (a) B4C, (b) SiC–AlN–C and (c) SiC–5 wt.% B4C ceramics.Figure optionsDownload full-size imageDownload as PowerPoint slide
Density (ρ), theoretical density (TD), average longitudinal (Cl) and shear (Cs) wave velocities, Young\'s modulus (E), shear modulus (G) and Poisson\'s ratio (ν) values for each ceramic sample.Sampleρ (g/cm3) (±0.001)% TDAv. Cl (m s−1) (±2%)Av. Cs (m s−1) (±1%)E (GPa) (±4%)G (GPa) (±2%)ν (±7%)B4C2.48698.813,24983784131770.167SiC–AlN–C3.13398.511,05671593661610.139SiC–5 wt.% B4C–ZrO23.20898.712,36678464601980.163Full-size tableTable optionsView in workspaceDownload as CSV
4.2. Knoop and Vickers indentation behaviour
Fig. 3 presents the Knoop hardness for each sample with increasing load. All samples exhibit an indentation size effect, albeit of varying magnitude, fitting the power–law relationship well with R2 values all greater than 0.9. At low indentation loads, SiC–5 wt.% B4C and SiC–AlN–C show a very similar hardness, as expected given the similar level of SiC composition; however, with increasing load, SiC–AlN–C demonstrates a significantly greater decrease in hardness. B4C exhibits the highest hardness at low loads but displays a similar decrease in hardness and ISE as SiC–AlN–C to an extent flagella at 19.62 N, the recommended load at which to compare the hardness of armour ceramics, 29 the hardness is less than SiC–5 wt.% B4C.