Fig. 1. (a) Programmed temperature profile and relative displacement curves of the punch for ZrB2-ZrN-B powder mixture during SPS. (b) The enlarged region in 1a showing the shrinkage burst in BN10, BN20 and BN37 during the initial heating.

Fig. 2. Calculated adiabatic temperature (Tad) and ΔHr/Cp in the ZrN-B-ZrB2 system. The calculations with different T0, i.e. 300 K and 1300 K, were conducted separately. The dash line presents the change of Tad with hBN contents when the melting enthalpy of boron was considered in the calculations.

Fig. 3. The effects of hBN volume contents and dwell time on the relative density and open porosity of ZBN ceramics sintered at 2000 °C with different holding time.

Fig. 4. The XRD patterns of ZBN ceramics with different BN additions SPSed at 2000 °C/20 min/60 MPa.

Fig. 5. The fracture surfaces of sintered ZBN ceramics with different hBN additions (a-f). The microstructure revolutions of ZBN with hBN contents are present in 5 g schematically.

Fig. 6. SEM images of as-polished surfaces for ZrB2-hBN ceramics, both the microstructure parallel and perpendicular to the loading direction were collected as marked. A scale bar of 20 μm is the same for all the pictures in Fig. 6, as shown in 6 h.

Fig. 7. A higher magnification view of the polished surfaces on BN5(a), BN10(b), BN20(c) and BN37(d) by SEM. EDS mappings show in 7e were collected from the rectangular area marked in 7d, noting that the signal of Si was from polishing media composed of colloidal silica.

Fig. 8. The mechanical properties of ZrB2-hBN ceramics. The effects of hBN contents on the elastic parameters including Poisson’s ratio and flexural strength including strain to failure were summarized in 8a and 8b, respectively.

Fig. 9. The surface morphology of in-situ ZrB2-hBN ceramics after cutting. The SEM images of as-cut surface of BN5 and BN10 were compared in 9a and 9b whilst their 3D morphologies were displayed in 9c and 9d.