Abstract
The incorporation of 1 wt% hexagonal BN (hBN) into ZrB2–30 vol% SiC could noticeably better the fracture toughness, hardness, and consolidation behavior of this composite. This research intended to scrutinize the effects of various amounts of hBN (0–5 wt%) on different characteristics of ZrB2–SiC materials. The hot-pressing method under 10 MPa at 1900 °C for 120 min was employed to sinter all designed specimens. Afterward, the as-sintered samples were characterized using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and Vickers technique. The hBN addition up to 1 wt% improved relative density, leading to a near fully dense sample; however, the incorporation of 5 wt% of such an additive led to a composite containing more than 5% remaining porosity. The highest Vickers hardness of 23.8 GPa and fracture toughness of 5.7 MPa.m1/2 were secured for the sample introduced by only 1 wt% hBN. Ultimately, breaking large SiC grains, crack bridging, crack deflection, crack branching, and crack arresting were introduced as the chief toughening mechanisms in the ZrB2–SiC–hBN system.
Highlights
Superior melting point, excellent hardness, high elastic modulus, and high thermal and chemical stability are some of the outstanding characteristics of zirconium diboride (ZrB2), which have made this ultra-high-temperature ceramic (UHTC) suitable for many applications, e.g., turbine blades, cutting tools, crucibles, armor, leaning edges, thermal shields, and so forth [1,2,3,4]
No impurity phase could be detected in the X-ray diffractometry (XRD) pattern of ZrB2 powders, it does not mean the absence of such surface oxides
4 wt% phenolic resin had been added to the system as a binder, no peak associated with graphite could be identified in the attributing XRD pattern
Summary
Excellent hardness, high elastic modulus, and high thermal and chemical stability are some of the outstanding characteristics of zirconium diboride (ZrB2), which have made this ultra-high-temperature ceramic (UHTC) suitable for many applications, e.g., turbine blades, cutting tools, crucibles, armor, leaning edges, thermal shields, and so forth [1,2,3,4]. The intrinsic characteristics of the HP and SPS routes have made them suitable to produce dense ZrB2-based ceramics at roughly low sintering temperatures [17,18,19,20]. Since the dwelling time of the SPS process is relatively short, the grains have not enough time to excessively grow, which may result in ceramics with improved mechanical properties [21,22,23,24]. Many scientists have tried to improve the densification behavior and mechanical features of ZrB2 by incorporating some appropriate sintering additives. A chemical reaction between a secondary phase and the matrix results in forming some nano-sized in-situ phases, which can affect the mechanical characteristics positively [29,30,31,32,33,34]
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