Conclusions
With increasing grain size a transition takes place from intercrystallite to dual-type (inter- and transcrystallite) fracture. The two-phase Geksanit-R is characterised by the smallest grain size, a uniform grain size, and the lowest inclusion and pore contents. It is to these characteristics that the material owes its high hardness and excellent fracture toughness (Kc≈50–55 kgf/mm3/2); its effective energy of fracture, y ≈ (6.2–7.5)·104 ergs/cm4, is an order greater than its true surface enrgy γo. The hardness of Geksanit-R sinterings is virtually independent of the ratio between the relative amounts of BNw and BNs. The presence in Geksanit-R specimens of 2–7% of graphitelike boron nitride embrittles the material, without substantially altering its hardness. The other BNs-base superhard materials (including Elber-R, Belbor, and PTNB-IB-1) are less hard than Geksanit-R, which is attributable to their larger grain size and the presence of foreign substances and phases, and exhibit a marked tendency toward brittle rupture.
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Translated from Poroshkovaya Metallurgiya, No. 10(202), pp. 61–69, October, 1979.
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Bochko, A.V., Grigor'ev, O.N., Dzhamarov, S.S. et al. Effect of structural factors on the mechanical properties of superhard materials based on boron nitride. Powder Metall Met Ceram 18, 729–736 (1979). https://doi.org/10.1007/BF00797446
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DOI: https://doi.org/10.1007/BF00797446