Nanostructured diamond-TiC composites with high fracture toughness

Abstract

We report the preparation of nanostructured diamond-TiC composites with high fracture toughness and high hardness starting from a ball-milled mixture of nano-sized Ti3SiC2 and submicron-sized diamond by simultaneously tuning the pressure-temperature conditions. The phase segregation of Ti3SiC2 at pressure of 5.5 GPa were investigated by X-ray diffraction and high resolution transmission electron microscopy, we found that the Ti3SiC2 could decompose into nanosized TiC and amorphous Ti-Si at 600–700 °C. The subsequent reaction between diamond and Ti-Si led to an amorphous Ti-Si-C matrix in which diamond and TiC crystals are embedded. With a loading force of 98 N, the measured fracture toughness KIC and Vicker's hardness HV of the synthesized composites reach up to 14 MPa m1/2 and 45.5 GPa, respectively. Our results demonstrate that the nanocrystalline/amorphous bonding matrix could largely enhance the toughness of the brittle composites.

Submicron cubic boron nitride as hard as diamond

“…Table I lists the values of q, E, G, and B for the sample sintered at HPHT, while the corresponding theoretic values as well as the reported bulk modulus of other super hard materials are also listed. 8,13,20,22,24 For the sample sintered at 8 GPa and 2300 K, the density reaches 3.48 g/cm 3 , almost the same with the theoretical value (3.49 g/cm 3 ). Also, the modulus values (Young's modulus ($901 GPa), bulk modulus ($384 GPa), and shear modulus ($406 GPa)) are close to the theoretical values of cBN.…”

Sound Velocities, Elasticity, and Mechanical Properties of Stoichiometric Submicron Polycrystalline δ-MoN at High Pressure

“…The shear rigidity of δ-MoN (∼190 GPa) is comparable to those of superhard diamond-TiC composites (PDC: ∼204 GPa), hexagonal ε-NbN (∼200.5 GPa), and superhard/hard γ-B (227 GPa) . Similarly, our experimentally obtained Young’s modulus of E = 484.7 GPa for δ-MoN is comparable to those of materials with high hardness ε-NbN and γ-B, but surpasses those of superhard PDC (∼446 GPa) and hexagonal δ-WN (∼395 GPa) …”

“…Using this hardness model and our obtained elasticity data, the Vickers hardness of submicron δ-MoN is estimated to be ∼17.4 GPa. As clearly seen in Table and Figure S1a in the Supporting Information, the hexagonal submicron polycrystalline δ-MoN is not so hard as previously reported by Wang et al We find that this nitride is almost as hard as hexagonal ε-NbN ( H v = ∼18.5 GPa), but is ∼21% harder than the hexagonal δ-WN ( H v = 13.8 GPa) by direct experimental Vickers hardness measurements, and significantly softer than those of other superhard/hard materials, such as cBN, PcBN, PCD, and γ-B …”

“…As compared with superhard materials/composites, we find that the hexagonal-structured δ-MoN exhibits a very high bulk modulus, comparable to that of B 0 = 384 GPa for superhard cBN . Its shear rigidity ( G 0 = 190.0 GPa) is comparable to that ( G 0 = 204 GPa) for the polycrystalline diamond-TiC composite (PCD) . It is proposed that the superior elastic/mechanical properties of hexagonal δ-MoN may have originated from the particular σ-band of bonding states between d orbitals for Mo and p orbitals for N, which exhibit a strong resistance of the shear strains.…”

“… a Ref . b Refs and . c Ref . d Ref . e Refs and . f Ref . g Calculated value using the empirical model. h Experimental value. …”