Brittle Nonmetallic Materials Research Articles

The significance of impact data for brittle non-metallic materials: Davidge R. W. and Phillips D. C. Journal of Materials Science, Vol 7, No 11 (Nov 1972) pp 1308–1314

The significance of impact data for brittle non-metallic materials: Davidge R. W. and Phillips D. C. Journal of Materials Science, Vol 7, No 11 (Nov 1972) pp 1308–1314

The significance of impact data for brittle non-metallic materials

Experimental data for the impact energy of a number of brittle materials are reviewed and their significance discussed in terms of material properties and test conditions. For each material and test method several interpretations need to be considered but it is not always possible to extract meaningful information from the data. At one extreme, for strong, very brittle materials like ceramics, the impact strength may be controlled by the elastic energy in the specimen at the instant of fracture initiation. At the other extreme, for weaker or tougher materials like graphite and fibre reinforced plastics, the impact strength may be controlled by the work of fracture of the specimen. However, in many cases, the situation is less clear and it is emphasized that great care should be taken in the interpretation of test data.

Effect of Surface Finish on Structural Ceramic Failure

The relation between fracture strength and surface finish of brittle nonmetallic materials was examined and related to surface‐crack theory. Specimens used in an experimental illustration were made of a commercially available 96%‐pure alumina with an average grain size of 3.8 μm and a porosity of about 6%. Several groups of specimens, each having a different surface finish, were used in a biaxial ball‐and‐ring

SYNTHESIS OF COMPOSITES BASED ON SILICON-MODIFIED DETONATION NANODIAMONDS

Scientific approaches to the formation of composite materials such as «nanodiamond-nanostructured SiC» have been developed. It is shown that, as a result of vacuum heat treatment, nanodiamonds are graphitized and nanostructured graphite-like coating forms on their surface. In this case, the reduction in the mass of the nanodiamond powder after vacuum annealing reaches 20 – 30 wt. % by removing oxygen-containing surface functional groups, physically and chemically adsorbed water. In accordance with the developed technology chemical-thermal modifying of nanodiamonds by silicon is carried out by annealing in a reducing atmosphere in the temperature range of 873–1273 К in the presence of silicon halides. On the basis of carbon and silicon modified nanodiamonds under vacuum annealing conditions a composite nanostructured powder of nanodiamond-SiC with particles of size from 0.1 to 5 μm is obtained. As a result of thermobaric sintering of the modified powder in the pressure range of 1.0 – 2.5 GPa, a compact diamond composite material consisting of polycrystalline diamond grains of 0.2 – 0.5 μm in size is formed. The size of diamond subgrains is 50 – 100 nm, and the presence of nanodiamonds measuring 10 – 20 nm is noted between large polycrystalline grains. As a result of grinding of the synthesized compacts, a polycrystalline diamond micropowder with particles of size up to 50 μm, characterized by submicron- and nanocrystalline structure is obtained. Due to the hierarchical structure of the sintered particles (particle-grain-subgrain-nanodiamond crystallite), powders based on the obtained material are promising in finishing technologies for brittle nonmetallic materials.