Investigation of a ceramic in indentation of a Vickers diamond pyramid

The results are given of hardness and crack resistance tests of the surface of silicon nitride- and zirconium dioxide-base material in indentation of a Vickers pyramid. For the investigated materials the presence on the curves of change in these characteristics of areas of stabilization of the mechanisms of deformation and fracture is established and also the fact that one of the reasons for nonlinearity of the strain curves is probably microcracking of the glassy phase and phase transformations occurring in the area of the indentor impression. In addition, a semiempirical relationship most applicable for calculation of K_Ic of the investigated constructional ceramics was determined.Translated from Problemy Prochnosti, No. 9, pp. 49–54, September, 1990.     

Phase transformations in materials studied by micro-Raman spectroscopy of indentations

 Phase transformations occurring in materials under high pressures are important for a wide range of problems in materials science and solid-state physics. Most of the results in this area have been obtained using various sophisticated high-pressure cells. We studied solid-state phase transformations and amorphisation under high non-hydrostatic pressures in very simple experiments using a combination of hardness indentation tests with micro-Raman spectroscopy. Amorphisation of diamond, that did not occur under hydrostatic loading, has been observed. Shearing and distortion of cubic diamond structure above 100 GPa resulted not only in its amorphisation, but also in the formation of threefold coordinated carbon. A carbon film that was squeezed between a SiC substrate and diamond indenter lost its graphitic structure and produced a Raman band typical of diamond-like carbon (DLC). Even for such a well-studied material as Si, principally new data have been obtained. High spatial resolution of the method allowed us to show that the Raman spectrum that was previously ascribed to a metastable Si-III phase originates from two different high-pressure phases of Si. Up to five different phases of Si were found within a single impression. Studies of reversible transformations that occur upon unloading or heating of samples by the laser beam have also been carried out. Amorphisation and/or phase transformations have been observed for some other materials, such as SiC, quartz, Ge, GaAs and other. The combination of indentation tests with micro-Raman spectroscopy provides a powerful and fast tool for in-situ and ex-situ monitoring of pressure-induced phase transformations in materials. Received: 2 January 1997 / Accepted: March 1997     

Mechanical behavior of zirconium dioxide crystals partially stabilized with yttrium oxide

The results are given of a composite investigation of the mechanical behavior of single crystals of zirconium dioxide partially stabilized with yttrium oxide and ytterbium oxide at temperatures up to 1400°C. It is shown that the elastic modulus of these materials lies in the 150–350 GPa range and their tensile strengths may reach 1,688 MPa. These materials have a nonincreasing relationship of the stress intensity factor to crack length (flat R-curves). The stress intensity factors determined on specimens with a sharp crack are significantly lower than on specimens with a notch. The picture of fracture of single crystals in penetration of an indentor, etc. differs significantly in relation to the stabilizing addition.Translated from Problemy Prochnosti, No. 1, pp. 73–77, January, 1991.     

Certifying advanced ceramics on the basis of mechanical properties

The authors propose a scientifically justified system of certifying the mechanical properties of ceramics, propose procedural approaches to evaluating these properties, describe a set of procedures and equipment for certifying ceramics, and also analyze the effect of test errors on the reliability of the data obtained for different certification stages.Translated from Problemy Prochnosti, No. 1, pp. 68–75, January, 1994.     

Mechanical behavior of ceramics not following Hooke's law

Conclusions The new characteristics of mechanical behavior, i.e., the degree of brittleness and the comparative brittleness, proposed previously by the author can be used efficiently in analysis of the results of strength tests on ceramics and other low-formability materials during mechanical and thermal loading.From the group of the low-formability materials it is convenient to separate the relatively brittle materials (materials not following Hooke's law) whose mechanical behavior differs greatly not only from the ductile but also brittle materials (materials which follow Hooke's law). This must be taken into account both in the course of investigations and in using the experimental results in practice.Translated from Poroshkovaya Metallurgiya, No. 11(311), pp. 79–85, November, 1988.