Micro-Vickers hardness

The plastic strains are measured by means of point marking method. The markings with 1 mm interval in a direction of tensile axis were made by a micro-vickers hardness tester before tensile tests. Tensile tests were conducted at room temperature at a cross-head rate of 0.5 mm/min with an Instron-type testing machine. After the tensile deformation, the relative displacements between markings were measured under a precision machinery microscope, and the corresponding local strains in the direction of tensile axis were calculated. Then deformed specimens were cut into pieces of 1 mm width by a low speed cutter perpendicular to the tensile axis. The saturation magnetization of each piece was measured by magnetic balance at room temperature. 

Some 3D Cgo polymers have been reported to be extremely hard and have bulk moduli even larger than those of diamond. Blank et al. [73-75] reported that the graphitized Cgo at high pressures and temperatures >700 °C could scratch the (111) crystallographic plane of diamond, and called it ultrahard fulleride. The micro-Vickers hardness Hv, kg/mm ) measured on various Cgo polymers are shown in Fig. 7.27. The monomer Ceo crystal is as soft as Hv = 15, and the 2D polymers have the values of the order of Hv = 200-300. The 3D polymer crystals having a density of 2.6-2.8 g/cm are in a range of Hv = 3,500, 500, comparable to c-BN values. The R3 3D polymer having 12 coordination units is the hardest polymer. 

Fig. 7.27 Micro Vickers hardness of various Cgo phases as a function of the observed density [67]...

Fig. 9.46 Variations in micro-Vickers hardness and normalized fracture toughness with true compressive strain for specimen tested at strain rates of a 6.9 x 10 s and b 2.1 x 10p s [21]. With kind permission of Elsevier...

Fig. 9.47 Variation in micro-Vickers hardness with average grain size [21]. With kind permission of Elsevier...

However, more recently a new brittleness rationalized index, denoted and expressed in Jim , has been introduced by Quinn and Quinn from the National Institute of Standards and Technology (NIST) as the ratio of the deformation energy per unit volume to the fracture energy per unit surface area. This brittleness index is more accurate than the previous one because it includes three intrinsic properties of the material rather than only two. Therefore, brittleness can be described in terms of the micro Vickers hardness (HV), Young s modulus (E), and the fracture toughness of the ceramic materials (X, ), as described in the following rationalized Quinn s equation ... 

Y Kumashiro, A Itoh, T Kinoshita, M Sobajima. The micro-Vickers hardness of TiC single crystals up to 1500°C. J Mater Sd 12 595, 1977. 

Figure 6 Variation of micro Vickers hardness with substrate bias voltage for a TiC film deposited by the HCD process. Inconel 625 substrate substrate temperature 500°C 10 xm thick 25-g load.

Figure 10 Influence of substrate temperature on critical load of TiN film deposited using HCD ion plating. Deposition rate 0.08 pm/min substrate bias voltage —20 V 2.1 pm thick micro Vickers hardness 1650 kg/mm under 10-g load. (From Oishi, 1990.)...

Cubic boron nitride (cBN) is a very promising material that, after diamond, displays the highest hardness, excellent thermal conductivity, and important characteristic properties such as high electrical insulation and chemical and thermal stability. The cBN film can be deposited on a cemented carbide insert using activated reactive evaporation with a gas activation nozzle. Figure 20 shows the relation between the micro Vickers hardness (10 g load) of a BN film and its... 

Figure 20 Micro Vickers hardness of BN film deposited using activated reactive evaporation with a gas activation nozzle. Load 10 g. (Reprinted from Ref. 12 with permission from Elsevier Science.)...

A superhard Ti-B-C film with a micro Vickers hardness of 7200 kg/mm was obtained by reactive DC magnetron sputtering with a TiB2 target and CH4 gas introduced (16). The implication of the very high hardness is that carbon atoms are included interstitially in the TiB2 lattice. 

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