The Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture resistance, or the K Ic of ceramics. Initiation and propagation of cracks during the VIF test are described and contrasted with the pre-cracking and crack growth for internationally standardized fracture toughness tests. It is concluded that the VIF test technique is fundamentally different than standard fracture toughness tests. The VIF test has a complex three-dimensional crack system with substantial deformation residual stresses and damage around the cracks. The VIF test relates to an illdefined crack arrest condition as opposed to the rapid crack propagation of the standardized fracture toughness tests.Previously published fracture toughness results employing the VIF technique are reviewed. These reveal serious discrepancies in reported VIF fracture toughness values. Finally, recent fracture resistance measurements by the VIF technique for the Standard Reference Material SRM 2100 are presented. These are compared with standardized test results for the same material. It is concluded that the VIF technique is not reliable as a fracture toughness test for ceramics or for other brittle materials. What the VIF actually measures in terms of fracture resistance cannot be readily defined. It is recommended that the VIF technique no longer be acceptable for the fracture toughness testing of ceramic materials.

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Grain growth in a high-purity ZnO and Jor the same ZnO with BiZ03 additions from 0.5 to 4 wt% was studied for sintering from 900" to 1400°C in air. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: G" -G ; = Kot exp(-Q/RT). For the pure ZnO, the grain growth exponent or n value was observed to be 3 while the apparent activation energy was 224 k 16 kJ/mol. These parameters substantiate the Gupta and Coble conclusion of a ZnZ+ lattice diffusion mechanism. Additions of Bi203 to promote liquidphase sintering increased the ZnO grain size and the grain growth exponent to about 5, but reduced the apparent activation energy to about 150 kJ/mol, independent of Bi203 content. The preexponential term K O was also independent of BizOj content. It is concluded that the grain growth of ZnO in liquid-phase-sintered ZnO-Bi203 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Biz03-rich liquid phase. [Key words: zinc oxide, sintering, bismuth oxide, grain growth, microstructure.]

The fracture toughness of a sintered dense a-Sic was estimated by the Vickers indentation microfracture method in the low-load Palmqvist crack regime. It was observed that the use of simultaneously obtained Vickers hardnesses does not yield reliable fracture toughness values, nor does application of the median-crack-derived equations. It is necessary to utilize a load-independent, crack-free hardness value with this toughness estimation method. Although several of the curvefitting equations yield similar toughnesses, it is concluded for the Palmqvist crack system in this a-Sic that the Niihara-Morena-Hasselman equation is the only one which yields fracture toughness values in agreement with conventional measurement techniques. [

This report was prepared as an account of work sponsored by an ardency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, re_:ommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. By acceptanceof th_sarhcle,the publisher recognizesthat the U S Government retainsa nonexcluswe, royalty-free licenseto pulohSh or reproduce the published form of this contr=buhon,or to allow others tO Oo SO, for US Government purposes The LOS Alamos Nahonal Laboratory requests that Ihe pubhsher _dentlfy this arhcle as work performed under the auspices of the U S Department of Energy |ll DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

Properties relating to the effects of thermal expansion anisotropy were measured as functions of grain size in hot-pressed dense MgTiAk. SampIes with grains smaller than ~3 g m exhibited none of the microcracking attributed to thermal expansion anisotropy, whereas those with larger grains had all the characteristics. An energy criterion is proposed to explain the grain-size effect on microcracking in ceramics exhibiting high degrees of thermal expansion anisotropy.

Grain growth in a high-purity ZnO with systematic additions of Sb203 from 0.29 to 2.38 wt% was studied for sintering in air from 1106" to 1400°C. The results are discussed and compared with previous studies of pure ZnO and ZnO with Bi203 additions in terms of the kinetic grain growth expression: G" -G," = KOt exp(-Q/RT).Additions of Sb20J inhibited the grain growth of ZnO and increased the grain growth exponent (n-value) to 6 from 3 for pure ZnO and 5 for the ZnO-BiZ03 ceramic. The apparent activation energy for the grain growth of ZnO also increased to about 600 kJ/mol from 220 kJ/mol for pure ZnO and 150 kJ/mol for the ZnOBiz03 ceramics. Both the grain growth exponent and the activation energy were independent of the S b z 0 3 content. Particles of the Zn7Sb2Ol2 spinel were observed on the grain boundaries and at the grain triple point junctions. It was also observed that the SbzO3 additions caused twin formation in each ZnO grain. It is concluded that both the Zn7Sb2Ol2 particles and the twins are responsible for the ZnO grain growth inhibition by Sb203. [

The role of friction between the microhardness indenter and the test specimen is addressed through the analysis of dry (unlubricated) and lubricated tests on iron by Atkinson and Shi. Quantitative evaluation through a proportional specimen resistance model accurately describes the results. It suggests that friction is a major portion of the observed hardness increase at low test loads, the indentation size effect. The ISE is related to the surface-area-to-volume ratio of the indentation, which is inversely related to the indentation dimension.