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Large gas-cluster-ion bombardment has been shown to be a unique tool for generating a variety of bombarding effects over a broad range of acceleration energies. A hardness measurement technique is proposed in this paper based on the use of the effect of crater formation by large gas-cluster beams. The cluster impact leaves a hemispherical crater on a surface, the size of which varies with surface hardness and cluster parameters ͑which can be predetermined͒. As shown in this paper, the crater depth h ͑or diameter d͒ and Brinell hardness B are correlated through the formula hϳ(E/B) 1/3 , where E is the cluster acceleration energy. The material hardness, binding energy, and the crater size have also been correlated with the sputtering yield Y, and hence this correlation can also be experimentally applied for measuring hardness. The proposed method is based entirely on surface effects which depend only on the surface material and not on the substrate and therefore should be particularly suitable for measuring hardness of thin deposited films. This technique also eliminates the need for indentors that are harder than the material measured.

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Hafnium oxide films were grown by ion beam assisted deposition on water-cooled Si (100) substrates, under conditions of oxygen starvation, using hafnium vapor and an oxygen ion beam. The transport ratio (TR), i.e., the ratio between the arrival rate of hafnium to that of oxygen, was varied between 0.5 and 10, and ion energy was varied between 1 and 20 keV. The films were analyzed using x-ray diffraction and x-ray photoelectron spectroscopy. Films having the CaF2 cubic structure with a lattice parameter of about 0.512 nm were repeatedly obtained. In addition, at 20 keV ion energy and TR values of 4 and above, films with a tetragonal structure were obtained. The latter structure, believed to be a distortion of the cubic structure, has a c/a ratio of 1.01 and its space group is considered to be different from the high temperature tetragonal HfO2 structure. The new tetragonal structure also presents high Knoop hardness, with values between 15 and 25 GPa. Substrate rotation speed was found to affect the structure and the orientation of the films. All films exhibit a stoichiometry in the vicinity of HfO1.6, with the tetragonal films apparently being Hf2O3. These structures are attributed to a very fast cooling rate during film formation. Films deposited without substrate water cooling, or with substrate heating up to 500 °C contain a large component of the monoclinic phase. The new cubic and tetragonal structures are stable at room temperature and upon annealing up to 450 °C in vacuum, but convert to the monoclinic structure upon annealing at 500 °C in air, indicating that their low oxygen content is a key factor for their stability.

is not a general rule, however, and that this conclusion depends The effects of grain size on the tribological behavior of on the test configuration, a parameter which has been rarely alumina were investigated. Alumina specimens with three different grain sizes, namely 4, 8, and 14 m, were used as studied. pins and disks in a flat-pin wear test in which the apparent contact area was maintained constant during the test. In II. Experimental Procedure contradiction with previously published reports obtained with the regular round pin, our work has found that in this A group of three different grain size alumina pins and disks case the alumina wear decreases with increasing grain size.were fabricated from commercially available pure powder The evidence presented here suggests that the effect of grain (0.6 m, 99.99%). The powders were isostatically pressed and size on alumina wear behavior is strongly influenced by the isothermally sintered at 1600ЊC for different periods of time test configuration. Small grains and large grains exhibit two in order to obtain grain sizes of 4, 8, and 14 m. The grain different wear mechanisms: brittle fracture such as grain size was determined by Optimas image analysis after chemical pull-out and microchipping as well as abrasive wear are etching. The pin-on-disk test used here uses a flat pin configuthe dominant mechanisms in the small grain size alumina, ration, details of which have been reported elsewhere, 13 with the whereas plastic deformation plays a significant role in the difference that here the surface of the pin was not elliptical wear behavior of coarser-grained alumina.but rectangular. In this configuration the apparent contact area remains constant during the test. The pin used in this test was I. Introduction made of a 3 ϫ 3 mm 2 bar ground to 45Њ in the contact area. The disk dimensions were 30 mm in diameter and 5 mm thick. The A LUMINA is a ceramic material which is widely used for experiments were conducted at room temperature (between 19Њ tribological applications and its wear behavior has been and 21.5ЊC) and relative humidity (rh) between 40% and 55%. investigated in numerous studies. 1-6 There seems to be broadThe wear track was examined by scanning electron microscopy agreement that alumina wear resistance is improved with (SEM). For the work presented here, all the wear tests were decreasing grain size. 3-7 Both intergranular and transgranular carried out at 1000 rpm sliding speed at a normal load of fracture were observed on fracture surfaces. 8,9 It has also been 10 N for 100 000 cycles, corresponding to a sliding velocity of shown that fracture toughness and hardness do not correlate 1.04 mиs Ϫ1 and a distance of 6.2 km. The data were collected with wear. 10 Published literature shows a large variability in the from 10 individual wear tests conducted for each group and the wear of alumina ceramics due to the test variables (load, cycles results are plotted such that the data points show the statistical per minute, and total number of cycles). With the comm...