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...

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In this study the wear and friction of uncoated sintered steels, their relationship with microstructure and toughness when tested against austenitic steel were investigated. The metallographic investigation and the quantitative testing are interrelated in such a way that one can explain the other, and together they explain the wear behaviour of the sintered parts.