to the Editor
Comments on “Guidelines for the selection of hardfacing alloys for sliding wear resistant applications” In his study of friction and wear of hardfacing alloys Dr. Foroulis [l] finds that the friction coefficients obtained between different alloy combinations do not correlate directly with the degree of wear experienced. As such this is not surprising; in fact it has been pointed out [ 21 that in general close correlations are highly improbable as, from one material combination to the other, a difference in friction may or may not be balanced by a difference in dynamic strength properties. Notwithstanding this, one would expect a positive trend, rather than the total lack of correlation that is implied by the data of Tables 6 and 7 of Foroulis’ article (coefficient of determination for linear regression r2 = 0.002). In this respect, closer inspection of Tables 6 and 7 of ref. 1 reveals a remarkable inconsistency. In Table 6 the entries for “A against B” are the same as those for “B against A”, which is in agreement with Foroulis’ statement that the wear data are average values, each alloy having been used as both ring and block. However, in Table 7, in which values of the friction coefficient p are listed, this is by no means the case (e.g. the p value for ST-l on ST-12 is given as 0.24 while the p value for ST-12 on ST-l is given as 0.28; much bigger differences occur as well). Thus it is to be concluded that the value of the friction coefficient depends on the test piece geometry. I wonder whether the same holds for the wear data and, if so, if a better correlation between friction and wear might not be obtained if the individual wear data, rather than the average data, were to be correlated with the p values. As to Foroulis’ main conclusion that alloy T-400 generally shows superior wear resistance, either self-matched or in combination with the other alloys, I would like to mention the results of development work  on materials for application in hydrostatic bearings of liquid sodium pumps, which showed an alloy of the T-400 type (i.e. 70 wt.% Co and 30 wt.% MO) to possess superior wear resistance in a field of 47 different candidate materials.
1 Z. A. Foroulis, Guidelines for the selection of hardfacing alloys for sliding wear resistant applications, Wear, 96 (1984) 203 - 218. 2 A. W. J. de Gee, A note on the relation between friction and wear, Wear, 65 (1981) 397 - 398. 0043-1648/85/$3.30
@ Elsevier Sequoia/F%inted in The Netherlands
280 3 J. P. Room, A. W. J. de Gee and A. van Wifligen, Devefopment of hardfacing materials for use in hydrostatic bearings of sodium pumps, Proc. Int. Colloq. on Hardfacing Materials in Nuclear Power Plants, Avignon, September 1980, Soci&P FranCake pour 1’Energie Nuclhaire, Paris, 1980. A. W. J. de GEE Metaalinstituut TN0 7300 AM Apeldoorn The Netherlands (Received October 5,1984;
accepted November 30,1%84)
Reply to comments on “Guidelines for the selection of hardfacing aRoys for sliding wear resistant applications” We appreciate the comments by Dr. A. W. J. de Gee regarding our paper in particular, his questions regarding the friction coefficient data shown in Table 7. The question of the possible dependence of friction and wear coefficients on the geometry of the test piece is an interesting question and is the subject of a paper to be submitted shortly for publication. Dis~u~~ons of this topic and mechanistic implications were outside the scope of the original paper, [ 11;
1 2. A. Foroulis, Guidelines for the selection of hardfacing alloys for sliding wear resistant applications, Wear, 96 (1984) 203 - 218. 2. A. FOROULXS Exxon Research and Engineering Co. P. 0. Box 101 Florkam Park NJ 07932 U.S.A. (Received August 30, ~38~~a~~epted September