01 

 SECKECATKt.N AND CltoWTll ( »F ("KVSTALS IX P.EAKIXG METALS. 



liV 



E. (J. .MaIIIN A.M> .1. F. I'.KOKKKK. Jk. 



I'lKDUK UnIVEUSITY 



P.t'iiriiii; iiictiils llijil li.Mc liccii used successfully in iiidustriiil practice are 

 all(iys that cryslalli/.c as (•(ni^'loiucratcs upmi cipdljri;,' from the li(iui(l con- 

 ilitioii. A coiimiuiiiy accciitcd thcnry acccaiuls for tlu' aiit i-frictional qual- 

 ities of su<li ali<iys iiiioii this liasis. II is understood that there must be 

 certain hard iiarlicies eniliedded in a softer and more yielding matrix. 

 The hard components serve to resist abrasion and to endure the wear and 

 they are enabled to assume a form to accommodate microscopic irregular- 

 ities of the moving; journal surface through the limited plasticity of the 

 supporting metal. 



This being true, the conclusion seems obvious that it is highly important 

 that a good bearing metal .should be .so constituted that the hard crystals 

 are relatively small and well distributed but this is a most difficult condi- 

 tion to obtain in practical bearing casting. The formation of various met- 

 allographic constituents occurs at different temperatures and continued 

 heating of the alloy results in rapid growth of any crystals that may have 

 f(»rmed at that temperature or at a higher temperature. Also it is generally 

 true that eitlu'r flotation or settling occurs in the semi-liquid mass during 

 cooling, since there are often considerable differences between the si>ecific 

 gravities of the solid and liquid portions. Growth and segregation may 

 thus result in the formation of a bearing of very poor anti-frictional pi'op- 

 erties, even though the composition of the alloy as a whole is cori-ect. 



The work described in this paper has to do with one phase of an investiga 

 tion of the relations existing between melting and pouring conditions on the 

 one hand, and crystal segregation and growth on the other, of the alloy 

 of tin, copper and antimony known as Babbitt metal or Navy Babbitt 

 metal. The alloy used in tlie experimental work had the composition : tin 

 85.70%, antimony 9.86%, copper 3.34%, zinc 0.70% and lead 0.40%. The 

 last two metals are to b? regarded as impurities rather than as essential 

 constituents. 



The constitutional diagrams for the binary tin-antimony and tin-copper 

 systems, respectively, are shown in Figs. 1 and 2. These represent the con- 

 clusions of a number of experimenters and the diagrams are reproduced 

 from Gulliver's '•Metallic Alloys". The constitutional diagram for tlie ter- 

 nary system tin-antimony-copper is not so well worked out but a part of 

 the diagram, more or less idealized, is shown in Fig. 3. Referring to the 

 composition of Babbitt metal, given above, it will be seen that the only 

 metallographic constituents that will have any considerable importance 

 in this connection are e-tin-copper and l^-tin-antimony crystals. In the 

 the photomicrographs the latter are shown as cubes, the former as pecul- 

 iarly shaped crystals arranged in straight chains, stars and triangles. 



7-tin-antimony is the liardest constituent of this alloy and it also has 

 the lowest specific gravity. It forms on the branch i-k of the liquidus of 



