91 
SEGREGATION AND GROWTH OF CRYSTALS IN BEARING METALS. 
BY 
EK. G. MAHIN AND J. F. BROEKER, JR. 
PURDUE UNIVERSITY 
Bearing metals that have been used successfully in industrial practice are 
alloys that crystallize as conglomerates upon cooling from the liquid con- 
dition. A commonly accepted theory accounts for the anti-frictional qual- 
ities of such alloys upon this basis. It is understood that there must be 
certain hard particles embedded 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 erystals 
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 
formed at that temperature or at a higher temperature. Also it is generally 
true that either flotation or settling occurs in the semi-liquid mass during 
cooling, since there are often considerable differences between the specific 
gravities of the solid and liquid portions. Growth and segregation may 
thus result in the formation of a bearing of very poor anti-frictional prop- 
erties, even though the composition of the alloy as a whole is correct. 
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 the experimental werk had the composition: tin 
85.70%, antimony 9.86%, copper 3.34%, zine 0.70% and lead 0.40%. The 
last two metals are to be 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 the 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 y-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. 
y-tin-antimony is the hardest constituent of this alloy and it also has 
the lowest specific gravity. It forms on the branch i-k of the liquidus of 
