WEAK AND LUBRICATION 



Fig. 4. Electron micrograph of a positive car- 

 bon replica of a finely ground steel surface (1212 

 micro-inches C. L. A.) 5000X 



Fig. 5. Direct reflection electron micrograph 

 showing a scratch on a mechanically polished sur- 

 face finished with finest abrasive paper. 2500X 



Debris from worn surfaces and abrasive 

 particles which have been separated from 

 the lubricant by centrifuging (9) may be 

 conveniently examined in the electron micro- 

 scopes by standard methods (Fig. 6). Such 

 examination may reveal the size, shape and 

 possibly the abrasive natiu'e of the debris 

 while micro-diffraction may be used for 

 identification. Both optical and electron 

 microscopy can be used together with metal- 

 lographic methods to elucidate changes 

 effected by deformation and strain. Elegant 

 extraction replica techniques (11, 12) are 



available which in conjunction with electron 

 diffraction can be used to determine pre- 

 cipitation segregation while the recent micro- 

 probe anal.ysis technique (13) can be applied 

 to elucidate solution segregation especially 

 on a micro-scale. 



In prevention of wear, the principal task 

 of a lubricant which maj^ be liciuid, solid or 

 gaseous is to enable one solid surface to move 

 over another wilh low friction and with a 

 minimum of damage. This object can be 

 achieved if the lubricant film is thick enough 

 to keep the surfaces apart and hydrodynamic 

 conditions prevail. However for these condi- 

 tions to be realized loads must generally be 

 low and sliding speeds high. If such ideal 

 conditions cannot be maintained other forms 

 of lubrication such as boundary or mixed 

 film may exist. Where this is so the surfaces 

 come into contact and damage in the form 

 of wear occurs (14, 15). 



Useful information concerning the be- 

 havior of lubricating oils can be obtained by 

 microscopic investigation of the insoluble 

 carbon with which they become contami- 

 nated in practice (Matthews et al. (16)). 

 Electron microscopy can also be used to 

 study the additives which are incorporated 

 in modern lubricating oils to impart or re- 

 inforce some desirable property. The elec- 



FiG. (i. Electron micrograph of debris from 

 fretting corrosion damage of a steel surface. Shad- 

 owed at 450° with gold-palladium. lO.OOOX (After 

 Scott and Scott^) 



311 



