|
|||||||||||||||
|
|||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Wear
resistance (1)“Thermal Spray Terminology and Company Origins” Published in 2001 by the ASM Thermal Spray Society, Materials Park, Ohio Mechanical wear is divided into five (5) categories each of which recognizes the mechanisms causing the damage. As noted previously, these are: · abrasive Abrasive wear There are two (2) recognizable types of abrasive wear – low temperature and high temperature. The dividing line is approximated at about 900°F (482°C) or the maximum service limit for tungsten carbide (WC) coatings. Abrasive wear occurs when hard particles, present between rubbing surfaces, cut and tear material from either or both surfaces. This results in a decrease in surface finish, dimensional tolerances and performance. Any hard particles as dust, sand, oxides, debris, etc. can cause abrasive wear. Typically, they are introduced by an outside source as ingested air, lubricants or the debris resulting from mate face rubbing. Some frequently used coating materials used to reduce/prevent abrasive type wear are: Low temperature wear: · Aluminum bronze alloys High temperature wear: · Aluminum quasicrystal alloys Adhesive wear Surfaces that resist adhesive wear are typically
bearings that rub and slide over/against a mating surface as a
tribological couple. Bearing coatings should be either softer
than the mate face or be of equal hardness. Either serves to prevent
loss of finish, dimensional tolerance and functional performance.
Soft bearings wear in preference to the mating surface and tend
to self align. Hard bearings are designed to be more precisely
aligned and to accept higher loads. · Aluminum bronze alloys · Triballoy 400 Fretting Anti-fretting coatings are used at either low
temperatures or high temperatures. As previously, the dividing
point is the usefulness of tungsten carbides. Anti-fretting coatings
must resist repeated loading over prolonged periods of time. Intended
loading may be as in an operating cycle or unintended where vibrations
set up small amplitudes between surfaces. With either condition
repeated loading sets up alternating stress that cause damage.
· 83/17 tungsten carbide/cobalt composites Erosion Erosion resistant coatings are also used at low and high temperatures and again tungsten carbide and 900°F (384°C) is the dividing point. Hard particles impacting upon a surface at high velocity causes erosion by dislodging material from it. Coatings with excellent erosion resistance are: Cavitation Cavitation resistant surfaces display a dynamic Materials used to resist cavitation include: · NiCrB self fluxing alloys |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
