Erosion cobalt-based alloys

The abrasion resistance of cobalt-base alloys generally depends on the hardness of the carbide phases and/or the metal matrix. For the complex mechanisms of soHd-particle and slurry erosion, however, generalizations cannot be made, although for the soHd-particle erosion, ductihty may be a factor. For hquid-droplet or cavitation erosion the performance of a material is largely dependent on abiUty to absorb the shock (stress) waves without microscopic fracture occurring. In cobalt-base wear alloys, it has been found that carbide volume fraction, hence, bulk hardness, has Httie effect on resistance to Hquid-droplet and cavitation erosion (32). Much more important are the properties of the matrix. 

Being less plentiful and more expensive than nickel, cobalt is usually alloyed with chromium for applications where the alloys have practical advantages over similar nickel- or iron-base alloys. The cobalt-base alloys, for example, are better resistant to fretting corrosion, to erosion by high-velocity hquids, and to cavitation damage. 

By virtue of these crystallographic features, the cobalt-based alloys are inherently resistant to those forms of wear that involve a microfatigue constituent, namely sliding wear, fretting, cavitation erosion, and liquid droplet erosion [7],... 

Fie. 10 Relative erosion factors for selected commercially available metals at an impingement angle of 90°. Stellite 6B cobalt-base alloy was used as the reference material. Source Ref 5... 

Make the eroding surface resistant to corrosion. Examples include the use of cobalt-base hardfacing alloys to resist liquid erosion, cavitation, and slurry erosion aluminum bronze hardfacing alloys to prevent cavitation damage on marine propellers or to repair props that have... 

The corrosion rate of Pb02 - often enhanced by mechanical erosion - is relatively high and may be a problem due to the toxicity of lead. Pb02 can be stabilized by modification with, for example, silver, antimony, tin, cobalt oxides (or by alloying of the lead base metal with these metals, respectively) [29]. 

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