Tham khảo tài liệu 'volume 18 - friction, lubrication, and wear technology part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | The cavitation erosion resistance of cobalt alloys is superior to that of the stainless steels but their cost is considerably higher. The economic factors together with a better understanding of the factors responsible for the high erosion resistance of the cobalt alloys have simulated the recent development Ref 12 of new cavitation-resistant iron-base alloys. The success of this development is evidenced by the erosion data given in Fig. 4 for the new alloys designated IRECA and several iron- and cobalt-base commercial alloys. More comparative data on the erosion rates of various materials are given in the article Liquid Impingement Erosion in this Volume. Fig. 4 Cavitation erosion weight loss as function of exposure time measured on various standard and experimental alloys in ASTM G 32 vibratory tests. Source Ref 12 Surface Coatings and Treatments. The recent trend in materials development has been to specify a component for bulk property requirements and subsequently coat or treat the surface to provide the required environmental resistance. Welded overlays of stainless steels or cobalt alloys are commonly used to provide resistance to cavitation erosion. Several alternative coating techniques that have been investigated in the laboratory in recent years include arc-sprayed coatings Ref 24 plasma-sprayed coatings Ref 25 26 laser hardening cladding and alloying Ref 10 27 ion implantation Ref 28 29 and electroless nickel coatings Ref 30 . Plasma-sprayed coatings and laser treatments are beginning to be applied in practice for this purpose. Of these techniques plasma spraying Ref 31 is probably the most commercially well developed and offers flexibility in terms of the types of materials that can be sprayed. In addition the technique can be carried out in air in inert gas atmospheres or in a reduced-pressure environment. There are two major disadvantages of plasma-sprayed coatings. One is that the coating is generally only mechanically bonded to the substrate and .
