Erosion-resistant blades

Niobium carbide is used as a component of hard metals, eg, mixtures of metal carbides that are cemented with cobalt, iron, and nickel. Along with tantalum carbide, niobium carbide is added to impart toughness and shock and erosion resistance. The spiraling rise in the price of tantalum has spurred the development of a hafnium carbide—niobium carbide substitute for tantalum carbide (68). These cemented carbides are used for tool bits, drill bits, shovel teeth, and other wear-resistant components turbine blades and as dies in high pressure apparatus (see Carbides). 

The seaweeds known as kelps and giant kelps (Laminariales) are built in such a way that they produce detritus more or less continuously. All are divisible into holdfast, stipe and blade (Fig. 7) and the blades normally have a growth zone at the base and a zone of erosion near the tip. They have been likened (Mann, 1972b) to "moving belts of tissue". Growth at the base compensates for erosion at the tip, and in the process large amounts of detritus, both particulate and dissolved, are released into the water. This detritus is readily colonized by bacteria (Laycock, 1974) and appears to be less resistant to digestion by animals than the detritus derived from vascular plants. 

By the nature of the feeding mechanism, rotary valves are more suited to relatively nonabrasive materials. This is particularly the case where they are used to feed materials into positive pressure conveying systems. By virtue of the pressure difference across the valve, and the need to maintain a rotor tip clearance, air will leak across the valve. Wear, therefore, will not only occur by conventional abrasive mechanisms, but by erosive wear also. Air leakage through the blade tip clearances can generate high velocity flows, which will entrain fine particles, and the resulting erosive wear can be far more serious than the abrasive wear. Wear resistant materials can be used in the construction of rotary valves, and removable... 

Applications. In addition to its high corrosion resistance, Ti-15Mo-5Zr-3Al has high strength. It can be used in various applications where many other titanium alloys cannot be used. For example, it is a candidate material for sour gas well plants because of its high strength-to-densily ratio and resistance to atmospheric stress-corrosion cracking. Moreover, it is currently used as an erosion shield material for 1015 mm (40 in.) titanium turbine blades in power plants. 

This inherent property reduces the amormt of heat treating and postmachining. 6B has outstanding resistance to cavitation erosion. Steam turbine erosion shields fiem 6B have protected the blades of turbines for years of continuous service. 6B has good impact and thermal shock resistance, resists heat and oxidation, retains high hardness even at red heat (when cooled, recovers ffill original hardness), and has resistance to a variety of corrosive media. 6B is useftd where both wear and corrosion resistance are needed. 

---