Abrasion 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. 

Fabrication of powder metallurgical steels especially hard materials such as tungsten carbide and nickel- or cobalt-based alloys showing maximum abrasion or corrosion resistance. HIP combines sintering and densification simultaneously in one process. 

Alloy Compositions and Product Forms. The nominal compositions of various cobalt-base wear-resistant alloys are Hsted in Table 5. The six most popular cobalt-base wear alloys are Hsted first. SteUite alloys 1, 6, and 12, derivatives of the original cobalt—chromium—tungsten alloys, are characterized by their carbon and tungsten contents. SteUite aUoy 1 is the hardest, most abrasion resistant, and least ductile. 

The process is used to apply abrasion protective coats of cobalt and nickel-based alloys. Tungsten carbides (there is a choice of square or round carbides) are used to enhance abrasion protection on the screw flights, they are not used on the drive faces as the roughness which appears there during their use impedes the transportation of the ceramic material (Fig. 5). 

P-BN tools work satisfactorily in hardened steel up to contact temperatures of 1000°C, since there is no chemical reaction between boron nitride and iron. This, however, also depends on the binding phase of the polycrystalline materials and can lead to adhesive wear [24, 25]. In hard steel, the main wear mechanism on the tool is abrasion by hard alloy carbide particles [26]. In the case of Co-based super alloy (Vitallium), the results on hard-BN tool wear are somewhat incongruous [27, 28], while Inconel 718 can be machined under proper selection of the cutting conditions [29]. Apparently, austenitic steels containing a high percentage of Co are difficult to cut by hard-BN tools, due to the formation of cobalt nitrides which leads to high tool wear [8]. 

The name Wallex designates a line of cobalt-base hard-surfacing alloys. All of them resist corrosion well, but they vary in their ability to resist abrasion and impact, and in the way they can be applied. Wallex alloys would seldom be recommended for protection against corrosion alone. In most cases, they are chosen for their ability to fight the twin hazards of corrosion and abrasion. The specific alloy choice depends on a careful analysis of the extent of the problem presented by each hazard. 

Shortly after the powder/liquid acrylic denture bases were introduced, they were adapted to customized crown and bridge use, (Fig. 2) first as full crowns and facings to be cemented to natural teeth. Because of poor abrasion resistance of the acrylics in such locations, techniques, have been modified to use metals such as the gold and the cobalt alloys, as the supporting and occluding surfaces with acrylic facings held thereon mechanically. Abrasion of crown... 

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