Cobalt-based alloy is a cemented carbide that can withstand various types of wear, corrosion and high-temperature oxidation. It is commonly referred to as cobalt-chromium-tungsten (molybdenum) alloy or Stellite alloy (Stellite alloy was invented by American Elwood Hayness in 1907). Cobalt-based alloys are based on cobalt as the main component, containing a considerable amount of nickel, chromium, tungsten, and a small amount of alloying elements such as molybdenum, niobium, tantalum, titanium, lanthanum, and occasionally iron. According to the different components in the alloy, they can be made into welding wire, powder used for hard surface welding, thermal spraying, spray welding and other processes, and can also be made into castings and forgings and powder metallurgy parts.
Classification
Classified by use, cobalt-based alloys can be divided into cobalt-based wear-resistant alloys, cobalt-based high-temperature alloys, and cobalt-based wear-resistant and aqueous solution corrosion alloys. In general operating conditions, in fact, they are both wear-resistant, high-temperature, wear-resistant and corrosion-resistant. Some operating conditions may require high-temperature, wear-resistant and corrosion-resistant at the same time, and the more complex the work is Under the circumstances, the more it can reflect the advantages of cobalt-based alloys.
Grade
The typical grades of cobalt-based high temperature alloys are: Hayness188, Haynes25(L-605), Alloy S-816, UMCo-50, MP-159, FSX-414, X-40, Stellite6B, etc. Chinese grades are: GH5188(GH188 ), GH159, GH605, K640, DZ40M, etc. Unlike other superalloys, cobalt-based superalloys are not strengthened by an orderly precipitated phase firmly bonded to the matrix, but are composed of an austenite fcc matrix that has been solid solution strengthened and a small amount of carbides distributed in the matrix. Casting cobalt-based superalloys relies heavily on carbide strengthening. Pure cobalt crystals have a hexagonal close packed (hcp) crystal structure below 417°C, which transforms to fcc at higher temperatures. In order to avoid this transformation during use of cobalt-based superalloys, virtually all cobalt-based alloys are alloyed with nickel to stabilize the structure from room temperature to melting point. Cobalt-based alloys have a flat fracture stress-temperature relationship, but they show better thermal corrosion resistance than other high temperatures above 1000°C. This may be due to the higher chromium content of the alloy, which is the most important of this type of alloy. A feature.
Development path
The development process of cobalt-based superalloys In the late 1930s, due to the need for turbochargers for piston aero-engines, the development of cobalt-based superalloys began. In 1942, the United States first succeeded in manufacturing turbocharger blades with dental metal material Vitallium (Co-27 Cr-5 Mo-0.5Ti). During use, this alloy continuously precipitates carbide phase and becomes brittle. Therefore, the carbon content of the alloy was reduced to 0.3%, and 2.6% of nickel was added to improve the solubility of the carbide forming elements in the matrix, thus developing into the HA-21 alloy. At the end of the 1940s, X-40 and HA-21 produced cast turbine blades and guide vanes for aviation jet engines and turbochargers, and their operating temperature could reach 850-870°C. S-816, which appeared in 1953 for forging turbine blades, is a solid solution strengthened alloy with a variety of refractory elements. From the late 1950s to the late 1960s, 4 cast cobalt-based alloys were widely used in the United States: WI-52, X-45, Mar-M509 and FSX-414. Most of the deformed cobalt-based alloys are plates, such as L-605 used to make combustion chambers and ducts. HA-188, which appeared in 1966, has improved oxidation resistance due to its lanthanum content. The cobalt-based alloy ∏K4 used in the Soviet Union to make guide vanes is equivalent to HA-21. The development of cobalt-based alloys should consider cobalt resources. Cobalt is an important strategic resource. Most countries in the world lack cobalt, which limits the development of cobalt-based alloys.