Description:

Cobalt chromium tungsten alloy (CoCrW) is one of the (Stellite) alloys. Stalli alloy is a kind of hard alloy that can resist various wear, corrosion and oxidation at high temperature. Commonly referred to as cobalt-based alloys. Stalli alloy was originally a Co-Cr binary alloy and later developed into a Co-Cr-W ternary alloy. Cobalt-chromium-tungsten alloy contains a considerable amount of chromium, tungsten and a small amount of nickel, molybdenum, silicon, carbon, niobium, tantalum and other alloying elements, and occasionally also contains iron. According to the alloy composition, it can be made into welding wire. The powder can be used for hard surface surfacing, thermal spraying, spray welding, etc., and can also be made into castings, forgings and powder metallurgy parts. The main carbides in cobalt-chromium-tungsten alloys are MC, M23C6 and M6C. In the cast cobalt-chromium-tungsten alloy, M23C6 precipitates between grain boundaries and dendrites during slow cooling. In some alloys, the fine M23C6 can form a eutectic with the matrix γ. MC carbide particles are too large, which has little effect on dislocations, and has little effect on alloy strengthening. However, finely dispersed carbides have a good strengthening effect. The carbides on the grain boundary (mainly M23C6) can prevent the grain boundary from slipping, thereby increasing the fracture strength. The microstructure of Co-Cr-W superalloy HA-31 (X_(?)_(40) is the dispersion strengthening phase (CoCrW)~(6C) carbide). In some Co-Cr-W alloys, topologically dense phases, such as Sigma and Laves phases, are harmful and make the alloy brittle. Cobalt-chromium-tungsten alloys are rarely strengthened with intermetallic compounds because Co3(Ti, Al) and Co3Ta are not stable enough at high temperatures, but non-cobalt-chromium-tungsten alloys reinforced with intermetallic compounds have also been developed. The thermal stability of carbides in Co-Cr-W alloys is better. When the temperature rises, the growth rate of carbides in the Ni-based alloy is slower than that of the γ phase, and the re-dissolution temperature in the matrix is ​​also higher (up to 1100°C). Therefore, when the temperature rises, the growth rate of the γ phase in the Ni-based alloy is The ratio is higher than that of Ni-based alloys. The strength decrease of Co-Cr-W alloy is generally slower. Cobalt-chromium-tungsten alloy has good heat resistance and corrosion resistance. It is generally believed that cobalt-chromium-tungsten alloys are superior to nickel-based alloys in this respect because of the melting point of cobalt sulfide (such as Co-Co4S3 eutectic). The sulfide melting point of nickel is higher than that of nickel (such as Ni-Ni3S2 eutectic 645°C), and the diffusion rate of sulfur in cobalt is much lower than that of nickel. Since the chromium content of most cobalt-chromium-tungsten alloys is higher than that of nickel-based alloys, a Cr2O3 protective layer of alkali metal sulfate (such as corrosion-resistant Na2SO4) can be formed on the surface of the alloy. However, the oxidation resistance of cobalt-chromium-tungsten alloys is generally much lower than that of nickel-based alloys. Cobalt chromium tungsten alloy is widely used in locomotive diesel engines, nuclear power plant valves, marine diesel engines and various aircraft. Early Co-Cr-W alloys were produced through non-vacuum melting and casting processes. Later developed alloys, such as Mar-M509 alloy, contain more active elements, such as zirconium, boron, etc., and are produced by vacuum melting and vacuum casting methods. Common cobalt-chromium-tungsten alloys lack coherent strengthening phases. Although the medium temperature strength is low (only 50% of the nickel-based alloy), it has higher strength, good thermal fatigue resistance, thermal corrosion resistance and wear resistance when it is higher than 980°C. And has good weldability. Suitable for jet engines, industrial gas turbines, marine gas turbine guide vanes and nozzle guide vanes, diesel engine nozzles, etc.

 

Application field：

lLocomotive diesel engine

lNuclear power plant valve

lMarine diesel engine

lAirplane