Effects Of Composition And Heat Treatment On Microstructure And Mechanical Properties Of CoCrW Alloys

CoCrW alloys have good wear resistance, corrosion resistance and high temperature oxidation resistance, which are often used to manufacture the blades and vanes of aviation jet engines, industrial gas turbines, marine gas turbine and the nozzle vanes. CoCrW alloys prepared by casting process ha ve low cost and good properties, which has been studied widely. The properties of the alloys mainly depend on the chemical compositions and microstructure of the alloys, when the chemical compositions of the alloys are changed and the alloys are treated by heat treatment, the microstructure of the alloys will be changed, the properties of the alloys will be changed accordingly.In this paper, two kinds of CoCrW alloys with different Fe contents were prepared by casting process and, the effects of different heat treatment processes on microstructure, hardness and wear resistance of two kinds of alloys were studied. The results show that the microstructures of the two as-cast alloys are composed of M23C6, M6 C and γ-Co matrix. The increase of Fe content promotes the precipitation of the γ-Co phase, and reduces the precipitation of the carbide phase, which makes the content of carbides in 3Fe alloy decrease. After heat treatment, the phase compositions of the two alloys have not changed, but the size, morphology and distribution of each phase change obviously. A large amount of M23C6 phase in the alloy are dissolved after solid solution treatment, with the increase of solid solution temperature, a large amount of M6 C phase are also solid soluted, and the matrix phase content increase, M23C6 and M6 C phase are precipitated in the matrix uniformly after aging treatment.The hardness of the two as-cast alloys is relatively high. The decrease of the number of the carbides makes the hardness of the alloy decrease after solid solution treatment, with the increase of solid solution temperature, the Cr、W and other alloying elements in the carbides are solid soluted into the γ-Co matrix so as to strengthen the matrix resulting in the improvement of the hardness of the alloy. The secondary precipitated carbides which distribute in the matrix uniformly after aging treatment play a dispersion strengthening effect, which increase the hardness of the alloy significantly.The hardness of the two as-cast alloys is relatively high, so the wear weight loss is few, the friction coefficient is low, and the wear resistance is good. The decrease of the hardness of the two alloys after solid solution treatment makes the wear resistance decrease, after aging treatment, the hardness of the two alloys increase significantly, and the wear resistance increase accordingly. In anyone state, the hardness of 1Fe alloy is always higher than that of 3Fe alloy, the wear resistance of 1Fe alloy is better than that of 3Fe alloy in this paper. The surface of the grinding crack of the two kinds of alloys under different state has a lot of fatigue spalling and oxide layer, which shows that the wear mechanism of the two kinds of alloys under different state was the interaction of abrasive wear, adhesive wear and oxidation wear.