Research For 700 ℃ Thermal Power Turbine Blades Nickel-based Heat-resistant Alloys

In this paper, it is regarded as the research object that several kinds of nickel-based alloy USC141, N105, A617and Waspaloy, which are foreign recommended to be used as700℃turbine blade. And on the basis of USC141, two kinds of test samples are designed by adjusted or added alloy element content. Through the contrast experiment study of the six test samples, two certain test samples, A617and Waspaloy, have been chosen to be used for the thermal power turbine blade material at700℃parameter.After the conventional heat treatment, the test material thermodynamics simulation and aging for100h,300h,500h,1000h,2000h and5000h, it was tested that the mechanics performance of conventional test and long-term aging precipitation in the process of the mechanical properties of the tested samples. And the comparative study was carried on.The result of the thermodynamics simulation calculation shows that, the main precipitated strengthening phase in equilibrium of all test samples at700℃are phase γ’ and phase M23C6. Waspaloy alloy has the optimal organization, with a higher quantity of the strengthening phase precipitation and the lowest harmful phase precipitation.After the conventional heat treatment, referenced to the recommended heat treatment process, in the test sample N105there is precipited a great number of y’ phase, a precipitation strengthening phase, as high as36%. That could significantly improve the strength and hardness of the material, and greatly reduce the plasticity and toughness of materials, what leads to a poor materials mechanical processing performance. Preliminary the alloy should be ruled out. Contrast the composition of other test samples in addition to the N105. For adding similar amount of element Cr (about20%), USC-1, USC-2, USC-3and A617are all added10-15%of Mo (or W). That could lead to a large number of precipitation of M6C carbide with rich Mo (or W) in the process of long-term aging, which could substantially reduce the plastic of the material at a high temperature. While with the less relative content of Mo, the type of carbide precipitation is M23C6which mainly rich Cr in the test sample Waspaloy, and its precipitation is very a little. The plastic of Waspaloy in a high temperature keep good.In the process of long-term aging, the main type of carbides precipitated in alloy Waspaloy are M23C6carbide and TiC, and they will be coarsening on the grain boundary during the process of aging. But because of their less precipitation and gradually leveling off, they don’t have much impact to material of plastic. The types of carbides precipitation in USC-1, USC-2, USC-3and A617mainly are M6C and M12C, or M23C6type and M6C type carbides. In the process of long-term aging, they are coarsening significantly. And the amounts of their precipitation are much more and continue to increase. In the process of long-term aging, M6C type carbides could transform to M12C type carbide, and the large amount of precipitation of Mo-rich M6C or M12C type carbides can significantly reduce the plasticity and toughness of materials.At the beginning of the aging, the precipitation amounts of γ’ phase in all test samples all increase in a large number, and they all have a tendency to grow up. After2000hours aging, the quantity and structure of γ’ phase in all test samples both become basic stable. Their size range mainly concentrated in the18nm-60nm, and their average size in about40nm-45nm. When aging5000h, the actual amount of precipitation of γ’ phase in Waspaloy alloy is the most, and there is still an increasing trend. Its precipitation strengthening for the matrix is the best.Experimental results show that in the process of long-term aging, comprehensive mechanical performance of Waspaloy is the most stable, and its structure is optimal. It is the best alternative materials for turbine blade of thermal power at700℃. Refer to the components of Waspaloy, simulation should be taken to optimize and design the components of other test samples by using the thermodynamic calculation software Thermo-Calc. It should be made sure that in the process of long-term aging they could be precipitated more γ’ phase and a small amount of M23C6type carbide. But it should be avoided precipitating a lot of M6C type carbides to ensure good plasticity and toughness, in order that the material has good mechanical properties at room and high temperature.