Strengthening Mechanisms And Hot Deformation Characteristics Of MP159 Alloy

With the development of the aerospace industry, higher and higher strength and corrosion resistance is needed for key fasterners. Many conventional superalloys can not meet the above demands any longer. MP159 alloy is so far the best suitable candidate for meeting the above needs. MP159 alloy, a new kind of cobalt-base wrought superalloy, possesses the unique combination of high strength, ductility and corrosion resistance, and is widely used for key fasterners of advanced aviation engines abroad.MP159 alloy has been introduced and applied since early 1990s in China, but many problems have occured during practical application due to lack of knowledge of many aspects such as strengthening mechanisms, the relationship between micro structure and properties and hot deformation characteristics. In order to solve these problems and promote its wide applications, it is necessary to investigate the strengthening mechanisms and hot deformation characteristics for MP159 alloy systematically.A software has been developed for computing and plotting composite electron diffraction patterns of MP159 alloy between fcc matrix and twin, and/or fcc matrix and hexagonal close packed e -martensite(hcp). Composite electron diffraction patterns of many low index matrix orientations in MP159 alloy are simulated by means of the developed software. As a result, the favorable matrix orientations which can unambiguously distinguish deformation twins from the hep-phase are <011>, <521> and <411>. Among them, the most favorable matrix orientation is <011>. According to favorable matrix orientations, the cold deformed microstructural features in MP159 alloy are investigated by TEM. The results show that the cold deformation strengthening of MP159 alloy results predominately from the formation of the intersecting network of thin deformation twin platelets with high density of stacking faults during cold deforming in equiaxed fcc grains under solution treated condition. No hep-phase has been found in many observed results of TEM, so it is worth to doubt about the opinion in available literature that the cold deformation strengthening in MP159 alloy is due to hep-phase.The results of investigating aging strengthening mechanisms by TEM in MP159 alloy indicate that both solution treated and cold deformed MP159 alloy can be strengthened byaging heat treatment. The strengthening is attributable to the precipitation of dispersively distributed Ni₃Al type ordered solution particles.Study on the hot deformation characteristics of MP159 alloy is carried out for the first...