Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Superalloy components are always produced by the way of investment casing. During investment casting, interfacial reactions may take place and bring about metal contamination and defect formation on the surface of the components. The influence of C content on the interfacial reaction and wettability between a Ni-based superalloy and ceramic mould was investigated by using a sessile drop method. The interfacial morphology and elements distribution were studied by SEM and EPMA. Activities of C, Cr and Al were calculated by using Thermo-Calc software. The relationship between interfacial reaction and wettability was discussed. It was found that when C content was higher than 0.1%, activity of C increased greatly and interfacial reaction took place. The wettability varied from non-reactive wetting to reactive wetting. In the reactive wetting systems, sand adhesions appeared and Al and Cr diffused to the ceramic surface.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The Ni- based single crystal superalloys are considered to be the major materials for advanced areo- engine blades. In order to improve the high temperature properties of Ni- based single crystal superalloys, many refractory elements are introduced into this kind of alloys. Recently Pt has been suggested to be the alloying elements of advanced Ni-based single crystal superalloys. However, there are no researches for the effects of Pt on creep rupture properties of advanced single crystal superalloys. In this work, the influence of Pt element on the creep rupture properties of a Re-containing single crystal superalloy was investigated. The high-temperature creep rupture properties of the Pt-containing Ni-based single crystal superalloy at 1100 ℃, 180 MPa and 1000 ℃, 310 MPa were investigated. The deformation microstructure and the morphology of dislocations were studied by SEM and TEM. The results show that the creep rupture life of Pt-containing superalloy decrease slightly at 1100 ℃, 180 MPa and decreased obviously at 1000 ℃ , 310 MPa. The fracture models of different alloys are all ductile fracture, and many irregular microviods and microcracks can be observed in the fracture surfaces. After high temperature creep deformation, regular dislocation networks formed at the g/g' interfaces. The differences of creep rupture properties among those alloys are that Pt element may promote the formation of TCP phase, and the interface between the TCP phase and g matrix may be favorite sites of the initiation of microvoids and microcracks.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni-based superalloys with high content of W are often used to manufacture gas turbine vanes and high temperature forging dies due to high temperature capability and low cost. The microstructure of Ni-based superalloys consists of g matrix, γ′ phase and carbides generally. The deformation mechanisms of alloy mainly include dislocation loops formation, shearing of dislocation into γ′ phase and formation of anti-phase boundary (APB) and stacking fault. Although the deformation mechanism of Ni-based superalloys has been studied widely, the relationship between tensile property and deformation mechanism of K416B superalloy at different temperature is still unclear up to now. Therefore, the influence of temperature on tensile behaviors of K416B Ni-based superalloy with high W content was investigated in the present work by means of tensile test at different temperatures. It has been found that the yield and tensile strengths of K416B alloy increase with rising temperature at 20~800 ℃. When the temperature exceeds 800 ℃, the tensile property of the alloy decreases gradually. The deformation feature of the alloy during tensile test at room temperature is that the dislocations shear into γ′ phase or cross γ′ phase by Orowan mechanism. As the dislocations shear into γ′ phase, they decompose to form the stacking fault. The dislocation density in the matrix of the alloy increases with the rising temperature and the dislocation tangles in the matrix play the role of strengthening in the alloy during tensile test at 800 ℃. As the temperature further enhancing, the amount of dislocations shearing into γ′ phase increases and then the tensile strength of the alloy decreases. Under the condition of middle-low temperature, the brittle fracture occurs in the alloy due to the fact that the cracks are initiated and propagated along M6C carbide with large size. During tensile test at high temperatures, the tensile fracture mode of the alloy is micro-porous aggregation along the g +γ′ eutectic interface, which is the main reason for the alloy exhibiting the ductile fracture.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni-based single crystal superalloys have been widely used to produce turbine blades for advanced aero-engines because of the super temperature-related microstructural stability and comprehensive mechanical properties. However, due to effects of the high temperature and complicated stresses in service, the microstructures of superalloys might gradually evolve and fail in different modes. The present paper reviews the progress of microstructural stability and mechanical behavior including the g' phase rafting, TCP phase precipitation, high temperature creep, low cycle fatigue and thermomechanical fatigue of single crystal superalloys. The addition of Ru improves the creep life of superalloys, but also indirectly promotes the occurrence of“topological inversion”. On the other hand, with the increase of aging temperature and time, the contents of refractory elements in m phase rise significantly. With the increase of applied tension stress, more m phase precipitate from the g matrix, whereas inverse tendency is shown under compression stress. Numerous planar defects are formed during precipitation of m phase, and these defects promote the nucleation of P and R phases. During high temperature and low stress creep, an important dislocation a<010> superdislocation is observed, which moves in the g' phase slowly by a combination of slide and climb. Under very high temperature, incubation with accelerating creep rate occurs before the primary stage, which relates to the extending process of the g width. At last, the stacking fault energy is significantly reduced after Ru additions, and thus a series of complex deformation mechanisms occur during low cycle fatigue, e.g. stacking faults penetrating g /g' interface, trailing a/6<112> Shockley dislocations shearing into the g' phase. During thermomechanical fatigue, the life of superalloys is influenced by the site of crack initiation, microstructural evolution and oxidation resistance.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： As-cast Ni-based superalloys with high W content are used extensively in the turbine vane of aeroengine due to their good heat resistance and temperature capability. During high temperature service, the creep deformations and microstructure evolution are occurred in the using materials, and the creep behavior mainly depends on their chemical composition and microstructure, such as size, distribution and morphology of g ' phase and carbides. Thereinto, the mophologies of carbide phases are closely related to creep resistance of the alloy. Generally, the carbide particles displaying dispersive distribution may enhance the creep resistance of the alloy, while the carbide with continuous morphologies distributed in the boundaries, they may provide easy paths for crack propagation and degrade the mechanical properties of the alloy. Besides the creep life of the alloy also depends on the microstructure evolution under high temperature. But the evolution mechanism of carbides in K416B superalloy during creep is still unclear up to now. For this reason, by means of creep property measurement and microstructure observation, the evolution behavior of precipitates in K416B Ni-based superalloy with high W content during high temperature creep has been investigated. The results show that the size of g ' phase is inhomogeneous in the as-cast alloy, and the stripe MC-carbide distribute in the inter-dendrite regions displaying Chinese structures. During high temperature creep applied stress, fine M6C carbide discontinuously precipitate in the deformed g matrix. The thermodynamics analysis indicates that the carbon element segregates in the regions of stress concentration and combines with carbide-forming elements W etc, which promoted the fine M6C carbide to precipitate from the g matrix. At the same time, the grooves are formed on the surface of stripe MC carbide, and then gradually decomposed and transformed into M6C particles. Thereinto, the additional press formed in the surface of stripe MC carbide is the main factor to promote the MC phase continuous dissolution and spheroidizing.
Subjects: Materials Science >> Materials Science (General) submitted time 2017-11-21 Cooperative journals: 《金属学报》
Abstract：本文采用低偏析异质籽晶法研究了定向凝固制备单晶高温合金的籽晶融合区形成机制，结果表明：籽晶回熔平衡界面前沿存在一个无微观偏析的融合区，该区域是凝固界面发生平面状-胞状失稳转变的过渡区。增加籽晶合金中W含量或提高定向凝固速率均会促进凝固界面的平面状-胞状失稳转变，且凝固速率的影响更显著。相比于传统籽晶法，低偏析异质籽晶融合区内的平界面凝固能有效避免籽晶回熔界面的枝晶熔断和成分过冷导致杂晶形核，从而提高铸件质量。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：研究了晶粒度对K417G高温合金在760℃/645MPa、900℃/315MPa和950℃/235MPa下的持久性能的影响。结果表明：晶粒度对合金持久性能的影响与实验条件有关。在760℃/645MPa下合金的持久性能随晶粒细化而提高，变形模式以晶内变形为主；900℃/315MPa下的持久性能随晶粒细化先升高后降低，变形模式由晶内变形和晶界滑移竞争作用；950℃/235MPa下的持久性能随晶粒细化而降低，变形模式以晶界滑移为主。TEM观察表明，760℃/645MPa 下，位错切过γ′相，基体通道中没有位错网产生；900℃/315MPa和950℃/235MPa下位错通过Orowan机制绕过γ′相，基体通道中产生位错网，并且M23C6在晶内析出。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：通过蠕变性能测试和组织形貌观察，研究了高钨K416B镍基合金高温蠕变期间析出相的演化行为，结果表明，铸态合金中γ￠相的尺寸不均匀，条状MC碳化物在枝晶间区域呈汉字型分布；在施加应力的高温蠕变期间，细小M6C碳化物可在形变基体中不连续析出，热力学分析认为：在应力诱导作用下，元素C偏聚在应力集中处，与W等碳化物形成元素结合，促使细小M6C相自基体中析出；同时，条状MC碳化物表面形成沟槽，并逐渐分解蜕变成粒状M6C相，其中，在条状MC相表面形成的附加应力是促使MC相不断溶解和发生球化的主要原因。
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