Papers by Keyword: Creep Mechanism

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Authors: G. Kausträter, A. Yawny, M. Wagner, Birgit Skrotzki, Gunther F. Eggeler
Authors: Brian Wilshire, H. Burt
Authors: Hassan Osman, Mohd Nasir Tamin
Abstract: Creep deformation process of austenitic stainless steel foil with thickness 0.25 mm was investigated. The foil specimen was creep tested at 750oC, 54 MPa to establish baseline behavior for its extended use as primary surface recuperator in advanced microturbine. The creep curve of the foil shows that the primary creep stage is brief and creep life is dominated by tertiary creep deformation. The curve is well represented by the modified theta-projection concept model with hardening and softening terms. Morphology of fractured foil surface reveals intergranular fracture with shallow network of faceted voids. The formation of w-type creep cavities is significant, as revealed by microstructure of ruptured specimen. Composition analysis indicates the formation of carbides, namely, Cr23C6, NbC and Fe3Nb3C.
Authors: Bong Kook Bae, Chang Sung Seok, Jae Mean Koo, Hyung Ick Kim, K.Linga Murty
Abstract: A burst rupture test has been mainly used for evaluating the burst properties of internal pressurized tubes. Although the burst creep test provides accurate results, its complicated and material-wasting process makes it difficult to perform this test. In the burst test, it is known that the hoop stress is a main reason of burst, so it can be expected that the burst rupture properties are strongly related with the hoop creep rupture properties. A ring test is occasionally used for obtaining the hoop directional properties of tube-shaped structures. In this study, the creep rupture properties of Zirlo tubing are investigated at temperature ranging from 365 to 570  using the ring specimens. An analysis of the fractography was performed and the estimation of service life with Larson-Miller parameter was conducted. Finally, In view of the Dorn equation of power-law, the creep mechanism was determined and discussed.
Authors: Li Wu Jiang, Shu Suo Li, Mei Ling Wu
Abstract: The creep behaviors of a Ni3Al-base single crystal superalloy IC6SX prepared by spiral grain selection method was studied systematically under the testing condition of 760/540MPa. The microstructure evolution, movement of dislocations, formation of the dislocation networks and dislocation configuration during the creep process were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the creep performance of the single crystal alloy IC6SX is excellent under 760/540MPa. The experimental results showed that the creep curve of the Ni3Al-base single crystal superalloy IC6SX was divided into three stages, including decelerating creep stage, steady-state creep stage and accelerated creep stage. The microstructure and the dislocation configuration were different at different stage during the creep and the raft microstructure has not been formed. The creep mechanism was main slipping characterized by dislocation glide mechanism.
Authors: Zong Wu Li, Hao Feng Xie, Guo Jie Huang, Xue Feng, Li Jun Peng, Zhen Yang, Xu Jun Mi, Xiang Qian Yin
Abstract: In this paper, nominal composition of Cu-0.3Cr-0.07Ag (at%) was designed. The high temperature properties and microstructure were investigated by Transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that the tensile strength of CuCrAg decreases as temperature rises, which was associated with the coarsen precipitates according to TEM observation. Furthermore, observations of fracture morphology reveal that the mechanism transforms into brittle fracture from ductile fracture at elevated temperature. Creep curves were found to vary as a function of applied stress and temperature, the stress exponent values are 8.7, 4.6, 4.3 at 673K, 773K, 873K respectively. The mechanism is dislocation climbing at 773K and 873K while creep behavior at 673K could be explained by the invariant substructure model.
Authors: Supamard Sujatanond, Yoshiharu Mutoh, Yukio Miyashita, Yuichi Otsuka
Abstract: Tensile and compressive creep tests of the extruded magnesium alloy AZ91D were carried out in vacuum at 150°C under constant engineering stresses ranged from 60 to 150 MPa. From the test results, the secondary creep rate in tension was found to be significantly higher than that in compression. Moreover, the estimation method of creep curve under a constant true stress was proposed by considering the reduction of cross sectional area during tensile loading where the specimen cross-sectional area and length were measured periodically until the end of creep test. The creep curve under a constant true stress obtained in the present study was still different between tensile and compressive loadings. Therefore, it should be noted that the different creep curves and creep exponents should be used in the creep deformation analysis of structures.
Authors: M.Z. Berbon, Terence G. Langdon
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