Papers by Keyword: Transformation Temperature

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Authors: Arne Kromm, Thomas Kannengiesser, Jens Gibmeier
Abstract: Tensile residual stresses introduced by conventional welding processes diminish the crack resistance and the fatigue lifetime of welded components. In order to generate beneficial compressive residual stresses at the surface of a welded component, various post-weld treatment procedures are available, like shot peening, hammering, etc. These post-weld treatments are, however time and cost extensive. An attractive alternative is to generate compressive stresses over the complete weld joint in the course of the welding procedure by means of so-called Low Transformation Temperature (LTT) filler materials. The volume change induced by the transformation affects the residual stresses in the weld and its vicinity. LTT fillers exhibit a relatively low transformation temperature and a positive volume change, resulting in compressive residual stresses in the weld area. In-situ measurements of diffraction profiles during real welding experiments using Gas Tungsten Arc (GTA)-welding process were realized successfully for the first time. Transformation temperatures during heating and subsequent cooling of LTT welding material could be assessed by means of energy dispersive diffraction using high energy synchrotron radiation. The results show that the temperature of martensite start (Ms) is strongly dependent on the content of alloying elements. In addition the results indicate that different phase transformation temperatures are present depending on the welding depth. Additional determination of residual stresses allowed it to pull together time and temperature resolved phase transformations and the resulting phase specific residual stresses. It was shown, that for the evaluation of the residual stress state of LTT welds the coexisting martensitic and austenitic phases have to be taken into account when describing the global stress condition of the respective material in detail.
Authors: Hua Ping Xu, Gao Feng Song, Xie Min Mao
Abstract: In this paper, single crystal of CuAlNiBe quaternary shape memory alloy was prepared in a high temperature gradient directional solidification furnace with a selective growing crystallizer. And its shape memory performance characters were systematically compared with other series copper base shape memory alloys. The results show that the single crystal of CuAlNiBe quaternary shape memory alloy has better shape memory properties.
Authors: Wei Sen Zheng, Yan Lin He, Xiao Gang Lu, Lin Li
Abstract: To predict phase equilibria of advanced high strength steels accurately, a new multicomponent thermodynamic database (FEDA) encompassing Fe, C, Mn, Si, Al and Ni is created according to relevant literatures. This study applies Thermo-Calc software to estimate phase transformation temperatures and phase fractions in ferrite and austenite two-phase region of test steels. Simultaneously, experiments are carried out with dilatometer and the quantitative metallographic analysis technology. It is found that the FEDA database is appropriate for predicting A1 temperature and phase fractions of Al-containing steels at low temperatures, while the TCFE6 database can be used to estimate A3 temperature. According to calculated phase fractions using FEDA database, a two-step heat treatment is made in order to achieve TRIP-aided steels. Samples annealed at 780°C for 3 min and held at 420°C for 5 min exhibit an optimum value of strength and ductility product up to 23690 MPa·%.
Authors: Kurnia Hastuti, Esah Hamzah, Jasmi Hashim
Abstract: Ti-50.7at.%Ni as one of Ni-rich TiNi shape memory alloy is very responsive to precipitation ageing treatment due to the formation of Ti3Ni4 precipitates. This study indicates that this alloy exhibits different transformation sequences under different ageing temperatures. Precipitation of Ti3Ni4 has introduced the formation of intermediate R-phase prior to martensitic transformation. The lack of 2-step R-phase transformation, B2→R1 and B2→R2 transformation in this alloy, suggested that Ti3Ni4 precipitation occurs homogeneously.
Authors: Zhao Wei Feng, Xu Jun Mi, Jiang Bo Wang, Zhi Shan Yuan, Jin Zhou
Abstract: Transformation behaviors and texture of Ni47Ti44Nb9 cold-rolled plates were studied by differential scanning calorimetry and X-ray diffraction test. R phase transformation does not occur in Ni47Ti44Nb9 cold-rolled plate annealed at 350°C-750°C followed by quenching into the water. Martensite transformation temperature first increases and then decreases with increment of annealing temperature, and the maximum achieves at 700°C. The heat of reverse martensite transformation increases, while hardness decreases as annealing temperature increases. The major texture of cold-rolled plate is {332} and spread from {332} to {110}. When the annealing temperature is above 600°C, the major textures are {332} and {111} recrystallization texture in secondary cold-rolled plate.
Authors: K.W.K. Yeung, Chun Yi Chung, K.M.C. Cheung, W.W. Lu, K.D.K. Luk
Authors: Hidefumi Date
Abstract: In order to clarify the effect of strain rates on phase transformation behaviors of Ni-Ti alloy, a compressive test using a cylindrical specimen of polycrystalline Ni-Ti alloy of Ti-50.69 at% Ni was carried out at a high strain rate and a low strain rate. The transformation temperatures were determined by a differential scanning calorimeter (DSC) using a sample cut from a compressed specimen. The transformation temperatures of the specimens before deformation were Ms= 303 K, Mf = 287 K, As = 297 K and Af = 319 K, respectively. The compressive test was carried out using specimen heated from liquid nitrogen temperature to room temperature. A universal testing machine as a static test apparatus and a Split Hopkinson Bar apparatus for a dynamic test were used. The specimen had a reoriented martensite phase after deformation because the superelastic effect was not observed upon unloading. Two reverse transformations during heating and a forward transformation during cooling were observed by DSC measurement. The first reverse transformation corresponds to that of thermal-induced martensite by immersion in liquid nitrogen and the second reverse transformation corresponds to that of reoriented martensite with slips in a polycrystalline matrix introduced by plastic deformation. The reverse transformation of the martensite phase with a slip exhibited strong strain rate dependency. Plastic strains and strain rate had strong influence on the shape recovery. The interaction between the temperature elevation by a conversion of plastic work and slip generated by dynamic plastic deformation is a complicated problem.
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