Papers by Keyword: In Situ X-Ray Diffraction (XRD)

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Authors: Esa Vuorinen, Xiang Chen
Abstract: The in-situ X-ray diffraction observations of the bainitic transformation of silicon alloyed steels were performed using the high temperature X-ray diffraction technique. The experimental results have shown that the volume fraction and carbon content of austenite remains a constant value which indicate that the transformation is almost finished after the early stages of austempering transformation. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation due to a heterogeneous distribution of carbon in different regions of austenite and thus exists two types of austenite: low-carbon austenite (γLC) and the high-carbon austenite (γHC). The experimental results supports that the bainite growth is by a non-diffusive mechanism when austempering temperature is in the lower bainite transformation temperature.
Authors: Musfiroh Jani, Mark E. Hodson, Ann M. Chippindale
Abstract: This study presents the experiments on the in-situ powder XRD on pure hydrous ferrous sulfate (FeSO4.nH2O) mineral. The progress of this mineral was monitored at different relative humidities and temperatures. The phase transformation from melanterite (FeSO4.7H2O) to rozenite (FeSO4.4H2O) and the phase transformation of rozenite (FeSO4.4H2O) to szomolnokite (FeSO4.H2O) were obtained.
Authors: Jean Marie Drezet, Bastien Mireux, Guven Kurtuldu
Abstract: During solidification of metallic alloys, coalescence corresponds to the formation of solid bridges between grains when both solid and liquid phases are percolated. As such, it represents a key transition with respect to the mechanical behaviour of solidifying alloys and to the prediction of solidification cracking. Coalescence starts at the coherency point when the grains begin to touch each other, but are unable to sustain any tensile loads. It ends up at the rigidity temperature when the solid phase is sufficiently coalesced to transmit macroscopic tensile strains and stresses. This temperature, also called mechanical or tensile coherency temperature, is a major input parameter in numerical modelling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. The rigidity temperature has been determined in Al Zn alloys using in situ X-ray diffraction (XRD) during casting in a dog bone shaped mould. This set-up allows the sample to build up internal stress naturally as its contraction is prevented. The cooling on both extremities of the mould induces a hot spot at the middle of the sample which is irradiated by X-rays. Diffraction patterns were recorded every 0.5 s using a detector covering a 426 x 426 mm2 area. The change of diffraction angles allowed us to observe agglomeration/decohesion of growing grain clusters and to determine a solid volume fraction at rigidity around 98 % depending on solidification time for grain refined Al 6.2 wt% Zn alloys.
Authors: John A. Francis, Richard J. Moat, Hamidreza Abdolvand, Alexander Forsey
Abstract: Residual stresses in welded joints must be quantified in order to carry out structural integrity assessments on critical nuclear components. This usually requires the application of finite element models for components with wall thicknesses exceeding 50 mm. In ferritic steels, the development of residual stresses is made more complex by the strains associated with the solid-state phase transformations that occur during heating and cooling. Finite element models often do not account for factors that contribute to anisotropy in the transformation strains, such as Greenwood-Johnson plasticity and variant selection. In this work, we search for evidence that might reveal which mechanism (s) contributes to this anisotropy. Coupons of SA508 steel were subjected to simulated welding thermal cycles, with and without external loading, and in-situ X-ray diffraction was used to track changes in crystal structure. The results were checked for evidence of plastic deformation in austenite and variant selection in its daughter phases.
Authors: Enrique Díaz Barriga-Castro, Armando Salinas-Rodríguez, Enrique Nava-Vázquez
Abstract: The aim of the present work is to determine the austenite to ferrite transformation temperatures in a Si-Al non-oriented electrical steel. Critical transformation temperatures on heating and cooling are determined using an in-situ X-ray diffraction technique where the specimen is heated or cooled in a stepwise manner. The transformation temperatures are estimated from changes in the intensities of the (110)α and (111)γ peaks as a function of temperature. The time evolution of the microstructure resulting from isothermal heat treatments at temperatures between 800 and 1000 °C applied after cooling from 1050 °C is followed by quantitative metallography on samples quenched into water. The results show that, on cooling, formation of ferrite starts at about 950 °C and ends at 790 °C, indicating a strong effect of Si and Al on the austenite to ferrite and eutectoid transformations. These results suggest that the low tensile ductility exhibited by this material at temperatures near 1000 °C can be attributed to strain localization in strain-induced ferrite formed at temperatures as high as 1025 °C.
Authors: Rui M.S. Martins, Norbert Schell, H. Reuther, Luís Pereira, Rui Jorge C. Silva, Karimbi Koosappa Mahesh, Francisco Manuel Braz Fernandes
Abstract: Ni-Ti SMA are smart materials undergoing first order martensitic transformations driven by temperature and/or stress. In the form of film they are very attractive candidates for microelectro- mechanical system (MEMS) applications. Future directions include the production of functionally graded films by changing deliberately the ratio Ti/Ni across their thickness. However, for the successful development of this type of films, it is important to characterize, model and control the variations in composition, crystalline structure and transformation temperatures. Our approach is in-situ XRD study of the actual growth of the films of varying composition along the thickness carried out using a deposition chamber installed at a synchrotron radiation beamline. These studies were complemented with ex-situ analysis techniques. The results achieved on a Ni-Ti film co-sputtered from Ni-Ti and Ti targets on a TiN buffer layer are presented in this paper. The deposition started by using optimised parameters for a near equiatomic composition. After 1 h (≈330 nm thick film), the Ti power was increased from 20 to 25 W, leading to the precipitation of Ti2Ni. The evolution of the lattice parameter values of the B2 phase, calculated from the corresponding XRD data, is clearly linked with the increase of the Ti power. The depth profile of the atomic concentrations determined by Auger Electron Spectroscopy (AES) is in agreement with the in situ XRD results. The temperature dependence of the electrical resistivity was used to monitor phase transformations, Scanning Electron Microscopy (SEM) has shown the presence of twinned martensite on the film’s surface at room temperature.
Authors: Yusoff M.S. Meor, Paulus Wilfred, Muslimin Masliana
Abstract: Pure calcium phosphate and ZrO2 doped calcium phosphate biomaterials were synthesized using an organic based phosphoric acid (DEHPA) as its starting material. The precipitated products obtained from the sol-gel reaction were then used to compare the phase transformation using in-situ XRD. The study shows that amongst the notable difference between these two samples is that the ZrO2 doped calcium phosphate tends to form the β-Ca(PO3)2, β-TCP and HA phases at lower heating temperatures compared to the pure calcium phosphate. Another major different seen in the phase transformation of the ZrO2 doped calcium phosphate is the transformation of β-TCP into HA before it leads to the formation of α-TCP at higher temperatures.
Authors: Ian Pong, Christian Scheuerlein, Carmine Senatore, Ludovic Thilly, Marco Di Michiel, Alexandre Gerardin, Simon C. Hopkins, Luc-Rene Oberli, Guillaume Geandier, Bartek A. Glowacki, Luca Bottura
Abstract: In order to investigate the high temperature exposure effect on Nb Ti/Cu superconducting strands, as might be encountered in joining by soldering and in cabling annealing, X-ray diffraction and resistometry measurements were performed in situ during heat treatment, and complemented by conventional metallography, mechanical tests and superconducting properties measurements. Changes of the Nb Ti nanostructure at temperatures above 300°C are manifested in the degradation of critical current in an applied external magnetic field, although degradation at self field was insignificant up to 400°C for several minutes. Above 500°C, the formation of various Cu Ti intermetallic compounds, due to Ti diffusion from Nb Ti into Cu, is detected by in situ XRD albeit not resolvable by SEM-EDS. There is a ductile to brittle transition near 600°C, and liquid formation is observed below 900°C. The formation of Cu Ti causes a delayed reduction of the residual resistivity ratio (RRR) and adversely affects the deformation behaviour of the strands.
Authors: N. Karimi, Henri Buscail, Frédéric Riffard, F. Rabaste, Régis Cueff, Christophe Issartel, Eric Caudron, Sébastien Perrier
Abstract: The aim of the present work is to investigate the effect of Lanthanum surface addition on the oxidation behaviour of the AISI 304 stainless steel, in air, at 1000°C. The in situ X-ray diffraction (XRD) analyses on the blank steel reveal that after the first 10h oxidation, a change in the structural composition of the oxide scale occurs. During the first ten hours oxidation an initial growth of chromia and Mn1,5Cr1,5O4 is observed. After 10 h oxidation, chromia is not detected anymore and iron-containing oxides such as hematite (Fe2O3) and iron chromite (FeCr2O4) are observed in the outer part of the scale. With blank AISI 304 specimens, the iron-containing oxides are generally not very protective and show severe spallation during cooling to room temperature due to thermal stresses. They do not allow a good adherence of the corrosion layer under thermal cycling. On the Lanthanum coated AISI 304 Stainless Steel the oxidation rate is 10 times lower. In situ XRD analyses show the absence of iron containing oxides. It reveals the formation of a fine convoluted Cr2O3 layer associated with the formation of the mixed oxides Mn1,5Cr1,5O4 and LaCrO3. LaCrO3 is found to be located at the oxide/steel interface. Our results show that, even though the scale formed under isothermal conditions is not composed of iron containing oxides, Lanthanum sol-gel coating does not prevent spallation during thermal cycling at 1000°C.
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