Papers by Keyword: Microstrain

Abstract: Characterization of advanced materials by neutron powder diffraction provides information not accessible by other techniques. Thanks to the low absorption of neutrons, the bulk of the material and large-grain samples can be investigated, moreover in situ at elevated temperatures. The neutron diffraction use is demonstrated on two types of technologically important materials: Ti-Zr alloy and Co-Re high temperature alloy. In Ti-Zr alloy, the residual stress relief and microstrain evolution after ECAP was established. Boron influence on TaC strengthening precipitates in Co-Re high temperature alloys was shown not to be significant at the foreseen alloy operation temperatures, although boron content has a strong influence on the matrix phase.

Abstract: A new method for a fast analysis of heavily deformed, multicomponent ferritic/pearlitic steels microstructure based on XRD measurements had been developed. Its practical application has been examined and proven during wire rod production of a high-strength eutectoid non-alloyed steel grade containing 0.81 weight percent carbon. For individual technological conditions, the lattice strains and their anisotropy were analysed quantitatively by means of fast X-ray diffraction measurements and correlated with the results of comprehensive mechanical testing. Obtained relationships between the microstructure characteristics and mechanical properties were described using physically based models and used to establish a material specific database for prediction of the mechanical properties from X-ray diffraction data. Depending on the deformation state different parameters have to be applied for the material’s macroscopic properties prediction. Additionally, the fast microstructure analysis can provide more detailed information in the case of deviations from the as-required material’s properties due to technological aberrations.

Abstract: Fe-doped (Ce_0.98Fe_0.02O_2−δ) cerium oxide nanoparticles were synthesized by a sol-gel-based method at 1000 °C during different calcination time (1.0, 1.5, 2.0, and 2.5h). The effect of calcination time on microstructure and structural properties of the Ce_0.98Fe_0.02O_2−δ nanoparticles was studied by X-ray diffraction (XRD) and Raman spectroscopy measurements. Analysis of the XRD pattern shows that all samples exhibited a single-phase fluorite structurewith lattice parameters ranging from 0.540991 Å (1.0h) to0.540635 Å (2.5h). Raman spectroscopy also confirms that the Fe atoms successfully displaced some of the Ce atoms in the CeO₂ lattice without forming any impure phases. XRD and Raman spectroscopy results showed that both crystallite size and the particle size increased as the calcination time increased from around 36 nm (1.0h) to 64 nm (2.5h).

Abstract: Using XRD method it was revealed that in the stress-strain state of Al nanopowder lattice a non-significant amount of energy was stored (~0.385 J/g). Nevertheless, according to the data obtained by differential thermal analysis (DTA) the total amount of stored energy in the nanopowder was 348 J/g. The estimated value might be caused by the significant contribution of nanoparticles surface energy, which cannot be detected by means of XRD method. However, the method proposed in the paper can be applied to estimate changes in the structural and energy states of the lattice for nanoparticles or another micro-and nanopowders.

Abstract: This work deals with the strain at the core-shell interface of Fe nanoparticles. Series of Fe nanoparticles with various mean diameters were prepared by precipitation in solid state in binary Cu-Fe alloy. Further, nanoparticles were isolated by dissolution of Cu matrix. High-energy X-ray diffraction (XRD) was used to probe structure of nanoparticles. XRD measurements suggest presence of the core-shell structure, where core and shell of the nanoparticles are formed of α-Fe and CuFe₂O₄ phase, respectively. Strains in core and shell were estimated as a function of nanoparticles size by Williamson-Hall method.

Abstract: Palladiums tubular membranes are developed to operate up to 400 °C, for the synthesis of H₂ and for the separation of CO₂ in Water Gas Shift (WGS) processes and reforming gas of methane [. Palladium has FCC lattice that allows the separation of hydrogen from carbon dioxide through a solution-diffusion mechanism [. To ensure high selectivity in the separation process, the functional Pd layer on the porous substrate of the membranes must have a microstructure with low defects and free from residual stresses [.MicroXRD measurements were performed to evaluate the effect of the stress-relief heat treatment, carried out for different time and temperatures, on the palladium layer. Microstrains were assessed before and after stress-relief by the Williamson-Hall method [. The use of microdiffraction was mandatory considering the tubular shape of membranes. The data were corrected for elastic anisotropy of palladium and the altered Williamson-Hall method was successfully applied.The XRD two-dimensional (2D) images and the integrated spectra collected from the samples allowed to study also the evolution of Pd microstructure and the reduction of micro-stresses due to stress relief. The results of the study allowed to identify the optimal thermal profile for the heat treatment of palladium membranes.

Abstract: The Ti-15Mo-xNb system integrates a new class of titanium alloys without the presence of aluminum and vanadium, which exhibit cytotoxicity, and that have low elasticity modulus values (below 100 GPa). This occurs because these alloys have a beta structure, which is very attractive for use as biomaterials. In addition, Brazil has about 90% of the world’s resources of niobium, which is very important economically. It strategically invests in research on the development and processing of alloys containing this element. In this paper, a study of the influence of heat treatments on the structure and microstructure of the alloys of a Ti-15Mo-xNb system is presented. The results showed grain grown with heat treatment and elongated and irregular grains after lamination due to this processing. After quenching, there were no changes in the microstructure in relation to heat-treated and laminated conditions. These results corroborate the x-ray diffraction results, which showed the predominance of the β phase.

Abstract: Ni-30wt%Fe elemental power mixture was mechanically milled under argon atmosphere for variuos times up to 25h.The evolution of Ni-Fe alloying during milling and the microstructure of the as-milled powders were characterized by XRD, EPMA (electron probe microanalysis), SEM and TEM, respectively. The results show that nanocrystalline Ni (Fe) supersaturated solid solution alloy powders with 30wt. % Fe in composition can be synthesized by mechanical milling of the elemental powder mixture. Both the content of Fe dissolved and the microstrain developed in the as-synthesized Ni (Fe) solid solution phase increase, while the crystallite size decreases, steadily with increasing milling time. In particular, the Ni-30wt%Fe alloy powders obtained by 25h milling consist of a single Ni (Fe) supersaturated solid solution phase with average crystallite size of about 15nm and accumulated microstrain as high as 1.12%. DSC tests show that the nanocrystalline Ni-30wt%Fe alloy powders have a lower melting temperature than the elemental powder mixture, attributed to the unique Ni (Fe) solid solution phase structure, the nanocrystallization, and the high strain energy.

Abstract: Microstrain broadening due to composition variations in -FeN0.407 has been evaluated using different evaluation procedures ranging from pattern decomposition to whole-powder-pattern modelling. Details how to set up these procedures in the TOPAS suite of programs have been described. The different procedures yield essentially the same results, but they have their advantages and disadvantages, which are discussed.