Study of structure of naturally aged aluminium after twist channel angular pressing

Twist channel angular pressing (TCAP), the severe plastic deformation (SPD) technology developed recently to increase the efficiency of the imposed strain and its homogeneity within a single pass, is an effective process combining channel bending and twist extrusion in a single die. The presented study analyses the phenomena of substructure development, precipitation, structural units' orientations, and the occurrence of residual stress, as well as electric resistivity and microhardness, in commercial purity aluminium naturally aged for two years at room temperature after processing via single pass TCAP. The results are compared with the findings for the TCAP sample right after processing; selected results are also compared with the results for the sample after TCAP and one year of natural ageing, and with a sample processed by conventional ECAP. The analyses showed the substructure to recover substantially, the grain size decreased to submicron size. The residual stress within the grains introduced by the energy accumulated via the severe imposed strain relaxed significantly by the structure restoration, as well as by intensive precipitation. The aged TCAP sample specific electric resistivity was comparable to the resistivity of the original commercially pure aluminium (2.652E−05 and 2.635E−05 Ω·mm2·m−1, respectively), however, the microhardness mapping showed increased mechanical properties with homogeneous distribution

Ordered Mesoporous Silica Prepared in Different Solvent Conditions: Application for Cu(II) and Pb(II) Adsorption

In this work, the synthesis of ordered mesoporous silica of MCM-41 type was investigated aimed at improving its morphology by varying the synthesis conditions in a one-pot process, employing different temperatures and solvent conditions. 2-methoxyethanol was used as co-solvent to ethanol. The co-solvent ratio and the synthesis temperature were varied. The pore morphology of the materials was characterized by nitrogen porosimetry and small angle neutron scattering (SANS), and the particle morphology by transmission electron microscopy (TEM) and ultra-small angle neutron scattering (USANS). The thermal behavior was investigated by simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) measurements. The SANS and N(2) sorption results demonstrated that a well-ordered mesoporous structure was obtained at all conditions in the synthesis at room temperature. Addition of methoxyethanol led to an increase of the pore wall thickness. Simultaneously, an increase of methoxyethanol content led to lowering of the mean particle size from 300 to 230 nm, according to the ultra-small angle scattering data. The ordered porosity and high specific surfaces make these materials suitable for applications such as adsorbents in environmental remediation. Batch adsorption measurements of metal ion removal from aqueous solutions of Cu(II) and Pb(II) showed that the materials exhibit dominantly monolayer surface adsorption characteristics. The adsorption capacities were 9.7 mg/g for Cu(II) and 18.8 mg/g for Pb(II) at pH 5, making these materials competitive in performance to various composite materials

Analysis of Anisotropic void system in electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings

Thermal barrier coatings (TBCs) deposited by EB-PVD protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines increasing the combustion temperature and/or diminishing the air-cooling requirements. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task and to improve the turbine efficiency is to optimize the TBC properties by tailoring its microstructure and/or material. The different kinds of pores in EB-PVD TBCs influence their thermal conductivity according to their size, shape, orientation and volume. These pores can be open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization becomes very complex and requires the use of sophisticated methods. This work describes the analysis of the anisotropic and nano-sized pores in PYSZ-based TBCs by means of small angle neutron scattering (SANS) method. In order to differentiate and analyse 3D closed and open pores in 400 µm thick coatings, a contrast matching SANS technique has been employed. Thermal derived changes in crystal structure as well as pore size and morphology have been correlated with thermal conductivity

Correlation of thermally induced changes at anisotropic nano-pores of EB-PVD deposited FYSZ-coatings with thermal conductivity,

Electron beam physical vapour deposited (EB-PVD) FYSZ-coatings were produced in different morphologies by varying the process parameters. Anisotropic and isotropic nano-sized pores in these FYSZ-coatings were analysed by means of Small Angle Neutron Scattering (SANS). In order to differentiate closed and open pores, SANS-measurements were carried out as the coatings were immersed in matching liquid. With in-situ high-temperature SANS-measurements, the thermally activated changes of aspect ratio and surface area of the pores were observed. Thermal conductivity values of as-coated and aged coatings are measured by Laser-Flash Analysis (LFA) and have been correlated with the changes in pore shape and size. All results were compared to those previously obtained from standard EB-PVD PYSZ-coatings

Analysis of pore morphology and thermal conductivity of alternative EB-PVD deposited TBC-compositions

Thermal barrier coatings (TBCs) consist of a ceramic top coat deposited onto a bond-coated superalloy substrate and are used to increase lifetime and efficiency of highly loaded turbine blades and vanes by reducing the average metal temperature and mitigating the detrimental effects of hot spots. Electron-beam physical vapor deposition (EB-PVD) of the standard top coat, partially yttria-stabilized zirconia (PYSZ), produces various anisotropic pores which contribute in the reduction of thermal conductivity. However, increases in combustion temperature for improved turbine efficiency causing greater thermal loading alters the pore morphology resulting in an increase of thermal conductivity. Long-term dignity of the ceramic top coat of TBCs can be provided through the development of new materials with ultra-low thermal conductivity, excellent phase stability and improved sintering-resistance. Fully yttria (14 wt.% Y2O3) stabilised zirconia (FYSZ) yields intrinsically lower thermal conductivity. Further optimization of the TBC properties is possible by tailoring its microstructure, since an important relationship exists between thermal conductivity and process-induced pore structure of EB-PVD-TBCs. Pore morphology and microstructure of EB-PVD pyrochlore differ significantly from those of PYSZ and FYSZ. The influence of the pore morphology on reduction of thermal conductivity and resistance to thermal loading are not well-investigated in the new TBC compositions. This work describes the anisotropic nano-sized pore morphology in FYSZ and Pyrochlore (La2Zr2O7) TBCs obtained by small angle neutron scattering (SANS) analysis method. In order to differentiate between the 3D closed and open pores in 400 µm thick coatings, a contrast matching liquid SANS technique was employed. Samples in several arrangements such as free-standing EB-PVD-layers and TBCs deposited on metallic substrates were analysed by the Laser-Flash technique for their thermal diffusivity in the as-coated condition and after ageing at 1100°C in air. The pore migration and pore morphology changes were investigated by advanced TEM/SEM-analysis on FIB sections. Thermal derived changes in crystal structure as well as pore size and morphology observed by TEM and SANS have been correlated with the thermal conductivity changes

Analysis of Anisotropic Void Sytem in Electron Beam-Physical Vapour Deposited (EB-PVD) Thermal Barrier Coatings

Thermal barrier coatings (TBCs) deposited by EB-PVD protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines increasing the combustion temperature and/or diminishing the air-cooling requirements. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task and to improve the turbine efficiency is to optimize the TBC properties by tailoring its microstructure and/or material. The different kinds of pores in EB-PVD TBCs influence their thermal conductivity according to their size, shape, orientation and volume. These pores can be open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization becomes very complex and requires the use of sophisticated methods. This work describes the analysis of the anisotropic and nano-sized pores in PYSZ-based TBCs by means of small angle neutron scattering (SANS) method. In order to differentiate and analyse 3D closed and open pores in 400 µm thick coatings, a contrast matching SANS technique has been employed. Thermal derived changes in crystal structure as well as pore size and morphology have been correlated with thermal conductivity

Focusing High-Resolution Three-Axis Neutron Diffractometer for Investigations of Special Tasks of Powder Diffractometry

Feasibility of focusing high-resolution three-axis diffractometer with the polycrystalline sample between the monochromator and the analyzer was tested for studies of finer effects of powder diffraction lines and for investigations of special tasks of powder diffractometry. The focusing 3-axis diffractometer set-up equipped with bent perfect crystal monochromator and analyzer offers the sensitivity in determination e.g. of strains in polycrystalline materials ε =Δd/d close to 10-5. Together with special tasks of strain/stress studies related namely, to plastic deformation, it permits to study a finer substructure of individual diffraction lines which can appear e.g. in case of polycrystalline alloys where more phases having very close values of the lattice spacing could exist. Resolution properties of the high-resolution diffractometer setting will be documented on several experimental results obtained on unconventional bulk samples

High-Resolution Strain/Stress Measurements by Three-Axis Neutron Diffractometer

Resolution properties of the unconventional high-resolution neutron diffraction three-axis setup for strain/stress measurements of large bulk polycrystalline samples are presented. Contrary to the conventional two-axis setups, in this case, the strain measurement on a sample situated on the second axis is carried out by rocking the bent perfect crystal (BPC) analyzer situated on the third axis of the diffractometer. Thus, the so-called rocking curve provides the sample diffraction profile. The neutron signal coming from the analyzer is registered by a point detector. This new setup provides a considerably higher resolution (at least by a factor of 5), which however, requires a much longer measurement time. The high-resolution neutron diffraction setting can be effectively used, namely, for bulk gauge volumes up to several cubic centimeters, and for plastic deformation studies on the basis of the analysis of diffraction line profiles, thus providing average values of microstructure characteristics over the irradiated gauge volume

Very-small angle neutron scattering study on grain coarsening inhibition by V-doping of WC-Co composites

The mechanical properties of cemented carbides can be tuned by controlling WC grain coarsening and the simultaneous growth of the binder pocket size during the sintering. So far, bulk studies considering this phenomenon are scarce, but here, we report the first very-small angle neutron scattering (VSANS) study on cemented carbides. VSANS is supplemented with electron backscatter diffraction (EBSD) and the microstructural refinement by increasing V-doping (0, 0.02, 022, and 0.76 wt%) is quantified. The capability of VSANS as a non-destructive bulk probe for cemented carbides is shown, paving way for forthcoming in-situ studies

Evolution of distance between ω particles in metastable β-Ti alloy determined from in-situ small angle neutron scattering

The evolution of distance between ω particles in metastable β Ti- 15Mo alloy (8.1 in at. %) was determined from in-situ small angle neutron scat- tering (SANS). SANS data were recorded during heating of the material from room temperature to 600 ◦C with the heating rate of 1 ◦C/min. The results agree with previously determined ordering of ω particles in a cubic three-dimensional array with the axes along the cubic axes ⟨100⟩β of the host lattice. The distance between particles, which increases with temperature, was investigated in three orientations with the incident beam parallel to [100]β, [110]β and [111]β