Changes In Phase Content Research Articles

The influence of cyclic creep on the long-term oxidation behavior of a directionally-solidified nickel-based superalloy

This work investigates the effect of cyclic creep on the long-term oxidation of a directionally-solidified nickel-based superalloy DZ445 up to 1800 h. The stress application of cyclic creep refines the oxides, increases the oxidation weight gain, reduces the oxidation rate exponent, and decreases the activation energy. It enhances the content of Al2O3 and TiO2 in the outermost layer and in the sub-outer layer of CrTaO4 in the film. It delays the formation of the continuous innermost layer of Al2O3 and the sub-inner layer that is rich in Al2O3. The change of phase content and type in the oxidation layers could be ascribed to the diffusion kinetic effect of cyclic creep stress in the superalloy.

Dilatometric inspection of phase changes in Mg-PSZ

Partially Stabilized Zirconia samples with 7, 8 and 9 mol% MgO (Mg-PSZ) were sintered at 1700 °C for 2 h and cooled to room temperature (2 °C.min−1), to obtain distinct phase compositions and microstructures. These materials were studied by dilatometry (DIL) up to about 1500 °C (heating rate of 10 °C.min−1). A detailed analysis of DIL curves is used to estimate the initial M (monoclinic) phase content and quantify the progressive conversion M→T (tetragonal) as a function of temperature. Microstructures observed by scanning electron microscopy and phase content estimates from X-ray diffraction (XRD) patterns of sintered samples and milled powders, are used to show the consistency of the DIL data analysis. Furthermore, combination of room temperature XRD and DIL data yields unique and comprehensive details on the microstructural and phase content changes with temperature (all phases, M, T and C-cubic), hardly obtained in any other manner.

Increasing dental zirconia micro-retentive aspect through ultra-short pulsed laser microstructuring: study on flexural strength and crystal phase characterization

ObjectivesAlthough ultra-short pulsed laser (USPL) microstructuring has previously improved zirconia bond-strength, it is yet unclear how different laser-machined surface microstructures and patterns may influence the material’s mechanical properties. Therefore, the aim of this study was to assess the flexural strength of zirconia after different USPL settings creating three different geometrical patterns with structures in micrometer scale.MethodsOne hundred sixty zirconia bars (3Y-TZP, 21 × 4 × 2.1 mm) were prepared and randomly divided into five groups (n = 32): no surface treatment (negative control-NC); sandblasting with Al2O3 (SB); and three laser groups irradiated with USPL (Nd:YVO4/1064 nm/2-34 J/cm2/12 ps): crossed-lines (LC), random-hatching (LR), and parallel-waves (LW). Bars were subjected to a four-point flexural test (1 mm/min) and crystal phase content changes were identified by X-ray diffraction. Surface roughness and topography were analyzed through 3D-laser-profilometry and SEM. Data were analyzed with parametric tests for roughness and Weibull for flexural strength (α = 5%).ResultsLR (Mean[95%CI]: 852.0 MPa, [809.2–894.7]) was the only group that did not show a significantly different flexural strength than NC (819.8 MPa, [796.6–842.9]), (p > 0.05). All laser groups exhibited higher Weibull moduli than NC and SB, indicating higher reliability and homogeneity of the strength data. An increase of monoclinic phase peak was only observed for SB.ConclusionIn conclusion, USPL created predictable, homogeneous, highly reproducible, and accurate surface microstructures on zirconia ceramic. The laser-settings of random-hatching (12 ps pulses) increased 3Y-TZP average surface roughness similarly to SB, while not causing deleterious crystal phase transformation or loss of flexural strength of the material. Furthermore, it has increased the Weibull modulus and consequently material’s reliability.Clinical significancePicosecond laser microstructuring (LR conditions) of 3Y-TZP ceramic does not decrease its flexural strength, while increasing materials realiability and creating highly reproducible and accurate microstructures. These features may be of interest both for improving clinical survival of zirconia restorations as well as enhancing longevity of zirconia implants.

Effect of calcination on the reactivity of natural clinoptilolite zeolites used as supplementary cementitious materials

This study examined several sources of natural clinoptilolite zeolite calcined at temperatures of 300 °C-965 °C, tracking changes in phase content, particle size, surface area, and pore size distribution. Changes in pozzolanic reactivity with calcination were measured through calcium hydroxide content of hydrated zeolite-cement pastes and compressive strengths of cement mortars. Calcination increased zeolite particle size and reduced porosity and surface area, resulting in decreased zeolite pozzolanic reactivity despite increased amorphous content in the samples. Overall, in contrast to what has been shown previously in literature, calcination was ineffective in increasing the reactivity of clinoptilolite zeolites for use as SCMs.

One-step electrochemical deposition of thin film titanium suboxide in basic titanyl sulfate solution at room temperature

This study reports direct electrodeposition of TiOx thin films on ITO substrate from an acetonitrile solution containing titanyl sulfate and tetra n-butyl ammonium hydroxide. The electrochemical behavior of titanyl sulfate in a basic medium is investigated using cyclic voltammetry. In this medium, different phases and/or compositions containing Ti3O5 (βTi3O5, λTi3O5, and ɣTi3O5) and Ti4O7 are obtained depending on electrolysis potential values (− 1.2 V, − 1.5 V, − 1.7 V, and − 2.0 V). The electrochemical properties of the TiOx coatings obtained from various cathodic potentials are investigated using electrochemical impedance spectroscopy (EIS). Depending on the increase of electrolysis potential values applied, thicker films with lower resistance are formed. The EIS analysis results are compatible with the results of XRD and SEM, which confirms the change of phase content and/or composition in the films obtained at different electrolysis potential values. The estimated band gaps of brownish thin films are obtained between 1.32 and 1.41 eV using UV–vis spectra. Herein the electrochemical deposition of crystalline TiOx films on ITO electrode is carried out at room temperature by a cost-effective and one-step method in basic acetonitrile solution.

Application of Raman Spectroscopy for Characterizing Synthetic Non-Metallic Inclusions Consisting of Calcium Sulphide and Oxides

The presence of non-metallic inclusions (NMI) such as sulphides and oxides may be detrimental to the control of the steel casting process and product quality. The need for their identification and characterization is, therefore, urgent. This study uses time-gated Raman spectroscopy for the characterization of synthetic duplex oxide-sulphide phases that contain CaS and the oxide phases of Al2O3, CA, C12A7, C3A, and MgO·Al2O3 (MA). Binary phase samples of CaS–MA, C3A–CaS, C12A7–CaS, Al2O3–CaS, and MA–CaS were prepared with varying phase contents. The relative intensities of the Raman peaks were used to estimate the samples’ phase content. For a quantitative estimation, linear regression calibration models were used to evaluate the change in phase content in the samples. The most suitable Raman peak ratios had mean absolute error (MAE) values ranging from 3 to 7 wt. % for the external validation error, and coefficients of determination (R2) values between 0.94 and 0.98. This study demonstrated the use of Raman spectroscopy for the characterization of the calcium sulphide, magnesium aluminate spinel, Al2O3, and calcium aluminate phases of CA, C3A, and C12A7 in a duplex oxide-sulphide system, and it offers potential for inclusion characterization in steel.

Effect of microstructure evolution on tensile fracture behavior of Mg-2Zn-1Nd-0.6Zr alloy for biomedical applications

The effect of microstructure evolution on tensile fracture behavior of biomedical Mg-2Zn-1Nd-0.6Zr alloy was investigated using OM, EPMA, SEM, TEM, EBSD and Nano-indentation. Results indicated that the as-cast Mg-2Zn-1Nd-0.6Zr alloy composed of α-Mg matrix, netlike and granular Mg35Zn40Nd25 (T3) secondary phases. Volume fraction of secondary phases in homogenized and solution-treated alloys decreased from 7.2% to 4.6% and 0%, respectively, whilst elements distributed more uniform and grain did not grow significantly. Grain size of extruded+aged alloy decreased from 110μm to 12μm, forming band-shaped phases with size of 0.2–1.5μm and high-density nanoscale precipitates with size of 5–20nm. Moreover, Mg35Zn40Nd25 phase exhibited higher elastic modulus (57.5GPa) and hardness (1.47GPa) than all matrices. With the change of phase content, phase morphology and grain size, the fracture mode of as-cast, homogenized, solution-treated and extruded+aged alloys during the conventional tensile test changed from intergranular fracture to quasi-cleavage fracture, transgranular fracture and ductile fracture. In addition, the effect of reduced surface integrity on cracking susceptibility could be ranked in the order of as-cast>homogenized>solution-treated>extruded+aged.

Electrochemical hydrogen storage behaviors of as-cast and spun RE–Mg–Ni–Co–Al-based AB2-type alloys applied to Ni–MH battery

Preparation of La–Mg–Ni–Co–Al-based AB2-type alloys La0.8−xCe0.2YxMgNi3.4Co0.4Al0.1 (x = 0, 0.05, 0.10, 0.15, 0.20) was performed using melt spinning technology. The influences of spun rate and Y content on structures and electrochemical hydrogen storage characteristics were studied. The base phase LaMgNi4 and the lesser phase LaNi5 were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). The variations of spinning rate and Y content cause an obvious change in phase content, but without altering phase composition, namely, with spinning rate and Y content growing, LaMgNi4 phase content augments while LaNi5 content declines. Furthermore, melt spinning and the replacing La by Y refine the grains dramatically. The electrochemical tests show a favorable activation capability of the two kinds of alloys, and the maximum discharge capacities are achieved during the first cycle. Discharge capacity firstly increases and subsequently decreases with spinning rate rising, while cycle stability is ameliorated and discharge capacity decreases with Y addition increasing. It is found that the amelioration of cycle stability is due to the enhancement of anti-pulverization, anti-corrosion and anti-oxidation abilities by both replacement of La with Y and melt spinning. Moreover, with the increase of Y addition and/or spinning rate, the electrochemical kinetics that contain charge transfer rate, limiting current density (IL), hydrogen diffusion coefficient (D) and the high rate discharge ability (HRD) firstly augment and then reduce.

Influence of barium borosilicate glass on microstructure and dielectric properties of (Ba,Ca)(Zr,Ti)O3 ceramics

Barium borosilicate (BBS) glass was added as a sintering aid to (Ba0.7Ca0.3)TiO3-Ba(Ti0.8Zr0.2)O3 (BCZT) ceramics at levels from 2 to 15 wt%, yielding enhanced densification. The addition of BBS also induced changes in phase composition, from predominantly tetragonal to orthorhombic at room temperature. It is shown that the changes in phase content are caused by a shift of the orthorhombic to tetragonal phase transformation from below room temperature to ≈50 °C. An additional high temperature transition around 120 °C was also identified. These observations are interpreted in terms of the development of chemical heterogeneity associated with the redistribution of dopant elements (particularly Zr and Ca) through the liquid phase during sintering. The relative permittivity and electric field-induced polarisation values were generally degraded by the presence of the glass phase, but a reduction in ferroelectric hysteresis and improved densification behaviour have potential benefits in dielectric energy storage applications.

Thermal behaviour of chromium nitride/titanium–titanium carbonitride multilayers

Chromium nitride/titanium–titanium carbonitride multilayers composed of a 40nm Cr interface followed by a 4.4μm thick Cr2N layer, a 150nm thick Ti layer, and a 1 μm thick TiCxNy top layer were deposited on silicon wafers by magnetron sputtering. The structural changes and the phase content changes of these multilayer samples were studied by means of high-temperature in-situ X-ray diffraction experiments at temperatures up to 550°C. The lattice constants of the Cr phase as well as the Ti phase display an aberrant expansion behaviour during these experiments which is influenced by the defect structure, a nitrogen incorporation, and residual stress in the layers. The results were compared with structural data obtained by ex-situ transmission electron microscopy investigations of pristine and heated material, revealing phase separation and strong diffusion phenomena.

The effect of material grain structure on the surface integrity of components processed by microwire electrical discharge machining (μWEDM)

The machining response of metallurgically and mechanically modified materials when processed by employing the microwire electrical discharge machining (μWEDM) technology is reported in this paper. In particular, the effects of the material microstructure on resulting surface integrity of Al5000 series aluminium alloys after μWEDM processing is studied. The machining response of an ‘as received’ aluminium alloy was compared against the results obtained on samples processed through extrusion strain hardening and severe plastic deformation. Especially, the process–material effects on the resulting microhardness, phase content changes, heat-affected zone, surface roughness, microcracks, recast layer, material removal rate, and element spectrum after both rough and finishing μWEDM cuts were investigated. This study shows that an ultrafine grained (UFG) Al5083 exhibits not only superior mechanical properties but also the machining response to μWEDM is favourable. A reduction of the recast layer after μWEDM was observed when compared with ‘as received’ and ‘conventionally’ processed Al5083.

Effects of thermo‐oxidative aging on chain mobility, phase composition, and mechanical behavior of high‐density polyethylene

AbstractThe thermo‐oxidative degradation behavior of high‐density polyethylene (HDPE) was investigated during oven aging at 100°C. 1H low‐field solid‐state nuclear magnetic resonance (NMR) was used to characterize the behaviors of molecular chains and the changes in phase content of HDPE during aging. NMR free induction decays (FIDs) were fitted by three components corresponding to the crystalline phase, interphase, and amorphous phase, respectively. The prolongation of aging led to a progressive increase in the crystalline phase at the expense of the other two phases. A slight decrease in chain mobility of the crystalline phase and interphase was observed simultaneously. The results obtained from other traditional technical approaches are also discussed in the context of the molecular dynamics properties revealed by NMR. The reduction in molecular weight, in chain mobility and the increase in crystallinity during thermo‐oxidation were the main factors, which caused the loss of mechanical performance of HDPE. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Influence of rotating magnetic field on the microstructure and phase content of Ni–Al alloy

Rotating magnetic field is introduced in the production process of Ni–Al precursor alloy of skeletal Ni catalyst. The results showed that the big dendrites of Al 3Ni 2 disappeared, the size of Al 3Ni 2 decreased from 64.5 μm to 37.2 and 35.5 μm, phase content of Al 3Ni 2 decreased while Al 3Ni increased after applying field current of 80 A and 140 A, respectively. The change of phase content is probably caused by the increase of surface area between the Al 3Ni 2 phase and fluid which is favorable to the peritectic reaction.

Phase development in normal and ultra high performance cementitious systems by quantitative X-ray analysis and thermoanalytical methods

Quantitative X-ray diffraction (QXRD) and thermogravimetry (TG) methods are used to determine the phase development up to 28 days of hydration in normal and ultra high performance cementitious systems (UHPC) that do not contain aggregate. The phase development in ultra high performance cementitious formulation is quantitatively and kinetically different from that in normal concrete formulation. This is related to the different components employed and their associated reactions. For both formulations the most remarkable changes of the phase contents are recorded between the first and second hydration day and up to the seventh day. After the seventh day less phase content changes are measured. Because of the non sufficient water amount for hydration, considerable amount of cement remains non hydrated in the UHPC formulation. The portlandite content, which is present in the UHPC specimen, gives evidence for non complete pozzolanic reactions even after 28 days of hydration, whereas the absence of calcite in the UHPC specimen indicates an insignificant carbonation in this specimen.

Phase Development during Mixed–Oxide Processing of a [Na<sub>0.5</sub>K<sub>0.5</sub>NbO<sub>3</sub>]<sub>1-x</sub> -[LiTaO<sub>3</sub>]<sub>x</sub> Powder

Powders of the solid solution series [Na0.5K0.5NbO3]1-x - [LiTaO3]x, with x = 0.06, are shown to transform from an orthorhombic to a tetragonal crystal system as calcination temperature is increased in the range 850 °C to 1100 °C. Addition of 3 wt% of each alkali carbonate prior to calcination allows retention of the orthorhombic phase to 1100 oC. The latter changes in phase content are attributed to a partial compensation of alkali oxide volatilisation losses. The approach of adding extra alkali carbonates lead to an increase in d33 coefficient in sintered ceramics.

Phase control of Al 2O 3 thin films grown at low temperatures

Low-temperature growth (500 °C) of α-Al 2O 3 thin films by reactive magnetron sputtering was achieved for the first time. The films were grown onto Cr 2O 3 nucleation layers and the effects of the total and O 2 partial pressures were investigated. At 0.33 Pa total pressure and ≥ 16 mPa O 2 partial pressure α-Al 2O 3 films formed, while at lower O 2 pressure or higher total pressure (0.67 Pa), only γ phase was detected in the films (which were all stoichiometric). Based on these results we suggest that α phase formation was promoted by a high energetic bombardment of the growth surface. This implies that the phase content of Al 2O 3 films can be controlled by controlling the energy of the depositing species. The effect of residual H 2O (∼10 − 4 Pa) on the films was also studied, showing no change in phase content and no incorporated H (< 0.1%). Overall, these results are of fundamental importance in the further development of low-temperature Al 2O 3 growth processes.

Structural Phase Transition in Tb5(Si0.6Ge0.4)4 at Low Temperature.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structural phase transition in Tb5(Si0.6Ge0.4)4 at low temperature

AbstractHerein we report on crystallographic details of a structural phase transition measured with powdered Tb5(Si0.6Ge0.4)4 at low temperatures (150 and 130 K). The pseudo‐binary compound is monoclinic at room temperature (P1121/a). Changes of reflection intensities and positions in the diffraction patterns indicate a structural phase transition between 100 K and 150 K, where the compound orders in an orthorhombic structure (Pnma). This is in accordance with a magnetic phase transition from paramagnetic to ferromagnetic state (TC = 150 K), where the compound exhibits the giant magnetocaloric effect. Split‐up crystallographic sites of the monoclinic unit cell degenerate to sites of higher symmetry in the orthorhombic structure. Changes in the corresponding bond lengths are listed in detail. It turned out that both phases coexist at the selected temperatures but the phase content changes significantly. The observed phase transition is very similar to that reported for Gd5Si2Ge2, that is a shear movement of pairs of nearly rigid slabs of atoms along a direction by 0.84 Å and the tremendous increase of selected (Si/Ge)‐(Si/Ge) distances from 2.64 to 3.59 Å in between those slabs. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The evolution of microstructure change and mechanical properties for a nickel silicide based alloy doped with carbon and boron

The Ni–19Si–3Nb alloy was selected as the base alloy and microalloyed with an increasing amount of carbon and boron to improve its mechanical properties. The specimens were prepared by arc melting and drop casting under argon atmospheres, annealing in a vacuum, and then machining for mechanical testing. The evolution of microstructure change and mechanical properties of the Ni–19Si–3Nb– xB– yC alloys were characterized by X-ray diffraction, DTA, SEM, microhardness tests, and tensile tests. The results of X-ray diffraction and DTA could not determine any change of phase content for the Ni–19Si–3Nb alloy with varied carbon and boron content. However, the consequences of the fracture behavior of the Ni–19Si–3Nb alloys with different carbon and boron additions exhibit significant change from brittle mode to ductile mode. The optimum additions of carbon and boron for improving the mechanical properties of the based alloy occur at the combination of 200-p.p.m. carbon and 300 p.p.m. boron addition. The relation between the effect of carbon and boron addition, the microstructures change, and the mechanical behaviors on these Ni–19Si–3Nb– xC alloys are discussed in this paper.

X-ray investigation of metastable crystalline phases in co-deposited Fe–Cr alloy nanometer films

Fe 100− x Cr x ( x=24.5–61.7, 100 at.%) alloy nanometer films prepared by crossed-beam pulsed laser deposition were examined by wide-angle X-ray scattering. On varying the Cr content, x, a change of phase content is observed starting from the known body-centered cubic phase at low Cr content. Indications for three new metastable Fe–Cr phases were found to form in body-centered tetragonal, face-centered orthorhombic and primitive orthorhombic lattice types, respectively.