Increase In Lattice Strain Research Articles

Microstructural evolution and interfaces in cold sprayed hybrid aluminum alloy powders of different hardness

The development of thick cold sprayed deposits of hard amorphous/nanocrystalline Aluminum High Entropy Alloys (Al HEA) is limited by their poor plastic deformability. To address this, Al HEA powder (Al90.05Ni4.3Y4.4Co0.9Sc0.35 (at. %)) is blended with soft Al 6061 in a 1:1 wt% ratio and cold sprayed. The microstructure of the composite deposits reveals that while Al HEA splats undergo limited deformation, Al 6061 splats deform extensively. Extreme deformation of Al 6061 captures the hard Al HEA particles, resulting in a composite deposit of 5 mm thickness, compared to 0.2 mm for pure Al HEA. Within the composite, Al HEA particles deform through shear band propagation and viscous flow, whereas Al 6061 splats deform via dislocation slip motion. These deformation mechanisms induce interface nanocrystallization, leading to a 123 % increase in lattice strain, a 67 % reduction in crystallite size, and an 800 % increase in dislocation density compared to the initial feedstock. This microstructural evolution, combined with the presence of hard Al HEA regions, results in a mean hardness of 2.56 GPa and an elastic modulus of 76 GPa. These values represent a 47 % and 6 % improvement over conventional polycrystalline cold-sprayed aluminum deposits. Thus, this study provides insights into the microstructural and interface evolution and its effect on indentation characteristics for making high-strength Al HEA deposits.

Deformation-induced grain boundary segregation in a powder-metallurgy ultrafine-grained MoNbTaTiV refractory high-entropy alloy

A powder-metallurgy MoNbTaTiV refractory high-entropy alloy synthesized by mechanical alloying (MA) and spark plasma sintering was subjected to hot deformations at different temperatures and strain rates. The microstructural morphologies were characterized, and component element segregation was elucidated. With grain refinement and lattice strain increase, the large inhomogeneous milled powder became refined and homogeneous after the MA. Component element segregation was observed at relatively low deformation temperatures and high strain rates. As the deformation temperature increased and the strain rate decreased, the segregation gradually disappeared, which was attributed to dislocation movement.

The effects of adding Si3N4 as a nitrogen source on the properties of Ni-Free Co-28Cr-6Mo-xN alloy powders developed by mechanical alloying

Co-Cr-Mo alloys, which also contain Ni, are often used as materials for implants in orthopedic surgery due to their excellent mechanical properties and resistance to corrosion. However, when these alloys are implanted into the body, they can release nickel ions into the host tissues, which can pose health risks over time. To address this issue, nitrogen can be substituted for nickel. This study involves the synthesis of cobalt-based alloy powders, following the chemical composition specified by ASTM F1537, using different percentages of silicon nitride as a nitrogen source via the mechanical alloying method in an argon atmosphere. The effects of increasing silicon nitride content on the particle morphology, particle size, phase transformations, microstructure, and hardness of the synthesized powders were investigated using XRD, SEM, TEM, and microhardness tests. The results obtained from the X-ray diffraction analysis indicate that the alloying process was conducted effectively. It was observed that the silicon nitride underwent decomposition, and a portion of its nitrogen reacted with chromium to form the chromium nitride phase. Additionally, it was observed that an increase in the silicon nitride content resulted in a decrease in crystallite size and an increase in lattice strain. Adding silicon nitride in varying percentages resulted in crystal sizes within the nanometer range. The SEM results indicated that the size of powder particles decreased with an increase in the content of silicon nitride, and there was a more uniform distribution of particle sizes, with less variation in size. The TEM images showed that all percentages of silicon nitride resulted in a fine-grained polycrystalline phase, where the size of the crystallites decreased with an increase in the amount of silicon nitride. The corresponding SAED patterns supported this observation. Moreover, the hardness of the material increased as the silicon nitride content increased.

Enhancement of thermoelectric performance in Mg3(Sb,Bi)2 through engineered lattice strain and controlled carrier scattering

Mg3(Sb,Bi)2 emerges as a promising thermoelectric (TE) material due to its rich elemental composition and high TE performance, offering potential for industrial applications. In this study, we found out that the elevated sintering temperatures can introduce dislocations, vacancies, and nanoscale precipitates in the lattice, inducing desirable lattice strain. Higher lattice strain broadens the phonon dispersion, effectively reducing lattice thermal conductivity. Simultaneously, high-temperature sintering increases grain size, significantly mitigating grain boundary carrier scattering and enhancing carrier mobility. As a result, we observe a 31.4 % increase in lattice strain, a 30 % reduction in lattice thermal conductivity, a 200 % rise in room temperature mobility, ultimately achieving an outstanding figure of merit (zT) of 1.7 at 750 K for Mg3.22Ho0.03Sb1.5Bi0.5. The synergistic effect of engineering lattice strain to minimize lattice thermal conductivity and controlling carrier scattering mechanisms to enhance mobility significantly provides a novel strategy to improve TE performance of Mg3(Sb,Bi)2-based materials.

Photo-induced luminescence mechanism and the correlated defects characteristics in the sol-gel derived samarium ion substituted tin oxide (Sn1-xSmxO2) nanoparticles

Rare earth complexes have gained attention in recent years for their remarkable luminescence properties, especially their long lifetimes, clear emission bands, and significant luminous quantum efficiency. In the ultraviolet area, the lanthanide ions exhibit relatively tiny absorption. The current investigation systematically portrays the tailoring of the micro-structural, opto-electonic and defect related features of the sol-gel derived pristine and rare earth element-samarium (Sm3+) substituted tin oxide (SnO2) i.e., Sn1-xSmxO2 (x = 0.0, 0.1, 0.2 & 0.3) nanoparticles (NPs). The structural, optical, electronic, morphological, photo-induced luminescence and defects related characteristics of the NPs were explored as a function of samarium (Sm3+) substitution level. In-depth analysis of the structure-property correlation of the Sn1-xSmxO2 NPs is the goal of this study, focusing especially on the properties related to vacancy evolution and luminescence. The elemental mapping results revealed through energy dispersive X-ray spectroscopic (EDS) technique confirmed that the Sm-substitution is distributed uniformly throughout the NPs. The X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) studies corroborate that the Sm3+ substitution in the SnO2 matrix causes the decrease in crystallite size of the NPs and increase in the dislocation density. A monotonic increase in lattice strain has been observed using the Williamson – Hall (W – H) approach, which is in line with the NPs' increased dislocation density and decreased crystallite size with the Sm3+ substitution level. The presence of vacancy-type defects inside the NPs was demonstrated by positron annihilation lifetime (PAL) spectroscopic measurements, and a decrease in defects was noticed as the level of Sm3+ substitution increased. To explore the optical characteristics and the evolution of the energy band gap with Sm3+ substitution level, the optical absorption (OA) spectroscopic measurement was carried out. As the Sm-substitution level rises, the optical energy band gap of the substituted SnO2 NPs widens relative to that of pure SnO2 NPs. The existence of various absorbance bands corresponding to the atomic vibrations within the NPs were investigated by the Fourier-transform infrared (FT-IR) spectroscopic technique. The photo-induced fluorescence (FL) emission spectroscopic analysis evidenced that the defect density decreased as the Sm-substitution level increased, which is in accordance with the PAL spectroscopic studies. The FL spectra showed the two typical near band edge (NBE) and deep level emission (DLE) peaks of the NPs. The proportion of different defects and vacancies associated with the FL emission transitions are portrayed as Pie-chart diagrams. The tailored NPs can establish to be effective candidates for possible spintronic and optoelectronic applications including magneto-optical devices.

Stress Evaluation Method by Neutron Diffraction for HCP-Structured Magnesium Alloy

Tensile deformation in situ neutron diffraction of an extruded AZ31 alloy was performed to validate conventional procedures and to develop new procedures for stress evaluation from lattice strains by diffraction measurements of HCP-structured magnesium alloys. Increases in the lattice strains with respect to the applied true stress after yielding largely vary among [hk.l] grains. Some [hk.l] grains have little or no increase in lattice strain, making it difficult to use the conventional procedures to determine the average phase strain by using lattice constants or by averaging several lattice strains. The newly proposed procedure of stress evaluation from the lattice strains shows very high accuracy and reliability by weighting the volume fraction of [hk.l] grains and evaluating them in many [hk.l] orientations in addition to multiplication by the diffraction elastic constant. When multiple hk.l peaks cannot be obtained simultaneously, we recommend to use the 12.1 peak for stress evaluation. The lattice strain value evaluated from the 12.1 peak shows a good linear relationship with the applied true stress for the whole deformation region.

The Effect of Thermal Treatment on the Characteristics of Porous Ceramic-Based Natural Clay and Chitosan Biopolymer Precursors

This study was conducted to determine the role of thermal treatment on the crystallinity and pore characteristics of porous ceramic, which was prepared from natural clay (NC) and chitosan (CS) biopolymer using the gel casting method. CS was used as an environmentally friendly pore-forming agent. The applied temperature treatment was based on thermal analysis (TGA/DTA) results and followed a sintering temperature of 900 to 1100 °C. The results showed that at sintering temperatures from 900 to 1000 °C, the crystallinities of the ceramic decrease (from 76.06 to 74.06%) and the crystallite size decreases (from 35.71 to 34.47 nm) while the lattice strain increases (calculated from the Full Width at Half Maximum (β) of the diffraction peak). The highest porosity of ceramic occurred at a sintering temperature of 1000 °C of 37.82 ± 0.19, but the formation of heterogeneous microstructure was observed. The resulting pore size for all temperature treatments was almost mesoporous (19.1 Å). Based on the results obtained, it is emphasized that the sintering temperature can be used to adjust the porosity and microstructure of porous ceramics.

Sodium-hydroxide molarities influence the structural and magnetic properties of strontium-substituted cobalt ferrite nanoparticles produced via co-precipitation

The Sr-substituted CoFe2O4 nanoparticles have been synthesized using the co-precipitation technique with three different molarities of the sodium-hydroxide. The XRD analysis reveals the increase in molarities (1.5 ​M, 3 ​M, 4.8 ​M) causing a decrease in crystallite size (33.9, 30.6, and 28.6 ​nm) and an increase in lattice strain (3.36 x 10−3, 3.71 x 10−3, and 3.98 x 10−3). The results of grain size measurements with Scanning Electron Microscopy were inversely proportional with crystallite sizes, namely 36 ​nm, 43 ​nm, and 47 ​nm. Meanwhile, the larger particle size is obtained for the higher molarities, which conforms with the lower Raman intensity for the higher molarities. Furthermore, the base solution molarity significantly controls the magnetic properties of Sr-substituted CoFe2O4. The increase in molarities leads to a decrease in coercivity, magnetization saturation, and magnetic remanent.

Structural mechanisms of large piezoelectric responses in BiFeO3-PbTiO3 based solid-solution ceramics

Achieving large piezoelectric response and high Curie temperature, simultaneously, are of great demand but have been rarely achieved in BiFeO3-PbTiO3 (BF-PT) based morphotropic phase boundary (MPB) systems. In this work, in-situ synchrotron x-ray diffraction and transmission electron microscopy were carried out in BF-PT-0.19Ba(Zr,Ti)O3 high-temperature piezoceramic, a recently reported MPB composition with high piezoelectric coefficient, to elucidate the underlying structural mechanism. A field induced irreversible transition from tetragonal (T) P4mm phase to rhombohedral (R) R3c phase is identified although R and T phases are still coexisted after poling. This induces the significantly enhanced irreversible domain switching of both R and T phases and the reversible domain switching of R phase but only a slightly enhanced reversible switching of T phase of as compared with other BF-PT-x Ba(Zr,Ti)O3 MPB compositions, leading to the significant increase of lattice strain up to ∼0.15% but only a slightly increase of strain from extrinsic domain switching due to the strong coupling between lattice strain and domain switching in both R and T phases, although the strain contribution seems to be composition independent after the field induced irreversible phase transition. The present study demonstrates a new performance enhancement mechanism to design the high-performance BF-PT based high-temperature piezoelectric ceramics in terms of the different roles of R and T phases within MPB.

Strain Engineering to Boost Piezocatalytic Activity of BaTiO3

AbstractPiezoelectric materials are sensitive to lattice strain, which is always related with their macroscopic properties. Therefore, it is of scientific significance to improve piezocatalytic performance by strain engineering and clarify the underlying mechanism. Herein, BaTiO3 (BTO) powder is fabricated by a solid‐state reaction and ball‐milling is employed to induce lattice strain in BTO. By prolonging ball‐milling time, the lattice strain increases, leading to an enhancement of tetragonality and piezocatalytic performance of BTO. The strain‐engineered BTO exhibited an excellent piezocatalytic activity, with a degradation rate constant k of ∼0.03 min−1 and a H2 evolution rate of 0.899 mmol g−1 h−1, which are 3 and 3.52 times those of the strain‐free one, respectively. The enhanced piezocatalytic performance can be ascribed to the improved piezoelectricity, piezoelectric polarization and adsorption activities for O2, OH and H of the strain‐engineered BTO. This work not only provides a simple and general method to improve piezocatalytic performance by strain engineering, but also unveils the enhancement mechanism.

Effect of low energy milling processes on the magnetic properties of Fe–Ni–Co soft magnetic materials

ABSTRACT This work reports the effect of micro strain of soft magnetic materials obtained by low-energy ball milling. It has been observed that the low energy of the ball milling changes the magnetic domain size, increasing magnetisation, remanence and magnetic permeability of the milled powders as ferromagnetic particles. It is due to the increase of linear defects and the increase of lattice strain. The magnetisation M S increases up to 70% by the accumulation of crystalline defects, although M S decreases with the reduction of particle size, due to the connections of voids between the lines of magnetisation across the crystalline defects obtained by milling. This response is produced by the cold working through the ball milling.

Synthesis of cerium aluminate by the mechanical activation of aluminum and ceria precursors and firing in controlled atmospheres

AbstractSingle‐phase cerium aluminate was synthesized from mixtures of ceria and metallic aluminum by milling and firing under controlled conditions in reducing (10%H2 + 90%N2) or inert atmospheres (N2 or CO2). Firing in an inert atmosphere (CO2) did not yield conversion to cerium aluminate, and conversion was also low after firing in reducing conditions (10%H2 + 90%N2) and only improved slightly on changing from powder mixtures with coarse Al powder (15 µm) to mixtures with submicron Al (0.77 µm). High‐energy milling promoted reactivity by the combined effects of improved homogeneity, decreasing grain size of the Al precursor, increase in lattice strain and decrease in crystallite size down to 40–50 nm. Extensive oxidation of the metallic Al precursor after long‐term milling prevented complete conversion to cerium aluminate even after firing under reducing conditions at temperatures up to 1400°C. Thermodynamic modeling of the Al–Ce–O system provided interpretation for differences between firing in reducing and inert atmospheres. Controlled milling time hinders oxidation of Al to the poorly reactive α‐Al2O3 polymorph. This was supported by thermogravimetry after controlled milling and yielded phase pure CeAlO3 at T ≥ 1200°C. The high conversion was achieved even by firing at 1100°C under an inert atmosphere.

Enhancement of Red Upconversion Emission of ZnS: Er3+/Yb3+ Powders Synthesized via Solid Phase Reaction Method by Introducing Metal Fluoride

AbstractZnS: Er3+/Yb3+ powders were synthesized by a common solid phase reaction method with NaF, CaF2, LiF, AlF3 and MgF2 as dopant. The enhancement mechanisms of different metal fluorides (NaF, CaF2, LiF, AlF3 and MgF2) and concentrations (0 wt% ∼9 wt %) on structure, morphology and optical properties of ZnS: Er3+/Yb3+ powders were investigated systematically. The results revealed that as synthesized ZnS: Er3+/Yb3+ powders are main exhibited as wurtzite phase, the lattice constant, unit cell volume and lattice strain increase with metal fluoride codoping, which indicates the increase of resultant distortion. As synthesized ZnS: Er3+/Yb3+ powders have an intense red upconversion emission centered at 663 nm and a weak green upconversion emission centered at 567 nm under the excitation of a 980 nm laser diode. Compared with ZnS: Er3+/Yb3+ powders synthesized without metal fluoride, the upconversion emission intensities of ZnS: Er3+/Yb3+ powders synthesized with LiF, NaF, MgF2, AlF3 and CaF enhance ∼12 times, ∼9 times, ∼5 times, ∼3 times and ∼3 times, respectively. The strong red upconversion properties make the ZnS: Er3+/Yb3+ powders synthesized with metal fluoride a potential application in the field of light emitting diodes.

Effect of vacuum system on porous product defects and micro structures on the ADC-12 aluminum material with cold chamber die casting machines

Research on the effect of the vacuum system on porous product defects and microstructure on the ADC-12 aluminum alloy material with cold chamber die casting machine has been carried out. In the injection process in cold chamber die casting, the aluminum material commonly used is namely ADC-12. The ADC-12 aluminum alloy has better resistance to corrosion, is lightweight, has ease of casting, good mechanical properties, and dimensional stability. The purpose of this study is to compare the vacuum system with overflow system using ADC-12 aluminum alloy material with observed parameters are porosity, trapped air pressure, hot spot level, hardness level of Vickers Hardness, XRD analysis, and microstructure analysis with Light Optical Microscope (LOM). The results of the analysis using the Magma flow software, the vacuum system is better than the overflow system in terms of porosity and product yield, which is influenced by the amount of air trapped and the hot spot level. The level of hardness in a product with a vacuum system is better than a product with an overflow system. The average hardness in the vacuum system is 162,235 while in the overflow system is 147,615. Thus, the use of a vacuum system can increase the level of hardness in products by around 9%. With the change in usage from the overflow system to the vacuum system, it shows an increase in dislocation density followed by an increase in lattice strain and a decrease in the level of crystal size of the product.

Effect of La-Substituted Barium Hexaferrite on the Structural Characteristics and Magnetic Properties for Microwave Absorbing Material

Ba1-xLaxFe12O19 with ion substitution La3+ (x = 0 – 0.7) has been produced via the mechanical milling technique of the solid reaction method. Considering that Ba1-xLaxFe12O19 is expected to be used as a microwave absorbent, it is necessary to characterize its structural and magnetic features. The refinement results of the X-ray diffraction (XRD) data show that a single-phase hexagonal structure (space group P63/mmc) is obtained for x = 0 and x = 1, while for the composition of x 0.1 is multiphase. The lattice parameters and crystal volume decreased, whereas the lattice strain was found to advance with increasing La substitution in the sample. For x = 0.1, the crystallite size is constant while the lattice strain increases. Employing a scanning electron microscope (SEM), the observation of particle morphology shows that the single-phase (x = 0 and x = 0.1) has a comparably unvarying particle size circulation, while for x 0.1, different particle shapes and sizes are found. The saturation magnetization raises while the coercivity field reduces due to the substitution of La for x = 0.1. Furthermore, for x 0.1, the saturation magnetization decreases while the coercivity field increases.

Modulating the metal-insulator transition in VO2/Al2O3 (001) thin films by grain size and lattice strain

A series of high quality VO2/Al2O3 thin films were prepared by DC sputtering, and the effects of surface topology change on their metal-insulator transition (MIT) behaviors have been discussion in this paper. A ~103 nm-thick VO2/Al2O3 thin film shows extremely large order of magnitude change (~4.2) and low TMIT (56 ℃), and both grain size and lattice strain have been determined as the main causes responsible for the improvement of metal-insulator transition. Specifically, the increase of crystalline size that results in enlarging the grain size, has been identified significantly improves the sheet conductivity of VO2 thin films in rutile phase, which indeed also implements large change in order of magnitude. Besides, the lattice strain has been proven strongly affects the electronic orbitals (π* and d||) occupancy in rutile phase, which has been identified as the one of significant signatures in indicating TMIT change, and thus the increase of lattice strain is believed efficient to modulate TMIT. The close relationships between the surface grain size, lattice strain, TMIT and sheet conductivity in this study for sure will open the door to the fabrication and research on highly quality VO2/Al2O3 thin films.

Crystal chemistry of arsenian pyrites: A Raman spectroscopic study

AbstractA Raman spectroscopic study on the nature of As-S substitution in natural arsenian pyrite [Fe(S,As)2] is presented, covering a compositional range of 0.01–4.6 at% As. Three Raman-active modes were identified in the Raman spectrum of a nearly pure pyrite: Eg (344 cm−1), Ag (379 cm−1), and Tg(3) (432 cm−1). The Raman vibrational modes exhibit one-mode behavior, and the wavenumbers of optical modes vary approximately linearly with As content, correlating with the change in bond constants with increasing substitution of As for S. The linewidth of the Ag mode increases with increasing As substitution, which may be attributed to the increase in lattice strain associated with the substitution of As for S. This study provides experimental evidence for As-induced structural evolution of pyrite from being stable to metastable before decomposing into other phases. Our results, together with those of another Raman study of arsenian pyrite whose As substitution is more complex, indicate that one cannot use Raman band shifts to determine As content, but for a given As content, can characterize the nature of As substitution, i.e., As for S or As for Fe or both.

Improvement in structural properties of SnTe by Co doping for thermo-electric applications

Solvothermal method is used to synthesize SnTe materials for thermal applications. Formation of nano-particles is confirmed from XRD data analysis. Presence of nano-particles decrease lattice thermal conductivity through increased phonon scattering, so the ‘figure of merit’ is enhanced. Cobalt doping in SnTe further decreased lattice thermal conductivity by introducing distortion in crystal structure. Distortion in crystal structure happened due to increase in lattice strain, stacking faults and dislocation density and, decrease in crystallite size. Therefore, Co is an efficient dopant to enhance the ‘figure of merit’ of SnTe for thermoelectric applications.

Microstructural Refinement and Mechanical Properties of Ferritic Stainless Steel Processed by Equal-Channel Angular Pressing

Ferritic stainless steel (FSS 430) has been deformed by equal-channel angular pressing (ECAP) at room temperature at an equivalent strain (evm) of 1.2 by adopting the route Bc. Microstructural developments were studied by optical microscopy, transmission electron microscopy, and microtexture by electron backscattered diffraction. Typical ultrafine-grains of less 0.2 µm could be identified. The XRD patterns confirm the presence of a BCC phase alone. An increase in peak broadening is attributed to the reduction of crystallite size and increase of lattice strain arising from deformation during ECAP. The grain refinement takes place through simple shear deformation by elongation of grains, splitting of grains into bands, the subdivision of bands into subgrains by dynamic recovery, and conversion of subgrains into grains by progressive lattice rotation (PLR). Weakly textured rolled ferritic stainless steel is strongly textured at an imposed equivalent strain of 0.6 with the development of ideal shear components of D2θ and $$\bar{E}_{\theta }$$ for bcc materials. On the second pass of ECAP texture is partially randomized and the intensity of components was decreased and new components of D1θ and Fθ are developed due to subdivision of grains into bands, bands into subgrains, and conversion of subgrains into grains of high angle of misorientation by PLR. The yield strength, tensile strength, and hardness are increased almost 1.5 times that of as-received coarse-grained material due to a high degree of grain refinement and an increase in defect density or strain. The yield strength of 687 MPa of as-received material was enhanced to 1093 MPa of ECAPed ferritic stainless steel. However, the material has lost its ductility significantly due to high defect density and a significant amount of non-equilibrium nature of grain boundaries.

Spark plasma sintering and structural analysis of nickel-titanium/coconut shell powder metal matrix composites

Spark plasma sintering eliminates the need for metal removal processes, which can enhance productivity and make possible the fabrication of materials impossible to get from a melt. In this study, elemental powders of titanium, nickel, and finely pulverized coconut shell powder (CSP) were prepared as a metal matrix composite using the powder metallurgy method. The concentration of CSP organic reinforcement was set at 1, 3, and 5 wt% to the nickel content, while titanium amount was fixed all through. The mild-milled powders were sintered at 850 °C at 10-min dwelling time, 50 MPa and 100 °C/min heating rate. The samples were analyzed using a scanning electron microscope with an energy dispersive X-ray (SEM-EDX) spectrometer, optical microscope, X-ray diffractometer (XRD), and Vickers microhardness tester. Chemical analysis showed the formations of phases consisting of major Ti-rich and Ni-rich compounds with TiNi3 intermetallic boundary layer. Sparse distributions of oxides and ceramic compound phases were also detected. Structural analysis indicates a decrease in crystallite size, D (45.50 to 33.58 nm), and a corresponding increase in lattice strain (0.344 to 0.429%) with organic reinforcement additions. Microstructural analysis indicates an increase in grain densification with CSP reinforcement, and this agrees with the evaluated densification and microhardness properties.