Induced Changes In Microstructure Research Articles

Mechanical Milling – Induced Microstructure Changes in Argyrodite LPSCl Solid‐State Electrolyte Critically Affect Electrochemical Stability

AbstractMicrostructure of argyrodite solid‐state electrolyte (SSE) critically affects lithium metal electrodeposition/dissolution. While the stability of unmodified SSE is mediocre, once optimized state‐of‐the‐art electrochemical performance is achieved (symmetric cells, full cells with NMC811) without secondary interlayers or functionalized current collectors. Planetary mechanical milling in wet media (m‐xylene) is employed to alter commercial Li6PS5Cl (LPSCl) powder. Quantitative stereology demonstrates how milling progressively refines grain and pore size/distribution in the SSE compact, increases its density, and geometrically smoothens the SSE‐Li interface. Mechanical indentation demonstrates that these changes lead to reduced site‐to‐site variation in the compact's hardness. Milled microstructures promote uniform early‐stage electrodeposition on foil collectors and stabilize solid electrolyte interphase (SEI) reactivity. Analysis of half‐cells with bilayer electrolytes demonstrates the importance of microstructure directly contacting current collector, with interface roughness due to pore and grain size distribution being key. For the first time, short‐circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter “mini” symmetrical cell and cryogenic focused ion beam (cryo‐FIB) electron microscopy. The branching sheet‐like dendrite traverses intergranularly, filling the interparticle voids and forming an SEI around it. Mesoscale modeling reveals the relationship between Li‐SSE interface morphology and the onset of electrochemical instability, based on underlying reaction current distribution.

Enhancement of the Microstructure and Fatigue Crack Growth Performance of Additive Manufactured Titanium Alloy Parts by Laser-Assisted Ultrasonic Vibration Processing

AbstractPost-processing techniques can efficiently improve the surface quality, address microstructural defects, and optimize mechanical properties in additively manufactured parts. Surface severe plastic deformation processes such as ultrasonic nanocrystal surface modification (UNSM) integrated with localized laser heating were explored to enhance the surface properties, microstructure as well as the fatigue crack growth properties (FCG) in both directions of built. We successfully induced greater plasticity flow and achieved beneficial refinement of the surface grain structure by precisely controlling the heat and impact energies during surface treatment process. The LA-UNSM process, with the parameters utilized in this study considerably decreased the FCG rates of treated samples, when compared to samples without surface treatment. Improved fatigue crack growth properties along vertical and horizontal orientations after the post-process treatment were attributed to the induced-microstructural changes, improved surface quality, induced compressive residual stresses through gradient structure deformation layer that was prepared on the surface of the material. The fractographic analysis revealed that the cracks mostly originated from the pores in the as-produced state. This observation shows a clear correlation between the surface treatment performed and a substantial improvement in fatigue crack growth resistance.

Different post-processing methods to improve fatigue properties of additively built Ti-6Al-4V alloy

The fatigue performance of the Ti-6Al-4V alloy built using the laser-powder bed fusion additive method was investigated in this study. Post-process methods such as heat-treatment (HT), machining (M), hot isostatic pressing (HIP), and different combinations thereof were explored to enhance the mechanical as well as the fatigue properties. Load-controlled uniaxial high-cycle fatigue tests were performed using a servo-hydraulic fatigue testing machine at room temperature. The machining (M) of the as-built samples increased its fatigue properties, irrespective of the HT and HIP conditions. The tensile strength decreased considerably after the HT, HIP, and HT + HIP treatment but with increasing ductility. On the other hand, the fatigue strength improved with the HT condition and was further enhanced by five times after the HT + HIP + M condition, in comparison to that of the as-built alloy. The X-ray computed tomography analysis revealed a drastic reduction in the percentage of internal defects after the HIP treatment, from 0.31% to 0.01%. The fractographic analysis revealed that the cracks were mostly initiated from the defects in the as-built and HT conditions while in the HIP condition, it was from the facets in the α-phase. The reasons for the improvement in fatigue properties after the different post-process treatments were attributed to the induced-microstructural changes, surface finish quality, relaxed or compressive residual stresses, and most importantly, the reduced fraction of the crack-initiating process-inherent defects, which are explained and argued in this article.

Temperature Induced Microstructural Changes in InGaN/GaN Quantum Wells Observed by Electron Microscopy

Temperature Induced Microstructural Changes in InGaN/GaN Quantum Wells Observed by Electron Microscopy

Combined Extension/Torsion Experiments for Assessing a Constitutive Theory for Elastomers Undergoing Thermally Induced Microstructural Changes

Combined Extension/Torsion Experiments for Assessing a Constitutive Theory for Elastomers Undergoing Thermally Induced Microstructural Changes

High hydrostatic pressure treatment induced microstructure changes and isothiocyanates biosynthesis in kale

Effects of high-pressure processing (HPP) on the myrosinase activity, glucosinolate (GLS) content, isothiocyanate (ITC) conversion rate, color, and bacterial count of kale leaves were investigated. Thermal process at 100 °C were used as negative control groups. The sample processed at 600 MPa exhibited the highest myrosinase activity and ITC conversion rate of 70.4%, while the GLS content was significantly lower than those in the raw and the thermally processed samples. However, processing of the samples at elevated temperatures results in gradual loss of myrosinase activity. SEM images showed that HPP induces irregular crushing damage to the veins, edges, and surfaces of the leaves, thereby promoting the conversion process in the myrosinase–GLS–ITC system. Additionally, HPP caused less significant color change of the kale leaves than thermal treatment. HPP achieved the same level of pasteurization as thermal treatment in terms of bacterial count.

Effects of multiaxial forging on microstructure and high temperature mechanical properties of powder metallurgy Ti-45Al-7Nb-0.3W alloy

Uniaxial forging (UAF) and multiaxial forging (MAF) were conducted on a Ti-45Al-7Nb-0.3W (at. %) alloy produced by powder metallurgy (PM) technique, and the deformed microstructures and deformation mechanism were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that the near-gamma microstructure (NG) transformed into a fine and uniform duplex microstructure (DP) after MAF, and the mean grain size of the multiaxial forged alloy was 5 μm. The microstructure of the uniaxial forged alloy was inhomogeneous and anisotropy, while the microstructure of multiaxial forged alloy was very uniform and a higher amount of the β phase was distributed at the grain boundaries. During forging, deformation induced microstructure changes include dislocation movements, mechanical twinning, layer decomposition and dynamic recrystallization (DRX). The DRX occurred repeatedly and more severely during MAF than UAF process. Correspondingly, the multiaxial forged TiAl alloy exhibited excellent high temperature mechanical properties compared to the uniaxial forged alloy. At a temperature of 750 °C, the yield strength, ultimate tensile strength and elongation of the multiaxial forged alloy were 623 MPa, 697 MPa and 4.5%, respectively. It was noteworthy that the multiaxial forged alloy achieved highly plastic deformation and the elongation reached 173% at 900 °C with a strain rate of 1 × 10−3 s−1.

A comparison of the DPSS UV laser ablation characteristic of 1024 and H10F WC-Co

An investigation on ablation characteristics of 1024 and H10F cobalt cemented tungsten carbide (WC-Co) with a DPSS nanosecond UV laser (50ns pulse width, 355nm wavelength, 90W average power and 10kHz repetition rate) is presented. The ablation characteristic parameters such as ablation threshold, incubation effect and optical penetration depth were evaluated based on the spot ablation diameter and depth. It was observed that the ablation threshold is significantly influenced by the number of pulses (NOP) and it decreases with increase NOP which is attributed to the incubation effect. Only one ablation region is observed at low laser fluence and an additional molten ablation region is observed at high laser fluence accompanied with cracks. The cracks formation is due to the thermal induced stress and changes in WC microstructure during laser beam irradiation. The crack depth is proportional to the thickness of the molten WC region. The ablation threshold of 1024 WC-Co and H10F WC-Co were found to be Fth1 =4.32J/cm2 and Fth1 =4.26J/cm2 respectively. The difference in chemical composition has insignificant effect on the ablation threshold value of the material. The incubation factor and optical penetration depth values of 1024 WC-Co and H10F WC-Co were found to be ξ=0.73, α−1 =411nm and ξ=0.75, α−1 =397nm respectively.

Effects of Electropulsing Induced Microstructural Changes on THz-Reflection and Electrical Conductivity of Al-Doped ZnO Thin-Films

Electropulsing induced phase transformation and crystal orientation change and their effects on electrical conductivity, THz reflection and surface roughness of thin-films of Al2O3 (2 wt%) doped ZnO were studied using XRD, SEM, AFM and Thz spectroscopy techniques. AZO-2 thin-films showed an effective response in THz spectroscopy under electropulsing. Electropulsing induced circular preferred crystal orientation changes and phase transformations were observed. The preferred crystal orientation changes accompanying decrease in stress and the secondary phase precipitation favored enhancing conductivity and THz reflection of the AZO-2 thin-films. After adequate electropulsing, both THz reflection and electrical conductivity of the thin-films were enhanced by 22.8% and 6.8%, respectively; meanwhile surface roughness reduced. The property responses of electropulsing are discussed from point view of microstructural change and dislocation dynamics.

Thermal Shock Induced Phases Transformation and Microstructural Changes in a Novel Hydrogen Transport Membrane

ABSTRACTBulk samples of a novel cermet (ceramic/metal composite) hydrogen transport membrane (HTM) were subjected to thermal cycling in the temperature range between 25-850°C to study phase transformations and microstructural changes under thermal shock. Scanning electron microscopy (SEM) and electron probe micro analyzer (EPMA) with energy dispersive spectroscopy (EDS) were used to characterize the microstructural and chemical changes in the membrane upon thermal cycling. SEM & EPMA analyses indicated that the temperature gradient during thermal cycling produced more micro-cracks inside the HTM disc, whereas, the chemical reaction between Pd and oxygen to form PdO disturbed the continuity of the metal palladium (Pd) - Yttria Stabilized Zirconia (YSZ) dual phases interconnection system from surface down. The agglomerates of un-crystallized YSZ grains found to be the inherent in the cracks of the as-received HTM. A combination of trans-granular and inter-granular crack propagation results around the YSZ grains and the new precipitates. Based on the electron fractography analyses by both SEM and EPMA, the micro voids coalescence develops ahead of the crack tips in the cross-section of the HTM after 500 thermal cycles.

From solid solution to cluster formation of Fe and Cr in α-Zr

To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques — atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed.

Effect of helium implantation on SiC and graphite**Project supported by the ITER-National Magnetic Confinement Fusion Program, China (Grant Nos. 2010GB109000, 2011GB108009, and 2014GB123000) and the National Natural Science Foundation of China (Grant No. 11075119).

Effects of helium implantation on silicon carbide (SiC) and graphite were studied to reveal the possibility of SiC replacing graphite as plasma facing materials. Pressureless sintered SiC and graphite SMF-800 were implanted with He+ ions of 20 keV and 100 keV at different temperatures and different fluences. The He+ irradiation induced microstructure changes were studied by field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM).

Electron Beam Induced Microstructural Changes and Electrical Conductivity in Bakelite RPC Detector Material

To explore the structural modifications in terms of crosslink density and electrical conductivity in polymer based Bakelite RPC detector material was exposed to 8 MeV electron beam with the irradiation doses of 20 kGy to 100 kGy in steps of 20 kGy. The microstructural changes of Bakelite upon electron beam irradiation have been studied using Positron Annihilation Lifetime Spectroscopy (PALS), X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. Positron lifetime parameters viz., o-Ps lifetime and its intensity showed chain scission at lower doses (at 20 kGy and 40 kGy) followed by crosslinking due to the radical reactions. These changes are effectively explained with the help of FTIR and XRD parameters. The reduction in electrical conductivity of Bakelite material beyond 60 kGy is correlated between conducting pathways and crosslinks in the polymer matrix. The appropriate dose of electron beam on Bakelite might reduce the leakage current of Bakelite RPC detector material and hence improves the performance of the detector.

Study on the applicability of the measurements of magnetoelastic properties for a nondestructive evaluation of thermally induced microstructure changes in the P91 grade steel

The paper presents the results of the investigation of the influence of duration and temperature of tempering process on the magnetoacoustic properties of P91 tempered martensite ferritic steel. During tempering of martensitic steels the dislocation density, which initially is very high, systematically decreases what is confirmed both by analysis of the width of X-ray diffraction peaks and hardness measurements. Magnetic hysteresis loops undergo a systematic change resulting in the monotonous decrease of magnetic “hardness” of the investigated samples. The influence of the tempering time on the Barkhausen noise (BN) and magnetoacoustic emission (MAE) signals intensity was investigated in order to verify the possibility of application of those methods for a nondestructive monitoring of heat treatment quality. Barkhausen noise signal envelopes change their shape very strongly during the initial stages of tempering, yet the overall signal intensity is weakly affected. As for the magnetoacoustic emission a very strong increase of its intensity is observed for almost all the tempering times and temperatures. It was concluded that the MAE signal intensity is a suitable parameter for the evaluation of tempering time, as for the BN signal the envelope shape analysis would be necessary for such a purpose.

Microstructure Changes in Zr-Based Metallic Glass Induced by Ion Milling

Abstract Four groups of transmission electron microscopy (TEM) specimens of Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 metallic glass were prepared by double-jet electropolishing, dimpling and ion milling. TEM observations indicate that the microstructures in electron-transparent areas change sensitively with ion milling conditions. Detailed comparisons between the selected area electron diffraction patterns of TEM specimens and the X-ray diffraction patterns of thermally annealed samples of the same composition show that significant heating effects exist in some severe milling processes, resulting in the formation of various ordered structures in thin areas. In TEM specimens prepared by intentionally long time ion milling, the peak temperature locally reached is estimated as high as 780 K, far above the glass transition temperature of this metallic glass. The results suggest that precautions must be taken to prepare TEM specimens of amorphous alloys by ion milling, particularly when the induced microstructure changes may lead to invalid judgments.

Coating Degradation in Hot Press Forming

The thermo-mechanically induced microstructure changes occurring in a type 1 aluminized coating on hot press forming (HPF) steel were studied in detail. The formation of intermetallic phases at the soaking temperature prior to die quenching revealed that the coating matrix consists mainly of FeAl2 intermetallic phase by the time the press forming carried out. Kirkendall void formation was observed to take place. The thermal oxidation of aluminized coating during HPF was found to be limited, with the coating acting as an effective barrier for the oxygen during heating. The deterioration caused by the high temperature plastic deformation was shown to lead to coating cracking without loss of adhesion. The steel surface was oxidized where it was exposed between the coating segments.

On the induced microstructure changes of the amorphous carbon nitride films during annealing

The analysis of the stress release and structural changes caused by postdeposition thermal annealing of amorphous carbon nitride thin films (a-CNx) has been carried out. The a-CNx films were deposited on Si (100) using reactive radio frequency (rf) magnetron sputtering of a high-purity graphite target in a pure nitrogen plasma under various different rf powers. Combined Fourier transform infrared (FTIR), Raman spectroscopy, transmission spectroscopy, photothermal deflexion spectroscopy, and residual stress measurements were used to fully characterize the films. Annealing of the samples in vacuum at temperature up to 600°C produces changes in their structural properties and the intrinsic stress. These changes are found to be strongly dependent on both the deposition conditions and microstructure changes occurring within the films during heating. FTIR spectra showed the existence of N–C sp3, NC sp2, and CN triple bonds in the deposited films. The analysis of the spectra versus annealing temperature (TA) reveals that the major microstructure changes are the reorganization of the C–N and C–C configurations, without significant densification of the deposited films. The Raman features combined to the optical measurements reveal that this progressive graphitization of the material, with increasing TA, is accompanied by a higher disorder form of C sp2 sites. These results are used to describe the stress variation that accompanies the nitrogen evolution within the deposited films.

Laser and thermal induced micro-structural changes and decompositionof hydrogenated carbon films

Micro-structural changes and decomposition of hydrogenated carbon films onmagnetic disk substrates prepared by DC-magnetron sputtering were studiedusing Ar+ laser irradiation and physical heating in air and nitrogenambience, respectively. It was found that a weak Ar+ laser of a fluenceof 0.3 mW µ m-2 could significantly decompose a-C:Hfilms. The decomposition rate was fast initially and slowed downsignificantly after about 20 min. The decomposition rate of a-C:H increasedwith hydrogen concentration in the film. Raman light intensities of theirradiated sites reduced exponentially with irradiation time. Physicalheating in air revealed that the oxidation-dominated decomposition tookplace between 320 and 350 °C within 15 min, and an increased hydrogenconcentration made the a-C:H film more vulnerable to decomposition. At150-300 °C, a phenomenon of nano-crystal graphite formation was observed fromRaman spectra. XPS analysis indicated that there was no significantdiffusion of carbon atoms into the substrate at 400 °C heating.

On the inelastic behavior of solids — Part 1: Twinning

Abstract Recently, Wineman and Rajagopal [1990] “On a Constitutive Theory for Materials Undergoing Microstructural Changes,” Arch. Mech., 42 , 53 and Rajagopal and Wineman [1992] “A Constitutive Equation for Nonlinear Solids which Undergo Deformation Induced Microstructural Changes,” Int. J. Plasticity, 8 , 385, developed a theory that was particularly well suited to describing the inelastic behavior of polymeric materials. Here, we draw upon their ideas and generalize them to include a much larger class of materials. The versatility and efficacy of the theory are illustrated by studying the problem of twinning within the context of the theory. We find that the predictions of the theory are remarkably close — both qualitatively and quantitatively — with the experimental results of Madhava et al. [1972] “Discontinuous Twinning during Essentially Elastic Compression of Steel at 4.2K,” Phil. Mag., 25 (2), 519 and Madhava and Armstrong [1974] “A Constitutive Relation for Deformation Twinning at High Strain Rates,” in Rohde, R.W., Butcher, B.M., Holland, J.R. , and Karnes, C.H. , eds., Metallurgical Effects at High Strain Rates. Plenum, New York, 1974.