Effect Of Microstructural Changes Research Articles

Effect of Microstructural Change under Pressure during Isostatic Pressing on Mechanical and Electrical Properties of Isotropic Carbon Blocks.

In this study, carbon blocks were fabricated using isotropic coke and coal tar pitch as raw materials, with a variation in pressure during cold isostatic pressing (CIP). The CIP pressure was set to 50, 100, 150, and 200 MPa, and the effect of the CIP pressure on the mechanical and electrical properties of the resulting carbon blocks was analyzed. Microstructural observations confirmed that, after the kneading, the surface of isotropic coke was covered with the pitch components. Subsequently, after the CIP, granules, which were larger than isotropic coke and the kneaded particles, were observed. The formation of these granules was attributed to the coalescence of kneaded particles under the applied pressing pressure. This granule formation was accompanied by the development of pores, some remaining within the granules, while others were extruded, thereby existing externally. The increase in the applied pressing pressure facilitated the formation of granules, and this microstructural development contributed to enhanced mechanical and electrical properties. At a pressing pressure of 100 MPa, the maximum flexural strength was achieved at 33.3 MPa, and the minimum electrical resistivity was reached at 60.1 μΩm. The higher the pressing pressure, the larger the size of the granules. Pores around the granules tended to connect and grow larger, forming crack-like structures. This microstructural change led to degraded mechanical and electrical properties. The isotropic ratio of the carbon blocks obtained in this study was estimated based on the coefficient of thermal expansion (CTE). The results confirmed that all carbon blocks obtained proved to be isotropic. In this study, a specimen type named CIP-100 exhibited the best performance in every aspect as an isotropic carbon block.

Evaluation of strength and electrical conductivity of copper clad-AA6063 bimetallic composite wire after annealing treatment

This study investigates the manufacturing of copper-AA6063 aluminum alloy composite wire and the effect of microstructural changes and metal-metal interface after annealing at 300 °C at different times on the strength and electrical conductivity. For fabrication of the composite wire, first AA6063 aluminum alloy wire was inserted inside an OFHC copper tube with a diameter of 6 mm. Afterward, a composite wire was produced using a cold drawing process in thirteen steps to a diameter of 1.5 mm. The tensile and microhardness tests used for evaluation of the composite wire's mechanical properties. Also, the light and scanning electron microscopes (SEM) used for microstructural characterization. The results showed that forming a region with a strain gradient at interface has a determinative effect on the strength and ductility of composite wire. The composite wire without annealing showed the highest strength, 278 ± 7 MPa. The annealing treatment result in strength reduction and negligible change in the electrical conductivity. The composite wire after annealing treatment for 30 and 60 min showed the highest electrical conductivity, 83 ± 1%IACS, and the highest elongation, 45 ± 4%, respectively.

Influence of post-heat treatment with super β transus temperature on the tensile behaviour of LPBF processed Ti6Al4V

This paper investigates the tensile behaviour of Laser powder bed fusion (LPBF) processed Ti6Al4 V samples under three build orientations. The effect of microstructural changes from the post-heat treatments (PHTs – 850 °C, 950 °C 1050 °C) was assessed. The microstructural characterization was performed using optical microscopy, X-ray diffraction, and SEM techniques. The tensile tests were performed using a uniaxial universal testing machine (UTM). The fractal dimension analysis was performed on the fractured surfaces using ImageJ software integrated with an open-source MultiFrac plug-in. The PHT at a higher temperature (i.e., 1050 °C) induces a higher amount of β phase than the other PHTs. The PHT performed at 1050 °C exhibited α-Widmanstatten microstructure consisting of elongated β and a small amount of α. The PHT induces an isotropic behaviour in the LPBF-processed samples. However, the ductility of specimens subjected to PHT at 1050 °C showed ∼ 67%, 40%, and 177% improvement under horizontal (0°), inclined (45°), and vertical (90°) orientations than as-printed samples. Further fractal dimension analysis corroborates well with the ductility values of PHT samples. Therefore, the combination of fractography analysis and fractal dimension approach can be a promising methodology towards fractured surface characterization of additively manufactured metal parts.

Study the effect of microstructure changes on the photocatalytic performance of Ni and Zn nanoferrites

Study the effect of microstructure changes on the photocatalytic performance of Ni and Zn nanoferrites

Effect on microstructural and mechanical properties of selective laser melted pure Ti parts using stress relief heat-treatment process

This study investigated the correlation between the microstructure and the mechanical properties of pure Ti specimens manufactured via selective laser melting (SLM) using the stress relief heat-treatment process. Similar heat treatments were performed at a rate of 10 °C/min with a dwell time of 2 h to reach post-treatment temperatures ranging from of 490–890 °C in intervals of 100 °C. Phase change analysis using X-ray diffraction was conducted to verify the effects of the post-treatment process, while electron backscatter diffraction analysis was conducted to study the effects of microstructural changes induced by the post-treatment process on the mechanical properties of pure Ti specimens. In addition, a comprehensive analysis was performed to analyze residual stress following the stress relief heat treatment. The findings of this study establish a clear relationship between the mechanical properties and microstructural changes in SLM-manufactured pure Ti after heat treatment across a broad temperature range. Furthermore, the study confirms that heat treatment effectively relieves the residual stress in SLM Ti specimens.

Effect of Microstructure Change on Mechanical Properties after High Temperature Forming of Ti-6Al-4V Alloy

Ti-6Al-4V alloy is not easy to machine complicated shapes due to its low thermal conductivity, so high-temperature forming techniques such as ring-rolling are being applied. When this high-temperature forming technology is applied, the microstructure is greatly changed by process variables, and the mechanical properties of the forming product are also different accordingly. In particular, in the case of the Widmanst tten structure, α lamellar spacing and colony size have a great influence on mechanical properties. Therefore, in this study, the most suitable process conditions were selected by performing a high-temperature compression test to apply the ring-rolling process to the Ti-6Al-4V alloy used as an aerospace material. After that, the microstructure of the forming product was observed, the effects of α lamellar spacing and colony size on the mechanical properties were confirmed, and the correlation between mechanical properties and microstructure was evaluated based on this.

Modeling polarization switching response of ferroelectric ceramics based on multiple natural configuration theory

Ferroelectric ceramics experience polarization switching, which is macroscopically shown by nonlinear hysteretic responses when subjected to high compressive stresses and/or high amplitude of the electric field. We model the nonlinear hysteretic response of ferroelectric ceramics by considering evolutions of microstructural changes associated with changes in the dipole orientations due to both electrical and mechanical stimuli. We adopt the theory of multiple natural configurations, associated with multiple stress-free and electric-field-free states, in incorporating the effect of microstructural changes on describing the nonlinear electro-mechanical hysteretic response of ferroelectric ceramics. The first stress-free and electric-field-free states are associated with the original microstructure of the materials, in which the dipoles in the ferroelectric ceramics are randomly oriented. The new configurations are formed when the ferroelectric ceramics are subjected to relatively large stimuli, which align the dipole orientations. As each configuration is associated with a specific microstructure (a state of dipole orientations), mechanical and electrical properties characterized at different configurations will be different. To examine the model, experimental data on PZT (lead zirconate titanate) ceramics under electric and stress fields, available in the literature, are used. The model is capable of describing the hysteretic response in PZT under electro-mechanical stimuli.

The effect of heat input in multi-pass GMAW of S960QL UHSS based on weaving and stringer bead procedure on microstructure and mechanical properties of HAZ

Quenched and tempered S960QL (yield strength ≥ 960 MPa) ultra-high strength steel (UHSS) thick plates were joined by multi-pass robotic gas metal arc welding (GMAW) using weaving and stringer bead techniques. The effects of microstructural changes in heat-affected zone (HAZ) of the joint on toughness and hardness were examined. Weaving and stringer bead techniques applied for the multi-pass welding procedure altered average peak temperatures and exposure time to those temperatures. Mechanical properties of HAZs were evaluated by utilizing notch impact and hardness tests, and these results were correlated with microstructural characterizations using optical (OM) and scanning electron microscopes (SEM). Prior austenite grain (PAG) coarsening occurred because of increased exposure time to peak temperature in coarse-grained HAZ (CGHAZ) of the W-5 (weaving pass) joint. CGHAZs at the face pass, which have not been subjected to a second thermal cycle, have the highest hardness in both joints. Hardness of SCHAZ and CGHAZ of S-12 joint was 7% and 1% higher compared with W-5 joint, respectively. Weld metal hardness of W-5 joint was 15% lower than that of S-12 joint. Both joints not only fulfilled the requirements of minimum 50 J per EN ISO 10025-6 at −20 °C but exceeded this limit by 50% (W-5) and 200% (S-12). Lateral expansions for impact toughness specimens were around 17.5% for S-12 joint, whereas it was 4% for W-5 joint. Since HAZ in the S-12 (stringer bead) joint is narrow compared with the one in the W-5 joint, impact toughness values were higher with the S-12 joint due to the locations of the notches of the impact specimens.

Tuning microstructures of TC4 ELI to improve explosion resistance

A reasonable heat treatment process for TC4 ELI titanium alloy is crucial to tune microstructures to improve its explosion resistance. However, there is limited investigation on tuning microstructures of TC4 ELI to improve explosion resistance. Moreover, the current challenge is quantifying microstructural changes’ effects on explosion resistance and incorporating microstructural changes into finite element models. This work aims to tune microstructures to improve explosion resistance and elucidate their anti-explosion mechanism, and find a suitable method to incorporate microstructural changes into finite element models. In this work, we systematically study the deformation and failure characteristics of TC4 ELI plates with varying microstructures using an air explosion test and LS-DYNA finite element modeling. The Johnson‒Cook (JC) constitutive parameters are used to quantify the effects of microstructural changes on explosion resistance and incorporate microstructural changes into finite element models. Because of the heat treatment, one plate has equiaxed microstructure and the other has bimodal microstructure. The convex of the plate after the explosion has a quadratic relationship with the charge mass, and the simulation results demonstrate high reliability, with the error less than 17.5%. Therefore, it is feasible to obtain corresponding JC constitutive parameters based on the differences in microstructures and mechanical properties and characterize the effects of microstructural changes on explosion resistance. The bimodal target exhibits excellent deformation resistance. The response of bimodal microstructure to the shock wave may be more intense under explosive loading. The well-coordinated structure of the bimodal target enhances its resistance to deformation.

Effect of in-situ formed oxide and carbide phases on microstructure and corrosion behavior of Zr/Y doped CoCrFeNi high entropy alloys prepared by mechanical alloying and spark plasma sintering

The present work has examined the microstructural evolution, thermal stability, hardness, and corrosion behavior of Zr/Y doped CoCrFeNi HEAs prepared through high-energy mechanical alloying followed by spark plasma sintering (SPS) at 1100 °C. The achieved microstructures were investigated by XRD and TEM techniques. The results showed that investigated HEAs consist of an fcc solid solution of CoCrFeNi matrix with in-situ formed Cr–C carbides and Cr/Zr/Y based oxide phases. The SPS processing of CoCrFeNi yielded grain growth to 370 ± 60 nm, while 240 ± 160 nm grain size with bimodal grain size distribution and 165 ± 38 nm grain size were achieved with Zr and Y additions, respectively. The effects of microstructural changes on the hardness and corrosion behaviors of HEAs were also investigated. Compared with 372 ± 15 HV hardness of CoCrFeNi HEA, 445 ± 26 HV and 563 ± 58 HV hardness values were determined with Zr and Y doped HEAs, respectively. The increase in hardness is mainly ascribed to the precipitation strengthening of carbide and oxide phases as well as smaller grain sizes. The corrosion analysis showed that, although the achieved smaller grain sizes and the presence of different oxide types when dopped with Y and Zr impaired the corrosion resistance, the investigated HEAs have reasonable resistance to corrosion when compared to SS304 stainless steel.

Effect of Structural Changes at Various Length Scales in SiVOC Ceramic Nanocomposites on Electrocatalytic Performance for the Oxygen Reduction Reaction.

Polymer-derived processing of ceramics (PDC) is an efficient technique to prepare porous nanocomposites with precise control over their phase composition and in relation to the Si-based ceramic matrix containing free carbon. The microstructure of these nanocomposites can be fine-tuned at the molecular scale for obtaining necessary properties by tailoring the chemical configuration of the preceramic polymer. In the present work, vanadium-based nanocomposites were synthesized as oxygen reduction reaction (ORR) catalysts with the objective of elucidating the effect of microstructure changes on catalytic efficiency. For this purpose, a single-source precursor (SSP) was synthesized by crosslinking phenyl- and hydrido-substituted polysiloxane and vanadium acetylacetonate followed by pyrolysis at 1100 °C. The resulting solid was composed of sparsely distributed nanodomains of vanadium carbide (VC) crystals precipitated within an amorphous silicon oxycarbide (-Si-O-C-) matrix. High-temperature treatment of the pyrolyzed samples beyond 1300 °C induced the crystallization of β-SiC as well as VC. Furthermore, Raman spectroscopy confirmed the segregation of sp2-hybridized, turbostratic free carbon. The samples exposed to 1300 °C revealed a specific surface area of 239 m2/g. The electrocatalytic activity of the sample heat-treated at 1300 °C showed the best performance with respect to the ORR performance with onset potential (Eo) and half-wave potential (E1/2) values of 0.81 and 0.72 V, respectively. In addition, improved kinetics with a Tafel slope of 57 mV/dec and enhanced current density in the diffusion-controlled region (Id) of 3.7 mA/cm2 were observed for this sample. The increase in Eo was attributed to the optimal interfacial characteristics between the VC and SiOC matrix with better embedment of VC with free carbon through V-C bonds. The higher E1/2 and faster kinetics are because of the higher electronic conductivity caused by the free carbon effectively connecting metallic VC crystallites. Besides, the higher specific surface area of this sample enhanced Id.

Effect of post-heat treatment with super β transus temperature on the damping behaviour of LPBF-processed Ti6Al4V thin rotor blade

This article investigates the damping behaviour of laser powder bed fusion-processed Ti6Al4V thin plate samples and thin rotor blades. The effect of microstructural changes owing to the post heat treatments (PHTs – 850 °C, 950 °C and 1050 °C) on damping behaviour was assessed. The microstructural characterisation was performed using optical microscopy, X-ray diffraction and scanning electron microscope techniques. The impact hammer test was performed on thin plate samples and rotor blades to characterise damping behaviour. The microstructure of the thin plate samples subjected to PHT conditions varied in grain structure and morphology compared to the as-printed ones. Further, PHT at a higher temperature (i.e. 1050 °C) induces a higher amount of β phase than the other PHT temperatures. The PHT performed at 1050 °C exhibited α- Widmanstätten microstructure consisting of elongated β and a small amount of α. Moreover, the frequency response function plots revealed broader peaks for thin plate samples and the rotor blade than others. The PHT was favourable in enhancing the α lath thickness and β volume fraction, increasing the damping ratio. The results showed that PHT performed at 1050 °C improves the overall damping of ∼348% and ∼140% of rotor blade and thin plate samples, respectively. The amplitude decay for the rotor blade subjected to PHT at 1050 °C was ∼66% shorter than the as-printed one due to high β phase content relieving the energy resulting in a high damping ratio.

Revealing the effects of microstructural changes of graphite anodes during cycling on their lithium intercalation kinetics utilizing operando XRD

Concerning cell ageing and lithium plating, electrode kinetics – in particular the one of the anode - plays an important role. In our study, we applied a holistic physicochemical post-mortem analysis including operando XRD and SEM-studies as well as electrochemical analysis to get deeper insights into the changes of the microstructure and phase composition of graphite anodes from LiNi0.6Co0.2Mn0.2O2//Graphite pouch cells during cyclic ageing and their influence on the lithium intercalation kinetics. The key findings are as follows: Li plating and loss of cyclable lithium is the main source of capacity fade of the investigated cells. Cycling causes pore clogging of the anode leading to an increased transport resistance for Li-ions and slower charge transfer reactions. Visual inspections and operando XRD measurements in turn indicate an inhomogeneous Li intercalation over the thickness of the electrode resulting in a Li gradient. In the cycled electrode LiC6 forms in surface-near regions, whereas in deeper regions LiC12 formation has not finished yet. As a result, Li plating occurs as the surface-near graphite is already fully intercalated and Li-ion transport to deeper regions is hindered due to pore clogging. By combining complementary methods we could consistently prove the hypothesis of pore clogging, deterioration of anode kinetics and subsequent inhomogeneous lithiation which is supposed to trigger the observed Li-plating.

Transformation of borides in directionally solidified nickel base superalloy and its mechanical response

Directionally solidified (DS) GTD444 is a boron-modified nickel base superalloy which is used in later stage tubine blades. Boron is added as a grain boundary strengthener and it modifies the grain boundary microchemistry. During service, the blades undergo thermal exposure that could lead to further changes in the grain boundary chemistry. This is known to influence the grain boundary strength and affects the overall mechanical response of the superalloys. In the present study high resolution characterization has been carried out to investigate the evolution of grain boundary precipitates in DS GTD444 alloy under thermal aging at 900 ºC. In addition, in situ picoindentation and high-temperature tensile tests were performed to determine the effect of changes in microstructure on the mechanical properties. Atom probe tomography, in conjunction with electron microscopy, shows that nano-sized borides present along grain boundaries in the as-received DS blades completely transform into carbides after aging. These carbides are of two types: M23C6, and M6C. These carbides are present discretely along the grain boundary. The evolved microstructure after 320 h of aging shows higher transverse ductility as compared to the as-received DS blades, and the failure in all tested samples was transgranular. This suggests that the presence of discrete precipitates (borides or carbides) along the DS boundaries strengthens the grain boundaries.

Investigating the effects of microstructural changes induced by myocardial infarction on the elastic parameters of the heart

Within this work, we investigate how physiologically observed microstructural changes induced by myocardial infarction impact the elastic parameters of the heart. We use the LMRP model for poroelastic composites (Miller and Penta in Contin Mech Thermodyn 32:1533–1557, 2020) to describe the microstructure of the myocardium and investigate microstructural changes such as loss of myocyte volume and increased matrix fibrosis as well as increased myocyte volume fraction in the areas surrounding the infarct. We also consider a 3D framework to model the myocardium microstructure with the addition of the intercalated disks, which provide the connections between adjacent myocytes. The results of our simulations agree with the physiological observations that can be made post-infarction. That is, the infarcted heart is much stiffer than the healthy heart but with reperfusion of the tissue it begins to soften. We also observe that with the increase in myocyte volume of the non-damaged myocytes the myocardium also begins to soften. With a measurable stiffness parameter the results of our model simulations could predict the range of porosity (reperfusion) that could help return the heart to the healthy stiffness. It would also be possible to predict the volume of the myocytes in the area surrounding the infarct from the overall stiffness measurements.

Effect of Heat Treatment on Microstructure and Properties of Improved 40CrNi2Si2MoV Steel

Ultrahigh‐strength steel (2000 MPa) is a key material widely used in national defense, aerospace, and various other sectors. This kind of steel is more likely to break as its strength increases. To improve its toughness, it is crucial to fully understand the strengthening and toughening mechanisms, microstructural evolution characteristics, and heat‐treatment parameters of ultrahigh‐strength steel. Herein, an improved 40CrNi2Si2MoV test steel is designed based on the composition of the 40CrNi2Si2MoV ultrahigh‐strength martensitic steel and is subjected to quenching at 860/900/930/1050/1150 °C. The effects of microstructural changes on the test materials are analyzed using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, electron backscatter diffraction, transmission electron microscopy, and other characterization methods. The results show that at a quenching temperature of 1050 °C, the material exhibits an elongation of 8.2% and a strength as high as 2200 MPa owing to the coupled effects of complex multicomponent laths, substructures, dislocations, and nano‐precipitates.

Effect of Heat Treatments on Microstructure and Mechanical Properties of Low-Cost Ti-6Al-4V Alloy Produced by Thermomechanical Powder Consolidation Route

This paper investigates the level of properties enhancement achievable by heat-treating Ti-6Al-4V alloy produced from a blended powder mixture using a thermomechanical powder consolidation route involving warm uniaxial pressing and vacuum sintering followed by extrusion at super transus temperature (1150 °C). The as-extruded material with a higher oxygen content of 0.55 wt.% was subjected to two different sub-transus annealing treatments: HT-A: 955 °C/1 h-furnace cooling and HT-B: 925 °C/4 h-cooling @ 50 °C/h to 760 °C-furnace cooling. Room temperature Charpy v-notch impact toughness tests and tensile tests were performed to ascertain the effect of microstructural changes during post-extrusion annealing treatments. After impact tests, analysis of microstructures and fracture surfaces of samples was carried out using optical and scanning electron microscopy. The as-extruded material displayed mean impact toughness of 4 J along with a yield strength of 956 MPa, an ultimate tensile strength of 1150 MPa, and an elongation to fracture of 2.4%. The annealing treatments gave a noticeable enhancement in the impact toughness (average values 5–6 J obtained) while maintaining a yield strength and ultimate tensile strength level of about 992 MPa and 1164–1181 MPa, respectively. Additionally, the level of change in ductility was limited for each sub-transus annealing treatment, and HT-A has given only a 30% increase compared to as-extruded material.

The effect of microstructural changes on the rupture behavior of gas turbine damping bolt superalloy (Nimonic 90) after long service time

The present study investigated the microstructure of superalloy gas turbine damping bolt. These damping bolts were selected from new and service-exposed ones made of nickel-based Nimonic 90, which had been served for a long time. The microstructure of new sample had an austenitic matrix with many twins. These twins were located in the intergranular and intragranular regions of the primary carbides. Fine gamma-prime precipitates also could be found in the field. However, due to the high amount of service time, the arranged structure turned into a complex one in which the Sigma and Mayo phases with the Widmanstätten pattern appeared near the grain boundaries. Therefore, secondary continuous carbides formed near the grain boundary, and γ′ precipitates grew, which increased the hardness of the samples by about 30 Vickers. The mentioned microstructural changes reduced the creep rupture to 140 MPa at 870 °C in 11 h, while the sample had a creep life of about 21 h. This indicates that the resulting microstructural changes reduced brittleness and creep life. The soft intergranular failure mechanism in the new damping bolt became an intergranular mechanism. Moreover, the effects of intragranular failure were also abundant.

Study of polarization behavior in BaTiO<sub>3</sub>-based multilayer ceramic capacitors using AC- and Uni-poling treatment ∼ Part 1: Effects of microstructural changes

To obtain guidelines for the microstructure design of BaTiO3-based multilayer ceramic capacitors from the viewpoint of polarization behavior, the effects of AC- and Uni-poling treatments were examined using intentionally grain-growth samples. For purposes of comparison, the DC-aging characteristics of each sample were also examined. From the results of the polarization behavior induced by AC- and Uni-poling treatments, it was confirmed that changes in the core–shell structure, grain size, and oxygen vacancy concentration of the dielectrics strongly affected the domain wall pinning. In comparison with DC-aging characteristics, AC- and Uni-poling treatments are also expected to be effective tools for clarifying the relationships among more detailed microstructure and polarization behaviors of dielectrics.

Correlation Analysis of the Change Law of Index Gas and Active Functional Groups in the Process of High-Temperature Spontaneous Combustion of Minerals in the Fushun West Mine.

The spontaneous combustion of underground minerals causes huge property losses and ecological damage. Coal and oil shale are co-associated minerals in the Fushun West Mine, and both have the ability to undergo oxidative spontaneous combustion. To study the effect of microstructure changes on the macroscopic gas product concentration during the mineral oxidation spontaneous combustion process in the Fushun West Mine, this study used a high-temperature temperature-programmed test to obtain the change trend of gas product concentration in different oxidation stages of minerals. Using Fourier transform infrared spectroscopy technology, the changes in active functional groups of surface molecules during the process of mineral oxidation and spontaneous combustion were identified. Finally, using the gray correlation degree, correlation analysis between the concentration of gas products and the concentration of active functional groups in different oxidation stages was carried out. The key reactive functional groups affecting mineral spontaneous combustion were identified. The essential reason for the change in the gas product was revealed.