Microstructural Modifications Research Articles

The role of heat treatment on the in vitro degradation and corrosion-initiated failure of the biodegradable Mg–Zn–RE alloy

ABSTRACT In the current work, magnesium (Mg) alloy containing zinc (4%) and rare earth (RE) elements (1%) was produced by stir casting and the role of heat treatment on altering the microstructure, in vitro degradation and corrosion-initiated mechanical failure. Solutionising has introduced considerable grain refinement from 122 ± 6.9 μm to 95 ± 7.1 μm and decreased the amount of intermetallic. Potentiodynamic polarization tests indicated improved corrosion resistance for the solutionised alloy as indicated by with a lower corrosion current value (0.021 × 10-4 A.cm -2) compared with base alloy (0.027 × 10-3 A.cm -2) and annealed alloy (0.168 × 10-3 A.cm -2). In vitro degradation studies conducted in simulated body fluid solutions demonstrated better degradation resistance for the solutionised alloy compared with base and annealed alloy. Tensile tests conducted before and after exposing the samples to a corroding environment for 24 h showed the promising role of microstructure modification by solutionising on enhancing the resistance to corrosion-initiated failure with improved ductility compared with the base and annealed alloys. From the results it is concluded that solutionising can be successfully adopted to enhance the corrosion and mechanical properties of Mg-Zn-RE alloy for manufacturing of degradable implants for bone fixing applications.

Microstructure Modifications to Enhance the Scattering Coefficient of Porous Yttria-Stabilized Zirconia Coatings

Microstructure Modifications to Enhance the Scattering Coefficient of Porous Yttria-Stabilized Zirconia Coatings

Effect of particle size of NanoSiO2 on cement-based stabilization/solidification of municipal solid waste incineration fly ash

As a part of by-product generated during the incineration, the municipal solid waste incineration fly ash (MFA) is a secondary pollutant. The ordinary Portland cement (OPC)-based stabilization/solidification (S/S) is a prevalent and robust technique for the treatment of MFA, which can not only effectively dispose the MFA, but also decrease the demand of OPC and reduce the greenhouse gas emissions. However, when MFA was directly utilized to partly replace the cement with a replacement ratio of 15%, the MFA-OPC based composites exhibited inferior mechanical properties. The nano silica (NS) was considered to be introduced to compensate for the strength loss caused by the MFA. In this research, the NS with varying dosages and particle sizes were integrated into the MFA-OPC composites and in total seven groups of the composites were prepared. The mechanical properties of the composites were examined and the results indicated that the composites containing 2 wt% 100 nm NS presented relatively superior mechanical properties. The incorporation of NS could increase the compressive strength of MFA-OPC composites by 37.5% at later age. Then, thermodynamic modelling and the micro-structural analysis including hydration heat, XRD, TG, MIP and SEM were coupling applied to probe into the NS modification mechanism. Experimental results indicated that the addition of NS enhanced the strength of OPC containing MFA at both early and later ages via pozzolanic reaction, hydration acceleration and micro filling effects. Overall considering the macro performance improvement and microstructure modification effect, the 2 wt% NS with particle size of 100 nm was recommended to be utilized. Therefore, this study expands the emerging application of NS and demonstrates that NS-augmented binders can ensure low-carbon and high-performance S/S of hazardous materials.

Microstructural modification and mechanical improvement of ultrafine-grained Ti alloy through electron wind force: An innovative approach

This study focuses on the effect of high-density pulsed electric current (HDPEC) on the microstructure and mechanical properties of ultrafine-grained (UFG) Ti–6Al–7Nb (mass%) alloy. After the UFG Ti alloy prepared by high-pressure torsion (HPT), the samples exhibit high tensile yield strengths of 1200 MPa with total elongation of ∼20 %. Interestingly, an unusual improved elongation of ∼33 % with a yield strength of 1100 MPa was obtained in samples processed by HPT plus HDPEC. Quantitative evaluation shows that the improved ductility is attributed to the decreasing of dislocation density. The electron wind force played an important role to promote the movement of dislocation easier with the assistance of local Joule heating during HDPEC processing. It is shown that the bimodal structure with a low dislocation density leads to the high strength and high ductility. It indicated that HDPEC give an effective method to improve the ductility in UFG alloys.

High Temperature Tensile Properties and Microstructure of Ni20Cr Alloy Fabricated by Laser Powder Bed Fusion

Additive Manufacturing (AM) brings about an array of modifications in microstructure with respect to conventional routes transforming mechanical performances. These new microstructure features depend on process parameters and especially on volume energy-density delivered by the laser on powder layer. Among the different alloys manufactured by AM, Ni-alloys exhibit high-strength at elevated temperature opening the way of fabrication of gas turbines and jet-engine parts. Ni-superalloys experience precipitation hardening due to the formation of γ′ and γ′′ phases leading to complex microstructures. To better study the influence of the AM microstructure on Ni-alloys mechanical properties, in particular at elevated temperatures, a theoretically monophasic and binary Ni20Cr-alloy manufactured by laser powder-bed fusion was studied in this work. Remarkable Yield Strength (400 MPa) and Ultimate Tensile Strength (UTS) (600 MPa) were observed at 500°C with hardly any loss of properties from room temperature, owing to the thermal stability of cellular dendrites till 700°C. Ductility drop was reported at 700°C due to anomalous brittle behaviour of Ni-alloys. Hardening behaviour vanished at 900°C signifying the deletion of dendrites, disappearance of dislocations, diffusion of Cr from dendritic walls and growth of oxides.

The effect of quenching/double quenching and tempering heat treatment cycles on the microstructure, impact energy and hardness of AISI H13 tool steel

ABSTRACT In this study, microstructure modifications of AISI H13 steel were studied with different heat treatments such as conventional quenching, quenching + tempering/double tempering and double quenching + tempering/double tempering. Carbide volume ratio analyses were performed. The XRD analysis was used to determine the type of carbide, the average crystallite size, and the dislocation density in the samples. Charpy impact tests were performed. The hardness values of the samples were measured with the Rockwell C scale. The presence of MC, M23C6, and M7C3 type carbides was determined in the microstructures. Heat treatment cycles caused a high dislocation density in martensite laths. The dislocation density of martensite laths decreased with double quenching. The tempering process caused the formation of fine carbide particles in the microstructure. In addition, tempering processes gave rise to an increase in the volume ratio of M23C6-type strip carbides. The length/width ratio of the strip-type carbides increased with the effect of double tempering. As a result of the applied heat treatments, the impact energies of the samples decreased. The tempering process caused a secondary hardening of the samples. While the double quenching process increased the impact energy value by approximately 2%, it caused a decrease in hardness by 24%.

Improving the mechanical and corrosion properties of aerospace-grade AA7075 through microstructural modification using low-temperature friction stir processing

Improving the mechanical and corrosion properties of aerospace-grade AA7075 through microstructural modification using low-temperature friction stir processing

Modification of Residual Stress and Microstructure in Al-Cu-Mg Alloy by Cryogenic Aging Treatment

Modification of Residual Stress and Microstructure in Al-Cu-Mg Alloy by Cryogenic Aging Treatment

Grain refinement, strain hardening and fracture in thermomechanically processed ultra-strong microalloyed steel

The current research in microalloyed steel has witnessed a continuous improvement in strength-ductility combination. The intention is to reduce the gauge thickness of automotive body sheets without compromising formability, thereby enhancing fuel efficiency. In this light, the present work has devised a novel thermomechanical controlled processing (TMCP) for a low-carbon automotive-grade (Nb+V)-stabilized microalloyed steel. The microstructural modification by TMCP has resulted in an excellent combination of yield strength (782 MPa), ultimate tensile strength (1059 MPa) and ductility (21%). The critical factor translating the investigated alloy towards advanced high strength steel is the ferrite grain refinement by dynamic recrystallization (DRX) and deformation-induced ferrite transformation (DIFT). The DRX predominated during TMCP at the intercritical temperature domain of 800–700 °C, imparting the average recrystallized grain size of 2 ± 0.8 µm. In contrast, the DIFT starts well above the upper intercritical temperature regime (i.e., around 810 °C), but it contributes less to the ferrite grain refinement. The thermodynamic reason has been analyzed keeping in view the changes in grain boundary energy and dislocation energy. The plastic deformation additionally leads to precipitation of cubic (Nb, V)-rich carbides in ferrite. The incoherency, coarse precipitate size (70–80 nm), and a poor phase fraction (⁓0.5%) are the key factors that the strengthening mechanism is governed by ferrite grain refinement majorly, followed by dislocation and solid solution strengthening. The segregation of Mn, Nb and S leads to MnS-type inclusion formation, which acts as potential sites for crack initiation due to plasticity mismatch with ferrite matrix during the tensile deformation.

2D and 3D Micropatterning of Mussel-Inspired Functional Materials by Direct Laser Writing.

This work addresses the critical need for multifunctional materials and substrate-independent high-precision surface modification techniques that are essential for advancing microdevices and sensing elements. To overcome existing limitations, the versatility of mussel-inspired materials (MIMs) is combined with state-of-the-art multiphoton direct laser writing (DLW) microfabrication. In this way, 2D and 3D MIM microstructures of complex designs are demonstrated with sub-micron to micron resolution and extensive post-functionalization capabilities. This study includes polydopamine (PDA), mussel-inspired linear, and dendritic polyglycerols (MI-lPG and MI-dPG), allowing their direct microstructure on the substrate of choice with the option to tailor the patterned topography and morphology in a controllable manner. The functionality potential of MIMs is demonstrated by successfully immobilizing and detecting single-stranded DNA on MIM micropattern and nanoarray surfaces. In addition, easy modification of MIM microstructure with silver nanoparticles without the need of any reducing agent is shown. The methodology developed here enables the integration of MIMs in advanced applications where precise surface functionalization is essential.

Deciphering the Effect of Microstructural Modification in Sodium Alginate-Based Solid Polymer Electrolyte by Unlike Anions.

Microstructure modification in sodium alginate (NaAlg)-based solid polymer electrolytes by the perchlorate (ClO4-) and acetate (CH3COO-) anions of sodium salts has been reported. ClO4- participates in the structure-breaking effect via inter/intramolecular hydrogen bond breaking, while CH3COO- changes the amorphous phase, as evident from X-ray diffraction studies. The larger size and negative charge delocalization of ClO4- have a plasticizing effect, resulting in a lower glass transition temperature (Tg) compared to CH3COO-. Decomposition temperature is strongly dependent on the type of anion. Scanning electron microscopy images showed divergent modifications in the surface morphology in both electrolyte systems, with variations in salt content. The mechanical properties of the NaAlg-NaClO4 electrolyte systems are better than those of the NaAlg-CH3 COONa system, indicating weak interactions in the latter. Although most of the studies focus on the cation influence on conductivity, the interaction of the anion and its size certainly have an influence on the properties of solid polymer electrolytes, which will be of interest in the near future for sodium ion-based electrolytes in energy storage devices.

Microstructural dynamics of motor learning and sleep-dependent consolidation: A diffusion imaging study

Memory consolidation can benefit from post-learning sleep, eventually leading to long-term microstructural brain modifications to accommodate new memory representations. Non-invasive diffusion-weighted magnetic resonance imaging (DWI) allows the observation of (micro)structural brain remodeling after time-limited motor learning. Here, we combine conventional diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) that allows modeling dendritic and axonal complexity in gray matter to investigate with improved specificity the microstructural brain mechanisms underlying time- and sleep-dependent motor memory consolidation dynamics. Sixty-one young healthy adults underwent four DWI sessions, two sequential motor trainings, and a night of total sleep deprivation or regular sleep distributed over five days. We observed rapid-motor-learning-related remodeling in occipitoparietal, temporal, and motor-related subcortical regions, reflecting temporary dynamics in learning-related neuronal brain plasticity processes. Sleep-related consolidation seems not to exert a detectable impact on diffusion parameters, at least on the timescale of a few days.

Effect of ultrasonic shot peening surface alloying on microstructure and tribological behavior of Inconel 718 superalloy

Ultrasonic shot peening (USP) surface alloying can enhance the surface strength and achieve the microstructure modification concurrently. In this paper, Inconel 718 superalloy was subjected to USP surface alloying with Nb powder, followed by post-annealing treatment. The microstructure and tribological behavior of the samples were investigated. After USP alloying and subsequent annealing, a Nb alloying layer with a thickness of ∼7 μm was fabricated on substrate surface, and a grain refinement layer with a depth of 100 μm was formed. The introduced alloying layer promoted the precipitation of additional reinforcing phases through thermal activation, thereby engendering heightened hardness values within the sub-surface layer as compared to samples treated only by USP. The frictional test results showed that the lowest friction coefficient and smallest wear rate were obtained in sample treated by USP alloying and annealing, which was closely related to the highest hardness in the near-surface layer. Moreover, the wear mechanisms of these samples were subsequently discussed.

Phase-dependent microstructure modification leads to high thermoelectric performance in n-type layered SnSe2

Microstructure control is crucial for thermoelectrics since it is intimately related to the scattering mechanism of both electrons and phonons. Herein, we propose a new strategy to modify microstructure by phase regulation that simultaneously induces high carrier mobility and low lattice thermal conductivity. As demonstrated in layered SnSe2, the addition of Cu can induce a phase transition from space group P3¯m1 to P63mc. Due to the enlarged formation energy of stacking faults in the later phase, the stacking fault density is greatly reduced after heat treatment that leads to an increased grain size. Accordingly, the carrier mobility of SnSe1.97Br0.03–3 % Cu sample is enhanced by 100 % at room temperature. Furthermore, the reduction of stacking fault density is accompanied by the formation of pores in the matrix, which results in low lattice thermal conductivity. As a result, a record peak zT of 1.13 for SnSe2-based materials is achieved at 773 K, and the attained ZTave of 0.62 is a record-high value among n-type polycrystalline layered materials working in intermediate-to-high temperature region. This work provides a feasible strategy to decouple the electron and phonon transport in layered thermoelectric compounds by phase-dependent microstructure modification.

Effect of microstructure modification on magnetic and mechanical properties of high-grade non-oriented silicon steel during annealing treatment

The optimization of magnetic and mechanical properties by microstructure modification is tremendously challenging for high-grade non-oriented silicon steel. In the current study, the microstructure of cold-rolled high-grade non-oriented silicon steel was modified by recrystallization annealing to achieve high strength and good magnetic properties. The results indicate that recrystallization annealing significantly improved the magnetic properties, while negatively impacting its mechanical properties. At the early stage of annealing (<2 min), recrystallization nucleation occurred in the deformation matrix, leading to a significant decrease in dislocation density. This decrease in dislocation density resulted in a notable reduction in coercivity and hence enhancement in magnetic properties. However, the mechanical properties deteriorated due to the elimination of dislocations. With further increasing the annealing time (>2 min), the recrystallization grains grew within the fully recrystallized matrix. There was a slight decrease in both dislocation density and grain boundary density, leading to a slight decrease in iron loss and yield strength. The magnetic induction intensity of the fully recrystallized annealed sheets was primarily influenced by the recrystallization texture. Thus, the critical annealing time was 2 min to meet the demands of both magnetic and mechanical properties for the studied high-grade non-oriented silicon steel.

Friction stir extrusion and mechanical alloying of LM13 casting ingot to produce LM28 tubes

Friction Stir Extrusion (FSE) is applied on the as-cast LM13 aluminum alloy to produce tubes accompanied with the microstructural modification. Then, the process was employed to transform LM13 to LM28 alloy by mechanical alloying by adding Si particles during the process. In addition, a numerical model on the Deform 3D software is developed to simulate the process and investigate the temperature and strain distributions at different zones as well as the material flow over the process. The experimental and numerical results show that the peak temperature and strain of 460 °C and 200 are attained in the zone 6–10 mm after the conical part finish, where the material completely enters the tube channel. The temperature and strain distributions were varying through the tube wall, and the result is that the average Si precipitates’ size in the wall inside reduced to almost 0.8 μm while is 2 μm at the center of the tube wall. Furthermore, the material flow from the primary cylindrical ingot towards the tube wall was not uniform in the sample cross-section due to tool design, and the velocity of material movement at various zones was different. Mechanical alloying of LM13 alloy, by the addition of Si particles in ∼6 %, transformed the alloy to LM28 by increasing the silicon content from 12.2 to 19.2 %. The ultimate compression strength of the LM13 base metal increased from 84.7 to 138.7 MPa and 158.2 MPa, respectively, for LM13 and LM28 by breakage of needle-like Si precipitates and fine dispersion of them in the aluminum substrate.

Modeling the hot deformation behavior of micro-alloyed steel in the single and two-phase fields

Continuous casting is a well-established process to produce steel slabs. However, the surfaces of the slabs may crack during processing. The occurrence of cracks is related to different phenomena, i.e., ferrite formation, presence of precipitates, and microstructural modifications during manufacturing processing. In the present work, we developed a physically based mesoscale model to describe the plastic deformation of micro-alloyed steel in the single and two-phase fields, as well as the microstructure evolution. We implemented a dislocation density-based constitutive model to calculate the strain hardening and the stress softening produced by dynamic recovery using the Kocks-Mecking (KM) formalism for the austenite and ferrite. We coupled the KM model with the Johnson-Mehl-Avrami-Kolmogorov model to consider the dynamic recrystallization of the austenitic phase. The nucleation and growth of the recrystallized grains, driven by the stored energy, compete with the annihilation of dislocations due to dynamic recovery. In the two-phase domain, the iso-work condition for the load partition is implemented. We calculated the ferrite volume fraction by fitting the data obtained using JmatPro software. Moreover, an Arrhenius-type equation correlates the yield stress to the Zener-Hollomon parameter. We validated the model with isothermal uniaxial compression tests of microalloyed steel over the temperature range of 650 °C-1100 °C and strain rates of 10−2 s−1 and 10−3 s−1 using a Gleeble® 3800 thermomechanical simulator.

Corrosion behavior of nanostructured ferritic stainless steel by the generation of LIPSS with ultrashort laser pulses

Femtosecond ultra-short laser pulses can induce various micro- and nanostructural changes in the surface of stainless steel, paving the way for new functionalities in the application of these materials. In this work, UV, visible, and IR femtosecond laser pulses have been utilized on ferritic stainless steel under differing conditions of fluence, pulses per spot and hatch distance. These variables resulted in various compositional and micro- and nanostructural changes on the steel surfaces. The texturing processes which originate these changes can be meticulously designed by selecting the appropriate strategy and laser parameters, leading to Laser-Induced Periodic Surface Structures (LIPSS) and other potential morphologies. A significant problem to consider during the laser treatment of stainless-steel surfaces is the effect that these microstructural modifications, induced by the ultra-short pulses, can have on the corrosion behavior and the brightness of the surface. On one hand, a detailed study of the effect that these treatments can have on the corrosion resistance of the stainless steel under investigation has been conducted. The study shows that under specific conditions, treatments with ultra-short laser pulses maintain the corrosion resistance of the surfaces. On the other hand, the study of the surface brightness after laser treatments, as measured by the Light Reflectance Value (LRV), shows that brightness is only slightly decreased (less than 10 %) for samples where Surface Density of Applied Energy (SDAE) is lower than 2 J/cm2. Furthermore, the diffuse LRV is increased in every textured sample due to the presence of ripples.

Microstructure and tribological properties of as-cast and multi-pass friction stir processed Mg-0.5Zn-0.5Zr/SiC composite fabricated by stir casting technique

In this investigation, the Mg-0.5Zn-0.5Zr/4%SiC composite fabricated by the stir casting method was subjected to multi-pass friction stir processing (MFSP) to evaluate its microstructure, hardness, dry-sliding wear, and friction properties in comparison to those of the as-cast composite (ACC). Microstructural observations revealed the formation of a Mg matrix with average grain size (AGS) of 107 ± 12 μm, uneven dispersion (agglomeration) of SiC particles in the structure, and the formation of Zr-rich phase with the chemical composition of Zr:78.42, C:19.46, Mg:1.86, and Zn:0.26 wt%, ZrC, as well as some new formed carbide-based phases mostly propagated along the grain boundaries. On the other hand, the MFSP implementation led to a significant microstructural modification, i.e., in the optimum circumstance, the AGS and SiC particle size in the stir zone was reduced by 97.28 % (107–2.9 μm) and 67.69 % (21.33–6.89 μm), respectively, and the density of the composite increased from 1.669 to 1.774 gr/cm3. According to dry-sliding wear test results, applying FSP and increasing the pass number to three reduced the wear rate and coefficient of friction (COF) of the composites by about 45 % and 24 %, respectively, compared to those of ACC. The wear resistance enhancement was ascribed to wear mechanisms changing from delamination/adhesion/severe abrasion to mild abrasion wear, which stemmed from the formation of a stable O-rich tribolayer on the worn surface of FSPed samples.

Correction to: Modification of Microstructure and Mechanical Properties of AA6082/ZrB2 Processed by Multipass Friction Stir Processing

Correction to: Modification of Microstructure and Mechanical Properties of AA6082/ZrB2 Processed by Multipass Friction Stir Processing