Microstructure-property Correlation Research Articles

Microstructure–property correlation and strain partitioning behavior in medium-carbon carbide-free bainitic steel

Microstructure–property correlation and strain partitioning behavior in medium-carbon carbide-free bainitic steel

Unraveling impacts of polycrystalline microstructures on ionic conductivity of ceramic electrolytes by computational homogenization and machine learning

The ionic conductivity at the grain boundaries (GBs) in oxide ceramics is typically several orders of magnitude lower than that within the grain interior. This detrimental GB effect is the main bottleneck for designing high-performance ceramic electrolytes intended for use in solid-state lithium-ion batteries, fuel cells, and electrolyzer cells. The macroscopic ionic conductivity in oxide ceramics is essentially governed by the underlying polycrystalline microstructures where GBs and grain morphology go hand in hand. This provides the possibility to enhance the ion conductivity by microstructure engineering. To this end, a thorough understanding of microstructure–property correlation is highly desirable. In this work, we investigate numerous polycrystalline microstructure samples with varying grain and grain boundary features. Their macroscopic ionic conductivities are numerically evaluated by the finite element homogenization method, whereby the GB resistance is explicitly regarded. The influence of different microstructural features on the effective ionic conductivity is systematically studied. The microstructure–property relationships are revealed. Additionally, a graph neural network-based machine learning model is constructed and trained. It can accurately predict the effective ionic conductivity for a given polycrystalline microstructure. This work provides crucial quantitative guidelines for optimizing the ionic conducting performance of oxide ceramics by tailoring microstructures.

Adapting high-speed indentation mapping for investigating microstructure-property correlations in chromium carbide-nickel alloy coatings: Challenges and solutions

This study investigates the microstructural and mechanical characteristics of chromium carbide‑nickel rich alloy coatings produced through laser cladding, detonation spraying, and plasma spraying techniques. While all three processing techniques used the same feedstock powder, each method yields coatings with unique microstructures encompassing varying compositions and length scales. Employing Field Emission Scanning Electron Microscopy (FE-SEM) in combination with Energy Dispersive Spectroscopy (EDS) and nanoindentation mapping, local microstructure and mechanical properties were assessed at the micrometre length scale. Laser-clad coatings exhibit a typical metal matrix composite microstructure with high carbide content, distinct (MoNb)C2 phases, and Fe in the metallic matrix, while the thermal sprayed coatings showed carbides of varying sizes and metallic matrix with varying degrees of chromium dissolved in it. The instrumented indentation technique helped precisely record the microstructural features in all the coatings. Chromium carbide consistently emerges as the hardest phase across all coatings, with variations in metallic matrix hardness. Higher matrix hardness in thermal sprayed coatings correlates with increased Cr content, attributed to extended solid solubility of Cr and the presence of Mo and Nb. Energy dispersive spectroscopy and transmission electron microscopy provided clearer insight into the microstructure. This study highlights a direct one-to-one correlation between microstructure and mechanical properties mapped using instrumented indentation techniques in chromium carbide‑nickel rich coatings across different deposition methods.

Strength and toughness balance in 7 %Ni steel by formation epsilon martensite, retained austenite and Low matrix strain

In the current study, 7 wt.%Ni alloy steel was prepared, hot rolled, and heat treated according to popular quenching, lamellarization, and tempering treatments. The inter-critical lamellarization temperature was varied and the microstructure-property correlation was evaluated in each stage of heat treatment to understand the metallurgical aspects. Optical and detailed electron microscopic techniques were used to characterize and quantify the microstructures. Mechanical responses under uniaxial and impact loading were also recorded for all the studied samples. Tempered martensite with blocky and lamellar morphology, along with retained austenite and ɛ-martensite, were observed in the microstructures after the above-mentioned heat treatment. The lamellarization at 700 ℃ leads to a more uniform distribution of alloying elements and, therefore, promotes the formation of finer retained austenite with uniform distribution, compared to 650 °C lamellarization temperature. The presence of lower matrix strain and uniformly distributed fine retained austenite provides the highest toughness with moderate strength in the 700 °C samples. ɛ-martensite is expected to provide the necessary strength to balance the softening arising due to tempered martensite and retained austenite. Moreover, the uniformly distributed fine and filmy-shaped retained austenite provides thermal stability, and arrests crack propagation, enhancing toughness. The XRD results after impact toughness show that the γ-ε-α transformation takes place during the -196 °C temperature, and during impact toughness testing, ε-α transformations also provide the toughening in the Ni-700+590 sample.

μ2mech: A software package combining microstructure modeling and mechanical property prediction

We have developed a graphical user interface (GUI) based package μ2mech to perform phase-field simulation for predicting microstructure evolution. The package can take inputs from ab initio calculations and CALPHAD (Calculation of Phase Diagrams) tools for quantitative microstructure prediction. The package also provides a seamless connection to transfer output from the mesoscale phase field method to the microscale finite element analysis for mechanical property prediction. Such a multiscale simulation package can facilitate microstructure-property correlation, one of the cornerstones in accelerated materials development within the integrated computational materials engineering (ICME) framework.

The microstructure effects on irradiation response of ferritic – martensitic steels

Microstructural optimization to achieve greater mechanical strength has been one of the focuses in ferritic–martensitic steels development. However, these optimized microstructures’ effects on the radiation response are not well known. In this work, two ferritic–martensitic steels (9Cr-NbMo and 9Cr-Ta) underwent neutron irradiation in the High Flux Isotope Reactor, and their room-temperature post-irradiation tensile properties and microstructure evolutions were investigated and compared. These two steels exhibit similar pre-irradiation tensile behavior, and their yield strengths are higher than that of other ferritic–martensitic steels by about 200–250 MPa. Microstructural characterization on pre-irradiated materials reveals a smaller grain size in 9Cr-Ta (2.8 ± 0.3 μm in 9Cr-Ta versus 4.3 ± 0.5 μm in 9Cr-NbMo) but higher dislocation density and precipitate density in 9Cr-NbMo. As is common for ferritic–martensitic steels at low irradiation temperatures (less than about 0.45Tm), irradiation-induced hardening at 400 °C was observed for both alloys. Irradiation at 490 °C causes the two alloys to exhibit different tensile behavior: 9Cr-Ta softens by 208 MPa in yield stress, whereas 9Cr-NbMo maintains strength. Microstructural characterizations were performed, including precipitate growth, dislocation, and defect formation. Using the barrier hardening model for microstructure–property correlation, the softening in irradiated 9Cr-Ta is primarily attributed to the significant dislocation recovery, while the strength lost from the slight dislocation recovery in 9Cr-NbMo was compensated by the additional strength from the irradiation-induced cavities. The microstructure effect (primarily precipitate, dislocation and boundary) on the radiation response is discussed herein.

Quantifying the influence of microstructure on the corrosion of Mg-Li alloys by using X-ray CT

The microstructure of multi-component Mg-Li alloys played a decisive role in their corrosion properties due to the potential differences between the matrix and the secondary phases. In this study, the effects of secondary phases (AlLi, AlX(Gd, Y, Mn), and Mg2Sn) on the corrosion behavior of Mg-Li alloys have been quantified by using in situ X-ray CT. The microstructure-property correlation was established between the type, morphology, distribution, and dimensions of the secondary phases and the microscopic corrosion behavior. The corrosion parameters, such as average equivalent diameter, distance, number density, and volume fraction of the secondary phases and corrosion pits, were quantified as a function of corrosion time. The dominating secondary phase was identified by combining SKPFM analysis and electrochemical testing, giving quantitative information on corrosion control by designing secondary phases.

Microstructural study of microwave welded austenitic stainless steel

The joining of austenitic stainless steels through microwave hybrid heating has gained much attention due to its advantages, like uniform and volumetric heating. However, to establish a microwave joining process for promising applications, a microstructural study of the welded joint is still an area to explore. In the present study, microstructural analysis of austenitic stainless steel (SS304) joints is explained through optical microscopy, scanning electron microscopy (SEM), elemental mapping, X-ray diffraction (XRD) and Vickers' micro-hardness tester. Further, detailed microstructural analysis of interlayer and heat-affected zone (HAZ) is studied through electron back-scattered diffraction (EBSD). XRD results reveal the development of various Ni, Cr and the M23C6 type carbides at the joint interlayer region. SEM results point toward non-epitaxial grain evolution along the fusion zone. The mean microhardness of 350 ± 20 HV was determined at the joint interlayer region. A relatively fine grain structure was observed along the fusion boundary. However, moving away from the joint, two different forms of coarse grain heat-affected zone (CGHAZ) were observed. The presence of two different forms of CGHAZ is confirmed through inverse pole figure maps and grain size plots. The presence of high-angle boundaries (HABs) at 60° rotation describes the twin boundaries characterized along the <111> axis. The existence of improved fractions of HABs in the microwave-joined specimen of SS will favor the microstructure to retard bulk deformation. The joint specimen endures a maximum force of 6.98 kN, and the ultimate tensile strength of 613 MPa with 4.75% of elongation. It is observed that microhardness observations and the microstructural studies in the research help establish a solid microstructure-property correlation for the joined material.

Evaluation of In Vivo Biocompatibility in Preclinical Studies of a Finger Implant Medical Device Correlated with Mechanical Properties and Microstructure.

The aim of the experiment was to evaluate the biocompatibility of four 3D-printed biomaterials planned for use in the surgical treatment of finger amputees: Ti-6Al-4 V (Ti64), ZrO2-Al2O3 ceramic material (ATZ20), and osteoconductive (anodized Ti64) and antibacterial (Hydroxyapatite, HAp) coatings that adhere well to materials dedicated to finger bone implants. The work concerns the correlation of mechanical, microstructural, and biological properties of dedicated materials. Biological tests consisted of determining the overall cytotoxicity of the organism on the basis of in vivo tests carried out in accordance with the ISO 10993-6 and ISO 10993-11 standards. Clinical observations followed by diagnostic examinations, histopathological evaluation, and biochemical characterization showed no significant differences between control and tested groups of animals. The wound healed without complication, and no pathological effects were found. The wear test showed the fragility of the hydroxyapatite thin layer and the mechanical stability of the zirconia-based ceramic substrate. Electron microscopy observations revealed the layered structure of tested substrates and coatings.

The effects of heat-treatment parameters on the mechanical properties and microstructures of a low-carbon dual-phase steel

The austenite decomposition phase transformation in a low-carbon dual-phase (DP) steel is studied as a function of inter-critical annealing parameters: annealing time, annealing temperature, and cooling rate. The austenization kinetics are obtained by dilatometric analyses, water-quenched metallography, and thermodynamic calculations, and the austenite formed at different inter-critical annealing temperatures influences the subsequent formation of secondary phases during continuous cooling. Results indicate that the austenite volume fraction increases with both annealing temperature and time; although their effect on the final microstructure and mechanical properties lessens when the cooling rate decreases to the slow cooling regime below air cooling. Interestingly, the yield strength (YS) values of samples cooled at ∼1 °C/s with sand cooling, are 75∼100 MPa greater than the corresponding values at a rate of ∼6 °C/s with air-cooling. The results indicate that the yield strength is positively correlated with yield-point elongation but negatively correlated with the ultimate tensile strength. The effects of the cooling rate on the mechanical properties can be explained by the formation of Cottrell atmospheres of carbon together with the increase of the pearlite volume fraction. Based on the secondary phase components and strength evolutions, there are four possible outcomes for the different cooling rates: (I) martensite (M); (II) ferrite-martensite (FM); (III) coexistence of martensite and pearlite (MP); and (IV) ferrite-pearlite (FP). Our results reveal that the microstructure-property correlation can be illustrated schematically as a function of cooling rates and can thereby direct the heat-treatment parameters required to obtain desirable mechanical properties.

Studying the relationship between microstructure and properties of polylactic acid/styrene-ethylene butyl-styrene blend reinforced by graphene

The main purpose of this study was to investigate the relationship between microstructure and mechanical performance of polylactic acid when mixed with styrene-ethylene butylene-styrene copolymer and also graphene nanoplatelets. For this purpose, a series of neat polymer blends were first prepared with varying mixing ratios through a one-step melt mixing technique. Subsequently, the effect of various loadings of graphene nanoplatelets on the best mixing ratio (optimal composition) of the binary blend was investigated. To understand the different performances of various nanocomposites, the correlation of mechanical, rheological, and microstructural properties was thoroughly investigated using X-ray diffraction, scanning electron microscopy, linear viscoelastic behavior, tensile testing, and impact strength analyses. Furthermore, the influence of the mixing sequence of nanocomposites preparation on the microstructure and mechanical performance of nanocomposites was studied. Results demonstrated that the incorporation of graphene nanoplatelets as well as mixing sequence has a substantial effect on the final properties of prepared nanocomposites which was deeply discussed.

Mechanical behavior and microstructure-property correlation of a metastable interstitial high entropy alloy with hierarchical gradient structures

Metastable high entropy alloys (MHEAs) are attractive materials due to their exceptional mechanical properties, particularly in addressing the challenge of the strength-ductility trade-off. However, one of the major hurdles of MHEAs is that their yield stresses are still relatively low compared to the engineering requirements, even with carbon-doped treatment and grain refinement. To further improve the strength of MHEAs, surface mechanical attrition treatment (SMAT) was applied to an interstitial MHEA (iHEA) with Fe49.5Mn30Co10Cr10C0.5 (at.%) compositions. Mechanical tests demonstrated that the yield stress of the iHEA had been improved by 32.6% after only 15 min of treatment without sacrificing ductility, and a 60-min treatment made the ultimate tensile strength approach 1 GPa. In-depth quantitative analysis indicated that hierarchical gradient microstructures were generated by SMAT, including grains, dislocations, twins, and dual phases. The theoretical analysis confirmed the synergetic extra-strengthening caused by the gradient distributions of various microstructures. Furthermore, the microstructural heterogeneity resulted in the hetero-deformation induced (HDI) hardening, contributing to strain hardening and maintaining sufficient ductility. The microstructure-property correlation revealed by this study provides guidance for the mechanical property design of MHEAs via gradient structure.

Microstructure and mechanical property correlation in Silicon-doped equiatomic FeMnNi MEA: Experiments and simulation

The effect of minor addition of Si to the FCC equiatomic FeMnNi medium entropy alloy (MEA) has been systematically investigated using experiments and DFT calculations. We report here a detailed investigation on 0.5 – 2 at% Si addition in FeMnNi MEA by using SEM, EBSD and TEM with uniaxial tensile tests and strain rate jump tests, to establish structural-property correlation. The experimental investigation reveals that the MEA with 2 at% Si exhibits remarkably improved combination of strength (YS = 249 MPa, UTS = 528 MPa) and ductility (70%), with (111) dislocation glide being the predominant mode of plastic deformation. A correlation with regard to lattice distortion and microstrain, in the context of dislocation plasticity and microband formation is made with DFT modelling. The SFE is found to increase due to Si addition and local lattice distortion, therefore contributing significantly to the solid solution hardening.

Microstructure Property Correlation of Partial Penetration Weld Deposited Stainless Steels for Weld Repair of Investment Castings

Microstructure Property Correlation of Partial Penetration Weld Deposited Stainless Steels for Weld Repair of Investment Castings

Microstructure-Property Correlation and Its Evolution during Aging in an Al4.4Co26Cr19Fe18Ni27Ti5.6 High-Entropy Alloy.

The efficient energy use in multiple sectors of modern industry is partly based on the efficient use of high-strength, high-performance alloys that retain remarkable mechanical properties at elevated and high temperatures. High-entropy alloys (HEAs) represent the most recent class of these materials with a high potential for high-temperature high-strength applications. Aside from their chemical composition and microstructure-property relationship, limited information on the effect of heat treatment as a decisive factor for alloy design is available in the literature. This work intends to contribute to this research topic by investigating the effect of heat treatment on the microstructure and mechanical performance of an Al4.4Co26Cr19Fe18Ni27Ti5.6 HEA. The solution annealed state is compared to aged states obtained at different heat treatment times at 750 °C. The temporal evolution of the matrix and the γ'-precipitates are analyzed in terms of chemical composition, crystallography, size, shape, and volume fraction by means of scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The yield strength evolution and strength contributions are calculated by classical state-of-the-art models as well as by ab-initio-based calculations of the critical resolved shear stress. The findings indicate promising mechanical properties of the investigated alloy and provide insight not only into possible strengthening mechanisms but also into the evolution of main phases during the heat treatment.

Microstructure and Tribological Property Correlations of Die Cast and Spray Formed Al-30 wt.% Si Alloy

Al-30 wt.% Si hypereutectic alloy was produced by die casting and spray forming technique. The microstructures, mechanical and tribological properties of the alloy were studied. The density of die cast and spray formed samples are measured using water displacement method by applying the Archimedes principle. The scanning electron micrographs of die cast and spray formed alloys revealed the morphological changes of silicon phase from coarse silicon needles to fine silicon needles due to high undercooling encountered in spray forming. The size of the hard silicon platelets are decreased from 22 µm to less than 10 µm as the processing method is changed from die casing to spray forming. The average Vickers micro hardness of die cast and spray formed alloy are 70.06±2.65 HV and 78.05±2.01 HV respectively. The respective yield strengths of die cast and spray formed alloy are 130±9MPa and 150 ±7 MPa and the compression strengths are 251±11.6 MPa and 283±6.32 MPa. The precipitation strengthening mechanism is found to be involved in spray formed alloy.

On microstructure and work hardening behavior of laser powder bed fused Al-Cu-Mg-Ag-TiB2 and AlSi10Mg alloys

In this paper, we investigate the correlation between microstructure and mechanical properties, including work hardening rates of two aluminum alloys, Al-Cu-Mg-Ag-TiB2 (A205) and AlSi10Mg, both additively manufactured using laser powder-bed fusion (LPBF) technique. Solutionizing followed by over-aging (T7) and artificial aging (T6) heat treatments were performed on as-built specimens of A205 and AlSi10Mg alloys, respectively, to investigate and compare the evolution of microstructure and tensile properties. Tensile tests based on ASTM E8/E8M standard were performed systematically on both materials in both as-built and heat-treated conditions. High-magnification microstructural characterizations including scanning electron and transmission electron microscopies and electron backscattered diffraction were performed to identify the microstructure-property correlations. The A205 alloy contains an ultrafine uniform equiaxed grain structure with no cell and/or epitaxial growth structure. However, the AlSi10Mg contains a cellular microstructure of primary α‐Al cells surrounded by a continuous cellular Si network. Tensile results on A205 (as-built) revealed discontinuous yielding, while the A205 (T7 HT) material serrated plastic flow instability. T7 heat treatment resulted in a 42.4% and 38% increase in yield stress (YS) and ultimate tensile strength (UTS), respectively, and elongation decreased from 12.5% to 9.5% consequently. However, considerable grain growth, coarsening of Si particles, and dissolution of some Mg2Si phases through solutionizing and T6 aging on AlSi10Mg resulted in increased elongation (5.49–14.20%) and decreased YS and UTS (14.5% and 19.4% respectively). The effect of distinct microstructural features of A205 and AlSi10Mg in as-built condition and their evolution in opposite directions upon aging (in terms of mechanical properties) is reflected in their work-hardening behavior. Considerably higher work hardening of AlSi10Mg alloy in both as-built and aged conditions compared to A205 is linked with the cellular structure containing hard eutectic-Si particles at the cell boundaries.

Microstructure and Near-Surface Tribological Property Correlations in Al-Cu Alloy Reinforced with Al2O3 Nanoparticles

Microstructure and Near-Surface Tribological Property Correlations in Al-Cu Alloy Reinforced with Al2O3 Nanoparticles

Microstructure and Mechanical Properties Correlation of Al-4.28Cu-1.60 Mg Alloy Micro-Alloyed with Titanium

Microstructure and Mechanical Properties Correlation of Al-4.28Cu-1.60 Mg Alloy Micro-Alloyed with Titanium

Microstructure-property correlations in as-built and heat-treated compositionally graded stainless steel 316L-Inconel 718 alloy fabricated by laser powder bed fusion

The microstructures and the mechanical properties of a laser powder bed fusion manufactured compositionally graded alloy of the austenitic stainless steel 316L and Inconel 718, in the as-built and heat-treated conditions, were investigated. In all the cross sections of the as-built compositionally graded alloy, along the compositional gradient direction, which is perpendicular to the build direction, the microstructure primarily consists of sub-micron sized cells embedded within <001> textured columnar grains of the γ phase along with Laves phases at their grain boundaries. Heat treatment, which involves solutionizing at 1040 °C for 1 h followed by annealing at 720 °C and 620 °C for 10 h each, leads to coarsening of Laves phases, slight modification in texture and the annihilation of the sub-grain structure of the compositionally graded alloy, but does not alter the columnar grain size. It also leads to precipitation of the γ" and γ' phases in the portions of the compositionally graded alloy with >70 wt% of IN718. The hardness, yield strength and tensile strength of the compositionally graded alloy increase but ductility decreases from the SS316L-rich end to the IN718-rich end along the gradient direction. Heat treatment smoothens the variations in YS and UTS along the gradient direction in cross sections with <82 wt% IN718 but reduces their relative magnitude compared to that of the as-built condition. The heat-treated compositionally graded alloy exhibits significantly higher YS and UTS but lower ductility than that in the as-built condition, in portions with ≥82 wt% IN718. These mechanical property variations are analyzed in detail by considering variations in the composition, microstructural features, and contents of different phases in the as-built and heat-treated compositionally graded alloy. Finally, an appraisal on the appropriate compositional gradient and utility of the heat treatment of the compositionally graded alloy is discussed in the context of specific requirements in structural applications.