Effects Of Microstructural Factors Research Articles

Exceptional combination of mechanical and corrosion properties in partially recrystallized CoCrFeNiMo medium-entropy alloys

Corrosion-resistant materials with good mechanical properties are an endless goal to develop reliable structural materials. Multiple strengthening mechanisms stemming from diverse microstructural factors have been developed, while the effect of microstructural factors on corrosion properties in high-entropy alloys has not been clearly defined yet. Herein, the corrosion behaviors of CoCrFeNiMo medium-entropy alloys with different annealing times are investigated. The influences of microstructures are summarized as follows: alloyed Mo accelerates repassivation, Mo-rich precipitates form micro-galvanic couples, and unrecrystallized microstructures induce pitting corrosion. Regarding mechanical properties, the alloyed Mo, Mo-rich precipitates, and unrecrystallized region with profuse dislocations lead significant solid solution strengthening, precipitation strengthening, and dislocation strengthening, respectively. Particularly, the sample annealed for 60 min possesses dissolved Mo in the matrix, fine precipitates, wide recrystallized regions, and low dislocation density, resulting in a wide passivation range of 1.512 V and high yield strength × fracture strain of 220.3 MPa simultaneously. The sample annealed for 60 min reveals a synergistic combination of diverse microstructural factors affecting corrosion and mechanical properties.

Excellent Balance of Ultimate Tensile Strength and Ductility in a Ti–6Al–2Sn–4Zr–2Mo–Si Alloy Having Duplex α + α′ Microstructure: Effect of Microstructural Factors from Experimental Study and Machine Learning

This research focuses on the systematic study of a Ti–6Al–2Sn–4Zr–2Mo–Si titanium alloy and the characterization of α + β (equiaxed and bimodal) and α + α′ (duplex) microstructures. It provides more insights on the outstanding advantages of the duplex (α + α′) microstructure, especially on its exceptional work hardening and strength-ductility balance. The heat treatment conditions required to form equiaxed, bimodal and duplex microstructures and their effects on the grain size and the phase proportion are discussed. It shows how the microstructural parameters can be controlled thanks to the heat treatment temperatures, the holding times and possible aging processes. The influence of such microstructural factors on the tensile properties of each alloy is investigated, especially on strength (proof stress, ultimate tensile strength), ductility (plastic elongation) and work hardening properties. The duplex (α + α′) microstructure is compared with the equiaxed and bimodal microstructures and its advantages are displayed, highlighting the better strength-ductility balance and superior work hardening properties of the duplex microstructure. Indeed, the deformed microstructure of the duplex (α + α′) microstructure reveals more homogeneous strain partitioning than that of the bimodal (α + β) microstructure. Thus, this work proved the potential of an optimized duplex (α + α′) microstructure for the enhanced tensile properties at room temperature. Finally, a machine learning model using gradient boosting regression trees is used to quantify the importance of the microstructural factors (type of microstructure, grain size and phase ratio) on the mechanical properties.

Inherited multimodal microstructure evolution of high-fracture-toughness Mg-Zn-Y-Al alloys during extrusion for the consolidation of rapidly solidified ribbons

The mechanisms of multimodal microstructure evolution and the effects of microstructural factors on mechanical properties must be elucidated to design new alloys with superior properties. In this study, high-fracture-toughness and ductile Mg96.75Zn0.85Y2.05Al0.35 alloys were developed using rapidly solidified (RS) ribbon-consolidation technique, and the inherited multimodal microstructure evolution during plastic flow consolidation of the RS ribbons was investigated. The use of extrusion for plastic flow consolidation of the heat-treated RS ribbons produced a multimodal microstructure consisting of the worked grains with high Kernel average misorientation (KAM) angles (Group 1), the ultrafine dynamically recrystallized (DRXed) grains with intermediate KAM angles (Group 2), and the fine DRXed grains with low KAM angles (Group 3). Groups 1 and 2 contribute to the alloy strengthening, while Group 3 contributes to improving ductility with strain-hardening, resulting in enhancement of the fracture toughness. To form the multimodal microstructure, it was necessary to apply plastic flow with equivalent strains of >2.3 to the heat-treated RS ribbons possessing duplex microstructures with different dispersions of the long-period stacking ordered phase.

Evolution of the microstructure and mechanical properties of interstitial-free steel during multi-axial diagonal forging

In this study, sound workpieces made of interstitial-free (IF) steel were manufactured by performing up to 4 cycles without the occurrence of forging defects via the use of a new multi-axis diagonal forging (MADF-ver2) process at room temperature. The microstructure that was developed in the deformed specimens was experimentally analyzed and compared. As the number of cycles increased, the average grain size gradually decreased, and both the average misorientation angle and the fraction of high-angle grain boundaries (HAGBs) continued to increase. As the number of cycles increased, the change in average geometrically necessary dislocation (GND) density was insignificant due to the occurrence of dynamic recovery. The effects of microstructural factors on the hardness, yield strength, and total elongation of the deformed specimens were investigated. The ultrafine-grained structure formed by MADF-ver2 continuously increased the hardness and yield strength with increases in the number of cycles. On the other hand, total elongation was not dependent on the number of cycles, and this independence was mainly the result of insignificant changes in the average GND density due to the dynamic recovery that occurred throughout the specimen.

Effect of Microstructural Factors and Mechanical Properties on Axial Crash Fracture of High Strength Steel Sheets

Effect of Microstructural Factors and Mechanical Properties on Axial Crash Fracture of High Strength Steel Sheets

Further insights on the stress equilibrium method to investigate macroscopic residual stress fields: Case of aluminum alloys cylinders

The stress equilibrium, SE, method has been shown to be a very powerful, reliable tool for calculating the un-stressed lattice parameter, a0, as a critical requirement for the determination of the residual stress, RS, by diffraction techniques. The method can be used in cases where others, such as the powder or comb ones, are limited (e.g., in age-hardenable aluminum alloys components, where a0 can be affected). Owing to its potential, this method can address complex cases that, however, have not yet been sufficiently exploited. In particular, it makes it possible to delve into the effect of microstructural factors (e.g., texture variations) on the macroscopic residual stress, M-RS. Here, the M-RS obtained after quenching and slow cooling of cylindrical samples of aluminum alloys has been investigated. Data obtained from neutron and synchrotron radiation diffraction in AA5083 and AA2014 alloy samples (of different size), respectively, have been used. Specifically, the development of a texture gradient, a very common consequence derived from conventional manufacturing processes of components, has been taken into account. The known fact that a parabolic profile of the M-RS is obtained in cylindrical samples is used to generalize the SE method to determine a0 and to strengthen its quality and reliability.

Effect of initial microstructure on the deformation heterogeneities of 316L stainless steels fabricated by selective laser melting processing

The selective laser melting (SLM) is a popular additive manufacturing (AM) technique used for the fabrication of metal parts. In the present study, two 316L stainless steel specimens (SLM-I and SLM-II) with different microstructures were fabricated with different levels of energy density by changing the laser power and scanning speed, which are the main SLM process conditions. The deformation and fracture behavior of miniature SLM specimens under uniaxial tension were experimentally measured via optical microscopy (OM), field emission scanning microscopy (FE-SEM), and an electron back-scattered diffraction (EBSD) technique. In order to analyze the deformation heterogeneities under uniaxial tension, the inverse pole figure (IPF) map, kernel average misorientation (KAM) map, Taylor factor (TF) map, grain boundaries (GBs), Σ3 twin boundaries (TBs), and melt pool boundaries (MPBs) developed in deformed SLM specimens were analyzed at different strain levels. The effect of microstructural factors on the deformation heterogeneities of SLM specimens was explained by the evolution of KAM, GBs, MPBs, and Σ3 TBs. The initial microstructures of the SLM specimens significantly influenced the generation and propagation of cracks under uniaxial tension.

Influence of microstructural morphology on pitting corrosion resistance of duplex stainless steel weld metals

ABSTRACT The formation mechanism of microstructure of duplex stainless steel weld metals with different N content and heat input and the effects of microstructural factors on pitting corrosion resistance of them were investigated. As N content of weld metal increased, ferrite content decreased and Cr nitride content increased. However, once N content exceeded a certain value, Cr nitride content decreased. As the ferrite content of the weld metal decreased, the critical pitting temperature (CPT) increased, and as N content increased, CPT increased. Thus, the pitting corrosion resistance of duplex stainless steel weld metals must be affected by both of N content and Cr nitride, and the precipitation of Cr nitride must also be affected by N content and the ferrite content due to N content and the weld heat input. The results indicated that these microstructural factors were an important index to evaluate the pitting corrosion resistance of duplex stainless steel weld metals.

Software realization of physical property calculation model based on effective medium theory

In this paper, a composite physical property calculation software—Composite Studio is developed based on the modified effective medium theory. The computing kernel of the software is written in C++ language and its GUI is designed by Qt. With the development of the computation technique, the material genome project is proposed, which tries to shorten the period of the material design by high-throughput computation, data mining and property database establishment. On a mesoscopic scale, there are several kinds of the models to calculate the physical properties of the composite materials. However, these models usually have the formula in quite a lot of kinds of forms. A general commercial software for physical property calculation on a mesoscopic scale is still leaking. The software uses Green’s function to solve the constitutive equations. It calculates the effects of microstructural factors on physical properties. These factors include volume fraction, aspect ratio of reinforce particles, orientation distribution, and macroscopic orientation. It can obtain more than 10000 composites by freely combining four microstructure factors. The operation process of software includes 5 steps. The first step is to choose the materials of matrix and reinforcement. The second step is to select the shape type of reinforcement. The third step is to set the range of values for the microstructure factors of the composite materials. The fourth step is to choose the calculation model and start calculations. The last step is to plot and analyze the results. In addition, researchers can directly have the calculation results through the single point analysis module of the software. We use several two-dimensional line plots to display multi-dimensional calculation results. This is convenient and efficient for researchers to observe and analyze the results. Until now, two calculation modules were developed in Composite Studio, i.e. the elastic modulus calculation module and the dielectric constant calculation module. The software can be applied to different computer systems. In the future, the Composite Studio can be used as a general-purpose calculation tool embedded into an server platform for popular composite design.

Effect of Microstructural Factors on the Strength and Deformability of Ferrite-Pearlite Steels with Different Mn and V Contents

Effect of Microstructural Factors on the Strength and Deformability of Ferrite-Pearlite Steels with Different Mn and V Contents

Microstructural Factors That Decrease the Local Strength of Grain Boundaries in Martensitic Steels

As a result of the phase transformation of austenite to martensite during steel quenching, weakened structural regions, specifically the boundaries of the original austenite grains, have been formed. They are weakened because of microstructural factors, such as the residual internal microstrains and segregation of embrittling impurities. The joint effect of microstructural factors, namely, residual microstrains and segregation of phosphorus and carbon at grain boundaries, on reducing the local strength of the boundaries of the initial austenite grains in martensitic steels is quantitatively evaluated, and the impacts of these microstructural factors have been separated. The dependences of the local grain-boundary strength on the ratio of various levels of residual microstrains and on the atomic concentration of phosphorus impurities at the grain boundary in segregation spots have been determined. It has been shown quantitatively that the adsorption enrichment of the austenite grain boundaries with phosphorus leads to a decrease in the intergrain adhesion and facilitates the emergence and development of cracks along the boundaries of the initial austenite grains. The quantitative dependence of the local strength of grain boundaries on the concentration ratio of carbon and phosphorus in them has been shown. Carbon in concentrations of up to 0.04% reduces the embrittlement of the boundaries due to the segregation of phosphorus and loses its neutralizing effect on the phosphorus segregation at concentrations of more than 0.04%, so the phosphorus concentration at the grain boundaries increases and the embrittlement resistance of the latter decreases. The applicability of the developed technique for the quantitative evaluation of the local strength of hardened steel grain boundaries by using tests on delayed fracture and applying the method of finite elements to determine the local strains has been shown.

Effect of microstructural factors on void formation by ferrite/martensite interface decohesion in DP980 steel under uniaxial tension

The effect of microstructural factors on ferrite/martensite (F/M) interface decohesion in DP980 steel under uniaxial tension was investigated using ex-situ tensile testing and the crystal plasticity finite element method (CPFEM). Ex-situ tensile testing of a miniaturized specimen with a 100 μm-thick grooved gauge region revealed that the main ductile failure mechanism in DP980 steel was F/M interface decohesion. First, the effect that the crystallographic orientation of ferrite exerted on the ductile fracture by F/M interface decohesion was investigated using the representative volume elements (RVEs) of single-crystalline ferrite matrix containing a hard martensite particle. Then, the effects of martensite morphology and grain boundary alignment on the heterogeneity of strain-stress partitioning, in-grain orientation gradient for the ferrite matrix, and the corresponding void formation by F/M interface decohesion were investigated using three types of RVEs with a bi-crystalline ferrite matrix that contained one of the followings: (i) a circular martensite particle, (ii) an elliptical martensite particle, and (iii) two adjacent elliptical martensite particles at the F/F grain boundary. To capture the void formation by F/M interface decohesion, a cohesive zone model based on traction-separation law was introduced along the interfaces between the ferrite and martensite phases. The simulation revealed that the crystallographic orientation for ferrite, the martensite morphology, and the grain boundary alignment all significantly affected the heterogeneity of strain-stress partitioning, the in-grain orientation gradient for the ferrite matrix, and the void formation by F/M interface decohesion in DP980 steel under uniaxial tension.

Effects of Microstructural Factors on Corrosion Behavior of As-Extruded Mg-Sn-Zn Alloys in Immersion and Salt Spray Environments

The effects of microstructural factors, including the fraction of second phase particles and solute content in the matrix, on the corrosion behavior of as-extruded Mg-Sn-Zn alloys were evaluated by immersion and salt spray testing. After immersion testing, the average corrosion rate increased with the increase in Sn content and decrease in Sn:Zn ratio. On the other hand, after salt spray testing, the average corrosion rate increased with the increase in Sn content, but it was minimized at the Sn:Zn ratio of 5:2. Hydrogen evolution appeared to be the dominant controlling factor of corrosion during immersion, while the partial protectiveness of the film also contributed to the corrosion during salt spray testing.

Effect of Microstructural Factors on Room- and Low-Temperature Impact Toughness of Hypoeutectoid Steels with Ferrite-Pearlite Structure

Effect of Microstructural Factors on Room- and Low-Temperature Impact Toughness of Hypoeutectoid Steels with Ferrite-Pearlite Structure

The effects of microstructural factors on the corrosion behaviour of Mg–5Sn–xZn (x = 1, 3 wt%) extrusions

The effects of microstructural factors, including fraction of second phase particles and solute content in a matrix, on the corrosion behaviour of Mg–5Sn–xZn (x=1, 3wt%) alloys were evaluated by using potentiodynamic polarisation and immersion tests. The hydrogen evolution rate and the corrosion potential increased with increasing Zn content, while the passive current density decreased. The average corrosion rate measured by immersion test increased with increasing Zn content, and was consistent with the hydrogen evolution rate. The increase of the corrosion rate with increasing Zn content resulted from increasing fraction of Mg2Sn particles and Zn content dissolved in the matrix.

Effects of Microstructural Factors on Adiabatic Shear Behaviors of Ti6441 Alloys

Abstract In term of newly developed titanium alloys Ti-6Al-4V-4Zr-Mo (Ti6441) modified from the commercial Ti-6Al-4V alloys, the adiabatic shear behaviors of equiaxed and lamellar microstructures were investigated. Unlike the Ti-6Al-4V alloys, Ti6441 alloys with the lamellar microstructure are less susceptive to adiabatic shear bands (ASBs), compared with the equiaxed one. In particular, the ASBs branch off in the lamellar microstructure, requiring additional energy by consuming metal bulk plastic deformation work. Besides, forced shearing experiment results show the lamellar microstructure exhibits outstanding dynamic ductility in contrast with the equiaxed one, though both microstructures perform the same strength value.

Deformation mechanism near crack-tip by finite element analysis and microstructure observation in magnesium alloys

The effects of microstructural factors, i.e., grain size and texture, on the deformation behavior near the crack-tip region during the fracture toughness test were investigated using wrought Mg–3 wt.%Al–1 wt.%Zn alloys, which were produced by extrusion or equal-channel-angular extrusion (ECAE). The stress distributions related to deformation twins were predicted by finite element analysis (FEA), and the microstructural evolutions were confirmed by experiment. Deformation twins were formed at the beginning of the fracture toughness test due to the creation of a large stress field near the crack-tip region. The formation region of deformation twins became small with grain refinement due to the changes in the dominant plastic deformation mechanisms. The results from microstructure observations showed similarities to the stress distribution, which used simple stress–strain relations that assumed a mechanical asymmetry following the Hill's potential function. The texture, i.e., basal plane distribution, also affected the formation of deformation twins. The formation region of deformation twins in the ECAE-ed alloy was predicted to be smaller than that in the extruded alloy by FEA, and this tendency was very similar to that in the microstructural observations of the deformed samples. These results can be used to predict the macroscopic deformation features near the crack-tip, and could be helpful for developing magnesium alloys with high performance mechanical properties.

Contribution of Microstructural Factors to Hardness Change during Creep Exposure in Mod.9Cr-1Mo Steel

The effect of microstructural factors on hardness was investigated in normalized, tempered, aged and crept materials for Mod. 9Cr-1Mo steel, using nanoindentation and microhardness tests. Nanohardness and microhardness decreased during tempering, aging and creep exposure. Dislocation spacing, lath width, high angle boundary (block and packet boundary) spacing and inter-particle spacing increased during tempering, aging and creep exposure. A converted Vickers hardness was introduced to compare directly nanohardness and microhardness to Vickers hardness. The converted Vickers hardness increased with indent size in all the materials tested. Hardness at an indent size less than 1μm mainly consists of dislocations inside lath grains. Hardness at an indent size larger than 1μm originates from not only dislocation but precipitates and high angle boundaries such as block and packet boundaries. Comparing the converted Vickers hardness with lath width and high angle boundary spacing in normalized material with no precipitates, it was found that the lath boundary does not contribute to hardness. The difference in converted Vickers hardness between tempered and aged material was obviously large at the indent size, greater than inter-particle spacing. The decrease in hardness during aging is caused by increase in inter-particle spacing due to coarsening and coalescence of precipitates. On the other hand, not only changes in precipitates but also increase in high angle boundary spacing and dislocation spacing contribute to decrease in hardness during creep exposure.

Effects of microstructural factors on quasi-static and dynamic deformation behaviors of Ti-6Al-4V alloys with widmanstätten structures

The effects of microstructural factors on the quasi-static tensile and dynamic torsional deformation behaviors in Ti-6Al-4V alloys with Widmanstatten structures were investigated in this study. Dynamic torsional tests were conducted using a torsional Kolsky bar for five Widmanstatten structures, in which microstructural parameters such as colony size and α lamellar spacing were varied by heat treatments, and then the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Under dynamic torsional loading, maximum shear stress was largely dependent on colony size, whereas shear strain at the maximum shear stress point was on colony size as well as α lamellar spacing. Adiabatic shear bands were found in the deformed area of the fractured torsional specimens, and their width was smallest in the structure whose colony size and α lamellar spacing were both large. The possibility of the adiabatic shear band formation was quantitatively analyzed in relation to microstructural factors. It was the highest in the coarse Widmanstatten structure, which was confirmed by the theoretical critical shear strain (υc) condition for the adiabatic shear band formation.

Mechanical response of 9% Cr heat-resistant martensitic steels to abrupt stress loading at high temperature

Microscopic deformation behavior upon abrupt stress loading at high temperature and the effects of microstructural factors on the behavior were investigated in 9% chromium martensitic steels with a variety of microstructures. Anelastic deformation occurs upon abrupt stress loading in steels with a martensitic lath structure. The anelastic deformation originates from the lath structure; that is, the cell structure independent of the presence of a high dislocation density, precipitates, or solute atoms of W or Mo. The lath boundaries, which correspond to sub-boundaries, elastically bend under applied stress, and the motion of the lath boundary requires time due to its complicated structure. This is the reason for the anelastic deformation in the martensitic lath structure. The anelastic strain of extremely low-carbon 9% Cr steel is smaller than that of conventional 9% Cr steels, indicating the difficulty of lath boundary motion in the low-carbon steel. The many MX precipitates present at the lath boundaries effectively retard the elastic bending of the lath boundary in the extremely low-carbon 9% Cr steel. The difficulty of lath boundary motion expected from the analysis of anelastic strain can reasonably explain the improvement of creep strength in extremely low-carbon 9% Cr steel reported in the literature.