Effect Of Initial Microstructure Research Articles

Effects of initial microstructure on the aging behavior and subsequent mechanical properties of Ti–Nb–O titanium alloy

Effects of initial microstructure on the aging behavior and subsequent mechanical properties of Ti–Nb–O titanium alloy

Correction to: Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Correction to: Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Cutting edge radius effect on the surface integrity of orthogonal turned aluminium alloy Al6082 with different initial microstructure

In the present study, the combined effect of initial microstructure and relative tool sharpness (RTS) on the surface integrity of aluminium(Al6082) alloy has been investigated. Orthogonal turning is carried out on as-received and heat-treated specimen with group of edge radiused tools. Surface roughness and micro hardness have been evaluated with respect to number of turns for varying RTS value. Results indicate that the workpiece material adhesion on the tool has significantly influenced the surface roughness. In addition, below the critical RTS, the surface integrity is greatly influenced by the grain size of the material.

Microstructure and Mechanical Properties of Dual‐Phase Steels by Combining Adjusted Initial Microstructures and Severe Plastic Deformation

Herein, the effects of initial microstructure in combination with the severe plastic deformation on the developed microstructures and mechanical properties of dual‐phase (DP) steels are investigated. DP steels are produced by an intercritical annealing from the preliminarily heat‐treated samples with different initial microstructures. The constrained groove pressing (CGP) process is additionally applied before the final intercritical annealing step. It is found that the martensitic and tempered martensitic microstructures lead to DP steels with a good balance of strength and elongation because of finer and more uniformly dispersed martensitic islands. The ferrite/pearlite banded initial microstructure is not a proper choice for intercritical annealing as all mechanical properties become worse. The CGP can be employed before intercritical annealing for refining microstructure and enhancing damage tolerance of DP steels. Nevertheless, the impacts of the CGP process on the resulted strength of DP steels are obviously different depending on the initial microstructures. The amounts, sizes, and distributions of dimples and cleavage facets on the fracture surfaces of DP steels correlate well with the corresponding microstructures and tensile characteristics.

Effect of initial microstructure on graphitization behavior of Fe–0.55C–2.3Si steel

In this study, the effect of the initial microstructure (i.e., ferrite + pearlite or martensite) on the graphitization behavior and microstructural evolution during heat treatment of a hot-rolled medium-carbon, high-silicon steel (Fe–0.55C–2.3Si) is investigated. When a sample consists of ferrite and pearlite, its microstructure gradually changes to ferrite and graphite during heat treatment via the decomposition of pearlite and the formation of graphite particles. In the sample with a martensite microstructure, the phase transformation occurs in the following step: martensite → ferrite + cementite → ferrite + graphite. Although the graphitization process of the martensite sample is more complex than that of the ferrite + pearlite sample, the graphitization rate is substantially faster in the former owing to more abundant grain boundaries and triple junctions that act as nucleation sites for graphite. When the initial microstructure changes from ferrite + pearlite to martensite, the graphite completion time significantly reduces from 16 to 2 h at 650 °C and from 6 to 0.5 h at 700 °C. After complete graphitization, the average size and number density of graphites in the martensite sample are respectively smaller and higher than those in the ferrite + pearlite sample. The rate of hardness decrease (i.e., material softening) during heat treatment is also faster in the martensite sample. These results demonstrate that changing the initial microstructure from ferrite + pearlite to martensite is an effective means to accelerate the graphitization behavior and acquire a graphitized steel with uniformly distributed fine graphite particles.

Effect of Initial Microstructure on the Hot Deformation Behavior and Microstructure Evolution of Aluminum Alloy AA2060

Effect of Initial Microstructure on the Hot Deformation Behavior and Microstructure Evolution of Aluminum Alloy AA2060

Effect of Initial Microstructure on the Toughness of Coarse-Grained Heat-Affected Zone in a Microalloyed Steel

Toughness of the coarse-grained-heat-affected-zone (CGHAZ) strongly depends on the prior austenite grain size. The prior austenite grain size is affected not only by chemical composition, thermal cycle, and dissolution of second-phase particles, but also by the initial microstructure. The effect of base metal microstructure (ferrite/pearlite obtained by air cooling and martensite obtained by water-quenching) on Charpy impact toughness of the CGHAZ has been investigated for different heat inputs for high-heat input welding of a microalloyed steel. A welding thermal cycle with a heat input of 100 kJ/cm and 400 kJ/cm were simulated on the MMS-300 system. Despite a similar microstructure in the CGHAZ of both the base metals, the average Charpy impact energy for the air-cooled base metal was found to be higher than the water-quenched base metal. Through thermo-kinetic simulations, it was found that a higher enrichment of Mn/C at the ferrite/austenite transformation interface of the CGHAZ of water-quenched base metal resulted in stabilizing austenite at a lower A1 temperature, which resulted in a coarser austenite grain size and eventually lowering the toughness of the CGHAZ.

Effect of initial microstructure on grain refinement under hot compression in CrMnFeCoNi high-entropy alloy with Al addition

The microstructural changes and flow behavior under hot compression at a temperature of 1173 K were examined for a six-component (CoCrFeMnNi)92Al8 high-entropy alloy. The homogenized alloy, which was a single-phase solid solution with a face-centered cubic (fcc) structure, possessed a deformation microstructure with shear bands after hot compression and exhibited steady-state flow over a wide strain range. In contrast, the thermomechanically processed alloy, which was composed of an unrecrystallized fcc matrix and second phases (bcc and σ), comprised fully recrystallized matrix grains of 0.8 µm diameter after hot compression and displayed gradual strain softening from the early stages of deformation. The results demonstrated that the dense dispersion of the second phases in the thermomechanically processed alloy was quite effective for attaining fine grains by dynamic recrystallization upon hot deformation.

Effects of initial microstructure before cold rolling on microstructure evolution and mechanical behaviour of CGLcompatible Q&P steel

Quenching and partitioning (Q&P) steels offer impressive combination of strength and ductility that can reduce the mass and improve the crash worthiness. In order to be able to meet consumer’s durability expectations, corrosion protection and galvanizability become crucial. In this paper, based on a cold-rolled high strength steel (0.225C-0.85Si-2.02Mn-0.91Al, in wt.%) and continuous galvanizing line (CGL) compatible Q&P treatment, the effects of the initial microstructure before cold-rolling were systematically investigated by means of SEM, EPMA, TEM, EBSD and XRD. It is shown that the resulting microstructure and mechanical properties after Q&P treatment are influenced by the initial microstructure. About 10.2-16.1vol.% RA are obtained, which is potential to gain the desired mechanical stability. Compared with “Q&P sample with initial microstructure prepared by quenching and austempering (i.e., Q&P(QAT))”, “Q&P sample with initial microstructure prepared by quenching and austempering followed by tempering (i.e., Q&P(QAT&T))” obtained a higher fraction of retained austenite (16.1%RA) and relatively low carbon content, thus resulted in an excellent ductility because of better mechanical stability and consequently more effective and sustained TRIP effect at high strain. With increasing the tempering time, the tempering degree of martensite increases markedly, while it does not have strong effects on the microstructures, leading to the similar fractions of RA and properties in “Q&P sample with initial microstructure prepared by quenching and tempering for 4min (i.e., Q&P(Q&T-1))” and “Q&P sample with initial microstructure prepared by quenching and tempering for 10min (i.e., Q&P(Q&T-2))”.

Investigation of the Correlation between Initial Microstructure and Critical Current Density of Nb-46.5 wt%Ti Superconducting Material

We have investigated the effect of initial microstructures on the change in critical current density (Jc) of Nb-46.5 wt%Ti (NbTi) superconducting material. It is well known that α-Ti phases distributed in NbTi material act as a flux pinning center, resulting in an improvement in critical current density. Therefore, it is crucial to obtain the grain-refined microstructure, which is strongly related with precipitation of uniformly distributed fine α-Ti phases and higher volume faction of α-Ti phases, as α-Ti phases are precipitated at the grain boundaries and triple points during heat treatments. Therefore, in order to characterize the effect of initial microstructure of NbTi on critical current density, different initial microstructures were obtained by applying equal channel angular pressing (ECAP) and hot rolling with different strains. It was revealed experimentally that hot rolling with a higher strain is efficient for obtaining the initial microstructure, which has equiaxed fine grains of β-NbTi with the aid of dynamic recrystallization, and which is helpful for precipitating fine α-Ti phases during intermediate heat treatment. Furthermore, it was confirmed that critical current density can be enhanced by obtaining a smaller α-Ti phase, a higher aspect ratio of α-Ti phase, a higher volume fraction of α-Ti phase and a ribbon-like folded α-Ti phase.

Effect of initial microstructure on hot deformation behavior of AlMg5Si2Mn alloy

In this study, the hot deformation behavior of high-temperature annealed and as-cast AlMg5Si2Mn aluminum alloy was investigated in compression tests carried out between 350 and 430 °C, with a strain rate of 0.005–0.5 s−1, using a DIL 805A/D quenching-deformation dilatometer equipped with an accessory that allowed hot compression tests to be performed in either a vacuum or an inert gas atmosphere. To reveal the mechanism of hot deformation, the flow stress behavior and microstructural evolution were investigated after the hot compression tests. Constitutive constants for the as-cast and annealed state were then calculated and compared. The results show that the alloy in the annealed state exhibited lower deformation resistance under the same deformation conditions, especially at low deformation temperatures. The activation energies for deformation, Q, for the as-cast and annealed conditions were calculated to be 181 kJ*mol−1 and 169 kJ*mol−1, respectively.

Effect of Initial Microstructure on Mechanical Properties of Pressure Vessel Steel after Intercritical Heat Treatment

Effect of Initial Microstructure on Mechanical Properties of Pressure Vessel Steel after Intercritical Heat Treatment

Mechanism of high-strength and ductility of Mg-RE alloy fabricated by low-temperature extrusion and aging treatment

Through studying the effect of initial microstructure on the precipitation behavior, microstructure evolution and mechanical properties of Mg-6Gd-4Y-0.5Zn-0.5Zr alloy, an effective way to fabricate high-strength and ductile Mg-RE alloy was proposed by low-temperature extrusion and aging treatment, where the contribution of various strengthening mechanisms was quantitatively analyzed. The results indicate that the difference of initial microstructures had no evident influence on the precipitation behavior of the Mg-RE alloy. Static recrystallization took place in the alloy with low-temperature extrusion of 300 °C during aging treatment at 200 °C due to relatively higher dislocation density in the deformed grains, which offset the reduction of elongation caused by aging treatment and resulted in the good combination of strength and ductility. In the high-strength Mg-RE alloy, grain boundary strengthening, solid solution strengthening, and precipitation strengthening are the main strengthening mechanisms. As shearable β’ particles by basal slip existed in the Mg matrix, precipitate shear strengthening other than Orawan bypassing strengthening should be utilized in predicting the precipitating strengthening behavior of Mg-RE alloy.

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 initial microstructure on the microstructure evolution and mechanical properties of 1.0C-1.5Cr steel in the laser surface quenching

Laser surface quenching was conducted on the 1.0C-1.5Cr steel with different initial microstructures. The effects of initial microstructure on the cementite dissolution and grain size were studied, and the distributions of temperature and stress were simulated. The results indicated that the thickness of hardened layer was larger when the initial microstructure is martensite, which is mainly because the martensite-to-austenite transformation is displacive transformation during laser heating. Within hardened layer, the volume fraction of cementite (VFC) increases with the increase of depth. For the initial microstructure composed of ferrite matrix and cementite, the refining of cementite will facilitate its dissolution, and within hardened layer, mean diameter of cementite (MDC) decreases first and then increases with the increase of depth. For the initial microstructure composed of martensite matrix and cementite, the MDC changes slightly at deeper position of hardened layer. Tensile stress will form in the heat affect zone, and due to the high sensitivity to tensile stress, the impact resistance and bending properties of spheroidized microstructure are worse after laser surface quenching. Under identical laser parameters, the impact absorbed energy of spheroidized microstructure is about 50% of tempered sorbite and 60% of martensitic microstructure, and its bending strength is about 60% of tempered sorbite, and 40% of martensitic microstructure. The impact absorbed energy can be increased by at least 26% through preheating at 160 °C. In addition, the refining of initial martensitic microstructure will enhance bending resistance.

Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel

Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel

Microstructure and hot deformation behavior of a new aluminum–lithium–copper based AA2070 alloy

The effects of initial microstructure on hot compression behavior of a new Al–Li–Cu alloy AA2070 were studied in the temperature range of 250 °C–450 °C and strain rate range of 0.001 s−1 - 0.1 s−1. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize microstructure prior to and post deformation. Two types of major strengthening precipitates were identified: Al2CuLi (T1) phase with habit planes parallel to {111}Al and Al2Cu/Al3Li (Ɵ'/δ′) composite precipitates with habit planes parallel to {100}Al, in the initial microstructure. The combination of these precipitates provides strong resistance to dislocation slip. While dynamic recovery is the main softening mechanism at compression temperatures below 450 °C, dynamic recrystallization dominates softening at 450 °C. T1 precipitate bands consisting of multiple fine T1 precipitates exist in microstructure after hot deformation at 250 °C and 350 °C. The formation mechanisms of T1 precipitate bands and fine T1 precipitates are discussed in light of shearing deformation of T1 precipitates. After hot deformation at 350 °C, Ɵ'/δ′ composite structure is lost and only Ɵ′ precipitates exist in the post-deformation microstructure. The interface between Ɵ′ precipitate and aluminum matrix becomes incoherent. The optimal processing conditions of this alloy have been identified as a temperature of 450 °C and a strain rate of 0.001 s−1, with significant grain refinement and the weakest deformation texture, which are consistent with the analysis results of hot work efficiency and instability using pseudo processing maps.

Austempered Ductile Iron with Dual Microstructures: Effect of Initial Microstructure on the Austenitizing Process

This work compares alternatives for the production of high ductility ADI, austempered from an intercritical austenitizing temperature range, with a microstructure of ferrite + ausferrite. Different initial microstructures were selected, including ferrite, pearlite, pearlite + ferrite, martensite and ausferrite. The samples were austenitized within the intercritical zone (795 °C) for different times (up to 12 h) and then austempered at 350 °C. The evolution of the formation and distribution of ferrite and austenite during the austenitizing process for the different initial microstructures was studied. For the selected austenitizing temperature, all of the initial microstructures produced 30% ferrite (70% ausferrite) in the final microstructure (after 12 h). The mechanical properties depend upon the distribution and refinement of the ferrite and ausferrite areas. Spheroidized carbides from pearlite are not completely dissolved during intercritical austenitizing for 2 h. Graphite nodules are an important source of carbon for the austenite formed from starting microstructures of ferrite, pearlite + ferrite and pearlite with grain boundaries being the main pathway for carbon diffusion. Austenitizing started away from the graphite nodules at eutectic cell boundaries due to Si segregation. For starting microstructures of ferrite, pearlite and pearlite + ferrite, a homogeneous distribution of austenite does not occur. Rather, it is concentrated on eutectic cell boundaries and ferrite grain boundaries with large areas of ferrite around the graphite nodules. For starting microstructures of martensite and ausferrite, carbon is evenly distributed and quickly dissolved, resulting in a homogeneous distribution of austenite and ferrite with the best combination of strength and ductility.

Effect of Initial Microstructure on Phase Precipitation and Mechanical Properties during Heat Treatment of TC21 Titanium Alloy

Phase precipitation and mechanical properties of TC21 titanium alloy with two different initial microstructures during heat treatment were determined. Result indicated that compared with coarse microstructure alloy, fine microstructure alloy developed finer microstructure, more unstable ω and α2 precipitates with much smaller size and lower volume fraction, and obtained better mechanical properties during heat treatment.