Effect Of Recrystallization Research Articles

Influence of Annealing Treatment on the Microstructure and Mechanical Properties of Cold-Sprayed CoCrFeNiMn High Entropy Alloy

AbstractIn this study, we developed a ~ 2 mm thick deposit of CoCrFeNiMn high entropy alloy (HEA) from cold spray. After cold-spraying, annealing at 600, 800 and 1000 °C for 5 hrs was conducted to improve and consolidate the microstructure. The influence of the annealing treatment on the microstructure, hardness and tensile strength of the HEA deposit was studied. The results showed that annealing treatment increased the fraction of metallurgical bonded areas due to diffusion, which resulted in enhanced mechanical performances of the deposit. The examined fractured surfaces of the tensile test samples revealed that the annealing treatment changed the failure behavior of the as-sprayed deposit from mostly particle-particle interface failure to void coalescence (ductile failure). Interestingly, a distinct microstructure was observed for the deposited annealed at 600 °C; a partially recrystallized microstructure with a small volume fraction of Cr-rich phase formed along grain boundaries, whereas fully recrystallized microstructure at higher two temperatures. The strengthening effect of partial recrystallisation, with a small volume fraction of the Cr-rich phase led to a greater reduced modulus and tensile strength (~196.7 GPa and 51.7 MPa) of the deposit annealed at 600 °C when compared with that annealed at 800 °C (~182.5 GPa and 43.6 MPa). It is believed that the small volume fraction of the Cr-rich phase partly constrained the deformation of the surrounding FCC HEA matrix during mechanical loading, leading to better mechanical properties as compared to the deposit annealed at 800 °C.

Research Progress on the Relationship Between Microstructure and Properties of AISI 321 Stainless Steel

AISI 321 stainless steel is widely used in chemical pipelines and nuclear power, prompting research on its high-temperature performance and corrosion resistance. This review focuses on the effects of alloy elements, second-phase particle formation, and heat treatment processes on the microstructure and properties of AISI 321 stainless steel. Fine tuning of alloying elements can affect the mode and effect of dynamic recrystallization, altering the high-temperature flow deformation of AISI 321 stainless steel. In order to achieve phase equilibrium, the relationship between corrosion resistance and high-temperature creep behavior and high-temperature mechanical behavior in the presence of second-phase particles was also analyzed. This review outlines the basic heat treatment procedures for improving material properties, providing a new perspective for solution treatment and improving corrosion resistance. In addition, the latest research progress on other factors affecting the high-temperature performance of AISI 321, such as coatings, was briefly introduced.

Stable and radiogenic strontium isotopes trace the composition and diagenetic alteration of remnant glacial seawater

A remnant of glacial seawater preserved in the pore fluids of sediment cores from the Maldives Inner Sea provided an opportunity to investigate the stable strontium isotopic composition (δ88/86Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of δ88/86Sr as a tracer of early marine diagenesis. We used paired measurements of δ88/86Sr and radiogenic Sr isotope ratios (87Sr/86Sr) in pore fluids and surrounding carbonate sediments to constrain the diagenetic history of the preserved glacial water mass at IODP Sites U1466 and U1468. These pore fluid profiles document variability in δ88/86Sr in a shallow marine setting, revealing distinct diagenetic processes dominating within different depth intervals. We find evidence for isotope fractionation during secondary calcite precipitation at intermediate depths and observe that in aragonite-dominated settings, fractionation during recrystallization may be obscured by the dissolution of aragonite in the uppermost sediments. Correcting for the effect of carbonate recrystallization on pore fluid Sr concentration ([Sr]) and isotopic composition, we estimate that glacial seawater [Sr] was higher (∼98μM) and δ88/86Sr lower (∼0.32‰) compared to the modern ocean, consistent with hypotheses attributing the present-day disequilibrium of the ocean Sr budget to glacial/interglacial changes in shelf carbonate weathering and burial. Our results provide evidence that the ocean [Sr] and δ88/86Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (∼2 Myr) and demonstrate that pore fluid δ88/86Sr measurements are a useful addition to multi-tracer studies of diagenesis in complex marine systems.

Microstructure and property alterations and toughening mechanism of cast TC4 alloy by solid state treatment with low-density DC electric field

In this paper, the impact of low-density DC electric field treatment (LDCT) on the microstructure and mechanical properties of cast TC4 titanium alloy (CTC4) was investigated. The findings indicate that the driving force for the current provided by LDCT enhances the texture of CTC4. When the current density is sufficiently high, the induced recrystallization effect weakens the texture, leading to an isotropic state. The polygonization of grain boundaries in the LDCT state CTC4 has been identified, along with the emergence of a secondary α phase due to recrystallization. Additionally, this study highlights the phenomenon of preferential nucleation and growth occurring at the grain boundaries. LDCT induces a grain refinement effect in the CTC4 material, whereby the average grain size of the LDCT3 sample decreases from 31.05 μm in the untreated sample to 28.93 μm. The observed reduction in dislocation density in the LDCT states is believed to result from the diffusion of impurity atoms and vacancies. The observation of dislocation plugging at the inner grain boundary of the LDCT3 sample suggests that the electron wind promotes dislocation slip toward the grain boundary. Furthermore, the simultaneous enhancement of strength and toughness in the LDCT state of the CTC4 alloy has been achieved. The LDCT3 sample demonstrates superior performance, exhibiting noteworthy increases of 7.7%, 22.0%, and 10.9% in tensile strength, elongation, and fracture energy, respectively, compared to the untreated sample. The significant role of non-thermal effects in LDCT and the mechanism of atomic diffusion induced by this effect are discussed. The origins of dislocation motion and phase transition are elucidated from the perspective of atomic diffusion.

Stability of large yellow croaker (Pseudosciaena crocea) as affected by temperature abuse during frozen storage: Quality attributes, myofibril characteristics, and microstructure

Temperature abuse occurs frequently during transportation and frozen storage, which affects the quality of frozen aquatic products. Recrystallization generated by temperature abuse leads to irreversible damage to the muscle tissue and microstructure, and exacerbates undesirable oxidation reactions, thus reducing the quality of frozen aquatic products. In this study, a modeling system of temperature abuse alternating between −24 °C and −7 °C was established to evaluate the effect of temperature abuse on the stability of frozen large yellow croaker. The results revealed that temperature abuse caused water migration with the extension of storage time, as well as poorer texture, color, and freshness. Furthermore, the structure of myofibrillar protein (MP) was severely damaged, with a gradual decrease in total sulfhydryl groups and Ca2+-ATPase activity, a loosening of the secondary structure, and a disruption of the protein conformation. The confocal laser scanning microscopy (CLSM) analysis also found that temperature abuse exacerbated protein aggregation. Therefore, temperature abuse during transportation and frozen storage could affect the stability of large yellow croaker negatively, and it mainly originated from the growth of ice crystals and the effect of recrystallization. The study was supposed to provide new insights into the improvement of frozen aquatic products quality.

Effects of stirring friction on the microstructure, texture and mechanical properties of 7055 aluminum alloy

Aluminum alloys are widely used in aerospace, transportation, and many other fields due to their excellent properties such as lightweight, ultra-strength, and high toughness. This paper analyzed the influence mechanism of friction stir on the microstructure, texture, and mechanical properties to realize the strength and toughness of 7055 aluminum alloys and optimize their deformation process. The results show that the aluminum alloys change from uneven banded grains to uniform and fine equiaxed grains after friction stir processing, and the grain size is refined from 14 μm to 0.71 μm. The high-angle grain boundary and texture intensity present an initial increase but a subsequent decrease due to the combined effect of recrystallization and high-temperature softening caused by the heat input of friction stir processing. The total texture intensity and volume fraction of the friction stir processed aluminum alloys decrease significantly, and the intensity of RtG {110} <110>, A {110} <111>, E {110} <111>, and F {111} <112> texture significantly decrease or disappear, while the Brass (B) {110} <112> texture increases. The yield strength of FSP aluminum alloys decreases with increasing heat input (w/v), which mainly depends on the weakening of the texture strengthening effect. However, the increase of geometrically necessary dislocations (GND) caused by grain boundary sliding leads to the significant improvement of the deformation hardening ability and plasticity of the material. In addition, the effect of texture on the plasticity of aluminum alloys was calculated by using Schmid law. It is found that the equivalent slip factor (ESF) and maximum Schmid factor (μmax) of A, E, and Cu textures are equal to 0. The small ESF and μmax of the S texture are not conducive to the plastic deformation property of materials, while the 1000 × 70 sample with more ESF (8) and μmax (0.41) of the Cube texture ({001} <100>) shows better plasticity.

The impact fretting corrosion behavior and damage mechanism of Inconel 690TT under different impact forces in high temperature pressurized water

The impact fretting corrosion of Inconel 690TT under different impact forces was investigated. The results indicated that there was a competitive relationship between formation of third body layer (TBL) and fragmentation of TBL caused by impact force. With the increase of impact forces, damage mechanism changed from adhesive wear to delamination wear, and crack initiation sites gradually shifted from TBL to internal oxidation zone in tribologically transformed structure (TTS) layer. Nanocrystalline boundaries and defects induced by impact force provided channels for internal oxidation. The formation mechanism of TTS was the combined effect of continuous dynamic recrystallization (cDRX) and twin-assisted cDRX.

Manufacturing of heavy tungsten alloys from nano-sized metal oxides via simultaneous reduction-sintering powder treatments

Heavy tungsten alloys are of great importance in the engineering and mining industries as well as the military and medical applications because of their stability at high temperatures, high strength and dense structures. The present study develops a novel technology for the production of heavy tungsten alloys via thermal treatment of nano-sized metal oxides based on simultaneous reduction and sintering processes. Heavy tungsten alloy (95W-3Ni-2Fe) was produced from the reduction of mixed nano-sized metal oxides precursor in H2 at 1000 o C followed by sintering at 1350–1450 o C for 30–90 min. The reduced and sintered samples were characterized by XRD to follow up the crystallinity, total porosity measurement was used to find out the densification properties, the grain structure and morphology were examined by RLM and SEM attached with EDAX. Micro-hardness tester was also used to investigate the influence of sintering conditions on the grain densification. A fundamental study on the kinetics of reduction of mixed nano-sized metal oxides precursor was performed by isothermal and non-isothermal techniques. Both results from isothermal and non-isothermal tests were used to calculate the activation energy which was correlated with macro- and micro-structures to predict the corresponding reduction mechanism. However, the influence of sintering temperature and time on the crystallinity of the produced phases, grain structure, morphology, total porosity, pore-size distribution, bulk and apparent densities, and the hardness of sintered compacts was extensively investigated. The results revealed that the presence of NiO and/or Fe2O3 in the mixed metal oxides precursor was very important to ease the reducibility of WO3 as the metallic phases of Ni and/or Fe act as a catalyst for the reduction of WO3. The rate of reduction proceeds faster in the following order: NiO > Fe2O3 > mixed oxide > WO3. In non-isothermal experiments, it was found that the heating rate has a considerable effect on the reduction of precursor, i.e., the lower the heating rate, the higher the degree of reduction. It might be reported that the use of nano-sized metal oxides particles in the fabrication of heavy tungsten alloys greatly affects the main properties of the produced alloy. With the increase in sintering time, larger sizes of dense grains were developed, and the matrix became denser as a result of sintering and re-crystallization effects. The higher the sintering time, the higher the grain densification and the less pores formed in the matrix. On the other hand, with the increase in the sintering temperature, the grain boundaries were well defined in which the grains were composed of tungsten metal and surrounded by inter-metallics. The higher the temperature, the higher the XRD peak intensities of metallic tungsten and intermetallics as a result of sintering and re-crystallization.

Fabrication of Medium Mn Advanced High-Strength Steel with Excellent Mechanical Properties by Friction Stir Processing.

Friction stir processing (FSP) manufacturing technology was used to fabricate medium Mn advanced high-strength steel in this study. The mechanical properties and microstructure of the steel fabricated using FSP were investigated. The steel obtained a total elongation of 35.1% and a tensile strength of 1034.6 MPa, which is about 59% higher than that of the steel without FSP. After FSP, a gradient structure occurs along the thickness direction. Specifically, across the thickness direction from the base material zone to the transition zone and finally to the stirring zone, both the grain size and austenite fraction decrease while the dislocation density increases, which results from the simultaneous effect of severe plastic deformation and recrystallization during FSP. Due to the gradient structure, an obvious difference in the strain across the thickness direction of the steel occurs during the deformation process, resulting in significant hetero-deformation-induced (HDI) strengthening. The deformation mechanism analysis reveals that HDI strengthening and dislocation strengthening are the main factors in the improvement in the strength-ductility balance. The obtained knowledge sheds light on the process of fabricating medium Mn steels with excellent properties using FSP manufacturing technology.

Effect of grain size on irradiation-induced bubble evolution in high burn-up UO2: A phase-field study

Due to economic reasons, uranium dioxide (UO2) ceramic fuel needs to operate under high burn-up conditions. The high burn-up structure (HBS) and micrometric irradiation-induced bubbles within it cause safety issues for the fuel. In this study, a phase-field model was developed to simulate the evolution of fission bubbles under high burn-up conditions. This model simultaneously couples the evolution of recrystallized grains and bubbles through explicit nucleation methods. By simulating the development of HBS in polycrystalline UO2, it was indicated that the microstructure is consistent with experimental observation. The variation of porosity was divided into three stages and found to be in good agreement with experimental data. Additionally, the HBS fraction was compared with experimental measurements to validate this HBS model. Furthermore, the effect of recrystallization on bubble evolution was investigated using the validated model. It was found that recrystallization accelerated bubble evolution by increasing GB area. In addition, the influence of grain size on bubble evolution was studied by constructing initial structures with different grain sizes. Results showed that both the development of recrystallization and the decrease in grain size enhance bubble evolution, but the enhancement becomes smaller as the grain size decreases.

Influence of synchronous-hammer-forging intervention temperature on the microstructure and properties of 316L components fabricated by laser directed energy deposition

Synchronous-hammer-forging has been proved to be an effective method to control the microstructure and properties of metal components in additive manufacturing, but the influence of the intervention temperature is still unclear. 316L stainless steel samples with different hammer-forging intervention temperature were prepared by laser directed energy deposition (LDED) technology. The results show that due to dynamic recrystallization and dislocation accumulation effect, the grain size of the component decreases first and then increases with the increase of hammer-forging temperature, while the dislocation density and tensile strength increase first and then decrease.

Effects of recrystallization on interfacial microstructure evolution and shear strength of TiAl alloy joints

The effects of dynamic recrystallization (DRX) and post-bonding heat treatment (PBHT) on the interfacial microstructure evolution and mechanical properties enhancement of Ti-43Al-4Nb-1Mo-0.2B alloy joints, subjected to various bonding parameters, were thoroughly investigated through detailed microstructural characterization and shear performance tests. A strip-like DRX area was observed at the interface when bonding at 1100 °C, ≥30 MPa, for 60 min. Equiaxial- γ grains underwent discontinuous dynamic recrystallization during the bonding process, and tended to form flat grains parallel to the lamellae direction during recrystallization annealing (1000 °C/6 h) owing to the hindrance imposed by the lamellae on both sides. The orientations of lamellae on the both sides of bonding interface affects the lamellae's stress distribution and deformation behavior at the bonding interface, subsequently influencing the DRX behavior and the width of the DRX zone. Static recrystallization (SRX) during the recrystallization annealing treatment can eliminate bonding defects of joints bonding at lower pressures or temperatures. Optimal joints with fully lamellar interfacial microstructure and excellent shear properties can be obtained through single-α phase annealing treatment. Lamellae microstructure tailored through PBHT can significantly enhance the quality of joints, attributed to the homogeneity of the microstructure between the interface and matrix. The highest shear strength of 478 MPa, accounting for 82 % of the matrix strength, was obtained under the bonding parameters of 1100 °C/30 MPa/60 min-1290 °C/15 min. This work provides important DB process parameters for fabricating of complex structural parts of TiAl alloy.

Delineating the role of dynamic and static recrystallization during hot working of nickel-based superalloy (IN600)

In the presented research, the dynamic working of nickel-based (IN600) superalloy was performed and the micro-mechanisms affecting the deformation behaviour were closely monitored, particularly the role of static and dynamic recrystallization. Hot deformation flow stress response indicated an increase in the true stress value with an increase in strain rate and decrease in temperature. The constitutive calculations indicated that deformation progressed mainly due to dislocation climb motion. The hot workability map indicated a peak power dissipation efficiency (PDE) of 0.39 in two working domains. The microstructural evolution in the hot deformed specimens depicted a consistent increase in dynamic softening at temperature ≥ 1000 °C, whereas, a steady decline in the extent of dynamic softening is observed with increase in strain rate from 0.01 s−1 to 1 s−1. The mechanism for microstructural evolution in this range (0.01–1 s−1) was identified as discontinuous dynamic recrystallization (DDRX). Moreover, at the highest strain rate of 10 s−1, a sudden surge in the recrystallization fraction was observed, which was attributed to the combined effect of DDRX and static recrystallization (SRX). Additionally, this study shows that the presence of twin boundaries (TBs) contributes to dynamic softening by serving as sites for nucleation of strain-free grains.

The Effect of Static Recrystallisation of Parent Austenite on the Lath Martensite Intervariant Boundary Network

The current study investigated the effect of static recrystallisation (SRX) of parent austenite microstructure on the lath martensite intervariant boundary network. In general, the misorientation angle distribution of lath martensite exhibited a bimodal distribution in the range of 10–22 deg and 47–60 deg for all thermomechanical conditions, closely matching the misorientations expected from the ideal Kurdjumov-Sachs orientation relationship. Nevertheless, the population of 60 deg misorientation angle initially reduced with the extent of softening up to 50 pct beyond which it progressively increased to a maximum in the fully recrystallised condition. This was closely consistent with the trend noticed for the 60 deg/[110] intervariant boundaries having twist character. This was explained through the distinct variant selection mechanism occurring due to the change in the parent austenite grain characteristics (i.e., size and deformed state) upon static recrystallisation. The recrystallisation initially led to the formation of fine dislocation-free parent austenite grains up to 50 pct softening, promoting a 4-variant (V1V2V3V4) clustering arrangement to decrease the strain related to the martensite transformation. In turn, this promoted the formation of symmetric tilt 60 deg/111¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left[ {11\\overline{1}} \\right]$$\\end{document} intervariant boundaries, which ultimately reduced the 60 deg/110\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left[ {110} \\right]$$\\end{document} boundaries. Further softening, accompanied with the growth and/or coalescence of parent austenite grains, altered the variant clustering to a 3-variant arrangement (V1V3V5) and the increase in 60 deg/110\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left[ {110} \\right]$$\\end{document} twist intervariant boundaries. Indeed, the martensite boundary network was largely controlled by the SRX parent austenite characteristics (i.e., size), which can be controlled to enhance the materials performance for a given application.

Hot Deformation Behavior and Microstructure Evolution Mechanisms of Ti6Al4V Alloy under Hot Stamping Conditions.

Through the study of the thermal rheological behavior of Ti6Al4V alloy at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C) and different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1, and 0.005 s-1), a constitutive model was developed for Ti6Al4V alloy across a wide temperature range in the hot stamping process. The model's correlation coefficient reached 0.9847, indicating its high predictive accuracy. Hot processing maps suitable for the hot stamping process of Ti6Al4V alloy were developed, demonstrating the significant impact of the strain rate on the hot formability of Ti6Al4V alloy. At higher strain rates (>0.05 s-1), the hot processing of Ti6Al4V alloy is less prone to instability. Combining hot processing maps with hot stamping experiments, it was found that the forming quality and thickness uniformity of parts improved significantly with the increase in stamping speed. The phase composition and microstructures of the forming parts under different heating temperature conditions have been investigated using SEM, EBSD, XRD, and TEM, and the maximum heating temperature of hot stamping forming was determined to be 875 °C. The recrystallization mechanism in hot stamping of Ti6Al4V alloys was proposed based on EBSD tests on different sections of a hot stamping formed box-shaped component. With increasing deformation, the effect of dynamic recrystallization (DRX) was enhanced. When the thinning rate reached 15%, DRX surpassed dynamic recovery (DRV) as the dominant softening mechanism. DRX grains at different thinning rates were formed through both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), with CDRX always being the dominant mechanism.

Compressive Property and Toughening Mechanism of Directionally Solidified Fe(Al, Ta)/Fe2Ta (Al) Eutectic Composites

Herein, Fe(Al, Ta)/Fe2Ta(Al) eutectic composites are prepared using the electron beam floating zone melting directional solidification technique. The compression and fracture toughness properties of Fe(Al, Ta)/Fe2Ta(Al) eutectic composites at different solidification rates are studied with compression and three‐point bending experiments. The toughening mechanism of the material is also analyzed from morphology, composition, and microstructure. The results show that the yield strength and compression properties of the Fe(Al, Ta)/Fe2Ta(Al) eutectic composite are increased with the increase of the solidification rate. The room‐temperature fracture toughness reaches 30.5 MPa m1/2 when the solidification rate is 4 mm min−1. In addition, the material exhibits high strength performance at room temperature. However, it exhibits poor strength and excellent plasticity due to the softening effect of recrystallization at 600 °C. The toughening mechanism of the Fe(Al, Ta)/Fe2Ta(Al) eutectic composites can be summarized as crack blunting, crack branching, crack deflection, and local deformation.

Microstructural changes induced in advanced tungsten grades under high temperature neutron irradiation

Recent studies addressing the change of mechanical properties after high temperature irradiation of tungsten have reported substantial increase of the ductile to brittle transition temperature as well as increase of the hardness. In this work, we performed microstructural analysis by means of transmission electron microscopy (TEM) on various tungsten grades earlier exposed to high temperature neutron irradiation at 1200 °C up to 1 dpa. The latter corresponds to the expected irradiation temperature on the surface of a tungsten monoblock during the steady state operation in ITER. TEM was applied to five tungsten (W) materials including ITER specification pure W and precipitate strengthened W alloys. The analysis of TEM data coupled with its discussion led to a number of important conclusions regarding the damage induced at 1200 °C neutron irradiation such as: (i) weak effect of recrystallization on the accumulation of the lattice damage; (ii) promising results on the tolerance of damage accumulation in W-Y2O3 grade and (iii) internal oxidation of TiC particles which may contribute to the huge increase of the irradiation induced hardening.

Effect of recrystallization on aging embrittlement and high temperature creep properties of AFA steel

As a kind of typical precipitate strengthened steel, alumina-forming austenitic (AFA) stainless steels usually suffer obvious aging embrittlement issue. Recrystallization treatment was performed by cold rolling followed with heat treatment at 1080 ℃ for a Fe-25Ni-15Cr-3.5Al based AFA steel to evaluate the effect of recrystallization on aging embrittlement. The materials before and after recrystallization were aged at 700 ℃ for 120 h to evaluate the effect of recrystallization on precipitation behavior. After recrystallization, the average grain size decreased and the density of grain boundaries increased obviously. The size of precipitates along grain boundaries was smaller and more uniform after recrystallization, and the precipitation of Cr rich phase was inhibited. Room temperature tensile test, Charpy impact, and creep behavior at high temperature of samples with different treatment states were measured and compared. The aging embrittlement of AFA steel was alleviated obviously after recrystallization. The creep resistant was also improved for sample treated by recrystallization and aging. The relevant mechanisms were discussed.

Quantification of static softening process and its effects on work hardening characteristics of a typical high strength steel during multi-pass deformation

Heavy components of 300 M steel are usually manufactured by multi-pass forging. It is necessary to study the flow characteristics of 300 M steel during multi-pass deformation, which helps to regulate the flow behaviors during the actual forging process. In the study, multi-pass compression experiments are conducted on the Gleeble-3500 device to mimic the forging process of 300 M steel. Results show that the deformation parameters and inter-pass holding parameters can affect the work hardening rate significantly. It can be ascribed to coupling effects of dynamic softening and static softening behaviors. A unified static softening kinetics model is established to evaluate the coupling effects of static recovery, static recrystallization, and metadynamic recrystallization on the static softening behaviors. The established static softening kinetics model shows high prediction accuracy with a reliability of 0.99605. Furthermore, a new constitutive model is established to describe the effects of dynamic softening and static softening on the flow stress during multi-pass deformation. The prediction accuracy of the new constitutive model is 0.98897 with a mean absolute error of 4.075%, which demonstrates that the established constitutive model is reliable.

Influence of tool geometry on mechanical and microstructural characteristics of friction stir welded cast alloys

Abstract Cast alloys find suitable applicability in aerospace sector owing to low porosity, high specific strength, corrosion resistance, fluidity and good machinability. The investigation focuses on friction stir welding (FSW) of cast A356 and A2014 alloys with varied range of process parameters, namely tool pin shape (cylinder, threaded cylinder, square, and conical), tool rotation speed (1800–2100 rpm) and welding speed (10–25 mm × min−1). Experimentation on stirwelding was performed based on selected tool pin shape between varied tool rotation and welding speed. The output responses, namely Ultimate tensile strength (UTS) and micro hardness, have been evaluated to study the effect of each tool. The microstructural characteristics of the weld samples were analyzed using optical microscope and scanning electron microscope (SEM) technique. The microstructural observation unveiled that complete fusion prevails between the parent alloys devoid of micro porosities and segregations. The re-crystallization effect resulted in the finer grains. The cylinder-shaped tool with a thread and square shaped tool rendered better strength and hardness properties of 136.6 MPa and 109.4 HV, respectively.