As-cast Samples Research Articles

Effect of Controlled Heat Treatment and Aluminum Additions on the Strengthening of Cu–Ni-Based Alloys

In this investigation, Cu–Ni alloys with different aluminum additions were synthetized under a vacuum atmosphere to reduce the material density. Annealed alloys in a He atmosphere with low aluminum concentration exhibited a coarse dendritic structure, while samples with high aluminum concentration exhibited a refined dendritic structure. Structural defects analyses have shown relatively low vacancy concentrations. Hardness evaluations indicated an increment by approximately 5 times i.e., 370 HVN, more than that for the alloyed samples compared with the as-cast and unalloyed samples. Compression tests have shown a noticeable strengthening improvement (360 MPa), mainly in samples heat treated with 10 at.% Al, while samples with 5 at.% Al showed an acceptable resistance (270 MPa) as well. In general, the sample with 10 at.% Al presented the best performance to be considered as potential structural material.

X-ray line profile analysis study on the evolution of the microstructure in additively manufactured 316L steel during severe plastic deformation

316L stainless steel was manufactured by additive manufacturing (AM), and then, the samples were severely deformed by the high-pressure torsion (HPT) technique. The evolution of the microstructure was monitored by X-ray line profile analysis. This method gives the crystallite size and the density of lattice defects, such as dislocations and twin faults. The AM-processing of the HPT disks was performed in two different modes: the laser beam was parallel or orthogonal to the normal direction of the disks. The subsequent HPT deformation was carried out for ½, 1, 5 and 10 turns. The microstructure and hardness evolution during HPT were similar regardless of the laser beam direction. For both sample series, the minimum achievable crystallite size was about 30 nm, while the dislocation density and the twin fault probability got saturated at the values of 300–350 × 1014 m−2 and 3.5–4%, respectively. The microstructure evolution during HPT of the AM-prepared 316L steel was compared with the HPT-induced changes in an as-cast counterpart. It was found that while the AM-prepared 316L steel remained a single-phase face-centered cubic γ-structure during HPT, in the as-cast samples a body-centered cubic (bcc) martensitic α-phase became the main phase with increasing the imposed strain of HPT due to the lower Ni content. In the saturation state achieved by HPT the initially as-cast 316L steel had a considerably higher hardness (about 6000 MPa) than that for the AM-prepared samples (~ 5000 MPa) due to the large fraction of the hard bcc phase formed during HPT.

Design and development of porous CoCrFeNiMn high entropy alloy (Cantor alloy) with outstanding electrochemical properties

CoCrFeNiMn high entropy alloys are among the most well-studied high entropy alloys that exhibit reasonable strength and outstanding ductility. In the present study, porous CoCrFeNiMn foams have been developed by the addition of copper in the base high entropy alloy by arc melting followed by its removal through an electrochemical dealloying process. Microstructure characterization of the as-cast samples confirmed limited solubility of copper in the matrix while the majority of the copper was found to segregate to interdendritic areas. Removal of copper from the interdendritic areas was successfully carried out by an electrochemical dealloying process which resulted in the development of foams with interconnected porosity. CoCrFeNiMn foams with different levels of porosities were successfully developed by varying the amount of added copper in the base HEA and its removal by a dealloying process. The electrochemical performance of the developed foams was assessed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). One of the developed foams was found to exhibit an areal capacitance of 1.56 F cm−2 at 2 mA cm−2 which is more than 2x times higher than the value reported for recently developed porous AlCoCrFeNi high entropy foam. Developed foam, besides showing excellent values of areal capacitance, demonstrated capacitance retention of 114.6% after 5000 cycles at 8 mA cm−2. The excellent electrochemical performance of the developed high entropy foams exhibits their potential to be used as electrode materials for supercapacitor applications and was attributed to the insertion of interconnected porosity in the base HEA.

Influence of B addition on the Mo diffusion-controlled eutectic dissolution process during homogenization of super austenitic stainless steel S31254

The influence of B addition on dissolution behavior of (σ + γ)e eutectics of a 6Mo super austenitic stainless steel S31254 during the homogenization process was investigated by SEM-BSE observations combined with EDS. The results showed that the addition of 0.005 wt% B accelerated the dissolution of the σ phase controlled by Mo diffusion, during homogenization from 30 to 90 min at 1180 °C. TOF-SIMS results showed that B segregated along the σ/γ interface in the as-cast samples. TEM observations combined with EDS investigated the phase interfaces in two as-cast samples in detail to correlate σ phase dissolution. Compared with the B-free sample, the wide transition zone (∼60 nm) with a composition gradient was more clearly observed at the σ/γ interface in the B-containing sample. The transition zone with B had two features: local segregation of B element and precipitation of R phases at the σ/γ interface. R phases owned larger contents of Mo, which was not almost observed in the as-cast S31254. The results indicated that B segregation changed the phase interface, accelerating Mo diffusion at the σ/γ interface. In addition, the results of nanoindentation indicated a more uniform distribution of hardness at the σ/γ interface after homogenization of the B-containing sample, which can be beneficial to improve the deformation compatibility of S31254 during hot working.

Effect of hot rolling and annealing on microstructure and mechanical properties of the Fe-Co-Cr-Ni-V-Zrx(x =0–5) high entropy alloys

The effect of hot rolling and annealing on the microstructural evolution and mechanical properties of the Fe25−xCo25Cr20Ni25V5Zrx (x=0, 2.5, 5) HEA with Zr variation has been investigated. The Fe25−xCo25Cr20Ni25V5Zrx (x = 0, 2.5, 5) HEA was designed using the CALPHAD approach with varying Zr content from 0 to 5 at%. The structural and microstructural characterization has been carried out by X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analysis. The microstructure of the investigated samples is found to be composed of FCC solid solution + lamellae of FCC solid solution and Ni7Zr2 intermetallic phase, which is consistent with CALPHAD prediction. Differential scanning calorimetry (DSC) analysis has also been carried out to confirm the evolution of different phases. The room temperature mechanical response of the alloys in as-cast and hot rolled annealed (HRA) conditions are evaluated by hardness and tensile testing. The hardness of the alloy increases by 70% for an increment of Zr content from 0 to 5%, respectively, which further increases after HRA. The tensile test performed on the as-cast samples shows a significant reduction in uniform elongation to 13.5% in the case of Zr5, whereas the yield strength increases by more than 125% for those compositions. After HRA treatment, the grain size and uniform elongation of the investigated samples reduced, and the yield strength further improved. The extent of grain size reduction depends on the distribution of the intermetallic Ni7Zr2 phase. The strain hardening exponent ‘n′ is found to be dependent on the grain size, and it reduces with the reduction in grain size. Also, the variation of n is dependent on the presence of the intermetallic Ni7Zr2 phase, and it is found to increase initially if the second phase is present inside the grain interior, whereas it fails to improve if the second phase is present at the grain boundary.

New insight into the strengthening mechanism of AlCoCrFeNi2.1 eutectic high-entropy alloy with dual-phase nanolamellar structures achieved via laser powder bed fusion

Recently, the AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) prepared by laser powder bed fusion (LPBF) could reach a good balance of strength and ductility. The strengthening effect was only qualitatively clarified, however, quantitative analysis remained unclear. In this study, the quantitative analysis of strengthening mechanisms and the relationship between microstructural characteristics and tensile properties were revealed in depth. The AlCoCrFeNi2.1 EHEA with FCC and BCC dual-phase nanolamellar structures (interlamellar spacings of 200–300 nm) fabricated by LPBF achieved an excellent combination of high yield strength (1116 MPa) and fracture elongation (20.3 %). Compared with as-cast EHEA samples, the FCC/BCC nanolamellar interfaces in the LPBF-printed AlCoCrFeNi2.1 EHEA were still semi-coherent but with a higher degree of coherency, and the Al concentration in the FCC phase increased. Post-deformation analysis showed that there were high-density dislocation pile-up and slip, stacking faults (SFs), and Lomer-Cottrell (L-C) locks in the FCC phase, and there were deformation nano-twins and SFs in the BCC phase. The back stress generated in FCC/BCC phases during tensile deformation could maintain the plastic co-deformation of the two phases. The theoretical calculation revealed that the strengthening mechanisms mainly stemmed from the nanolamellar structures, dislocation strengthening, and the solution strengthening induced by the increased Al concentration in the FCC phase. The calculated result (1096.3 MPa) was consistent with the experimental value, and the nanolamellar structures strengthening (∼720.7 MPa) was the main contributor. This work provides a theoretical quantitative understanding of the strengthening mechanism of the AlCoCrFeNi2.1 EHEA fabricated by LPBF and references for the strengthening mechanism of additively manufactured EHEAs.

Sub-rapid solidified high copper-bearing steel with excellent resistance to hot shortness

The removal of accumulated impurity elements during scrap refining has been regarded as the bottleneck to limiting scrap usage, among which copper is the crucial tramp element in scrap steel recycling, resulting in the final product's hot shortness and surface cracking. This study proposes sub-rapid solidification-based strip casting technology to eliminate the copper impurity introduced problems. The results reveal that strip casting could improve copper behavior in the as-cast sample. More importantly, the sub-rapid solidified sample has excellent high-temperature tensile properties and resistance to hot shortness. It suggested that strip casting technology could produce copper-bearing steel, which can tackle the hot shortness problem and provide a unique idea for steelmaking with scrap as raw materials.

Effect of Solution Heat-Treatment on the Oxidation Resistance of Ni-Base Single-Crystal Superalloy

To clarify the effect of solution heat-treatment on the oxidation resistance of Ni-base single-crystal superalloy TMS-238, the evaluation of dendrite/inter-dendrite segregation of alloying elements in the as-cast and heat-treated samples, and its effect on cyclic oxidation resistance were investigated. Cyclic oxidation test results at 1100 °C for up to 150 cycles clearly showed that the as-cast samples with element segregations had lower oxidation resistance compared to heat-treated samples with homogeneous structure. Further, for the as-cast sample, rapid growth and spallation of oxide consisting of NiO, Cr2O3, and Al2O3 were observed around the dendrite core for 10 cycles of oxidation. Analysis of sub-surface on sample isothermally oxidized at 1100 °C for 10 minutes showed that rapid oxide growth is due to the formation of discontinuous Al2O3 layer at dendrite core with lower Al concentration. Furthermore, in this study, the threshold value of Al concentration and Gibbs energy for the formation of continuous Al2O3 layer were estimated and determined to be around 5.2 wt pct and − 556.6 ± 0.5 kJ/mol, respectively. This indicated that the solution heat-treatment for TMS-238 should be conducted above 1305 °C for exhibiting oxidation resistance at 1100 °C, to meet the threshold value within the whole region between dendrite and inter-dendrite.

Heat Treatment Featuring the Key-Parameters of High Chromium White Cast Iron Microstructure

The high chromium white cast iron (HCWCI) has been on the scene for decades, with expectations to remain there due to its exceptional wear resistance. HCWCI is mostly applied as-cast, but it can also be used as a coating material. The carbides in HCWCI microstructure, whose composition depends on alloying and heat treatment regime, give this special feature to white cast irons. The investigation presented in this paper was carried out by examining two HCWCI alloys, denoted HCWCI_1 and HCWCI_2, both alloyed with molybdenum in addition to high chromium content. The HCWCI_1 alloy contains 24.48% Cr with 1.32% Mo, and HCWCI_2 contains 14.11% Cr with 2.47% Mo. Comprehensive qualitative microstructural characterization was performed on all types of samples: as-cast samples, those obtained after quenching (at -196 °C) and/or quenching followed by tempering (at 250 °C). Besides standard etching procedures, the selective color etching was also applied here. The microstructure parameters, such as width of secondary dendritic arms and carbides size, are measured and correlated with applied alloy obtaining procedure and heat treatment regime, so they can be discussed in relation to the microconstituent’s ratio (such as ratio of different carbides) and morphology.

Formation of a hard-soft core-shell structure by controlled annealing

A soft τ1 (Al2.68Ag0.32Zr) shell and hard τ2 (Al1.84Ag0.16Zr) core, were formed in the Al0.46Ag0.32Zr0.22 alloy by annealing. The microstructure, crystal structure, and hardness of the core–shell structure were characterised in detail. Compared with the as-cast sample, the sample annealed at 500 °C for 120 days formed τ1 at the interface of the τ2 phase. The coexistence of some τ1 grains and the (Ag) matrix was observed. Additionally, nano-indentation demonstrated that the hardness values of τ1 and τ2 were 3.82 and 10.20 Gpa, respectively. The formation of a hard-soft core–shell structure may enhance comprehensive performance of the material.

Achieving high strength-ductility synergy in Mg-6Sn-3Zn-0.3Zr (wt.%) alloy via a combination of casting, pre-treatment and hot extrusion

Achieving the strength-ductility synergy in Mg alloys is a gigantic challenge, especially in rare-earth-free Mg alloys. In this study, a new Mg-Sn-Zn-Zr alloy with high ultimate tensile strength (∼284–326 MPa) without sacrificing elongation-to-failure (∼22.1–27.6%) was developed by utilizing casting, pre-treatment and hot extrusion. Strong random rather than basal texture is observed both in as-cast and pre-treatment samples. Subsequently, the strong texture is effectively weakened via hot extrusion whilst remaining random. More importantly, after hot extrusion, the grain sizes of as-cast and pre-treatment samples were significantly refined down to about 10 µm. Examination of as-extruded microstructures of the alloy reveals that the grain refinement is highly associated with the particle stimulated nucleation (PSN) and continuous/discontinuous dynamic recrystallization (C/DDRX) mechanisms. Moreover, the results suggest that the combination of pre-treatment and hot extrusion not only promotes multiplication of geometrically-necessary dislocations (GNDs) but enhances dynamic precipitation, which boosts the formation of fine and homogenous precipitates. Based on the results of X-ray diffraction (XRD), transmission electron microscope (TEM) and selected area electron diffraction (SAED), the precipitates are Mg2Sn phases. Furthermore, the main orientation relationship identified by high resolution TEM (HRTEM) between Mg2Sn phases and α-Mg matrix could be described as (111)Mg2Sn or (220)Mg2Sn ∥ (0001)Mg with a coherent interface. The refined grains size, ultra-fine precipitates and high density of GNDs would substantially contribute to the enhancement of the strength and the corresponding contributions are calculated to be ∼183–185 MPa, ∼30.9–38 MPa and ∼14.2–31.7 MPa, respectively. Besides, texture weakening or randomizing, grain refinement and coherent interfaces are mainly responsible for the high ductility. The current study can provide beneficial insights into the development of high-performance rare-earth-free Mg alloys with favorable microstructure via a combination of casting, pre-treatment and hot extrusion processing.

Prediction of age-hardening behaviour of LM4 and its composites using artificial neural networks

This research work highlights the prediction of hardness behaviour of age-hardened LM4 and its composites fabricated using a two-stage stir casting method with TiB2 and Si3N4. MATLAB - Artificial Neural Networks is used to predict the age-hardening behaviour of LM4 and its composites. Experiments (hardness and tensile tests) are conducted to collect data for training an ANN model as well as to investigate the effect of reinforcements and age-hardening treatment on LM4 and its composites. The results show that with an increment in the reinforcement wt%, there is an enhancement in hardness and ultimate tensile strength (UTS) values within the monolithic composites. As-cast hybrid composites display a 37 to 54% improvement in hardness compared to as-cast LM4. Heat-treated samples, specifically those treated with peak aging with MSHT and 100 °C aging, perform better than as-cast samples and other heat-treated samples in terms of UTS and hardness. Compared to as-cast LM4, MSHT, and 100 °C aged samples display an 85 to 202% increment in VHN. Hybrid composites perform better in terms of hardness, while composites with 3 wt% of TiB2 (L3TB) perform better in terms of UTS, peak aged (MSHT and 100 °C aging) L3TB display 68% increment in UTS when compared to as-cast LM4. ANN model is developed and trained with five inputs (wt% of TiB2, wt% of Si3N4, type of solutionizing, aging temperature, and aging time) and one output (VHN) using different algorithms and a different number of hidden neurons to predict the age hardening behaviour of composites. Among them, Lavenberg-Marquardt (LM) training algorithm with normalized data and 30 hidden neurons performs well and shows a least average error of 1.588364. The confirmation test confirms that the trained ANN model can predict the output with an average %error of 0.14 using unseen data.

Effect of rolling reduction on the microstructure, texture, and mechanical behavior of AZ91 alloy

In this study, the effect of rolling reduction on the microstructure, crystallographic texture, and mechanical properties of the AZ91 alloy is studied. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and tensile and hardness tests were used. The homogenization process significantly increased the grain size of the as-cast sample. The results showed that {101¯2}⟨101¯1⟩ extension twinning during rolling leads to rotation of {0001}∥RD initial orientation toward {0001}‖ND basal texture. During asymmetric hot rolling up to 15%, the intensity of {0002} basal texture increased to 10 multiples of random distribution. After 15% deformation, the average grain size decreased due to the occurrence of dynamic recrystallization. It was found that by increasing the rolling reduction up to 15%, the hardness and tensile strength greatly increased owing to an increase in the fraction of twins and the intensity of basal texture. The occurrence of the CDRX mechanism and the formation of strong basal texture resulted in an excellent combination of strength and ductility for the 15% rolled sample. The as-homogenized and 8% rolled samples had the maximum and minimum inhomogeneity factor (IF), respectively. The fracture surfaces indicated that the mixture of ductile and brittle fracture is the main failure mode.

Effects of cold rolling and heat treatment on the microstructure and hardness of pure aluminium

The present investigation aims to assess the effects of thermomechanical treatments on both the grain refinement and microhardness of aluminium 1145. Aluminium 1145 is commonly utilized in electronic applications owing to its lightweight features and high thermal and electrical conductivities. Despite its low microhardness, which poses a challenge for such applications, its mechanical properties can be improved by means of thermomechanical treatments such as cold rolling and annealing. The experimental procedure involved casting the sample in an open mould, followed by cold rolling at reductions of 50%, 70%, and 80% from the initial 10 mm thickness. Optical microscopy (OM) was employed to investigate the microstructural changes caused by plastic deformation. A greater degree of deformation was observed along the rolling direction with higher reductions, particularly in the 80% cold-rolled sample, where flattened and elongated grains were evident in the normal plane, whereas a lamellar layered structure was observed in the rolling plane. The Vickers microhardness tester was used to measure the microhardness of the cold-rolled samples. The findings revealed that the microhardness increased with greater rolling reductions, with the 80% cold-rolled sample exhibiting a 72% increase compared with the initial 25HV of the as-cast sample. Moreover, recrystallization was identified at 400 °C, and the grain size increased with increasing annealing temperature and duration. At 450 °C, the grains exhibited equiaxed and finer structures with an average size of 95 μm. The trends in microhardness were aligned with recrystallization and grain growth, as they decreased with increasing annealing temperature and time. Notably, at 450 °C, the microhardness reached 25HV, which was equivalent to the as-cast condition.

Study on the microstructure and hydrogen storage property changes of cast TiFe0.9Cr0.1 alloy by homogenization annealing

This study investigated the changes in the microstructure and hydrogen storage properties of cast TiFe0.9Cr0.1 alloys by homogenization annealing. The as-cast and homogenized samples consisted of B2 and C14 Laves phase. After annealing, compositions of the B2 phase in both samples were similar, while the Laves phase fraction decreased and the Cr concentration in the Laves phase increased. To understand the microstructure changes caused by annealing, the fraction and the composition of the phases in the equilibrium state were derived using thermodynamic calculation, where the microstructure of the as-cast sample changed to the direction in the equilibrium state by annealing. The first hydrogenation kinetics were examined in the as-cast and homogenized samples, which slowed in the latter as the Laves phase fraction decreased. The hydrogen absorption and desorption behaviors were compared using a pressure-composition-temperature diagram at 50 °C. Since the compositions of the B2 phase in the two samples were almost the same, the two samples represented similar hydrogen storage behaviors. From the first-principles density functional theory calculation, the hydride-forming enthalpy of the B2 phase was calculated. By using an equation to predict the desorption plateau pressure from the hydride-forming enthalpy, the desorption pressure was predicted to be 1.34 bar, a value similar to the desorption pressure obtained from the experiment.

Comparison of microstructures, mechanical and tribological properties of Al0.3CoCrFeNi high-entropy alloy prepared by induction melting and selective laser melting

Different preparation processes provide high-entropy alloys (HEAs) with distinct microstructures and properties, opening up a wider range of potential applications. In this work, Al0.3CoCrFeNi HEA is chosen as the reference alloy for understanding the effect of two different processes (induction melting and selective laser melting) on microstructures, mechanical and tribological properties. The as-cast sample exhibits coarse grains with a small amount of particles precipitated along grain boundaries. The as-printed sample exhibits heterogeneous microstructures and strong < 001 > preferred orientation. As compared to the as-cast sample (proof strength: 240 MPa, elongation: 56.5%), the as-printed sample shows a remarkable increment in proof strength (473 MPa) induced by refined grain strengthening and dislocation strengthening while a sharp drop of elongation (14.7%) induced by micropores, high-density dislocations, and residual stress. The tribological properties reveal that both the as-cast and as-printed samples exhibit the same wear mechanisms (abrasive wear and oxidative wear), while the as-printed sample with higher hardness shows superior wear resistance compared to the as-cast sample.

Biodegradable implant application: Electrodeposition of HA/TiO2/ZrO2 coating onto Zn-composite substrates

Zinc has currently emerged as a promising biodegradable metal due to its good biocompatible property and promising degradation behaviour. Additionally, inadequate mechanical strength and a lower cell viability value fall short of what is needed for biodegradable implants. In this work, we used the stir-casting process to create a biodegradable Zn-1Mg-1Cu-1HA (ZHA) and Zn-1Mg-1Cu-1ZrO2 (ZZR) composite onto which ceramics composite coating is done by electrodeposition technique to enhance the biocompatibility. The as-cast sample has uniformly distributed fine MgZn2 and CuZn2 phases in a α-Zn matrix, according to microstructural analysis. The mechanical test confirms that ZZR composite exhibited high tensile and compressive properties, including compressive yield strength of 369.562 MPa, a yield tensile strength of 88.725 MPa and ultimate tensile strength of 116.21 MPa. The result of potentiodynamic polarization test shows that the coated ZZR composite sample gives a corrosion rate value of 0.112 mm/year. From immersion tests, the degradation rate obtained a much lower value after immersing the sample in PBS solution for 55 days (0.067 mm/year). Moreover, an extract of coated ZZR composite shows good cell viability in comparison to the uncoated sample at a concentration of 25%, 50% and 75%. Also, the hemolysis percentage for coated ZZR sample is lower than the other prepared uncoated sample (3.072%) Overall, the result obtained proves that the coated ZZR composite sample can be expected as a capable material for implant application.

Elucidating the evolution of long-period stacking ordered phase and its effect on deformation behavior in the as-cast Mg-6Gd-1Zn-0.6Zr alloy

Herein, the evolution of long-period stacking ordered (LPSO) phases in the as-cast Mg-6Gd-1Zn-0.6Zr (wt.%) alloy are investigated via transmission electron microscopy (TEM) and atom probe tomography (APT). The TEM results reveal that two types of LPSO phase (a bulky interdendritic phase and a plate-like matrix LPSO phase) are formed in the as-cast sample. Most of the LPSO phases are confirmed to be of the 14H type, with a smaller proportion being of the 18R LPSO. Further, the APT results reveal that the composition of the interdendritic LPSO phase is closer to that of the ideal 14H phase compared to the matrix LPSO phase, and both the interdendritic and matrix LPSO phases exhibit a Gd/Zn ratio of 2.5, thereby indicating a deficient Zn content compared to the ideal 14H phase (i.e., 1.3). In addition, the influence of the LPSO phases on the deformation behavior is investigated at different compressive plastic strains using electron backscatter diffraction (EBSD) analysis to reveal twinning and slip behavior during deformation. The results indicate that the LPSO phase induces additional work hardening in the late stage of deformation via the suppression of {101¯1} compressive twinning and the activation of non-basal slip systems.

Effect of Nb content on mechanical reinforcement of the Cu-10Fe composites

The Cu-10Fe-based composites with different Nb content were fabricated by vacuum mold casting. The effect of Nb content on the solidification behavior and microstructure was investigated systematically and the optimal composition was determined as Cu-10Fe-1.0 Nb (wt%). The as-cast samples were rolled by 90% reduction at room and then aged at 250 ℃ for different time. The properties results showed that, after aging for 1800 min, microhardness, tensile strength and elongation of the Cu-10Fe-1.0 Nb samples reached 145 HV, 553 MPa and 21.5%, respectively. The microstructure results showed that the primary Fe-rich phases in the Cu-10Fe-1.0 Nb samples were significantly refined due to the heterogeneous nucleation induced by Fe2Nb phases, and then led to the refinement of the matrix. The enhanced mechanical properties could be attributed to the Orowan strengthening, refinement strengthening and work hardening resulted from the numerous submicron-/nano-sized Fe particles, fine sub-grains and high-density dislocation in the matrix formed during thermo-mechanical treatment.

Vacuum melting of compressed powders and hot rolling of the as-cast Ti-48Al-2Nb-0.7Cr-0.3Si intermetallic alloy: Mechanical properties and microstructural analysis

The amalgamated effect of hot-rolling, rapid cooling and heat treatment on the grain refinement and the resultant mechanical properties of an intermetallic sheet of nominal composition Ti-48Al-2Nb-0.7Cr-0.3Si was investigated. The sheet of 4 mm thickness was fabricated by hot-pack rolling from the vacuum arc remelted (VAR) ingot using a conventional two-high rolling mill. After the final rolling pass, the canned specimen was rapidly cooled in the air to room temperature followed by heat treatment in the α + γ region. The scanning electron microscopy (SEM) micrographs of the as-rolled sheet revealed slightly elongated grains of a typical “duplex (DP)” microstructure with a mean grain size of about 3 μm which grew to about 4 μm and became more equiaxed and homogeneous after heat treatment. Moreover, the EBSD micro-texture indicated a weak cube texture in the rolled + heat-treated sheet. Furthermore, the results from the profilometry-based indentation plastometry of the rolled + heat treated specimen illustrated the balanced and improved mechanical properties compared to the as-cast and as-rolled samples, and also those of similar alloy systems found in the literature.