Microstructure Mechanical Properties Research Articles

Comparative analysis of microstructure and mechanical properties in FeMnAlNi alloys fabricated via casting and additive manufacturing

This study provides a comprehensive analysis of FeMnAlNi alloys fabricated via casting, laser-based directed energy deposition (DED-LB), and powder bed fusion-laser beam (PBF-LB) techniques, highlighting the profound impact of manufacturing processes on their microstructural characteristics and mechanical properties. The investigation reveals distinct two-phase distributions, with PBF-LB samples retaining the high-temperature α-phase due to rapid cooling, contrasting with the γ-phase predominance in as-cast and DED-LB samples. Notably, PBF-LB samples also exhibit fine γ′ martensites, likely a result of stress-induced martensitic transformation. Mechanical testing shows significant variations across the samples: as-cast and DED-LB samples demonstrate similar microhardness values (211 ± 22 and 209 ± 7 HV0.2, respectively), while PBF-LB samples exhibit higher microhardness (321 ± 9 HV0.2) due to the dominance of α-phase. Specifically, the DED-LB samples demonstrate elongation exceeding 50 %, with a notable improvement in ductility compared to the as-cast samples. The Kurdjumov–Sachs orientation relationship between α-phase and γ/γ′-phases is found. These insights reveal that considerable work remains to be done, including exploring post-processing heat treatments, which have the potential to induce superelasticity in DED-LB samples and further enhance the application potential of FeMnAlNi alloys in advanced engineering fields.

Electric field enhanced diffusion welding of alloy 617: Microstructural characteristics and mechanical properties

This study investigated the microstructural characteristics and mechanical behavior of diffusion welded nickel-based Alloy 617 obtained by electric field-assisted sintering (EFAS) using various parameters. The interfacial microstructure exhibited different characteristics including good grain boundary (GB) migration across the interface in the samples diffusion-welded at 1100 °C and a flat interface in the samples joined at 1000 °C and 1050 °C. The interface consisted of fine Al2O3 oxides, while precipitation of interfacial M23C6 carbides was not observed. Grain boundaries migrated across the Al2O3 oxides, leaving these oxides within the grains. Graded grain size was observed, with grain coarsening being more significant near the sample surface due to the temperature gradient induced by EFAS. Tensile testing revealed that the specimens fractured in the matrix away from the interface, indicting strong diffusion-welded joints. The peak tensile strength of 807 MPa was obtained in the samples welded at 1000 °C due to minimal grain growth. The materials obtained at 1100 °C exhibited reduced tensile strength but improved ductility. Strain maps revealed by digital image correlation showed alternating high and low strain segments in the samples produced at 1000 °C and 1050 °C, indicating that the flat interfaces with no GB migration were less ductile compared to the matrix. A greater strain uniformity was observed along the bond interfaces with improved GB migration. The hardness reduced near the sample surfaces due to enlarged grains induced by temperature gradient. This study demonstrates that GB migration and enhanced mechanical strength can be achieved in diffusion-welded Alloy 617.

Improved mechanical properties and thermal conductivity of laser powder bed fused tungsten by using hot isostatic pressing

In this study, the microstructure evolution, mechanical properties and thermal conductivity of laser powder bed fused tungsten subjected to the subsequent hot isostatic pressing (HIP) processes with natural cooling (NC) and ultra-rapid quenching (URQ) were investigated. The results showed that the relative density was significantly improved after HIPping regardless of the cooling rates. The HIP-URQ treatment led to a near defect-free component with increased recrystallization and reduced dislocation density. The enhanced comprehensive mechanical properties, including the ultimate compressive strength of 1180 MPa without sacrificing microhardness was achieved for the HIP-URQ sample. Furthermore, the highest thermal conductivity of 168.6 W/(m·K) related to the densification behaviour and microstructure evolution during the HIP treatments was reported.

Flash sintering of HUST-1 lunar regolith simulant: Effects of processing temperature on microstructure characteristics and mechanical properties

In-situ construction method is expected to be considered for lunar base construction because of its reducing transportation cost. Among the many in-situ construction processes, the flash sintering process can significantly reduce the processing time and become a potentially effective in-situ resource utilization (ISRU) technology. In this study, the flash sintering process was investigated for the first time to realize the sample forming of HUST-1 lunar regolith simulant (LRS). The effects of sintering temperature on the micro- and macrostructural characteristics and mechanical properties of the samples were systematically studied. The results showed that the densities and mechanical properties of the sintered samples were improved with the increase of the sintering temperature (from 1050 °C to 1290 °C) in a low vacuum environment for 4 minutes. Joule heating effect was investigated to cause rapid high-temperature solid-phase reactions between the LRS particles. At 1290 °C, the compressive strength of the sintered sample reached maximum 59.47 MPa. This study provides an efficient forming method for lunar construction in the future.

Microstructure evolution and properties of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloy prepared by SIMA

The semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were prepared by strain induced melting activation method (SIMA), and the microstructure evolution, mechanical properties and corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were investigated. The results indicate that the ideal globular or near-globular microstructures with an average grain size of 29.1 μm and a shape factor of 0.86 can be obtained when the Al80Mg5Li5Zn5Cu5 light weight high entropy alloys with 20% deformation held at 500 °C for 15 min. The coarsening coefficient is 35.8 μm3/s when the temperature is 500 °C, which is lower than the traditional single major element alloys due to the sluggish diffusion effect of high entropy alloys. The compression strength of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is 558.4 MPa, which is 11% higher than that of as-cast state. The corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is also significantly improved.

Spinning-additive hybrid manufacturing of Al-Zn-Mg-Cu alloys: Microstructure evaluation and mechanical properties

This study employs wire-arc direct energy deposition (wire-arc DED) to produce high-strength aluminum alloys on the spinning matrix. Spinning-additive hybrid manufacturing specimens were produced. The evolution mechanism of the interfacial microstructure and fracture behavior of the hybrid manufacturing (HM) specimens was analyzed. The results indicate that the microstructure morphology can be divided into three regions: the spinning zone (SZ), columnar grain (CG) zone of additive manufacturing (AM), and equiaxed grain (EG) zone of AM. The SZ exhibits a bimodal grain structure, while the AM-CG zone consists of epitaxial growth from the SZ, and the AM-EG zone comprises equiaxed grains. Due to the influence of the hot spinning process, a large amount of eutectic structure and η phase coexist in the spinning matrix, resulted in a small amount of undissolved η phase remaining in the spinning matrix after heat treatment. A small amount of η' phase was generated in the AM zone at as-deposited state, due to the effect of in situ thermal cycling of the subsequent additive manufacturing process. Nearly all of η phase which dissolves into the α-Al matrix after heat treatment. The tensile strength of the hybrid manufactured samples increased from 256 MPa in the as-deposited state to 528 MPa after heat treatment. The fine-grained region of the spinning matrix experiences deformation and crack propagation initially, attributed to the softer properties of the fine-grained region within the bimodal grain structure of the SZ matrix, ultimately resulting in fracture at the SZ in all hybrid manufactured specimens.

High-speed laser cladding (Fe,Cu)-dopped Ni-Co protective coatings for SOFC MICs: From long-term oxidation behavior to mechanical stability

The long-term operation of intermediate temperature-solid oxide fuel cells (IT-SOFCs) could be significantly influenced by the stability of the interconnect itself, especially, its oxidation resistance under the cathode environment. To effectively prevent Cr-volatilization and improve the interconnector performance, application of highly dense and stable protective coatings over the interconnector is indispensable. In this work, Ni-Co-based alloy protective coatings doped with Fe and Cu were applied onto the 441 interconnector via a novel high-speed laser cladding technology. The microstructure evolution, phase composition, oxidation resistance, electrical conductivity and mechanical properties of the coated steels were investigated at different oxidation stages at 800 °C. It was found that the Ni33.8Co34Fe32.2-coated steel shows the best oxidation resistance and electrical properties. The oxidation rate (kp) and ASR of Ni33.8Co34Fe32.2-coated steel is respectively 4.44 × 10−13 g2 cm−4 s−1 and 25.55 mΩ cm2, significantly lower than the uncoated steel and Ni44.6Co44.7Cu10.7-coated steel at the end of 1000-h test cycle. The resultant conductivity of the Ni44.6Co44.7Cu10.7 and Ni33.8Co34Fe32.2-coated steels is approximately 7.8 and 4.1 S cm−1, respectively, which could meet the requirement for SOFC stacks. In addition, the nano-hardness of the Ni33.8Co34Fe32.2 and Ni44.6Co44.7Cu10.7-coated steels was found to be 8.3 GPa and 8.8 GPa, respectively, through nanoindentation testing. The improved surface hardness is attributed to grain refinement and increased oxide content on the coating surface. The results indicated that the Ni-Co-based alloy coatings effectively improved the long-term stability and mechanical property of the 441 interconnector under the SOFC cathode environment.

Microstructure evolution and mechanical properties of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite with a crossed-lamellar structure

Microstructure evolution and mechanical properties of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite with a crossed-lamellar structure

Microstructure evolution and mechanical property of B4C/Ti65 composites via laser directed energy deposition

Application of laser additive manufacture technique to fabricate the discontinuous reinforced high-temperature titanium matrix composites found its great potential in the complex components of aerospace industry. This work prepared the B4C/Ti65 composites by laser directed energy deposition (LDED) with special attention paid to the relationship between microstructure and mechanical property of composites. The microstructure of B4C/Ti65 composites under different laser power and B4C content were investigated, based on which the tensile strength and ductility evolution and the underlying strengthening mechanism of the B4C/Ti65 composites were discussed. The submicron TiBw were randomly distributed in the composites with additions of 0.1 wt% and 0.2 wt% B4C. The TiBw and TiCp in the composites with addition of 0.3 wt% B4C exhibited a uniform distribution rather than distributed along the prior β grain boundaries at high laser power. There existed the network structure of TiBw and TiCp in the 0.5 wt% B4C/Ti65 composites. TiCp always adhered to TiBw, and both TiBw and TiCp acted as the nucleation sites for equiaxed α grain, which is responsible for the finer α colonies that benefit to strength with higher B4C content. The tensile tests showed that the 0.3 wt% B4C/Ti65 composite shows a good combination of ultimate tensile strength (1201 MPa) and elongation (5.54 %). The grain refinement strengthening played the dominant role in the strength increment of the B4C/Ti65 composites. In addition, the formation of clustered submicron-TiBw and network structure of TiBw and TiCp in the 0.5 wt% B4C/Ti65 composites greatly upgraded the yield strength.

Enhancing mechanical properties and corrosion resistance of Fe–Cr–B–Mo alloy via the 'Divide and Conquer' strategy for Ti regulation

The corrosion of molten aluminium on components in the aluminium industry poses a significant bottleneck, hindering the development of aluminium products and equipment. This study focused on the Fe–Cr–B–Mo alloy, addressing challenges related to the susceptibility of the matrix to corrosion, the excessive brittleness of M2B borides (M = Fe, Cr, etc.), and the detachment of corrosion products. A comprehensive study was performed to study the microstructure evolution, mechanical properties, and corrosion behavior of Fe–Cr–B–Mo alloy, considering the 'Divide and Conquer' strategy for Ti regulation. The findings indicate that the heterogeneous nucleation, induced by in situ TiB2 particles, significantly impacts the refinement of M2B borides size and enhances the matrix strength. Notably, the addition of 4.5 wt. % Ti to the T3 alloy significantly enhances its mechanical properties and corrosion resistance. The T3 alloy exhibits an impact toughness of 32.4 kJ/m2 and a compressive fracture strain of 19.5 %, representing a considerable increase of 58 % and 167 % over the Ti-free alloy, respectively. Furthermore, the alloy has a volume loss rate of 11.0 mm3 cm−2 h−1, which is substantially lower, by 73.5 % compared to H13 steel and by 21.4 % compared to the Ti-free alloy. The synergistic presence of TiB2 and M2B borides, along with their corrosion products, functions as an effective diffusion barrier against molten aluminium corrosion.

Achieving superior high-temperature strength in an additively manufactured high-entropy alloy by controlled heat treatment

High-entropy alloys (HEAs) usually exhibit high strengths at ambient and low temperatures but rapidly degraded tensile properties with increased temperature. In this study, a high-strength HEA, (CoCrNi)94(TiAl)6, is selected and subjected to laser powder bed fusion (L-PBF) and ageing treatment. The microstructural evolution and mechanical property development of the material over a wide range of temperatures are thoroughly investigated. It is found that the as-printed microstructure is dominated by numerous ultrafine cellular structures (∼1 μm) with cell boundaries decorated by Al2O3 nanoparticles, leading to high 0.2% yield strength (YS = 725∼750 MPa) and excellent elongation (>28%) at room temperature. The cellular structures remain up to 700 °C but disappear at or above 800 °C. Ageing at or above 600 °C leads to significant γ′ precipitation with the particle size increasing constantly with increased temperature. The samples containing both cellular structures and coarsened γ′ precipitates (aged at 700 °C) exhibit the highest YS (∼1227 MPa) and ultimate tensile strength (UTS∼1539 MPa) at room temperature and display unprecedented YS at high temperatures, i.e., 949 MPa at 600 °C and 728 MPa at 700 °C, respectively. The exceptional tensile strengths are mainly due to the γ′ precipitates and cell boundaries decorated by Al2O3 nanoparticles which may have acted as strong barriers for dislocation motion. At room temperature, the sample deforms mainly by dislocation slip and formation of stacking faults while at elevated temperatures, deformation becomes increasingly planar as characterized by the formation of increased number of stacking faults and the activation of twinning.

Research Paper on Analytical Investigation of the Effect of 3d Printing Process Parameters on Anisotropic Mechanical Behaviour of Additively Constructed Concrete

This research identifies key challenges in additively constructed concrete, including the need for understanding the scalability of mechanical behaviour from small to large structures, addressing variability in material properties, and predicting failure mechanisms. It highlights the need for improved finite element modelling for accurate 3DCP simulation, and further investigation into concrete foundation interactions and initial imperfections. The study acknowledges difficulties in simulating complex shapes and calls for refinement of the numerical model for better predictive accuracy. It also emphasizes the need to understand long-term behaviour, durability, and the impact of the 3DCP process on microstructural morphology and mechanical properties. The influence of pores and time gaps between layers on the overall capacity of the specimen, and the development of a model considering different properties of 3D concrete material are also identified as areas for future research.

The effect of thermal cycle on microstructure evolution and mechanical properties of Co-free maraging steel produced by wire arc additive manufacturing

Microstructures and mechanical properties are closely related to thermal cycles during additive manufacturing. For maraging steel, the research on the effect of thermal cycles during additive manufacturing is limited. Based on the above issues, this work investigated the effect of thermal cycles in the process of wire arc additive manufacturing Co-free maraging steel on microstructure evolution and mechanical properties, and attempted to establish the relationship between thermal cycles and microstructure as well as mechanical properties of maraging steel on the basis of quantitative thermal cycle data. The results show that in the additive manufacturing process, the thermal cycles affect the cooling rate, so that the primary dendrite arm spacing and grain size gradually increase along the height direction. For maraging steel, in additive manufacturing, welding or other hot processing processes, the thermal cycles make the martensite reverse change, resulting in an increase in austenite content, resulting in grain refinement. Thermal cycles in additive manufacturing result in differences in the grain size, grain boundary ratio, dislocation density and primary dendrite arm spacing, resulting in inhomogeneity of the mechanical properties in the height direction. The difference in microstructure in different directions of additive manufacturing samples leads to anisotropy of tensile properties. The results of this work can elucidate and refine the action mechanism of thermal cycles on maraging steel. In addition, this work can be used to control thermal cycles by changing the process and cooling conditions, etc., to obtain maraging steel samples with homogeneous or gradient properties, which is highly important.

Microstructure and cryogenic mechanical properties of dissimilar friction stir welding joints between nitrogen-alloyed CoCrFeMnNi high-entropy alloy and high-manganese austenite steel

The microstructures and cryogenic mechanical properties of dissimilar friction stir welding (FSW) joints between nitrogen-alloyed CoCrFeMnNi high-entropy alloys (HEAs) and Fe–32.1Mn–7.5Cr–0.6Mo–1.2 N steel were investigated. The results reveal that defect-free dissimilar joints can be achieved through FSW. Furthermore, the grains of nitrogen-alloyed CoCrFeMnNi HEAs in the stir zone of the dissimilar joint are significantly more refined than those of Fe–32.1Mn–7.5Cr–0.6Mo–1.2 N steel. Joint efficiency at room and low temperature both exceed 90% of the base metal. Moreover, the cryogenic yield and ultimate strength of the dissimilar joints are higher than those recorded at room temperature. The fracture position is at the heat-affected zone of HEAs under two temperature conditions.

Effects of temperature on the microstructural evolution and mechanical properties of copper − bearing medium manganese steel during tempering

This work introduced the effects of higher tempering temperatures on the microstructural evolution of Cu − bearing medium Mn steel. After quenching steel at 860 °C for 1 h, it was tempered at 600, 640, and 670 °C for 2 h. The results indicated that the low − temperature impact toughness initially increased and then decreased, while the yield strength consistently decreased with increasing temperature. At a tempering temperature of 640 °C, the steel exhibited a relatively high content of reversed austenite and demonstrated the best low − temperature toughness and plasticity. The low − temperature toughness and plasticity of the steel significantly diminished, when the temperature exceeded 640 °C. This is because the degree of alloying element enrichment in the reversed austenite is reduced, accompanied by an increase in dislocation density and the formation of twins. These reversed austenites exhibit a diminished ability to hinder crack nucleation and propagation. The yield strength decreased with increasing temperature, primarily due to the coarsening of the Cu particles, which reduces their precipitation strengthening effect. This study advances the development of high − strength tough medium − manganese steels.

High-strength aluminum alloy processed by micro laser powder bed fusion (μ-LPBF): Coordination of laser formability, microstructure evolution, and mechanical properties

As the scale of additive manufacturing process (e.g., laser spot size, powder particle size, powder layer thickness) decreases, the application of micro laser powder bed fusion (μ-LPBF) involves novel mechanisms for process, microstructure and performance coordination. This study provides a systematic view of the processing window and performance enhancement of high-strength Al-Mg-Sc-Zr alloy fabricated by μ-LPBF. The effects of μ-LPBF parameters on defect control and densification activity of the printed parts were analyzed, so as to obtain the suitable processing window. The influence of building orientation and heat treatment on microstructural characteristics and mechanical properties of μ-LPBF processed parts was studied. The μ-LPBF Al-Mg-Sc-Zr exhibited sound surface quality (Ra of 6.088 μm) and considerably refined grains with an average size of 1.102 μm, which was related to the high cooling rate (8.6 × 107 K/s) induced by a small-sized laser beam (25 μm) and a tiny powder particle size distribution (2–20 μm) applied in μ-LPBF. After aging treatment (325 °C/4 h), the superior ultimate tensile strength of 590.24 ± 4.75 MPa combined with the sufficiently high elongation of 11.99 ± 1.17 % was achieved. Due to the significantly decreased scale of μ-LPBF production, the anisotropy caused by the variation of building directions was negligible. These enhanced mechanical properties were attributed to the combined effect of the grain size refinement, the higher number density (1.2 × 1024/mm3) of interior precipitates within grains, and the small-sized molten pool size of μ-LPBF. Computational fluid dynamics (CFD) simulation was applied to reveal the molten pool thermodynamics, indicating that a higher thermal temperature gradient (up to 9.8×107 K/m), a smaller molten pool size (with the width of 38.7–69.8 μm and depth of 8.7–30.0 μm) were generated in μ-LPBF. This work presents great potential in processing high-precision metallic components with fine structural feature size and satisfactory manufacturing quality.

The influence of graphene oxide on the microstructure and properties of ultrafine-grained copper processed by high-pressure torsion

New metal matrix nanocomposites with enhanced thermal stability were produced in a three step process consisting of mechanical milling, spark plasma sintering and High-Pressure Torsion (HPT). The nanocomposites consisted of a copper matrix and the addition of 1 wt% Graphene Oxide (GO) as a reinforcement. A nanocrystalline microstructure, enhanced hardness and improved thermal stability were achieved. The grain size of the nanocomposites was ∼55 nm which is almost four time smaller than for Cu HPT at 210 nm. Hardnes and ultimate tensile strength of the nanocomposites reach 250 Hv and 700 MPa, respectively, which was more than three times higher than for the initial material. The most important result is that the nanocomposites remained ultrafine-grained up to 500 ⁰C whereas the Cu HPT fully recrystalized after annealing at 300 ⁰C The report also includes an investigation of the electrical conductivity of the copper-based composite which was slightly better than for copper after HPT together with the wear behaviour of this material. This is one of the first reports on copper reinforced with graphene oxide composites produced by HPT and it gives information on its thermal stability, electrical conductivity and wear behaviour together with the microstructural characteristics and mechanical properties.

Effect of dislocation density on microstructure and mechanical properties of cold-rolled medium Mn steel

This study investigated the effect of dislocation density on microstructural transformation and mechanical properties of Fe-7.23Mn-4.42Al-0.09C-1.99Si (wt.%) steel. By the tempering treatment, the dislocation density was reduced. The effect of of dislocation density on the plasticity of the steel was analyzed. The dislocation density was reduced from 2.3 × 10−16 m−2 to 1.6 10−16m−2 by tempering. Reducing dislocation density in the metastable austenite resulted in a higher metastable austenite transformation rate. And the low dislocation density steels exhibited a longer strain length during tensile deformation. It was obvserved that the dislocation density of the test steel decreased by 30% after tempering, the austenite transformation rate increased to 53.3%, and tensile strength and elongation increased to 1010 MPa and 44% respectively.

Effects of residual Laves phase on microstructural evolution and mechanical properties of wire arc additive manufactured GH4169 Ni-based superalloy

The GH4169 Ni-based superalloy is prepared by wire arc additive manufacturing and the sizes and morphologies of Laves phases under different heat treatment strategies are obtained to further investigate the influence of residual Laves phases on the tensile properties of the superalloy. After the solution treated at a higher 1150 °C and followed by aging, the Laves phase is completely dissolved, with limited δ phase with varying sizes distributed at the grain boundaries. While for lower 1020 °C solid solution heat treatment temperature, the Laves phase in the sample changes from chain-like to particle-like shapes by partially dissolving, and the needle-like δ phase exists around the particle-like Laves phase. Such residual "Laves + δ" impede high-temperature tensile crack propagation, significantly enhancing plasticity. This mechanism makes the lower temperature solid solution treated sample exhibit similar tensile stress but ∼2 times of elongation when compared to the sample treated by higher solid solution.

Flash sintering mechanism in multiphase materials system of copper smelting slags

Flash sintering (FS) is of great interest today, as it allows the production of high-density ceramics in seconds at lower temperatures than conventional sintering. In this study, the effects of conventional sintering at 1250°C for 4 h and FS at various electric fields (12.5, 25, 50 and 75 V/mm) on copper smelting slag (CSS), which is a multiphase material system, are investigated. The results show that FS occurs at substantially lower temperatures with much shorter times than conventional sintering, in conjunction with improved density and hardness values for CSS. The optimum condition for better densification is observed for the sample applied the 25 V/mm electric field in 554 s, and the maximum power density of about 76.49 mW/mm3. On the other hand, the shortest FS duration is achieved with the sample applied 75 V/mm in 114 s. Flash sintering at lower temperatures also stabilizedthe magnetite-hematite the phase transition, which arouses at higher temperatures. Overall, FS has made a huge contribution to reducing sintering time and temperature while providing better microstructure integrity and mechanical properties in multiphase materials systems.