Higher Ultimate Tensile Strength Research Articles

Influence of laser power on mechanical properties of FGM of SS316L and IN625 fabricated by direct metal deposition

Direct Metal Deposition (DMD) is a metal Additive Manufacturing (AM) process. It is used for producing sustainability Functionally Graded Materials (FGM) and repairing of sophisticated parts. In this present research, a commercially available DMD machine deposited three partial FGM blocks of size 26 mm wide × 34 mm thick × 32 mm heights. The commonly influence parameters on Ultimate Tensile Strength (UTS) are scan velocity and laser power. The powders used for deposition were Stainless Steel 316L (SS316L), Inconel 625 (IN625), and their three different compositions. ASTM E8 tensile samples were cut from those blocks by wire cut-EDM. Micro-tensile tests were carried out on ASTM E8 samples using a SHIMADZU micro-tensile machine. The results revealed that partial FGM sample-2 had high sustainability UTS of 532 MPa as compared to remaining two samples. It is illustrated that for joining two dissimilar materials to obtain high UTS thick layered (i.e., thickness more than 1 mm) gradient path method should be selected at the medium laser power available on the DMD machine. However, the sample-3 has higher hardness at high laser power.

Composition design and optimization of Fe-C-Mn-Al steel based on machine learning.

The purpose of this study is to explore the composition space of Fe-C-Mn-Al steel using machine learning in order to identify materials with high-strength mechanical properties. A dataset of 580 steel samples was collected from the literature, each containing information on elemental composition, heat treatment processes, specimen dimensions, and mechanical properties (ultimate tensile strength and total elongation). Eight common machine learning models were constructed to predict the ultimate tensile strength (UTS) and total elongation (TE) of the steel. It was observed that the random forest regression (RFR) model, when trained, demonstrated superior overall performance in predicting UTS, with an average absolute error of approximately 90 MPa, and TE, with an average absolute error of about 7.9%. Validation of the model using eight sets of data that were not part of the dataset revealed that the predictions were in close agreement with experimental results, indicating the strong predictive capability of the RFR model. Subsequently, the trained RFR model was used to explore the composition space of Fe-C-Mn-Al steel, identifying the top fifty combinations of elemental compositions and heat treatment parameters, all of which manifest high ultimate tensile strength (UTS). This provides valuable research directions and methods to expedite the development of high-strength Fe-C-Mn-Al steel.

Enhancing the fatigue property of high entropy alloy by regulating characteristics of grains and precipitates

High entropy alloys (HEAs) are a new class of alloys with many excellent mechanical properties, having the potential as structural materials. One advantage of HEAs is the vast space for designing compositions and microstructures, which provides more possibilities to develop fatigue-resistant materials. In this study, a multi-phase fine-grained microstructure was engineered through cold rolling and annealing treatment in Al0.3CoCrFeNi HEA to obtain an enhanced fatigue property. This alloy consists of FCC matrix phase with an average grain size of ∼ 1.13 ± 0.84 μm, and B2 and σ precipitates with sub-micron scale. Their phase fractions are ∼ 90 %, ∼ 9 % and ∼ 1 %, respectively. Stress-life (S-N) data indicate that fatigue endurance limit and ratio in terms of stress amplitude are ∼ 281 MPa and ∼ 0.3, based on stress ratio of 0.1. Good fatigue property is related to high ultimate tensile strength derived from good work-hardening ability and fine microstructure. In addition, activation of deformation twins, blunting of microcracks and deflection of fatigue cracks associated with precipitates are beneficial for enhancement of fatigue resistance. The above results provide theoretical guidance on how to enhance fatigue resistance of HEAs by regulating microstructures.

Markedly improved tensile property and corrosion resistance of ZTC4 titanium alloy by hot pressing

The effect of hot pressing (HP) holding time on the microstructure, mechanical properties, and corrosion resistance of ZTC4 titanium alloy were investigated. The results show that HP treatment could effectively heal pores and increase sample density. The highest ultimate tensile strength, yield tensile strength, elongation, and lowest corrosion current of the sample at room temperature are 790 MPa, 722 MPa, 16.8 %, and 0.29 µA/cm2, respectively, when HP holding time is 1 h, which is markedly better than that of the ZTC4 sample (793 MPa, 688 MPa, 12.3 %, and 21.66 µA/cm2), indicating the promise of utilizing low-cost HP technology for high-performance titanium alloys.

Fabrication of Graphene-Modified Polyvinylidene Fluoride-co-Hexafluoropropylene Porous Polymeric Flat Sheet Membranes

We report the fabrication of porous hydrophobic flat sheet membranes composed of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), which is incorporated with graphene (GNP) concentrations of (0.2, 0.5, and 0.8 wt.%) as the hydrophobic filler. FTIR, XRD, and SEM results were used to analyze the composites' functional groups, crystallinity and surface morphology. The water contact angles were 116 ±1.2°; 120 ±0.9°; 126 ±0.7°; 130 ±0.6° for pristine, 0.2 wt%, 0.5 wt%, and 0.8 wt% of GNP membranes, respectively. Moreover, the graphene incorporation enhanced the fabricated polymer's ultimate tensile strength (UTS). The UTS was as follows 2.4±0.01, 5.43±0.02, 7.485±0.015 and 6±0.01MPa for pristine, 0.2 wt% GNP, 0.5 wt% GNP and 0.8 wt% GNP respectively. The highest UTS was (7.485 ±0.015 MPa) for the 0.5 wt% GNP. Graphene incorporation (0.5 wt%) enhanced the membranes’ porosity (78 ±1.9%). This study explored the effect of graphene to improve the flat sheet membranes' mechanical strength, hydrophobicity, and porosity, which can then be applied in desalination using membrane distillation to mitigate clean water shortages and crises.

Evaluation of dissimilar TIG welded joints of novel high strength low alloy steel for automotive applications: Experiment and numerical comparative approach

Modern automotive, aerospace, and manufacturing sectors use tungsten inert gas (TIG) welding widely as a critical procedure due to the weld's quality and joint efficiency. In this study, mechanical characterization of TIG-welded joints of high strength low alloy (HSLA) steel with two different grades (S1 and S2) was performed experimentally and mechanical properties were calculated in terms of hardness profile along the weldment and load-displacement curves. True stress-strain curves of base metal, heat-affected zone, and melted zones were used for calibration of the 8-node solid numerical model. The highest hardness value of 386 HV was obtained in the melted zone whereas a softening zone was observed in the heat-affected zone (HAZ) of S2 where the Vicker's microhardness value was 270 HV. During the comparison of simulation results with experimental data, it was found that the overall error was less than 5% which reflects a good accuracy of material models used for numerical modeling. A higher ultimate tensile strength was found in similar S1-S1 steel joints as compared to similar S2-S2 and dissimilar S1-S2 steel joints. Furthermore, the results of simulations revealed that the maximum von Mises stress (1050 MPa) concentrations were found in the HAZ of a similar S1-S1 welded joint, whereas the minimum von Mises stresses (880 MPa) in S2-S2 welded joint, and intermediate von Mises stresses (1010 MPa) on the side of S1 HAZ in S1-S2 dissimilar welded joint. The results of simulations and experimental study of TIG welding joints show good agreement with reasonable accuracy.

Degradable Zn–5Ce alloys with high strength, suitable degradability, good cytocompatibility, and osteogenic differentiation fabricated via hot-rolling, hot-extrusion, and high-pressure torsion for potential load-bearing bone-implant application

Zinc (Zn)-based alloys are considered the next-generation biodegradable material for promising bone-implant devices due to their good degradability, formability, and functionality. Nevertheless, the as-cast Zn alloys showed a low strength-toughness, making it challenging to meet the mechanical properties requirements for high-load-bearing bone implants due to their hexagonal close-packed structure, coarse grain size, and less sliding system. Herein, we have developed biodegradable Zn–5Ce alloys by cerium (Ce) alloying followed by hot-rolling, hot-extrusion, and high-pressure torsion (HPT), respectively, for potential bone-implant application. Mechanical testing revealed that the HPT sample exhibited the best mechanical performance matching among the Zn–5Ce samples with a high ultimate tensile strength of ∼345 MPa, yield strength of ∼230 MPa, a moderate elongation of ∼11.4%, and macro-hardness of ∼96.6 HB. Electrochemical corrosion and static immersion testing revealed that the HPT sample showed the highest electrochemical corrosion rate of ∼416 μm/y and degradation rate of ∼43.8 μm/y in Hanks' solution among the Zn–5Ce samples, which is suitable for degradation rate requirements for bone-implant application. Bio-tribological testing revealed that the HPT sample showed high bio-tribological properties matching in Hanks’ solution with the lowest friction coefficients of ∼0.530 and moderate wear loss of ∼2.2 mg. Cytocompatibility and osteogenic differentiation assessment revealed that the diluted extract of the HPT sample showed the highest cytocompatibility towards 3T3 and MG-63 cells and osteogenic differentiation performance towards 3T3 cells among the most diluted extracts. Accordingly, the HPT Zn–5Ce sample is expected to be used for high-load-bearing degradable bone-implant devices, including bone fixation and guided bone regeneration systems.

Influence of Quenching and Partitioning on the Mechanical Properties of Low‐Silicon 33MnCrB5 Boron Steel

Quenching and partitioning (QP) is a heat treatment that is designed to enhance both the mechanical properties and ductility of low‐ and medium‐carbon steels. This treatment is performed on steels with a tailored chemical composition. Herein, QP treatments are designed and performed on commercial low‐silicon 33MnCrB5 boron steel. Different temperatures (evaluated using thermodynamic simulations) and times are tested. Scanning electron microscopy investigations are conducted to observe the microstructure, whereas X‐ray diffraction and electron backscattered diffraction analyses are performed to assess the presence and amount of retained austenite (RA). Tensile tests are performed to investigate the mechanical properties. The designed treatments introduce a fraction of up to 4.6% of RA in the final microstructure. Tensile tests show that the QP samples are characterized by high ultimate tensile strength (1633–1756 MPa) with an increased elongation at break with respect to the reference quenching and tempering condition (16–18% versus 9%). Hardening coefficients are linked to martensite tempering in the initial stages of plastic deformation, whereas at higher strains, they are mostly influenced by RA presence. The proposed treatments are successfully performed on 33MnCrB5 grade, leading to a set of tensile properties that are not exploitable with traditional treatments.

Achieving superior mechanical properties: Tailoring multicomponent microstructure in AISI 9254 spring steel through a two-stage Q&P process and nanoscale carbide integration

In the pursuit of lightweight, durable steel, we have successfully developed a multicomponent structure in AISI 9254 spring steel using a two-stage quenching and partitioning (Q&P) process. The primary objective of this process was to engineer an optimized microstructure consisting of nanobainite, martensite, and nano-carbides. Utilizing the insights gained from the results of advanced techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT) performed on the as-received AISI 9254 spring steel, we refined the quenching and partitioning (Q&P) path, leading to the successful establishment of a bainitic transformation for superior mechanical properties. Our tensile tests revealed a high yield strength (≈ 1600 ± 25 MPa) and ultimate tensile strength (≈ 1850 ± 50 MPa), along with considerable elongation (≈ 11.15 ± 0.25%). We also identified that pre-formed martensite lath defects and high silicon content play crucial roles during the Q&P process, preventing carbide coalescence and increasing strain-hardening capacity. This study demonstrates the potential of a Q&P process to generate high-strength, ductile steel for automotive and aerospace applications.

High-Strength Amorphous Silicon Carbide for Nanomechanics.

For decades, mechanical resonators with high sensitivity have been realized using thin-film materials under high tensile loads. Although there are remarkable strides in achieving low-dissipation mechanical sensors by utilizing high tensile stress, the performance of even the best strategy is limited by the tensile fracture strength of the resonator materials. In this study, a wafer-scale amorphous thin film is uncovered, which has the highest ultimate tensile strength ever measured for a nanostructured amorphous material. This silicon carbide (SiC) material exhibits an ultimate tensile strength of over 10 GPa, reaching the regime reserved for strong crystalline materials and approaching levels experimentally shown in graphene nanoribbons. Amorphous SiC strings with high aspect ratios are fabricated, with mechanical modes exceeding quality factors 108 at room temperature, the highest value achieves among SiC resonators. These performances are demonstrated faithfully after characterizing the mechanical properties of the thin film using the resonance behaviors of free-standing resonators. This robust thin-film material has significant potential for applications in nanomechanical sensors, solar cells, biological applications, space exploration, and other areas requiring strength and stability in dynamic environments. The findings of this study open up new possibilities for the use of amorphous thin-film materials in high-performanceapplications.

Achieving superior strength-ductility synergy in a unique multi-scale heterostructured titanium laminate fabricated by temperature-controlled rolling and subsequent annealing

Here we proposed a low-cost and high-efficiency strategy for fabricating novel multi-scale gradient-structured/heterogeneous lamella structured (GS/HLS) pure titanium laminates with superior strength-ductility synergy, by temperature-controlled rolling and subsequent annealing of as-sintered multilayered pure titanium foils with preset grain size gradient. A preliminary gradient structure with the average grain size decreasing from the center layer (alternating stacking of equiaxed fine grain bands and elongated grain bands) to the surface layer (equiaxed fine grains) is formed by optimizing the rolling process. Generalized Schmidt factor analysis based on electron backscatter diffraction indicated that there were slip-dominated and twin-dominated grain refinement mechanisms during the rolling process. In addition to the prismatic slip, two kinds of contraction twinning could be activated to achieve the grain refinement in hard domains where slip systems were hard to be activated. After subsequent annealing, equiaxed fine grains in the laminates did not significantly coarsen, while the elongated grains in the center layer had partially merged and grew up into the elongated coarse grains. Thus, the microstructure of the center layer displayed a typical heterogeneous lamella structure composed of alternately stacking of elongated coarse grains and fine grain bands, together with the grain size gradient, a unique multi-scale heterostructured titanium laminate was formed. Tensile test indicated that the as-rolled Ti laminates exhibited extremely high ultimate tensile strength (UTS) of 930 MPa with an acceptable total elongation to fracture (ETF) of 12.3 %, while GS/HLS Ti laminates after annealing at 425 °C possessed a superior combination of high UTS (823 MPa) and high ETF (22.4 %). The main reason was that the annealing treatment significantly reduced the dislocation density in the elongated coarse grains of GS/HLS Ti laminates. This meant that more geometrically necessary dislocations (GNDs) could accumulate in the plastic deformation process, resulting in the hetero-deformation induced (HDI) strengthening and an extra HDI hardening caused by the unique GS/HLS structure, therefore, an excellent strength-ductility synergy of final GS/HLS Ti laminates was achieved.

Interface characteristics and mechanical properties of a Ti–TiAl laminated composite

In this study, a laminated composite (Ti–6Al–4V (wt%)/Ti–44Al–8Nb–0.2 W–0.2B–0.03Y (at.%) (Ti–44Al–8Nb)) was successfully fabricated via a hot-pack rolling process. The microstructure and mechanical properties of the composite were investigated. No defects were observed at the interfacial region, thereby indicating a high bonding strength between Ti–44Al–8Nb and Ti–6Al–4V alloys. Electron back-scattered diffraction analysis exhibited a few dislocations, sub-structures, and residual stress in the interfacial region. The flexural strength of the composite in the arrester orientation (AO) was 2001.7 MPa, which was 53% higher than that of the Ti–44Al–8Nb alloy. The fracture toughness of the composite in AO (44.5 MPa·m1/2) was 3.4 times to that of Ti–44Al–8Nb alloy. Tensile test at 25 °C indicated higher ultimate tensile strength (802 MPa), yield strength (688 MPa), and tensile plastic strain of the composite (0.94%) than those of the monolithic Ti–44Al–8Nb alloy. The toughening, strengthening, and fracture mechanisms of the composite were discussed in detail.

Electron beam welding of L12-nanoparticle-strengthened strong and ductile medium-entropy alloys for cryogenic applications

The weldability, microstructures, and mechanical properties of two L12-nanoparticle-strengthened medium-entropy alloys (MEAs) Ni43.4Co25.3Cr25.3Al3Ti3 and Ni42.4Co24.3Cr24.3Al3Ti3V3 (at.%) are explored after electron beam welding (EBW). Strong yet ductile defect-free joints were produced with coarse columnar grains (118–245 μm) in the fusion zones, which were larger than the equiaxed grains in the heat-affected zones (15.6–22.3 μm) and in the base materials (4.6–5.6 μm). Both EBWed MEAs showed high yield strengths (838–858 MPa), high ultimate tensile strengths (1416–1420 MPa), and good fracture strains of 20–21 % at 77 K, which are 66∼83 %, 84–89 %, and 57–81 %, respectively, of those of the respective thermo-mechanically treated (TMT) MEAs. The V-doping improved the cryogenic mechanical properties of the TMT MEA while not influencing those of the EBWed MEA. High back-stress hardening contributes to over 50 % of the cryogenic strength. Both EBWed MEAs exhibited abundant dislocation networks, stacking faults, and nanoscale deformation twins after fracture, producing a high strain hardening rate and good ductility.

Achieving synergy of strength and ductility in powder metallurgy commercially pure titanium by a unique oxygen scavenger

Excessive interstitial oxygen (O) contamination, usually causing a dramatic loss of ductility, remains a longstanding challenge for titanium (Ti) and its alloys. Here, we propose to solve this critical problem by adding a minor CaC2 oxygen-scavenger via a simple powder metallurgy (PM) pressureless sintering approach. It is found that the surface oxide layer of hydride-dehydride (HDH) Ti powder begins to dissolve into the Ti matrix between 700 °C and 800 °C during the PM sintering process. The incorporation of CaC2 can react with the surface oxide layer (617-676 °C) prior to its active dissolution and form micrometer-sized TiC and nano-sized CaTiO3 particles, significantly refining the α-Ti grains and creating clean and well-bonded interface with Ti matrix. Therefore, the unique oxygen-scavenging effect by CaC2 produces high strength and superior ductility for Ti alloy. Even with an initially high oxygen content (∼4000 ppm), the Ti-0.4 wt.%CaC2 sample still exhibits a high ultimate tensile strength of 621±25 MPa and superior elongation of 29.3±2.6%, respectively. These values correspond to an increase of 17.6% and 301.4% compared to the as-sintered commercially pure titanium (CP-Ti) properties and far exceed the ASTM standard B381 for Grade 4 wrought Ti alloy (550 MPa and 15%) with the same O content. This work offers a novel method to develop high-strength and superior-ductility Ti materials from much more affordable Ti powder.

Significant enhancement in high temperature performance of TiAl matrix composites by a novel configuration design

Ti5Si3/TiAl composites were successfully prepared by pressure infiltration and subsequent reactive annealing. Final microstructure of Ti5Si3/TiAl composites was dependent on the reactive annealing temperature, which varied from 1350 °C to 1420 °C, two typical microstructures could be achieved: (i) An unique core-shell structure (Core: fully lamellar α2-Ti3Al/γ-TiAl with in-situ synthesized Ti5Si3 particles predominantly distributed at the interfaces of α2/γ lamellar colonies; Shell: equiaxed γ-TiAl with Ti5Si3 particles distributed in γ grain boundaries); And (ii) A novel quasi-network structure composed of fully lamellar α2/γ and a majority of Ti5Si3 particles with a quasi-network distribution. The formation of the two microstructures could be attributed to the chemical composition heterogeneity which was caused by the difference in interdiffusion rate of Ti and Al elements in different annealing temperatures. The comparative investigations on high temperature tensile properties and creep behavior showed that the core-shell Ti5Si3/TiAl composites exhibited a better specific strength (165 MPa⋅g−1⋅cm3) and higher ultimate tensile strength (633 MPa) at 800 °C, which was 12 % higher than that of the quasi-network Ti5Si3/TiAl composites. While the creep behavior analysis showed that in compassion with equiaxed γ phase, the slip distance of dislocations in fully lamellar α2/γ phase was shorter, impeding the motion of dislocations more effectively. And core-shell Ti5Si3/TiAl composites possessed a large number of grain boundaries concentrating in the shell which became weaker in the high temperature, facilitating the formation of creep pores in the shell and the final premature fracture. Hence, the quasi-network Ti5Si3/TiAl composites containing a higher content of fully lamellar α2/γ exhibited a better creep resistance than that of core-shell Ti5Si3/TiAl composites. More importantly, the steady state creep rate at 750 °C under the fixed stress of 250 MPa of quasi-network Ti5Si3/TiAl composites was relatively low, only 3.305 × 10−8 s−1, comparable to that of third-generation TiAl alloys.

Process development for laser powder bed fusion of GRCop-42 using a 515 nm laser source

Copper is widely used in high heat flux and electrical applications because of its excellent electrical and thermal conductivity properties. Alloying elements such as chromium or nickel are added to strengthen the material, especially for higher temperatures. Cu4Cr2Nb, also known as GRCop-42, is a dispersion-strengthened copper-chromium-niobium alloy developed by NASA for high-temperature applications with high thermal and mechanical stresses such as rocket engines. Additive manufacturing (AM) enables applications with complex functionalized geometries and is particularly promising in the aerospace industry. In this contribution, a parametric study was performed for GRCop-42 and the AM process laser powder bed fusion (PBF-LB/M) using a green laser source for two-layer thicknesses of 30 and 60 μm. Density, electrical conductivity, hardness, microstructure, and static mechanical properties were analyzed. Various heat treatments ranging from 400 to 1000 °C and 30 min to 4 h were tested to increase the electrical conductivity and hardness. For both layer thicknesses, dense parameter sets could be obtained with resulting relative densities above 99.8%. Hardness and electrical conductivity could be tailored in the range of 103–219 HV2 and 24%–88% International Annealed Copper Standard (IACS) depending on the heat treatment. The highest ultimate tensile strength (UTS) obtained was 493 MPa. An aging temperature of 700 °C for 30 min showed the best combination of room temperature properties such as electrical conductivity of 83.76%IACS, UTS of 481 MPa, elongation at break (A) at 24%, and hardness of 125 HV2.

Influence of bimodal copper grain size distribution on electrical resistivity and tensile strength of silver - copper composite wires

In order to obtain the best compromise between high strength and low resistivity it was decided to introduce a controlled content of copper (Cu) large grains in copper-silver (Ag-Cu) composite wires. Composite powders are prepared by mixing of 1 vol% Ag nanowires and bimodal Cu powder. The so-obtained composites powders are consolidated into cylinders (8 mm in diameter and 30 mm long) by Spark Plasma Sintering (SPS) at only 450 °C. The cylinders served as starting materials for room temperature wire-drawing (WD) for the preparation of fine wires (1–0.2 mm diameter). The microstructure of the cylinders and the wires was investigated by scanning electron microscopy imaging and electron backscattered diffraction analysis. The electrical resistivity and the tensile strength were measured at 293 K and 77 K. The electrical resistivity of the wires is the lowest when the large Cu grain content is the highest. Cu large grains greatly limit the electronic scattering, forming areas with few grain boundaries and no Ag/Cu interfaces and therefore can be considered as fast conduction channels. Conversely, the addition of Cu large grains leads to a moderate decrease in mechanical strength. By presenting a 12 % lower electrical resistivity and an equivalent ultimate tensile strength (UTS) wires with bimodal Cu matrix show a better compromise between low electrical resistivity and high UTS (0.45 μΩ cm, 1082 MPa at 77 K) compared to wires with a fine-grained Cu matrix (0.51 μΩ cm, 1138 MPa at 77 K).

Combined strengthening from nanoprecipitates, stacking faults and nano-twins enables a strong and ductile medium-entropy alloy

Single-phase face-centered cubic (fcc) alloys typically exhibit remarkable strain-hardening capability and large ductility but possess low yield strength. Conventional strengthening strategies inevitably lead to the loss of ductility. Here, an Nb alloyed CrCoNi-based medium-entropy alloy with a superb yield strength of ∼1.82 GPa, an ultimate tensile strength of ∼1.94 GPa, and good ductility of ∼24 % at 93 K is designed through the combined strengthening from nanoprecipitates, stacking faults, and nano-twins. The cold-rolling is employed to introduce high-density stacking faults and nano-twins, while subsequent low-temperature annealing generates numerous Nb-rich γ″ nanoprecipitates in the fcc matrix. The combined effects of precipitation strengthening, stacking fault- and nanotwin-induced strengthening contribute to an increase in flow stress to surpass the critical stress for the formation of stacking faults and deformation twinning. Moreover, the precipitation of high-density Nb-rich γ″ nanoprecipitates reduces the stacking fault energy of the fcc matrix. Therefore, the precipitation of γ″ nanoprecipitates produces more stacking faults and nano-twins during tensile deformation. The formation of stacking faults and nano-twins in turn, by dynamically introducing high-density interfaces for reducing the mean free path of dislocations, generates a high strain-hardening rate, thus high ultimate tensile strength and large ductility. More importantly, the coherent interfaces between γ′′ nanoprecipitates and the fcc matrix facilitate the transmission of stacking faults and nano-twins across the γ′′ nanoprecipitates. This mechanism could relieve the stress/strain concentrations at interfaces that could otherwise lead to premature crack initiation. This kind of combined strengthening from nanoprecipitates, stacking faults, and nano-twins provides a new avenue to further enhance the strength of nano-twinned materials or precipitation-strengthened materials while maintaining good ductility.

Effect of solid solution temperature on microstructure and mechanical properties of Sc-containing 7085 alloy

The microstructure, mechanical properties, and electrical conductivity of 7085 alloy sheet without and with Sc (0.25 wt%) at different solid solution temperatures were investigated by using OM, SEM, TEM, EBSD, XRD, and the strengthening mechanism of the alloys were analyzed. The results show that the micrometer-scale second phases in the 7085 alloy are mainly the T(AlZnMgCu) phase and the Al7Cu2Fe phase, while Al3(Sc, Zr) particle and the AlZnMgCuSc phase are also formed in the 7085-Sc alloy. The Mg, Zn, and Cu elements in the soluble second phase of both alloys are mainly dissolved as the solid solution temperature increases from 460 °C to 510 °C. The 7085-Sc alloy shows a smaller grain size, higher ultimate tensile strength (UTS, 624 MPa) and yield strength (YS, 580 MPa) after treatment of 480 °C/1 h + 120 °C/24 h. The high strength of 7085-Sc alloy could be attributed to fine-grained strengthening & dislocation strengthening of Al3(Sc, Zr) particles and the precipitation strengthening of MgZn2 phases. The optimum solid solution temperature of 7085 alloy should be controlled in the range of 470–480 °C and that of 7085-Sc alloy is higher, should be 480–490 °C.

Simultaneously healing cracks and strengthening additively manufactured Co34Cr32Ni27Al4Ti3 high-entropy alloy by utilizing Fe-based metallic glasses as a glue

Solidification cracking issues during additive manufacturing (AM) severely prevent the rapid development and broad application of this method. In this work, a representative Co34Cr32Ni27Al4Ti3 high-entropy alloy (HEA) susceptible to crack formation was fabricated by selective laser melting (SLM). As expected, many macroscopic cracks appeared. The crack issues were successfully solved after introducing a certain amount of Fe-based metallic glass (MG) powder as a glue during SLM. The effect of MG addition on the formation and distribution of defects in the SLM-processed HEA was quantitatively investigated. With an increasing mass fraction of the MG, the dominant defects transformed from cracks to lack of fusion (LOF) defects and finally disappeared. Intriguingly, the MG preferred to be segregated to the boundaries of the molten pool. Moreover, the coarse columnar crystals gradually transformed into equiaxed crystals in the molten pool and fine-equiaxed crystals at the edge of the molten pool, inhibiting the initiation of cracks and providing extra grain boundary strengthening. Furthermore, multiple precipitates are formed at the boundaries of cellular structures, which contribute significantly to strengthening. Compared to the brittle SLM-processed Co34Cr32Ni27Al4Ti3 HEA, the SLM-processed HEA composite exhibited a high ultimate tensile strength greater than 1.4 Ga and enhanced elongation. This work demonstrates that adding Fe-based MG powders as glues into SLM-processed HEAs may be an attractive method to heal cracks and simultaneously enhance the mechanical properties of additively manufactured products.