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The combination of severe plastic deformation, deformational heat, and frictional heat generated during the high-pressure torsion process has a great effect on microstructural evolutions, including grain refinement, dynamic recrystallization and recovery. In particular, the low melting temperature metallic alloys (e.g., aluminum and magnesium) also induce nano-precipitations in the matrix during high-pressure torsion, which results in both unique microstructure and mechanical properties of the nanocrystalline metallic materials. In this study, the mechanical properties and microstructural evolution of high-pressure torsion-processed aluminum 7068 alloy at room temperature were investigated. In the early deformation stage, both grain refinement and nano-precipitates were formed that increase the strength of ultrafine-grained aluminum alloy, and a maximum strength of 844 MPa was obtained for the 5T sample. However, in the later deformation stage, tensile strength decreases with the increase in shear strain due to grain growth, and coarse precipitates act as crack initiation sites during plastic deformation. In summary, the mechanical properties of high-pressure torsion represent the strength-ductility trade-off as the increase of the number of revolutions. Their mechanical properties are superior to those of recent severe plastic deformation-processed aluminum alloys. This result shows that the severe plastic deformation of the HPT process positively contributes to their mechanical properties by inducing multiple strengthening paths, such as grain refinement and nano-precipitation of the aluminum alloy.

Artificial intelligence and Internet of Things (IoT) technology, which are the core of the 4th industrial revolution, can resolve many problems that optimization of production times in the manufacturing process and reduction of materials required etc. In order to utilize the 4th industrial revolution technology, real-time monitoring technology of metal parts is essential, so technology for embedding sensors and IC chips into parts is essential. Using metal 3d printing technology, it is possible to embed IC chips into metal parts, which was impossible because of the existing high-temperature metal manufacturing process of casting or forging. Here we introduce a novel new method for sensor embedding into SUS316L by hemisphere design to avoid direct laser exposure onto sensors during selective laser melting process. Thermal and microstructural analysis was carried out to characterize the property of inner hemisphere for safe thermal couple embedding into SUS316L.

Previously reported low-Mn ferritic-based lightweight steels are potential candidates for industrial applications, however, they typically exhibit lower strength, with < 1 GPa and lower strength-ductility balance, than medium- and high-Mn austenitic lightweight steels. Herein, we introduce a low-temperature tempering-induced partitioning (LTP) treatment that avoids the strength-ductility dilemma of low-Mn ferriticbased steels. When the LTP process was performed at 330 oC for 665 s, the strength of typical ferritic base Fe-2.8Mn5.7Al0.3C (wt%) steel with heterogeneously sized metastable austenite grains embedded in a ferrite matrix, exceeded 1.1 GPa. Notably, the increased strength-ductility balance of the LTP-processed ferritic steel was comparable to that of the high-Mn based austenitic lightweight steel series. Using microscale to nearatomic scale characterization we found that the simultaneous improvement in strength and total elongation could be attributed to size-dependent dislocation movement, and controlled deformation-induced martensitic transformation.

Process optimization of additively manufactured Ti–6Al–4V alloy is an important aspect of the production of engineered, high-performance parts for the aerospace and medical industries. In this study, the microstructural evolution and mechanical properties of direct energy deposition processed Ti–6Al–4V alloy were investigated using different processing parameters. Experimental analyses revealed that the line energy density corresponding to the processing parameters of the direct energy deposition process influences the properties of additively manufactured Ti–6Al–4V alloy. First, an optimal line energy density limits the incidence and size of voids resulting from a lack of fusion to enhance both alloy strength and ductility. Second, an excessively high energy density induces the coarsening of prior-β grains to impair both alloy strength with the Hall–Petch relationship and alloy ductility due to the plastic deformation instability caused by the limited number of grains. These results indicate that both the extent of fusion and prior-β grain size affect the mechanical properties of additively manufactured Ti–6Al–4V alloy. Moreover, the results demonstrate the utility of the line energy density-based approach in determining the optimal processing parameters for realizing high-performance materials.

Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles, which can crucially affect the quality of human life in terms of normal walking or daily activities. For successful patient recovery, it is necessary to remove the cancer-affected minimal bone area and quickly replace it with a biocompatible metal implant within less than 2 weeks. An electron beam-melted Ti-6Al-4V implant was designed and applied in a patient to preserve the natural knee joint close to the bone tumor. The developed implant fits the bone defect well, and the independent ambulatory function of the natural knee joint was restored in the patient within six weeks after surgery. A delayed fracture occurred six months after the successful replacement of cancer-affected bone with Ti-6Al-4V implant at the proximal meshed junction of the implant because of a minor downward slip. Microstructural, mechanical, and computational analyses were conducted for the fractured area to find the main reason for the delayed fracture. Our findings pertaining to the mechanical and material investigation can help realize the safe implantation of the three-dimensionally printed titanium implant to preserve the natural joints of patients with massive bone defects of the extremities.

The rapid melting and solidification cycle in additive manufacturing creates a non-equilibrium environment that induces metastable microstructures. These metastable microstructures include solute heterogeneity, dislocation cell structure and nano-sized precipitation, which contributes to the strength of additively manufactured alloys. Because the presence of metastable microstructure contributes to the mechanical property enhancement of additively manufactured alloy, quantification and estimation of strength by metastable microstructure becomes important issue. In this study, the role of dislocation cell structure on the mechanical property of additively manufactured stainless steels was investigated. The evolved cell networks not only interrupted dislocation gliding, but also acted as crack propagation paths during plastic deformation. The finer cell networks found in the additively manufacture 304L stainless steels induced more interactions with dislocations than those found in the additively manufacture 316L stainless steels, and that is related to the higher strength during tensile test. This result demonstrates the dislocation cell structure is a main strengthening mechanism for additively manufactured materials and the modified Hall–Petch hardening model successfully estimate the strengthening by cell boundaries.

The correlation between microstructure and tensile properties of selective laser melting (SLM) processed STS 316L and Inconel 718 were investigated at various heights (top, middle and bottom) and planes (YZ, ZX and XY). Columnar grains and dendrites were formed by directional growth during solidification. The average melt pool width and depth, and scan track width were similar in both specimens due to fixed processing parameters. SLM Inconel 718 has moderate tensile strength (1165 MPa) and tensile elongation (11.5%), whereas SLM STS 316L has outstanding tensile strength (656 MPa) and tensile elongation (75%) compared to other SLM processed STS 316L. Fine columnar diameter (0.5 μm) and dense microstructures (porosity: 0.35%) in SLM STS 316L promoted the enhancement of tensile elongation by suitable processing condition. Fractographic analysis suggested that the lack of fusion pore with unmelted powder should be avoided to increase tensile properties by controlling processing parameters.

The microstructural evolution of Al–Zn–Mg–Cu alloys has been investigated for the homogenization time effect on the texture, grain orientation and dislocation density. The Al–Zn–Mg–Cu alloys were casted and homogenized for 4, 8, 16 and 24 hours. Electron backscatter diffraction (EBSD) analysis was conducted to characterize the microstructural behavior. Micropillars were fabricated using focused ion beam (FIB) milling in grains of specific crystallographic orientations. Coarse precipitations in the grain boundaries are S (Al2CuMg) and T (Al2Mg3Zn3) phases verified by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) observation. With increasing homogenization time, equiaxed cell sizes increased. The volume fraction of S and T phases decreased with the diffusion of atomic elements into matrix. The Vickers hardness and tensile strength values decreased with homogenization temperature. The micropillar compression analysis was compared to macro tensile test results to understand the size effect and strain burst phenomenon on the mechanical properties of Al–Zn–Mg–Cu alloys.

Boron doping with an adequate concentration is highly desirable for alloy development because it profoundly improves the material's interface cohesion via interfacial segregation. However, scientific and applicable potentials of soluble boron that resides at the alloy internal grains are generally overlooked. Here we report a strategy for overcoming the typically low strengths of face-centered cubic high-entropy alloys (HEAs) through exploiting soluble boron instead of the interfacial boron. We find that soluble boron increases stress/strain field at the recrystallized HEA grain structure, leading to the generation of short-range order (SRO) in those deformation structure under load at 77 K. The highly increased degree of SRO at planar dislocation slip band that forms during straining, proved by electron microscopy and synchrotron X-ray diffraction, strengthens a typical non-equimolar Fe40Mn40Co10Cr10 (at%) HEA, particularly increasing yield strengths by ∼32%, to ∼1.1 GPa compared to those of boron-free reference materials with similar grain sizes. The advent of deformation-induced SRO domains causes severe lattice distortion (specifically, contraction), leading to the increased cryogenic yield strength of ∼210 MPa, but generating micro-voids at grain boundaries. This study on deformation-induced SRO via boron advances the fundamental understanding of SRO impacts on HEA grains and mechanical properties at cryogenic temperatures, which may pave a general pathway for developing a wide range of ultrastrong alloys for cryogenic applications.

Despite recent progress in achieving high mechanical properties of metal additive manufacturing, the low productivity represented by slow manufacturing speeds still remains a bottleneck of the technology. We improved the scanning speed of selective laser melting (SLM) with Ti-6Al-4V up to 1800 mm/s for high printing speed with affordable mechanical properties. In addition, the hot isostatic pressing (HIP) process was applied as post-treatment process to remove porosity of the high-speed printed SLM specimens. However, the HIP process caused a microstructural change from α′-lath martensite to a Widmanstӓtten α-lamellar structure. This microstructural change was most pronounced on the surface area and caused inter-lamellar fracture. Here, we investigate this phenomenon with microstructural and computational analysis. The results indicate that this deterioration phenomenon is highly dependent on surface roughness, which can be controlled with a build angle set-up.

Steel sheet is often shaped by straining to form a final product, and deformation process can influence the fatigue resistance. In this study, high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of precipitation hardened (PH) high strength steel with pre-straining levels of 0, 5 and 9% were investigated. Regardless of pre-straining level, fatigue cracks were found to be initiated at surface pits formed during pickling. The effect of pre-straining was not significant on the HCF resistance of PH steel, while the FCP rates increased with increasing level of pre-straining only in low and intermediate ΔK regimes. It was suggested that marginal increase on HCF resistance of PH steel was due to the combined effect of enhanced resistance to crack initiation and reduced resistance to crack propagation with pre-straining. The effect of pre-straining on HCF and FCP behavior of PH steel was discussed based on micrographic and fractographic observations.

An artificial neural network (ANN) model is developed for the analysis and simulation of correlation between flake powder metallurgy parameters and properties of AA2024-SiC nanocomposites. The input parameters of the model are AA 2024 matrix size, ball milling time, and weight percentage of SiC nanoparticles and the output parameters are density and hardness. The model can predict the density and hardness of the unseen test data with a correlation of 0.986 beyond the experimental data. A user interface is designed to predict properties at new instances. We have used the model to simulate the individual as well as the combined influence of parameters on the properties. Moreover, we have analyzed the calculated results from the powder metallurgical point of view. The developed model can be used as a guide for further composite development.

The J-integral fracture toughness values of high-Mn steel (Fe-25 wt pct Mn) and 304L stainless steel were evaluated at 25 °C, 0 °C, − 50 °C, − 100 °C, − 163 °C, and − 196 °C using precracked compact tension (CT) specimens and compared to those determined using Charpy impact tests. The high-Mn steel exhibited excellent J-integral fracture toughness at both room and cryogenic temperatures, with values comparable to those of 304L stainless steel. However, the trend of the J-integral fracture toughness of high-Mn steel with the decreasing temperature differed from that of the Charpy impact test results. Electron backscattered diffraction and micrographic analyses suggest that the varying stacking fault energies of high-Mn steels at different temperatures affected the deformation behavior in the stretch zone at the crack tip of the CT specimen. The effect of this temperature-dependent deformation behavior of high-Mn steels on the fracture process in the J-integral test could differ from that in the Charpy impact test, resulting in the different trends in the fracture resistance with the decreasing temperature.

The high-cycle fatigue (HCF) behavior of dissimilar metal welds between high-Mn (HM) steel and 304L stainless steel was investigated at 298 K and 110 K. The resistance to HCF of the 25Mn/304L weld joint was comparable to that of a 304L/304L weld, even at 110 K. The HCF behavior of the dissimilar metal joints between HM steel and 304L could be reasonably predicted by the ultimate tensile strength at both room and cryogenic temperatures, as with the base metal. The failure locations and micro-hardness studies suggested that both geometrical and metallurgical factors were important in determining the HCF behavior of 25Mn/304L weld joints.

General design concept used in high-entropy alloys (HEAs) have deviated from forming an fcc single phase to utilizing hard intermetallic phases in ductile fcc matrix. Here, we effectively exploited strengthening effects of a brittle intermetallic sigma (σ) phase to improve cryogenic tensile properties of a non-equi-atomic ductile VCrFeNi four-component HEA. We preferentially selected vanadium as a candidate alloying element to efficiently produce the σ phase through computational thermodynamic approach. This σ phase has beneficial effects on grain refinement through retardation of grain growth due to grain-boundary pinning, thereby leading to yield strength of 0.79–0.93 GPa. The extensive strain hardening results in tensile strength of 1.33–1.49 GPa and ductility of 23–47% at cryogenic temperature, which are enabled by nano-sized dislocation substructures rather than deformation twinning. Our results demonstrate how the intermetallic σ phase, which has been avoided in typical HEAs because of ductility deterioration, could be used in high strength HEA design.

The fatigue crack propagation (FCP) behavior of β-annealed Ti-6Al-4V (Ti64) alloy was examined in air and 0.6 M NaCl solution under anodic and cathodic applied potentials and at two different R ratios of 0.1 and 0.7. β-annealed Ti64 alloy was sensitive to environmental FCP in NaCl solution under both anodic and cathodic applied potentials at an R ratio of 0.1, while the environmental effect was almost negligible at an R ratio of 0.7. The extent of crack branching in air and at an R ratio of 0.1 decreased substantially in NaCl solution and/or at an R ratio of 0.7. The EBSD (electron backscatter diffraction) and SEM (scanning electron microscope) fractographic analyses on the FCP tested specimens showed that microstructure-sensitive cracking, rather than crystallographic cleavage cracking, became encouraged in NaCl solution and/or high R ratio. It was suggested that the extent of crack branching played an important role in determining the environmental FCP behavior of β-annealed Ti64 alloy.

The effects of cooling rate on the stress corrosion cracking (SCC) susceptibility of β-processed Ti–6Al–4V (Ti64) alloy, including BA/S specimen with furnace cooling and BQ/S specimen with water quenching, were investigated in 0.6M NaCl solution under various applied potentials using a slow strain rate test technique. It was found that the SCC susceptibility of β-processed Ti64 alloy in aqueous NaCl solution decreased with fast cooling rate, which was particularly substantial under an anodic applied potential. The micrographic and fractographic analyses suggested that the enhancement with fast cooling rate was related to the random orientation of acicular α platelets in BQ/S specimen. Based on the experimental results, the effect of cooling rate on the SCC behavior of β-processed Ti64 alloy in aqueous NaCl solution was discussed.

A variety of factors affect the fatigue behavior of high-Mn steels, which include both extrinsic (i.e., loading type, R ratio, specimen type, surface condition, temperature, and environment) and intrinsic (i.e., chemical composition, grain size, microstructure, stacking fault energy) factors. Very often, the influence of extrinsic factors on the fatigue behavior is even greater than that of intrinsic factors, misleading the interpretation of fatigue data. The metallurgical factors influence the initiation and propagation behaviors of fatigue by altering the characteristics of slip that is prerequisite for fatigue damage accumulation. It is however not easy to separate the effect of each factor since they affect the fatigue behavior of high-Mn steels in complex and synergistic way. In this review, the fatigue data of high-Mn steels are summarized and the factors complicating the interpretation are discussed.