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Zn alloy has attracted much attention as a biodegradable material for biomedical applications. However, due to the significant strain softening of Zn alloys, how to break the bottleneck of synergistic yield strength and uniform elongation is an urgent problem to be solved. In this work, a Zn-2.3Cu-0.8Mn (wt.%) alloy was fabricated via low-temperature extrusion and annealing at 330 °C for 1 h to attain dual heterostructures with bimodal grains and multi-scale second phases, focusing on the effect of heterostructure on the mechanical properties. Uniaxial tensile test and loading-unloading-reloading test were applied to reveal the mechanical properties of the Zn-2.3Cu-0.8Mn alloy, while scanning electron microscope, electron backscatter diffraction, and transmission electron microscope were used to characterize its microstructure. Compared with the as-extruded alloy with uniform and fine grains, 330–1 alloy achieves a better combination of strength and uniform elongation (yield strength: 287.8 ± 8.5 MPa, ultimate tensile strength: 321.4 ± 6.8 MPa, and uniform elongation: 14.2 ± 1.8%). The high strength was primarily attributed to the coordination of grain boundary strengthening, hetero-deformation induced strengthening, Orowan strengthening, and dislocation strengthening. Besides, the coarse grains, twinning, as well as the suppression of grain boundary sliding and phase boundary sliding promoted dislocation proliferation and storage capacity, thereby improving work hardening capacity. The large strain hardening capacity was responsible for excellent plasticity. This study provides a feasible strategy for the design of Zn-based alloys with an excellent combination of high strength and strain hardening capacity. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) allows for manufacturing intricate and accurate component designs that are challenging, expensive, or impossible to achieve using traditional methods. To achieve a high-quality final product with SLM, it is necessary to optimize the process parameters carefully. This optimization helps to minimize internal structural defects and control the microstructure. In this study, the optimum production parameters of Ti6Al4V alloy were determined using the Response Surface Method (RSM). The micro-CT analysis was utilized to calculate the relative densities of the samples fabricated using different production parameters. Furthermore, the influence of heat treatment, conducted below and above the β transformation temperature, on the mechanical properties was examined. The results were analyzed by considering the microstructure images obtained from Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) analysis. The optimum production parameters for the SLM method were found to be 80W laser power, 1125 mm/s scanning speed, 25 μm layer thickness, and 45 μm hatch distance. Samples created with these optimized parameters achieved 99.919% relative density, 1050 MPa ultimate tensile stress, and 13.8% elongation, surpassing the minimum standards outlined in ASTM F3001-14. Additionally, the systematic parameter reduction approach used in the study led to savings in both powder consumption and time in SLM, a method that could be applied to various metallic materials. • Ti6Al4V-ELI alloy was manufactured with selective laser melting method. • The response surface method was used to determine the optimum production parameters. • Micro-CT analysis was performed and density ratios were calculated. • Mechanical properties were improved with post processing operation. [ABSTRACT FROM AUTHOR]

Solute clustering and precipitation in an Al–Cu–Mg–Ag–Si model alloy has been investigated by atom probe tomography (APT) as well as high-angle annular dark-field (HAADF) imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Nine types of solute clusters (Cu, Ag, Mg–Cu, Mg–Ag, Mg–Cu–Si, Mg–Ag–Si, Mg–Ag–Cu, Cu–Ag–Si and MgAgCuSi) were observed by APT in both the as-quenched alloy and after ageing the alloy at 180 °C for 1 h. Three types of precipitates (Ω (AlCuMgAg), θ (Al 2 Cu) and Mg 2 Si) were observed by APT and HAADF-STEM after further ageing at 180 °C for 24 h and 100 h. We propose that MgAgCu and MgAgCuSi clusters are likely to be responsible for the formation of the Ω (AlCuMgAg) phase. Furthermore, we also suggest that the θ (Al 2 Cu) phase forms from Cu clusters and the Mg 2 Si phase forms from the decomposition of MgAgSi and MgAgCuSi clusters by losing Ag to Ω phase growth. Many early binary clusters (Mg–Cu, Mg–Ag) do not seem to undergo a significant further growth during ageing; these are more likely to be transformed into complex ternary and quaternary clusters and be subsequently consumed during the growth of large clusters/precipitates. Furthermore, it is proposed that the plate-like Ω (AlCuMgAg) precipitates evolve continuously from the MgAgCu and MgAgCuSi clusters, rather than via heterogeneous nucleation on their precursors (i.e. MgAgCu and MgAgCuSi clusters). More interestingly, even after ageing at 180 °C for 100 h, the Ω (AlCuMgAg) precipitates remain coherent with the α-Al matrix, indicating that these precipitates have a high thermal stability. This can mainly be attributed to the presence of a single Mg–Ag-rich monolayer observed at the interface between the Ω precipitate and the α-Al matrix, significantly improving the coarsening resistance of the Ω (AlCuMgAg) precipitates. Our results thus reveal links between a variety of solute clusters and the different types of precipitates in the Al–Cu–Mg–Ag–Si model alloy. Such information can in the future be used to control the precipitation by tailoring solute clustering. [ABSTRACT FROM AUTHOR]

The issue of hydrogen embrittlement (HE) in face-centered (FCC) structured alloys is significant for H storage and transportation application due to unanticipated damage beyond its predicted service life. This unpredictable situation may harm human life and limit hydrogen to a reliable source of renewable energy in industrial fields. Recent research has suggested that multi-principal element alloys possess high resistance to HE. However, there has been limited exploration of how their unique properties affect the HE mechanisms. In this study, using simple model VCrCoNi alloys with analogous grain sizes, the reduction rate of ductility by hydrogen uptake was measured through a slow strain rate tensile test following electro-chemical H charging. Further, the origin of HE resistance was investigated by analyzing various factors such as hydrogen contents, fracture and deformation behaviors, and grain boundary properties using thermal desorption spectroscopy, scanning electron microscope, and electron backscatter diffraction. Despite the consistent trends of the H content, stacking fault energy, and stress with increasing V content, the resistance to HE is the highest for the alloy with an intermediate ratio of V and Cr, namely, for the V 0.7 Cr 0.3 CoNi alloy. Through the analysis of grain boundary characteristics, the high resistance is attributed to large fractions of special boundaries and special triple junctions and large twin-related domain size, which suppresses crack growth and interlinkage. The favorable grain boundary characteristics result from mechanical dynamic recovery, achieved by the competitive effects of solid-solution strengthening and stacking fault energy. Thus, the present study provides novel insights into enhancing HE resistance in FCC-structured alloys. [Display omitted] • Hydrogen embrittlement (HE) is investigated for V x Cr 1-x CoNi medium-entropy alloy. • Resistance to HE is the highest at an intermediate ratio of V and Cr, V 0.7 Cr 0.3 CoNi. • High resistance results from grain boundary characteristics and twin-related domains. • These two factors depend on the difference in mechanical dynamic recovery (MDR). • MDR results from the competitive effects of solid-solution strengthening and SFE. [ABSTRACT FROM AUTHOR]

Three kinds of high-performance as-extruded Mg-Gd-Zn-Zr alloys were successfully prepared by controlling Zn and Gd contents and atomic ratio. The microstructure, mechanical properties and corrosion resistance of the three alloys were studied by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), electron backscattering diffraction (EBSD), tensile-compressive experiment and electrochemical experiment. The results showed that the coarse grains and continuous second phase of as-cast alloys were refined and broken after hot extrusion, and the main components were α-Mg, W–Mg 3 Gd 2 Zn 3 , I–Mg 3 Zn 6 Gd and MgZn 2 phases. The mechanical properties and corrosion resistance tests revealed that the as-extruded GZ22 alloy had the highest ultimate tensile strength (UTS) of 362 ± 6 MPa and the lowest corrosion rate of 0.94 mm/year, which was attributed to the fine grains and a small amount of dispersed second phase. The strength of as-extruded GZ56 alloy decreased due to excessive hard and brittle W-phase. Meanwhile, a large amount of second phase content made the alloy had the lowest corrosion resistance. In addition, the as-extruded GZ26 alloy with high Zn/Gd atomic ratio had good comprehensive mechanical properties, and its UTS and elongation (EL) were 332 ± 3 MPa and 24.5 ± 0.6%, respectively. The unique feature of this alloy was that weak texture intensity led to good tension-compression yield symmetry, and its corrosion resistance was second only to that of the as-extruded GZ22 alloy. [ABSTRACT FROM AUTHOR]

Zn alloy has attracted much attention in recent years as a new biomedical degradable material. However, how to simultaneously achieve its high strength and high ductility is a bottleneck problem to be solved. In this study, the Zn-2.0Cu-0.1Ti alloy with ununiform heterostructure, consisting of the barren areas without CuZn 5 phase and the regions enriched with CuZn 5 phase, was designed and successfully fabricated through controlled stir casting and hot extrusion. Uniaxial tensile test and Vickers hardness test were applied to reveal the mechanical properties of the Zn-2.0Cu-0.1Ti alloy, while electrochemical test and immersion test were used to characterize its degradation properties. The novel heterostructure was systematically examined by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). It was found that the yield strength and ultimate tensile strength of the present Zn-2.0Cu-0.1Ti alloy reach 241.2 ± 4.7 MPa and 265.8 ± 1.3 MPa, showing 294.4% and 230.3% improvement over those of pure Zn. Even more surprising is that the improved strength can be achieved without sacrificing ductility. The substantially increased strength can be mainly attributed to the strengthening mechanisms of grain refinement and Orowan looping, and the maintenance of good ductility thanks to the excellent dislocation storage ability of the present heterostructure. At the same time, the corrosion rate of the alloy in simulated body fluids also reaches the industry standard for orthopedic implants. This study not only sheds light on the design and fabrication of Zn-based material for surgical implantation application but also provides a feasible route to improve the mechanical properties of other precipitates reinforced alloys. • Heterostructure with ununiform dispersion of CuZn 5 was constructed in Zn-2.0Cu-0.1Ti alloy. • The significant strength improvement over pure Zn was achieved without sacrificing ductility. • The involved strengthening and toughening mechanisms were deeply discussed. • The slightly increased corrosion rate was explained in terms of the heterostructure. [ABSTRACT FROM AUTHOR]

Mg-xAl alloys (x = 3–12 wt%) were prepared by high pressure solidification. The microstructure of the alloys was studied using Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD), and the strengthening mechanism was analyzed in combination with the compressive properties of the experimental alloys. Furthermore, the grain boundary segregation of Al solute was investigated by experiments and first-principles calculations. For the Mg-xAl alloys solidified under atmospheric pressure, the microstructure will be a single solid solution when the Al content of the alloy is less than 5 wt%. However, for the Mg-xAl alloys solidified under 4 GPa pressure, the microstructure will always ba e single solid solution when the Al content of the alloy is less than 12 wt%. Moreover, the segregation of Al solute with a high concentration gradient can be observed at plenty of grain boundaries (area fraction is as high as 46%), because α-Mg dendrites are significantly refined under high pressure. In addition, many Al atoms are dissolved in the α-Mg matrix owing to high pressure. On this basis, it is found that grain boundary segregation of Al solute can decrease the grain boundary energy, and increase the bonding strength of grain boundaries. As a result, the Mg–Al alloys solidified under high pressure have superior compression properties. The compression strength of the Mg–9%Al alloy and the Mg–12%Al alloy solidified under 4 GPa is as high as 458 MPa and 490 MPa respectively, the alloys retain superior plasticity simultaneously. [ABSTRACT FROM AUTHOR]

Hot compression test was performed on Ti–6Al–2Zr–1Mo–1V alloy below the β-transus (T β) with the temperature range of 940–970 °C. Microstructural evolution, especially on the equiaxed primary α phase (α p), was characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The results showed that the α p could transform into β during hot deformation at α+β two-phase region, i.e., deformation-induced transformation of α→β (DIT). DIT, as an additional softening mechanism, caused the unusual stress response on the flow curves, which was reflected by the fact of the steady stress (σ st)

The grain boundary sliding and its accommodation mechanism during superplastic deformation have been identified by surface observations with focused ion beam in an Al–Zn–Mg–Cu alloy. The high-temperature in-situ tensile test is carried out in the scanning electron microscope under the region Ⅱ superplastic conditions. The experiment results indicate that the grain boundary sliding is the dominant superplastic deformation mechanism accommodated by diffusion creep and a little dislocation activity. The grain rotation also plays an essential role in superplastic deformation. There are no striated zones found in a vacuum environment, just cracks. A grain boundary sliding model is proposed based on the surface features. [ABSTRACT FROM AUTHOR]

Aggregation of Y 2 O 3 particles with relatively large size along grain boundaries is a main limiting factor for performance improvement in W–Y 2 O 3 alloys. In order to tailor the distribution and achieve size refinement of Y 2 O 3 dispersoids, W–Y 2 O 3 alloy was prepared using ball milling with extended milling time and subsequent spark plasma sintering (SPS) in this study. Microstructure evolution of Y 2 O 3 during the preparation process was characterized in detail using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Mechanical properties of SPSed alloy were evaluated in terms of microhardness, three-point bending and compression tests. Structure transformation of Y 2 O 3 from BCC to FCC during the process of ball milling and subsequent sintering was first identified in W–Y 2 O 3 alloy in this study. Compared with the raw micron sized Y 2 O 3 powders, the transformed Y 2 O 3 dispersoids experienced significant size refinement. Around 76% of the nanosized Y 2 O 3 dispersoids were distributed inside grain interior, and they exhibited semi-coherent relationship with tungsten matrix. These microstructural characteristics contributed to the high compressive strength of 1804.2 MPa and microhardness of 625.7 HV in the SPSed W–Y 2 O 3 alloy. • W–Y 2 O 3 alloy were prepared by extended ball milling and SPS. • Structure transformation of Y 2 O 3 from BCC to FCC was identified in W–Y 2 O 3 alloy. • Y 2 O 3 also experienced size refinement and 76% of them were inside grain interior. • The nanosized Y 2 O 3 exhibited semi-coherent relationship with tungsten matrix. • Y 2 O 3 dispersoids contributed to improved strength mainly through grain refinement. [ABSTRACT FROM AUTHOR]

Aggregation of Y 2 O 3 particles with relatively large size along grain boundaries is a main limiting factor for performance improvement in W–Y 2 O 3 alloys. In order to tailor the distribution and achieve size refinement of Y 2 O 3 dispersoids, W–Y 2 O 3 alloy was prepared using ball milling with extended milling time and subsequent spark plasma sintering (SPS) in this study. Microstructure evolution of Y 2 O 3 during the preparation process was characterized in detail using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Mechanical properties of SPSed alloy were evaluated in terms of microhardness, three-point bending and compression tests. Structure transformation of Y 2 O 3 from BCC to FCC during the process of ball milling and subsequent sintering was first identified in W–Y 2 O 3 alloy in this study. Compared with the raw micron sized Y 2 O 3 powders, the transformed Y 2 O 3 dispersoids experienced significant size refinement. Around 76% of the nanosized Y 2 O 3 dispersoids were distributed inside grain interior, and they exhibited semi-coherent relationship with tungsten matrix. These microstructural characteristics contributed to the high compressive strength of 1804.2 MPa and microhardness of 625.7 HV in the SPSed W–Y 2 O 3 alloy. • W–Y 2 O 3 alloy were prepared by extended ball milling and SPS. • Structure transformation of Y 2 O 3 from BCC to FCC was identified in W–Y 2 O 3 alloy. • Y 2 O 3 also experienced size refinement and 76% of them were inside grain interior. • The nanosized Y 2 O 3 exhibited semi-coherent relationship with tungsten matrix. • Y 2 O 3 dispersoids contributed to improved strength mainly through grain refinement. [ABSTRACT FROM AUTHOR]

Abstract: High-intensity pulsed ion beam (HIPIB) treatment is a new technology for surface modification of materials. In this paper, the surface of 316L stainless steel was irradiated by high-intensity pulsed ion beams at ion current density of 100, 200 and 300A/cm2 with 1, 5 and 10 shots. The surface morphology and the phase structure in the near surface region of original and treated samples were analyzed with scanning electron microscope (SEM) and X-ray diffraction (XRD). Electron probe microanalysis (EPMA) was used to study the distribution of elements on the irradiated surfaces. It is found that the HIPIB irradiation can smooth the surface of the targets, and a preferred orientation presents in the surface layer of the treated samples. Otherwise, selective ablation of impurities occurs during the interaction between HIPIB and the targets. The influence of HIPIB irradiation on the electrochemical corrosion resistance of 316L stainless steel in 0.5mol/L H2SO4 was investigated. The polarization curves show that under the cooperation of the smooth surface and the grain refinement with the selective ablation of impurities, the corrosion resistance of the irradiated samples was improved significantly. [Copyright &y& Elsevier]

Abstract: For the purpose of reducing the diameter and the weight of the propulsion shaft of a high-speed craft, the high strength alloy is normally used. In general, the stainless SUS 630 is selected as the shafting material. While pitting corrosion existed in such kind material can be a problem to considerably reduce the fatigue life of the shaft. In this paper, the prediction model of the fatigue crack propagation behavior of SUS 630 in accordance with the Paris law has been established. Together with the rotating bending fatigue tests with various loads on shaft specimens in various extent of pitting corrosion conditions and the fatigue fracture surface analyses through the scanning electron microscope (SEM), the material the coefficient n is 2.71 and C is 1.63E−14 for 450N/mm2, n is 3.25 and C is 8.96E−16 for 400N/mm2, and n is 3.04 and C is 3.60E−15 for 350N/mm2 based on the range of ΔK is from 26 to 46 (MPa√m). In addition, the fatigue lifetime of SUS 630 shaft under various extent of pitting corrosion condition is found to be in a range of only 2.5–27% of that of the uncorroded condition. [Copyright &y& Elsevier]

Abstract: In this paper, hot cracking in Al–(1–4.5%) Cu direct-chill (DC) cast billet was investigated by means of controlled DC casting followed by structure examination. No hot cracks were found in the billets of alloys containing more than 4% Cu. The hot tear surfaces of the DC cast billets with different compositions were observed in a scanning electron microscope. The porosity fraction measurement was also performed. It was found that decreasing the copper concentration from 3 to 1% caused a decrease in the amount of eutectic observed on the hot tear surface. Special features appeared on the hot tear surface of an Al–1% Cu alloy in which the hot tear predominantly propagated through the solid phase, i.e., bridged grain boundary. A solute-rich (eutectic) path along grain boundaries ahead of the hot-crack tip was observed in billets with hot tears, which could be an evidence of crack healing. The porosity concentrated in the center of the billet and its amount was lower in alloys with high hot tear susceptibility and in alloys not susceptible to hot tearing. Increased casting speed lead to increasing porosity. [Copyright &y& Elsevier]

Abstract: Variant selection of intergranular bcc-Cr precipitates in a Ni–43mass% Cr alloy was studied by electron backscattering diffraction (EBSD) in a scanning electron microscope equipped with a field emission gun (FESEM) and Kikuchi line analysis in transmission electron microscope (TEM). A single variant was invariably selected at the underlying grain boundaries (GB) when GB-precipitates were KS-related with respect to both the adjacent matrix grains. Meanwhile multiple variants were formed at the GB when GB-precipitates were KS-related to one of the adjacent matrix grains. Theses variant selections were examined with the tilt angle to underlying GB of low-energy interphase boundaries and the orientation relationship with respect to both the adjacent matrix grains. The underlying mechanism was discussed from the viewpoint of activation energy for nucleation of two-dimensional nuclei. [Copyright &y& Elsevier]

Abstract: Effects of crystalline phase particles formed in a strip-cast Zr-base bulk amorphous alloy on strength, ductility, and fracture toughness were investigated by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope chamber. The compressive and fracture toughness test results indicated that strength, ductility, and fracture toughness of the strip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5vol.%) of hard, brittle crystalline particles. According to the in situ microfracture observation, crystalline particles were easily cracked under low stress levels, acted as blocking sites of shear band or crack propagation, and provided initiation sites of multiple shear bands. Thus, the improvement of mechanical properties in the strip-cast alloy could be explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles. [Copyright &y& Elsevier]

Fracture of the Ni–Ti superelastic alloy for endodontic instruments such as files was investigated with a sustained tensile-loading test in sodium hypochlorite (NaOCl) solution of various concentrations. It was found that the time to fracture was reduced when the applied stress exceeded the critical stress for martensite transformation. When the applied stress was higher than the critical stress, the 0.3 mm diameter wires of the Ni–Ti superelastic alloy sometimes fractured within 60 min. From the results of observations of the fracture surface using a scanning electron microscope, it was revealed that the fracture of the Ni–Ti superelastic alloy is significantly influenced by corrosion when the applied stress was higher than the critical stress for martensite transformation. The results of the present study suggest that one of the causes of the fracture of Ni–Ti files during clinical use is corrosion under the applied stress above the critical stress for martensite transformation in NaOCl solution. [Copyright &y& Elsevier]

Changes in morphology and surface-enhanced Raman scattering (SERS) activity due to air ageing of Cu-based amorphous alloys (AAs) were followed by microscopic and vibrational spectroelectrochemical methods. Freshly fabricated ribbons are highly homogeneous and thus SERS-inactive materials. Air ageing results in partial devitrification; Cu-rich domains are formed on the wheel side of Cu–Zr and Cu–Hf ribbons with a ZrO2 or HfO2 supporting layer below. Sporadic small Cu-rich domains are also formed on Cu–Ti ribbons, which however, are generally less susceptible to devitrification. Partially devitrified Cu–Zr, Cu–Hf, and Cu–Ti AAs appear active targets for in situ SERS measurements of adsorbed pyridine. We have found that large SERS signals are measured from the Cu-rich domains, whereas the SERS intensity drops down by as much as two orders of magnitude outside the Cu-rich domains. The effect of electrode potential on the SERS signal for various surface domains varies greatly, suggesting that SERS activity at different sites differs accordingly, probably due to a difference in the degree of local oxidation. [Copyright &y& Elsevier]

High-energy shot peening (HESP) was employed to obtain a nanocrystalline surface layer in Ti–6Al–4V alloy with bimodal and lamellar structure. The microstructure and residual stress after HESP treatment were characterized by transmission electron microscope (TEM) and X-ray diffractometer (XRD), respectively. The fracture morphology of fatigue was analyzed by scanning electron microscope (SEM). The results showed that the average grain sizes of Ti–6Al–4V alloy with bimodal and lamellar structure were 18.9 nm and 17.1 nm at the topmost surface layer, respectively. The maximum compressive residual stress of the bimodal structure was −906MPa, which was higher than that of the lamellar structure (−859 MPa). The fatigue limits of the HESP-treated Ti–6Al–4V alloy with the bimodal and lamellar structure were increased by 13.5% and 32.8%, respectively. Finally, a Goodman equation was employed to calculate the local fatigue strength and analyze the residual stress-fatigue strength correlation. Highly defected substructure, reduced effective slip length and improved yield strength were important factors for the improvement of fatigue strength. The synergy effect of surface gradient nanostructure and compressive residual stress improved the fatigue limit of the HESP-treated Ti–6Al–4V alloy with bimodal and lamellar structure. [ABSTRACT FROM AUTHOR]

In the present work, strain-controlled low cycle fatigue (LCF) tests were performed at 704 °C using 0.25 Hz in cyclic frequency with tension-compression loading on the forged alloy 718Plus to investigate the fatigue performances determined by structures, and the corresponding microstructure evolutions and deformation mechanisms were analyzed through techniques of scanning electron microscope (SEM) and transmission electron microscope (TEM). The fatigue specimens from different locations (core and rim) showed similar response on cycle stress, but smaller grain size contributed to superior fatigue performance. Fatigue deformation induced the generation of η precipitates in grain interior and promoted the growth of grains and η precipitates, but brought insignificant change on the morphology of spherical γ′ phase and slightly increase in particle size and γ′/γ lattice misfit, indicating its excellent mechanical stability at 704 °C. A transition area was observed between the η precipitates and γ matrix, which was determined to be γ phase via high resolution transmission electron microscopy (HRTEM) and elements mapping techniques. Twinning and dislocation planar slip bands were confirmed to be the primary fatigue deformation modes of alloy 718Plus. Dislocations piled up and formed networks at the edges of η precipitates during the fatigue process, inducing the initiation and propagation of micro-cracks. As the cycle accumulated, the η and γ′ precipitates were sheared by gliding dislocations, resulting in weakened resistance to deformation and fatigue softening. [ABSTRACT FROM AUTHOR]

The mechanical properties and fatigue strength of titanium–aluminide (TiAl) alloys are sensitive to the environmental conditions, such as temperature, and their microstructures can be controlled by thermomechanical processing. In this study, two samples of a forged TiAl alloy were manufactured through high-temperature forging followed by different heat treatments to obtain a near-lamellar microstructure and a triplex microstructure, which contains lamellar and equiaxed γ and β grains. The fatigue crack propagation tests were conducted under isothermal low-cycle fatigue (LCF) and the out-of-phase type thermomechanical fatigue (OP-TMF) conditions. The experimental results indicated that the microstructure strongly affects the crack propagation behavior because the near-lamellar microstructure had a higher resistance to fatigue crack propagation compared to the triplex microstructure. This also revealed that the fatigue crack was remarkably accelerated by the OP-TMF conditions compared to the LCF conditions. The oxygen diffusion into the β phase occurred at the crack tip and lead to the transformation of the β phase into the brittle α phase. The results of the scanning electron microscope (SEM), energy dispersive X-ray (EDX), and electron backscatter diffraction (EBSD) analyses indicated that this transformation induced the acceleration of crack propagation under the OP-TMF loading conditions. [ABSTRACT FROM AUTHOR]

Slip/twinning activity and theoretical critical shear strengths (τ max) during room-temperature tensile deformation of as-extruded pure Mg and Mg-1wt.%Y sheets were investigated quantitatively via electron back-scattered diffraction (EBSD), scanning electron microscope (SEM) and first-principles calculation. Slip trace analysis results indicated the relative frequency of the active slip modes transformed from basal slip (100%) for pure Mg, to basal slip (84.8%), prismatic slip (9.7%) and pyramidal slip (5.5%) for the alloy. The proportion of grains containing twins reduced significantly from 20.5% to 5.92% with Y addition. To explain the mechanism for the enhancement of the non-basal slip activity in Mg–Y alloy, the critical resolved shear stress of basal slip and pyramidal II slip were assessed by calculating τ max. The calculated results showed that the τ max ratio of the pyramidal II slip to basal slip decreased from 13.7 to 7.5, which may be responsible for the observed enhanced activity of non-basal slip. [ABSTRACT FROM AUTHOR]

The mechanical properties of Al-Zn-Mg alloys via multi-stage aging treatments were studied to explore the strength-toughness trade-off. The microstructures of aged alloys were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results indicated that large numbers of GP zones and some part of η′ phases were formed during the low-temperature (90 °C) aging at the third-stage aging, which consumed considerable solid solubility. This prevents fast growth and coarsening of precipitates at the fourth-stage aging (150 °C). Finally, the mixed precipitation state of mainly η′ phases and some η phases formed. The grain boundary phase grew insignificantly, which is beneficial to decrease the strength gap between intragranular and grain-boundary. The intragranular equilibrium η phase is beneficial to pin the movement of dislocation, which avoids fracture caused by accumulation of dislocations around the large second-phase and on the grain boundaries. Although the strength of materials decreased slightly, the impact toughness of materials significantly increased due to the positive effect of the intragranular equilibrium η phase. Compared with the conventional retrogression and re-aging (RRA) treatment (120 °C/24 h + 185 °C/105min + 120 °C/12 h), the designed four-stage ageing treatment (FSA) (120 °C/24 h + 185 °C/105min + 90 °C/12 h + 150 °C/12 h) resulted in the decrease of tensile strength and yield strength by only 3% and 4%, respectively, but contributed to the increases of elongation and impact toughness by 15% and 17%, respectively. [ABSTRACT FROM AUTHOR]

In this study, the plastic flow and ductile fracture of three 6000-series aluminium alloys commonly used for crash components in the automotive industry are characterised experimentally and the observations are related to microstructural features. The three alloys are used in the cast and homogenised condition after artificial ageing to temper T6 to ensure isotropic behaviour. Tension tests on smooth and notched axisymmetric specimens are carried out to reveal the stress–strain behaviour, ductility and fracture mechanisms of the materials for different stress states. Through the use of optical and scanning electron microscopes, the initial microstructure of the alloys and the fracture surfaces of the tension test specimens are investigated. The work-hardening of the alloys is analysed up to large strains. Whereas the ductility of two of the alloys falls into the trend of previous experimental data on 6000-series aluminium alloys, where the strain to failure decreases linearly with increasing yield stress, the third alloy stands out by combining high strength with high ductility. The excellent properties of the latter alloy are assumed to be due to a favourable size distribution of constituent particles. [ABSTRACT FROM AUTHOR]

In this paper, Ti–6Al–4V alloy was fabricated by selective laser melting (SLM) with different build orientations, namely SLM-1 and SLM-2, respectively. Microstructures of SLM-1 and SLM-2 were characterized by X-ray diffraction, optical microscope, scanning electron microscope and transmission electron microscope. The results show that the α and α′ phases in the hexagonal close-packed (hcp) structure, as well as the residual β phase in the body centered cubic (bcc) structure, exist in both samples. However, different SLM build orientations led to varied cooling rates and α/α′ ratios in the final materials. The SLM-1 alloy with build orientation along its thickness direction had higher cooling rate and thus lower α/α′ ratio than the SLM-2 alloy with build orientation along the length direction. Besides, minor martensitic (α'') phase was observed in the SLM-1 alloy and acted as an intermediate phase between β and α′ phases. The low α/α′ ratio and existence of α'' phase in the SLM-1 alloy result in a relatively high tensile strength but deteriorated plasticity. Comparatively, the higher α/α′ ratio in the SLM-2 alloy without α'' martensite leads to a much better plasticity regardless of the slightly reduced tensile strength. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a promising additive manufacturing technique with growing acceptance in aerospace applications. In this work, a new aeronautical material of near-α Ti alloy (TA15) for SLM was firstly investigated and analyzed before and after annealing, mainly including mechanical properties, microstructural evolution. The distinctions between SLMed TA15 and wrought TA15 are also discussed in this study. Firstly, near full density TA15 samples (99.98%) were fabricated by SLM utilizing the optimized processing parameters. Then microstructures and textures are characterized and analyzed by optical microscope, X-ray diffractometer, scanning electron microscope and transmission electron microscope. Furthermore, mechanical properties of TA15 samples are measured via tensile and hardness test, considering the impacts of building direction. The results show that both the as-built and the annealed SLMed samples exhibit significantly weak textures and unconspicuous anisotropy of mechanical properties. It has been identified that αʹ martensite is dominant in the as-built microstructure thus contributing to ~1296 MPa in ultimate strength and ~398 HV in hardness which are 35% and 24% higher than those of wrought material. However, a low plasticity with ~7.6% of elongation at break was observed. After annealing, SLMed samples exhibited excellent comprehensive mechanical properties with 51% improvement at elongation through elimination of residual stress and precipitation of nanometer size β phase in the fine basket-weave structure. [ABSTRACT FROM AUTHOR]

The Mg–1Al– x Y (x = 3, 5, 8) alloys were prepared by melting technology and extruded at 400 °C. Microstructures of the alloys were investigated by X-ray diffraction (XRD), optical microscope (OM), and scanning electron microscope (SEM). Tensile properties of the alloys were measured. The results showed that the as-extruded Mg–1Al– x Y (x = 3, 5, 8) alloys were composed of α-Mg phase and Al 2 Y phase and the microstructures were main dynamic recrystallization. The eutectic Al 2 Y phase was broken down to finer particles and dispersed more uniformly after the extrusion. The extruded alloys have (0002) basal plane texture. The tensile strength, yield strength and elongation of Mg–1Al–8Y alloy were 288 MPa, 174 MPa and 20% at room temperature, respectively. Therefore, the alloys have good mechanical properties and the fracture morphology with ductile features. [ABSTRACT FROM AUTHOR]

In this work, the effects of shear-resistant plate-shaped θ′ (Al 2 Cu) precipitates on mechanical performance and fracture behavior of a heat-treatable Al–Cu alloy were studied. The precipitates, dislocations and micro-voids around grain boundaries were observed using transmission electron microscope and scanning electron microscope equipped with electron backscatter diffraction. The Al–Cu alloy was overaged to ensure that the θ′ phase was the only precipitate in the material. The results show that concentration of local strain and pile-up of dislocations occurred along grain boundaries during tensile deformation. A method was developed to calculate the total dislocation density nearby the grain boundaries in the deformed alloy, from which a quantitative relation was established between precipitate number density and void areal density on intergranular fracture surface. The effect of precipitates on the mechanical properties of Al–Cu alloy was also discussed qualitatively. The precipitate number density of the over-aged Al–Cu alloy acted as the dominating factor that influenced the dislocation density and void density on grain boundaries, which thus determined the mechanical properties and fracture behaviors of the alloy. [ABSTRACT FROM AUTHOR]