Main Strengthening Mechanisms Research Articles

Microstructure, mechanical properties and interfacial features of graphene oxide reinforced 7075 composites fabricated by ultrasonic assisted casting

Graphene oxide reinforced 7075 (GO/7075) composites were successfully prepared via ultrasonic assisted casting. In this study, the microstructure, mechanical properties and interfacial structure of GO/7075 composites with varying GO contents were investigated. The experimental results showed that GO could refine grain size and produce many dislocations at the GO/Al interface, and was well bonded with Al matrix. Meanwhile, a few rod-like Al4C3 phases were observed at the active prism planes of GO in the composite. When the content of GO reached 1.0 wt%, the optimal mechanical properties of GO/7075 composites were obtained. The yield strength and ultimate tensile strength of 1.0 wt% GO/7075 composites were 212.3 MPa and 285.6 MPa, which were 61.8 % and 41.1 % higher than those of 7075 alloy, respectively. The thermal mismatch strengthening and load transfer strengthening were the main strengthening mechanisms. Moreover, in order to control the interfacial reaction between GO and Al matrix, the thermodynamic/kinetic condition and growth mechanism for the formation of Al4C3 were analyzed in details.

Microstructure and Mechanical Properties of Mg-Al-La-Mn Composites Reinforced by AlN Particles

The Mg-Al-RE series heat-resistant magnesium alloys are applied in automotive engine and transmission system components due to their high-temperature performance. However, after serving at a high temperature for a long time, the Al11RE3 phase coarsened and even decomposed, while the Mg17Al12 phase grew and dissolved, which limits the service temperature of Mg-Al-RE series heat-resistant magnesium alloys to a maximum of 175 °C. In this study, a new preparation method for in situ AlN particles was presented. The AlN/Mg-4Al-4La-0.3Mn composites were prepared by a master alloy and casting method. The effects of various contents of AlN (0.5–3.0 wt.%) on the microstructure and mechanical properties of the Mg-4Al-4La-0.3Mn (AE44) alloy at room (25 °C) and high temperatures (150–250 °C) were investigated. Microstructure analysis revealed that the inclusion of AlN led to a reduction in both the grain size and second phase size in the AE44 alloy, while also improving the distribution of the second phase. The average grain size, Al11La3 phase, Al2La phase, and Al3La phase of the 2.0 wt.% AlN/AE44 composite were 135.7, 9.6, 1.9, and 12.6 μm, respectively, which were significantly lower than those of the AE44 matrix alloy (179.8, 12.6, 3.3, 17.8 μm). The refinement was attributed to the ability of AlN particles to serve as heterogeneous nucleation cores for α-Mg and, at the same time, impede the growth of the solid–liquid interface, eventually leading to grain refinement. With the increase in the AlN content, the mechanical properties of composites initially exhibited an increase at both room and high temperatures, followed by a subsequent decrease. When the AlN content was 2.0 wt.%, the composite exhibited optimal strength and plasticity matching. At room temperature, the TYS, UTS, and EL values of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite were 96 MPa, 175 MPa, and 7.0%, respectively, which were increased by 26 MPa, 27 MPa, and 0.7% when compared with the base alloy. The TYS of the 2.0 wt.% Mg-4Al-4La-0.3Mn composite at 150 °C, 200 °C, and 250 °C were 17 MPa, 14 MPa, and 22 MPa higher than those of the matrix alloy, respectively. The main strengthening mechanisms were second phase strengthening, load transfer strengthening, and thermal mismatch strengthening. At elevated temperatures, AlN particles effectively pinned the grain boundaries, inhibiting their migration, and hindered dislocation climbing, resulting in excellent mechanical properties of the composites at high temperatures. This study contributes to the advancement of in situ AlN particle preparation methods and the exploration of effects of AlN on the properties and microstructure of Mg-Al-RE alloys at high temperatures (150–250 °C).

Optimizing strength and electrical conductivity of 6201 aluminum alloy wire through rotary swaging and aging processes

Age-hardened 6201 aluminum alloy wires utilized in high-voltage transmission lines need to have high strength, high conductivity and high ductility. However, simultaneously obtaining high values for the above three parameters remains a challenge, as there are trade-off relationships between strength and ductility, strength and conductivity. In this article, we employed solid solution, under-aging and peak-aging treated 6201 aluminum alloys as initial samples, then performed rotary swaging (RS) on them equally and subsequent aging at different temperatures. Performance testing found that RS plus aging improved the strength and conductivity of all three samples. The best combinations of electrical conductivity and ultimate tensile strength are 50.6 %IACS and 363 MPa, 51.7 %IACS and 352 MPa, which were obtained through under-aged (550 ℃/3 h + 175 ℃/2 h) + RS + re-aging (160 ℃/4 h) and peak-aged (550 ℃/3 h + 175 ℃/8 h) + RS + re-aging (160 ℃/4 h). Quantitative analysis show that precipitation strengthening is the main strengthening mechanism, contributing about 50 % of the yield strength. Grain boundary strengthening and dislocation strengthening contribute comparable amounts of 25 % and 20 %, respectively. The theoretical model can well predict the yield strength of RSed Al alloys based on the microstructure. The conductivity increase was caused mainly by the precipitation of solid solutions and fiber grain boundaries. In addition, RS reduced the tensile ductility to 6–10 % and subsequent aging regain it up to 10–13 % due to decrease of dislocation density and precipitation hardening. Our results indicate that high strength, high conductivity and high ductility of aging-hardened alloys can be achieved through optimizing deformation and aging processes.

Unveiling the Stacking Fault-Driven Phase Transition Delaying Cryogenic Fracture in Fe-Co-Cr-Ni-Mo-C-Based Medium-Entropy Alloy.

In this work, the tensile deformation mechanisms of the Fe55Co17.5Cr12.5Ni10Mo5-xCx-based medium-entropy alloy at room temperature (R.T.), 77 K, and 4.2 K are studied. The formation of micro-defects and martensitic transformation to delay the cryogenic fracture are observed. The results show that FeCoCrNiMo5-xCx-based alloys exhibit outstanding mechanical properties under cryogenic conditions. Under an R.T. condition, the primary contributing mechanism of strain hardening is twinning-induced plasticity (TWIP), whereas at 77 K and 4.2 K, the activation of martensitic transformation-induced plasticity (TRIP) becomes the main strengthening mechanism during cryogenic tensile deformation. Additionally, the carbide precipitation along with increased dislocation density can significantly improve yield and tensile strength. Furthermore, the marked reduction in stacking fault energy (SFE) at cryogenic temperatures can promote mechanisms such as twinning and martensitic transformations, which are pivotal for enhancing ductility under extreme conditions. The Mo4C1 alloy obtains the optimal strength-ductility combination at cryogenic-to-room temperatures. The tensile strength and elongation of the Mo4C1 alloy are 776 MPa and 50.5% at R.T., 1418 MPa and 71.2% in liquid nitrogen 77 K, 1670 MPa and 80.0% in liquid helium 4.2 K, respectively.

Precipitation behavior of supersaturated solid-solubility CuCrZr alloy by additive manufacturing

As a typical precipitation-strengthened alloy, the improvement of CuCrZr alloy performance can be achieved by promoting the precipitation of alloying elements. However, the low solubility of Cr limits further enhancement of the performance of conventionally processed CuCrZr alloys. In this study, a supersaturated solid solution CuCrZr alloy was prepared using laser powder bed fusion (LPBF), and the precipitation of solute atoms was promoted through heat treatment, resulting in an alloy with excellent comprehensive performance. The influence of different heat treatment processes on the precipitation behavior and performance of the alloy was investigated. Microstructural analysis revealed the presence of micrometer-scale Cr particles in the specimens after solution treatment (ST) and solution-aging treatment (SAT), while the direct-age-hardening (DAH) specimen exhibited dispersed nanoscale Cr precipitations. Notably, a Nishiyama-Wassermann (N-W) relationship was observed between the Cr precipitations and the Cu matrix, significantly enhancing the mechanical properties of the alloy. The DAH specimen exhibited an ultimate tensile strength (UTS) of 661.54 MPa, a hardness of 231.03 HV and an electrical conductivity of 65.05 % IACS, demonstrating the best match between mechanical properties and electrical conductivity. The outstanding properties can be credited to the uniformly distributed Cr nano-precipitates and slim lattice distortion. Additionally, the main strengthening mechanism is precipitation strengthening for CuCrZr alloy.

γʹ and γ″ co-precipitation phenomena in directly aged Alloy 718 with high δ-phase fractions

Co-precipitation of γ′ and γ′′ is the main strengthening mechanism that provides superior high-temperature strength in directly aged Alloy 718 aerospace parts. Control of their morphology, fraction, and configuration might allow exposure to more demanding operation environments in next-generation aircraft engines. The density of geometrically necessary dislocations introduced during hot deformation has been shown to significantly affect the co-precipitate morphology of γ′ and γ′′ in materials free of the δ-phase. However, the combined effects of geometrically necessary dislocation density and lower Nb content due to higher δ-phase fractions on co-precipitation behaviour and strengthening remain unknown. We verify these effects by hardness testing as a proxy for high-temperature strength in materials with 4.1 % δ-phase fraction. Deformation at 950 °C yields a remarkable increase of 12 % in hardness after direct ageing, explained by the prevalence of complex co-precipitate configurations. Deformation at 1000 °C decreases the δ-phase fraction and geometrically necessary dislocation density but achieves up to 19 % volume fractions of γ″, leading to a predominance of monoliths and duplet co-precipitates and a better direct ageing response. Atom probe microscopy reveals the flux of elements during co-precipitation. We recommend a δ-annealing treatment before the final forging step for manufacturing stronger Alloy 718 aerospace parts.

Phase transformation and strengthening of the gas-atomized FeCoCrNiMo0.5Al1.3 high-entropy alloy powder during annealing

Phase evolution and strengthening of the FeNiCoCrMo0.5Al1.3 powder alloy produced via inert gas atomization and annealed in the temperature interval of 300–800 °C have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and microhardness testing. It was found that annealing at 300–600 °C leads to an increase of the element segregations between the several solid solutions with a rise of the lattice misfit (ε) to 1.5 % and microhardness growth to 1070 HV. It was assumed that elastic stress caused by the element partitioning is the main strengthening mechanism: microhardness rises linearly with misfit rise with dHV/dε = 43400 MPa. Sigma arises after the maximum elastic deformation (in 1.5 %) was reached. Formation of the dispersed coherent sigma phase in the annealing interval 600–800 °C results in the microhardness rise. Oxidation that began at 800 °C in 27 h is accompanied with FCC formation due to a depletion of the B2 in Al caused by Al2O3 formation. Estimation of the activation energy of the initial stage of the solid solution decomposition gives a very low value in 0.65eV, apparently caused by the high concentration of quenched vacancies. The activation energy of sigma formation approximately coincides with the activation energy of self-diffusion in BCC metals (about 2.60 eV).

Microstructure and mechanical properties of ultra-light Mg[sbnd]8Li[sbnd]3Al[sbnd]2Zn[sbnd]0.5Y alloy manufactured by directed energy deposition-Arc

The ultra-light Mg8Li3Al2Zn0.5Y (LAZ832–0.5Y) thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding (GTAW) in this study. The microstructure of the top, middle and bottom regions of the thin wall fabricated under various conditions was examined and the mechanical properties of these thin walls were tested. The results showed that much finer microstructure was obtained by GTAW than that made by conventional casting method. In the as-deposited samples, the needle-like shaped α-Mg phase emerged at the top of the thin wall whereas the bar-shaped α-Mg phase showed up in the middle and bottom regions of the thin wall due to the complex thermal history. The Al2Y phase was dispersed throughout both α-Mg and β-Li while the AlLi phase was mainly located in the β-Li. The best combination of ultimate tensile strength (UTS), yield strength (YS) and elongation to fracture of the as-deposited thin wall were 218.9 MPa, 171.4 MPa and 20.9%, respectively, which was manufactured under the optimal condition of 120 A 1800 mm/min 220 mm/min. After solid solution treatment at 350 °C for 4 h, the UTS increased slightly by 13% but the YS increased significantly by 65% compared with the samples before solid solution. The solution of the AlLi phase was believed to be the main strengthening mechanism. It is interesting to note that the UTS and YS of the as-deposited sample was better than those of the as-cast sample while the opposite situation took place after solid solution treatment.

Excellent strength-toughness combination of NiAl–30Cr composites with novel in situ composite microstructure containing NiAl matrix and Cr single-phase

Lightweight NiAl alloys are expected to replace high-density nickel-based superalloys, but their mechanical performance needs to be improved. In this work, NiAl–30Cr composites with a novel heterogeneous microstructure composed of fine NiAl matrix and Cr single-phase was successfully prepared. Nanoscale Cr particles with 15 nm in size precipitated in NiAl matrix are coherent with NiAl matrix owing to very low interplanar and interatomic spacing mismatch. Such a composite microstructure makes NiAl–30Cr exhibit high strength and high toughness. The yield strength (1207 MPa), ultimate compressive strength (2307 MPa), product of strength and plasticity (29.3 GPa%), and fracture toughness (10.76 MPa m1/2) of NiAl–30Cr increased by 96.6%, 85.6%, 55.1% and 19.7% respectively at room temperature compared to the corresponding ones of NiAl. At 1000 °C, the yield strength (144 MPa) of NiAl–30Cr was 85.9% higher than that of NiAl. Solution strengthening and precipitation strengthening were the key strengthening mechanisms at room temperature. The enhancement in toughness was attributed to grain refinement, increased crack propagation paths, weakened Ni–Al covalent bonding and coordinated deformation of Cr single-phase and NiAl matrix. By contrast, the main strengthening mechanism at 1000 °C is the solid solution Cr atoms hindering dislocation climbing and the stable interface bonding between the Cr nanoprecipitation phase and the NiAl matrix. This work provides new ideas for preparing high-strength and tough NiAl alloy.

Effects of Zn and Gd contents and their ratios on microstructure and mechanical properties of as-cast and as-extruded Mg−8Li alloys

The effects of contents of Zn and Gd elements and their mass ratios on microstructure and mechanical properties of as-cast and as-extruded Mg−8Li alloys were investigated. After extrusion, the precipitates are broken, and fine spherical particles with size about 100 nm are found to disperse in the β-Li. The bi-modal structure consisting of long-strip-like coarse-grain α-Mg and recrystallized fine-grain β-Li is formed. The strength and plasticity of the alloys are greatly improved after extrusion, and the YS and UTS increase with the increase of Zn and Gd contents. The Mg−8Li−8Zn−2Gd alloy exhibits an optimum comprehensive performance with the YS of 274 MPa, UTS of 283 MPa, and EL of 39.9%. The bi-modal structure strengthening consisting of the fine crystal strengthening of β-Li and texture strengthening of α-Mg, and the dispersion strengthening of precipitations are the main strengthening mechanisms.

Improving mechanical performance of heat-resistant eutectic Al-Fe-Ni alloy by in-situ TiB2 particles

The mechanical performance and strengthening mechanism of in-situ TiB2 ceramic particles reinforced eutectic Al-Fe-Ni alloy were researched. The smaller-sized TiB2 particles are uniformly distributed inside the grain and larger-sized particles tend to gather at the eutectic grain boundary. The hardness and room temperature tensile tests show that TiB2 particles improve the comprehensive mechanical properties of the eutectic alloy. Meanwhile, the high temperature tensile strength of eutectic alloys is also enhanced by particles. The pinning effect of TiB2 particles on dislocation and eutectic boundary are the main strengthening mechanisms. The study on the microstructures and properties of TiB2 particles reinforced eutectic alloys provides guidance for enhancing the mechanical performance of eutectic Al alloys.

Laser Powder Bed Fusion of GH4099 Superalloy: Parameter Optimization and Effect of Heat Treatment on Microstructure and Mechanical Properties

Ni-Cr-Co-W superalloy (GH4099) can be used to manufacture high-temperature structural components of aero-engine combustion chambers for long-term service below 900 °C. This study provides a comprehensive evaluation of the GH4099 superalloy fabricated using the laser powder bed fusion (LPBF) technique, focusing on the optimization of processing parameters and a systematic investigation of the microstructural evolution and mechanical properties of the as-deposited and heat-treated samples. An optimal parameter combination was established using the response surface method (RSM) design and the variance method. The as-deposited GH4099 alloy is primarily composed of columnar crystals grown epitaxially and M23C6 carbides without the generation of the γ′-phase. After solution treatment, recrystallization and grain growth occurred, with the alloy remaining as large, irregularly shaped polygonal columnar crystals. The aging process precipitated substantial γ′-phase, which internally existed as a mixture of equiaxed and columnar crystals. LPBF-GH4099 superalloy exhibited a maximum room-temperature tensile strength of 1137.80 MPa and a high-temperature tensile strength of 780 MPa at 800 ℃. Various strengthening mechanisms were observed in the as-deposited and heat-treated samples. The most significant grain boundary strengthening effect was observed in the deposit state, while solution strengthening was primarily due to the segregation of elements, such as Mo, W, and Cr, in the γ matrix. Precipitation strengthening, predominantly due to the γ′-phase, emerged as the main strengthening mechanism for the GH4099 superalloy post-aging treatment. This study presents significant insights into the LPBF-GH4099 alloy and provides a solid foundation for future studies and practical applications in this field.

Effects of cold deformation and aging on the phase transformation and mechanical properties of a Cu-15Ni-8Sn alloy

A Cu-15Ni-8Sn alloy ingot was prepared in a medium-frequency induction melting furnace. First, the hot extruded alloy was subjected to solution treatment at 840 °C for 60 min, after which cold drawing treatment was applied under different deformation conditions (0–70%). Finally, the cold-deformed alloy was subjected to aging at different temperatures (340–520 °C) and insulation times (0–480 min). The evolution of grain characteristics, micromorphology and mechanical properties during cold drawing deformation and aging were systematically studied. The results show that during cold drawing deformation, the grains in the solid solution Cu-15Ni-8Sn alloy gradually elongate along the drawing direction with increasing deformation, and the texture changes from a discrete distribution to a hard orientation. Cold drawing deformation promoted coarsening of the modulated structure and the transition of the D022 ordered phase. Dislocations and twins increased the occurrence of nucleation for the discontinuous precipitates and promoted the growth of the discontinuous precipitates, but cold deformation inhibited the transition of the D022 ordered phase to the L12 ordered phase. The hardness, tensile strength and elongation of the Cu-15Ni-8Sn alloy after 50% cold deformation were 109.2 HRB, 1258.3 MPa and 7.5%, respectively, after aging at 400 °C for 60 min. The main strengthening mechanisms of the peak-aged alloy were precipitation strengthening and dislocation strengthening.

Effects of different mass ratios on mechanical properties and impact energy release characteristics of Al/PTFE/W and Al/PTFE/CuO polymer composites

AbstractAluminum/polytetrafluoroethylene (Al/PTFE) is an impact‐initiated material that is extensively utilized in military and civilian applications due to its insensitivity, high energy density and ease of manufacturing. To increase both its compressive strength and energy density, Al/PTFE was doped with various amounts of W and CuO particles. These polymer composites exhibit elastoplastic properties, as well as significant strain hardening and strain‐rate hardening during compression deformation. At a strain rate of 5000 s−1, the compressive strength of the Al/PTFE/W and Al/PTFE/CuO specimens with an additive content of 30% reaches a peak of 194.1 and 189.2 MPa, which corresponds to an increase of 40.3% and 36.8%, respectively, compared with the compressive strength of Al/PTFE (138.3 MPa). The homogeneous bonding strength between the additives and PTFE and the fact that the elastic PTFE nanofibers inhibit the extension of microcracks are the main mechanical strengthening mechanisms. The reaction of the composites under high‐speed impact is violent and accompanied by sputtering sparks, and the reaction efficiency was determined using an improved drop‐hammer apparatus. As the W content increases, the impact reactivity of Al/PTFE/W decreases monotonically. However, as CuO content increases, the reaction intensity of Al/PTFE/CuO initially increases, and then decreases. At a CuO content of 30%, the energy release efficiency of Al/PTFE/CuO reaches its maximum (10.49%), which is 84.4% higher than that of Al/PTFE. TG‐DSC and XRD tests were performed to analyze the pyrolysis process and elucidate the reaction mechanism. A gas–solid chemical reaction model was developed, and the reactivity arises from multiple factors.Highlights Typical elastoplastic characteristics as well as strain hardening and strain‐rate hardening were observed. The mechanical strengthening effect of W particles is higher than that of CuO particles of Al/PTFE specimen. The addition of W particles decreases the impact reactivity, but the addition of CuO particles improves the energy density of Al/PTFE. The reaction efficiency of Al/PTFE/CuO reaches a peak of 10.49%, which increased by 84.4% compared with that of Al/PTFE.

Enhanced Yield Strength and Total Elongation of an Ultrahigh Strength Hot‐Stamped Steel via Tempering Treatment

A 2460 MPa ultimate tensile strength (UTS) has been achieved in this experimental steel, which was processed by a conventional hot stamping process with water quenching to room temperature. Additionally, comparing the microstructure evolution and strengthening mechanism before and after tempering, the microstructure has changed from fresh martensite transformed into tempered martensite with acicular carbides, and the fracture mode has also changed from brittle fracture transformed into ductile fracture mainly. Meanwhile, the main strengthening mechanism has changed from dislocation strengthening to precipitation and dislocation strengthening. Overall, the tempering process reduces dislocation density and produces acicular carbides, which decrease UTS. However, the tempering process reduces the quenching residual stress and changes the morphology of twin martensite, resulting in an increase in ductility. Meanwhile, it enhances the effect of carbide pinning dislocations, significantly enhances precipitation strengthening, and improves yield strength.

Composition and Element Distribution Mapping of γ' and γ″ Phases of Inconel 718 by High-Resolution Scanning Transmission Electron Microscopy and X-ray Energy-Dispersive Spectrometry.

The main strengthening mechanism for Inconel 718 (IN718), a Ni-based superalloy, is precipitation hardening by γ' and γ″ particles. It is thus essential, for good alloy performance, that precipitates with the desired chemical composition have adequate size and dispersion. The distribution of the γ' and γ″ phases and their chemical composition were investigated in the nickel-based Inconel 718 superalloy by taking advantage of the new capabilities of scanning transmission electron microscopy and energy-dispersive X-ray spectrometry using a windowless multiple detector, a high-brightness Schottky electron gun, and a spherical aberration corrector in the illumination probe optics. A small routine was developed to deconvolute the respective compositions of γ' and γ″ nanoprecipitates embedded in the γ matrix. Keeping the electron probe current low enough-a few hundred pA-prevented excessive irradiation damage during the acquisition of element maps and brought their spatial resolution down to the atomic column level to track their element compositions. The present results agree with and complement atomic probe tomography observations and Thermo-Calc predictions from the literature. The presence of an Al enrichment at the γ'/γ″ interface-which may control the γ″ phase coarsening-is observed in the last row of Al-Nb-Ti columns along this interface. In addition, a few columns with similar composition changes are found randomly distributed in the γ' phase.

Correlation between microstructure, mechanical properties, and slurry erosion behavior of hot-rolled dual-phase steel

A low alloy dual-phase steel was produced via a thermo-mechanical control process to improve production efficiency and reduce costs. The study investigates the influence of martensite volume fractions on the mechanical properties and slurry erosion behavior of the hot-rolled dual-phase steel, and the correlation between the mechanical properties and slurry erosion behavior was revealed to provide insights into the material's wear resistance. Microstructure of dual-phase steel with varying martensite were characterized, and nanohardness, Vickers hardness, tensile propertiy, and slurry erosion were tested. Result indicates that martensite content significantly affects the mechanical propertiy of the hot-rolled dual-phase steel. Hardness and strength increase with increased martensite content, exhibiting a linear relationship. The main strengthening mechanisms are dislocation and solid solution strengthening. Slurry erosion result reveals that matrix hardness, martensite content/size, and work hardening ability significantly impact the slurry erosion performance of hot-rolled dual-phase steel. Martensite plays a crucial role in resisting wear failure, with higher content and larger size providing better protection to the soft ferrite and reducing erosion weight loss. Work hardening ability also leads to a decrease in periodic erosion weight loss.

Strengthening mechanisms and wear performance of Al/APC/micro-B4Cp hybrid composites prepared by HTCDC process and hot extrusion

An Al/APC/micro-B4Cp hybrid composites were fabricated using the hydrothermal carbonized deposition on chips (HTCDC) process and hot extrusion process. The microstructure and mechanical properties and wear resistance of the Al/APC/micro-B4Cp hybrid composites were characterized. APC spheres and irregular micro-B4Cp could be observed on the Al chips surface after the HTCDC process, and the micro-B4Cp were also coated with an APC film. Al/APC/micro-B4Cp hybrid composites were prepared by hot extrusion from the Al chips covered with APC and micro-B4Cp. With the increase of micro-B4Cp content, the α-Al grain sizes of composites decrease from 18.8 µm to 12.8 µm, because the dispersed micro-B4Cp in the composites can pin the grain boundaries, hinder the migration of grain boundaries, and inhibit the growth of recrystallized grains. The highest values were obtained when the micro-B4Cp content was 3 wt%, and the UTS and hardness values of Al/APC/B4Cp hybrid composites (223.66 MPa and 101.8HV) were increased by 14.07% and 24%, respectively, compared with Al/APC composite. The results of the YS calculation show that thermal mismatch strengthening is the main strengthening mechanism, followed by grain-refined strengthening, and load transfer strengthening. Because the APC of the self-lubricating effect can form a lubrication film on the wear surface during sliding, the COF and wear rate of the Al/APC composite are low. When the micro-B4Cp is added to the matrix, the micro-B4Cp will strip the APC film from the wear surface, so the COF increases. However, the addition of micro-B4Cp can greatly increase the hardness of the composite, as a consequence that the wear rate of the composite material is still low(1.44 ×10−5 mm3/Nm).

Strengthening mechanism and precipitation behavior of advanced ultrahigh-strength titanium microalloy weathering steels for photovoltaic support

This study developed an 800 MPa grade ultrahigh-strength titanium microalloy weathering steel for photovoltaic support with yield and tensile strengths of 869 MPa and 956 MPa, respectively, and elongation above 12%. A comprehensive analysis was conducted to reveal the strengthening mechanisms and precipitation behavior of ultrahigh-strength weathering steel. The results illuminated that grain refinement, dislocation, and precipitation strengthening contribute 70.7% of total yield strength, the main strengthening mechanism of the ultrahigh-strength weathering steel. Notably, the average size of the elliptical TiC particles was 6.9 nm, and a long-to-short axis ratio of TiC particles ranging from 1.62 to 2.03 aligned with the theoretical shape factor of 2.16. The thermodynamic calculations agree with the experimental results, and the precipitated phase can be regarded as TiC. The precipitation kinetics indicated that optimal finishing rolling and coiling temperatures (CT) are critical for obtaining many nano-sized TiC precipitates. Compared to the CT of 630 °C, 570 °C retains more dislocations, promotes the nucleation site of TiC precipitates, and slows the post-nucleation coarsening, which is the main reason for the higher precipitation and dislocation strengthening than 630 °C. The first observation of multi-atomic layer GP clusters near precipitated phases within the ultrahigh-strength titanium microalloy weathering steel was noteworthy. The GP clusters, acting as intermediate precipitates containing Ti precipitates, keep a co-lattice relationship with the iron matrix by the dislocations around the GP clusters adjusting the mismatch. The contribution of the interaction of GP clusters and dislocations to the yield strength was estimated to be ∼53 MPa.

The synergetic effect of TaC particles and Re alloy on microstructure and mechanical properties in tungsten alloy

TaC enhancement particles and Re alloy were used to improve the strength and ductility of the tungsten alloy. The synergetic effect of TaC addition and Re alloying on relative density, microstructure, and mechanical properties of tungsten alloy were investigated. The results indicated that a W-based composite with 2.5 wt% TaC addition and 25 wt% Re alloying exhibited yield stress of 1.23 GPa, the ultimate compressive stress of 2.86 GPa, bending strength of 1.30 GPa and strain capacity of 42 %, which was increased by 114 %, 140 %, 226 %, and 133 % than those of pure W. Further analysis revealed that the grain boundary purification, grain refinement, and kinematic strain gradient contribution because of the addition of TaC, lattice distortion, and the generation of dislocations because of the addition of Re alloying are the main strengthening mechanisms in W–TaC-Re composite.