Al-0.5 wt% GNP nanocomposites with both microcrystalline and nanocrystalline matrices, were synthesized via spark plasma sintering. The strengthening effects of nanocrystalline Al matrix and GNP ...reinforcement have been systematically studied. Nanocrystalline Al compact (without GNPs), in comparison to microcrystalline one, exhibited 57% and 53% improvement in yield strength and ultimate tensile strength. Addition of 0.5 wt% physio-chemically functionalized GNPs in the nanocrystalline Al matrix led to further enhancement in the yield strength and ultimate tensile strength by 85% and 44%, respectively. This is attributed to the homogenous distribution of the functionalized nanometric GNPs with high elastic modulus and strength, resulting in 99% densification. The elastic moduli of the nanocomposites measured by nanoindentation matched well with the values estimated by applying micromechanics models, owing to the very good densification of the nanocomposites. Contributions from different strengthening mechanisms viz. load transfer, grain refinement, CTE mismatch and Orowan strengthening were calculated. Load transfer strengthening mechanism showed highest (73%) contribution in enhancing the strength of the nanocomposite. The mode of failure in microcrystalline Al compact was ductile and changed to mixed mode with the incorporation of GNPs. On the contrary, the Al-GNP nanocomposite with nanocrystalline matrix exhibited completely brittle mode of fracture.
A novel Cu-2.5Fe-0.2Si-0.3Mg-0.3Cr-0.1Zr-0.2Y (wt.%) alloy is designed, which exhibits nice comprehensive properties under multi-stage thermo-mechanical processing, with a conductivity of 57.11 %IACS ...and a tensile strength of 672 MPa. The main secondary phases in the alloy include micron-scale FeCrSi and CuZrY phases, as well as nanoscale precipitate of FeCrSi. Conductivity and strength of the alloy are mainly improved by the precipitation of nanoscale FeCrSi phases, which increases dislocation obstruction and matrix purity. The (220) plane of the precipitate exhibits a 9.5° misfit angle with the (020) plane of the matrix under the 112 FeCrSi zone axis. The formation of low angle grain boundaries (LAGBs) results in significant grain refinement effects. The average grain diameter of the alloy is about 1.58 μm, which is related to the piles-up of dislocations along the boundaries and the different deformability between the micron-scale second phase and the matrix.
•Aging process is an effective strategy for precipitation strengthening and conductivity improvement in Cu–Fe alloy. However, the recrystallization effect eliminates work hardening, texture defects, and stress localization, making it difficult to combine precipitation strengthening with work hardening. Based on this, a novel Cu-2.5Fe-0.2Si-0.3Mg-0.3Cr-0.1Zr-0.2Y alloy is designed.•A low interface energy can be determined by the trace elements, so that recrystallization is hindered and refined crystal is observed.•The primary second phases also have a contribution to the grain refinement as a result of different deformability between the second phases and matrix.•Incoherent but tiny precipitates play a role on dislocation bypass strengthening and improving matrix purity. Tensile strength and electrical conductivity of the final state is 672 MPa and 57.11%IACS.
The effects of fine precipitates on the austenite grain refinement of micro-alloyed steel during cyclic heat treatment were investigated under different solution treatments. After three rounds of ...cyclic heat treatment of Ac3 and Ar3 transformations of the as-received steel rod with rapid heating and cooling, the austenite grain size was 3–10 µm. On the other hand, three rounds of cyclic heat treatment after solution treatment at 1300°C reduced the austenite grain size to 2–5 µm. The as-received sample included AlN–Ti(C,N)–MnS composite particles with a mean diameter of 30 nm and a number density of 11 µm−3, and the mean diameter did not change during cyclic heat treatment. Thus, it was considered that the reduction in austenite grain size without solution treatment was caused by the increase in the nucleation site of austenite phase with increasing number of cycles, due to the refinement of the prior austenite grains with martensitic structure during the cyclic heat treatment. When solution-treated at 1300°C, the AlN–Ti(C,N)–MnS composite particles were solved, and they were precipitated during the cyclic heat treatment with a mean diameter of 12 nm and an increased number density of 85 µm−3. Thus, it was considered that the further reduction in austenite grain size with solution treatment was caused by the pinning effect of the fine precipitates, in addition to the increase in the number of austenite phase nucleation sites with increasing number of heat treatment cycles.
Mn
Al
.
C
.
flakes with different sizes were prepared with two distinct surfactant-assisted ball-milling methods using cylindrical and barrel containers. Different microstructure and magnetic ...properties were measured based on the sequence of the container shape and different ball-milling times (2, 5, and 10 h). Morphology investigations showed that for powders milled in a barrel container, the amount of τ-phase was more compared to the samples milled in a cylindrical container. Moreover, in the powders milled with barrel containers, considerably higher magnetic properties were obtained in terms of saturation magnetization (M
) and remanent magnetization (M
) compared to those powders milled with cylindrical containers. Magnetic properties were found to be a function of the ball-milling time. High remanent magnetization and saturation magnetization have been found for powders milled in barrel containers, whereas only mediocre remanent magnetization and saturation magnetization have been measured in the case of milling in cylindrical containers. The highest M
= 52.49 emu g
and M
= 24.10 emu g
were obtained for the powders milled in barrel containers for 2 h. The higher magnetic properties taken from the milling in barrel containers is due to the higher shear stress and more uniform strain distribution induced by the barrel configuration, resulting in the stable τ-phase at a reasonably low-strain microstructure.
•Precipitation behavior of (Ti, V)C precipitates was elucidated.•(Ti, V)C precipitation can induce the grain refinement after reheating-quenching process.•Ultra-fine austenite grains with the average ...size smaller than 5μm were obtained.•The microstructure transformed from ultra-fine austenite was analyzed.•Excellent mechanical properties were achieved in ultra-fine grained steel.
The precipitation behavior of vanadium-rich carbides formed during the reheating processes and its influence on the microstructure and mechanical properties have been systematically investigated in a high strength low alloy martensite steel. It was found that the nano-sized (Ti, V)C particles mainly precipitated during reheating rather than soaking at the austenitization process. For their pinning effect on grain growth, ultra-fine austenite grain with the average size of 3.5μm formed during holding at 880°C for 1h. As the austenitization temperature increased, the prior nano-sized (Ti, V)C coarsened and its volume fraction decreased, which led to increment of austenite grain size. Excellent combined mechanical properties such as tensile strength 1670MPa, yield strength 1460MPa, elongation 10% at room temperature and impact energy (Akv) 57J at −40°C were obtained in the ultra-fine grained steels. In particular, the low-temperature toughness was improved by grain refinement. The strengthening mechanisms were also investigated by comparing the experimental results with theoretical calculation. The variation of yield strength with the condition of heat treatment was discussed in detail.
Al–Nb–B master alloy has been regarded as a promising grain refiner that can reduce grain size of hypoeutectic Al–Si casting alloys. However, its grain refinement performance remains to be improved. ...In this work, the grain refinement efficacy of Al–Nb–B master alloy is significantly enhanced by modifying the Nb/B ratio through thermodynamic calculation. An Al–Nb–B master alloy with optimum Nb/B ratio of ~ 10:1 provides a fully equiaxed structure across the sections of the Al–10Si and commercial Al–9Si–0.08Ti alloys with an average grain size below 220 μm. The phenomenon is attributed to the existence of NbAl
3
and the higher number density of NbB
2
at the Nb/B ratio of ~ 10:1, which offers sufficient active nucleating sites to promote the formation of smaller grains. Moreover, the segregation behavior of Si atoms and interfacial energies after doping Si are investigated by first-principles calculations, and the results reveal that Si tends to segregate to the NbAl
3
/α-Al interface, whereas grain refining potency of NbAl
3
for Al remains unchanged. This study has implications for strategic design of Al–Si cast alloy with fine and equiaxed grain structure inoculated by grain refiner.
Conventional friction stir processing (FSP) and ultrasonic-assisted friction stir processing (Ua-FSP) were applied to modify the microstructure and enhance the mechanical properties of as-cast A356 ...aluminium alloy. A series of experiments with different processing parameters were conducted in these two processing methods. Forming characteristics, grain-refinement, and mechanical properties in FSP and Ua-FSP were compared to determine the effect of ultrasound. The results revealed that ultrasound improved the grain-refinement level in both grain size and grain uniformity. Further, the effect of ultrasound on microstructural evolution was more significant with relatively high processing heat-input. Ultrasonic vibration also positively affected the hardness, tensile strength, and elongation.
Graphic Abstract
In this study, Al-Zn-Mg-Cu alloys with high strength and ductility were successfully prepared by wire arc additive manufacturing technology. Innovatively, the effect of composite processing ...(heterogeneous particles and heat treatment) on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy arc additive manufacturing deposition was studied. After composite processing, the grain morphology of the deposition was successfully transformed from coarse columnar crystals to dense equiaxed crystals, and the precipitation of nano-precipitated phases was greatly promoted. The influence of microstructure on mechanical properties was deeply investigated. Because of the modification of the microstructure, the tensile strength of the depositions increased from 206.8 ± 14.3 MPa to 503.6 ± 10.1 MPa (horizontal direction) and 256.2 ± 13.1 MPa to 501.2 ± 10.0 MPa (vertical direction), and the elongation increased from 4.1 ± 0.9 % increased to 10.9 ± 1.0 % (horizontal direction) and 6.6 ± 0.3 % to 13.4 ± 0.3 % (vertical direction), and the hardness was also increased from 117.9 HV to 197.9 HV. Finally, investigations revealed that the composite processing not only promotes the simultaneous increase of strength and elongation, but also greatly improves the anisotropy of the deposition. Fine grain strengthening is the main mechanism of increasing elongation. Precipitation strengthening is the main mechanism of strength enhancement. This research can provide theoretical guidance for improving the strength and elongation of Wire Arc Additive Manufacturing Al-Zn-Mg-Cu alloys, thus promoting engineering applications.
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•Al-Zn-Mg-Cu Alloy WAAM depositions were successfully prepared by composite manufacturing.•The composite manufacturing has improved the microstructure of Al-Zn-Mg-Cu Alloy WAAM depositions.•Simultaneously increased strength and elongation of Al-Zn-Mg-Cu alloy depositions.•The effect of each performance enhancement mechanism is discussed in detail.•The properties of Al-Zn-Mg-Cu alloy depositions have reached the standard properties of commercial Al alloys.
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