Nano-sized Phase Research Articles

The ultrahigh functional response of CuAlMnNb shape memory alloy by selective laser melting

In this study, the Cu-11.85Al-3.88Mn-1.6Nb (wt.%) shape memory alloy with low cost and a highly functional response was manufactured by selective laser melting(SLM). The effects of energy inputs (123–185J/mm3) on their microstructure, mechanical, and shape memory properties were investigated. It was observed that all of the samples were composed of 18R and 2H martensite, and the nanosized (Cu, Mn)3Al3Nd4 phase was formed during selective laser melting(SLM). In addition, the good compressive fracture strength and strain were 1652Mpa, and 15.1% respectively. An excellent shape memory effect of 99.26% recovery ratio and 5.32% shape memory strain was obtained by SLM.

Tailoring the microstructure, mechanical properties and damping capacities of Mg–4Li–3Al–0.3Mn alloy via hot extrusion

The microstructure, mechanical properties, and damping performance of Mg–4Li–3Al–0.3Mn alloy were systematically investigated in this research. The results show that the microstructure of Mg–4Li–3Al–0.3Mn alloy is significantly refined after extrusion. The average grain size of the as-extruded Mg–4Li–3Al–0.3Mn alloy is ∼1.5 μm and many nano-sized AlMn phases are precipitated during hot extrusion. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the as-extruded Mg–4Li–3Al–0.3Mn alloys reach 248 MPa, 332 MPa, and 14.3%, respectively, which are higher than most of the reported Mg–Li alloys. The high strength of as-extruded Mg–4Li–3Al–0.3Mn alloy is associated with the refined grains, residual dislocations, and nano-sized precipitates. The as-extruded Mg–4Li–3Al–0.3Mn alloy has better damping properties than its as-cast counterpart, with the damping capacity (Q−1) of 0.028 and 0.022 at the strain amplitude of 1 × 10−3, respectively. The relatively high Schmid factor of non-basal slip and the high dislocation density are attributed to the improved damping performance.

Microstructure evolution, mechanical property response and strengthening mechanism induced by compositional effects in Al–6 Mg alloys

Based on the compositional design concept, an Al–6 Mg–0.8Mn (–0.2Sc) alloy with a good combination of strength and ductility was obtained by hot extrusion deformation with a large extrusion ratio. The microstructure evolution and mechanical property of an Al–6 Mg alloy with adding Mn and/or Sc elements were investigated. The results showed that the addition of Sc element resulted in the grain refinement and promoted the precipitation of nano-sized Al6Mn phases in the Al–6 Mg–0.8Mn–0.2Sc alloy. After hot extrusion, the number of nano-sized Al6Mn phases decreased with the morphology transforming into the rhomboidal/plate-like shape. The combined effect of nano-sized Al6Mn phases and Al3Sc dispersoids offered a strong pinning effect on both grain boundaries and dislocations, leading to a significant refinement for recrystallized grains. Strengthening mechanism analysis indicated that the grain boundary and dislocation strengthening play important roles in enhancing the yield strength of the alloy. In addition, the uniform distribution of solid solution Mg atoms and high recrystallized fraction contributed to the high ductility of the extruded alloy. The aim of this work is to provide a strategy to acquire Al–Mg alloys with excellent mechanical performance.

Metallographic, mechanical and reciprocating wear characterization and behavioural studies of untreated and T6 treated Al2O3/Al7Si0.3Mg functional composite material

The microstructural, mechanical and unlubricated reciprocating wear characteristics of functionally graded 10 wt% Al2O3/Al7Si0.3Mg composite were analysed under untreated (UT) and heat-treated (HT) conditions. Microstructural analysis revealed Al2O3 particle gradation across the thickness and particle clusters in UT composite, whereas fine α-Si spheroids were observed in HT composite. Transmission electron microscopy studies on the HT composite revealed iron intermetallic and nano-sized β-Mg2Si precipitate phases, whilst electron backscatter diffraction studies show morphological changes in the α-Al grain structure after heat treatment. UT and HT composites underwent reciprocating wear trials under varying wear parameters (applied load and sliding distance) using a pin-on-flat plate linear reciprocating tribometer. Worn morphologies for both UT and HT composites were studied using a scanning electron microscope to investigate the wear mechanisms involved and atomic force microscopy to understand the difference in surface roughness. Response Surface Methodology is used to conduct statistical analysis and response optimisation on UT and HT composites. Due to Al2O3 particles and silicon spheroids, the HT composite outperformed the UT composite. According to the investigation, the wear resistance of both composites had increased (20–40%) with increasing reinforcement content but decreased with increasing wear parameters.

Improvement of Resistance to Hydrogen Embrittlement for 1300MPa Ultra-high Strength Steel by Introducing Nano-sized Cu-rich Phase Precipitation

Improvement of Resistance to Hydrogen Embrittlement for 1300MPa Ultra-high Strength Steel by Introducing Nano-sized Cu-rich Phase Precipitation

On the nucleation site and formation sequence of secondary phases during isothermal high-temperature aging of wire arc additively manufactured PH13–8Mo stainless steel

For the first time, the nucleation site and the formation sequence of secondary phases during isothermal high-temperature (600 °C) aging process of a wire arc additively manufactured PH13–8Mo martensitic stainless steel were investigated herein. The microstructural characterizations revealed that the aging process starts with the nucleation of homogenously distributed spherical nano-sized β-NiAl phase within the martensite laths, followed by the formation of ellipsoidal M23C6 carbides, which promoted the formation of reverted austenite within the martensite laths and also along the lath boundaries at intermediate aging times. Lastly, new M23C6 carbides were formed within the reverted austenite at the final stage of the aging process.

Deformation behavior and dynamic recrystallization during hot compression in homogenized Al–6Mg–0.8Mn alloys

In this work, Al6Mn phases with various sizes and morphologies were achieved in homogenized Al–6Mg–0.8Mn alloys. The homogenized alloys were compressed at 450 °C with strain rates of 0.001 s–1 and 1 s–1 to investigate the deformation and recrystallization behaviors induced by Al6Mn phases. The microstructure evolution in the alloys homogenized at 360 °C and 460 °C for 24 h and a two-stage homogenization (TS) was discussed. The results demonstrated that the homogenization had a good effect on improving the segregation of Mg elements and dendritic structures in the alloys. The low homogenization temperature of 360 °C resulted in the generation of a large number of nano-sized Al6Mn phases, which caused a high peak flow stress during hot compression. The Al6Mn phases with a large size were formed due to the inhomogeneous precipitation when the homogenization temperature was 460 °C. The Al6Mn phases with a large volume fraction and a small size in the alloy homogenized at “TS’’ were beneficial for promoting the recrystallization process and inhibiting the growth of recrystallized grains. In addition, in terms of pinning and driving forces for dynamic recrystallization, the role of Al6Mn phases participated in the alloys under different homogenization conditions was analyzed.

The aging behavior, microstructure and mechanical properties of AlN/AZ91 composite

Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy (OM), high resolution scanning electron microscopy (HRSEM) with an energy dispersive spectrum (EDS), and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The results show that the higher fracture elongation (14 ± 1%) and ultimate tensile strength (275 ± 6 MPa) were simultaneously obtained in the peak-aged AlN/AZ91 composites. Comparied with AZ91 matrix alloy, the strength was increased by about 44% and the elongation was approximately five times higher, which mainly attributed to the precipitation of nano-sized γ-Mg17Al12 phase and the activation of non-basal slip systems induced by in-situ AlN particles at room temperature. However, the in-situ formation of AlN reinforcements consumed part of Al element in the matrix alloy, which resulted into the volume fraction decreasing of γ-Mg17Al12 precipitates, and then the age hardening and strengthening efficiency were reduced in the AlN/AZ91 composites. On the other hand, the mismatch of thermal expansion coefficient between AlN particles and AZ91 matrix generated high density dislocations around AlN particles, which promoted the precipitation of γ-Mg17Al12 phase, and then the peak aging time and temperature were decreased.

Underestimated Properties of Nanosized Amorphous Titanium Dioxide.

Titanium dioxide is one of the best described photosensitive materials used in photocatalysis, solar cells, self-cleaning coatings, and sunscreens. The scientific and industrial attention has been focused on the highly photoactive crystalline phase of titanium dioxide (TiO2). It is commonly accepted that the smaller TiO2 particles, the higher photoactivity they present. Therefore, titanium dioxide nanoparticles are massively produced and widely used in everyday products. The amorphous phase of titanium dioxide has been treated with neglect, as the lack of its photocatalytic properties is assumed in advance. In this work, the complex experimental proof of the UV-protective properties of the nano-sized amorphous TiO2 phase is reported. Amorphous n-TiO2 is characterized by photocatalytic inactivity and, as a consequence, low cytotoxicity to fibroblast cells. When exposed to UV radiation, cells with amorphous TiO2 better survive under stress conditions. Thus, we postulate that amorphous n-TiO2 will be more beneficial and completely safe for cosmetic applications. Moreover, the results from in situ FTIR studies let us correlate the low toxicity of amorphous samples with low ability to form hydroperoxo surface species.

Optimizing strength and electrical conductivity of Cu-Cr-Zr alloy by two-stage aging treatment

Cu-Cr-Zr alloy can be strengthened by modulating the aging process. In this work, the effect of two-stage aging on the properties of Cu-Cr-Zr solid solution was studied. Hardness, tensile properties and electrical properties were tested, and the microstructures were examined by transmission electron microscope. The results show that pre-aging can facilitate the formation of GP zones in the matrix, and thus accelerate the precipitation of high-density nano-sized phase in a shorter time as compared to that in the one-stage aging process. The two-stage aging route harmonizes the strength, ductility and electrical conductivity of the alloy, and provides an accessible strategy to ameliorate the comprehensive properties of the Cu-Cr-Zr alloy.

Facile self-assembly approach to construct a novel MXene-decorated nano-sized phase change material emulsion for thermal energy storage

In recent years, phase change material emulsions (PCMEs) with enhanced energy storage capacities and good flow characteristics have drawn significant attention. However, due to the thermodynamically unstable nature and tiny particle confinement, the nanomaterial modification strategies at PCM/water interface to improve stabilities and reduce supercooling of nano-sized PCMEs (NPCMEs) are very limited and challenging. Herein, we report a facile strategy for constructing MXene-decorated NPCME with good stability, little supercooling, and high thermal conductivity by self-assembly of MXene nanosheets at PCM/water interface. The concentrations of MXene have great influences on the average droplet diameters, stabilities, and thermophysical properties of the NPCMEs. The results show that the PCMs have been well dispersed into the water in the form of quasi-spherical droplets, with average droplet diameters of 242–805 nm. The thermal conductivity of 10 wt% n-tetradecane/water NPCME containing 9 mg ml-1 MXene is 0.693 W m-1·K-1, achieving an enhancement by 15.5%, as compared to that of water. Besides, the MXene-decorated paraffin/water NPCMEs exhibit little supercooling and enhanced heat storage capacities. More importantly, this facile self-assembly strategy opens a new platform for preparing high-performance NPCMEs, which can be used as novel heat transfer fluids for thermal energy storage systems.

Microstructures and tensile properties of Mg-2Zn-0.8Sr-0.2Ca alloy extruded at relatively slow speed and low temperature

In this work, a new Mg-2Zn-0.8Sr-0.2Ca alloy with low content of alloying elements was subjected to extrusion at relatively low-temperatures (240 and 200?C) and slow-speed (1.0 mm/s and 0.1 mm/s). The average size and volume fraction of recrystallized grains in the extruded Mg-2Zn-0.8Sr-0.2Ca alloy gradually decreased with the reduction in extrusion rate or extrusion temperature. Some broken second phases including Ca2Mg6Zn3 and Mg17Sr2 appeared in the extruded Mg-2Zn- 0.8Sr-0.2Ca alloy along with some precipitated nano-sized MgZn2 phases. The volume fraction of MgZn2 phases gradually in the alloy increased as extrusion rate or temperature decreased. High performance with yield strength of 393.1 MPa, ultimate tensile strength of 418.4 MPa and the elongation of 5.7% was obtained in the Mg-2Zn-0.8Sr-0.2Ca alloy extruded at 200?C & 0.1 mm/s. The main strengthening mechanisms could be attributed to grain-boundary strengthening, dislocation strengthening, precipitation strengthening, which were related to the change in grain size, second phases and basal texture intensity for the extruded Mg-2Zn-0.8Sr-0.2Ca alloy.

Composites epoxídicos de fibra de carbono modificados con velos electrohilados de PA6 funcionalizados con nanopartículas

Epoxy resin composites inherent brittleness and poor crack resistance make necessary some form of toughening. Recently, several types of nanoparticles are being incorporated due to their theoretical high stiffness and strength. However, the addition of tougheners to the entire matrix resin could lead to a decrease in in-plane mechanical properties and to an increased viscosity of the system, being reduced the processing ability of matrix resin. Moreover, a homogeneous dispersion of these nanoparticles is still a problem. Thermoplastic nanofibrous structures can tackle these problems. They offer a solution for the dispersion issue, since they can be readily embedded in the resin and incorporate a nanosized phase in the composite. These nanofibres also do not increase the viscosity of the resin. Moreover, due to their macro scale length, no health hazards are involved in the production and use of these nanofibres. This paper investigates the effect of electrospun nanofibrous veils made of polyamide 6 modified with TiO2 nanoparticles on the properties of a carbon fibre/epoxy composite. The nanofibres were incorporated in the carbon fibre/epoxy composite as stand-alone interlayered structure during a vacuum infusion process. The effect of positioning these veils in different composite positions has been investigated. Incorporation of polyamide nanofibers increases the stress at failure and the Young’s modulus. Furthermore, mode I tests showed a slight improvement. When TiO2 modified veils are incorporated in the composite, similar mechanical properties were obtained, but new antibacterial properties were achieved when irradiated with UV light widening the application area of these composites.

Thin films of thermoelectric Mg2Sn containing nano-sized metal Sn phase by magnetron sputtering

Mg2Sn films with nano-sized metal Sn phase were prepared by magnetron sputtering. The nano-sized metal Sn phase in films gradually increased with increasing single sputtering time on alloy target. The carrier concentration increased and the carrier mobility first decreased and then slightly increased with increasing nano-sized metal Sn phase. The resistivity and Seebeck coefficient all exhibited a trend of first increasing and then decreasing with the increase of nano-sized metal Sn phase. The Seebeck coefficient greatly increases due to existing moderate nano-sized secondary phase. It is beneficial to increase the power factor that the cubic Mg2Sn thin films contain an appropriate amount of conductive nano-sized metal Sn phase.

Precipitation behavior of a Co-free Fe-Ni-Cr-Mo-Ti-Al maraging steel after severe plastic deformation

Maraging steels are martensitic steels that are strengthened by the precipitation of nano-sized intermetallic phases. Severe plastic deformation is known to influence diffusion, stability and properties of metallic materials. The goal of this study is to reveal the influence of severe plastic deformation on the hardness and the precipitation behavior of a Co-free maraging steel. For this study the as-quenched material was deformed with high-pressure torsion. Afterwards, a series of heat treatments were conducted. The hardness increase was measured and correlated with micro-to-nanoscale microstructural characteristics, focused on the precipitate characterization with atom probe tomography. Severe plastic deformation transformed the microstructure to a globular microstructure, delayed and minimized austenite reversion as well as accelerated and influenced the precipitation reaction, affecting the size, morphology and type of intermetallic phases.

Evolution of nanosized Cu-rich clusters in a Fe–15Cu–15Ni alloy produced by laser powder bed fusion

Designing a metastable microstructure with a coherent nano-sized precipitation phase in the matrix is an effective strategy in improving the strength of materials. Recently, the rapid fusion and solidification cycle associated with laser-based additive manufacturing (AM) has emerged as a promising strategy to design unique microstructures with lattice distortion, solute segregation, and nano-sized precipitations. In this study, the evolution of nano-sized Cu-rich clusters in an AM-processed Fe–15Cu–15Ni alloy (wt.%) was investigated by conducting multiscale microstructural characterization. The results reveal that nano-sized Cu-rich clusters were generated inside the matrix due to a phase decomposition induced by the intrinsic heat treatment during the AM process. The heat energy generated by the laser beam not only initiated Cu-rich cluster formation, but also induced precipitation growth. Therefore, the average Cu-rich cluster size increased with an increase in the volumetric energy density. The hardness of the AM-processed Fe–15Cu–15Ni alloy at first increased with an increase in the energy density until a medium energy density level (140 J/mm3), due to formation of Cu-rich clusters. The hardness decreased with further increase in energy density (185 J/mm3), due to the Cu-rich cluster growth and retained austenite. The results reveal that laser-based AM successfully induces nano-cluster without the need for post-treatment and that the mechanical properties of materials can be optimized by adjusting the processing parameters in a way to enable nano-sized cluster and phase formation.

Effects of Sc alloying on the evolution of solidification microstructure and formation of W phase in as-cast 2519 aluminum alloys

In this study, the effect of Sc content on the phase transformation of the 2519 alloy during solidification is investigated through microstructure characterization and thermodynamic calculations. The results show that the grain size of the 0.3–0.4Sc alloy is reduced by 70% (approximately 28.9 µm) to achieve maximum refinement in the as-cast 2519(Sc) Al alloy. The phase diagram calculation shows that the sequence of intermetallic formation during the solidification of 2519(Sc) Al alloy is as follows: Al3Sc, W phase, θ. The primary Al3Sc particles appear at the center of the α–Al grains and evidently acted as heterogeneous nucleating agents. Transmission electron microscopy shows that the nano-sized bean-like Al3Sc phase precipitated from the saturated solid solution. Moreover, the phase transition analysis of the 0.3–0.4Sc alloy during solidification shows that the formation of the W phase underwent two different types of reactions: the peritectic-eutectic reaction (L + Al3Sc → αAl + W) and eutectic reaction (L → αAl + W, L → αAl + θ + W). The W phase formation mechanism of these two reactions is revealed through experiments. Simultaneously, W phases with different morphologies are observed in the 0.3–0.4Sc alloy, i.e., the W phase of the spherical-shell structure is formed by the peritectic-eutectic reaction, and the long strip W phase (~6 µm in size) is precipitated by the eutectic reaction.

Structural origin of low Li-ion conductivity in perovskite solid-state electrolyte

Perovskite solid-state electrolyte, Lithium Lanthanum Titanium Oxide, has long been considered as a promising candidate enabling all-solid-state Li batteries due to its high bulk Li-ion conductivity and wide electrochemical window. However, the Li-ion conductivity at so called “grain boundaries” (GBs) off LLTO pellets is much lower than that of its bulk phase. Thus, understanding the structural origin of the low Li-ion conductivity of LLTO is critical yet remains largely elusive. Here, we identify two types of GBs at different length scales, namely “macro” and “micro” GBs in LLTO pellets and originate them to the processing of LLTO. We also find a nanosized Li-poor orthogonal phase at micro-GBs, which largely deteriorate the Li conduction. Corroborated by electrochemical measurements, we revealed the phase transformation from tetragonal Li0.33La0.56TiO3 to orthogonal Li0.18La0.6TiO3 during the heat-treatment process is responsible for this deterioration. During phase transformation process, La atoms move to the original Li-rich layer and block the diffusion path of Li-ions in LLTO. These results reveal the structural origin of low Li-ion conductivity in LLTO pellets and provide insights to prevent Li-loss induced phase transformation for commercial application of LLTO.

Effect of heat treatment on microstructural heterogeneity and mechanical properties of 1%C-CoCrFeMnNi alloy fabricated by selective laser melting

In this study, we quantitatively investigated the effect of heat treatment on microstructural evolution and mechanical properties in the selective laser melting (SLM) processed 1%C-CoCrFeMnNi high-entropy alloy (C-HEA). The addition of carbon atoms resulted in a nano-sized Cr23C6 carbide phase in the SLM-processed C-HEA, significantly retarding the kinetics of recrystallization and grain growth during the annealing heat treatment. The volume fraction of the carbide in SLM-processed C-HEA increased from ~1.7 vol% to ~2.9 vol% after exposure to the annealing heat treatment in the temperature range of Cr-rich carbide formation. After annealing, the combination of ultimate tensile strength and uniform elongation is improved with enhanced strain hardening ability. The increased volume fraction of finely distributed nano-carbides at cell boundaries in the annealed C-HEA can effectively generate high back stress by profuse geometrically necessary dislocations (GNDs) during plastic deformation. This work demonstrates that the heat treatment of the SLM-processed C-HEAs is an attractive method to enhance mechanical properties and the reliability of product quality used in high-tech applications. This work also provides theoretical support to beneficially control the microstructural heterogeneity in the SLM-processed alloys to obtain the desired performance in structural parts.

Combustion Synthesis of CuO Nanomaterials: Effect of Different Fuels on the Structural, Thermal, and Optical Properties

The wet chemical combustion synthesis and the effect of different (aniline, citric acid monohydrate, dextrose, glycine, hexamine, oleic acid, sucrose, and urea) fuels on the combustion products of CuO nanomaterials are reported for the first time as a comparative study. The pure nano-sized CuO phase combustion products were produced from hexamine, urea, and glycine as fuels, whereas fuel-like sucrose yielded nearly a single phase of the CuO combustion product. The quality of the combustion products revealed mixed phases of CuO and Cu2O for aniline, dextrose, citric acid monohydrate, and oleic acid as fuels. The pure combustion products crystallized in a monoclinic structure with a space group, C12/c1 (15). For the mixed phases of combustion products, weight gain (102.5%–109%) is noted >400 °C in the TG curves owing to the oxidation of the Cu2O phase into the CuO phase. The bandgap of the different CuO powder was in the range of 2.1–2.6 eV. From the NIR spectra, we conclude that the nanocrystallinty of the CuO phase plays a major role in the enhancement (∼35%) of NIR reflectance owing to the difference in the fuels used. The observed Raman modes confirm the characteristics of the CuO phase. Different morphologies are observed for the different CuO combustion products obtained from hexamine, urea, and glycine as fuels.