Longer Aging Times Research Articles

Effect of Different Mo Addition on Microstructure and Mechanical Properties of Cu-15Ni-8Sn Alloy.

In the present study, Mo was added to Cu–15Ni–8Sn alloy as the fourth element to solve the limitation of service performance of the alloy by composition design. The phase composition, microstructure transformation and mechanical properties of Cu–15Ni–8Sn–xMo (x = 0.3, 0.9, 1.5 wt.%) alloy were systematically studied by simulation calculation and experimental characterization. The results show that the addition of Mo can improve the as-cast structure of Cu–15Ni–8Sn alloy and reduce segregation and Cu–Mo phase precipitates on the surface with the increase in Mo contents. During solution treatment, Mo can partially dissolve into the matrix, which may be the key to improving the properties of the alloy. Furthermore, the discontinuous precipitation of Sn can be effectively inhibited by adding the appropriate amount of Mo to Cu–15Ni–8Sn alloy, and the hardness of alloy does not decrease greatly after a long-time aging treatment. When Mo content is 0.9 wt.%, the alloy reaches the peak hardness of 384 HV at 4 h of aging. These results provide new ideas for composition optimization of Cu–15Ni–8Sn alloy.

Effects of atmospheric aging processes on carbonaceous species and water-soluble inorganic ions in biomass burning aerosols

Biomass burning (BB) has been considered as a major source for primary aerosols and gas pollutants in the atmosphere, but the influence of atmospheric aging processes on the chemical compositions of BB aerosols remains unclear. In this study, a combustion chamber and an oxidation flow reactor were combined to simulate fresh and 7-day aged PM2.5 from burning of rice, maize, and wheat straws in a laboratory. The emission factors (EFs) of PM2.5 mass, carbonaceous species (i.e. organic carbon (OC) and elemental carbon (EC)), and water-soluble inorganic ions in both fresh and 7-day aged samples were determined. The EFs of PM2.5, OC, EC, and ions were 7.2–45, 2.8–24, 0.3–0.8, and 1.6–4.7 g kg−1 in the fresh particles from the straws burning, and 12–63, 3.0–25, 0.3–1.3, and 4.1–13 g kg−1 in the aged ones. Cl− and K+ were the most abundant ions in the fresh samples. EFs of NO3− and NH4+ were increased by 35–100 and 1.6–126 times, respectively, becoming the most abundant ions in the aged particles. By comparison with the results in experiments on 2-day aged specimens, we found a continuous formation of secondary aerosols in the atmospheric aging processes (especially for secondary inorganic ions), and that the deficit of anion equivalents increases with longer aging time. These results are valuable for studying the transportation effects of plumes from wildfires of forest and agriculture, or intensive domestic BB in some rural regions.

Interfacial micro and macro rheology of fractionated asphaltenes

Asphaltenes are a fraction of crude oil that can stabilize undesirable water/crude oil emulsions. Only a small fraction of the asphaltenes plays an active role in emulsion stabilization and this fraction has a relatively high heteroatom content. However, the transient behavior and the microstructural evolution of these asphaltene fractions at the water/oil interfaces are not fully understood. In this study, interfacial rheology and microstructural evolution of Athabasca asphaltene and its subfractions at the water/toluene interface were studied using passive microrheology and dilatational rheology. Asphaltenes (labeled A) were fractionated based on their surface activity via an emulsion-based method to obtain interfacially active (IA) and partially active (PA) subfractions. The passive microrheology experiments demonstrated that the IA asphaltenes adsorbed much faster at the water/toluene interface than A and PA asphaltenes. The IA asphaltenes formed rigid interfacial films within a few minutes which fully immobilized the probe particles. The same adsorption trend was observed in the interfacial pressure measurements and dilatational rheology experiments. Particle tracking microrheology over the entire interface showed that, during the adsorption process, asphaltene films grew heterogeneously and eventually turned into homogeneous structures at longer aging times. The IA asphaltene films were more homogeneous than the other asphaltene films offering fewer weak points for coalescence. The drop size distributions in emulsions prepared using IA and PA asphaltene showed significant coalescence after 1.5 h in the PA fraction but not the IA fraction, confirming the ability of IA asphaltenes to stabilize emulsions.

Study on surface wettability of nickel coating prepared by electrodeposition combined with chemical etching

Nickel coatings with different surface characteristics were prepared on copper substrate by electrodeposition. Subsequently, the as-coating surface was etched with a mixed solution of FeCl3, HCl and H2O2 at different times, to obtain different surface morphologies and special microstructures. The surface morphologies, element composition, roughness and liquid contact angle were characterized by scanning electron microscope, energy dispersive X-Ray spectroscopy, 3D digital microscope and contact angle measurement. The van Oss-Chaudhury-Good method was used to calculate the solid surface free energy and discuss the variation of surface wettability. The results show that etching time has a significant effect on surface morphology, roughness and wettability. After long-time physical aging, the multiple polygonal-layered architectures and larger-sized layered microstructure can maintain high surface free energy and keep the liquid metal in a good hydrophilic state, which provides a reference for optimizing the surface morphologies of the casting roll. This will improve the heat transfer efficiency and promote heterogeneous nucleation during twin-roll continuous casting.

Microwave Irradiation: Effects on the Change of Colour Characteristics and Main Phenolic Compounds of Cabernet Gernischt Dry Red Wine during Storage.

Wine colour is an essential organoleptic property considered by consumers. In this paper, the potential effects on colour characteristics and the content of main phenolic compounds in red wine under microwave irradiation were investigated during wine storage. The results showed that the changing trend of colour characteristics of microwave-treated and untreated wines was very similar. Moreover, total phenolic compounds, total monomeric anthocyanins, main anthocyanins, main flavonoids, and main phenolic acids (gallic acid; caffeic acid; syringic acid; (+)-catechin; Cy-3-glu; Mv-3-glu) also showed similar change trends during storage. In other words, microwave irradiation had a long-term effect on the colour properties and main phenolic compounds of red wine, changes that require long-time aging in traditional processing. In terms of the studied parameters, the changes in microwave-treated wine were faster than those in untreated wine. These results showed that microwave technology, as a promising artificial aging technology, could in a short time produce red wine of similar quality to traditional aging.

Constructing ultra-stable photothermal plastics assisted by carbon dots with photocaged reactivity

Constructing ultra-stable photothermal plastics assisted by carbon dots with photocaged reactivity

A novel short-process manufacturing method of γ′-strengthened superalloy: Modulation of nano-scaled γ′ precipitates during hot deformation

The tailoring of precipitates during hot deformation provides an opportunity to eliminate lengthy post-process heat treatment and removes the inherent disadvantages, such as abnormal grain growth. In this work, a novel short-process manufacturing method consisting of only pre-annealing and hot deformation steps was proposed for fabricating γ′-strengthened GH4720Li superalloy. Diverse nanoscale precipitation strengthening phases with bimodal distributions but similar matrix grain sizes were successfully modulated by this integrated two-step manufacturing method. The modulated superalloys fabricated under low deformation resistance and without typical long-time aging treatment exhibited high yield strength (∼1196 MPa) and ultimate tensile strength (∼1561 MPa) while maintaining a decent uniform elongation (∼19%) during tensile tests at room temperature. The dominant tertiary γ′ strengthening precipitates originate from the supersaturated matrix and dynamic evolution of secondary γ′ precipitates during hot deformation. In addition, the shearing of secondary γ′ through dislocation pairs promotes their dissolution during hot deformation. This study provides a novel pathway for the integrated short-process manufacturing of multimodal γ′ nickel-based superalloys and a new understanding for dynamically modifying the microstructure of precipitate-containing alloys during hot deformation.

Evolution of thermal behavior, mechanical properties, and microstructure in stereocomplexable poly(lactic acid) during physical ageing

Polymer glasses are metastable below their glass transition temperature (Tg) and the process of structural relaxation towards equilibrium state is known as physical ageing. However, the evolution of structure mechanics during ageing is still a long-standing question, especially the interpretation in chain level. In this work, we illustrate the critical role of intermolecular interaction on physical ageing of stereocomplexable poly(lactic acid) (PLA). By melt-blending the two enantiomers of PLA [poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA)] with different ratios, we obtain a typical system with tunable intermolecular interactions and investigate the effect of such interactions on physical ageing behavior. Compared with a neat PLLA, we found that the chain mobility is lower in stereocomplexable PLLA/PDLA blend, which clearly exhibits a retarded ageing kinetics. Besides, the stereocomplexable PLLA/PDLA blend exhibits a stiffer chain network, manifested by a high elastic modulus, which improves steadily with longer ageing time. We propose that the retarded ageing kinetics and high stiffness in stereocomplexable blends are results of intermolecular interactions between PLLA and PDLA chains. This work has shed light on the critical role of intermolecular interactions on physical ageing kinetics and evolution of physical performances of glassy polymers.

Novel Transparent TiO2/AgNW-Si(NH2)/PET Hybrid Films for Flexible Smart Windows.

The application of flexible indium tin oxide (ITO)-free electrochromic devices (FCDs) has always been a research hotspot in flexible electronics. Recently, a silver nanowire (AgNW)-based transparent conductive film has raised great interest as an ITO-free substrate for FCDs. However, several challenges, such as the weak binding of AgNWs to the substrate, high junction resistance, and oxidation of AgNWs, remain. In this paper, a novel method for surface modification of AgNWs with N-aminoethyl-γ-aminopropyltrimethoxysilane [Si(NH2)] solution is proposed to enhance the bonding with the flexible substrates and the active materials, thereby inhibiting the delamination of AgNWs from the substrate and reducing the high junction resistance between nanowires. The TiO2/AgNW-Si(NH2)/poly(ethylene terephthalate) (PET) films show outstanding mechanical properties, of which the resistance remains almost unchanged after mechanical bending of 5000 cycles (ΔR/R0 ≈ 3.6%) and repeated peeling off cycles with 3M tape 100 times (ΔR/R0 ≈ 6.0%). In addition, we found that the oxygen-containing groups on the TiO2/AgNW-Si(NH2)/PET surface form hydrogen bonds with the TiO2 sol, resulting in tight contact between the TiO2 sol and the AgNWs, which prevents the AgNWs from oxidation. As a result, the TiO2/AgNW-Si(NH2)/PET film exhibited long-time aging (ΔR/R0 ≈ 4.9% in the air for 100 days) stability. A FCD was constructed with the TiO2/AgNW-Si(NH2)/PET film, which showed excellent electrochromic performance (94% retention) after 5000 bending cycles, indicating high stability and mechanical flexibility. These results present a promising solution to the transparent conductive films for flexible energy devices.

Microstructure and Superelastic Properties of FeNiCoAlTi Single Crystals with the <100> Orientation under Tension

The microstructure and superelastic response of an Fe41Ni28Co17Al11.5Ti2.5 (at.%) single crystal along the <100> orientation was investigated under tension at room temperature after aging at 600 °C for 24 h. From the superelastic results, the samples aged at 600 °C for 24 h exhibited 4.5% recoverable strain at room temperature. The digital image correlation (DIC) method was used to observe the strain distribution during the 6.5% applied strain loading. The DIC results showed that the strain was uniformly distributed during the loading and unloading cycles. Only one martensite variant was observed from the DIC results. This was related to the aging heat treatment times. The martensite morphology became a single variant with a longer aging time. The thermo-magnetization results indicated that the phase transformation and temperature hysteresis was around 36 °C. Increasing the magnetic field from 0.05 to 7 Tesla, the transformation temperatures increased. The maximum magnetization was 160 emu/g under the magnetic field of 7 Tesla. From the transmission electron microscopy results, the L12 precipitates were around 10 nm in size, and they were high in Ni content and low in Fe content.

Microstructure evolution and mechanical properties of Cu-Sn intermetallic joints subjected to high-temperature aging

In this work, full Cu3Sn joints were aged at 500°C, 550°C, and 600°C for various durations. Microstructure evolution and grain morphology of the joints were systematically investigated by OM, SEM, EBSD, and TEM technology. In addition, the mechanical properties of hardness and shear strength for the CuSn intermetallic compounds were studied using a Micro Vickers hardness tester and uniaxial tensile equipment. Upon heating to 500°C, the phase transformation pathway was Cu3Sn–Cu41Sn11–α(Cu); aging at 550°C demonstrated a pathway of Cu3Sn–Cu41Sn11–Cu41Sn11&α(Cu)–α(Cu); and finally, heating to 600°C resulted in a phase transformation pathway of Cu3Sn–Cu20Sn6–Cu20Sn6&α(Cu)–α(Cu). It was found that longer aging times and higher temperatures had effects on grain size and morphology. For the 500°C group, the average grain size of the fully formed Cu41Sn11 phase increased from 1.93 μm at an aging time of 20 min to 4.20 μm at 30 min. The grain sizes of the fully formed Cu41Sn11 phase in joints subjected to 550°C for 11 min was lower than 2.36 μm, which were in turn smaller than joints treated at 500°C for 30 min (4.2 μm). Treatment with higher temperatures resulted in more cores and a higher growth rate of Cu41Sn11 grains formed on the interface of Cu/Cu3Sn, which eventually led to the small grain size of the Cu41Sn11 phase. The grain morphologies of the formed Cu41Sn11 phase and Cu20Sn6 phase were mainly column grain. After an aging time of 11 min for the 550°C group, the grain morphology of α(Cu) included in a two-phase microstructure (Cu41Sn11&α(Cu)) mainly exhibited dendritic properties at the grain boundary of Cu41Sn11, its crack tendency broke the hardenability of single grains for the Cu41Sn11 phase, which resulted in a decline in strength from 107 MPa to 42 MPa for Cu41Sn11&α(Cu) compared to the Cu41Sn11 phase. Nevertheless, for the joints treated at 600°C after an aging time of 7 min, the dispersion of α(Cu) particles mainly followed granular shapes within the one large Cu20Sn6 grain in the two-phase microstructure (Cu20Sn6&α(Cu)). This blocked the extension of dislocation, which finally led to an enhancement in strength for the Cu20Sn6 & α(Cu) phase (51 MPa) compared to the Cu20Sn6 phase (73 MPa).

Assessment of Cd bioavailability using chemical extraction methods, DGT, and biological indicators in soils with different aging times

Total cadmium (Cd) cannot be used to accurately assess the ecological risk of Cd pollution in soil. Currently there is no universally recognized method to evaluate Cd bioavailability in soil. In this study, chemical extraction methods, diffusive gradients in thin films (DGT) and bioindicator methods were used to evaluate Cd bioavailability in soils with the same properties but different aging times. Results indicate that aging decreased the Cd bioavailability in soil and its toxicity to barley. This was primarily due to a decrease in the proportion of ion-exchangeable Cd. Correlation analyses were conducted on the Cd bioavailable content obtained via the soil extraction methods and the toxicity effect of barley. Results showed that the order of the minimum value of the linear regression determination coefficient (R2) of chemical extraction methods and DGT was as follows: DGT-Cd (0.7385, p < 0.05) > total Cd (0.6931, p < 0.05) > acetic acid-Cd (0.6078) > ion-exchangeable Cd (0.5933) > DTPA-Cd (0.5842) > CaCl2-Cd (0.4980) > water-soluble Cd (0.4602). The order of minimum value of R2 of biological indicators of barley was integrated biomarker response (IBR) (0.8501, p < 0.01) > length (0.6492) > dry weight (0.6320) > fresh weight (0.4980) > Cd concentration (0.4602). The root is more suitable for indicating the plant uptake and accumulation of Cd in soil. Meanwhile, the shoot can effectively evaluate the toxic effect of Cd stress on plants. DGT is more suitable to reflect Cd bioavailability to barley compared to chemical extraction methods, Furthermore, it can be used to evaluate stable polluted soil with longer aging time. In the study of the bioavailability of heavy metals in soil, IBR can be used as a reliable reference index to contribute to the comprehensive evaluation of metal bioavailability in addition to considering plant uptake.

Localized alteration of ferrihydrite natural organic matter coprecipitates following reaction with Fe(II)

AbstractCoprecipitation of natural organic matter (NOM) with ferrihydrite (Fh) can alter the trajectory of Fe(II)‐catalyzed transformation. High C/Fe molar ratio Fh‐NOM coprecipitates are expected to resist transformation completely and preserve organic matter (OM). To explore how heterogeneous NOM would influence this process, we reacted low (0.8) and high (1.8) C/Fe molar ratio Fh‐NOM coprecipitates (synthesized with a 13C‐labeled plant litter extract) with 2 mM Fe(II) for 1 and 14 d under anoxic conditions and examined changes in the solid phase with Mössbauer spectroscopy (MBS) and secondary electron images using scanning transmission electron microscope. Mössbauer spectroscopy data suggests Fe(II) interaction with coprecipitates increases Fe mineral crystallinity, as did lower molar C/Fe ratios and longer aging times. However, de novo crystal phase development was only observed (via secondary electron images) in the Fe(II)‐reacted coprecipitates and only when the organic carbon (OC) loading was low. For example, the low C/Fe coprecipitate developed localized lath‐like crystal phases after 1 d of reaction with Fe(II), while the lath‐like phases only developed in the high C/Fe coprecipitates after they lost some NOM (C/Fe ratio decreased from 1.8 to 0.7) and reacted with Fe(II) for 14 d. In addition, partial exchange of coprecipitate 13C‐NOM for C in the media (likely the organic PIPES buffer) occurred in all treatments but was accentuated by reaction with Fe(II), suggesting coprecipitate OM composition likely evolves over time, especially when exposed to Fe(II). Our findings suggest that Fe(II) mediated Fh‐NOM transformation is highly dynamic and has the potential to influence the stability of NOM in Fh.

Understanding the effect of aging treatment on the electrical properties of Al-4Cu (wt.%) alloy

Binary Al–Cu alloy has always been used to illustrate the phenomenon of precipitation hardening. Meanwhile, Al–Cu alloy has good heat resistance and is a potential heat-resistant conductor material, but there is not much research work on its electrical properties. In this work, the residual resistivity variation of Al-4Cu alloy at different aging stages was investigated. At the aging temperature of 160 °C, the residual resistivity of the Al-4Cu alloy decreases with the longer aging time, and it decreases rapidly in the early stage and slowly in the later stage, mainly due to the precipitation of solid solution Cu atoms and the interface electron scattering effect of different precipitates. In the early stage, massive precipitation of Cu atoms from the matrix can effectively reduce the crystal lattice distortion of Al matrix and significantly decrease the residual resistivity. Specifically, the residual resistivity of Al-4Cu alloy that aged at 160 °C for 13 h is 3.353 μΩ·cm, which is only 82.6% of that in the supersaturated solid solution state. In later stage of aging, the main change is the evolution of the precipitated phase, i.e., the gradual disruption of the coherent relationship between the second phase and the Al matrix. And the coherency-strain fields decrease gradually, which is also beneficial in decreasing the residual resistivity. The results show that Al–Cu alloys can also be a potential heat-resistant conductor material for the power transmission industry.

Occurrence of the R-phase with increased stability induced by low temperature precipitate-free aging in a Ni50.9Ti49.1 alloy

The R-phase transformation presents low thermal hysteresis, high stability against thermal cycling and ultrahigh internal friction (IF). However, a clear explanation for the occurrence of the R-phase after low temperature aging and systematic characterization of the condition are still lacking. In this study, the evolution of the phase transformation behaviors and IF values after aging at 250 °C for different times are investigated in a Ni50.9Ti49.1 alloy. Direct experimental evidence for the microstructure evolution of the B2 phase and the corresponding R-phase is provided utilizing in-situ transmission electron microscopy (TEM) techniques, together with geometric phase analysis (GPA). The reason for the occurrence of a nanodomain-structured R-phase after low temperature precipitate-free aging and the mechanism of ultrahigh intrinsic IF are illustrated. The results show that Ni segregation indicated by the localized strain fields is responsible for the formation of the R-phase after low temperature aging. Longer aging time causes larger element heterogeneity in the matrix, as a result, a wider existing temperature window for the R-phase. The ultrahigh intrinsic IF plateaus (IFInt = 0.120 ∼ 0.183) found in NiTi shape memory alloys (SMAs) are predominantly determined by the volume fraction of nanodomain boundaries. These findings provide basic insights into the R-phase formation mechanism and provide a simple way to adjust ultrahigh IF performance suitable for different application scenarios.

Comparison of intermetallic compound growth and tensile behavior of Sn-3.0Ag-0.5Cu/Cu solder joints by conventional and microwave hybrid heating

Microwave hybrid heating (MHH) is a possible approach for soldering; yet, the long-term reliability of solder joints is still unclear. In this work, a comparative study was carried out on the influence of isothermal aging on SAC305/Cu solder joints by conventional reflow and MHH. The conventional reflow oven was set to 260 °C at 60 s holding time, and MHH was carried out at high operating power at 40 s. The reflowed sample was isothermally aged at 150 °C for various aging times (0, 240, 480 and 960 h) in a laboratory oven. The conventional reflow and MHH transformed the IMC structure from scallop-like to a planar-like Cu6Sn5 with a linear increase in thickness and a thin layer of Cu3Sn was observed at 240 h of aging. While Ag3Sn particles grew larger at longer aging time. The MHH shows a thinner Cu6Sn5 layer, and a smaller grain size compared to conventional reflow. The ultimate tensile strength (UTS) for conventional reflow (32.7 MPa) is 26.8% lower compared to MHH (44.7 MPa). The UTS for MHH is greater than conventional reflow as the isothermal aging time increases.

Design of cuboidal&lt;i&gt; γ&lt;/i&gt;/&lt;i&gt;γ′&lt;/i&gt; coherent microstructure and its stability in low-density Co-Ni-Al-Mo-Cr-Ti/ Nb/Ta superalloys

Co-base superalloys generally have high strengths, good oxidation- and corrosion-resistances, as well as excellent creep-resistant properties at high temperatures (HTs), which are ascribed to the coherent precipitation of cuboidal&lt;i&gt; γ′&lt;/i&gt; phase into face-centered-cubic (FCC) &lt;i&gt;γ&lt;/i&gt; matrix induced by co-alloying of multiple elements. However, the cuboidal &lt;i&gt;γ&lt;/i&gt;/&lt;i&gt;γ′&lt;/i&gt; coherent microstructure is liable to be destabilized after a long-time aging at HTs in Co-base superalloys. In the present work, the cluster formula is used to design a series of low-density Co-base superalloys with the composition of [Al-(Co&lt;sub&gt;8&lt;/sub&gt;Ni&lt;sub&gt;4&lt;/sub&gt;)]((Al&lt;sub&gt;0.5&lt;/sub&gt;(Ti/Nb/Ta)&lt;sub&gt;0.5&lt;/sub&gt;Mo&lt;sub&gt;0.5&lt;/sub&gt;)(Mo&lt;sub&gt;0.5&lt;/sub&gt;Cr&lt;sub&gt;0.5&lt;/sub&gt;Co&lt;sub&gt;0.5&lt;/sub&gt;)) (=Co&lt;sub&gt;8.5&lt;/sub&gt;Ni&lt;sub&gt;4&lt;/sub&gt;Al&lt;sub&gt;1.5&lt;/sub&gt;Mo&lt;sub&gt;1.0&lt;/sub&gt;Cr&lt;sub&gt;0.5&lt;/sub&gt;(Ti/Nb/Ta)&lt;sub&gt;0.5&lt;/sub&gt;). Alloy ingots are prepared by arc melting under an argon atmosphere, and are solid-solutionized at 1300 ℃ for 15 h and then aged at 900 ℃ for up to 500 h. Microstructural characterizations and mechanical properties of these alloys in different aged states are obtained by using XRD, SEM, EPMA, TEM, and HV. It is found that all these alloys with Ti/Nb/Ta, Ti/Nb, and Ti/Ta in an equi-molar mixing have a special coherent microstructure with cuboidal &lt;i&gt;γ′&lt;/i&gt; phase uniformly-precipitated into the γ matrix, which is contributed to the moderate lattice misfit of &lt;i&gt;γ&lt;/i&gt;/&lt;i&gt;γ′&lt;/i&gt; (0.27%–0.34%). Moreover, these cuboidal&lt;i&gt; γ′&lt;/i&gt; phase are coarsened slowly during aging, in which the microhardness does not vary obviously with aging time (275 HV–296 HV). Especially, the alloy with (Ti/Ta)&lt;sub&gt;0.5&lt;/sub&gt; exhibits the highest &lt;i&gt;γ&lt;/i&gt;/&lt;i&gt;γ′&lt;/i&gt; microstructural stability with a slow coarsening rate after aging 500 h, and no other second phases appear near the grain boundaries. While needle and bulk particles would precipitate on grain boundaries in other alloys after 500 h-aging.

Laser Powder Bed Fusion of an Al-Mg-Sc-Zr Alloy: Manufacturing, Peak Hardening Response and Thermal Stability at Peak Hardness

This study shows a rapid and systematic approach towards identifying full density and peak hardness for an Al-Mg-Sc-Zr alloy commonly known as Scalmalloy®. The alloy is tailored for the laser powder bed fusion process and has been shown to be printable with &gt;99.8% relative density. The microstructure suggests Al grain refinement in melt pool boundaries, associated with formation of primary Al3(Sc,Zr) particles during solidification. Peak hardening response was identified by heat treatment tests at 573,598 and 623 K between 0 and 10 h. A peak hardness of 172 HV0.3 at 598 K for 4 h was identified. The mechanical properties were also tested with yield and ultimate strengths of 287 MPa and 364 MPa in as-printed and 468 MPa and 517 MPa in peak hardened conditions, respectively, which is consistent with the literature. Such an approach is considered apt when qualifying new materials in industrial laser powder bed fusion systems. The second part of the study discusses the thermal stability of such alloys post-peak-hardening. One set of samples was peak hardened at the conditions identified before and underwent secondary ageing at three different temperatures of 423,473 and 523 K between 0 and 120 h to understand thermal stability and benchmark against conventional Al alloys. The secondary heat treatments performed at lower temperatures revealed lower deterioration of hardness over ageing times as compared to the datasheets for conventional Al alloys and Scalmalloy®, thus suggesting that longer ageing times are needed.

Effect of post-solutionizing cooling rate on microstructure and magnetic properties of 2:17-type Sm-Co-Fe-Cu-Zr magnets

The fabrication of 2:17-type Sm-Co-Fe-Cu-Zr magnets that have served as the strongest high-temperature permanent magnets for nearly half a century requires a strict processing control to form full cellular nanostructure. Considering that slow cooling after solution-treatment may enable a more homogeneous temperature field inside the chamber and more slight magnetic properties difference among the magnets in mass production than rapid cooling, here we performed a comparative study on a model magnet Sm25Co46.9Fe19.5Cu5.6Zr3.0 (wt%) to investigate how the post-solutionizing cooling rate affects the microstructure and magnetic properties. In comparison with the rapid cooling condition, slow cooling produces coarser cellular nanostructure and lower defects density at the solution-treated state. Such initial microstructural difference leads to slower 1:5 H growth kinetics and slower defects dissociation kinetics during the subsequent aging process, characterized by the smaller fraction of 1:5 H cell boundary phase and the higher density of remanent defects in the slowly-cooled final magnets. Since the 1:5 H phase plays a dominant role on the coercivity and the remanent defects are harmful to hard magnetic properties, further work reveals that longer aging time can promote the formation of 1:5 H phase and to reduce the harmful defects for achieving better magnetic performance in the slowly-cooled magnets. These findings may be helpful for achieving uniform magnetic performance in mass production of 2:17-type Sm-Co-Fe-Cu-Zr magnets.

Evolution of the role of molybdenum in duplex stainless steels during thermal aging: From enhancing spinodal decomposition to forming heterogeneous precipitates

Thermal aging of ferrite in duplex stainless steels leads to a complex microstructural evolution that can give way to large deleterious changes in mechanical properties. The microstructural evolution mechanisms that happen concurrently are strongly linked to minor changes in composition. By characterizing duplex stainless steels with various compositions over a range of aging conditions, it was revealed that adding a modest amount of Mo to cast austenitic stainless steel (such as changing from grade CF3 to grade CF3M) not only increases the kinetics of spinodal decomposition and Ni-Si-Mn-rich G-phase precipitation, but it also forms a separate Mo-rich phase. At shorter equivalent aging times, Mo segregates from Fe and towards Cr accelerating spinodal decomposition. At longer aging times, Mo enriches in the Ni-Si-Mn clusters before phase separating into an adjoined Mo-rich cluster. These phase changes and precipitation events result in a rather steep drop in fracture and impact toughness. These results will inform the design of similar alloys for use at high temperatures.