Heat-treated Samples Research Articles

The effect of biosecurity heat treatment on soils: implications for soil analytical methods and mineral exploration

Soils are widely used as geochemical sample media. A recent advancement in soil analytical methods for exploration developed in Australia, the UltraFine+ ® method, concentrates the clay-sized fraction of <2 µm and then analyses this fraction for over 50 elemental concentrations, pH, electrical conductivity and spectral mineralogy/properties (i.e., visible –near- to shortwave and mid- infrared reflectance spectroscopy). This new approach was initially limited to Australian soils due to strict biosecurity legislation. However, since 2022 samples can be shipped to Australia and heat-treated to 160 °C to be released from quarantine-approved premises prior to analysis. A study was undertaken to determine the influence of the temperature heat treatment on the spectral and geochemical properties of soils. One hundred and three soils were collected from multiple regions of Australia to provide a background set of samples to test the effect of heat treatment on the analytical response using the clay-sized fraction analytical method. These soils comprised multiple clay types and are representative of general soil types and target commodities in mineral exploration settings. Results show that heat treatment did not significantly impact elemental abundance of common pathfinder and target elements in minerals exploration with strong correlation and linear trends between the treatments. Spectral parameters measured in the visible to mid infrared range were also unaffected by heating. Some observed elemental changes were related to inconsistent extraction of resistate elements (Hf, Nb, Zr). Counter to other studies, a pH decrease was observed in heat-treated samples. The study concludes that biosecurity release heat treatment at 160 °C does not hinder analysis of the ultrafine fraction soils with a concentrated aqua regia assay and spectral mineralogy measurements.

Effect of heat treatment on chemical durability and TL dosimetric properties of Na2O-SrO-B2O3 glass system

Na2O-SrO-B2O3 glass system prepared by the known melting-quenching method was applied to a progressive heat treatment (HT) at 600 °C for 4, 6, 8 and 10 h. Glass (G) and its corresponding heat treated (HT) samples were characterized by density, molar volume and XRD technique that revealed the complete amorphous structure of the glassy matrix and the coexistence of two crystalline phases in the corresponding glass ceramics; monoclinic phase of NaSrBO3 and the triclinic phase of sodium strontium pentaborate Na3SrB5O10. Testing chemical durability of G and HT samples at 95 °C for 24 h, revealed higher chemical stability in aqueous (H2O) and acidic (H2SO4) solutions, while the highest leachability was detected in the alkaline medium (NaOH). pH of leaching solution was found to control the leaching process and displayed rising behavior with time of immersion. The progressive rising of leaching solution temperature; 25, 40, 60 and 95 °C, revealed a quiet leachable enhancement as well. SEM photographs represented rough and heterogeneous surface morphology with continual leaching and the formation of colloidal layers at the later stages of corrosion.The TL-dosimetric properties indicated extremely higher thermoluminescence properties of HT samples than the untreated glass. The analysis of the exhibited TL signals revealed the composition of the glow curves of the treated and untreated samples of eight TL components. The obtained results recommend the acceptable chemical durability of the heat treated samples especially in the neutral medium that displayed no more than 8.5% leachability rate yearly, besides their promising TL-dosimetric features, accordingly their possible application in the field of radiation dosimetry.

Numerical and experimental behavior of fiber reinforced polymer type and layer number effect on the flexural properties of heat-treated black pine wood

Heat treatment is one of the environmentally friendly methods applied to improve the structural properties of wooden materials. While heat treatment improves some properties of wood material, it also negatively affects its mechanical properties depending on the heat treatment conditions applied. The decrease in mechanical properties due to heat treatment limits the use of wood material in various applications requiring mechanical strength. For this purpose, various fiber-reinforced polymers have been used in recent years. In this study, it was aimed to experimentally and numerically examine the flexural properties of unheat-treated and heat-treated black pine (Pinus nigra Arnold.) wood reinforced 1, 2 and 3 times with carbon, glass and aramid. Following the experimental flexural tests, the samples were modeled and analyzed in the finite element software program. The average flexural strength of the heat-treated sample is 11.72% lower, and the elasticity modulus is 1.23% lower than the unheat-treated sample.It has been determined that carbon-based polymer fabrics, among fiber-reinforced polymer fabrics, have the best reinforcement effect. The flexural strength of the UHT-C-3 sample is 6.1% and the elasticity modulus is 3.52% higher than the UHT-C-1 coded sample. Compared to the sample without reinforcement, flexural strength increased by 30% and elasticity modulus increased by 7%. It is seen that as the number of fiber reinforced polymer layers increases, the flexural properties also increase. When the experimental and numerical analysis results were examined, the flexural strength and modulus of elasticity values gave similar results at the R2: 0.88–0.99 level. In addition to technologies using kinds of reinforcement evaluated in conservation applications, it may be utilized for numerical analysis in the field of repairing or reinforcing different grades, patterns, and types of reinforcement in already-existing wooden structures.

Microstructural stability and mechanical properties of the as-cast and heat-treated newly developed TiNbCrTa refractory complex concentrated alloy

In this study, a TiNbCrTa refractory complex concentrated alloy (RCCA) was prepared using vacuum arc remelting. The microstructural evolution and mechanical properties of both as-cast and heat-treated RCCA samples were analyzed. Heat treatment (HT) was performed at 800–1200 °C for 1 h in a vacuum-sealed environment. These samples exhibited a formation of Cr2Nb and Cr2Ti Laves phases. A variation in elemental distribution was observed, with interdendritic (ID) regions showing higher fractions of Ti and Cr, while the dendritic regions had a greater concentration of Ta and Nb. Micro-segregation at the IDs was confirmed through energy dispersive x-ray spectroscopy mapping, which inferred the formation of Cr- and Ti-rich phases during HT at 800–1200 °C. High-temperature HT at 1200 °C for 1 h led to the evolution of the hcp omega phase. Prolonged HT at 1200 °C for 96 h resulted in the evolution of a Cr-rich Laves phase (Cr2Ta), which was homogeneously distributed within the microstructure, indicating an unstable microstructure. Furthermore, despite prolonged HT, a variation in the elemental distribution persisted due to the presence of dendritic and ID regions. Electron backscattered diffraction analysis revealed the presence of bcc and hcp phases in the dendritic and ID regions, respectively, of the as-cast and HTed samples. The as-cast samples demonstrated a high compressive strength of approximately 2 GPa. Micro-hardness values increased with the HT temperature up to 1000 °C. Further increases under HT conditions did not significantly reduce the microhardness value, whereas prolonged HT at 1200 °C led to an increase in the microhardness value. Overall, the newly developed TiNbCrTa RCCA exhibited high-strength behavior even after the phase transformation.

Uniformity improvement of microwave heating with switchable frequency selective surface

Microwave heating has attracted interests in many industrial applications, yet heating inhomogeneity remains a critical issue. This study proposes a novel approach to enhance microwave heating uniformity employing a switchable frequency selective surface (FSS). The PIN diodes in each FSS unit cell can be toggled ON or OFF by controlling voltage biases, enabling the FSS to either reflect or transmit incident electromagnetic waves. Placing this switchable FSS in front of a heating cavity wall creates a dynamic reflecting boundary, which, through periodic alterations of the FSS and metallic wall, effectively improves the heating uniformity. To validate this method, we simulated the heating of a potato sample at 2450 MHz using COMSOL Multiphysics and conducted experimental tests. Both simulation and experimental results demonstrate that the proposed method significantly enhances microwave heating uniformity across various materials and sample sizes. This work provides a promising solution for designing microwave heating reactors.

Purification and investigation of tellurium rich Te-As-Se chalcogenide glass for extended far-infrared transmission

In the present study, tellurium-rich (45–55 mol%) As-Se-Te chalcogenide glasses were synthesized and purified further to eliminate the impurities for achieving extended far infrared transmission. The glasses were characterized and studied for physical, thermal, optical, structural and mechanical properties. All the glasses have shown transparency in the wavelength range of ∼1.6–19 µm, with >45 % transmission with impurities. The purification process through vacuum distillation has eliminated the oxide impurities in the glass and the glass displayed ∼52 %T in the wide infrared region. The refractive index for purified glass decreased from 3.487 at 2 µm to 3.362 at 10 µm. The purified glass was heat treated for four hours, and the most dominant crystal phase, As2Te3 was observed in XRD analysis. Presence of sharp Raman peak at ∼120 cm−1 belonging to As2Te3 pyramids in heat-treated sample well agreed with the XRD results.

Effect of heat treatment on microstructure of near-eutectic Al-Ni-Mn alloy, and determination of mechanical and thermoelectrical properties

This study examined the impact of solution heat treatment on the microstructure, mechanical characteristics, thermophysical properties, and electrical resistivity of an Al-Ni-Mn near-eutectic alloy. The investigation focused on varying temperatures and holding periods. The composition of the Al-Ni-Mn near-eutectic alloy system was chosen as Al-5.3%Ni-1.0%Mn (wt). In the non-heat-treated sample, the matrix phase (α-Al) is in equilibrium with the intermetallic Al9(Mn,Ni)2 and Al3Ni phases. The hardness value of the non-heat-treated sample (49.8 kg mm−2) increased to 70.1 kg mm−2 with 2 h of solution heat treatment at 570 °C and then 8 h of artificial aging at 180 °C. The hardness value increased by approximately 41%. TE: 651.81 °C for the non-heat-treated sample and TE:648.79 °C for the heat-treated sample. Fusion enthalpy (ΔH) value was determined as 336.79 (J g−1) for the non-heat-treated sample and 516.36 (J g−1) for the heat-treated sample. Heat Capacity (Cpl) value was found to be 0.364 J g−1.K for the non-heat-treated sample and 0.560 J g−1.K for the heat-treated sample. The electrical resistivity value of the 2 h’ solution heat-treated sample at 600 °C reached its highest value.

Facile synthesis of novel bismuth oxide/bismuth molybdate nanocomposites as advanced anodes for high performance Li‐ion batteries

In this study, a novel nanocomposite material consisting of Bi2O3 and Bi2MoO6, named as Bi2O3@Bi2MoO6, was successfully fabricated by co-precipitation method in ethylene glycol solvent. Morphological analysis of the heat-treated sample at 400 °C for 12 h in Ar atmosphere (Bi2O3@Bi2MoO6 _400 °C) showed that it contained nano-sized particles of Bi2O3 and Bi2MoO6; in addition, an amorphous phase along with a crystalline structure was also observed. When used as an anode for Li-ion batteries (LIBs), Bi2O3@Bi2MoO6 _400 °C anode exhibits excellent electrochemical properties such as high Coulombic efficiency, high specific capacity, excellent capacity retention, and outstanding rate capacity. Specifically, the Bi2O3@Bi2MoO6 _400 °C anode presented a reversible capacity of 786 mAh g−1 at the beginning cycle at 0.1 A g−1 and retained about 90 % of the charging capacity value after 80 cycles. The advanced electrochemical properties of the nanocomposite anode are related to the combination of many aspects such as nanostructure, existence of amorphous phase, and pseudo-behaviour of metal-based components. The structural stability and electrochemical performance of the anode material, therefore, are improved. These results demonstrate Bi2O3@Bi2MoO6 _400 °C as a promising material for establishing high-performance LIB anodes.

High-temperature fretting wear behavior of IN738LC alloy formed by laser powder bed fusion

The fretting wear behavior of IN738LC alloy formed by laser powder bed fusion at 850 ℃ with various load (35 N and 100 N) were systematically studied. The results demonstrate that increases the load, leading the fretting wear mode gradually transitions from the gross slip region (GSR) to the mixed slip region (MSR). Judging with the radar map drawn by experimental data, the high-temperature comprehensive performances of fretting wear for supersolvus heat-treated sample improved significantly. The analysis of fretting wear cross-section microstructure indicates that the thermoplastic deformation of L-PBFed IN738LC alloy occurs under the interaction of different normal loading and force of tangential friction, which results in the accumulation of strong dislocation densities and diverse deformed tissue in damage zone.

High-temperature fracture behavior of an α/β Titanium alloy manufactured using laser powder bed fusion

The room and high temperature (up to 600 °C) mechanical properties, with emphasis on the fracture toughness and fatigue resistance, of an α/β titanium alloy that was additively manufactured using the laser powder bed fusion (LPBF) technique were evaluated in the as-printed (α’ lath martensite with negligible β phase content) and heat-treated (α/β structure with a significant volume fraction of the β phase) states for critically examining the β phase's role in the fracture and fatigue behavior (given the significantly higher diffusion rates of various species in β compared to α). Experimental results reveal that the heat-treated sample exhibits superior ductility and fracture initiation toughness at elevated temperatures, compared to the as-printed sample, due to the presence of β ligaments in the former. They also prevent strain localization along the prior β grain boundaries, and their absence in the as-printed state leads to cracking along those boundaries. While the fatigue crack growth (FCG) rates in both the as-printed and heat-treated samples deteriorated with increasing temperature, the threshold for FCG generally increased, which is attributed to creep-induced crack tip blunting. Moreover, a double Paris exponent phenomenon is observed for the heat-treated sample at 300 °C, attributed to the hydrogen-assisted crack growth, with β phase providing an accelerated diffusion pathway. Overall, the experimental results and their analyses illustrate the intricate relationship between creep, hydrogen diffusion, and the β phase in dictating the fracture behavior of LPBF α/β titanium at elevated temperatures.

Calorimetric and Volumetric Studies of Dislocations During Martensitic Transformations in Shape Memory TiNi Alloy

Based on the use of appropriate approaches, methods and results of the analysis of a number of topical problems of physical materials science, an in-depth analysis has been done of calorimetric and volumetric data for direct, reverse and deformation martensitic transformations in a nanostructured Ti49.3Ni50.7 shape memory alloy obtained by cold rolling with simultaneous action of pulsed high-density current. For the first time, by applying a new technique for processing calorimetric spectra (peaks), the staging and “kinetics” of changes in heat content, as well as thermal effects (enthalpies of individual stages) during direct and reverse martensitic transformations during cooling or heating of samples at a constant rate (3 × K/ min) in the range 170–370 K has been done. It is shown, by processing volumetric data, using theoretical values of the dislocation density and elements of the classical theory of dislocations, that in the Ti49.3Ni50.7 shape memory alloy subjected to cold deformation accompanied by the action of a pulsed current, a deformation martensitic transformation occurs, leading to a positive volume effect (∆V/V) ≈ 3 × 10–3), which can be largely due to dislocations. It is shown, by applying the theoretical values of the dislocation density and elements of the classical theory of dislocations, that the possible contributions of dislocations to the enthalpies of direct and reverse martensitic transformations (in the Ti49.3Ni50.7 alloy) can and should be significantly lower in absolute value, but opposite in sign to the observed enthalpies of direct and reverse martensitic transformation in a given alloy. It is shown that the physics of the processes under consideration is contained to a certain extent in scientific discoveries No. 239 “The phenomenon of thermoelastic equilibrium during phase transformations of the martensitic type – the Kurdyumov effect” and No. 339 “The phenomenon of the formation of non-equilibrium grain boundaries in polycrystals when they absorb lattice dislocations”.

Novel TiO2-Supported Gold Nanoflowers for Efficient Photocatalytic NOx Abatement.

In this study, we pioneered the synthesis of nanoflower-shaped TiO2-supported Au photocatalysts and investigated their properties. Au nanoflowers (Au NFs) were prepared by a Na-citrate and hydroquinone-based preparation method, followed by wet impregnation of the derived Au NFs on the surface of TiO2 nanorods (TNR). A uniform and homogeneous distribution of Au NFs was observed in the TNR + NF(0.7) sample (lower Na-citrate concentration), while their distribution was heterogeneous in the TNR + NF(1.4) sample (higher Na-citrate concentration). The UV-Vis DR spectra revealed the size- and shape-dependent optical properties of the Au NFs, with the LSPR effect observed in the visible region. The solid-state EPR spectra showed the presence of Ti3+, oxygen vacancies and electron interactions with organic compounds on the catalyst surface. In the case of the TNR + NF(0.7) sample, high photocatalytic activity was observed in the H2-assisted reduction of NO2 to N2 at room temperature under visible-light illumination. In contrast, the TNR + NF(1.4) catalyst as well as the heat-treated samples showed no ability to reduce NO2 under visible light, indicating the presence of deformed Au NFs limiting the LSPR effect. These results emphasized the importance of the choice of synthesis method, as this could strongly influence the photocatalytic activity of the Au NFs.

Dual-phase polycrystalline crystal plasticity model revealing the relationship between microstructural characteristics and mechanical properties in additively manufactured maraging steel

To elucidate the relationship between microstructural characteristics and mechanical properties in additively manufactured (AM) maraging steel, this study introduces a computational approach that addresses two fundamental challenges. Firstly, it addresses the creation of representative volume elements (RVEs) that mimic the observed microstructural complexities, such as meltpool boundaries, prior austenite grains, packets and blocks of lath martensite. This is accomplished through the application of Potts Monte-Carlo methods and grain segmentation techniques in accordance with the Kurdjumov–Sachs orientation relationship. Secondly, this study develops a comprehensive crystal plasticity (CP) model encompassing both bcc and fcc plasticity. Inspired by atomistic and discrete dislocation dynamics studies, the proposed CP model incorporates characteristics intrinsic to bcc plasticity, including non-Schmid effects, dislocation and precipitate strengthening, and Hall–Petch type strengthening of elongated martensitic blocks. Utilizing the created RVEs and the proposed CP framework, finite element simulations are conducted based on an update-Lagrangian formulation. The purpose of this study is to investigate the deformation behavior, texture evolution, tension–compression asymmetry, and evolution in dislocation density in RVEs representative of as-built and heat-treated samples of maraging steel. This computational approach and its findings deepen our understanding of the intricate interplay between microstructural characteristics and mechanical properties in maraging steel and also provide valuable guidelines for refining its additive manufacturing and heat treatment processes.

Effect of post-deposition heat treatments on the microstructure and tensile properties of wire-fed electron beam directed energy deposition GH4169 Ni-based alloy

The microstructure and tensile properties of GH4169 alloy fabricated by wire-fed electron beam directed energy deposition (EB-DED) were investigated in both as-deposited (As-Dep) and homogenization plus double aging heat treatment (HA) condition. The results show that thermal cycling caused an aging effect in the As-Dep samples, resulting in the precipitation of the γ’/γ” phases in close proximity to the Laves phase. The dissolution behavior of Laves phase in GH4169 alloy at various homogenization heat treatment temperatures and holding times was studied. Based on experimental results and Johnson-Mehl-Avramie-Kolmogorov (JMAK) analysis, the dissolution activation energy of Laves phase was calculated as 218.2 kJ/mol. The heat treatment regime utilized in HA treatment consisted of 1150 °C × 60 min/WC + 720 °C × 8 h/FC to 620 °C × 8 h/WC. After HA treatment, most of the Laves phases were dissolved and the γ’/γ” phases were precipitated. The mechanical properties of HA samples are superior to those of As-Dep samples. The morphology, distribution and evolutionary mechanism of the Laves phase, γ’/γ” phases are discussed and analyzed.

Dynamic Response of Ti-6Al-2Zr-1Mo-1V Alloy Manufactured by Laser Powder-Bed Fusion.

Titanium parts fabricated by additive manufacturing, i.e., laser or electron beam-powder bed fusion (L- or EB-PBF), usually exhibit columnar grain structures along the build direction, resulting in both microstructural and mechanical anisotropy. Post-heat treatments are usually used to reduce or eliminate such anisotropy. In this work, Ti-6Al-2Zr-1Mo-1V (TA15) alloy samples were fabricated by L-PBF to investigate the effect of post-heat treatment and load direction on the dynamic response of the samples. Post-heat treatments included single-step annealing at 800 °C (HT) and a hot isotropic press (HIP). The as-built and heat-treated samples were dynamically compressed using a split Hopkinson pressure bar at a strain rate of 3000 s-1 along the horizontal and vertical directions paralleled to the load direction. The microstructural observation revealed that the as-built TA15 sample exhibited columnar grains with fine martensite inside. The HT sample exhibited a fine lamellar structure, whereas the HIP sample exhibited a coarse lamellar structure. The dynamic compression results showed that post-heat treatment at 800 °C led to reduced flow stress but enhanced uniform plastic strain and damage absorption work. However, the HIP samples exhibited both higher stress, uniform plastic strain, and damage absorption work owing to the microstructure coarsening. Additionally, the load direction had a subtle influence on the flow stress, indicating the negligible anisotropy of flow stress in the samples. However, there was more significant anisotropy of the uniform plastic strain and damage absorption. The samples had a higher load-bearing capacity when dynamically compressed perpendicular to the build direction.

Designing the mechanical behavior of NiTi self-expandable vascular stents by tuning the heat treatment parameters

The remarkable mechanical properties of nickel-titanium (NiTi) shape memory alloy, particularly its super-elasticity, establish it as the material of choice for fabricating self-expanding vascular stents, including the metallic backbone of peripheral stents and the metallic frame of stent-grafts. The super-elastic nature of NiTi substantially influences the mechanical performance of vascular stents, thereby affecting their clinical effectiveness and safety. This property shows marked sensitivity to the primary parameters of the heat treatment process used in device fabrication, specifically temperature and processing time. In this context, this study integrates experimental and computational analyses to explore the potential of designing the mechanical characteristics of NiTi vascular stents by adjusting heat treatment parameters. To reach this aim, differently heat-treated NiTi wire samples were experimentally characterized using calorimetric and uniaxial tensile testing. Subsequently, the mechanical response of a stent-graft model featuring a metallic frame made of NiTi wire was assessed in terms of radial forces generated at various implantation diameters through finite element analysis. The stent-graft served as an illustrative case of NiTi vascular stent to investigate the impact of the heat treatment parameters on its mechanical response. From the study a strong linear relationship emerged between NiTi super-elastic parameters (i.e., austenite finish temperature, martensite elastic modulus, upper plateau stress, lower plateau stress and transformation strain) and heat treatment parameters (R2 > 0.79, p-value < 0.001) for the adopted ranges of temperature and processing time. Additionally, a strong linear relationship was observed between: (i) the radial force generated by the stent-graft during expansion and the heat treatment parameters (R2 > 0.82, p-value < 0.001); (ii) the radial force generated by the stent-graft during expansion and the lower plateau stress of NiTi (R2 > 0.93, p-value < 0.001). In conclusion, the findings of this study suggest that designing and optimizing the mechanical properties of NiTi vascular stents by finely tuning temperature and processing time of the heat treatment process is feasible.

Investigation of the Microstructure and Dry-Sliding Wear Behavior of Co Containing Al-Si-Fe Scrap Alloy

This study investigates the influence of cobalt (Co) addition on the microstructural and wear properties of an aluminum (Al) scrap alloy containing high iron (Fe) impurity content (3%). Microstructural analysis using scanning electron microscopy and optical microscopy confirmed the presence of Co in Fe-rich intermetallics. Upon increasing the Co concentration, β-Al5FeSi phase was seen to be refined without significant morphological modifications. Furthermore, Co addition promoted the formation of a new quaternary phase Al32Si7Fe4Co phase, which was finely distributed throughout the microstructure and acts as a tribo-layer in the Al scrap alloy, offering enhanced wear resistance and improved stability against wear. Standard EN-31 steel disk with compositions chromium (Cr)-1.6%, manganese (Mn)-0.75%, silicon (Si)-0.35%, and carbon (C)-0.9% was used for the wear test. Microhardness and wear properties were evaluated for both the as-cast and heat-treated alloys, with the as-cast samples exhibiting superior wear resistance and a lower coefficient of friction compared to the T6 heat-treated samples. Addition of Co showed refinement in the β-Fe rich intermetallics over the morphological modifications. Similarly, Co addition enhanced the hardness and wear resistance in the as cast alloys. This work provides a detailed analysis contributing significant understandings into the wear mechanisms and potential applications of Co modified recycled Al in various industrial sectors.

Powder-blown laser-based directed energy deposition of (14M) Ni-Mn-Ga magnetic shape memory alloy

Ni-Mn-Ga-based magnetic shape memory (MSM) alloys are renowned for their large magnetic-field-induced strains, making them attractive for compact magnetically controlled actuators requiring high response frequencies and large reversible deformations. In this study, Ni-Mn-Ga alloy samples were deposited using powder-blown laser-based directed energy deposition (DED-LB), employing gas-atomised powder pre-alloyed with excess Mn. The samples were deposited following a systematic experimental design, varying the applied laser power and employing two melting strategies: unidirectional and bidirectional. The results demonstrate the feasibility of achieving high relative densities (>97.5 %) in multi-layered Ni-Mn-Ga samples through DED-LB. All as-deposited samples exhibited a consistent 0.7–0.9 at% Mn loss in comparison to the powder feedstock, thus showing that the Mn overdosing requirements for DED-LB differ from those in laser powder bed fusion. Both as-deposited and heat-treated samples exhibited seven-layered modulated (14 M) martensite structures at ambient temperature. In contrast, the heat-treated samples also exhibited fully reversible martensite transformation at around 66 ºC and a Curie temperature at around 94 ºC. Distinct microstructural characteristics were observed based on the melting strategy, with bidirectional melting promoting the formation of large columnar grains with a strong <100> texture approximately along the build direction. This study highlights the potential of DED-LB processes in manufacturing relatively large (mm to cm scale) functional Ni-Mn-Ga actuators and contributes to the ongoing efforts in laser additive manufacturing of functional materials.

Toward additive manufactured crack-free NiTiCu shape memory alloys with low-hysteresis and tailorable phase transition behavior supported by theoretical design

In this study, a novel NiTiCu alloy composition (i.e., Ni41.5Ti49.5Cu9.0 in at%) with low hysteresis and two-step martensitic transformation was first designed for laser powder bed fusion (LPBF) technique through a combination of CALPHAD and machine learning techniques. The LPBF-fabricated NiTiCu alloy displayed a cellular grain structure devoid of discernible cracks. Following solution and aging treatments, the NiTiCu samples exhibited the desired two-step martensitic transformation with a low thermal hysteresis of 8.9 K, aligning closely with the design specifications. Interestingly, the heat-treated samples demonstrated enduring stability in recovery strain, achieving a remarkable 5.76 % over the course of 50 cyclic loading tests. Fundamentally, the sustained recovery strain observed and the nuanced variations in superelastic behaviors can be ascribed to the interaction between dislocations and Ti2(Ni, Cu)/Ni4Ti3 precipitates. The saturation of dislocations around precipitates stabilized the partial martensite and hindered the slip deformation, thereby ensuring stable superelastic behavior. Finally, an effective roadmap toward crack-free LPBF-fabricated NiTiCu shape memory alloys with desired phase transition behavior was proposed. It is envisaged that such a roadmap holds promise for broader applicability across other NiTi-based shape memory alloys.

Insight into the relationship between the mineralogical characteristics and adsorption properties toward pollutants of oil shale semi-coke

It is urgent and indispensable to develop the sustainable approach to realize the resource utilization of the industrial solid wastes. In this study, the oil shale semi-coke obtained from Yaojie, Longkou, Wangqing and Huadian were selected to study the relationship between the mineralogical characteristics and adsorption properties of oil shale semi-coke toward pollutants of Pb2+, Cd2+, and PO43-. The results indicated that the sample of Yaojie was mainly composed of quartz (55.1 %) and kaolinite (29.3 %) defined as silicate type, while the one of Longkou was a typical carbonate type with high calcite content of 29.7 % equaled the amount of quartz. Due to the unique mineralogical properties of quartz, kaolinite and calcite, the involved raw oil shale semi-coke had a poor adsorption capacity to the model pollutants. By contrast, the calcined samples exhibited good adsorption properties toward three pollutants, especially the samples derived from Longkou, in which the samples prepared at 600℃ and 800℃ presented the maximum capacity toward Pb2+ (257.03 mg/g), Cd2+ (131.72 mg/g) and PO43- (129.53 mg/g), respectively, which was higher than most of the reported similar adsorbents. Furthermore, the adsorption kinetics and isotherm of the heat-treated oil shale semi-coke from Longkou for Pb2+, Cd2+ and PO43- conformed to the quasi-second order kinetic model and Langmuir isothermal adsorption model, respectively. Due to the synergistic effect of the functional groups adsorption, mineral precipitation and ion exchange of the heat-treated samples, the adsorbates of PO43-, Cd2+, and Pb2+ were well adsorbed and then transformed into CaHPO4·2 H2O, CdCO3, PbCO3, Pb3(CO3)2(OH)2, respectively.