The present work aims to study the influence of hot deformation on microstructural development and flow behavior in the Al-4.8Mg-0.3Sc alloy produced by the laser powder bed fusion (LPBF) technique. Uniaxial compression tests have been conducted within a temperature regime of 200–350 ºC at a 0.01–1 s?1 strain rate using a Gleeble-3800™ thermomechanical simulator. The major results show that the flow behavior is governed mainly by strain hardening at 1 s?1 strain rate and dynamic recrystallization (DRX) at 0.1 s?1 within 250–350 ºC. The constitutive equations have been developed by employing activation energy (Q) and other material constants to forecast the influence of deformation temperature and strain rates on flow stress. Compared to other Al alloys (114–227 kJ/mol), the mean Q for hot deformation is found to be significantly higher (?340 kJ/mol at a 0.69 true strain), indicating more stress requirement for deformation, also confirmed by the flow curves. Moreover, the processing map developed with MDMM+Poletti instability criteria is found to be appropriate compared to DMM and MDMM models. The safe workable zone is obtained in the range of 250–350 ºC/0.01–1 s?1 with a maximum power dissipation efficiency of 45.8 %. Microstructural analysis shows that recrystallization starts primarily at melt pool boundaries which formed during the LPBF process. The highest recrystallization fraction is observed for the specimen deformed at 350 ºC/0.01 s?1 (59.3 %). SEM analysis of the samples deformed at 200 ºC/0.01–1 s?1 and 250 ºC/1 s?1 depict the formation of various defects, such as voids and micro-cracks, mainly governed by the non-uniform deformation at the particle/matrix interface and due to the presence of voids/pores. A detailed investigation of Q, stress exponent (n), flow stress behavior, and constitutive equations suggests that the hot deformation is mainly governed by both dislocation climb and cross-slip mechanisms.

The present work reports the synthesis and mechanical behavior studies of Mg–3Ca alloy foams stabilized by ultrafine MgAl 2 O 4 (spinel) particles. The MgAl 2 O 4 particles was created in-situ in the Mg–3Ca alloy melt through the reaction of Mg, Al and O. Foaming was done by adding dolomite (CaMg(CO 3 ) 2 ) as blowing agent in the melt. The foaming behaviour was studied for different MgAl 2 O 4 content in Mg–3Ca and holding times (10 and 15 min). The study reveals that the presence of MgAl 2 O 4 significantly influences the foaming behavior of Mg–3Ca alloy resulting in equiaxed cell structure, uniform cell size distribution, higher expansion in comparison to the Mg–3Ca alloy foam which contains only MgO and CaO. An in-depth phase and microstructural analysis were performed to investigate the particles present in the gas-solid interface of the foam that contributes to foam stabilization. The quasi-static compression studies of foams exhibited better compressive strength (?3–11 MPa) and energy absorption capacity (?1.3–5.7 MJ/m 3 ) in comparison to the Mg foams reported in the literature. The ductility of the Mg foams was also measured and compared with that of existing aluminium foams.

The paper investigates the stabilization behaviour of in-situ created, sub-micron sized MgAl 2 O 4 (spinel) particles at various concentration in Al-11 wt%Si foams. The foam evolution (expansion, coalescence and drainage) as a function of particle concentration and foaming time was monitored in-situ using X-ray radioscopy. The foam containing higher concentration (3.4 vol%) of MgAl 2 O 4 exhibited higher stability and expansion until solidification. Decreasing the MgAl 2 O 4 concentration to 2.5 vol% exhibited similar foam expansion like 3.4 vol% particle-containing foam, however the stability of the former is poor due to higher drainage. The foam containing lower MgAl 2 O 4 concentration (1.7 vol%) showed poor stability and expansion due to further increase in drainage. The 3D visualisation of MgAl 2 O 4 particles in the gas solid interface embedded in the oxide skin was brought out by FIB tomography. TEM analysis revealed that the nano-sized MgAl 2 O 4 particles are closely embedded in the oxide skin.

The present study aims at investigating the effect of pre-milling nickel (Ni) and aluminium (Al) powders on the sintering behaviour of NiAlFeCoCr high entropy alloys (HEA). As-milled NiAlFeCoCr HEA was prepared by mixing the Ni, Al, Fe, Co and Cr powders (in equiatomic ratio) for 10 h in a planetary ball mill. In case of pre-milled (NiAl)FeCoCr HEA, Ni and Al powders were initially milled for 5 h and this mixture was then further milled with Fe, Co and Cr powders for another 10 h. XRD, SEM-EDS, TG-DSC and Dilatometric analysis were performed for the characterization of these HEAs. The formation of FCC and BCC phases was observed in both, as-milled and pre-milled HEAs. The sintering behaviour (at 1000–1200 °C) of the HEAs was compared and observed that as-milled HEA sintered by viscous flow mechanism, which was absent in case of pre-milled HEA. An exothermic reaction observed in the as-milled HEA at 518 °C representing Ni and Al reaction, was absent in the pre-milled HEA, indicating that Ni and Al had reacted during the pre-milling process. The micro-Vickers hardness of as-milled HEA also increased from 638 ± 8.73 HV to 662 ± 12.24 HV upon pre-milling.

Pure Mg foams stabilized by ex-situ added CaO particles were developed in this study. Mg/xCaO foams (x = 5, 7 and 10 wt.%) exhibited uniform pore distribution, thinner yet stable pore wall cross-sections. Mg-Ca-O transition phase and MgO particles were formed at the interface of Mg-CaO, which improved the wetting of CaO particles in the Mg melt. The CaO particles, Mg-Ca-O transition phase and blocky MgO particles collectively stabilized the foam. Mg-Ca-O and MgO phases disperse along the gas-liquid interface of foams thereby preventing from wrinkling of interfaces during solidification. TEM analysis of Mg/10wt.% CaO foam powder also confirmed the formation of nano-sized (~ 200 nm) MgO particles of different morphologies. TG-DSC analysis confirmed the exothermic Mg-CaO reaction at 610 ºC, resulting in formation of MgCa and MgO phases, as identified using XRD analysis. 7 wt.% CaO addition exhibited the best foam structure in terms of mean pore diameter (2.19 mm) and circularity (0.75). The lowest foam density of 0.38 g/cm and relative density of 21 % was achieved in case of Mg/10wt.% CaO foams.

Mg-3Ca alloys with varying Zn concentration (0 to 5 wt pct) were foamed using CaCO3 via liquid processing route and their compressive and energy absorption behavior were investigated. The Mg-Zn-Ca alloy foams revealed a uniform cell structure with minimum defects and improved expansion in comparison to Mg-3Ca foams without zinc. The cell wall microstructure of Mg-3Ca alloy foam revealed micro-cracks and MgO particle agglomerates at the gas-solid interfaces. Upon Zn addition, the micro-cracks were diminished to larger extent and finely MgO particles were dispersed homogenously at the gas-solid interface. Pore diameter of the foams decreased from 2.29 to 2.06 mm, while circularity improved from 0.60 to 0.72 with increasing Zn content from 0 to 5 wt pct. The peak compressive stress also improved from 1.64 to 5.09 MPa with 5 wt pct Zn addition to Mg-3Ca foam. The ductility number improved from 0.66 to 0.75 while retaining energy absorption efficiency ~ 60 pct in the plateau region. The improved mechanical properties of Mg-Zn-Ca foams are due to elimination of brittle Mg2Ca and increase in the Mg6Zn3Ca2. The reduced pore diameter, circular and equiaxed pores and crack-free interfaces in the foams were also contributed to the better mechanical properties

The present paper investigates the stabilization of Mg-3Ca alloy and Mg-3Ca/SiC/5p composite foams with and without the addition of 0.12 wt.% beryllium. In Mg-3Ca alloy foam, Be addition has shown a significant improvement in the expansion and pore structure. Whereas, in case of Mg-3Ca/SiC/5p composite foams, the SiC particles stabilized the foam effectively, while Be addition does not show any distinguishable improvement in the foam structure. The formation of BeO and the dense coverage of SiC particles in the gas–solid interface of Mg-3Ca and Mg-3Ca/SiC/5p composite foams, respectively, are the reasons for the foam stabilization. Mg-3Ca/SiC/5p composite foam exhibited lowest foam density of 0.10 g/cm. The quasi-static compression test shows that Mg-3Ca-0.12Be/SiC/5p composite foam containing Be exhibited lower foam density and higher normalized compressive strength. The energy absorption capacity per unit foam density in Be containing foams was also higher.

Stabilization is an essential requirement to produce closed-cell metal foams. In the melt route of foaming, usually ceramic particles are used as foam stabilizers. For the first time, the present study introduces ZrB 2 particles as foam stabilizers. We demonstrate the foaming of in-situ based Al composite containing submicron ZrB 2 particles. The effect of foaming temperature and holding time on the structural and mechanical properties of the foams was studied. The composites and foams were characterized using XRD, SEM/EDS, and optical scanning techniques. The mechanical properties of the foams were determined by subjecting the foams to a quasi-static compression test. Submicron ZrB 2 particles present in the cell wall and at the gas-solid interface promoted foam stability. All the foams exhibited a good cellular structure with high expansion. Among all the foams, the foams prepared at 680 °C with a holding time of 120 s exhibited the smallest cell size and the best mechanical properties. The structural and mechanical properties of the Al–5ZrB 2 foams were found to be comparable to conventional foams.

The present work is the first ever study where the influence of beryllium (Be) addition on the stability of Mg alloy foam was investigated. Mg-3Ca alloy foams were produced by the liquid processing route with and without Be micro-addition. CaCO 3 was used as a blowing agent. Mg-3Ca alloy foam without Be resulted in stable foam but exhibited low expansion with poor foam structure. Be addition significantly increased foam expansion and improved their structure. The expansion and the structure of the Mg foams obtained are comparable with that of commercially available aluminum foams. The XPS analysis confirmed the presence of BeO at the gas–solid interface of Mg foam. Be stabilizes the gas–solid interface of the foam by forming a smooth and crack-free surface of BeO layer which prevents the continuous oxidation of liquid foam and also minimizes the loss of blowing gas thereby enhancing the stability of Mg-3Ca alloy foams.

The risk of developing COVID-19 and its variants may be higher in those with pre-existing health conditions such as thyroid disease, Hepatitis C Virus (HCV), breast tissue disease, chronic dermatitis, and other severe infections. Early and precise identification of these disorders is critical. A huge number of patients in nations like India require early and rapid testing as a preventative measure. The problem of imbalance arises from the skewed nature of data in which the instances from majority class are classified correct, while the minority class is unfortunately misclassified by many classifiers. When it comes to human life, this kind of misclassification is unacceptable. To solve the misclassification issue and improve accuracy in such datasets, we applied a variety of data balancing techniques to several machine learning algorithms. The outcomes are encouraging, with a considerable increase in accuracy. As an outcome of these proper diagnoses, we can make plans and take the required actions to stop patients from acquiring serious health issues or viral infections.

The present work reports on foaming of magnesium alloys and composites using MgCO as the blowing agent. Foaming was done via the molten metal route by direct addition of MgCO in molten Mg. The alloys and composites required for foaming were prepared by varying the concentration of aluminum (10 to 30 wt pct) and calcium (0 and 2 wt pct) in Mg. SiC of 10-µm size and about 10 to 20 vol pct was added as reinforcement particles in the composite. The liquidus temperature of the alloys and composites, the decomposition behavior of MgCO, and the intrinsic oxides that formed in the melt have a significant effect on the structure of the foams. Mg alloys and composites with 30 wt pct Al showed better foaming behavior with higher expansion, lower density, good cell structure, and uniform cell size distribution due to the smaller difference between their liquidus temperature and the decomposition temperature of MgCO. The addition of 2 wt pct Ca showed a significant effect on foaming, and the MgO and MgAlO (spinel) particles formed in situ in the molten Mg during foaming acted as the stabilizing agents.

The age hardenability of 22 karat gold (Au-5.8wt.%Cu-2.5wt.%Ag) alloyed with Ti at various concentrations (0.5, 0.75, and 1 wt.%) was studied. The addition level of Ti is compensated with Ag to maintain the purity of gold in 22 karat, i.e., 91.75 wt.%. The Ti containing 22 karat gold was prepared by melting Au, Cu, and Ag and adding Ti via Au-6wt.%Ti master alloy. The castings obtained were cold-rolled into thin sheet (90% reduction). Both the cast and cold-rolled sheets were subjected to age hardening treatment (solutionizing and artificial aging). Artificial aging was performed as a function of time at 550 °C to identify the peak aging. At all addition level of Ti, the 22 karat gold responded well to the age hardening treatment. The cold-worked sheet samples showed faster peak aging within 30 min. and higher peak hardness than their cast counterpart. Increasing the Ti concentration increases the peak hardness of both cold-rolled sheet and casting samples. Transmission electron microscopic analysis of the peak aged cold-rolled sheet samples shows uniformly distributed coherent AuTi precipitates in Au matrix which contribute to the higher hardness.

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It was shown that aluminum powder can be used as stabilizing particles for the fabrication of aluminum foams by melt route. When Al powder was mixed with the TiH 2 before adding into the melt, it also acted as dispersing agent for the TiH 2 thus further improving the structure of the foams. Stirring during powder mixing also contributed towards foam stability by introducing oxides into the melt. The oxides were examined using SEM/EDS and oxygen analyzer.

The 24 karat (99.99 wt.% pure) and 22 karat gold (Au-5.8wt.%Cu-2.5wt.%Ag) were grain refined with Au-6wt.%Ti master alloy and the mechanism of grain refinement was studied. The Au-6wt.%Ti master alloy containing AuTi and AuTi intermetallic particles was added into 24 karat and 22 karat gold at various addition levels of Ti (0.1, 0.2 and 0.3 wt.%) for grain refinement. The intermetallic particles undergo peritectic reaction with liquid Au in sequence to nucleate ?-Au solid. It is observed that both the 24 karat gold and 22 karat gold showed efficient grain refinement at the lowest addition level of Ti (0.1 wt.%). However, 22 karat showed better grain-refining efficiency than 24 karat at all addition level of Ti studied. The mechanism of grain refinement of gold in this study matches with the “Peritectic theory” and “Solute paradigm” proposed for the grain refinement of aluminium. It is also observed that increasing the master alloy addition level to 0.2 and 0.3 wt.% Ti coarsening in the grain size in both 24 karat and 22 karat, but significant in the case of 24 karat gold due to recalescence effect. The grain-refined 24 karat and 22 karat gold at 0.1 wt.% Ti showed improvement in the hardness in comparison to the un-grain refined one.

The electrochemical corrosion behaviour of 22k gold (Au-5.8wt.%Cu-2.5wt.%Ag) and Ti containing 22k (Ti-22k) gold (Au-5.8wt.%Cu-2.0wt.%Ag-0.5wt.%Ti) was studied. Elemental Ti was added as the quaternary element to 22k gold by replacing Ag, resulting in the formation of secondary phase precipitates during age hardening treatment, thereby improving the hardness of the alloy. Anodic polarization tests were conducted for both 22k and Ti-22k samples in their as-cast annealed, cold-rolled annealed and age-hardened conditions using 0.9% sodium chloride and 1% lactic acid as medium. The as-cast and annealed 22k samples showed better corrosion resistance in both corrosion media whereas the 22k samples in the cold-rolled, annealed condition and Ti-22k samples in the as-cast, annealed condition showed poor corrosion resistance. After age-hardening treatment, cold-rolled Ti-22k samples showed better corrosion resistance due to the formation of passive layer (of TiO) on the surface. However, corrosion gets initiated in the age-hardened Ti-22k due to the breaking and decomposition of the passive layer (TiO) at a potential > 1.3 V.

Al-4 wt pct Cu/TiC composite was synthesized by the molten salt route that contains submicron-sized TiC particles in the Al-4 wt pct Cu matrix. The concentration of the TiC particle in the base alloy is 7.5 wt pct. Melt ultrasound treatment was done by remelting the as-cast composite at 1023 K (750 °C) in a view to refine the size of TiC particles to nanoscale and distribute them evenly in the matrix. The microstructure and age hardenability of the untreated and ultrasound-treated composites were investigated. The TiC particles accelerate the precipitation kinetics of CuAl phase in Al-4 wt pct Cu alloy. In the present study, the hardness obtained for untreated Al-4 wt pct Cu/TiC composite is 120 VHN within 5 hours of peak aging time, which is higher than the hardness of the monolithic Al-4 wt pct Cu, which is 104 VHN at 35 hours of peak aging time. Melt ultrasound treatment of Al-4 wt pct Cu/TiC composite shows no significant effect on the distribution and refinement of TiC particles in the matrix. However, it partially disintegrates the TiC into AlTi and AlC particles. The ultrasound-treated composite showed an improved hardness of about 132 VHN at 5 hours of peak aging, in comparison to that of the untreated composite, by forming denser and homogeneous CuAl precipitates.