In recent years, advanced high strength steels have been the main choice of automobile manufacturers due to their excellent strengths and decent formability. In this study, the forming behaviour of a martensitic steel (MART 1200) at elevated temperatures, where higher formability and an acceptable strength can be achieved, has been investigated. For this purpose, tensile test experiments have been conducted at room temperature, 175°C, 275°C, 375°C and 475°C in two different strain rates (0.005 s–1, 0.05 s–1). The flow behaviour, elongation capacity, strain rate sensitivity, strain hardening and strain hardening rate of MART1200 have been investigated and fracture surfaces and microstructures have been examined by scanning electron microscope. It has been shown that the strain rate sensitivity of MART1200 increases significantly after 275°C and, for the higher strain rate, a significant improvement up to 80% in the elongation capacity has been achieved in return for a 19% strength reduction at 375°C.

The current paper demonstrates friction-assisted surface alloying to produce Mg-Sn-Pb alloy within the solid state by using friction stir processing (FSP) principle. A groove is machined on the surface of pure magnesium sheet and a thin wire of Sn-Pb was inserted into the groove and then FSP was carried out on the surface. In order to achieve uniformity in the alloy formation, second pass was also carried out on the stirred region. Development of Mg-Sn-Pb alloy was observed at the surface as reflected from the corresponding X-ray diffraction peaks. Surface micro-hardness of the produced surface Mg-Sn-Pb alloy was significantly increased than pure Mg. Corrosion behavior was assessed by polarization tests and the result indicated higher corrosion resistance for the produced alloy due to the developed solid solution grains. Both the first-pass and second-pass samples have exhibited similar levels of corrosion resistance. Higher tensile strength (148.7 ± 5.1 MPa) was observed for the produced surface alloy and second-pass marginally elevated the tensile strength (152.1 ± 3.8 MPa) compared with Mg (106.2 ± 4.2 MPa). Higher ductility was also observed as reflected from the increased % of elongation (7.4 ± 0.8 and 8.2 ± 1.1) for the produced alloys compared with Mg (4.3 ± 0.7). The present work demonstrates the potential of friction surface alloying to develop Mg-Sn-Pb alloy without melting the base material that exhibits improved corrosion and tensile properties. Furthermore, it is also concluded that the second pass marginally increases the corrosion and mechanical performance of the alloy.

Recent surface composite developments have impacted the aerospace, energy, and construction sectors. Friction Stir Processing (FSP) can manufacture high-quality surface composites from lightweight materials. This research optimizes process parameters, including Rotational Speed (RS), Travel Speed (TS), and Number of Passes (NoP), utilizing the design of experiments (DoE) statistical quality tool. The design matrix was created using the Response Surface Methodology (RSM) technique, and the experiments were based on the central composite design (CCD). ANOVA was used to validate the actual and projected models. Optimal FSP process parameters were utilized to create a surface composite of AA7075 with rGO and (rGO + MWCNT) reinforcements. The homogeneous reinforcement distribution on the surface composite was tested using optical microscopy. The average grain size of AA7075-T6 measured as 157±23 μm reduced to an average grain size of 7.5±1.2 μm for the rGO reinforced surface metal matrix composite (SMMC) and ultimately reduced to an average grain size of 6.5±0.7 μm for the (rGO + MWCNT) reinforced SMMC. The reduced fraction of intermetallic was identified in the microstructures, and the altered intensity of the significant XRD peaks was confirmed by X-ray Diffraction (XRD) analysis. Increased microhardness from 168±1.7 Hv (for BM AA7075-T6) to 190±2.4 Hv (for rGO reinforced SMMC) and further improved to a greater hardness of 196±1.8 Hv (for (rGO + MWCNT) reinforced SMMC). The impact strength improved drastically from 16±0.8 J (for BM AA7075-T6) to 21.3±1.1 J (for rGO reinforced SMMC) and greatly enhanced to 24±0.6 J (for (rGO + MWCNT) reinforced SMMC) were observed. The average thermal conductivity value of (rGO + MWCNT) reinforced SMMC showed a greater increase of 30-80 W/mK when compared to the BM. FSPed (rGO + MWCNT) SMMC specimen showed enhanced tribological properties with a reduction of nearly 65% compared to the BM. These results confirmed that the modified surface microstructures in the SMMCs by using FSP help to improve the characteristics of the AA7075-T6 alloy.

The utilization of complex polymetallic secondary sulfide concentrate (CPSSC) is difficult, owing to its special structure and composition. In this paper, CPSSC was firstly activated by roasting under atmosphere, followed by hydrothermal leaching under oxygen pressure with water. The mineral phase structure and morphology of the activated products and leached residues were characterized by XRD and SEM-EDS to study the leaching behavior and kinetic characteristics of copper from CPSSC. The obtained results show that the optimum conditions for hydrothermal leaching of the roasting activated products of CPSSC under oxygen pressure with water are as follows: leaching temperatures 185℃, oxygen partial pressure 0.6 MPa, liquid solid ratio 12.5:1, stirring rate 600 r/min. Under the above conditions, the iron and lead existing in the activated products were mostly transferred and remained in leached residue with the state of iron oxide and lead sulfate respectively, and the leaching rate of Cu reached 95.73%. The kinetic analysis show that the extracting of copper from the activated product by hydrothermal leaching under oxygen pressure obeys chemical reaction control model, with activation energy calculated as 41.98 kJ/mol by Arrhenius equation, and the leching kinetic equation of copper could be expressed as: 1-(1-X)1/3=0.437Po21.258w0.728e-5049.7/T t.

To attain the goal of receiving the well toughened ceramic matrix composite material for radioactive jackets to protect from nuclear radioactivity for commercial and defense applications. This research task is initiated to prepare the composites by preparing the Al-Si alloy at different propositions and infiltrate the alloy into the B4C pellets at different temperatures. This task dealt with the methodology of reactive melt infiltration (RMI) technique and processing of ceramic matrix composites in lightweight. Moreover, it registered the phenomenon and factors influencing the infiltration process and characterization of constituents of the ceramic matrix infiltrated composites. Fine particles of 10 μm boron carbide powder (B4C) was characterized by determining the free carbon content and thermal behavior experiments. By the addition of binder, the densification of porous B4C green preforms and its pressing efficiency were analyzed. Four sets of Si-Al alloys were produced with various combinations and smelting parameters; and were investigated its property through XRD/EDS tests and SEM images. Nominal 50% porosity B4C preforms were infiltrated by various proportions of hypereutectic Si-Al alloys at various batches through pressureless reactive melt infiltration process under inert argon atmosphere with different infiltration temperatures and infiltration duration. The poor infiltration, partial infiltration, changes in physical aspect, wetting phenomena were also discussed.

Mechanical properties of Al6061-B4C composites fabricated by stir casting method, even though over 120 µm B4C reinforcement was used, was evaluated. The big reinforcement also could exert an impact on mechanical properties such as hardness and wear resistance. The presence of the harder particles dispersed in Al6061 increased hardness, which would in turn affect wear performance. The high hardness reduced the contact area between the sample and ball and thus, leaded to the reduced coefficient of friction (COF) and wear loss. The Al6061-12 wt.% B4C composite showed the best wear resistance, resulting in the narrowest and shallowest scar. The higher hardness of the Al6061-12 wt.% B4C composite changed wear mechanism changed from adhesive to abrasive wear so that the best wear resistance could be achieved.

Directly brazing titanium (Ti) alloy and copper (Cu) using silver (Ag) based filler alloy has been recognized to be of limited success owing to the embrittlement of intermetallic compounds (IMCs) presented at joint interface. In the current investigation, strong and reliable brazing of Ti-6Al-4V and Cu was achieved by using a niobium (Nb) diffusion barrier deposited on Ti-6Al-4V base material and Ag-Cu-Ti active braze. The Nb diffusion barrier effectively suppressed the interaction between Ag-Cu-Ti filler and Ti-6Al-4V base material, avoiding formation of brittle Ti-Cu IMCs. Joint consisting of Ti-Nb solid solution, unconsumed Nb interlayer, remnant Ag-based braze and small quantity of tiny Ti-Cu IMC particles was obtained via diffusion bonding at Ti- 6Al-4V/Nb interface and active brazing between Nb interlayer and Cu based material. Bonding strength exceeding the Cu base material property was achieved in the resultant joint, ascribed to elimination of continuous bulk brittle interfacial reaction products.

The shear capacity of reinforced beam concrete was designed to resist the stirrup reinforcement, Vs, and by the concrete itself, Vc. Previous studies of geopolymer concrete show the mechanical properties of this proposed green concrete, yet the structural investigation is infrequently investigated. These studies mostly observed the impact of using alternative binder resources that affect the workability, setting time, compressive strength, split tensile strength, and drying shrinkage. Therefore, this study aims to observe the structural behavior of geopolymer concrete, precisely its shear capacity. Four geopolymer concrete beam types were designed to have shear failure mode when tested using a Universal Testing Machine by four-point load bending method. The results showed that geopolymer concrete has ductile behavior. Comparison between the Vu value of the test results with Vn calculation of nominal cross-sectional capacity according to standard concrete rules in an average of 2.11 higher than the nominal capacity conventionally calculated according to SNI. Two models of linear regression equations for concrete Vc values were created to explore this further. It was found that the presence of a constant increases the value of the coefficient of determination by up to 29% for the Vc equation in geopolymer concrete. In addition, cracking patterns observed with the DIC method using GOM Correlate software also showed that all the beam specimens had failure both in flexure and shear, even though they all are designed in a shear failure state.

In this paper results of the thermodynamic and kinetic analysis of cobaltite oxidation process were presented. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive X-ray fluorescence (ED-XRF) were used to determine the chemical composition of the examined cobaltite. The results of the chemical analysis showed that the tested sample of cobaltite mainly consists of cobalt, sulfur, calcium, arsenic, and iron, with a trace amount of some other elements. Also, some analyses were obtained by X-ray diffractometry (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Mineralogical analysis by X-ray diffractometry shows the existence of four phases: the minerals cobaltite, calcite, pyrite, and jaipurite. Based on the calculated phase stability diagram of the Co-S-O and As-S-O systems, a thermodynamic analysis of the cobaltite oxidation process was performed. The results of thermogravimetric analysis and differential thermal analysis (TG/DTG) were used to determine the mechanism of the oxidation process. Using the Sharpe method of reduced reaction half-time, a kinetic analysis was performed under isothermal conditions in the temperature range from 300°C to 900°C. The calculated value of the activation energy of the oxidation process is 8.3 kJ/mol–1.

Intermetallic compounds (IMCs) including transition metals and p-block metals exhibit high resistance to corrosion and oxidation, low density, high conductivity, and magnetic polarizability. In this study, the first-principles calculations method based on Density Functional Theory (DFT) has been used to investigate the structural and electronic properties, charge density distribution, spin polarizability, and magnetic behavior of Cu(3–x)MnxAl (x = 0, 1) intermetallic compounds. Generalized Gradient Approximation (GGA) was employed with Perdew-Burke-Ernzerhof (PBE) exchange-correlation. Calculation of metallic and conductive nature and structural properties was performed simultaneously for all crystal lattices of Cu(3–x)MnxAl (L12, D03, and Heusler L21) with 221-Pm3m, 225-Fm3m space groups. Notably, the study clarifies the stoichiometric similarity and difference between L12 and D03 type structures by presenting a detailed discussion of the D03 structure and its targeted properties for the first time. The lattice constant values obtained by performing various optimizations are in excellent agreement with previously reported experimental and theoretical data. The electron density distribution and population analysis are consistent and reveal the dominant bonding type in each IMC. Furthermore, Spin Polarizability analysis has been carried out to demonstrate the magnetic nature of the Cu2MnAl (L21) Full Heusler alloy upon the addition of the Mn atom.