Optimization of spark plasma sintering parameters for NiTiCu shape memory alloys

Nanostructured nickel titanium copper-shape memory alloys (NiTiCu-SMAs) were fabricated using spark plasma sintering (SPS) by varying the significant process parameters. The NiTiCu elements with different particle size were consolidated in a temperature range of 700–900°C and pressure from 20 to 40 MPa with 5 min of soaking time. The sintered products were subjected to mechanical analysis such as density and microhardness. Genetic algorithm (GA) and particle swarm optimization (PSO) techniques were used with integrated artificial neural network (ANN) to optimize the SPS process parameters to obtain better mechanical characteristics. The results indicate that the density and microhardness can be enhanced by the reduction of particle size and increase in pressure and temperature. A maximum density of 6.21 g/cc and Vickers hardness of 766 Hv were obtained the optimal for process parameters of temperature, pressure, and particle size of ~ 800°C, ~ 26 MPa and ~ 6 µm, respectively, in case of NiTiCu nanostructured SMAs.     

Influence of Solid Fraction Casting on Microstructure of Aluminum Alloy 6061

Semi-solid processing of AA6061 alloy near liquidus temperature with the addition of micro- and nanoparticles of same alloy may be highly attractive for small intricate shapes due to excellent mechanical properties. The present work utilizes semi-solid behavior of AA6061 alloy, which reduces macro- and nanosegregation of particles, porosity, and forming forces during the shaping process. The experiment utilizes the semi-solid slurry of different solid fractions mixed with a melt at pouring temperature range of 400 ? 640°C. The potential of solid fraction to produce semi-solid slurry has been investigated with the help of microstructure analysis, which is a crucial need for aluminum industries. The result shows that during the stirring, every dendrite modified itself to fine solid grains and dispersion of these grains takes place inside the molten metal. Alloy cooled directly from semi-solid state results in higher relative density with respect to conventional casting. With increase of solid fraction to 25%, the un-melted solid structure inside the pores and cavities in the direction of elongated grains results in the subsequent enhancement in the impact strength, hardness, and compressive strength as 19 kJ/m², 93 BHN, and 550 MPa, respectively, without any alteration in the basic metal matrix composite.     

Effect of SiC Nanoparticles Content and Mg Addition on the Characteristics of Al/SiC Composite Powders Produced via In Situ Powder Metallurgy Method

In the present study, the effect of the nanosized SiC particles loading and Mg addition on the characteristics of Al/SiC composite powders produced via a relatively new method called “in situ powder metallurgy” (IPM) was investigated. Specified amounts of SiC particles (within a size range of 250 to 600 µm) together with SiC nanoparticles (average size of 60 nm) were preheated and added to aluminum melt. This mixture was stirred via an impeller at a certain temperature for a predetermined time. The liquid droplets created by this process were then subsequently cooled in air and screened through 250 µm sieve to separate micron-sized SiC particles from solidified aluminium powder particles containing nanosized SiC particles. Results of SEM and TEM studies together with microhardness measurements revealed that the commercially pure (CP) Al could not embed as-received SiC particles. However, the nanosized particles were distributed uniformly in the Al-1 wt% Mg powders. The process yield and microhardness of the Al-1Mg composite powders increased with increasing the contributed amount of nanosized SiC particles.     

Influence of stirring speed on the synthesis of Al/SiC based functionally gradient materials

In the present study, thick aluminum–silicon carbide based functionally gradient materials, with starting weight of 18% SiC were successfully synthesized, using different stirring speeds and an innovative gradient slurry disintegration and deposition technique. The results revealed, in common, an increase in: (a) the weight percentage of SiC particulates, (b) the clustering tendency of SiC, (c) porosity and (d) microhardness, and a reduction in grain size with increasing distance from the base of the functionally gradient material ingots. The results of X-ray diffraction studies indicated no evidence of interfacial reaction products. Furthermore, results revealed an increase in stirring speed increases the homogeneity of SiC particulates' distribution, thus resulting in a decrease in the average gradient of reinforcement along the deposition direction. An attempt is made in this study to establish the trend between processing parameter such as stirring speed with the gradient of SiC particulates realized in the ingots.     

Enhanced pyroelectric properties of lead free KNN/P(VDF-TrFE) composite film by optimizing KNN sintering temperature

The effect of potassium-sodium niobate (KNN) powder sintering temperature on the structure and properties of the KNN/{poly(vinylidenefluoride-co-trifluoroethylene 70:30) [P(VDF-TrFE) 70:30]} composite thick films have been studied in this paper. KNN powders were sintered by solid-state reaction at different temperatures ranging from 750 to 900 °C. Then the KNN powders were used to fabricate composite thick films by casting the KNN/P(VDF-TrFE) suspension on to ITO substrates. The pyroelectric and dielectric properties of the composite thick films have been investigated systematically. It was found that sample made up of KNN ceramic powders sintered at 850 °C show optimal properties for pyroelectric appliance. The highest pyroelectric coefficient was 63 μCm^?2/K and the highest detectivity figure-of-merit was 4.94 μPa^1/2.     

Properties of SiCf/SiC composites fabricated by slurry infiltration and hot pressing

Abstract

Two-dimensional SiC fibre reinforced SiC ceramic matrix composites (SiC_f/SiC) were fabricated by vacuum infiltration and hot pressing using a 200 nm thick pyrolytic carbon coated Tyranno SA3 fabric and 50 nm sized β-SiC powder. Hot pressing was carried out at 1750°C for 3 h in an Ar atmosphere under a pressure of 20 MPa. Al₂O₃–Y₂O₃–MgO sintering additive (10 wt-%) and polyvinyl butyral resin (45 wt-%) with respect to the matrix SiC were found to be the optimum contents for the high density composite. Vacuum infiltration with a force gradient produced much higher amount of slurry infiltration than simple dipping. Much improved density of 3·02 g cm^?3, compared to the previous reports, was achieved for the SiC–SiC_f containing approximately 67 vol.-% of fibre. This composite showed a step increase with a stress–displacement behaviour during the three-point bending test due to the fibre reinforcement. The displacement for failure and flexural strength were 0·58 mm and 342 MPa respectively, which were much larger than those for monolithic SiC.     

Microstructure and energy-storage performance of BaO–B2O3–SiO2 glass added (Na0.5Bi0.5)TiO3 thick films

(Na_0.5Bi_0.5)TiO₃ lead-free thick films were successfully fabricated on alumina substrates via a screen printing method with 0–10 wt% BaO–B₂O₃–SiO₂ glass addition. Microstructure, dielectric properties and energy-storage performance of the thick films were systematically investigated. The results show that the denser thick films were obtained by addition of glass. Thus, the breakdown strength, the energy-storage density and efficiency were greatly improved. The maximum recoverable energy-storage density and efficiency of sample with 1 wt% glass were 2.0 J/cm³ and 44.1 %, respectively. Meanwhile, a low leakage current density of about 10^?6 A/cm² was obtained for all samples at 100 kV/cm.     

Influence of Process Parameters on Cu–Fly Ash Composite by Powder Metallurgy Technique

In this study influence of compaction pressure, sintering temperature, and sintering time on mechanical and wear behavior of the fly ash reinforced copper-based composites are analyzed. The composites were prepared by powder metallurgy (P/M) technique with copper as matrix, 5 and 10 wt% of fly ash as reinforcement. The green compacts were prepared at three different pressures such as 350, 400, and 450 MPa. The prepared green composites were sintered at 700, 800, and 900 °C for the time period of 30, 60, and 90 min, respectively. From the results it is observed that when the process parameter increases the density, hardness, compression strength, and wear resistance increases.     

Surface Roughness and Microhardness Evaluation for EDM with Cu–Mn Powder Metallurgy Tool

In the present research, composite electrode (Cu–Mn) manufactured through powder metallurgy has been used to machine hot die steel (H11) by electrical discharge machining (EDM) process with the aim of inducing manganese and carbon into the machined surface. Such alloying is expected to improve the microhardness and other surface characteristics. Best level of process parameters for better surface finish and high microhardness are found using Taguchi method. Six processing parameters are considered and their significance is investigated by analysis of variance. Techniques like energy dispersive spectroscopy, scanning electron microscopy, and X-ray diffraction are used to ascertain the surface characteristics. Surface machined at optimum process conditions for microhardness shows 93.7% improvement due to formation of cementite, ferrite and manganese carbide phases. Surface roughness having Ra value of 3.11 µm has been achieved.     

Influence of different boron precursors on superconducting and mechanical properties of MgB2

The superconducting, structural and mechanical properties of MgB₂ bulk samples have been studied as a function of precursor B powder particle size by means of AC susceptibility, XRD and microhardness measurements, respectively. The in situ processed MgB₂ samples have been prepared by means of conventional solid state reaction method with magnesium powder (99.8 %, 325 mesh) and four different types of boron powders (95.2, >95, 91.9 and 86.7 %) from two sources, Pavezyum and Sigma Aldrich. The XRD measurements showed that the diffraction peaks for our samples belong to the main phase of the MgB₂ diffraction patterns. The highest critical temperature T _c = 37.7 K was achieved for the MgB₂ sample which was fabricated by using >95 % purity amorphous boron. Microhardness measurements were performed to investigate the mechanical properties. Load independent hardness, Vickers microhardness, Young’s modulus, fracture toughness, and yield strength values were calculated separately for all samples. The results were analyzed by using the Meyer’s law, proportional sample resistance model, elastic–plastic deformation model, Hays Kendall approach, and indentation induced cracking (IIC) model. It was found that the IIC model is the most successful model to describe the mechanical properties of our samples.     

渗剂中铝粉含量对Cu基Ni镀层表面Cr-Al渗层组织和性能的影响

为了提高铜金属表面硬度和耐磨性,在铜表面预先镀镍,然后对镍镀层进行渗cr,Al,制备Cr-Al渗层.研究了渗剂中铝粉含量对其微观组织、显微硬度和耐磨性的影响.结果表明:当渗剂中铝粉含量在5%～20%(质量分数,下同)范围,渗层组织为Ni(Cr,Al)固溶体,晶面(200)出现明显的择优生长,显微硬度从HV170增加到H...     

Production and characterization of AA6082-(Si3N4 + Gr) stir cast hybrid composites

The present research work emphasizes the development of hybrid aluminum (AA6082) matrix composites (HAMCs) reinforced with different weight percentages (wt.%) of ball-milled (silicon nitride (Si₃N₄) + graphite (Gr)) ceramic particulates by conventional stir casting process. Si₃N₄ and Gr are ball milled to obtain a definite density of combined powder. The weight percentage of ball-milled ceramic powder is varied from 0 to 12 wt.% in a stage of 3%. The microstructures as well as mechanical properties of the fabricated hybrid composites are analyzed. The scanning electron micrograph reveals the uniform distribution of ball-milled (Si₃N₄ + Gr) ceramic particulates in the aluminum matrix. The distribution of ball-milled (Si₃N₄ + Gr) ceramic particulates has also been analyzed with x-ray diffraction (XRD) technique. Both the hardness and ultimate tensile strength have enhanced with a reduction in percentage elongation with increase in weight percentage of ball-milled (Si₃N₄ + Gr) ceramic particulates in the aluminum matrix.     

Improvement of Superconducting Parameters of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ Added with Nano-Ag

Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_10+δ superconductor samples were synthesized by the conventional solid-state reaction technique. Nano-Ag was introduced by small weight percentages (0.2, 0.4, 0.6, 1, and 1.5 weight %) in the final step of the synthesis process. Phase formation and microstructure were investigated using x-ray powder diffraction, differential scanning calorimetry, and scanning electron microscopy. The real elemental-content and oxygen-content were examined using particle induced X-ray emission (PIXE) and Rutherford backscattering (RBS) techniques, respectively. Electrical resistivity as function of the temperature was carried to evaluate the relative performance of samples. Moreover, Electric field-Current density (E–J) characteristic curves were measured at 77 K. The electrical and granular properties were greatly enhanced, indicating more efficient pinning mechanisms. An improvement of the critical current density of 229 % was obtained with x=0.6 wt.%, while the superconducting transition temperature is improved by 2.5 %.     

Selective laser melting of novel nanocomposites parts with enhanced tribological performance

Selective laser melting (SLM) was applied to build the nanocrystalline TiC/Ti nanocomposites parts. The influence of linear laser energy density (λ) on densification, microstructures, microhardness, and tribological performance of SLM-processed parts was investigated. It showed that the densification rate of TiC/Ti parts remained above 97% using linear laser energy density λ≥600 J/m. A decrease in λ caused the balling effect and lowered densification. The TiC reinforcement in SLM-processed parts had unique microstructures distinctly different from the initial nanoparticle morphology. A proper decrease in λ led to the formation of the uniformly dispersed nanoscale lamellar TiC reinforcement. The SLM-processed parts had an enhanced microhardness of 566 HV_0.2, a low average coefficient of friction (COF) of ~0.25 and a reduced wear rate of ~4×10^?16 m³/(Nm) during dry sliding tests. The insufficient SLM densification at a low λ and the disappearance of nanoscale TiC reinforcement at a high λ generally lowered the tribological performance of SLM-processed TiC/Ti parts.     

Synthesis of Nanograined Ti-Al-Cr-Nb-X [X = Ni-P-Coated Graphite and Carbon] Intermetallic Matrix Composites by Mechanical Alloying

In the present work, TiAl-based intermetallic matrix composite with second phase reinforcement as Ni-P-coated carbon and graphite powders were synthesized by mechanical alloying route. Graphite powder (20–30 µm) and elemental carbon powders (1–5 µm) were coated with Ni-P by the electroless coating technique, which was added to the elemental powder mixtures of Ti-48Al-1%Cr -1%Nb with 1% composition of either of the two. The powder mixtures were subjected to mechanical alloying at 300 rpm up to 250 h using toluene as a process control agent. The samples were collected after 25 h duration and characterized. The formation of TiAl (γ) and Ti₃Al (α ₂) phases are confirmed by x-ray diffraction. The formations of these phases were found after milling for 75 h in case of graphite addition and 100 h in case of carbon addition in the intermetallic matrix. The mechanically alloyed samples milled for different extents of time were examined by a field emission scanning electron microscope (FESEM) and energy dispersive x-ray (EDAX) spectroscopy; the grain size was determined to be in the size range of 140–189 nm for the mechanically alloyed mixture.     

Improvement of the Nature of Indentation Size Effect of Bi-2212 Superconducting Matrix by Doped Nd Inclusion and Theoretical Modeling of New Matrix

Neodmium (Nd) inclusions at different stoichiometric ratios (x=0.0, 0.001 %, 0.005 %, 0.01 %, 0.05 %, 0.1 %) are doped in the Bi-2212 superconducting samples and the samples obtained are subjected to the sintering process at 840 ^°C constant temperature for 72 hours. The effect of Nd doping on the structural and mechanical properties of prepared samples is investigated by the standard characterization measurements. XRD and SEM measurements are performed to obtain information about surface morphology, phase ratios, lattice parameters and particle size. Moreover, Vickers microhardness (H _V ) measurements are exerted to investigate the mechanical properties of the all samples in detail. It is found that all the properties given above retrogress with the increase of the Nd concentration in the Bi-2212 superconducting core. However, the ISE nature of the materials improves systematically. Additionally, the experimental results of microhardness measurements are analyzed using Meyer’s law, PSR, MPSR, EPD models and HK approach. The results show that Hays–Kendall approach is determined as the most successful model.     

Production of Ti–13Nb–13Zr Alloy by Powder Metallurgy (P/M) via Sintering Hydrides

The blended elemental method was selected for the manufacture of Ti–13Nb–13Zr alloy by a cold isostatic pressing process and sintering densification under high vacuum. The samples were sintered at the different temperatures from 1250°C to 1450°C with a pressure of 10^?3 ～ 10^?5 Pa. The decomposition of titanium, niobium, and zirconium hydride powders was discussed by thermal gravimetric analyses and differential scanning calorimetry. The phase composition, microstructure and fracture morphology of Sintered Ti–13Nb–13Zr samples were determined by X-ray diffraction and scanning electron microscopy. The results indicate that the hydrogen can be removed effectively. Chemical analysis shows that the Nb, Zr alloying element and hydrogen contents accord with the standard of the ASTM-1713. The final density of sintered Ti–13Nb–13Zr specimens is 4.99 g cm^?3 after sintering at 1450°C for 4 h, representing 99.69% of the theoretical density. The microstructure of sintered Ti–13Nb–13Zr alloys by powder metallurgy is a typical Widmannstätten (α + β).     

Development and analysis of high density poly ethylene (HDPE) nano SiO2 and wood powder reinforced polymer matrix hybrid nano composites

ABSTRACT

The Hybrid composites are the emerging materials which uses two or more reinforced particles or fibres simultaneously. As potential applications of the composites, wood reinforced thermoplastic composites are commercially attractive for high volume applications, but their properties can be enhanced by adding Nano SiO₂ particles. Wood powder and nano SiO₂ were mixed with high density polyethylene as matrix material. Wood powder with fixed 5 wt. % and Nano SiO₂ with varying weight % (3, 5, 7 wt. %) are reinforced in HDPE to manufacture composite materials by compression moulding process. Mechanical properties including tensile strength, flexural strength and Izod impact strength were evaluated and it was revealed that tensile strength and flexural strength were obtained maximum at 5 wt. % of Nano SiO₂ and impact strength was obtained maximum at 3 wt. % of Nano SiO₂.     

Structural,electrical, optical properties and reliability of ultra-thin tin doped indium oxide films for touch panels

Ultra-thin ITO films with thickness of 4–56 nm were deposited on glass by dc magnetron sputtering using 5 wt% SnO₂ doped ITO target. The effect of film thickness on the structural, electrical, optical properties and reliability was investigated for its application to touch panels. The 4 nm thick ITO film shows amorphous structure and other films present polycrystalline structure and the (222) preferred orientation. The ultra-thin ITO films show smooth surface with low Ra surface roughness smaller than 1 nm. The sheet resistance and visible transmittance of the ITO films decrease with the increase in film thickness. The 4 nm thick ITO film shows the highest resistivity (3.08 × 10^?3 Ω cm) with low carrier density and Hall mobility, and other films have excellent conductivity (<4.0 × 10^?4 Ω cm). The ITO films show high transmittance (>85 %) in visible light range and do not generate interference ripples between film and substrate interface. The ITO films with thickness of 18–56 nm show stable reliability under high temperature, high temperature & high humidity and alkaline environmental conditions. The only electrical degradation corresponds to the increase of sheet resistance in the ITO films with thickness of 4–12 nm.     

The mechanical properties and abrasive wear behavior of functionally graded aluminum/AlB2 composites produced by centrifugal casting

Functionally graded aluminum composites reinforced with different average sized (15, 44, and 74 µm) aluminum diboride (AlB₂) particles (10 wt%) have been fabricated through centrifugal casting process. The outer, middle, and inner surfaces of all the functionally graded composites were tested for their microhardness using a Vicker's hardness tester. The outer and inner zones of all the composites were investigated for their tensile strength using a universal testing machine. The abrasive wear test was conducted using dry abrasion tester on the outer region of the composites based on Taguchi's design of experiments, under the influence of parameters such as load, speed, and reinforcement size. The analysis of variance was performed and determined that load has major significance on the wear rate followed by reinforcement size and speed. Scanning electron microscopy analysis was performed on the worn-out surfaces and it was observed that outer surface of coarser particle reinforced composite with lesser scratches and minimum loss of material.