Formation of an amorphous phase and its crystallization in the immiscible Nb-Zr system by mechanical alloying

Mechanical alloying of binary Nb-Zr powder mixtures was carried out to evaluate the formation of metastable phases in this immiscible system. The milled powders were characterized for their constitution and structure by X-ray diffraction and transmission electron microscopy methods. It was shown that an amorphous phase had formed on milling the binary powder mixture for about 10 h and that it had crystallized on subsequent milling up to 50-70 h, referred to as mechanical crystallization. Thermodynamic and structural arguments have been presented to explain the formation of the amorphous phase and its subsequent crystallization

THE USE OF AN OPEN CYCLE ABSORPTION SYSTEM IN AUTOMOBILES AS AN ALTERNATIVE TO CFCS

Increased awareness of the impact of chlorofluorocarbons (CFCs) on the global environment has become the impetus in searching for alternative refrigerants and cooling methods for automotive air conditioning. Automotive air conditioning is one industry that heavily uses CFC compounds, and the leakage of CFCs from such air conditioners is substantial compared to that from stationary air conditioners. Therefore, the use of non-CFC air conditioners in automobiles is apparently becoming very important. The main objective of this paper is to study the feasibility and design of an air conditioning system for automobiles using the Open Cycle Absorption System, with LiBr-H2O as the working fluid. Also, some suggestions are given to minimize the power loss like making use of the exhaust gas to pre-heat the weak desiccant. Evaluating the COP, of the designed air conditioning system for buses is the main scope, and it is found that the COP of the system is increasing with the increase in regeneration temperature at fixed evaporator and absorber temperatures. The system components are plotted in a schematic and flow chart as well as psychometric chart showing the complete process of conditioning and dehumidifying air

Processing of CNTs Reinforced Al-Based Nanocomposites Using Different Consolidation Techniques

In this work, the development of two types of Al-based alloys with different concentrations of Si reinforced with MWCNT’s at 0.5–2.0 wt% is presented. Sonication of the CNT’s in ethyl alcohol was carried out for dispersion, and the mixtures were ball milled for 1, 3, and 5 hrs. SEM/EDS were used to study the morphology and the effects of changing milling parameters in addition to changes caused due to increasing concentration of the CNT’s. Furthermore, three sintering techniques, namely, Spark Plasma Sintering (SPS), Microwave Sintering (μWS), and Hot Isostatic Press Sintering (HIP) were employed to consolidate the ball milled powders at varying temperatures of 400, 450, and 500°C. It was found that SPS consolidated samples showed the most promising results amongst the three with the highest hardness values; around 100% densification, as well as the finest microstructure. On the other hand, microwave sintered samples showed the least appealing results, this could be attributed to the poor temperature distribution and the pressureless nature of the technique. A sintering temperature of 500°C was found to be the most suitable for these types of alloys

THE USE OF AN OPEN CYCLE ABSORPTION SYSTEM IN AUTOMOBILES AS AN ALTERNATIVE TO CFCS

Increased awareness of the impact of chlorofluorocarbons (CFCs) on the global environment has become the impetus in searching for alternative refrigerants and cooling methods for automotive air conditioning. Automotive air conditioning is one industry that heavily uses CFC compounds, and the leakage of CFCs from such air conditioners is substantial compared to that from stationary air conditioners. Therefore, the use of non-CFC air conditioners in automobiles is apparently becoming very important. The main objective of this paper is to study the feasibility and design of an air conditioning system for automobiles using the Open Cycle Absorption System, with LiBr-H2O as the working fluid. Also, some suggestions are given to minimize the power loss like making use of the exhaust gas to pre-heat the weak desiccant. Evaluating the COP, of the designed air conditioning system for buses is the main scope, and it is found that the COP of the system is increasing with the increase in regeneration temperature at fixed evaporator and absorber temperatures. The system components are plotted in a schematic and flow chart as well as psychometric chart showing the complete process of conditioning and dehumidifying air

The Synthesis of Nanostructured WC-Based Hardmetals Using Mechanical Alloying and Their Direct Consolidation

Tungsten carbide- (WC-) based hardmetals or cemented carbides represent an important class of materials used in a wide range of industrial applications which primarily include cutting/drilling tools and wear resistant components. The introduction and processing of nanostructured WC-based cemented carbides and their subsequent consolidation to produce dense components have been the subject of several investigations. One of the attractive means of producing this class of materials is by mechanical alloying technique. However, one of the challenging issues in obtaining the right end-product is the possible loss of the nanocrystallite sizes due to the undesirable grain growth during powder sintering step. Many research groups have engaged in multiple projects aiming at exploring the right path of consolidating the nanostructured WC-based powders without substantially loosing the attained nanostructure. The present paper highlights some key issues related to powder synthesis and sintering of WC-based nanostructured materials using mechanical alloying. The path of directly consolidating the powders using nonconventional consolidation techniques will be addressed and some light will be shed on the advantageous use of such techniques. Cobalt-bonded hardmetals will be principally covered in this work along with an additional exposure of the use of other binders in the WC-based hardmetals

Fabrication Of Nano-Grained Ti-Nb-Zr Biomaterials Using Spark Plasma Sintering

Nanostructured near-β Ti-20Nb-13Zr at % alloy with non-toxic elements and enhanced mechanical properties has been synthesized by spark plasma sintering (SPS) of nanocrystalline powders obtained by mechanical alloying. The consolidated bulk product was characterized by density measurements and Vickers hardness (HV), and X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) combined with energy-dispersive spectroscopy (EDX), and transmission electron microscopy (TEM) for structural details. The temperature during spark plasma sintering was varied between 800 and 1200. °C, while the heating rate and holding time of 100°K/min and 10. min were maintained constant in all the experiments. The effect of SPS temperature on the densification, microstructure, and HV was discussed. The results show that a nearly full density structure was obtained after SPS at 1200. °C. The microstructure of the obtained alloy is a duplex structure with the α-Ti (hcp) region having an average size of 70-140. nm, surrounding the β-Ti (bcc) matrix. The obtained alloy was chemically homogenized with a micro hardness value, HV of 660. The developed nanostructured Ti-20Nb-13Zr alloy is suggested for biomedical use as in implant material in dental and orthopedic applications

Phase Evolution During High Energy Ball Milling Of Immiscible Nb-Zr Alloys

Mechanical alloying (MA), a solid-state processing technique used extensively to synthesize metastable phases, was employed to synthesize solid solution and amorphous phases in Nb-rich Nb-Zr powder blends. These metastable phases could be synthesized by MA, under different processing conditions, even though the heat of mixing between Nb and Zr is positive, which makes alloying them difficult. The effect of alloy composition, milling time, and the ball-to-powder weight ratio (BPR) were varied and their effect studied on phase evolution and microstructure in the milled powders. The composition of the milled powders was varied starting from a low value of 5 to about 50 at.% Zr. At a Zr content below 40 at.%, amorphization was achieved at a higher BPR of 30:1, i.e. more milling energy. The formation of an amorphous phase at Zr contents lower than 40% was achieved for the first time in this work and confirmed using TEM. However, this amorphous phase crystallized rapidly on continued milling (mechanical crystallization) to form an FCC phase. Additionally, milling of powders with low Zr contents primarily resulted in the formation of Nb-based Nb-Zr solid solutions