N.H. Tariq

Effect of Li addition on microstructure and mechanical properties of Al-Mg-Si alloy

Abstract The ever increasing utilization of Al – Li alloys for light weight structural applications is limited chiefly due to their lower room temperature formability compared to their Li-free counterparts. In the present work, the effect of 1, 2 and 3 wt.% Li addition to Al – Mg – Si alloy (containing 0.5 wt.% Mg and 0.2 wt.% Si) was studied. Experimental work showed that microstructural features of the second phase particles and mechanical properties changed substantially with Li addition. It was observed that 1 wt.% Li addition resulted in significantly large elongation of over 38 % resembling a super-plastic behavior with decent strength and hardness due to the formation of second phase precipitates uniformly dispersed in α (Al) matrix. Scanning electron microscopy and X-ray diffraction analysis revealed that the addition of Li promotes the formation of second phase precipitates, which strongly affect the mechanical properties of Al – Mg – Si alloy. Quite surprisingly, the alloys containing 2 and 3 wt.% Li showed a much reduced ductility and a much higher hardness after aging.

Plasticity enhancement in centrally confined Zr-based bulk metallic glass

Abstract In the present work, a new idea is presented to enhance the plasticity of Zr65.5Cu22.4Al5.6Ni6.5 bulk metallic glass. A considerably large compressive plastic deformation (over 8%) was achieved by confining Zr65.5Cu22.4Al5.6Ni6.5 bulk metallic glass from its center. Numerical analysis was also carried out to investigate the stress distribution under the same mechanical conditions. It was revealed that loading induced high stress gradients facilitating large plastic strains through the generation of dense multiple shear bands.

Modeling glass-forming ability of bulk metallic glasses using computational intelligent techniques

Various intelligence approaches are employed to model the Dmax for GFA.The improved R2-values are found using the proposed CI approaches.The performances of CI approaches are compared to the existing modeling approaches. Modeling the glass-forming ability (GFA) of bulk metallic glasses (BMGs) is one of the hot issues ever since bulk metallic glasses (BMGs) are discovered. It is very useful for the development of new BMGs for various engineering applications, if GFA criterion modeled precisely. In this paper, we have proposed support vector regression (SVR), artificial neural network (ANN), general regression neural network (GRNN), and multiple linear regression (MLR) based computational intelligent (CI) techniques that model the maximum section thickness (Dmax) parameter for glass forming alloys. For this study, a reasonable large number of BMGs alloys are collected from the current literature of material science. CI models are developed using three thermal characteristics of glass forming alloys i.e., glass transition temperature (Tg), the onset crystallization temperature (Tx), and liquidus temperature (Tl). The R2-values of GRNN, SVR, ANN, and MLR models are computed to be 0.5779, 0.5606, 0.4879, and 0.2611 for 349 BMGs alloys, respectively. We have investigated that GRNN model is performing better than SVR, ANN, and MLR models. The performance of proposed models is compared to the existing physical modeling and statistical modeling based techniques. In this study, we have investigated that proposed CI approaches are more accurate in modeling the experimental Dmax than the conventional GFA criteria of BMGs alloys.

Effect of Ag, In and AgIn Alloying Additions on Microstructure and Texture of Mg-3Al-1Zn Alloy during Multi-Pass Warm Rolling

In the present investigation the rolling response, microstructure and texture evolution of four Mg alloys during multi-pass warm rolling were evaluated. The nominal composition of the base alloy (alloy-1) was Mg-3Al-1Zn. The alloy-2, 3 and 4 were developed by separate additions of non-rare earth elements Ag and In, and a master alloy 85Ag15In (wt.%) to make target compositions Mg-3Al-1Zn-0.5x, (x = Ag ,In, AgIn). Samples from all four alloys were subjected to multi-pass warm rolling at 300 °C to accumulative reductions of 50, 75 and 90% with 8 minutes inter-pass annealing. For all four alloys, crack free sheets of less than 1 mm thickness were produced successfully with true strain corresponding to 90% reduction. The as-cast microstructures revealed second phase particles at grain boundaries and grains interiors for all alloys. A slight scatter in the size of the deformed grains was observed for alloy-1, 2 and 3 after rolling reductions of 50, 75 and 90%. However, a sustained decrease in grain size with increasing the rolling reductions was only observed in alloy-4, despite inter-pass annealing. XRD macro-texture results of alloy-2 and 3 presented very strong basal texture showing almost concentric contours around normal direction (ND). Such strong sheet texture is attributed to a preferential alignment of basal planes parallel to the sheet surface. On the other hand alloy-1 and alloy-4 revealed a weaker texture with basal poles spread more towards transverse direction (TD) as compared to rolling direction (RD) and may be due to the activation of some non-basal slip and twinning in addition to basal slip under the same processing parameters.

A Comparison of the Electrical and Thermal Behavior of ZrO2-Ni Interpenetrating Phase Composite Produced by Microwave and Conventional Sintering

The ceramic-metal composites that have all phases continuous throughout the structure are known as Interpenetrating Phase Composites (IPCs) and they have many applications in various fields. In this investigation ZrO2-Ni IPCs of varied compositions were synthesized using tubular furnace and microwave furnace routs. Samples were Characterized using BET surface area, Pycnometer density, dilatometry and scanning electron microscopy. The Electrical parameters of the composites were measured using impedance spectrometer. Results indicate that threshold percolation reached at 40 volume percent of Ni in both cases. Moreover, no significant difference was observed in BET surface area and CTE of composites prepared by conventional and microwave sintering processes.

Effect of sand blasting on structural, thermal, and mechanical properties of Zr58.3Cu18.8Al14.6Ni8.3 bulk metallic glass

Abstract In the present work sand-blasting-induced structural, thermal, and mechanical effects were studied in Zr58.3Cu18.8Al14.6Ni8.3 bulk metallic glass. It was observed that sand blasting favors disordering of the atomic configuration, formation of free volume and evolution of multiple intersecting shear bands. As a result, considerable compressive plasticity was achieved in sand-blasted samples. It was also observed that in order to superimpose the effect of pre-straining and extra free volume for improving compressive plasticity, there exists a limit to both parameters.

Effect of Interconnectivity of Nickel on Electrical and Thermal Properties of Alumina-Ni Interpenetrating Phase Composite

In this work percolation range for Al2O3-Ni interpenetrating phase composite (IPC) was studied to find the optimal combination of electrical conductivity and coefficient of thermal expansion (CTE). The impedance spectroscopy and scanning electron spectroscopy were used to study the percolation limit.