Rupa Dasgupta

Alternative flat coil design for electromagnetic forming using FEM.

Electromagnetic forming (EMF) is a high velocity forming process that uses impulse magnetic force. Coil is an important component of EMF system which needs to be designed depending on application. Flat spiral coils are generally used for electromagnetic forming of sheet metals. However, with this type of coil the central portion of the workpiece experiences marginal magnetic force. This leads to in-sufficient deformation at this portion and other problems like air entrapment. In this study, a conceptual design of flat coil was proposed for better distribution of magnetic forces over the workpiece. Comparative analysis of distribution of magnetic force, magnetic field and current density using the proposed and the existing coil designs were carried out using FEM. The result indicates that the proposed coil design produces comparatively better magnetic force distribution over the workpiece. Calculation of self-inductance of such coils was also carried out and was compared with FE simulation.

Effect of Varying Al/Mn Ratio on Phase Transformation in Cu-Al-Mn Shape Memory Alloys

In the present study, an attempt has been made to study the effect of the proportion of the main alloying constituents in a Cu–Al–Mn alloy, which is a known shape memory material. Four compositions of the alloy with varying ratios of Al:Mn, varying from 1 to 4 [added to copper], were synthesized using the liquid metallurgy route. After appropriate heat treatment to induce shape memory behaviour, they were studied for microstructure, X-ray diffraction, hardness and transformation temperature in an attempt to understand the effect of the varying ratios of the major alloying constituents on the properties mentioned. With an increase in the Al:Mn ratio, increase in grain size as well as cast hardness were observed. On the other hand, an increase in percentage decrease in hardness was observed with increase in Al:Mn ratio. Increase in Al:Mn ratio also favoured formation of martensitic structure with less amount of retained austenite.

Effect of extrusion on properties of Al-based composite

An aluminium alloy and its composite with dispersed SiC particles made by liquid metallurgy route were extruded under optimized conditions. The properties were characterized in terms of microstructure, hardness and sliding wear behaviour and then compared between the extruded and cast alloys and composites, in order to understand the benefits of composite and extrusion on the alloy. It was observed that composites drastically increased the hardness and the extruded composites further increased this value. The advantage of composites was realized in sliding wear tests.

Titanium Foams Processed Through Powder Metallurgy Route Using Lubricant Acrawax as Space Holder Material

AbstractnIn the present work titanium foams have been synthesized using acrawax as the space holder material. Acrawax has generally been used as a lubricant for easier compaction of aluminium alloy powders. This study deals with the use of this space holder material in the form of beads for creating pores in titanium metal matrix. Acrawax facilitates the formation of continuous dense cell walls which is difficult to obtain using ordinary space holder materials. Moreover, acrawax is compressible in nature and it facilitates the formation of better and uniformly sized pores. Titanium foams have been synthesized utilizing acrawax in two different sizes. The effect of using differently sized acrawax on the cell walls and mechanical properties has also been carried out in this study.n

Compressive Deformation Behavior of Open-Cell Cu-Zn-Al Alloy Foam Made Through P/M Route Using Mechanically Alloyed Powder

Cu-Zn-Al foams of varying porosity fractions using mechanical alloyed powder have been made through powder metallurgy route. Here, NH4 (HCO3) was used as a space holder. Mechanically alloyed Cu-Zn-Al is made using a planetary ball mill taking the ratio of Cu/Zn/Alxa0=xa070:25:5 (by weight ratio). The ball/powder ratios were varied in the four ranges 10:1, 15:1, 20:1, and 25:1. Green compacts of milled powder and space holder samples were sintered at three stages at three different temperatures 350, 550, and 850xa0°C for 1xa0h at each stage. The crystalline size and particle size as a function of ball/powder ratios were examined. The compressive deformation responses of foams are varied with relative density and the ball/powder ratio. The plateau stress and energy absorption of these foams increase with an increase in relative density but decreases with increase in ball/powder ratio, even though crystalline size decreases. This has further been explained on the basis of particle morphology as a function of ball/powder ratio.

Study of effect of Fe, Cr and Ti on the martensite phase formation in Cu-12.5wt%Al-5wt%Mn SMA

Copper based shape memory alloys are studied throughout the world for their high transition temperatures and high thermal stability. Among Copper based shape memory alloys(SMAs), Cu-Al-Mn SMAs have shown good ductility and high transition temperature. Only those alloy systems that can show the formation of β phase are capable to demonstrate the shape memory properties. In this paper the effects of the alloying elements on the formation of martensite phase have been studied exclusively. Addition of 1 wt% of Fe, Cr and Ti to the Cu-12.5Al-5Mn shape memory alloy has been investigated in detail. Therefore, four alloys have been synthesized through liquid metallurgy route using pure metals of 99.9% purity in a melting furnace weighing 1kg each. Samples were heat treated at the temperature of 920 ̊C for 2 hours and then quenched in ice water. The optical micrographs show the formation of the martensite structures in all the samples except in the samples in which 1 wt% Fe was added. X-Ray diffractions also revealed the same facts as obtained in the optical microscopy. Vickers Hardness of all four samples were carried out. The result shows no sign of martensite formation in sample containing Fe; therefore, this alloy should not be used for further study in the direction of understanding shape memory behaviors of the copper based shape memory alloys. Moreover, it was also observed that the addition of Cr yielded good martensitic formation as compared to the alloy containing Ti. Copyright

Effect of Relative Density and Strain Rate on the Deformation Behaviour Ni-Ti Foam Made through Powder Metallurgy Route Using NH4(HCO3) as Space Holder

Ni-Ti foams of varying relative densities have been made by varying the size and volume fraction of NH4(HCO3), which was used as space holder. The green compacted pellets, after evaporation of NH4(HCO3), were sintered at 1100°C for 2 hrs. The XRD and EDX analysis confirms that there is no residual space holder. The extent of openness of cell walls increases with increase in porosity. The compressive stress-strain behavior of these foams varies with the relative density. The peak stress and energy absorption of these foam increases with relative density following power law and linear relationships respectively, and the densification strain decreases with relative density following a linear relationship. The pseudo elastic recovery strain and shape recovery strain decrease with increase in porosity. The overall recovery increases with decrease in degree of deformation. This phenomenological behavior indicates that these foams can be used for their shape memory effect.

Use of Cenosphere for Making Metal-Microspheres Syntactic Foam through Powder Metallurgy Route

Cenospheres are very cheap, and are reasonably strong and thermally stable upto 1200°C. In view of this attempt has been made to use these cenosphere for making Titanium syntactic foams with varying relative densities. Precautions were taken for selecting cold compaction pressure to minimize cenosphere crushing. The sintered samples were then characterized in terms of microstructures primarily to see the extent of cenosphere crushing, distribution of cenosphere, and extent of sintering. The foams made using optimized pressure and sintering parameters, exhibits uniform distribution of cenosphere without any significant crushing. The plateau stress, energy absorption and modulus of these foams are varying with the cenosphere content or the relative density, and these parameters can be engineered by varying cenosphere content in the foam. These foams exhibit considerably higher strength and stiffness than the conventional foam and show the possibility of using them for biomedical and engineering applications.