3rd Metallic Nanostructure Group Seminar
December 15, 2005, 9:00 am
7th floor seminar room, Sengen
Interrupted ageing of Al-Mg-Si-Cu alloys
Joka Buha
The effects of a recently developed modified ageing procedure of aluminium alloys, termed the T6I6 temper, on the microstructural development and mechanical properties of the Al-Mg-Si-Cu alloy 6061. The T6I6 temper was found to cause simultaneous increases in tensile properties, hardness, and toughness as compared with 6061 T6. Al-Mg-Si-Cu alloys are medium strength alloys widely used in the automotive industry and their further improvement is underpinned by stringent demands for weight reduction placed on the transportation industry in recent years.The overall improvement in the mechanical properties of 6061 T6I6 was attributed to the formation of finer and more densely dispersed precipitates in the final microstructure. The refinement of precipitates was facilitated by control of the precipitation processes and gradual evolution of the microstructure throughout each stage of the T6I6 treatment.The evolution of the microstructure was studied using Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and Three Dimensional Atom Probe (3DAP). Vacancy-solute interactions were studied using Positron Annihilation Lifetime Spectroscopy (PALS) and 3DAP. The distribution of the solute was studied using 3DAP and Nuclear Magnetic Resonance (NMR). Differential Scanning Calorimetry (DSC) was used to identify precipitation reactions and to determine the stability of vacancy-associated aggregate.

Study on the Criteria for high Glass Forming Ability of Bulk Metallic Glasses
B. Srinivasa Rao
Metallic glasses are metals and metal alloys with no long range atomic order. These are also called amorphous metallic alloys or non-crystalline alloys. These materials have unique magnetic mechanical, electrical and corrosion properties which are superior to crystalline materials. The main problem with these materials is they cannot be obtained in Bulk form. The thickness varies from micrometer to few centimeters. There was a lot of research going on to form metallic glasses in Bulk form. In the present context, the glass forming ability was studied with the help of Miedema, Mismatch entropy and Miracle models. All these models were unified into a single one and it was applied to Zr-base metallic glasses made with Rapid solidification process which is taken from the literature. The model correlates well with the Literature data. The present model was also applied to Mechanical alloying process and some correlation was found with the total energy given to an alloy to form amorphous.

Microstructure and magnetic properties of quaternary Co2Cr1-xVxAl Heusler alloys
Sankar Vijay Karthik
The microstructure, magnetic properties and spin polarization of quaternary Co2Cr1-xVxAl Heusler alloy systems were investigated. The ordered L21 structure becomes more stable with increasing concentration of vanadium (x ? 0.35) explained by strain relaxation theory. On the other hand, occurrence of two-phase separation into A2 and B2 structure is unavoidable for Co2CrAl alloy. It was found that the saturation magnetization of Co2Cr1-xVxAl alloy increases from 1.63 to 2.0μB with increase in the concentration of vanadium from x = 0.0 to 0.5 and then decreases to about 1.7μB for x = 1.0, which can be accounted to the variation in the local magnetic moment of Co atoms. The spin polarization (P) of the Co2Cr1-xVxAl alloys was measured by Point Contact Andreev Reflection (PCAR) technique. The spin polarization decreased from ~ 0.55 to ~ 0.34 with increase in the concentration of vanadium from x = 0.0 to x = 0.5 and then increased to ~ 0.50 for the composition x = 1.0. Possible reasons for this reduced spin polarization of these alloys are discussed.