Devinder Singh

Effect of Ti addition on the quasicrystalline phase formation and indentation characteristics of Zr69.5Al7.5Cu12Ni11 alloy

The crystallisation behaviour and indentation characteristics of melt-spun (Zr69.5Al7.5Cu12Ni11)100− x Ti x (x = 0–16 at. %) metallic glasses was investigated. Differential scanning calorimetry traces revealed changes in crystallisation behaviour with addition of Ti. Formation of a nanoquasicrystalline phase by annealing the glass was found up to x = 12. Further increase of Ti content gives rise to formation of a Zr2Ni-type crystalline phase. In addition to this, the size of nanoquasicrystals decreases with increasing addition of Ti. The load-dependent hardness behaviour of the metallic glasses and nanoquasicrystal–glass composites is reported in detail. The value of the yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. The formation of shear bands around the indentation periphery was observed. It was found that microstructural and morphological changes alter the indentation characteristics of glasses as well as composites formed after controlled crystallisation.

Synthesis and Indentation Behavior of Amorphous and Nanocrystalline Phases in Rapidly Quenched Cu–Ga–Mg–Ti and Cu–Al–Mg–Ti Alloys

AbstractnRapidly solidified ribbons of Cu–Ga–Mg–Ti and Cu–Al–Mg–Ti alloys show the formation of γ-brass type phase, which is an approximant of quasicrystals. The Cu–Ga–Mg–Ti alloy displays ordered γ-brass structure, whereas Cu–Al–Mg–Ti leads to the formation of amorphous and nanocrystalline disordered bcc γ-brass phase. The hardness values of as-synthesized ribbons of Cu–Ga–Mg–Ti and Cu–Al–Mg–Ti alloys are ~7.36 and ~9.01xa0GPa, respectively. The high hardness value of the Cu–Al–Mg–Ti alloy can be attributed to the combined effects of amorphous and nanocrystalline phases. The absence of cracks around the indentation up to 100xa0g of load of this alloy suggests better toughness in comparison with Cu–Ga–Mg–Ti alloy. The formation of shear bands is more prominent in case of Cu–Al–Mg–Ti alloy. The value of yield strength and Meyer exponent of the material has been estimated. It has been found that the indentation parameter seems to be sensitive to structural and microstructural variations.

Formation of quasicrystalline phase in Al70−x Ga x Pd17Mn13 alloys

In the present investigation, the formation and stability of icosahedral phase in Al70− x Ga x Pd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with xu2009=u20092.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x ≥5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ξ′ crystalline (orthorhombic structure with unit cell au2009=u200923.5u2009Å, bu2009=u200916.6u2009Å and cu2009=u200912.4u2009Å) phases. In the case of the melt spun ribbon for xu2009=u20095 at% Ga, only an icosahedral phase has been found, but for 15u2009>u2009xu2009>u20095 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For xu2009=u200915 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. However, for xu2009=u200920, only a hexagonal Al3Pd2 phase results.

ESR and optical study of Mn2+ doped diglycine barium chloride monohydrate

ESR study of Mn 2+ doped Diglycine Barium Chloride Monohydrate single crystals has been done at room temperature. The Mn 2+ spin-Hamiltonian parameters have been evaluated employing a large number of resonant line positions observed for different orientations of the external magnetic field. The values of g , A , B , D , E , and a are 1.9922±0.0002, 89±2×10 -4 cm -1 , 88±2×10 -4 cm -1 , 237±2×10 -4 cm -1 , 80±2×10 -4 cm -1 , and 5±1×10 -4 cm -1 respectively. The optical absorption study of the crystal has also been done. The observed bands are assigned as transitions from the 6 A 1g (S) ground state to various excited quartet levels of a Mn 2+ ion in a cubic crystalline field. These bands are fitted with four parameters B , C , D q , and α and the values found for the parameters are B =771 cm -1 , C =3053 cm -1 , D q =755 cm -1 , and α=76 cm -1 . On the basis of the data obtained the surrounding crystalline field and the nature of metal–ligand bonding have been discussed.