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This study concerns the development of high-specific-strength Al-based amorphous and/or nanocrystalline alloys by mechanical alloying of Al40TM40Si20 and Al30TM40Si30 (TM = transition metal, Nb and Zr) elemental powder blends by high-energy ball milling. Microstructure of the milled product in different stages of milling has been characterized by X-ray diffraction, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. Both the systems are amenable to partial solid state amorphisation and development of a composite microstructure comprising varying amounts of nanocrystalline face-centred cubic Nb- or Zr-based solid solution and amorphous phase by appropriate hours of milling. The body-centred to face-centred cubic polymorphic change in Nb or Zr seems closely related to grain refinement and plastic strain.

The present investigation concerns a systematic kinetic analysis of discontinuous precipitation (DP) in a Pb-9.87 at.% Sn alloy. The study includes a quantitative estimation of the Arrhenius parameters of grain boundary chemical diffusion of Sn in this alloy in the temperature range 258 to 333 K using the Petermann-Hornbogen model for DP. In the course of DP under isothermal condition, the reaction front migrates with a steady-state velocity, v, and the interprecipitate repeat distance, λ, remains statistically constant. The variation of v and λ with temperature has been determined. Finally, the DP reaction in this alloy seems to be a boundary diffusion controlled process, the activation energy of which lies in between 39.8 and 42.2 kJ/mol.

The development of a sharp cube or {100} texture in two Ti and Ti+Cr added Ni-Fe-Cu alloys is presented. Texture studies in deformed as well as recrystallized conditions have been carried out by both conventional pole figure and orientation distribution function analysis. Microstructural evolution in course of recrystallization texture development has been extensively studied with both optical and electron microscopes. Heavy cold deformation (97 to 98%) followed by annealing at 1050 o C for 2 h has been found to optimize the conditions for the desired texture development

A one-dimensional unsteady-state heat transfer model based on explicit finite difference method of solution has been developed to simulate the thermal profile in the course of laser surface alloying of a Cr-deposited Cu substrate with a continuous-wave CO 2 laser. In this model, a suitable temperature/phase dependence of the material properties has been considered. The temperature profile and depth of melting are found to be strong functions of the incident power density and interaction time. The mechanism of transient melting and solidification following laser irradiation is discussed in the light of the present model

A modification to Cahn's solution for the solute distribution profile in the solute depleted matrix (α) within a discontinuous precipitate (DP) colony is presented. The proposed modification is based on the premises that (a) the average solute content in the α phase following DP approaches the metastable solvus instead of the equilibrium solvus, and (b) the reaction front migrates in discrete steps of «stop» and «go», as proposed by Gust and evidenced by Abdou. The modified model fits the experimentally determined composition profile better for DP in an Al-22 at.% Zn alloy than that obtained from Cahn's original formulation