S. Meher

Evolution of a honeycomb network of precipitates in a hot-rolled commercial Mg–Y–Nd–Zr alloy

Coupled processes of dynamic recovery and precipitation, occurring during hot-rolling and subsequent aging, lead to the formation of a unique honeycomb network of precipitates in commercial Mg–Y–Nd–Zr or WE43 alloy. The honeycomb network is developed on the (0 0 0 1)Mg basal planes and consisted of fine Nd-rich β 1 platelets lying on all three planes presumably decorating recovery-generated dislocation subcell boundaries. Three variants of β 1 platelets are connected by Y-rich precipitates at the nodes of the hexagonal honeycomb network.

Probing the crystallography of ordered Phases by coupling of orientation microscopy with atom probe tomography

The determination of atomic scale structural and compositional information using atom probe tomography is currently limited to elemental solids and dilute alloys. In the present article, a unique coupling of orientation microscopy and atom probe tomography successfully facilitates the crystallographic study of non-dilute alloy systems, with high evaporation fields. This reproducible methodology affords a new perspective to the conventional atom probe tomography of ordered precipitate strengthened superalloys. The high accuracy in crystallographic site-specific sample preparation results in high spatial resolution in APT, which has been demonstrated in Co-base superalloys. The practical applications of this technique can be extended to accurately characterize the nature of buried order/disorder interfaces at the atomic scale, as well as the site occupancies associated with different solute atoms in multi-component superalloys.

Enhancing elevated temperature strength of copper containing aluminium alloys by forming L1(2) Al3Zr precipitates and nucleating theta `' precipitates on them

Strengthening by precipitation of second phase is the guiding principle for the development of a host of high strength structural alloys, in particular, aluminium alloys for transportation sector. Higher efficiency and lower emission demands use of alloys at higher operating temperatures (200 °C–250 °C) and stresses, especially in applications for engine parts. Unfortunately, most of the precipitation hardened aluminium alloys that are currently available can withstand maximum temperatures ranging from 150–200 °C. This limit is set by the onset of the rapid coarsening of the precipitates and consequent loss of mechanical properties. In this communication, we present a new approach in designing an Al-based alloy through solid state precipitation route that provides a synergistic coupling of two different types of precipitates that has enabled us to develop coarsening resistant high-temperature alloys that are stable in the temperature range of 250–300 °C with strength in excess of 260 MPa at 250 °C.

Coarsening behaviour of gamma prime precipitates and concurrent transitions in the interface width in Ni-14 at.% Al-7 at.% Cr

Coupling atom probe tomography and transmission electron microscopy, the temporal evolution of γ′ precipitate morphology and size distribution and compositional width of the γ/γ′ interface, have been tracked in a model Ni-14Al-7Cr (at.%) alloy, during isothermal annealing at 800 °C subsequent to rapid quenching. During the initial annealing period, coalescence-dominated growth and coarsening of γ′ precipitates are accompanied by a gradual decrease in the interface width, eventually leading to classical LSW coarsening with a constant interface width at extended annealing time periods.

Probing the Crystallography of Ordered Phases by coupling Orientation Microscopy and Atom Probe Tomography

Superalloys are a class of materials that possess stable microstructures at elevated temperatures due to the presence of coherent L12 ordered γ’ precipitates spatially aligned along elastically soft directions in a face centered cubic (FCC) γ matrix [1]. Nickel-base superalloys are used in a variety of applications such as in turbine blades of aircraft engines and land-based turbine engine [1]. The recent discovery of novel Co-base alloys [2] which also form γ-γ’ microstructures, similar to nickel base superalloys, has led to rapid research in these alloys as potential next generation superalloys.