T.K. Nandy

Microstructural stability and creep of rare-earth containing magnesium alloys

Abstract The creep behavior of die cast magnesium alloys is examined for the high temperature alloys AE42 and MEZ. Creep behavior in these fine-grain die castings is dependent on the stability of the near grain boundary microstructure and is improved by rare-earth element additions and reductions in aluminum content.

Solidification of high-refractory ruthenium-containing superalloys

Abstract The effect of alloy chemistry on single crystal solidification has been investigated in a series of model high refractory Ni-base superalloys with variations in ruthenium, rhenium and aluminum. Over the range of composition investigated, the initial phase to form during solidification was either the γ phase (FCC Ni-solid solution) or the δ phase (HCP Re-rich phase). In a quaternary Ni-Al-Ta-Re alloy containing 1.7 at.% (5.6 wt.%) Re, δ-Re nucleated at a temperature well above the liquidus temperature of pure Ni and grew unconstrained into six-fold Re-rich dendrites. These dendrites served as potent nucleation sites for γ grains as temperature decreased during directional solidification. Ruthenium additions in the range of 2.5∽9.0 at.% (4.1∽14.1 wt.%) lowered the temperature at which the δ nucleated and eventually suppressed the formation of this phase during solidification. Ru additions also increased the liquidus temperatures of the multicomponent superalloys. The implications for the design of Ru-containing superalloys are discussed.

Microstructural characterization of a die-cast magnesium-rare earth alloy

Abstract Microstructural characterization of high-pressure die-cast alloy MEZ (Mg–2.5RE–0.35Zn–0.3Mn) reveals equiaxed dendrites of α-Mg with a partially divorced interdendritic eutectic. Detailed diffraction studies coupled with WDS analysis reveal the presence of a continuous Mg 12 RE intermetallic phase in the eutectic aggregate along with fine Mg particles.

Elevated temperature deformation and dynamic strain aging in polycrystalline RuAl alloys

Abstract The flow behavior and dislocation substructure in RuAl intermetallics have been studied in the temperature range of 298–1173 K. A number of characteristics indicative of dynamic strain aging are observed: serrated flow, flow stress plateau, maxima in the rate of work-hardening and minima in strain-rate sensitivity. Static aging experiments reveal that the serrated flow is associated with the presence of solute atoms that are mobile at T T m ≈0.3 . Dislocation substructures following elevated temperature deformation consisted of and dislocations present in the form of tangles and within cell walls. Typical features of the flow behavior of these intermetallic alloys are compared with those of NiAl, another B2 intermetallic that exhibits dynamic strain aging. Mechanisms for the DSA phenomenon in RuAl are proposed.

Deformation of a platinum-containing RuAl intermetallic by 〈111〉 dislocations

Abstract A detailed analysis of dislocations in a RuAl alloy following room temperature deformation indicates the presence of a significant density of 〈1 1 1〉 dislocations. The deformation behavior of this alloy with 2 at.% Pt is compared to other RuAl alloys and reasons for the presence of 〈1 1 1〉 dislocations, which are not preferred in high melting point B2 compounds, are explored.

Mechanical Behavior of Ternary and Quaternary Rual Alloys

The mechanical behavior of RuAl-base intermetallic alloys with alloying additions of boron, niobium and platinum has been investigated. Compression tests have been performed at room temperature and 973 K. While the addition of alloying elements results in solid solution strengthening, the strain-rate sensitivity and the activation volumes do not show a significant variation, thereby suggesting that the macroscopic flow mechanisms are not strongly affected. Deformation substructure analysis of the niobium-containing alloy shows the presence of and dislocations, while the platinum-containing alloy additionally contains a significant density of dislocations.