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Abstract: Effects of Ti alloying addition on the microstructure and room temperature compression deformation behavior of a NiAl–Cr(Mo)–Hf near eutectic alloy were investigated by SEM, TEM, EDX and compression test. The results showed that compared with base alloy, the compressive fracture strain and 0.2% yield strength of the Ti-containing alloy were enhanced simultaneously. Disordered (Ti,Hf) solid solution phase together with the blocky Heusler phase Ni2Al(Ti,Hf) precipitation presented at eutectic cell boundaries is responsible for the enhancement in ductility due to the better deformation ability of (Ti,Hf) solid solution phase. The improvement in strength depends mainly on the solid solution strengthening in NiAl matrix by large amount of Ti due to its larger solid solubility relative to Hf in NiAl. [Copyright &y& Elsevier]

Abstract: Influence of Ti and Hf combined additions on the Ni2AlX (X=Ti,Hf) Heusler phase precipitation in as-cast NiAl–Cr(Mo) eutectics was investigated by XRD, SEM and TEM observation. The results show that with the increasing of Ti content, the Ni2Al(Ti,Hf) precipitation with blocky morphology at NiAl/Cr(Mo) interface and cellular boundary is nearly suppressed; however, this precipitation with cuboidal or granular morphology within the NiAl matrix promoted. The mechanisms of this transition of precipitation behavior are attributed to the decrease of interfacial energies due to the coherency between NiAl and Heusler phase Ni2Al(Ti,Hf) with the increasing of Ti addition. The size of Ni2Al(Ti,Hf) coherent precipitates inside the NiAl matrix decreased progressively with the increasing of Ti content in NiAl phase, showing a Gibbs–Thomson relation-like trend. In addition, another (Ti,Hf) solid solution phase along with the Ni2Al(Ti,Hf) precipitates was observed for lower Ti addition alloys, which is the precipitation from NiAl matrix prior to Ni2Al(Ti,Hf) precipitation. This may be ascribed to the fast formation kinetics of (Ti,Hf) solid solution phase relative to the Ni2Al(Ti,Hf) phase for lower level Ti-containing alloys. [Copyright &y& Elsevier]

Abstract: With the development of superconducting technology, high magnetic fields (HMF) provide unique opportunity for materials and physics scientists to extend or exploit high performance of existing materials. In this paper, we report our findings of the improvement of compressive strength and ductility in a NiAl based eutectic alloy induced by high uniform magnetic field treatment. It shows that the compressive strength and ductility of NiAl–Cr(Mo)–(Ti,Hf) eutectic alloy were improved by 100 MPa and 12% respectively after 11T uniform magnetic field treatment. Microstructural characterization and fractography observation suggested that the modification of morphology and dispersed distribution of constituent phases through atomic diffusion induced by the HMF treatment could be responsible for the improvement of mechanical performance. [ABSTRACT FROM AUTHOR]

Abstract: The effect of large range Be addition (0–20.83at.% Be) on the lattice distortion as well as dislocation mobility in TiAl was examined by density functional theory (DFT) calculations. The calculation of the formation energy showed that Be obviously decreases the phase stability. The shearing energy barrier of the TiAl alloys with Be solute is weakened by stages during the static shear deformation process. Further analysis of the partial density of states reveals that the physical origin is closely related with the content and atomic configuration of Be. The weakening effect of shearing energy barrier at the first stage occurs because of the decrement in the phase stability, which is induced by low Be addition related long-range alloying effect. The notable weakening effect at the second stage originates from the reduced p–d and enhanced p–p bonding, which is induced by large Be addition related short-range alloying interaction. [Copyright &y& Elsevier]

Abstract: The effects of combined additions of Ti and Hf to NiAl–Cr(Mo) eutectics on the as-cast microstructure and its thermal stability are investigated through SEM, EDS and TEM, with focus on the formation mechanism of β-Ti(M, M =Hf,Cr,Ni) solid solution phase and its thermal stability after short-term heat treatment. The results show that, due to the presence of large concentrations of β-phase forming and stabilizing elements dissolved into the Ti solid solution phase during solidification, the thermodynamically metastable β-phase was preserved at room temperature. With respect to its thermal stability, within the experimental range examined, the β-Ti(M) solid solution phase, is not influenced. From the practical application point of view, this β-Ti(M) solid solution phase may offer application as a strengthening phase for the design of NiAl–Cr(Mo)–Hf based alloys. [Copyright &y& Elsevier]

Abstract: The microstructural characteristics and thermal stability of a rapidly solidified NiAl–Cr(Mo)–Hf near-eutectic alloy fabricated by water-cooled copper mold method were investigated by SEM, EDAX, TEM, and HIP treatment. Rapid solidification resulted in the following effects which encompass refinement of the microstructure: cell size, lamellar spacing and precipitates, deviation from the equilibrium composition, solubility extension, and a transition from a Heusler phase to a Hf-rich phase. With respect to thermal stability, it is proposed that the localized destabilization of the microstructure after hot isostatic pressing (HIP) treatment is closely related to the presence of primary NiAl dendrites. [Copyright &y& Elsevier]