Thermal evidence for the structural instability in Ni3Al alloys

Abstract

The thermal expansion coefficient (a) and calorimetric data were obtained as a function of temperature in order to clarify some of the significant variations reported with regard to these values in the literature. Stoichiometric and off-stoichiometric compositions of Ni3Al alloys (with and without boron addition) were investigated. Dilatometric experiments were performed on all the alloys and the a values were estimated over the temperature range from ambient to 1000 °C. Two runs were made on each sample under different initial conditions and differences in a values were noticed. The results were analysed based on our earlier X-ray diffraction results. Additional isothermal dilatometric tests were also carried out and a significant volume change was noticed (0.45% contraction) when the alloy quenched from 1000 °C was heated to 600 °C and held for a long duration. The calorimetric data were obtained over the same range of temperature and enthalpy changes, though less distinct, were noticed at around 360, 660 and 900 °C. The variations seen further augment our earlier results on the instability of the L12 structure and the existence of a structural transformation.

Thermal evidence for the structural instability in Ni3Al alloys

“…In contrast to the first run, no peak in a variations was noticed during the second run, which seems to indicate a higher phase stability in the quenched sample. Before discussing these results further, it is appropriate to make a few remarks about our latest results obtained using high temperature diffractometry, the details of which will be published elsewhere [ 11 ]. High temperature X-ray measurements were carried out on alloy 7B using an Enraf-Nonius PDS 120 integrated powder diffractometry system which showed three distinct transformation regions.…”

Particle penetration during spray forming and Co-injection of Ni3Al + B/Al2O3 intermetallic matrix composite

“…[17][18][19][20] The fundamental problem associated with this processing route is linked to the interaction of the ceramic particles with the moving liquid, semisolid, and solid metallic droplets. [1,6,[26][27][28] Selection of Al 2 O 3 particles as the reinforcement material was prompted by its compatibility with nickel aluminide intermetallics, its potential improvement on the mechanical properties of nickel aluminide intermetallics, and its well-documented fundamental thermodynamic properties. As a result, choosing the right combination of critical processing parameters, such as the atomization pressure, gas to metal flow ratio, appropriate position of the second phase injectors, and the flight path length of the droplets prior to impingement on the deposition substrate, directly determines the solidification behavior of the droplets and, consequently, the microstructures and mechanical properties of the spray formed IMCs.…”