High temperature deformation behaviour of a directionally solidified Ni3Al- Based alloy

The influence of alloying addition of chromium and iron on the mechanical p roperties and structure evolution of directionally solidified Ni3Al-based a lloy was investigated. Addition to the Ni3Al intermetallic compound of such elements as chromium (8 at.%) and iron (2 at.%) enables, within a limit ra nge of temperature and strain rate, the formation of the alloy. The sequence of structural changes of directionally solidified Ni-20 Al-8 C r-2 Fe alloy has been correlated with mechanical characteristics (sigma-eps ilon) of high temperature deformation process, determined in isothermal, un iaxial compression tests. Two ranges of work hardening have been identified on the stress-strain curves described by the equation sigma = K(1)epsilon( n1)+Delta. Microstructural observations as well as analyses of the chemical compositio n of the particular components of structure were carried out for selected s amples. The typical microstructure of the as-grown alloy consisted of well- aligned and equally spaced lamellae which undergoes coagulation during high temperature deformation. The great strength of Ni-20 Al-8 Cr-2 Fe alloy, e specially at the temperature 873 K, is the evidence of the stability of pha ses in the deformation process. On the basis of the analysis of the triple system Ni-Al-Cr at the temperature 1023 K there have been identified the ph ases occurring in the particular structural components: lamellae built of t he phases beta+gamma surrounded by the phases gamma+gamma', while the phase s beta+gamma+gamma' form the matrix of the examined alloy.