Thermodynamic activities and phase boundaries for the alloys of the solid solution of Co in Ni 3 Al
- PDF / 389,750 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 2 Downloads / 232 Views
I.
INTRODUCTION
THE g ' phase of the type Ni3Al is important for the strengthening of the fcc g matrix in Ni-base superalloys and for the development of alloys on the basis of ordered intermetallic phases. The Ni3Al phase has a face centred cubic L12 structure. Transition metals occupy different lattice sites in the g ' phase if they are added to Ni3Al. Mo¨ssbauer effect measurements on Ni3Al,[1] axial electron channeling microanalysis,[2] and atom probe field-ion microscope measurements[3] revealed a preference of the Co atoms for the Ni sites. The experimental results on the site preference are supported by an analysis of the g '/g equilibrium in the NiAl-Co system by the cluster variation method with the Lennard–Jones potential[4] and by other theoretical computations on the site preference of a third component in the Ni3Al lattice.[5,6] The substitutional behavior of Co was inferred in References 5 and 6 from the direction of the g ' solubility lobe in the Ni-Al-Co phase diagram. Different theoretical approaches were taken to explain the solubility behavior.[5,6] Wu et al.[7] used the tetrahedron approximation of the cluster variation method to model generally the ternary site occupation in L12 ordered intermetallics. A review of the knowledge on the phase diagram of the Ni-Al-Co system is given by Hubert-Protopopescu and Hubert.[8] Kek et al.[9] determined calorimetrically the enthalpy of formation of Ni3Al with different additions of cobalt. The determination of partial thermodynamic properties with emphasis on chemical potentials is reported in this work for the first time for the ordered intermetallic phase Ni3Al with different additions of cobalt. The investigations were carried out by vaporization measurements using Knudsen effusion mass spectrometry. Phase diagram studies were additionally conducted for the evaluation of the vaporization studies. M. ALBERS, Ph.D., a former Graduate Student with Institute of Physical Chemistry, Technische Hochschule Darmstadt, Germany, is now with Leybold Vakuum GmbH, 50986 Ko¨ln, Germany. D. KATH, Engineer, is with the Institute of Materials in Energy Systems, Research Centre Ju¨lich. K. HILPERT, Professor, is with the Institute of Materials in Energy Systems, Research Centre Ju¨lich, 52425 Ju¨lich, Germany, and with the Institute of Physical Chemistry, Technische Hochschule Darmstadt. Manuscript submitted May 7, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
The work on the Ni-Al-Co system reported here is part of our systematic thermodynamic studies of the systems NiAl[10,11] and Ni-Al-M, where M is boron or a transition metal (Hf,[12] Ti,[13] and Fe,[14]), carried out essentially in the solubility range of the Ni3Al phase and the adjacent phase fields. The work complements our recent studies on the TiAl[15] and Ni-Hf[16] systems. The potential of Knudsen effusion mass spectrometry for the study of alloys is described in a review article by Hilpert.[17] II.
EXPERIMENTAL
Eight alloy samples, each with a weight of of about 10 g, with compositions (Ni3Al)12xCox (x
Data Loading...
