Papers by Keyword: Ternary Alloys

Abstract: Coupled, regular eutectic growth of α(Al) and Al2Cu from ternary Al-Cu-Ag liquid alloys is investigated with focus on the formation and the characteristics of eutectic cells in unidirectionally solidified, polycrystalline, bulk samples. The topologic anisotropy of the lamellar eutectic leads to destabilization along the lamellae with elongated cells being intermediate to stable cells, irrespective of the crystallographic orientation of the phases. The formation of stable cellular patterns with elongated or regular cell structure is explained with reference to the crystal orientation of the phases α(Al) and Al2Cu, measured by electron backscatter diffraction (EBSD).

Abstract: Activity of tin in liquid Sn-Ag-Bi alloys was derived by EMF measurement of galvanic cell with fused salts electrolyte in the temperature range of 700 to 900K in the whole composition range. Activity of tin at 900K shows very small positive deviation from Raoult’s low for Sn-Bi alloys. Activity of ternary alloys was measured along three pseudo binary systems of Sn-(Ag,Bi) (where xAg/xBi =1/3,1/1 and 3/1). Its concentration dependence is very complex. From the iso-activity curves in the ternary system excess free energy of mixing is derived using Darken’s method for Gibbs-Duhem equation

Abstract: Interdiffusion in Co-Fe-Ni alloys was studied in 1373-1588 K temperature range. The Danielewski-Holly model was used for the description of the interdiffusion process in ternary Co- Fe-Ni diffusion couples both for the finite and infinite geometry. Using the inverse method the average intrinsic diffusivities of components in the Co-Fe-Ni system were calculated and compared with the results of the other authors. The activation energies of cobalt, iron and nickel intrinsic diffusion have been found in 1373-1588 K temperature range.

Abstract: Small amounts of silver have been added to the intermetallic compound β-NiAl for the purpose of improving its mechanical properties. Four ternary NiAl-Ag alloys NiAl-0.5Ag, NiAl-1Ag, NiAl-5Ag and NiAl-10Ag (at.%), and an Ag-free β-NiAl have been oxidized at 900oC for 24 h in 1 atm O2 to study the effect of the presence of silver on the oxidation of β-NiAl. The kinetics of all the alloys were generally composed of two main parabolic stages with slightly larger parabolic rate constants for the second stage, except for NiAl-10Ag, which has an instantaneous parabolic rate constant decreasing with time. A continuous external layer of Al2O3 formed on all the alloys. In particular, the scales formed on NiAl-5Ag and NiAl-10Ag contained a thin and discontinuous layer of silver at the alloy/Al2O3 interface. Furthermore, NiAl-10Ag formed also isolated Ag particles or even a discontinuous Ag layer occasionally surmounting the Al2O3 scale. The addition of minor amounts of silver does not affect significantly the oxidation of β-NiAl, because silver is essentially present as a second phase due to its very small solubility in this intermetallic compound.

Abstract: The effect of the addition of 5 and 10 at.% Cr on the oxidation of a binary Fe-10 at.% Al alloy (Fe-10Al) was studied in 1 atm O2 at 1000°C. Fe-10Al underwent a very slow initial nearly-parabolic stage followed by a breakaway composed of two subsequent parabolic stages with a smaller rate constant for the final period. The two ternary alloys (Fe-5Cr-10Al and Fe-10Cr-10Al) presented two parabolic stages with final rate constants similar to each other and much lower than that for Fe-10Al. The alumina scale developed initially on Fe-10Al was replaced later by a layered scale containing mixtures of Fe and Al oxides plus many Fe-rich oxide nodules. Fe-5Cr-10Al was mostly covered by a thin alumina layer just above the alloy surface with some Fe-rich nodules formed in the beginning of oxidation, which later on were healed by alumina with a large decrease of the oxidation rate. A continuous alumina layer formed on the whole sample surface without any Fe-rich nodule for Fe-10Cr-10Al. Therefore, the addition of chromium is obviously beneficial for the oxidation resistance of Fe-10Al by inhibiting the formation of fast-growing Fe-containing oxides and promoting the development of an exclusive alumina layer. However, the effect of chromium is different from the classical third-element effect.