Addition Of Ternary Alloying Elements Research Articles

Phase stability and elastic properties of β Ti–Nb–X (X = Zr, Sn) alloys: an ab initio density functional study

Alloying effects of Zr and Sn on β phase stability and elastic properties in Ti–Nb alloys are investigated within the framework of first-principles density functional theory. Our results suggest that the stability of β phase can be significantly enhanced by the addition of Zr and Sn in Ti–Nb alloys. The computed results indicate that Zr and Sn behave as strong β stabilizers in the Ti–Nb system. The elastic properties are found to be altered considerably by the addition of ternary alloying elements (Zr and Sn). The computed elastic moduli of Ti18.75 at%Nb6.25 at%Zr and Ti25 at%NbxZr compositions are found to be lower than that for Ti18.75 at%Nb6.25 at%Sn and Ti25 at%NbxSn system. The lowest value of ∼54 GPa is obtained for Ti25 at%Nb6.25 at%Zr composition. Furthermore, the directional Young’s modulus is found to be in the order of E100 < E110 < E111 for all the compositions of Ti–Nb–Zr and Ti–Nb–Sn system.

The influence of Cu, Mg and Ni on the solidification and microstructure of Al-Si alloys

The influence of alloying elements (Cu, Mg, and Ni) on eutectic nucleation, eutectic grain morphology and the final microstructure of an Al-10Si commercial purity alloy in unmodified and Sr-modified conditions was investigated. It was found that the nucleation and eutectic grain growth morphologies of both the unmodified and Sr-modified Al-Si eutectic were significantly influenced by the addition of ternary alloying elements to a degree dependent on when the intermetallic phase formed during the solidification of the alloy with respect to the Al-Si eutectic. In cases where an intermetallic phase nucleated prior to the onset of the Al-Si eutectic reaction, the eutectic nucleation frequency was affected by changes to the available nuclei population. In cases where the intermetallic nucleated after the Al-Si eutectic, segregation of the ternary solutes in front of the Al-Si eutectic interface changed the nucleation and macroscopic growth dynamics. The changes in nucleation and growth dynamics of the Al-Si eutectic due to the presence of solute altered the morphology of the eutectic silicon considerably. This study has revealed a number of insights into the mechanisms of nucleation and growth of the Al-Si eutectic.

The influence of ternary alloying elements on the Al–Si eutectic microstructure and the Si morphology

The influence of the ternary alloying elements Cu, Mg and Fe on the Al–Si eutectic microstructure is investigated using a commercial purity Al–10wt%Si alloy in unmodified and Sr-modified conditions. A change in the Al–Si eutectic microstructure was associated with a change in the nucleation density of the eutectic grains caused by the addition of ternary alloying elements. When the ternary alloying element addition resulted in an increase in the eutectic nucleation frequency, a fibrous to flake-like transition was observed within the eutectic grain. When the ternary alloying element addition decreased the eutectic nucleation frequency significantly, a change in the eutectic morphology from flake-like to a mixture of flake-like and fibrous morphologies was observed. The mechanism of Al–Si eutectic modification is discussed. The growth velocity of the eutectic grain – liquid interface and the constitutional driving force available for growth are proposed as important parameters that influence the degree of eutectic modification in Al–Si alloys.

Modeling of site occupancies in B2 FeAl and NiAl alloys with ternary additions

The addition of ternary alloying elements to FeAl and NiAl based intermetallic compounds could potentially influence their mechanical properties in a significant manner. Knowledge of the site occupancies of different species in these ternary compounds is of importance since it influences the bonding characteristics and consequently the mechanical properties. In this paper a simple approach involving chemical rate theory has been used to calculate the site occupancies in the ternary B2 compounds. These calculations predict that with increasing atomic number of 3 d transition metal additions to B2 FeAl, the site occupancy of the ternary addition increases on the Fe site with the exception of Cu. The predicted exception for Cu has been experimentally verified using ALCHEMI. In addition, the site occupancies in B2 Ni–Al–Fe compounds of different compositions have been predicted and experimentally verified. The role of the relative ordering or clustering tendencies of the three different binary pairs in the ternary compound on the site preferences has also been discussed.

L1 2 (Al,Cr) 3Ti-based two-phase intermetallic compounds-I. Plastic deformation behavior

A number of recent works on intermetallic compounds in the Ti-Al system have concentrated on gamma-based TiAl, but Al{sub 3}Ti is especially attractive because of its low density and good oxidation resistance. However, Al{sub 3}Ti, with a low-symmetry tetragonal D0{sub 22} structure, exhibits less than 1% compressive strain in the temperature range of 298 K to 893 K, for which the primary deformation mode is ordered twinning. Therefore, its brittleness limits its practical application as a structural material. More recently, much work has been conducted on the transformation of crystal structure through the addition of ternary alloying elements to improve the ductility of Al{sub 3}Ti. In this study, the plastic deformation behavior of two-phase intermetallic compounds consisting of mainly L1{sub 2} phase and the second phases in Al-Ti-Cr system was investigated. As in the case of {alpha}{sub 2}/{gamma} two-phase TiAl compounds, the possibility of ductilizing two-phase intermetallic compounds based on L1{sub 2}-type (Al,Cr){sub 3}Ti was examined. The influence of pore formation, ingot cast structure and second phase morphology on ductility of the alloy was also examined.

L12-type ternary titanium aluminides as electron concentration phases

The structural change from aluminium-rich titanium aluminides (TiAl2 or TiAl3) to L12 type ternary titanium aluminides is examined in terms of the two alloying variables; these are atomic radius ratio (R A/R B) and electron concentration (e/a). Similarity in the stoichiometry of the L12 alloys (generally Ti25X8Al66 where X=Cr, Mn, Fe, Co, Ni, Pd, Ag or Zn) and the differences in the atomic radii of ternary alloying elements makes it difficult to useR A/R B criterion as an alloy variable. It is also found that the structural change in these alloys cannot be explained by the classical definition ofe/a because it gives an increase in this ratio rather than a decrease upon the addition of the ternary alloying element to TiAl2 or TiAl3. On the other hand, if a definition given by the Engel-Brewer theory is used, a decrease ine/a is found to occur upon the addition of ternary alloying element to either TiAl2 or TiAl3 with the consequence of achieving L12-type ternary titanium aluminides at definitee/a values around 2.5.

The wetting of alumina by copper alloyed with titanium and other elements

The wettability of alumina by ternary alloys of copper, titanium and aluminium, gallium gold, indium, nickel or silver has been investigated using sessile drop tests conducted in vacuum at 1050–1250° C. Substantial additions of titanium are known to induce copper to wet alumina due to the formation of a titanium rich reaction product at the alloy/ ceramic interface, but the present work has shown that the concentration of titanium can be reduced by the addition of ternary alloying elements. Additions of indium are very beneficial, of aluminium, gold or silver are moderately beneficial, and of gallium or nickel are of negligible benefit or detrimental. These observations, and previous work with copper-tin-titanium alloys [1] can be interpreted in terms of effects on the activity of titanium which it is argued will be enhanced if the ternary alloying element has a low surface energy and is readily saturated by titanium. The correlation of the experimental wetting observations with the surface energy and titanium solubility data for the ternary alloying elements provides a basis for the rational development of reactive metal brazes for joining unmetallized ceramics.