Microstructure and properties of duplex δ-Al3(Ti, V)/β-(Ti, V) alloys

Abstract

The microstructures of multiphase intermetallic alloys with compositions Al 70 Ti 10 V 20 and Al 62 Ti 10 V 28 based on the trialuminide Al 3 Ti have been characterized, following chill casting and postsolidification heat treatment, using a combination of scanning electron microscopy and transmission electron microscopy (TEM). Evidence of a eutectic reaction of the form L → ␦-Al 3 (Ti, V) ϩ -Al 8 V 5 , not previously reported in the Al-Ti-V system, has been observed in both alloys solidified at sufficient levels of undercooling. The phase is replaced by metallic ␤-(Ti, V) phase during subsequent heat treatment in the range 1073 to 1273 K, and differential thermal analysis (DTA) of samples preannealed at 1173 K revealed an endothermic peak at ϳ1560 K, consistent with equilibrium eutectic melting of the form (␦ ϩ ␤) → L. Although the chill-cast alloys retained metastable intermediate high-temperature phases, duplex metallic-intermetallic microstructures, containing uniform fine-scale distributions of metallic ␤-(Ti, V) solid solution in a ␦-Al 3 (Ti, V) intermetallic matrix, have been produced in both alloys during isothermal heat treatments at temperatures in the range 1073 to 1273 K. For both alloys, the bulk Vickers hardness of such microstructures remained in excess of that of binary Al 3 Ti, while in the Al 62 Ti 10 V 28 alloy, where the increased volume fraction of ␤ phase took the form of a near-continuous network within ␦ matrix, there was evidence arising from indentation tests of a substantial improvement in the cracking resistance compared to both chill-cast ternary alloy and binary Al 3 Ti.

Effects of microstructure on high temperature mechanical properties of Al3Ti–Mo3Al two-phase intermetallic alloys

“…If there is a certain crystallographic relationship between A2-b and the intermetallic phase(s), it results in the reconstruction of the former A2-b grain. Chang and Muddle reported that there is Bain relationship between D0 22 -Al 3 (Ti, V) and A2(b)-(Ti, V) [8]. The variations of Bain relationship between A2-b and D0 22 -Al 3 Ti are shown in Fig.…”

Structure and stability of a new ternary hexagonal phase in Al3 Ti-based Al-Ti-V alloys

“…[2] In adopting 1073 to 1673 K. However, there is already evidence that an alternative approach to improving the low-temperature current understanding of the ternary-phase equilibria is properties of monolithic Al 3 Ti, the present work has involved incomplete. The present authors have observed evidence of selection of the Al-Ti-V system as a ternary alloy system a eutectic reaction of the form liquid (L) → ␦ -Al 3 (Ti,V) ϩ offering an attractive range of phase relationships near the -Al 8 V 5 [15] that is not recognized on current phase diagrams, composition Al 3 Ti, suitable for the design of multiphase as well as an extended range of intermediate high-temperaintermetallic or duplex intermetallic/metallic-phase microture intermetallic phases in the composition range between structures.…”

“…The eutectic microstructure contained standard ratio method, [19] and the required k-factors were discontinuous rod-like particles of -Al 8 V 5 in a continuous determined experimentally using the Al-rich aluminides matrix of ␦ -Al 3 (Ti,V) (D) in dark contrast, which is consisAl 3 Ti and Al 3 V. Since the permitted composition range is tent with the ␦ / eutectic microstructure first observed in extremely narrow for both line compounds, these two interan Al 70 Ti 10 V 20 alloy. [15] metallic phases should be suitable for use as standards in…”

“…A novel hexagonal phase (designated H (2) ) has been solidified via the eutectic reaction L → ␦ ϩ . [15] In summary, detected as a major constituent of both Al 62 Ti 10 V 28 and the solidification path in the Al 62 Ti 10 V 28 alloy is suggested Al 55 Ti 10 V 35 alloys, following chill casting and after to be such that homogenization at 1523 K. The phase H 2 has an ordered L → L ϩ ␤ → L ϩ ␤ ϩ H → L ϩ ␤ ϩ H ϩ → ␤ hexagonal crystal structure (space group P6 3 /mmc, a ϭ 0.558 Ϯ 001 nm, c ϭ 0.450 Ϯ 0.001 nm), similar to that ϩ H 2 ϩ ϩ ␦ of ␣ -Ti and ␣ 2 -Ti 3 Al, and an atomic composition of 54 Ϯ 1 Al-11 Ϯ 1 Ti-35 Ϯ 1 V in the chill-cast condition. In the microstructure of the chill-cast Al 55 Ti 10 V 35 alloy, 2.…”