Al-B-Ti (Aluminum-Boron-Titanium)

Abstract

The previous review of this ternary system by [2004Bon] presented partial liquidus and solidus surfaces, partial isothermal sections at 1000, 820, and 727°C and a vertical section at 98 mass% Al. [2005Rag] reviewed briefly the experimental and calculated results of [2001Fje] and presented for Al-rich alloys a schematic liquidus projection, a reaction scheme and two isothermal sections at 1000 and 800°C. These reviews concluded that the diborides AlB 2 and TiB 2 do not form a continuous solid solution and that there are no stable ternary phases in the system. In their thermodynamic treatment, [2005Gro] ignored ternary interactions and based their calculations solely on the binary parameters. Their results showed a miscibility gap in the liquid phase, which has no experimental support. Very recently, [2009Wit] carried out additional experiments on selected ternary and binary alloys and used the new results along with selected experimental data from the literature to recalculate in detail the phase equilibria. Binary SystemsIn the Al-B system [2004Mir], two borides are known: AlB 2 (C32, AlB 2 -type hexagonal) and AlB 12 (AlB 12 -type tetragonal). The Al-Ti phase diagram [2006Sch] has the following intermediate phases: Ti 3 Al (D0 19 , Ni 3 Sn-type hexagonal, denoted a 2 ), TiAl (L1 0 , AuCu-type tetragonal, denoted c), TiAl 2 (HfGa 2 -type tetragonal, denoted g by [2009Wit]), TiAl 3 (HT) (D0 22 -type tetragonal, denoted e by [2009Wit]), and TiAl 3 (LT) (tetragonal, space group I4/ mmm, denoted e(l) by [2009Wit]). Based on their own assessment [2008Wit2], [2009Wit] included two previously known compounds: Ti 2+x Al 5Àx (tetragonal, space group P4/ mmm, denoted f) and Ti 3 Al 5 (tetragonal, space group P4/ mbm), which were excluded by [2006Sch] in their assessed diagram. The Ti-B phase diagram [2004Ma, 2008Wit1] shows three intermediate phases: TiB (B27, FeB-type orthorhombic), TiB 2 (C32, AlB 2 -type hexagonal) and Ti 3 B 4 (D7 b , Ta 3 B 4 -type orthorhombic). Ternary Phase EquilibriaWith starting metals of 99.99% Al, 99+% B and 99.9% Ti, [2009Wit] arc-melted under Ar atm 10 ternary alloys with B contents up to 2 at.% (with the exception of one alloy with 7.5 at.% B). Five binary alloys free of B were also made with Al/Ti atom ratio of either $1 or $3. The alloys were annealed between 1350 and 1400°C for 4-10 h. The phase equilibria were studied with the scanning electron microscope equipped with energy dispersive x-ray analyzer, x-ray powder diffraction and differential thermal analysis at heating/cooling rate of 20°C per min. The thermal arrests and the deduced phase changes were listed Ti Atomic Percent Aluminum A to m ic P e r c e n t T it a n iu m A to m ic P e r c e n t B o r o n Al B Fig. 1 Al-B-Ti computed liquidus projection [2009Wit] Atomic percent Aluminum Atomic percent Boron Fig. 2 Al-B-Ti computed partial liquidus projection showing the primary fields of (bTi), (aTi) and c [2009Wit]

Control of Solidification Process and Surface Microstructure of Large Size Ingot ZALCu5MnA Alloy

“…2) Boundary condition. The heat exchange of among casting, casting mold and air is air convective heat transfer, which belongs to the third kind boundary condition [7,8,9].…”