Reactive infiltration of 25 vol pct TiO2/Al composites

Abstract

The purpose of this investigation was to establish the reaction path during processing of a 25 vol pct TiO 2 preform and molten Al composite by pressure infiltration. Initial preform temperatures between 550 Њ and 850 ЊC, melt temperatures from 715 Њ to 850 ЊC, and two postinfiltration cooling rates were considered. The reaction path between molten Al and TiO 2 under the conditions examined involved three steps: the final products being ␣ -Al 2 O 3 , Al 3 Ti, and excess Al. It was further observed that the morphology of the reactant TiO 2 whisker was maintained throughout the reaction sequence, the M 2 O 3 to Al 2 O 3 transformation involving diffusion-controlled replacement of Ti atoms by Al. Finally, reaction completion involved heterogeneous nucleation of Al 3 Ti from the Ti-saturated melt at the Al 2 O 3 interface.

Formation of Corundum, Magnesium Titanate, and Titanium(III) Oxide at the Interface between Rutile and Molten Al or AlSi7Mg0.6 Alloy

“…Specifically for Ti 2 O 3 that was identified by XRD (see Figure 1c, also refs. [9,10] ), the intermediate reaction step can be written as:…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] As products of the reduction process, titanium suboxides like Ti 3 O 5 , Ti 2 O 3 , TiO, and concurrently released metallic titanium were reported. [9,10,12,17,19,21] Ti is initially dissolved in the melt. However, when its concentration in the melt exceeds the solubility limit, intermetallic phases like TiAl 3 , TiAl 2 , TiAl, or Ti 3 Al are formed.…”

“…However, when its concentration in the melt exceeds the solubility limit, intermetallic phases like TiAl 3 , TiAl 2 , TiAl, or Ti 3 Al are formed. [5,6,9,10,[13][14][15][16][17][18][19][20][21] Titanium dissolved in the Al melt is incorporated into the face-centered cubic Al lattice during solidification. [9][10][11]13] Oxygen from reduced TiO 2 forms Al 2 O 3 with Al from the melt.…”

“…[5,6,9,10,[13][14][15][16][17][18][19][20][21] Titanium dissolved in the Al melt is incorporated into the face-centered cubic Al lattice during solidification. [9][10][11]13] Oxygen from reduced TiO 2 forms Al 2 O 3 with Al from the melt. [5,6,9,10,[13][14][15][16][17][18][19][20][21] The kind of the alumina formed depends on the temperature, at which the reduction takes place.…”

“…[9][10][11]13] Oxygen from reduced TiO 2 forms Al 2 O 3 with Al from the melt. [5,6,9,10,[13][14][15][16][17][18][19][20][21] The kind of the alumina formed depends on the temperature, at which the reduction takes place. Besides the thermodynamically stable corundum, metastable alumina phases like g-, h-, or d-Al 2 O 3 can be formed at temperatures below 1 000 C. [13,17,19,21] If the aluminum melt contains magnesium, the magnesium aluminate spinel MgAl 2 O 4 , [7] magnesium titanate MgTiO 3 , [14,15] or magnesium dititanate MgTi 2 O 5 [8] form additionally.…”