Solid-state reactions during heating mechanically milled Al/TiO2 composite powders

Abstract

Solid-state reactions between Al and TiO 2 during heating high-energy mechanically milled Al/TiO 2 composite powders have been investigated by using a combination of thermal analysis, X-ray diffraction (XRD), and various microstructural characterization techniques. When the TiO 2 particles and their interparticle spacing in the Al/TiO 2 composite powder particles are sufficiently large, the reaction between Al and TiO 2 proceeds by two steps. The low-temperature step is an interfacial reaction, which starts at a temperature close to 660 °C. The high-temperature step is a reaction facilitated by bulk diffusion and starts at a temperature above 820 °C. The first phase formed from the reaction is always Al 3 Ti irrespective of the starting powder composition or milling time. Al 2 O 3 is difficult to form at temperatures below 800 °C. The formation of the ␣-Ti(Al,O) phase proceeds slowly and requires either continuous heating to a temperature above 1000 °C or holding at a temperature close to 1000 °C for a period of time. Mechanical milling of the Al/TiO 2 powder enhances the interfacial reaction between Al and TiO 2 . This enhancement is originated from the establishment and refinement of Al/TiO 2 composite microstructure.

Fabrication and characterizations of new glassy Co71Ti24B5 alloy powders and subsequent hot pressing into a fully dense bulk glass

“…MECHANICAL alloying (MA), using the ball-milling or rod-milling techniques, has been widely employed for fabrication of useful advanced engineering materials, [1] including metal nitrides, [2,3,4] carbides, [5] hydrides, [6] silicates, [7] composite and nanocomposite materials, [8,9,10] and nanocrystalline materials. [11,12] The rapid solidification technique, using melt spinning or casting methods, has been used for preparing several attractive promising hard and soft magnetic metallic glassy alloys (for example, References 13 through 17), which attract increasing interest with their unique short-range atomic order.…”

Mechano-thermal treatment of TiO2-Al powder mixture to prepare TiAl/Al2O3 composite

“…The ordered Al 3 Ti may be formed through ordering of Al(Ti) solid solution at temperatures close to the melting point of Al [9]. In the present case, gradual formation of Ti from the first step of reduction of TiO 2 and its presence together with Al causes formation of Al 3 Ti phase.…”

“…There is no detailed study on the formation mechanism of TiAl/Al 2 O 3 composite. It has been observed that the reaction takes place after the melting of Al even after extended milling [9]. It seems that the low ball-topowder mass ratio in this case did not provide sufficient energy for occurrence of the reaction in the solid state.…”

“…In addition, the final phases in such a composite are thermodynamically compatible [7,8]. This composite material can be produced by mechanical activation and subsequent heat treatment of aTiO 2 and Al powder mixture [9][10][11]. N. J. Welham produced an Al 3 Ti/Al 2 O 3 composite using this method and characterized the mechanism of the process [10,11].…”

Fabrication of an r-Al2Ti intermetallic matrix composite reinforced with α-Al2O3 ceramic by discontinuous mechanical milling for thermite reaction

“…These intermetallics have low density, high elastic modulus, and strength at high temperatures, as well as the dimensional stability because of the passive layers resistant to oxidation and corrosion. Several potential applications have been identified for titanium aluminide alloys in aerospace, automotive, and turbine power generation industries [1][2][3][4][5][6][7][8][9][10][11][12][13].…”