Reactive synthesis and characterization of titanium aluminides produced from elemental powder mixtures

Abstract

The formation of titanium aluminides in Ti-Al elemental powder mixtures containing 25, 50 and 75 at.% Al, has been studied using differential scanning calorimetry (DSC). Phase evolution in the mixture was followed by heating the compacted samples up to 1273 K at 7.5 and 15 K min -1 . The cooled samples were characterized using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. The results showed that the primary combustion product in all the samples was TiAl 3 , and the combustion reaction occurred below the melting point of aluminum only in Ti-rich samples. In Alrich samples (75 at.% Al), TiAl 3 was obtained as a porous, single-phase product after combustion. In samples containing 25 and 50 at.% Al, the combustion reaction was incomplete and the unreacted titanium particles were covered by a layer of TiAl 3 . In these samples, other intermetallic compounds such as TiAl 2 , TiAl and Ti 3 Al were observed to form upon heating beyond the combustion peak and are attributed to the solid-state reaction between unreacted titanium and TiAl 3 . Heating the samples with 25 at.% Al to 1273 K for an hour led to the formation of a homogenous Ti 3 Al product, while a multiphase product with a dominant TiAl phase was observed in samples containing 50 at.% Al. Calculations based on DSC data show that the formation of TiAl 3 through the reaction between solid titanium and molten aluminum is associated with an apparent activation energy of 195 ± 20 kJ mol -1 and an enthalpy of -114 ± 5 kJ mol -1 .

Heat Treatment of In Situ Laser-Fabricated Titanium Aluminide

“…The absence of γ grains at this heat-treatment temperature allows the unhindered growth of the lamellar microstructure [1]. The grain boundaries are jagged and give good creep behaviour [1,[14][15][16][20][21][22]. It is possible to see that increasing aluminium content and heat-treatment temperature led to twinning [24].…”

“…The brittleness and low fracture toughness of γ-Ti-Al makes it difficult to manufacture parts using conventional methods. The lack of ductility in these alloys has necessitated alternative manufacturing routes such as additive manufacturing (AM) of γ-Ti-Al parts for aerospace applications [10][11][12][13][14]. Electron beam melting and laser beam melting are the most used AM process for both research and parts production [15,16].…”

Microstructure Evolution and Pore Formation Mechanism of Porous TiAl3 Intermetallics via Reactive Sintering

“…Intermetallics are potential functional and structural material with a mixture of metallic and covalent bonds enabling their excellent properties such as high melting point, good strength and oxidation resistance at elevated temperature [1]. The combination of these properties make intermetallics suitable for industrial applications in automotive industry and energy generation [2][3][4]. In particular, Al-based intermetallic compounds attract much attention due to the outstanding properties of low density, high specific strength, excellent corrosion and oxidation resistance at high temperatures [5,6], including Ti-Al, Fe-Al, Nb-Al, Ni-Al and TiAl-Nb [7][8][9][10][11].…”

“…The final products kept the original shape and avoided deformation and cracking due to the even heating of powder compacts. In addition, TE is a highly exothermic reaction, and hence has the advantage of low energy consumption, simplicity of equipment and short sintering time [3]. Wang et al [19] prepared porous TiAlbased intermetallics via TE with high open porosity of 84%, and the total sintering time only took about 6 h. Porous TiAl 3 intermetallics have the higher oxidation resistance in Ti-Al system, compared to Ti 3 Al and TiAl phases and relative low density [3,18,21].…”

Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions

“…The DTA/DSC based methods are the most widely used for gasless SHS systems, with multiple studies into intermetallics, specifically the Ni/Al [35][36][37][38][39][40][41][42][43], Ti/Al [44][45][46], Co/Al [47], Al/Ru [48], Nb/Al [49], and Mg/Al [50] systems, in addition to other binary solid-solid compositions, i.e., the Si/C [51], Mo/Si [52], Zr/B [53], Fe/Se [54]. More complicated ternary systems were also investigated [54][55][56][57][58][59][60][61].…”