Abstract
The Laser Engineered Net Shaping (LENS) technique was combined with direct synthesis to fabricate L21-ordered Fe-Al-Ti based intermetallic alloys. It was found that ternary Fe-Al-Ti alloys can be synthesized using the LENS technique from a feedstock composed of a pre-alloyed Fe-Al powder and elemental Ti powder. The obtained average compositions of the ternary alloys after the laser deposition and subsequent annealing were quite close to the nominal compositions, but the distributions of the elements in the annealed samples recorded over a large area were inhomogeneous. No traces of pure Ti were observed in the deposited alloys. Macroscopic cracking and porosity were observed in all investigated alloys. The amount of porosity in the samples was less than 1.2 vol. %. It seems that the porosity originates from the porous pre-alloyed Fe-Al powders. Single-phase (L21), two-phase (L21-C14) and multiphase (L21-A2-C14) Fe-Al-Ti intermetallic alloys were obtained from the direct laser synthesis and annealing process. The most prominent feature of the ternary Fe-Al-Ti intermetallics synthesized by the LENS method is their fine-grained structure. The grain size is in the range of 3–5 μm, indicating grain refinement effect through the highly rapid cooling of the LENS process. The Fe-Al-Ti alloys synthesized by LENS and annealed at 1000 °C in the single-phase B2 region were prone to an essential grain growth. In contrast, the alloys annealed at 1000 °C in the two-phase L21-C14 region exhibited almost constant grain size values after the high-temperature annealing.
Highlights
Fe3Al and FeAl-based iron aluminides are potential structural materials for high temperature applications in hostile environments
The results of our preliminary studies show that the manufacture of components using the Laser Engineered Net Shaping (LENS) method combined with direct alloy synthesis is a very promising freeform technique that has the significant advantage of rapid cooling
It is observed that fully dense bulk ternary Fe-Al-Ti intermetallic samples can be produced using LENS combined with direct alloy synthesis from pre-alloyed FeAl and elemental Ti powders
Summary
Fe3Al and FeAl-based iron aluminides are potential structural materials for high temperature applications in hostile environments. Collins et al [14] and Schwendner et al [15] used this approach to study Ti-Mo-Nb-Al-Si, Ti-Cr-Nb-Al-Si, Ti-Cr, and Ti-Nb alloys fabricated using the LENS technique Their results reveal that the thermodynamic enthalpy of mixing of the constituent elements is the most important factor determining the microstructure and compositional homogeneity of these alloys. The results of our preliminary studies show that the manufacture of components using the LENS method combined with direct alloy synthesis is a very promising freeform technique that has the significant advantage of rapid cooling (up to 104 K/s). Such conditions should lead to a significant non-equilibrium solute-trapping effect, thereby avoiding component segregation and relieving solubility limitations. Binary Ti-Fe and ternary Ti-Fe-Ni alloy libraries were fabricated either from elemental powders delivered from different powder feeders or from pre-blended powder mixtures
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