Synthesis of Fe-Al-Ti Based Intermetallics with the Use of Laser Engineered Net Shaping (LENS)
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.
Laser powder micro-deposition of compositional gradient Ti–Cr alloy
Laser powder deposition allows preparing fully dense metallic parts in a layer-by-layer additive manufacturing manner. The method presents great flexibility in controlling the materials composition as well as its microstructure and properties. In this paper, composition gradient thin walls from Ti to Ti–60 at.%Cr were prepared by the laser powder micro-deposition process. The microstructure, phase constitution, micro hardness, and modulus were characterized by scanning electron microscope (SEM), micro X-ray diffraction (micro-XRD) and ultra micro indentation testing along the composition gradient direction. The results show that the composition along the wall height change as predetermined. Metastable β-Ti(Cr) was formed for compositions with more than 25 at.%Cr. TiCr2 phase was formed and its percentage increased with further increase of Cr content. The hardness and modulus changed conformably with the composition gradient.
Effects of early transition metal solutes on the D03-B2 critical temperature of Fe3Al
The effects of dilute concentrations of the ternary solutes Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W on the critical temperature of the D0{sub 3}-B2 transformation in Fe{sub 3}Al were measured by differential thermal analysis (DTA). Additional studies by X-ray diffractometry showed that Mo, Ta, and W atoms occupied predominantly the 4(b) Wyckoff sites in D0{sub 3}-ordered Fe{sub 3}Al. Most solutes caused an increase in the D0{sub 3}-B2 transformation temperature, which was approximately linear in the limit of dilute solute concentrations. The efficacy of a particular ternary element in raising the D0{sub 3}-B2 transformation temperature was shown to be related to its metallic radius. The authors argue that the energetics of atom size mismatch are the major cause of the effects of ternary solutes on the D0{sub 3}-B2 transformation temperature of Fe{sub 3}Al.