Spray Forming of Bulk Ultrafine-Grained Al-Fe-Cr-Ti

Abstract

An Al-2.7Fe-1.9Cr-1.8Ti alloy has been spray formed in bulk and the microstructure and properties compared with those of similar alloys produced by casting, powder aomization (PA), and mechanical alloying (MA) routes. In PA and MA routes, a nanoscale metastable icosahedral phase is usually formed and is known to confer high tensile strength. Unlike previous studies of the spray forming of similar Al-based metastable phase containing alloys that were restricted to small billets with high porosity, standard spray forming conditions were used here to produce a~98 pct dense 19-kg billet that was hot isostatically pressed (''HIPed''), forged, and/or extruded. The microstructure has been investigated at all stages of processing using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and synchrotron X-ray diffraction (XRD) at the Diamond Light Source. Consistent with the relatively low cooling rate in spray forming under standard conditions, the microstructure showed no compelling evidence for the formation of metastable icosahedral phases. Nonetheless, after downstream processing, the spray-formed mechanical properties as a function of temperature were very similar to both PA rapid solidification (RS) materials and those made by MA. These aspects have been rationalized in terms of the typical phases, defects, and residual strains produced in each process route.

Solidification Sequence of Spray-Formed Steels

“…[2] Several types of alloys such as steels, cast irons, Ni-alloys, Al-alloys, and Cu-alloys, as well as different geometries (billets, tubes, and rings) have been successfully produced by spray-forming. [3][4][5][6][7][8][9][10][11][12][13][14] In all cases, the spray-formed microstructures present noticeable features: (1) equiaxed grains with diameters from 10 to 50 lm; (2) a high level of microstructural homogeneity and macrosegregation free; (3) uniform and homogeneous distribution of eutectic and second phases. The advantageous microstructure produced by the spray-forming process is well-known from research; however, solidification at the deposition zone and the creation of such a characteristic microstructure are still an open discussion.…”

μ-EXAFS and μ-XRD study of selected regions of a Al–Fe–Cr–Ti complex alloy

“…These Figure 2 and the main peaks are labelled. In these samples the size of the intermetallics was around a few hundred nanometres (Banjongprasert et al 2010). μ-XRD was able to detect differences in the phases present in the individual selected regions, confirming the heterogeneity of the alloy.…”

“…A billet of 19.2 kg was produced by spray forming at Oxford University; the details are reported elsewhere (Banjongprasert et al 2010). Samples from selected regions of the billet were prepared with a FEI NOVA 600 Nanolab focused ion beam microscope.…”

“…The Al 93 Fe 3 Cr 2 Ti 2 alloy composition has shown the most interesting combination of mechanical properties and industrial feasibility (Banjongprasert et al 2010). The microstructure is generally characterized by an α-Al matrix with 40-60 vol% of Al 13 Cr 2 , Al 13 Fe 4 and Al 3 Ti second-phase intermetallic particles (Inoue & Kimura, 2000;Banjongprasert et al 2010).…”

Characterization Of An Equal Channel Angular Pressed Al-Zn-In Alloy

“…Recently, metals and alloys with ultrafine-grained (UFG) structure have becoming active research areas. Many processing techniques have been proposed to produce alloys containing UFG structure such as ball milling [3], rapid solidification [4], spray forming [5], and severe plastic deformation [6]. Among those techniques, severe plastic deformation (SPD) has gained increasingly interests as it provides many advantages e.g.…”