Processing and characterisation of nanocrystalline iron aluminide coatings prepared by thermal spraying of milled powders

Spray forming thick nanostructured and microstructured FeAl deposits

“…In addition, it is clear from this figure that, despite their higher amount of porosity (7.8-11.4%), the deposits obtained from milled powder have their hardness enhanced by the presence of the retained nanostructured unmelted particles. This effect, suggested by local measurement of microhardness on unmelted particles [14,15], was confirmed recently by modifying the amount of unmelted particles retained in FeAl HVOF nanostructured coatings [40]. The trends shown in Fig.…”

“…These two porosity morphologies are fairly common in thermal sprayed materials and have also been observed, in [19] and in Ni-5 wt% Al coatings [38]. Thus, in the thick nano-deposit, all the kinds of visible structural features are very similar to those found within the thin nanostructured FeAl coatings previously investigated [14,15]. A micrograph of the APS micro-deposit is shown in Fig.…”

“…Among the available deposition methods, thermal spraying of nanocrystalline powders has been successfully applied to produce nanostructured coatings with a typical thickness in the range 100-300 mm. For example, synthesis of nanostructured metallic coatings by high velocity oxy-fuel (HVOF) thermal spraying of milled powder has been achieved for Ni based alloys [9], Inconel 718 [10], Cr 3 C 2 -NiCr [11], WC/Co [12] and FeAl [13][14][15]. Plasma sprayed nanostructured ceramic coatings have also been synthesized Intermetallics 13 (2005) by Gell et al [16,17] for Al 2 O 3 /TiO 2 as well as by Berndt et al [18,19] for ZrO 2 /Y 2 O 3 .…”

Grain refinement, hardening and metastable phase formation by high current pulsed electron beam (HCPEB) treatment under heating and melting modes

“…3 shows the evolution of the microhardness as a function of the depth from the top surface. Because of a smaller grain size and the presence of the oxide dispersion, the bar of the ODS alloy is characterized by a higher hardness (about 390 HV) than the conventional one (about 300 HV) [26,27]. In both cases, even after only 2 pulses, an increase of about 50 HV in hardness is associated with the LEHCPEB treatment at the surface of the FeAl sample (curves with squared dots).…”

“…Further information concerning these alloys can be found elsewhere [23,24]. The initial extruded bars were obtained by extrusion from milled (with Y 2 O 3 addition at the milling stage) [25][26][27][28] or atomized [25,26] FeAl powders. The extrusion temperatures (1250 • C and 1100 • C) and the result- ing average grain sizes (4 m and 40 m) obtained for these ODS and conventional FeAl alloys are recalled in Fig.…”