Microstructure of a High-Velocity Oxy-Fuel Thermal-Sprayed Nanostructured Coating Obtained from Milled Powder

Abstract

The mechanisms responsible for the different types of microstructure present in a nanostructured coating prepared by high-velocity oxy-fuel (HVOF) spraying of the Y 2 O 3 -reinforced milled FeAl powder have been established. Nano-and microsized grains were present both in the melted splats and the retained unmelted powder particles. In the unmelted powder particles, equiaxed grains formed by recrystallization from the heavily deformed and disordered structure present in the initial powder. Their size was controlled by the degree of advancement of the recrystallization process and the larger grains contained ribbonlike antiphase boundaries (APBs) separating large, ordered domains. In the melted zones, the grain size (and shape) was controlled by the local efficiency of the heat extraction during solidification. The Al evaporation during thermal spraying led to a modification of the local chemistry that resulted in the formation of the Fe 3 Al and FeAl phases containing fine networks of APBs. These APBs formed by sequential ordering from the high-temperature disordered FeAl phase that formed from the melt. Despite the high-temperature processing and recrystallization processes, both the melted and unmelted zones contained dislocations that result from residual stresses as well as from peening by the powder particles during spraying.

Processing conditions, microstructure and mechanical properties of hetero-nanostructured ODS FeAl alloys produced by spark plasma sintering

“…They include for example heavy deformation [2,3] and consolidation from a nanostructured milled powder by using conventional hot compaction [4,5] or rapid sintering techniques authorizing to retain the fine structure present in the powder. The latter consists of thermal spraying by different processes such as high velocity oxy-fuel (HVOF) [6][7][8], atmospheric plasma spraying (APS) [9], detonation gun [10], arc and cold spraying [11,12] as well as the electric field assisted spark plasma sintering (SPS) [13][14][15].…”

Thermal spraying of transition metal aluminides: An overview

“…Blackford et al [66] obtained a polycrystalline splat structure from their dendritical spherical powder, while nanograins were retained in the assprayed Fe40Al milled powder. Grosdidier et al and Guilemany et al arrived at similar conclusions spraying the same powder but at slightly different conditions; equiaxed small grains were displayed in the unmelted areas, while columnar grains, which are typical from rapid solidification processes, were visible in the melted regions [53,60,71]. Interestingly, as result of the thermal history of the milled particles within the flame, the final FeAl phase results to be the ordered B2 lattice, actually present in the areas that reached the molten state, since the non-fully melted regions exhibit just some ordering due to the starting recrystallization step.…”

The Effect of Hot Treatment on Composition and Microstructure of HVOF Iron Aluminide Coatings in Na2SO4 Molten Salts

“…Numerous thermal spray techniques, most notably plasma spraying ( Ref 28,31,32), high-velocity oxy-fuel (HVOF) ( Ref 17,27,28,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] and D-gun spraying processes ( Ref 26,29,[48][49][50][51][52][53][54][55][56][57][58][59] are considered for Fe-Al intermetallic coating materials. In comparison with other industrially used coatings such as CVD, PVD and hard chromium plating, a much thicker coating can be obtained by thermal spraying, which is a prerequisite in the energy sector.…”

“…The growing interest in the promising properties of intermetallic alloys based on the Fe-Al equilibrium phase diagram contributed to the gradual development of the HVOF spraying technique, which proved useful for the production of such intermetallic coatings in terms of their practical application on various steel elements, exposed to corrosive and erosive environment in the energy sector ( Ref 28,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][70][71][72][73][74]. The focus in these works was mostly placed on the structural properties of Fe-Al coatings and their wear resistance under dry friction (in congruence with ASTM G99-03), abrasive wear (in accordance with ASTM G65-00) and erosive wear, along with the involvement of Al 2 O 3 particles (Ref 44).…”