The effect of hot treatment on composition and microstructure of HVOF iron aluminide coatings in Na2SO4 molten salts

The paper deals with the hot corrosion performance of FeAl base intermetallic HVOF coatings in molten Na2SO4 at 850 C in an isothermal process over the span of 45 h under static conditions. The test was validated with electron microscopy and compositional analyses in the cross-section area, as well as x-ray diffraction techniques. All the coatings were characterized by Al-depleted regions, intersplat oxidation and different stoichiometric ratios of iron aluminides. The results were discussed in relation to the formation of oxide scales on the surface after exposition to corrosive media, as well as heterogeneity and defects of the sprayed coatings. The Fe40Al (at.%) powder showed quite uniform phase distribution after spraying and preserved its integrity after corrosion test; the FeCr25% ? FeAl-TiAl-Al2O3 (wt.%) and Fe46Al-6.55Si (at.%) powders exhibited interface oxidation, with localized corrosion attacks proceeding through particle boundaries and microcrack networks with no evidence of Na and S penetration. FexAly alloys are susceptible to accelerated damage and decohesion of the coating, whereas the formation of sulfides is observed at certain points

Sliding wear behavior of Fe-Al coatings at high temperatures

The medium and high temperature tribological behavior of different iron aluminide thermal spray coatings was investigated. Several powders synthesized through different routes (ball milling, self-decomposition, and self-propagating high-temperature sintering (SHS)) were evaluated. High heterogeneity of conventional High Velocity Oxygen Fuel (HVOF) coatings plays a vital role in their sliding performance, but as long as their integrity is preserved under high temperature oxidizing conditions, the wear rates are found to be acceptable, as it occurs in the case of ball milled Fe-40Al (at.%) powder. The friction phenomenon and wear mechanisms were analyzed in detail through the wear track morphology, contact surface, and friction coefficients. The occurrence of brittle phases in the sprayed coatings, which are also present when tested at high temperatures, appeared to be crucial in accelerating the coating failure

Powłoki Fe-Al osadzane detonacyjnie Część I: warstwy pośrednie Ni(Al) i Cr(Ni) oraz powłoki Fe-Al osadzane detonacyjnie na podłożu ze stali 045

The microstructure of transition layers of Ni(Al) - pure Ni with Al and NiAl particles as well as Cr(Ni) - pure Cr in the Ni matrix, occurred between the coating of Fe-Al type intermetallic phases and the 045 carbon steel substrate was analysed in the present work. The investigations were aimed at the adherence of transition layers and the outer coating deposited with the detonation-gas spraying. The structure was examined using the methods of scanning (SEM) and transmission electron (TEM) microscopies as well as the analysis of chemical composition in microareas (EDS). Silica grains at the boundary of the substrate and the layer of Ni(Al), aluminium oxide at the boundary and inside the Ni(Al) layers, an Al based AlNiOx phase, columnar crystals at the boundary of the coating of Fe-Al type phases and an adjacent Cr(Ni) layer were observed. The results were discussed in reference to earlier examinations of bending strength considering cracking and delamination of the coating off the substrate. They were then compared with the state of the boundary between the coating and the steel substrate analysed in former works. It seems, that the substrate boundary free from silica inclusions and the prevention of the formation of aluminium oxides at the boundary of transition layers and the substrate should improve the adherence of the whole multi layer and the coating.W pracy poddano analizie mikrostrukturę warstw pośrednich: Ni(Al) - czystego niklu z cząstkami Al i faz NiAl oraz warstwy Cr(Ni) - chromu w osnowie Ni, występujących pomiędzy powłoką faz międzymetalicznych typu Fe-Al i podłożem ze stali węglowej 045. Badania wykonano z punktu widzenia przyczyn przyczepności warstw pośrednich i powłoki zewnętrznej, naniesionych przez natryskiwanie detonacyjno-gazowe DGS. Analizę struktury przeprowadzono na podstawie badań metodą skaningowej (SEM) i transmisyjnej mikroskopii (TEM) elektronowej oraz analizy składu chemicznego w mikroobszarach (EDS). Stwierdzono wystąpienie ziaren krzemionki na granicy podłoża z warstwą Ni(Al), obecności ziaren tlenku glinu na granicy i wewnątrz warstw Ni(Al) oraz fazy na bazie glinu AlNiOx i kryształów kolumnowych na granicy powłoki faz typu Fe-Al oraz warstwy Cr(Ni) chromu do niej przylegającej. Wyniki badań mikrostruktury dyskutowano w odniesieniu do rezultatów wcześniejszych pomiarów wytrzymałości na zginanie w aspekcie pękania powłoki oraz delaminacji podwarstwy od podłoża. Porównano je także do stanu granicy powłoki z podłożem stalowym dokonanych w poprzednich pracach. Jest prawdopodobne, iż granice podłoża pozbawione wtrąceń krzemionki oraz zapobieżenie tworzeniu tlenków glinu na granicy warstw pośrednich i podłoża powinno poprawić przyczepność całej multiwarstwy i powłoki

Research into the application of explosive welding of metal sheets with Hadfield’s steel (Mangalloy)

Celem pracy było otrzymanie zgrzewanych wybuchowo blach stalowych 22G2A i 15HM z odpornym na ścieranie staliwem Hadfielda za pomocą amonowo-saletrzanych materiałów wybuchowych. Analizowano właściwości strukturalne oraz stopień umocnienia utworzonego złącza, określając jednocześnie odporność na zużycie erozyjne staliwa Hadfielda w stanie po zgrzaniu wybuchowym, w porównaniu do stali 65G stosowanej na elementy koła bijakowego w kotłach pyłowych.The purpose of this work was to weld steel sheets with sheets made of Hadfield steel (mangalloy) using industrial explosives. The degree of strengthening of the Hadfield steel layer and the structure of the bond between the welded steels, was examined. The results of erosive wear testing between steel 65G (used in hammer mills) and welded Hadfield steel has been compared

Functional and Fractal Properties of Fe-Al Coatings After Gas Detonation Spraying (GDS)

The paper presents the results and provides an analyse of the geometric structure of Fe-Al protective coatings, gas-treated under specified GDS conditions. The analysis of the surface topography was conducted on the basis of the results obtained from the SEM data. Topographic images were converted to three-dimensional maps, scaling the registered amplitude coordinates of specific gray levels to the relative range of 0÷1. This allowed us to assess the degree of surface development by determining the fractal dimension. At the same time, the generated three-dimensional spectra of the autocorrelation function enabled the researchers to determine the autocorrelation length (Sal) and the degree of anisotropy (Str) of the surfaces, in accordance with ISO 25178. Furthermore, the reconstructed three-dimensional images of the topography allowed us to evaluate the functional properties of the studied surfaces based on the Abbott-Firestone curve (A-F), also known as the bearing area curve. The ordinate describing the height of the profile was replaced by the percentage of surface amplitude in this method, so in effect the shares of the height of the three-dimensional topographic map profiles of various load-bearing properties were determined. In this way, both the relative height of peaks, core and recesses as well as their percentages were subsequently established