Microstructure and Oxidation Behavior of Low Pressure Plasma Sprayed Iron Aluminides.

Abstract

Microstructure and oxidation behavior of plasma sprayed iron aluminide have been investigated focusing on the spraying conditions of atmosphere and pressure. Iron aluminide powder for spraying was prepared by ball milling of turnings fabricated from an Fe-40at%Al ingot. Microstructure of laminated layers including cavities was observed in all samples and particles with a size of about 100 mm were observed only in the sample sprayed in 50 Torr Ar atmosphere. Chemical analysis revealed an amount of aluminium loss and oxygen pick-up in samples sprayed in air, while X-ray diffraction analysis exhibited only the iron aluminide spectra without the second phase. The intensity of superlattice spectra of aluminide was strong in the samples sprayed in Ar compared with in air. Change of mass gain in oxidation testing was small in the sample sprayed in 50 Torr Ar, which is equivalent to as-cast bulk sample, while large in other samples. SEM observation revealed the evolution of iron oxides in the samples sprayed in air, which was not observed in the sample sprayed in Ar. The mechanism for superior resistance to oxidation in the sample sprayed in 50 Torr Ar is attributed to infusible particles deposition, which inherited the intrinsic oxidation resistant property of iron aluminides.

High Temperature Oxidation of Spark Plasma Sintered and Thermally Sprayed FeAl-Based Iron Aluminides

“…Refs. [6,19,22,26,27]. Unfortunately, the occurrence of dierent polytypes of Al 2 O 3 at higher temperatures or in dierent environments makes it dicult to extrapolate the results obtained at higher temperatures to the experiments performed in this work.…”

Novel Nanocrystalline Intermetallic Coatings for Metal Alloys in Coal-fired Environments

“…In this respect, the PTA technique is uniquely suitable compared to other thermal spray techniques, because the PTA torch is designed to offer a heat flux towards the substrate high enough for the substrate surface to melt. In other thermal spray coating processes, such as arc spray [21], low pressure plasma spray [22], air plasma spray [23] and high velocity oxyfuel (HVOF) spray [24][25][26][27][28], the torches are designed to operate with a "cold" (in comparison to the melting point of the substrate) substrate surface and thus no surface melting can occur. It is interesting to note that the dilution from the substrate, which is inevitable in the PTA process and usually regarded as a disadvantage in comparison with other thermal spray techniques, is a pre-requisite for an in-situ reaction coating process to be successful.…”

“…Many thermal spray coating techniques, such as arc spray [21], low pressure plasma spray [22], air plasma spray [23] and high velocity oxyfuel (HVOF) spray [24][25][26][27][28], have been explored for depositing thick aluminide coatings on various steel substrates, with aluminide powder as the feeding materials. Among the above processes, the HVOF process is most attractive because the high velocity of sprayed and melted powders in this process produces coatings with higher density and better bonding to substrates than the coatings obtained with conventional thermal spray processes.…”

“…Aluminide intermetallics coatings have been explored with various coating processes, among which two categories of processes are notable: a) reaction coating processes including conventional chemical vapor deposition (CVD) processes [14], fluidized bed reactor CVD (FBR-CVD) [15][16] process, and pack cementation process [17][18][19][20], for producing thin coatings with thicknesses typically less than 20 μm; and b) thermal spray processes for making thick coatings with thicknesses from 0.5 to >3 mm [21][22][23][24][25][26]. For many structural applications, including coalfired power generation systems, thick coatings are often necessary due to the severe environments of high-temperature corrosion and erosion and the required long service lifetime.…”

Laminates based on an iron aluminide intermetallic alloy and a CrMo steel

“…Through modification techniques such as pre-heating and post-weld heating, crack-free iron aluminide layers could be deposited and outstanding sulfidation resistance was achieved [24]. Masahashi et al [25] applied a low-pressure plasma spray technique to deposit iron aluminide on pure iron substrate. They revealed that the existence of non-melting particles in the iron aluminide layer is beneficial for oxidation resistance, because aluminium volatilization and impurity contamination is suppressed in the non-melting particle deposition.…”