Multistage heat treatment and the development of a protective oxide-scale layer on the surface of FeCrAl sintered-metal-fibers

Abstract

This study investigates the effects of Multistage Heat Treatment (MSHT) on the development of an oxide-scale layer on the surface of FeCrAl sintered-metal-fibers. The oxide-scale layer was developed using an MSHT cycle at 930 °C for 1 h, followed by 960 °C for 1 h, and finally at 990 °C for 2 h. In this study, three samples were considered: Sample 1 was kept without thermal oxidation, while Samples 2 and 3 were exposed to one and eighteen MSHT cycles. Thermo-gravimetric analyses show that the weight gain of the heat-treated sample slows with time, confirming the growth of the protective oxide-scale layer. Scanning electron microscope images, after one MSHT cycle, reveal nonuniform oxide-scale growth with platelet-like on the surface. After eighteen MSHT cycles, however, clumped particles formed on the surface of the fibers. Atomic force microscopy was utilized to study the surface topography of the fibers. The results show that MSHT increases the surface roughness, where the surface roughness of one and eighteen MSHT cycles are the same. The x-ray diffraction analyses of the baseline sample and the sample with one MSHT cycle show pattern peaks of crystalline Fe2CrAl. In contrast, the results of eighteen MSHT cycles displayed diffraction pattern peaks of crystalline Cr and stable α-Al2O3. In summary, the results of this study reveal the changing nature of the oxide-scale layer. The findings of this study form the foundation for new techniques to protect and prepare the FeCrAl fibers as a support for catalysts.

The Microstructure Formation of a Protective Oxide-Scale Layer on Small-Diameter FeCrAl Fibers

“…Sample 2 was subjected to one MSHT cycle, while Sample 3 was subjected to multiple MSHT cycles. The results of Ibrahim et al [ 36 ] for one MSHT cycle were similar and confirmed the results presented by Samad et al [ 17 ]. However, after multiple MSHT thermal oxidation cycles, the oxide-scale layer evolved into a different microstructure and revealed diffraction pattern peaks of a stable α-Al 2 O 3 and crystalline Cr.…”

“…Figure 2 displays the weight change versus time of the 12 and 17 μm fibers, compared with the 40 µm fibers’ TGA results obtained from Ibrahim et al [ 36 ]. The inset in Figure 2 shows the weight change versus time during the first complete MSHT cycle.…”

“…Various experimental studies have investigated the effects of rare earth elements on oxidation behavior [ 23 , 24 , 25 , 26 , 27 , 28 ]. However, the literature survey reveals few technical papers on FeCrAl fibers [ 17 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Li et al [ 31 ] and Fornasiero et al [ 32 ] investigated FeCrAl fibers as a substrate and support of catalysts.…”

“…Ibrahim et al [ 36 ] conducted a study to examine the effects of MSHT on FeCrAl sintered metal fibers 40 µm in diameter. In their research, the oxide-scale layer was developed using an MSHT cycle.…”

“…The investigation of Ibrahim et al [ 36 ] was focused on large-diameter FeCrAl fibers. Small-diameter FeCrAl fibers offer a high surface-area-to-volume ratio, making them more suitable for special applications, such as a catalyst substrate and in hot gas filtration [ 37 ].…”