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In this paper, oxidation behavior of 9-12% Cr steels P91 and HCM12A is studied in air and in a mixture of air and water vapor. Comparison is made between these steels in uncoated condition and coated with aluminum diffusion coating by a slurry method. Oxidation tests were carried out at 550, 600, and 650 degree C for a discontinued duration of 1000 h; every 250 h the specimens were slowly cooled to room temperature and weighed. SEM + EDS and XRD characterization were performed after 500 and 1000 h. The results showed that oxidation rate of uncoated P91 and HCM12A was significantly higher in the mixture of air and water vapor than in air. Oxidation resistance of the studied materials improved substantially when they were aluminized.

This study compares the effect of very fast induction heating for two competitive and cost effective aluminizing process, namely, hot dip aluminizing (HDA) and slurry aluminizing (SA) of Inconel 718 superalloy. Each process produced well adhered coating layers, which comprise two or more layers. Morphological, structural and chemical characterizations of each layer were extensively studied, and formation mechanisms of the coatings were discussed in comparison to each other. The HDA process performed in a molten Al-11 wt. Si bath at 700 °C formed a 120 μm coating layer, mostly comprising of NiAl3. The induction heating for 20 s at 1000 °C increased the coating thickness more than two times (250 μm), transformed the aluminides to Ni2Al3, made the elemental distribution more uniform within the coatings, and also formed CrSi2 precipitates, which might be beneficial for an improved oxidation resistance. In the SA process, the induction heating forms a coating of 43 μm in thickness, which is more uniform than the HDA coatings, and also comprises of two layers having Ni2Al3 and NiAl type aluminides. EBSD examination revealed that the SA coating has a uniform grain size and random grain orientation, which are promising for improved oxidation resistance. Evaluation of the results in comparison to each other provided a better understanding of the effect of induction heating on different aluminizing processes. For example, a coating uniformity similar to that of the SA coating can be achieved only after the application of the induction heating in the HDA coatings. Also, the SA process assisted with the induction heating can be applied to various substrates without subjected them to a high temperature for a long time, and would be a promising method for partial and complete aluminizing of Ni-based substrates.

The surface of austenitic stainless steel (304 SS) was modified with aluminium and alumina powders using a slurry aluminizing route to enhance its lifespan at high temperatures. The substrate was subjected to low heat treatment temperature (680°C) at various aluminizing times (4, 6, 8, and 10 hours). The corrosion resistance of the aluminide coating was evaluated by exposing them to a mixture of molten solar salt containing 60 wt.% NaNO 3 and 40 wt.% KNO 3 at 600°C for 100 hours. The coatings were characterized using FESEM, EDX, and XRD. Coating thickness, hardness, multi-layered phases, and corrosion products were determined before and after corrosion. The results indicated that a dense and continuous inner layer made up of FeAl-based intermetallic improved the corrosion resistance of 304SS. Coating thickness increased with increasing aluminizing time, with a maximum thickness of 75.12 µm observed for samples with 10 hours of aluminizing. The highest coating hardness of 1060 HV was observed on Fe 2 Al 5 of aluminide layer heat treated at 10 hours. The corrosion product found on the aluminide layer was NaAlO 2 and the sample heat treated for 6 hours exhibited the lowest corrosion rate of 0.21 mm/year.

This study systematically investigates the effect of surface aluminizing treatment on the microstructure of Fe-20Cr-5B-3Al alloy and its corrosion behavior in liquid zinc. Aluminizing treatment was performed using the powder pack method with NH4Cl (5 wt.%) as a catalyst. Aluminide layers were prepared on the surface of the Fe-20Cr-5B-3Al alloy, and the microstructure of the aluminide layer was observed and analyzed. The corrosion performance of the alloy in liquid zinc was compared before and after aluminizing treatment in a 128 h corrosion test. The results show that after aluminizing treatment, the α-Fe phase on the alloy surface transforms into the Fe2Al5 phase, while the original Fe2B phase breaks into finer structures that disperse over the Fe2Al5 phase. The Cr2B phase is not affected and maintains its structural integrity. After 128 h of exposure to liquid zinc, although the alloy exhibited good corrosion resistance in liquid zinc, the α-Fe phase was still preferentially corroded, with zinc liquid infiltrating along the α-Fe phase toward the interior. In contrast, after aluminizing treatment, the transformation of α-Fe into Fe2Al5, which has excellent corrosion resistance, significantly reduces the corrosion rate and enhances the alloy’s resistance to liquid zinc corrosion.

This study experimentally investigates the effect of RDX particle size and crystal quality, as well as aluminum particle size and content on the critical diameter of aluminized DNAN/RDX melt-cast explosive using the continuous wire method. Ultimately, the critical diameter increases when the particle size of both RDX and aluminum, as well as RDX crystal quality increases. Contrastingly, the critical diameter decreases when the aluminum content increases. Besides, we employed the Ignition and Growth reaction flow model to simulate the effect of RDX particle size and crystal quality, as well as aluminum particle size and content on the critical diameter.

In this work, the oxidation behavior of an aluminide coating at 900, 1000, and 1100 °C was investigated. The aluminide coating was prepared on a cobalt-based superalloy using a vapor phase aluminizing process, which is composed of a β-(Co,Ni)Al phase outer layer and a Cr-rich phase diffusion layer. The experimental results showed that the oxidation of the coating at 900–1100 °C all obey the parabolic law. The oxidation rate constants of the coating were between 2.19 × 10−7 and 47.56 × 10−7 mg2·cm−4·s−1. The coating produced metastable θ-Al2O3 at 900 °C and stable α-Al2O3 at 1000 and 1100 °C. As the oxidation temperature increases, the formation of Al2O3 is promoted, consuming large amount of Al in the coating, resulting in the transformation from β-(Co,Ni)Al phase to α-(Co,Ni,Cr) phase. And the decrease in the β phase in the coating led to the dissolution of the diffusion layer.

This paper addressed the issues of both direct and indirect synthesis of Ni aluminides by pack cementation (pure Ni and IN 718 superalloy). On the Al-Ni diffusion twosome under pressure, at temperatures below and above the Al melting temperature, the appearance and evolution of diffusion porosity because of the Kirkendall–Frenkel effect manifestation was highlighted. It has been confirmed that, as the temperature rises above the Al melting temperature, the porosity decreases. Nickel-based superalloys, and in particular IN 718, significantly increase their performance by increasing the aluminides proportion in the top diffusion coating. This is made possible by changing the value of the Al and Ni weight percentage ratio in this area (noted as Al/Ni). In the case of the diffusion twosome between IN 718 and pack aluminizing mixtures, having in their composition as active components Al powder, Ferroaluminum (FeAl40) or mixtures of Al and Fe powders, at processing temperatures above the Al melting temperature, by modifying the active component of the mixture, substantial changes in the Al/Ni values were observed, as well as in the maximum %Al in the diffusion coating and of its thickness. It was found that, when switching from Al to FeAl40 or powder mixture (Al + Fe), the Al/Ni value changes between 3.43 and 1.01, from initial subunit values. The experiments confirmed that the highest %Al in the top aluminized diffusion coating, for IN 718, was obtained if the powder mixture contained 66.34 wt.% Al.

In this research, a silicon-aluminizing diffusion coating constituted of homogenous Ti(Al, Si) 3 phase was prepared on γ -TiAl alloy using cold spraying Al-40Si (wt.%) alloy coating followed by thermal diffusion treatment. The oxidation behavior of the diffusion coating was tested for 300 h at high temperatures of 900, 950 and 1000 °C. The differences in microstructure evolution at three different temperatures, as well as antioxidant properties of the coating, were investigated. The results showed that the weight gain of the coating after 300-h oxidation at 900, 950 and 1000 °C was sharply reduced to only 1.195, 1.550 and 1.925 mg cm −2 , respectively. Although the alumina-based oxide scale formed on the coating became thicker with the increasing oxidation temperature, it had a good adherence to the coating even at 1000 °C. Thus, the coating can significantly improve the oxidation resistance of the γ -TiAl alloy at three temperatures because the generated oxide scale can act as a barrier to prevent the outward diffusion of Ti and the internal diffusion of O. The degradation rate of the coating also increased with the increasing oxidation temperature. Following 300 h of oxidation test at 1000 °C, the homogenous Ti(Al, Si) 3 phase in the coating almost entirely degraded. However, the in situ formed Ti 5 Si 3 diffusion layer maintained a good stability at 1000 °C, which can block the further invasion of O to a certain extent.

Aluminum powder particle size is a crucial parameter concerning the energy release of aluminized explosives. This study aimed to examine the effect of single aluminum powder particle size and particle size gradation on the explosive energy release characteristics of aluminized explosives in confined spaces by using a self-developed confined explosion experimental device. Aluminized explosive samples having aluminum powder particle sizes of 6, 24, and 43 μm and particle size gradation of 6/24/43 μm were tested for explosion parameters generated by an internal explosion. The results indicate that the quasistatic pressure of the measured aluminum powder samples decreased gradually with the increase of the particle size. The quasi-static pressure of the particle size gradation explosive samples was the largest, and the quasi-static pressure increased by 5.0%, 9.9%, and 12.0%, respectively, compared with a single particle size. The highest peak temperature was observed for the 6 μm particle size sample. However, the highest equilibrium temperature was obtained for the particle size gradation sample, indicating that particle size gradation promotes the reaction of aluminum powder in the afterburning stage; this helps maintain the temperature of a confined space for a certain duration and increase the energy release of the aluminized explosives.

The reaction between MoAlB MAB phase and molten ZnCl 2 salt resulted in the formation of metastable Mo 2 AlB 2 MAB phase. In our previous work, it was first discovered by us that the periodic layered structure (PLS) was formed at the solid (Cr, Fe) 2 B/molten Al interface during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe–Cr–B cast steel. The interaction between PLS form in situ, especially the Cr–Al–B MAB phase contained in the PLS, and molten ZnCl 2 salt was studied for the first time in this work. There were complex reactions between the PLS and molten ZnCl 2 . Specially, the Zn 2+ in the molten ZnCl 2 salt could partially occupy the positions of Al atoms in the Cr–Al–B MAB phase contained in the PLS through the A-site replacement reaction. The topochemical reaction was: Cr 3 AlB 4 (s) + ZnCl 2 (l) → Cr 3 (Al, Zn)B 4 (s) + Zn(l) + AlCl 3 (g). Graphical Abstract