In this research, Aluminizing packs containing NaF and NH4Cl activators were used for Aluminizing of pure titanium samples at 1100oC. The results showed that the layers of TiAl3, TiAl2, g-TiAl, a2-Ti3Al, and a-solid solution are formed on titanium samples in both cases. However, the weight gain and the thickness of TiAl3 layer in treated samples with NH4Cl activator are greater than those when NaF activator is used. Using a thermodynamic model showed that the partial pressures of aluminum-containing gases when NH4Cl is used are much greater and accordingly, the experimental results were justified.

In this research, Aluminizing behavior of ultrafine-grained nickel was investigated. For this purpose, nanocrystalline nickel samples with the grain size of ~25 nm were prepared via direct current electrodeposition and aluminized for different durations by pack cementation method at 500oC. The aluminide layers were examined by means of SEM, EDS and XRD techniques. According to results, short time Aluminizing resulted in the formation of a single aluminide layer whereas at long duration two distinct aluminide layers were formed. The growth kinetics of the coating was non-parabolic at short times while it obeyed the parabolic law at long duration. The parabolic growth rate constant of single phase coating formed on electrodeposited samples was about 30 im / h1/2 approximately 3 times greater than the data reported for coarse grained nickel (8.4 im / h1/2). Meanwhile, the overall growth rate constant was decreased to 11.7 im / h1/2, when double aluminide layers formed on nanocrystalline nickel.

In this study, the effect of platinum-aluminide coating parameters on surface roughness of nickel-based superalloy Rene ® 80 was evaluated. For this purpose, different thicknesses of Pt-layer (2, 4, 6 and 8µ m) were plated on the Samples. Then diffusion aluminide coating in two types, high tempeature-low activity and low temperature-high activity was performed. The results of structural investigations by scanning electron microscope and X-Ray diffraction indicated a three-zone structure of coating in all thicknesses of platinum layer, as well as in the two methods of Aluminizing. Surface roughness of coatings was measured in three steps: 1-after Pt plating, 2-after Pt diffusion, and 3-after Aluminizing and final aging. The results showed that the thickness of Pt and the final thickness of the coating directly affected the surface roughness. The minimum surface roughness was created by high temperature low activity with 2µ of Pt-layer (2. 6μ m) and the maximum of surface roughness was obtained in low-temperature high activity with 8µ of the Pt-layer (8. 8 μ m).

In this research a reducing slag (NaCl-KCl-Na3A1F6-AlF6) was used for surface preparation of AISH010 steel, effect of immersion time on alloy layer thickness, layer phases and durability against corrosion at 800 °C, 30 hours investigated. The results of study show that: by making use of Na3AlF6 slag the preparation of surfaces of samples is possible, the growing up alloyed layer until 15 seconds in a melted Al is noticeable, but after 15 seconds the process is so slow. The phases of the layer before heat treatment are Fe2Al5, FeAl3 and Fe Al but after heat treatment these phases replaced by FeAl and #aFe. The results of the corrosion tests show that: the weight reduction of aluminized samples is very low in comparison to non-aluminized samples. On the other hand, the stable phase at the above condition is #aFe.

In this research, effects of changes in Aluminizing conditions on microstructure of Pt - aluminide coating applied oil a Ni - base superalloy GTD -111, has been studied. A thin layer (i.e.68,#mm ) of Pt was electroplated onto the surface of the .samples, and then they were aluminized by pack cementation technique under various conditions of time, temperature, rate of heating and pack powder compositions In addition, by application of a thin Ni layer on the substrate before applying Pt, the source of nickel available for diffusing into Pt layer during Aluminizing process enhanced and the need for an extra heat treatment cycle before Aluminizing process was practically omitted. Addition of a nickel layer, also prevented scaling of Pt layer during its electroplating and Aluminizing processes that helps enhancement of cohesiveness of the coated layers. The general microstructure of the coating consisted of four layers, which are PtA12layer internal diffusion layer; external diffusion layer and interdiffusion zone. The structure of each layer has been studied by optical and scanning electron microscopes as well as XRD technique. The results show the presence of the original Pt - electroplated layer had no effect on the thicknesses of the coating layers, but higher Aluminizing time and temperature had increased the thicknesses of interdiffusion and internally diffused layers. In addition, at high temperature, Aluminizing with a lower heating rate caused an increase in the thickness of internal diffusion layer. Aluminizing with a lower heating rate at high temperature (more than 900°C) had increased the thickness of interdiffusion laver Attempt has been made to justify , the changes occurred in microstructures and thick nesses of various coating layers as they exposed to different Aluminizing conditions.

In this study, the effects of molten Al temperature and immersion time of steel samples on the joining of Al and steel and the formation and growth of intermetallic compounds, at the interface, were examined. Following surface pretreatment, steel rods were immersed into the pure aluminum melt (in an Alumina crucible) at temperatures of 680, 720, 760 and 800 Celsius and kept for different times of 5, 10, 15 and 20 minutes, at each temperature followed by air cooling after being taken out of the melt. (Then were taken out and cooled in airwhere. ) Afterwards, the microstructure of interface between steel substrate and aluminium was examined by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Vickers hardness tests. The results showed that the main (two) intermetallic compounds formed at the Al/ steel interface are FeAl3 and Fe2Al5 (were observed in reaction interface of steel substrate and aluminium. These intermetallic compounds were FeAl3 and Fe2Al5. ) with a larger part of the intermetallic layer being the Fe2Al5 layer with a tongue-like morphology. As the temperature and time of immersion increase, only the thickness of the intermetallics changed without changing their composition. (the composition of the compounds formed is not (un) changed and only the thickness of the intermetallic layer has changed). Thus, with increasing melt temperature and immersion time, the thickness of the intermetallic layer, especially Fe2Al5 layer, increased to a maximum value and then reduction of the thickness of the intermetallic layer was observed with further increase in temperature and time.

In this paper, the creep strength of Rene 80 superalloy in both uncoated and coated states is studied experimentally. The operation temperature range of this superalloy is 760–982 °C, in order to increase its resistance to surface degradation factors such as oxidation, hot corrosion and erosion at high temperatures, a coating is applied on it and its use without coating is not recommended. In this paper, diffiosion aluminide coatings were applied to this superalloy by two separate methods of pack cemantation and slurry under the brand names of Codep B and IP1041, respectively, and the effect of these coatings on the creep life of this superalloy at 982 °C and metallography is examined by SEM was investigated. For this purpose, samples according to ASTM-E8 standard were produced and after coating along with uncoated samples were subjected to creep test according to ASTM-E139 standard. Control parameters including temperature, stress and service life of uncoated samples are evaluated according to C50TF28 standard. Uncoated creep samples lost their strength after an average of 33 hours and rupture occured. Codep-B coated samples lost their strength after on average of 45 hours and slurry-coated samples lost their strength after on average of 51 hours. The results showed that the coatings increased the creep life of the coated samples compared to the uncoated samples by at least 12 hours.

The wear and hardness properties of the protective aluminide coatings can be enhanced by reinforcing the surface, using hard materials such as diamonds. In this research, prior to the Aluminizing process by pack cementation, an intermediate Nickel-Nano diamond (Ni-ND) layer was fabricated on the surface of the Ni-based superalloy Hastelloy X with electroplating process. The electroplating of Ni-ND layer was accomplished by continuous direct current in nickel Watts electroplating bath containing 1 and 4 g/l ND particles. The coated and uncoated samples were aluminized by pack cementation method using aluminum, ammonium chloride and alumina powders. The Aluminizing process was designed as a two-step procedure at 760 ° C following the annealing process at 1080 ° C. The cross-sections of the coated specimens were studied by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis. The results showed that during Aluminizing process, the nano-diamond particles prolonged the nickel and aluminum diffusion path and as a consequence, the aluminum content of the coating layer was increased. This gave rise to the conversion of the Ni-based intermediate composite layer into an aluminum-rich NiAl layer. The hardness of the treated coating with ND particles was significantly higher than the untreated coating in a way that microhardness of the coating with no ND particles was 663 Vickers while the coating containing ND particles showed a value of about 968 Vickers.

Aluminide coatings are widely used as a protective coating material due to their high corrosion and oxidation resistance properties. In this research, an aluminide coating was fabricated through Aluminizing on UNS S30815 austenitic stainless steel using pack cementation method at 950 ° C for 5 h. The isothermal oxidation was exerted on uncoated and aluminide coated steels for 200 h at 1050 º C. Also cyclic oxidation was applied for 50 cycles at 1050 º C on coated and uncoated steels. Surface morphology and cross section of coated and oxidized samples were characterized by means of scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). X-Ray diffraction (XRD) was used to identify the formed phases in the surface layer of as-coated and oxidized specimens. As-coated UNS S30815 consisted of Al5Fe2, FeAl3 and Al2O3 phases. The results of the isothermal oxidation showed that the coated steel had lower weight gain (2. 9 mg. cm-2) after 200 h of oxidation in comparison with uncoated one (7 mg. cm-2). Also the results of cyclic oxidation showed that the coated specimens had good resistance to thermal cycles.

nickel base superalloy alloys are used in the manufacture of gas turbine engine components, which in use are exposed to high temperatures and corrosive environments. The platinum aluminide coatings described here have been developed to protect nickel base superalloy alloys from oxidation. In this study, the effect of cyclic oxidation, platinum layer thickness and Aluminizing process on behavior of Pt-Aluminide (Pt-Al) coating on nickel-based superalloy Rene® 80 have been investigated. For this purpose, after applying different thicknesses of Pt-layer (2, 6 and 8μ m), diffusion aluminide coating in two types, high temperature-low activity (HTLA) and low temperature-high activity (LTHA) methods was performed. The results of microstructural investigations by Scanning Electron Microscopy and the X-ray diffraction analysis indicated that coatings include three zones in all thicknesses of the platinum layer and in both methods of Aluminizing. The results of cyclic oxidation (1100 ° C and 120 cycles) test showed that Pt-Al in all conditions improved the oxidation resistance of Rene® 80. The best oxidation resistance is related to the specimen coated with 6 μ m Pt by LTHA method, whereas the lowest resistance was related to 2μ m Pt in the case of HTLA method. The weight changes during cyclic oxidation of 6μ m Pt (LTHA) and 2μ m Pt (HTLA) coatings were 3. 8 and 6 mg, respectively. Also, the parabolic oxidation rate constants of these coatings were calculated as 1. 5
10-12 and 3. 8
10-12, respectively. Prog. Color Colorants Coat. 13 (2020), 11-22© Institute for Color Science and Technology.