SiC coatings were prepared with pack powder in different particle sizes in a vacuum atmosphere by pack cementation technique to protect the C/SiC composites substrate from oxidation. The phase and microstructure of the coatings were investigated by XRD, SEM analyses. The relationship between powder granularity in the pack and microstructure of SiC coatings was studied. Cyclic oxidation test at 1573K in air atmosphere was performed and the effect of powder particle size in the pack on high-temperature oxidation resistance of SiC coatings was discussed in detail. It is observed that with powder granularity in the pack increasing thickness and density of SiC coatings increases, corresponding oxidation resistance of the coating is improved. Possible mechanisms related to oxidation were preliminarily discussed.

In this work, SiC coatings varying in content were prepared on carbon-fiber-reinforced silicon-carbide composite (C/SiC) substrates in order to study the effect of free silicon on oxidation resistance. The coatings were formed in a vacuum atmosphere by means of pack cementation using a powder mixture ranging in content as follows: 20-50 wt% SiC, 20-60 wt% Si, 7-12 wt% graphite, and 6-10 wt% Al 2 O 3 . Coating surface and cross-sectional morphologies were examined using SEM, EDS, and semiquantitative XRD analysis and oxidation resistance was determined by cyclic oxidation testing in air at 1300 °C. The results show that cracks and voids decrease with increasing free silicon content and that coatings with an appropriate amount of free silicon have better oxidation resistance than those with no free silicon at all. However, further increases in silicon content were found to be detrimental to oxidation behavior for a number of reasons that are discussed.

In this study, FeCr coatings with different percentages of chromium were deposited on Grade 91 steel substrates by HVOF spraying, followed by aluminum enrichment via pack cementation. Overaluminizing parameters were optimized to prevent changes in the substrate microstructure, making it possible to determine the role of Cr and the effect of Al enrichment on anticorrosion behavior. The combination of HVOF spraying and pack cementation are shown to be adequate techniques for depositing intermediate and top layers in protective coating systems.

Degradation of components that operate under elevated temperature and carburizing environments involves the diffusion of C and the precipitation of carbides. Industries have been seeking for materials that can withstand these service conditions. The present work aimed to develop coatings to address this challenge through the enrichment of a Ni based alloy with Al. An atomized Ni alloy without Al and different powder mixtures with 15 and 30wt%Al were deposited by PTA on a carbon steel. Coatings were analyzed in the as deposited condition and after temperature exposure in an air furnace and pack cementation tests at 650º and 850ºC. Vickers microhardness profiles under a 500gf load, X-ray diffraction, optical and scanning electronic microscopy were done Results revealed that the presence of Al lead to the development of a complex intermetallic phases which were associated with the enhanced metallurgical stability of the coatings under the tested temperatures. The superior performance of the coatings deposited with the powder mixture containing 30wt%Al after pack cementation was associated with the development of the NiAl intermetallic phase and of the oxide layer Al 2 O 3 that stabilized the microstructure at the tested temperatures and reduced the diffusion of C.

In order to address deficiencies in thermal spray coatings applied using air plasma spraying (APS) and high velocity oxygen fuel (HVOF), namely, adhesion, cohesion, porosity and line of sight limitations, novel hybrid coatings using post - thermal spray chemical vapor deposition via the pack cementation process were developed. Coatings based on tungsten carbide-cobalt chrome and chrome carbide-nickel chrome followed by boron or chrome diffusion were applied to multistage and single stage pump components for severe service applications in sand and alumina catalyst. Field testing established the effectiveness of using the dual coating approach.