Oxidation Resistance and Microstructure Evaluation of a Polymer Derived Ceramic (PDC) Composite Coating Applied onto Sintered Steel.

Tercius Justus,Sônia Probst,Priscila Gonçalves,Aloisio Klein,Mateus Leite,Cristiano Binder,Martin Seifert,Günter Motz

doi:10.3390/ma12060914

Tercius Justus, Sônia Probst + Show 6 more

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https://doi.org/10.3390/ma12060914

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Abstract

Powder metallurgy is a competitive technology to produce ferrous near net shape parts for diverse engineering applications. However, their inherent porosity increases the susceptibility to oxidation and sealing their surface is mandatory to avoid premature degradation. Alongside, polymer derived ceramics (PDCs), such as silicon-carbonitride, have drawn attention concerning their high temperature and chemical stability. However, PDCs undergo volume shrinkage during ceramization that leads to defect formation. The shrinkage can be compensated by the addition of fillers, which are also capable of tailoring the ceramic resulting properties. This work evaluates the processing of PDC-based coatings loaded with ZrO2 and glass fillers to compensate for the shrinkage, densify the coating and seal the sintered steel surface. Therefore, polymeric slurries were sprayed onto sintered steel substrates, which were pyrolyzed at different temperatures for microstructural and oxidation resistance evaluation. Microstructural modifications caused by the enhanced glass viscous flow during pyrolysis at 800 °C resulted in more homogeneous, dense and protective coatings, which reduced the mass gain up to 40 wt% after 100 h of oxidation at 450 °C in air in comparison to the uncoated substrate. Moreover, no macrocracks or spallation were detected, confirming the feasibility of PDC composite barrier coatings for sintered steels.

Highlights

Increasing the lifetime of materials by improving specific and functional surface properties have fomented a millionaire growing market of engineered surfaces, due to the economic losses induced by deterioration of metallic parts [1], as reported by the latest National Association of Corrosion Engineers (NACE) international study on the global cost of corrosion [2]
Lourenço et al reported that the surface porosity of steels sintered in conventional furnaces can range from 17% to 23%, depending on the sintering temperature [35], which is significantly higher than the 10.6% of porosity measured for the sintered steel sample volume
The results suggest that the rates move towards similar values from 20 h on, it is possible to notice a separation of the curves in Figure 8a, while the mass gain of the uncoated steel further increases with time, that of the coated samples tend to stabilize

Summary

Introduction

Increasing the lifetime of materials by improving specific and functional surface properties have fomented a millionaire growing market of engineered surfaces, due to the economic losses induced by deterioration of metallic parts [1], as reported by the latest National Association of Corrosion Engineers (NACE) international study on the global cost of corrosion [2]. The powder metallurgy industry meets the requirements from orthodontic, household appliances, hand tools to the automotive sector, which is responsible for almost 70% of the market [3,4,5,6]. This processing technology allows for microstructural and chemical composition control, besides economic benefits, especially in the case of high-volume production of small and complex geometries near net shape parts. The common methods for pore sealing of sintered metallic parts range from steam treatments, impregnation with hydrophobic compounds and infiltration with low melting point alloys as well as mechanical methods, e.g., shot pinning processes. After pore sealing, the sintered metal part is usually coated to further enhance the corrosion resistance by methods as painting, electroplating, electroless deposition, hot-, dip- and spray-coating methods [5,10,11,12,13]

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