Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
Processing and characterization of Si based diffusion coatings on metallic Nb
Submission Author:
Ana Sofia D'Oliveira , PR
Co-Authors:
Mariane Thomé, Ana Sofia D'Oliveira
Presenter: Mariane Thomé
doi://10.26678/ABCM.COBEM2017.COB17-1807
Abstract
Refractory metals, such has Nb based alloys have been referred to as the next generation high temperature metals. These alloys have an attractive combination of mechanical properties and a high melting point. However, the application of these alloys is restrained by their reduced oxidation resistance associated with the non-protective nature of Nb2O5. This study addressed this issue, using Si diffusion coatings processed by pack cementation to protect metallic Nb plates. Si diffusion coatings have been reported to have a positive impact on the oxidation resistance at elevated temperatures. The impact of pack composition and temperature on the characteristics of diffusion coatings on metallic Nb plates were evaluated. In the pack procedures with a processing time of 6 hours and pack activator 5 wt.%Nh4Cl were used. Pack composition analyzed processing samples at 1000°C using 10 wt.%Si and 30 wt.%Si. The effect of processing temperature was assessed using this same processing parameters of pack composition at 1150°C. Subsequently, as-processed surfaces were characterized regarding the structure of coatings including chemical composition profile and microstructure of expected intermetallic layers. Results showed that an increase in the silicon content in the pack mixture produced coatings composed of a silicide layer NbSi2. At the higher processing temperature tested, 1150°C, thicker coatings associated with the presence of NbSi2 and a richer silicon phase Nb5Si3 were obtained. However, pack mixture conatining 10 wt.%Si failed to process silicides coatings regardless of the processing temperature used. This worked showed that the processing parameters used strongly influenced the reservoir of Si in coatings, associated with the layered coating structure and silicides phases present, therefore are expected to impact the behavior of Si diffusion coatings.
Keywords
Diffusion coatings, Metallic Nb, Silicides
