Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
Silicon-titanium codeposition on niobium: properties and behavior at high temperatures
Submission Author:
Beatriz Aparecida Pinto , PR
Co-Authors:
Beatriz Aparecida Pinto, Ana Sofia D'Oliveira, Helga Holzmann
Presenter: Beatriz Aparecida Pinto
doi://10.26678/ABCM.COBEM2023.COB2023-2310
Abstract
Niobium silicide coatings have been studied for their potential application at high temperature components that require resistance to creep and oxidation. The Halide Activation Pack Cementation (HAPC) is the most used technique to process these coatings that involves the deposition and diffusion of silicon on niobium substrates through chemical reactions in the pack. The literature presents the formation of NbSi2 on the niobium substrate when these coatings are processed at 1000°C.This silicide acts as a source of silicon for the formation of a protective oxide (SiO2) when exposed to high temperatures, preventing the penetration of oxygen to the niobium. However, the difference in the thermal expansion coefficients between NbSi2 and Nb substrate makes niobium silicide coatings susceptible to cracks formation and oxidation at high temperatures. Titanium is frequently added to alloys to increase the toughness of these materials mitigating crack propagation. Therefore, this study investigated how the addition of titanium to the pack mixture impacts properties and high temperature behavior of niobium silicides coatings processed by HAPC. Coatings were processed at 1000°C for 6 hours with a pack composition of 15% Si, 10% Ti, 5% NH4Cl, and 70% Al2O3, using pure niobium as the substrate. To understand the behavior at high temperatures, coatings were exposed to a temperature scan up to 1350°C in a TGA. Coatings were also exposed to temperatures of 800°C and 1100°C for 2 hours after processing. Characterization used SEM, EDS, XDR, and microhardness tests to evaluate the properties of coatings. Results showed that Ti did not alter the formation of single phase NbSi2 coatings, with no detectable presence of titanium in the coatings composition. An analysis of the cross-section showed that the presence of Ti in the processing does not cause a significant impact on the thickness or hardness of the processed coatings. The weight gain after the scan at 1350°C show that the silicide coatings processed with titanium have much less weight gain than the silicide coatings with only silicon in the pack mixture. After exposure to isothermal temperature, coatings only exhibited the formation of SiO2, regardless of the test temperature, confirming the integrity of the coatings. The promising results related to the behavior of niobium silicide coatings processed with titanium confirm the need for further investigation in this subject.
Keywords
Silicides, niobium, High temperatures, titanium, Pack cementation
