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COBEM 2021
26th International Congress of Mechanical Engineering
PROCESSING NIOBIUM SILICIDES COATINGS MODIFIED WITH COPPER
Submission Author:
Beatriz Aparecida Pinto , PR
Co-Authors:
Beatriz Aparecida Pinto, Ana Sofia D'Oliveira
Presenter: Beatriz Aparecida Pinto
doi://10.26678/ABCM.COBEM2021.COB2021-2149
Abstract
Advancements in aeronautical and aerospace industry impose the need for materials that operate effectively in aggressive environments under high temperatures. Niobium is an attractive option for these applications due to an interesting set of properties, such as density similar to nickel superalloys, creep resistance and high melting point. However, the low resistance to oxidation of niobium makes it necessary to apply a protective coating. Silicide coatings exhibit promising results regarding the protection of niobium against oxidation at high temperatures. The attractive behavior is associated with the coating layered structure, of NbSi2 and Nb5Si3 , that act to maintain structural integrity of coatings and to provide Si to form a protective oxide layer (SiO2) under high temperatures. The formation of double silicide layers diffusion coatings high processing temperatures, above 1200 °C, increase the cost of processing making the system more complex to control. An alternative approach to the processing of silicide coatings at lower temperatures would involve the addition of alloying elements in the system that would assist the synthesis of silicides. Extrapolating reports on the effect of Cu, this work analyzes silicide coatings modified with Cu, processed under two different procedures. One of the processing routes, involves the electrodeposition of a copper layer on the niobium substrate before the pack cementation of Si, at 1000 °C for 6 hours. The other approach tested added copper to the Si pack mixture powder and for pack cementation used similar processing parameters. The silicide coatings modified with copper processed with both routes are analyzed through confocal microscopy and microhardness tests, and compared to coatings without copper. Coatings processed with the electrodeposited Cu exhibited a thickness almost tripled of that measured on the non-copper coatings, containing layers with NbSi2, Nb5Si3 and Nb5Cu4Si4. In contrast, coatings processed by the codeposition of Si and Cu were thinner than the non-copper, exhibiting a NbSi2 layer and a Nb5Si3 layer at the interface with the Nb substrate. The microhardness of the coatings shows that the Cu induced a reduction on the hardness of the NbSi2 layer that increases with increasing Cu availability in the system.
Keywords
Silicides, niobium, Copper, High temperatures, Diffusion coatings
