Interacción químico entre nitruros de silicio y aleaciones de acero

Abstract

Metal/ceramic diffusion experiments are helpful to study bonding mechanisms or the effect of metal composition on the chemical wear of ceramic cutting tools. The reaction kinetics of Fe alloys/Si 3 N 4 ceramic diffusion couples was investigated in the temperature range 1050ºC-1250ºC, for 0.5h to 80h, under inert atmosphere. Optical microscopy, SEM and EPMA were carried out in cross sections of the reacted pairs. Si 3 N 4 decomposes into Si and N that dissolve and diffuse through the metal. Both the diffusion zone on the metal side and the reaction zone on the ceramic side obey parabolic growth laws of time, with activation energies in the range Q=310-460kJmol -1 . The amount of dissolved Si, the length of the diffusion zone and thus the reactivity of the ceramic increase as the alloy carbon content decreases. Due to Si accumulation, the α-Fe solid solution is stabilised at the reaction temperature and a steep decrease in the Si concentration is observed beyond the diffusion zone. The reinforcement of the Si 3 N 4 composites with A1 2 O 3 platelets enhances the chemical resistance of the ceramic due to the inertness of this oxide and to the partial crystallisation of the intergranular phase. Other dispersoids such as HfN, BN and TiN do not improve the chemical resistance of the matrix by iron attack. Keywords: silicon nitride, steels, diffusion couples, interface kinetics Interacción químico entre nitruros de silicio y aleaciones de aceroLos experimentos de difusión metal/cerámica permiten estudiar mecanismos de unión y analizar el efecto de la composición del metal en el desgaste químico de herramientas de corte cerámicas. En este trabajo se investigó la cinética de reacción en pares de difusión aleaciones de Fe/Si 3 N 4 a temperaturas entre 1050ºC-1250ºC, tiempos entre 0.5h a 80h, en atmósfera inerte. Las secciones transversales de los pares de difusión se analizaron mediante microscopía óptica, SEM y microsonda electró-nica. El Si 3 N 4 se descompone en Si y N que se disuelven y difunden en el metal. Tanto la zona de difusión en el metal como la zona de reacción en la cerámica obedecen una ley parabólica de crecimiento, con energías de activación de 310-460 KJ.mol-1. La cantidad de Si disuelto, el tamaño de la zona de difusión y, por lo tanto, la reactividad de la cerámica aumenta al diminuir el contenido de carbón de la aleación. Debido a la acumulación de Si, la solución sólida de a-Fe se estabiliza a la temperatura de reacción, y se observa un descenso significativo en la concentración de Si más allá de la zona de difusión. El reforzamiento del Si 3 N 4 con plaquetas de Al 2 O 3 aumenta la resistencia química del Si 3 N 4 debido a la inercia de este oxido y a la cristalización parcial de la fase intergranular. La incorporación de HfN, BN y TiN no mejoran la resistencia química de la matriz al ataque por Fe. Palabras clave: nitruro de silicio, aceros, pares de difusión, cinética de interfases

Microstructure and Hardness of Diffusion Bonded Sialon-AISI 420 Martensitic Stainless Steel

“…The nitrogen content in the nitrided steel was further increased during joining process due to diffusion of nitrogen from the sialon's decomposition. The tendency to form nitrides was increased when it met metallic nitrides formers such as Cr and Fe [14,15]. The significant volume of Cr and N in the precipitates disclosed the existence of nitrides (Cr x N y ) in these regions.…”

Suppression of Iron Silicide Formation in the Reaction Layer of Sialon – 7.5% Cr Ferritic Steel Joint

“…This might suggest that the nitrided steel had reduced the silicon diffusion into the steel. [2,3,5] have recognized that the initial contact of the materials in the diffusion bonding was at the border between the two reaction layers (refer to Fig. 1).…”

“…Ferrite (α) phase that appeared from the matrix of the layer was also observed. Other than Fe, the matrix also contains Cr and Si that are both ferrite formers [2]; therefore, the phase in the layer matrix is most probably ferrite solid solution with dissolved Cr and Si.…”

“…The silicide was not formed in the reaction layer of Si 3 N 4 joined with Fe or Fe alloy [1,2]. It was not found either in the reaction layer of sialon -steel [3].…”