The reaction rate is thought to be determined by solid-state diffusion through the reaction layer. The activation energy was estimated to be 217kJ/mol under an argon atmosphere. The rate is thought to be determined by the combination of gas-phase diffusion through interparticle pores and chemical reaction.(5) On producing iron silicides, the reaction kinetics could be described by a parabolic rate law. At 1373K and above, an activation energy of 106kJ/mol was obtained under both atmospheres. The reaction rate is thought to be controlled by a chemical process.
Below 1373K, the activation energies were 626kJ/mol under a nitrogen atmosphere and 477kJ/mol under argon atmosphere. The following results were obtained:(1) An Fe-Si solid solution was produced at low temperatures, which with an increase in temperature changed to iron silicides in the following order of occurrence: Fe3Si, Fe5Si3 and FeSi.(2) As the reaction proceeded, the lattice constant of the bcc crystal structure successively decreased throughout α-Fe, the Fe-Si solid solution and Fe3Si.(3) The incubation period was long at low temperatures, but shortened markedly with increasing temperature.(4) The initial stage followed a linear rate of reaction. The products and kinetics of the reaction between Si3N4 and iron were studied at 1173 to 1573K under both nitrogen and argon. It was concluded that the measured shoulder temperatures ranging from 680 to 800☌ were effective for SiAlON tools to be used for FSW of SPFC980. The most likely mechanism of the tool wear was elimination of grain clusters due to softening of glass phases contained in the SiAlON tool at high temperatures. On the other hand, the wear progress was hardly observed in the case when the average measured shoulder temperature was less than 700☌. The wear of the shoulder progressed rapidly with increasing travel distance when the measured shoulder temperature reached more than 1080☌. The durability of SiAlON tools was strongly influenced by the measured shoulder temperatures.
Sound joint conditions were found when temperature measured at the shoulder part of the tool ranged from 686 to 1080☌.
FSW tests were done under various tool rotation speed (VR) and traveling one (VT) to search appropriate FSW conditions. Characteristics of SPFC980 work-pieces after FSW tests and durability of the SiAlON tools were evaluated. La incorporación de HfN, BN y TiN no mejoran la resistencia química de la matriz al ataque por Fe.įriction stir welding (FSW) of high tensile strength steel plate formed by cold-rolling (SPFC980) was conducted by using SiAlON tools. El reforzamiento del Si3N4 con plaquetas de Al2O3 aumenta la resistencia química del Si3N4 debido a la inercia de este oxido y a la cristalización parcial de la fase intergranular. 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. 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. 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. El Si3N4 se descompone en Si y N que se disuelven y difunden en el metal.
Las secciones transversales de los pares de difusión se analizaron mediante microscopía óptica, SEM y microsonda electrónica. En este trabajo se investigó la cinética de reacción en pares de difusión aleaciones de Fe/Si3N4 a temperaturas entre 1050✬-1250✬, tiempos entre 0.5h a 80h, en atmósfera inerte. Los 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.
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