The role of nitrogen in the intergranular glass phase of Si3N4 on high temperature applications and wear

Silva, Rui; Moreira, Ana; Gomes, João; Miranda, A. S.; Vieira, J.M.

doi:10.1016/0921-5093(93)90270-o

Cited by 7 publications

(2 citation statements)

References 23 publications

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“…This high value was attributed to a mixed control for the reaction, the ceramic decomposition and the diffusion in the metal. The values found in the present work are higher than the activation energy for Si diffusion in α-Fe (240kJmol -1 ) [22], but closer to 400kJmol -1 , a value reported for the Si 3 N 4 densification kinetics [24] and for the Si-N bond energy [25]. This is a first indication that the ceramic decomposition, dissolution and diffusion in the intergranular glassy phase are among the slowest steps of the overall reaction kinetics.…”

Section: Resultsmentioning

confidence: 54%

Interacción químico entre nitruros de silicio y aleaciones de acero

Oliveira¹,

Silva²,

Vieira³

2000

Bol. Soc. Esp. Ceram. Vidr.

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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

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Section: Resultsmentioning

confidence: 54%

Interacción químico entre nitruros de silicio y aleaciones de acero

Oliveira¹,

Silva²,

Vieira³

2000

Bol. Soc. Esp. Ceram. Vidr.

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“…V L values were calculated from the amount and composition of the sintering aids, using the density of glasses of similar composition. 28 Hardness (H) was measured using a Vickers indenter with a load of 9.8 N and taking the average from 20 indentations for each sample. Fracture toughness (K Ic ) was determined from crack lengths at indentation corners, according to Niihara's equation.…”

Section: Experiments and Materialsmentioning

confidence: 99%

Tribooxidational Effects on Friction and Wear Behavior of Silicon Nitride/Tool Steel and Silicon Nitride/Gray Cast Iron Contacts

Gomes

Miranda

Silva

et al. 1999

Journal of the American Ceramic Society

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Unlubricated pin‐on‐disk wear tests of Si3N4 against tool steel and gray cast iron were performed at 5 N of normal load, 0.5 m/s of sliding speed, and environmental temperature in the range 22°‐600°C. The friction coefficient of Si3N4 sliding against tool steel and gray cast iron had maximum values of 0.88‐0.98 for tests at 100°C. The friction coefficient of Si3N4 sliding against gray cast iron couples had minimum values of 0.48‐0.57 at 400°C. Because of the increased third‐body protection, the wear coefficient of the Si3N4 pins of the Si3N4/gray cast iron couples decreased by 1 order of magnitude from 1.6 10‐5 mm3/(Nm) at room temperature to 1.3 10‐6 mm3/(Nm) at 600°C. Fe2O3 and Fe3O4 resulting from tribooxidation of the metallic disks were the main constituents of the wear debris and adherent tribolayers. Activation energy values (6.3‐13.7 kJ/mol) were comparable to those of oxidation wear of steel (7.3‐11.8 kJ/mol) but were much lower than the activation energy for oxidation of iron alloys in static conditions. Calculations of the activation energy of the oxidation wear corroborate the morphological observations of a sacrificial action of the metallic surface protecting the ceramic material.

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Hot hardness of Si3N4-based materials

Silva

Vieira

1995

JOURNAL OF MATERIALS SCIENCE

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The role of nitrogen in the intergranular glass phase of Si3N4 on high temperature applications and wear

Cited by 7 publications

References 23 publications

Interacción químico entre nitruros de silicio y aleaciones de acero

Interacción químico entre nitruros de silicio y aleaciones de acero

Tribooxidational Effects on Friction and Wear Behavior of Silicon Nitride/Tool Steel and Silicon Nitride/Gray Cast Iron Contacts

Hot hardness of Si3N4-based materials

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