Mechanical properties of mullite materials

Ramos

2007

Ceramics International

Mullite was produced from a mixture of raw wastes with high contents of silica and aluminium hydroxides. The first were wastes from slate rocks and had muscovite, chlorite and quartz as their main crystalline phases. The second were aluminium sludges resulting from the physicochemical treatment of the wastewaters generated by aluminium surface treatment industries. As-received raw materials were weighed to produce the 2:1 alumina:silica stoichiometric mixture, corresponding to an excess of alumina relatively to the ideal 3:2 mullite composition. The nonisothermal activation energies for primary (431 kJ/mol) and secondary mullite crystallization (454 kJ/mol) were determined by differential dilatometry. Sintered products were composites of mullite and a-alumina dispersed in a glassy phase and presented flexural strengths higher than 100 MPa after sintering temperatures at 1285 8C. #

Section: Sintered Products Characterizationcontrasting

confidence: 50%

Mullitization kinetics from silica- and alumina-rich wastes

Ramos

2007

Ceramics International

Bol. Soc. Esp. Ceram. Vidr.

“…M ‡s detalles sobre sus propiedades mec ‡nicas, as' como los procesos de elaboraci-n se encuentran en trabajos previos (29,39,43,45).…”

Section: Materiales Estudiadosunclassified

Determinación de la presencia de fatiga mecánica en materiales cerámicos

Casellas¹,

Nagl²,

Vélez³

et al. 1999

INTRODUCCIîN Materiales cer ‡micos avanzadosLos materiales cer ‡micos son candidatos para varias aplicaciones estructurales, puesto que presentan buena resistencia frente a la corrosi-n en medios agresivos, mantienen sus propiedades mec ‡nicas a temperaturas elevadas (superiores a los 1000 ¼C) y ofrecen una buena relaci-n resistencia/peso. En cambio, el principal problema es su fragilidad intr'nseca y la dificultad en controlar y detectar los defectos producidos durante su procesamiento. Con el fin de aumentar la tenacidad en estos materiales se han desarrollado los denominados materiales cer ‡micos avanzados o de ingenier'a. ƒstos pueden tener valores de tenacidad de fractura (K IC ) superiores a 10 MPa m 1/2 (1-4), y de esta manera aumentar sus posibilidades como materiales estructurales. Esta nueva aplicaci-n obliga a estudiar y caracterizar su comportamiento bajo los principales tipos de solicitaci-n: aplicaci-n de una carga constante o aplicaci-n de cargas fluctuantes. El primero de ellos es un fen--meno bastante bien conocido y reportado. En cambio, la aplicaci-n de cargas c'clicas abre un nuevo campo de estudio, puesto que los materiales cer ‡micos avanzados, a diferencia de los vidrios y cer ‡micas monol'ticas, presentan degradaci-n debido a las cargas fluctuantes aplicadas. El efecto de cada uno de estos casos se estudia en detalle en los siguientes apartados. Comportamiento bajo cargas constantesEn materiales cer ‡micos y en vidrios se observa que la aplicaci-n de una carga constante produce una disminuci-n de la resistencia a fractura (σ F ) en funci-n del tiempo. Este fen-meno es conocido desde hace a-os (5-8) y en la literatura cer ‡mi-ca recibe el nombre de fatiga est ‡tica. Su causa es la degradaci-n que ejerce sobre el material el agua ambiental (5-15), facilitando la propagaci-n de fisuras preexistentes. Esto se pone de manifiesto viendo la influencia que tiene el grado de humedad en la disminuci-n de σ F . As', en agua el efecto de fatiga est ‡tica es mucho m ‡s acusado que en aire y m ‡s que en nitr--geno seco o en vac 'o (8-14). Dado que muchos materiales cer ‡-micos presentan una fase v'trea intergranular procedente de los procesos de sinterizaci-n, algunos autores proponen mecanismos basados en la interacci-n de esta fase v'trea con el agua B O L E T I N D E L A S O C I E D A D E S P A Ñ O L Cerámica y Vidrio Determinación de la presencia de fatiga mecánica en materiales cerámicosLos materiales cer ‡micos son susceptibles al crecimiento de fisuras por la acci-n combinada del medio ambiente y la aplicaci-n de carga (fatiga est ‡tica). Por otra parte, el crecimiento subcr'tico de fisuras en cer ‡micas tambiŽn puede ser producido por la aplicaci-n de cargas fluctuantes (fatiga mec ‡nica). Este fen-meno no se observa en vidrios ni en cer ‡micas monocristalinas, pero si en muchos de los llamados materiales cer ‡micos avanzados. En este trabajo se describe una metodolog'a utilizada para detectar la presencia de fatiga mec ‡nica en materiales cer ‡micos, basada en la obtenci-n de estimaciones de ...

Science and Technology of Advanced Materials

“…The nonstoichiometric titanium tribo-oxide (7.3%) and rutile TiO 2 (5.5%, table 2) are also formed on the friction surface. Along with the lubricious Cr-O (table 2), protective and high-temperature lubricous Si-O phases are formed as well [17,[211][212][213][214][215][216][217][218]. The phase composition of tribo-oxides differs for monolayered and nanomultilayered coatings: a considerably higher concentration of Al 2 O 3 is formed during tribo-oxidation of the multilayered coating (table 2).…”

Section: Tribofilms (Secondary Structures)mentioning

confidence: 99%

“…That is why this coating can sustain even ultrahigh-speed [207][208][209][210][211][212][213][214][215][216], which is two times higher compared to the monolayered coating (table 2). XPS data indicates the formation of Al-Si-O bonds in Al 6 Si 2 O 13 mullite tribofilms [209][210][211][212]. The nonstoichiometric titanium tribo-oxide (7.3%) and rutile TiO 2 (5.5%, table 2) are also formed on the friction surface.…”

Section: Tribofilms (Secondary Structures)mentioning

confidence: 99%

“…This leads to formation of a nonstoichiometric titanium oxide films and rutile TiO 2 (table 2). XPS indicate formation of sapphire-like [207] triboceramics and nanofilms with a phase composition close to Al 6 Si 2 O 13 mullite [209][210][211][212][213][214]. A partial chemical transformation of aluminum in the TiAlCrSiYN monolayer coating has taken place: 28.6% of Al was retained in the complex nitride, 17.6% of aluminum oxidized with the formation of Al-Si-O oxide (mullite) and 8.8% of aluminum oxidized with the formation of trivalent Al 2 O 3 (sapphire, table 2).…”

Section: Tribofilms (Secondary Structures)mentioning

confidence: 99%

See 1 more Smart Citation

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Fox-Rabinovich

Yamamoto

Beake

et al. 2012

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating Topical Review design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.