44 research outputs found
Fracture behaviour of refractory ceramics after cyclic thermal shock
Two commercially available refractory ceramic materials primary used as substrates for fast firing of porcelain stoneware were investigated. The first one, commercially known as CONC, contains cordierite and mullite in the ratio 50:50. The REFO refractory composite material with coarser microstructure compared to CONC has a cordierite-to-mullite ratio of 50:45 and the balance is filled by quartz. Both materials were exposed to water-quench tests from 1250 degrees C, applying various numbers of thermal cycles (shocks). Subsequently the fracture toughness was evaluated on both as-received and shocked samples using the Chevron notched specimen technique. The results were analysed with respect to the microstructure damage caused by the thermal loading. Scanning electron microscopy was used to analyse both microstructure and fracture surfaces in samples with different thermal loading history
Homogenization of steady-state creep of porous metals using three-dimensional microstructural reconstructions
Assessment of thermal shock induced damage in silicon carbide fibre reinforced glass matrix composites
El desarrollo de daño microestructural en materiales
compuestos de matriz de vidrio reforzados con fibras de carburo
de silicio (Nicalon™) sometidos a choque térmico fiie
investigado mediante la técnica no-destructiva de resonancia
forzada y por mediciones de indentación "push-out " de fibras.
Los ensayos de choque térmico involucraron el enfriamiento
brusco en un baño de agua a temperatura ambiente de las piezas
previamente calentadas a una temperatura elevada (650 "Q. La
técnica de resonancia forzada permitió medir cambios en el
módulo de Young de elasticidad y en la fricción interna de las
muestras, ocurridos al aumentar el número de choques térmicos
como consecuencia del daño microestructural inducido. La
investigación del "push-out" défibras mostró que las
propiedades de la interfase fibra/matriz no variaron
apreciablemente bajo las condiciones de choque térmico
estudiadas. Los resultados demostraron que la única forma de
daño microestructural inducido por choque térmico en el
material compuesto fue el agrietamiento de la matriz de vidrio.
Además se observó que la fricción interna es un parámetro
altamente sensible para detectar el inicio y desarrollo de tal
agrietamiento. Se presenta un modelo semi-empÃrico simple, el
cual permite correlacionar el nivel de fricción interna medido
con la densidad de agrietamiento de la matriz de vidrio.
Finalmente, se dedica especial atención a la importancia de
detectar en forma no-destructiva la presencia de microgrietas en
¡a matriz de vidrio, en conexión con la posibilidad de inducir un
proceso de curado de tales microgrietas mediante un
tratamiento térmico, aprovechando el flujo viscoso del vidrio.The development of microstructural damage in silicon carbide
fibre (Nicalonâ„¢) reinforced glass matrix composite samples
subjected to thermal shock was investigated by using a nondestructive
forced resonance technique and fibre push out
indentation tests. Thermal shock testing involved quenching
samples in a water bath maintained at room temperature from
a high temperature (650 "Q. Changes in the Young's modulus
and internal friction of the samples with increasing number of
shocks were measured accurately by the forced resonance
technique. Fibre push-out tests showed no significant changes
in the properties of the fibre-matrix interface, indicating that
damage in the composite was concentrated mainly in the
development of matrix microcracking. It was also shown that
the internal friction is a very sensitive parameter by which to
detect the onset and development of such microcracking. A
simple semi-empirical model is proposed to correlate the
internal friction level with the microcracking density in the
glass matrix. Finally, the relevance of detecting nondestructively
the existence of microcracks in the glass matrix,
before any significant interfacial degradation occurs, is
emphasized, in conextion with the possibility of inducing a
crack healing process by a thermal treatment (annealing),
taking advantage of the viscous flow properties of the glass
Bonding characteristics of glass seal/metallic interconnect for SOFC applications: Comparative study on chemical and mechanical properties of the interface
Surface Optimization of Commercial Porous Ti Substrates by EPD of Titanium Nitride
In this work, the infiltration of TiN powders by electrophoretic deposition (EPD) in aqueous media was considered as alternative method to reduce the size craters and the roughness of commercial porous Ti substrates. Ti substrates can be used as suitable supports for the deposition of dense hydrogen separation TiNx-based membranes by physical vapor deposition (PVD) techniques. The influence of various EPD deposition parameters on surface morphology and roughness of TiN-infiltrated substrates were investigated in order to optimize their surface properties. The results suggest that a multi-step EPD procedure is an effective technique for reducing substrate surface defects of commercial porous Ti substrates which could then be successfully used as proper supports for the deposition of dense and defect-free TiNx layers, also aligning the thermal mismatch between the active layer and the porous substrate