Characterization of the thermo-mechanical behaviour of smart composites

Composites Science and Technology, 2006

The present work deals with the development of anisotropic damage in alumina/alumina continuous fiber ceramic composites (CFCCs). The composites were isothermally exposed to a corrosive/high temperature environment at 1100°C, which simulates the working conditions of a gas turbine. Stiffness matrix components and strength were experimentally defined as a function of exposure duration by means of ultrasonic stiffness measurements and quasi-static tensile tests.

Journal of Synchrotron Radiation, 2022

A high-temperature multi-axial test is carried out to characterize the thermo-mechanical behaviour of a 3D-woven SiC/SiC composite aeronautical part under loads representative of operating conditions. The sample is L-shaped and cut out from the part. It is subjected to severe thermal gradients and a superimposed mechanical load that progressively increases up to the first damage. The sample shape and its associated microstructure, the heterogeneity of the stress field and the limited accessibility to regions susceptible to damage require non-contact imaging modalities. An in situ experiment, conducted with a dedicated testing machine at the SOLEIL synchrotron facility, provides the sample microstructure from computed micro-tomographic imaging and thermal loads from infrared thermography. Experimental constraints lead to non-ideal acquisition conditions for both measurement modalities. This article details the procedure of correcting artefacts to use the volumes for quantitative expl...

Ceramics International, 2020

Titanium carbide (TiC) composites containing 10 vol% silicon carbide whisker (SiC w) were spark plasma sintered at different temperatures of 1800, 1900, and 2000°C under a pressure of 40 MPa and a holding time of 7 min. At the sintering temperature of 1900°C, the relative density, Vickers hardness, and flexural strength of the sintered samples hit their maximum values of 98.7%, 24.4 GPa, and 511 MPa, respectively. The microstructural characteristics of the sintered samples were assessed by optical and field emission scanning electron microscopy (FESEM) and XRD. The results revealed that at 1900°C, the dispersion of SiC w in the TiC matrix was homogenous, no chemical reaction took place between the reinforcement and the matrix, and produced a fine-grained microstructure. It was found that the thermal conductivity of SPSed samples did not have the same trend with relative density and mechanical properties. A maximum value of 32.3 W/mK was measured for the thermal conductivity of the composite sintered at 2000°C.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011

Dense SiC-TiB 2 composites with 24 vol% TiB 2 were fabricated by pressureless sintering at 1940 • C. Al 2 O 3 and Y 2 O 3 were used as sintering additives to create a liquid phase and promote densification. TiB 2 was formed by an in situ reaction between TiO 2 , B 4 C and C. The sintered samples were subsequently heattreated at temperatures ranging from 1850 • C to 2000 • C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC-TiB 2 composite was presented. Heat treatment at 1970 • C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of ␣-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 • C led to a deterioration of mechanical properties.

Open Chemistry

The scope of this study, that is, the effect of the elastic modulus obtained by ultrasonic method on the physical and mechanical properties of tungsten carbide (WC)-based ceramic–metal composites, which have Ni and Co metallic binder composition produced by powder metallurgy and represented by high strength and hardness criteria, was investigated. In order to obtain composite samples in the study, it was sintered in a microwave furnace at different temperatures to combine the powder particles prepared at the rate of 60% Ni, 20% Co, and 20% WC by weight. Then, the velocities and longitudinal attenuation values of longitudinal and shear ultrasonic waves along the composite sample were measured using the ultrasonic pulse-echo method. The elastic modulus of the composites was determined using ultrasonic velocities and sample density. Hardness testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses were also performed. The results show that the elastic modulus i...

European Journal of Science and Technology

In this study, an experimental study was carried out to examine the variation of some ultrasonic parameters such as wave attenuation coefficients on metal matrix SiC doped composite samples. Ultrasonic longitudinal and shear attenuation values of produced coppersilicon carbide composite samples were measured at 4 MHz frequency by pulse-echo technique. Variations of longitudinal and shear attenuation values and hardness with % SiC volume percentages were determined. The experimental results obtained are discussed and analyzed to improve the ultrasonic nondestructive testing method for microstructure determination

Journal of Materials Science Letters, 1998

Ceramics International, 2018

SiC-TiC composite containing 5-30 vol% TiC particles was fabricated by conversion of TiO 2 to TiC during pressureless sintering. The presence of very fine and uniformly distributed, in-situ created TiC particles increased driving force for sintering allowing fabrication of high density SiC-TiC composite without the use of external pressure. The highest mechanical properties were measured in samples sintered at 1885 o C for 1 h. The highest values for hardness (~20 GPa) and fracture strength (~490 MPa) were measured in samples containing 5 vol% TiC, whereas the highest fracture toughness (~5.5 MPa•m 1/2) was measured in samples containing 10 vol% TiC. The presence of in-situ created, uniformly distributed TiC particles was beneficial for activation of not only the crack deflection mechanism but also mechanism called toughening by residual stress crated due to the difference of thermal expansion between SiC matrix and TiC particles. The 2 compressive stress field around TiC particles acts to close the propagating crack and thus to increase fracture toughness.

Composites Part A: Applied Science and Manufacturing, 2014

The acoustic emission (AE)-based technique is considered to be a promising way to real-time monitoring of microstructural changes and damage evolution in Ceramic Matrix Composites (CMCs). The present paper proposes a testing protocol that combines acousto-ultrasonics (AU) and acoustic emission (AE) monitoring, with a view to obtain both global and local definite characteristics on damage modes and kinetics. It is developed and assessed on SiC/SiC minicomposites, which are appropriate test specimens to establish sound relations between mechanical behavior and damage modes. AU wave velocity measurements provide a global measure of matrix cracking damage and the relations between crack growth and damage characteristics. AE monitoring allows accurate localization of AE sources taking into account wave velocity dependence to damage as well as differentiation of the damage modes, which control the mechanical behavior. Finally, multivariate analysis of AE data allowed classification of signals into clusters, which were successfully associated to the various damage modes.

Materials Science and Engineering: A, 2001

Microyield phenomena during thermocycling of Al 7075 alloy/15 vol.% SiC metal-matrix composite due to mismatch of the thermal expansion coefficients of the matrix and the SiC particles are studied over the temperature range from 50 to 300 K by means of internal friction techniques. The transient component of the internal friction is measured in the infrasonic frequency range, whereas the structural strain amplitude-independent and strain amplitude-dependent internal friction is investigated at ultrasonic frequencies. Combining the two techniques enables us to follow the variation of the defect structure during thermocycling as well as to evaluate basic contributions to the microyield phenomenon. The following conclusions are drawn: (1) thermal stresses are responsible for creation of fresh, i.e. mobile dislocations, whose density does not differ significantly, for the same temperature, during heating and cooling or in consecutive thermocycles; (2) yielding is much more pronounced during the first cooling from a stress-free state than in the consecutive thermocycles; this pronounced yielding is due to long-range motion of approximately the same amount of fresh dislocations as in consecutive thermocycles; and (3) during thermocycling, the matrix undergoes dynamic strain ageing; its intensity depends strongly on temperature and therefore varies continuously in a thermocycle.