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Carbon fibre reinforced CVI-SiC matrix (Cf/SiC) composite is well known for its superior properties such as low density, high specific modulus, high fracture toughness, and high temperature mechanical properties. In the present work, 2.5-Directional Cf/SiC composites with (PyC/SiC) n=4 multilayer interface having two different thicknesses with a density of ~2.1 g cm-3 are prepared through isobaric isothermal chemical vapour infiltration technique. High temperature tensile properties of the prepared composites with and without Si-B-C seal coating are studied and the results are presented. Samples prepared without seal coat exhibited a KICof ~ 30 MPa m1/2, and tensile strength of ≥200 MPa at room temperature. Si-B-C seal coated Cf/SiC composites has shown significant increase (28%) in high temperature tensile strength at 1200 °C and 1500 °C respectively compared to uncoated composites. Microstructural observations, XRD, and XPS studies support the observed thermomechanical behaviour of these composites at 1200 °C and 1500 °C.

Continuous carbon fiber (Cf) reinforced silicon carbide (SiC) matrix composite (Cf/SiC) was processed through hot pressing (HP) using polycarbosilane (PCS) in matrix and polysilazane in interphase regions as polymer binders. HP experiments were conducted at 4 MPa, 1200 °C and 1 h; followed by PCS polymer impregnation and pyrolysis (PIP) at 1200 °C under vacuum. The BN/SiC-Si3N4 interphase formed on the Cf cloth during BN dispersed polysilazane polymer coating and pyrolysis. The influence of PCS quantity during HP experiments on Cf/SiC composites was studied. Results suggest that sintering of SiC matrix in Cf/SiC composite improves by increasing PCS content during HP; however, high PCS content increases the liquidity of SiC-PCS mixture to flow out of the composite structure. The Cf/SiC composites with relative density ranging from 79 to 83% and flexural strength from 67 to 138 MPa was achieved.

Magnesium (Mg)-titanium aluminum carbide (Ti3AlC2) composites were produced by hot pressing (HP) at 0.15 to 1 MPa, 923 K (650 °C) for 30 minutes; Mg-Ti3AlC2 (10 to 30 vol pct) composite produced at 0.15 MPa, 923 K (650 °C) for 30 minutes exhibited 95 to 99 pct relative density (RD), while Mg-40Ti3AlC2 produced at 1 MPa, 923 K (650 °C) for 30 minutes exhibited full density. Improved densification results are mainly due to the flow of liquid Mg between the Ti3AlC2 particles. The monolithic Mg processed at 5 MPa, 873 K (600 °C) for 5 minutes also exhibited full density. Further, Mg-Ti3AlC2 composites produced at low pressure (1 MPa) exhibited maximum density as compared to other research works. Monolithic Mg exhibited a microhardness of 62 ± 8 HV0.5. Besides, as the Ti3AlC2 content was varied from 10 to 40 vol pct, the microhardness of Mg-Ti3AlC2 composites increased from 62 ± 5 to 158 ± 11 HV0.5. The compressive strength of Mg-Ti3AlC2 (10 to 40 vol pct) composite at room temperature (RT) was in the range of 180 ± 10 to 617 ± 13 MPa. The compressive strengths of Mg-Ti3AlC2 (30 and 40 vol pct) composites at 473 K (200 °C) were 366 ± 20 and 480 ± 71 MPa, respectively. The flexural strength of Mg-Ti3AlC2 composites (20 to 40 vol pct) was determined to be in the range of 335 ± 12 to 513 ± 3 MPa.

An experimental study was undertaken to understand the tensile behavior of metal–ceramic composite joint with bolted configuration. Nickel based super alloy (GTM-Su-263) and SiCf/SiC composite were the material systems with an aerospace grade MJ6 bolt of GTM-Su-718. This bolted assembly was pulled at temperatures 25, 600 and 750 °C which were likely to be experienced in a typical aero engine. In case of metal–ceramic composite joint, the net tensile stress decreased from 110 to 88 MPa with increase in temperature from 25 to 600 °C. Similarly, the bearing stress reduced from 146 to 118 MPa. In all the metal–ceramic composite joints, the fracture initiated at the hole edge experienced the maximum tensile stresses. With further increase in temperature, reduction in the net tensile and bearing strength was significant and was attributed to the oxidation of the interface between the fiber and matrix. SEM studies clearly suggested that debonding and fiber pullout resulted in inferior tensile strength properties at elevated temperatures.

SiCf/SiC composites are class of high temperature structural materials being developed for use in nuclear fusion and fission reactor systems because of their superior high temperature mechanical properties, low radiation damage and low induced radioactivity. Two types of 2D SiCf/SiC composites were made through isothermal and isobaric chemical vapor infiltration process using eight harness satin-woven ceramic-grades Nicalon� fibers with boron nitride (BN) interface, namely: one with lower interface thickness and a second type with higher interface thickness. The BN interface was applied to the fiber prior to SiC matrix addition to modify the interfacial bond strength leading to better toughness and improved oxidation resistance. The density achieved was around 2.6 g/cc. The composite specimens were subjected to thermal cycling treatment using an in-house furnace. The mechanical properties such as tensile strength, fracture toughness and interfacial bond strength were also studied for all the composites before and after thermal cycling. It is seen from the results that both composites withstood thermal shocks and thermal cycling treatment. It was also concluded from the present work that good balance between load transfer and crack arresting was established. � 2013 Elsevier B.V. All rights reserved.