High Temperature Mechanical Behavior of UHTC Coatings for Thermal Protection of Re-Entry Vehicles

Abstract

In this work, the high temperature mechanical properties of ultra high temperature ceramics (UHTC) coatings deposited by plasma spraying have been investigated; particularly the stress-strain relationship of ZrB(2)-based thick films has been evaluated by means of 4-point bending tests up to 1500 A degrees C in air. Results show that at each investigated temperature (500, 1000, and 1500 A degrees C) modulus of rupture (MOR) values are higher than the ones obtained at room temperature (RT); moreover at 1500 A degrees C the UHTC coatings exhibit a marked plastic behavior, maintaining a flexural strength 25% higher compared to RT tested samples. The coefficient of linear thermal expansion (CTE) has been evaluated up to 1500 A degrees C: obtained data are of primary importance for substrate selection, interface design and to analyze the thermo-mechanical behavior of coating-substrate coupled system. Finally, SEM-EDS analyses have been carried out on as-sprayed and tested materials in order to understand the mechanisms of reinforcement activated by high temperature exposure and to identify the microstructural modifications induced by the combination of mechanical loads and temperature in an oxidizing environment

Al2O3/ZrO2/Y3Al5O12 Composites: A High-Temperature Mechanical Characterization

“…The test duration varied from about 20 to 200 s (depending on the test temperature and maximum deformation reached during the test), according to the standard recommendations. A properly designed displacement transducer, pushing against the tension face of the sample using three alumina rods, is able to reconstruct and to measure the sample curvature and, afterwards, the deformation [29,30,31]. Finally, the stress-deformation curves, the elastic constants and the mechanical properties were assessed.…”

Basalt Short Fibres Dispersion and Fabric Impregnation with Magnesium Alloy (AZ63): First Results

“…The samples obtained were cut longitudinal to the casting axe, and perpendicular to the woven fabric. The rods obtained (4 x 3 x 50 mm) and (4 x 2 x 50 mm) respectively for short and long fibres were prepared to the four bending tests [13] [14] (at room temperature) with a Zwick Roell Z2.5 testing machine. Before mechanical tests, the samples described were used for evaluation of porosity by density measurement and through ME54 Mettler-Toledo (Italy) analytical balance, equipped with the tool for solid density measurements by the Archimedes principle.…”

High temperature mechanical characterization of plasma-sprayed zirconia–yttria from conventional and nanostructured powders

“…Stress-strain curves elaboration was performed by Zwick-Roell TestXpert II software. The measurement of sample deflection on three separated points allowed to exclude the undesired contribution of thermal expansion both of alumina extensometer rods and loading tubes: the described experimental setup enables a direct and reliable measurement of sample curvature, with appreciable improvements as compared to the control of crosshead travel or the direct LVDT measurement of sample deflection performed only in the central section of the sample [29][30][31].…”