Temperature Dependence Of Fracture Behavior Research Articles

Characterization of temperature dependence of fracture behavior of monolithic and laminated ultra‐high temperature ceramic matrix composites

AbstractThe fracture behavior of ultra‐high temperature ceramic matrix composites at high temperature has received increasing attention. However, few studies consider the effect of particle/crack interaction on the high temperature fracture strength of materials. In this work, the effect of particle/crack interaction is introduced into temperature‐dependent fracture strength model of monolithic ultra‐high temperature ceramic matrix composites, which also considers effects of flaw size, grain size, and residual thermal stress. Furthermore, by considering the influence of laminated structure, a theoretical model of the temperature‐dependent fracture strength of laminated ceramic matrix composites is developed. The effect of particle/crack interaction is also included in this model. It should be noted that the predictions of models agree well with the experimental data of both monolithic and laminated materials without using any fitting parameters. The effect of particle/crack interaction is found to have a significant weakening effect on the strength of materials at different temperatures.

Temperature Dependence of Fracture Behavior and Mechanical Properties of AISI 316 Austenitic Stainless Steel

A combination of fractographic and metallographic analysis during tensile tests over the temperature ranging from 20 °C to 750 °C were carried out to investigate the fracture behaviors and deformation modes so as to clarify the temperature dependence of mechanical properties of AISI 316 austenitic stainless steel. Planar slip mode of deformation was observed during tensile tests at 20 °C due to a relatively low SFE (stacking fault energies). Pronounced planar slip characteristics were observed in the range of 350–550 °C, and the resultant localized deformation led to the formation of shear bands. The dislocation cross-slip was much easier above 550 °C, leading to the formation of cell/subgrain structures. The preferential microvoid initiation and subsequent anisotropic growth behavior in the shear bands led to large-size and shallow dimples on the fracture surfaces in the range of 350–550 °C. However, the microvoid tended to elongate along the tensile direction in the localized necking region above 550 °C, resulting in small-size and deep dimples. The shear localization reduced the uniform deformation ability and accelerated the fracture process along shear bands, leading to a plateau in uniform elongation and total elongation in the range of 350–550 °C. The higher capability to tolerate the localized deformation through sustained necking resulted in a significant increase in the total elongation above 550 °C.

Temperature dependence of fracture behavior of in situ synthesized TiC/Ti-alloy matrix composite

In this paper, 10 vol.%TiC/Ti–6Al–3Sn–3.5Zr–0.4Mo–0.75Nb–0.35Si composite was fabricated by in situ casting route. The fracture behavior of the composite in the temperature range from ambient temperature to 900 °C has been researched. The results indicate that the damage mechanism of the composite is dominated by particle fracture followed by the ductile failure of the matrix below 700 °C. Plastic deformation occurs locally and the fractured TiC particles located mainly in the region of strain localisation at ambient temperature. Distribution region of broken particles increases with the increase in matrix plastic deformation below 700 °C. The strain is the main factor influencing the number of fractured particles below 600 °C, whereas TiC clusters and particle size are the dominant factors at 700 °C. Interface decohesion is the main feature above 800 °C, contributing to the damage of the composite. The generation of voids is always associated with larger particles and TiC clusters since they can impede the plastic flow of the matrix much more prominently above 800 °C.

Temperature and Orientation Dependence of Fracture Behavior of Directionally Solidified Duplex-Phase Crystals Composed of Ni<sub>3</sub>X-Type Intermetallic Compounds

Fracture behaviors of three directionally solidified (DS) duplex-phase alloys composed of Ni3Nb(D0a)/Ni3Al(L12), Ni6TaAl(D024)/Ni3Al(L12) and Ni3Ti(D024)/Ni3Si(L12) phases, respectively were investigated by three-point bending tests, focusing on temperature and orientation dependence. The temperature-toughness relation showed dissimilar curves depending on alloy. The increasing rate of fracture toughness was the highest in the Ni3Al/Ni3Nb alloy with fine lamellar structure and was the lowest in the Ni3Al/Ni6TaAl alloy with rod-like precipitates. The controlling mechanism for the temperature dependence of fracture behavior of Ni3Al/Ni3Nb alloys was discussed.

Brittle-to-Ductile Transition and High-Temperature Deformation in ZrO<SUB>2</SUB>(Y<SUB>2</SUB>O<SUB>3</SUB>) and Al<SUB>2</SUB>O<SUB>3</SUB> Ceramics as Evaluated by Small Punch Test

Temperature dependence of fracture behavior in two representative oxide ceramics, 3 mol%Y2O3-partially stabilized ZrO2 and pure Al2O3, was investigated to explore the high-temperature deformation mechanisms associated with ceramic superplasticity. Both the zirconia and alumina ceramics were found to show apparent brittle to ductile transitions. The transition temperatures (BDTT) were determined by means of the Small Punch (SP) test. Linear relationships were obtained between the BDTT and the logarithmic deforming rate in both ceramics. The high-temperature deformation mechanisms were discussed on the basis of the relationship between BDTT and deforming rate, and they were found to be intrinsically the same both in the present zirconia and alumina ceramics. Superplasticity can be easily achieved in tetragonal zirconia ceramics mainly because of the stability of the fine-grained microstructures. High ductility and even superplasticity can be achieved also in alumina, provided that its grain growth can be suppressed during deformation at high temperature.