Papers by Keyword: Transgranular Fracture

Abstract: Mixtures of ZrO₂-Al₂O₃ ceramic composite were prepared using zirconia powder, ZrO₂-Al₂O₃ composite powder synthesized by sol-gel process as main starting materials and zirconia gel as a binder. Then the mixtures were pressed into the mold, and then sintered at 1650°C for 3h. Finally, the ZrO₂-Al₂O₃ ceramic composite samples were prepared. Then the mineral phases of ZrO₂-Al₂O₃ ceramic composite were analyzed by X-ray diffraction (XRD), and the fracture model of ZrO₂-Al₂O₃ ceramic composite was analyzed by press, scanning electron microscopy (SEM) and energy dispersive X-ray Spectroscope (EDS). The results show that, zirconia is the main phase and alumina is the secondary phase mainly present in the matrix. The fracture model of ZrO₂-Al₂O₃ material was jointly composed by intergranular fracture and transgranular fracture, of which the coarse particle shows the intergranular fracture model and the fine particle shows the transgranular fracture model.

Abstract: Life of an aero-engine is limited by the life of the turbine blade in particular and that of hot end components in general. Design of aero-engine is always conservative in nature considering the flight safety as paramount important. Earlier engines have been assigned life in hours but the life of the component is limited by LCF cycles particularly during the start-stop cycles. In this paper LCF behaviour of a typical Russian origin nickel base wrought super alloy AP220BD used for turbine blade has been studied at room temperature (RT), 400 °C and 700 °C that corresponds to idle rating and cruise rating of a typical aero-engine. Low cycle fatigue (LCF) tests have been carried out at RT, 400°C and 700 °C at three strain amplitudes of ±0.3%, ±0.5% and ±0.8%. Hysteresis loop have been developed at each strain and temperature. It has been observed that LCF life of the nickel base wrought alloy AP220BD is not influenced significantly at strain amplitude of ±0.3% till it reaches 400° C. Reduction in LCF life with increase in strain amplitude from ±0.3% to ±0.8% is much significant compared to that of increase in temperature up to 700°c.The higher life at intermediate strain of ±0.5% may be due to DSA(dynamic strain aging) of the material. Transgranular fracture has been observed at RT & 400° C while intergranular fracture at 700° C.

Abstract: Interstitial free (IF) steels are widely used as thin sheet in the automobile industries because of their many favorable properties. Although, fatigue properties of IF steels do not have significant importance to auto body makers, however, they are very concerned about the tensile and fatigue strength of the steels used for structural purposes to ensure safety of passengers. So, fatigue results of this steel might help researchers to understand the behaviors of high strength steels. In this study cyclic and static properties have been studied at room temperature in the air. Initiative has also been taken to observe the fatigue fracture morphology of this steel. Experimental results show that the fatigue limit is corresponding to about 40% of tensile strength and 80% of the yield strength of this steel. Fractographic observations reveal a mixed type of fracture mode (intergranular and transgranular cracking) fractures.

Abstract: Observation of fracture surfaces in ceramics is useful for improving their mechanical properties. In this study, fracture surfaces of polycrystalline alumina were observed using scanning-probe microscopy (SPM) on a nanoscale, also called “nano-fractography.” The average grain size of polycrystalline alumina specimen used in this study was 4.5µm, and the fracture toughness was 3.0MPa･m-1/2. The fracture mode was found to be a mixture of intergranular and transgranular fractures. The fracture surface of intergranular fractures consisted of smooth and rough areas composed of very small steps, whose detection was impossible using scanning electron microscopy. Cleavage and non-cleavage fractures were observed in transgranular fracture grains. The fracture surface of single-crystalline alumina, which is the typical model of the transgranular fracture, was also observed by SPM. The cleavage plane of alumina macroscopically exhibited a very smooth, glass-like surface. However, sub-nano meter steps can be observed on the cleavage fracture surface and appear to be formed by plastic deformation during crack propagation because the size of the step nears that of the Burgers vector.