Research On Influencing Factor Of Thermal Fatigue Performance In Unidirectional Solidification Of Al-Cu Alloy

With the development of the society, there is an increasing demand for the use of materials. Materials are needed to possess of better performance when in practical environment. In practical use, fracture is one of the most important forms for materials to be invalided, which will cause great loss for people. A lot of fracture accidents take place because of material fatigue. Unidirectional solidification alloy is developed to be with de development of the high-temperature alloy. The use of the unidirectional solidification is mostly involved in hot environment, while fatigue fracture a main use incipient fault. Accordingly, there is a great demand to the study on its thermal fatigue performance. For the moment, we see little of study on the thermal fatigue performance of Al-Cu unidirectional solidification, especially the systemic study. Therefore, this subject has considerable great practical application value.The experiments are carried out under the conditions which similar to the practical surroundings, using the thermal fatigue tester to do the study on the rule of initiation and propagation of thermal fatigue crack. Optical microscope, SEM, and thermal fatigue tests have been processed on Al-Cu unidirectional solidification alloy to study the effect of RE and superheat treatment on thermal fatigue performance of Al-Cu unidirectional solidification alloy and the mechanism of initiation and propagation of thermal fatigue crack. In addition, simulation has been done to the temperature field and analyses to the thermal-stress distribution of the samples.The thermal fatigue samples with prefab crack have been chosen. The period from the initiation of the crack to the length reaches 0.1mm has been defined as the initiation period of thermal fatigue cracks. The period that the cracks propagate to more than 0.1mm and later has been defined as the propagation period of thermal fatigue cracks. The cold and hot cycle times when the length of the cracks reach to 0.1mm is used to measure the resistance to the initiation of thermal fatigue of different microelements; The length of thermal fatigue cracks under same cycle times is used to measure the resistance to the propagation of the thermal fatigue cracks from different microstructure.The main conclusions that gained under the above conditions are as follows:...