Study On Strengthening Mechanism And High Temperature Creep Theory In Second Phase Strengthened Alloys

The second phase strengthened superalloys is not only the main material of thermal end components such as aerospace propulsion system,nuclear reactor,gas turbine,weapon equipment,but also the high temperature corrosion-resistant parts required by energy,chemical industry,transportation and other industrial departments,due to their prominent resistance to high temperature creep,great tensile strength,and excellent irradiation damage tolerance.In recent years,with the increasingly bad working environment of high temperature materials,people need more and more high temperature strength and creep properties of materials.It is a key scientific problem to design and control the second phase particles in the alloy and further improve the mechanical properties at high temperature.Therefore,the interaction between the second phase particles and defects in high temperature environment is deeply understood in this paper.The strength and creep model of coupled statistical theory is established,which solves the accuracy and rationality of the existing models.The addition of oxide particle would lead to a remarkable improvement of the mechanical properties in solid-solution alloys,due to their pinning effects for dislocation motion.However,the prediction of the classical oxide particle strengthening model can be not well consistent with the experiments,especially in the transition region from the dislocation cutting mechanism to the Orowan mechanism.Here,a unique predictive model,which considers not only the relative position between the dislocation slip plane and oxide particle center,but also the distribution effect of oxide particle size,is proposed to describe oxide particle strengthening.The calculated results of our work agree well with the experiments,compared with that calculated from the classical oxide particle strengthening theory.The critical particle radius does not rely on the volume fraction of oxide particle,in good agreement with the previous work.Moreover,the optimal oxide size is found to maximize the oxide particle strengthening.In order to improve the applicability of probability-correlative oxide particle strengthening model,the oxide particle strengthening in the larger particle volume fraction and size range is obtained.The coupling statistics method present results provide a universal framework for modeling and analyzing the physical reality of oxide particle strengthened solid-solution alloys.For studing on the creep behavior of nickel-base superalloys,there is still a lack of the physical models that do not include any adjustable parameters from the further experimentally measure,which limits classical model wide application.In this paper,a new creep model is proposed based on dislocation climbing time as the evaluation index,to evaluate the influence of precipitations on the secondary creep rate.The model can accurately quantify the internal stress from the precipitation that varies with the microstructure and temperature,which is different with previous models that take the internal stress as a constant.Moreover,in order to more precisely predict the contribution of precipitation to the secondary creep rate,the new model coupling the climbing mechanism and the Orowan bypass mechanism,and considering the effect of precipitation size distribution.And,the model can solve the imperfection that the classical creep model excessively overestimate threshold stress.TThe theoretically predicted results agree well with experiments and do not use any adjustable parameters.The effect of precipitation volume fraction and temperature on the creep rate is discussed,to uncover the underlying reason behind the high creep property of advanced nickel-base superalloys.The research work in this paper provides an effective theoretical model for the high-throughput design and development of second-phase strengthening superalloys with excellent high-temperature strength and creep properties,and provides scientific guidance for improving the application of materials in high-temperature complex stress environments.