Theoretical Characterization Method Study On Temperature-dependent Properties Of Alloys And Semiconductor Materials

Metallic materials are widely used in aerospace,energy,electric power and other industrial engineering fields due to their superior thermal-mechanical properties,and they play a very important role in high-temperature components.The mechanical properties of metallic materials used at high temperatures are different from those at room temperature.High-temperature strength is one of the most active research fields in material science and engineering.Characterization and improvement of high-temperature mechanical properties of metallic materials have always been the focus and hotspot in hightemperature field.Nowadays,the creation of complex high-temperature environment is very difficult and the measurement work also faces a great challenge,so the current experimental temperatures and experimental conditions are still difficult to fully meet the requirement of engineering application.Although the high-temperature experimental research and theoretical research at room temperature of metallic materials have reached a very high level,the theoretical characterization of high-temperature mechanical properties are still relatively lagging behind,and the temperature-dependent theoretical models are few.The existing theories are semi-empirical phenomenological models,which are not helpful to deeply understand the underlying mechanism under physical phenomena and practical application.Therefore,the theories of high-temperature strength need to be further studied and enriched.It is urgent to establish the temperature-dependent theoretical models to characterize and predict the mechanical properties of a wider range of metallic materials at high temperatures.And it is also the difficult point of mechanical properties study on high-temperature metallic materials.Similarly,semiconductor materials play an important role in the electronic field.Because the wide variations of temperature usually occur in service process,which causes a significant influence on their optical and electrical properties.Semiconductor devices need to maintain a high accuracy and sensitivity in the work,thus necessitating studies on the optical and electrical properties other than room temperature.It requires to study the optical and electrical properties of semiconductor materials at different temperatures,analyze the controlled mechanism and its evolution with temperature,and establish the temperature-dependent theoretical models.These will be helpful in the design and application of semiconductor materials at high temperatures.In this paper,the modeling idea considering the effect of temperature on materials properties is applied to metallic and semiconductor materials.The effect of strain rate on temperature-dependent yield strength of bulk centered cubic metallic materials and the effect of precipitation strengthening on yield strength anomaly of Ni-base superalloy and its evolution with temperature were studied.The influence of temperature on the band gap energy and refractive index of semiconductor materials were also studied.The corresponding theoretical characterization models are also established.The specific research work is as follows:(1)Based on the modeling idea the effects of distortion strain energy and heat energy on yield of plastic materials,the influence of strain rate effect on the temperaturedependent yield strength of metallic materials were studied,the evolution mechanism of strain rate effect with temperature were analyzed,and the temperature-dependent yield strength model considering strain rate effect is established.The model establishes the quantitative relationship among yield strength,temperature,strain rate,Young's modulus,Poisson's ratio and the heat capacity at constant pressure.At the same time,we put forward a strain rate sensitivity factor to consider the coupling effect of temperature and strain rate on the yield strength.Compared with the existing yield strength models,our model contains less fitting parameters and is more convenient to apply.The model is verified by a series of iron-based FCC metallic materials,and the yield strength of temperature and strain rate is reasonably predicted using this model.This research provides a simpler and effective way to predict yield strength of metallic materials at different temperatures and strain rates,and provides the further guidance for reliability design of materials.(2)Combining the temperature-dependent yield strength model of metallic materials and the traditional precipitation strengthening theory,the effect ?? precipitation on the temperature-dependent yield strength of nickel-based superalloy were studied.For yield strength anomaly of ?? precipitation strengthened nickel-based superalloy,we established a temperature-dependent yield strength model which can consider the effect of precipitation strengthening,and the model is verified by experiments.The predicted results agree well with experimental results,which proves the excellent prediction ability the model.This study provides a quantitatively theoretical characterization method for yield strength anomaly of Ni-base superalloy at elevated temperature.(3)The modeling thought considering the effect of temperature on materials properties is successfully applied to semiconductor materials,and we develop a novel temperature-dependent band gap energy model for semiconductor materials.The nofitting-parameters model considers the two main factors affecting band gap energy(thermal expansion and phonon-electrical interactions)and the variation with temperature.Using this model,we theoretically predicted the temperature-dependent band gap of several semiconductor materials,and compared with the available experimental results.The model predicted results and experimental results agree very well.Compared with the widely quoted Varshni's semi-empirical model,the model has distinct advantages from the aspect of modeling,our model in modeling,physical meaning and applications.This study provides a simple way to determine the band gap energy of semiconductors at different temperatures,and is also helpful for the theoretical study of other electrical properties of semiconductor materials,including intrinsic carrier concentration,intrinsic transition temperature and maximum breakdown voltage.(4)Combining the temperature-dependent band gap energy model proposed in the previous work and classical Moss' s relation,we studied the effect of temperature on refractive index,and we developed a novel model to theoretically study the effect of temperature on the refractive index in semiconductors.This model establishes the quantitative relationship among the refractive index,band gap energy and linear expansion coefficient.It can be used to predict the refractive index at temperatures from near absolute zero to high temperatures.In order to validate the model,we calculate the refractive index of a series of semiconductor materials at different temperatures and wavelengths and compared with the experimental results.Away from the band edge region,the theoretical results agree well with the experimental results.In near band-edge region,the redshift will have an obvious effect on the refractive index at elevated temperatures,and we also give the specific method to consider the effect of redshift.The further verification of the model considering redshift is added as well,which is consistent with the experimental results.The study provides a new theoretical method for the prediction of temperature-dependent refractive index of semiconductors,which may be helpful for the design of the optical devices.