Research On The Mechanical Properties And Constitutive Equations Of Tial-based Alloy

TiAl based alloy is a new type high temperature alloy, because of its high specific strength,rigidity, creep resistance, oxidation resistance, low density it has become an ideal Material inaerospace field. This paper is mainly based on tensile testing, constitutive relation and engineeringapplication of Ti-47Al-2Cr-3Nb.The tensile tests of Ti-47Al-2Cr-3Nb are investigated at the temperature range of25-850℃andstrain rate of10-3/s and10-4/s to get the true stress-strain data. Through the test result, elasticmodulus, yield strength, tensile strength and other material properties of the material has beenobtained to analyze material properties with change in temperature and strain rate. The results showthat the mechanical property has great influence on temperature change. Strain rate change hasaffected weakly as compare with the other parameters. It has been conformed that the elastic modulusand yield strength declines to increase in temperature, except for the temperature of700~780℃, inwhich case slight increase in material properties has been detected.The deformation mechanism for the temperature range780~850℃is changed with compare toits initial performance. At the temperature of850℃significant plastic deformation has been noticed.Investigation was carried out by using scanning electron microscopy (SEM) for the specimendamaged by tensile test. From the obsrevation of materials fracture mechanism on the basis ofmicroscopic analysis, it has been found that the main fracture forms two kinds of damage patterns,one is Wear layer fracture and the other is layerwise fracture. Increasing in the temperature causedlayer cracking or layer tearing and at the temperature of850℃, there are certain amounts of dimples.Based on J-C and Z-A model constitutive equations were derived which improves the J-C modelfor efficiently predicting the deformation behavior of the TiAl alloy. J-C and Z-A model predictionresults with test data comparision showed that two models can be used effectively to accuratelypredict true stress and strain at the temperature of25~780℃to provide theoretical reference for theengineering. The development of these two prediction methods builds a complete stress-strainconstitutive relation that is relatively simple and agrees well with the experimental results.With deploying the predictive models developed in this work a3D finite element model of acompresser blade were created with the ANSYS to do the analysis work related to stress and strain.The result showed that constitutive models developed in this work can be applied in real Strucural stress analysis; the density of TiAl based alloy is half of the currently used alloy while the two alloyhave the similar safety factor.