The Effect Of Ti/TC4 On High Temperature Tensile Properties And Deformation Mechanism Of The ?-TiAl Based Alloy

?-TiAl based alloys have both the great plasticity of metal and the high temperature strength of ceramic because of structural characteristics.It shows excellent high temperature performance at high temperature?800?¹100??.Its high elastic modulus,low density and good creep resistance make it possible to replace the traditional structural materials to prepare structural components such as aero-engines.In recent years,some progress has been made in the practical application of?-TiAl based alloys,but its application scope is restricted due to its low plasticity and complex production process.Therefore,on the basis of guaranteeing the high temperature strength and other properties to improve the plasticity of the alloy is the focus of study on?-TiAl based alloys.In this paper,a kind of core-shell structure?-TiAl based alloy with pre-alloyed powder?Ti-48Al-2Cr-2Nb?as the core and Ti/TC4 powder as the shell was prepared by powder metallurgy.The high temperature properties of the alloy were improved by using the core-shell structure.The mechanical properties of alloys with different Ti/TC4contents?6%¹4%Ti/6%¹0TC4%?at 800?¹000? and strain rate of 5×10^-5s^-11×10^-3s^-1were studied.It provides a new material and research idea for the study of?-TiAl based alloys.The powder was prepared by Ti-48Al-2Cr-2Nb and Ti/TC4 in proportion.The content of Ti was 6%,8%,10%,12%and 14%.The content of TC4 was 6%,8%and 10%.The powders were uniformly mixed by ball mill and then sintered by vacuum hot pressing.The microstructure of sintered samples was observed by SEM.Electronic universal testing machine?WDW-200?was used to conduct high temperature tensile test.The microstructure of stretched samples was analyzed by TEM and HREM.The effect of different contents Ti/TC4 alloy on the high temperature properties was studied.The characteristics of true stress-strain curve and thermal deformation mechanism of the alloy during high temperature deformation were analyzed.The results showed that:1.Use the method of vacuum hot-pressing sintering to prepare the core-shell structure?-TiAl based alloy which is Ti/TC4 as the shell to cover the Ti-48Al-2Cr-2Nb??-TiAl and?₂-Ti₃Al?.The shell of the alloy prepared by adding Ti powder is?-Ti.The shell of the alloy prepared by adding TC4 powder are?-Ti and?-Ti.With the increase of Ti and TC4contents,the integrity of the cladding layer is better and the thickness of the cladding layer increases.2.Ti has great influence on the tensile properties of?-TiAl based alloy at high temperature.With the increase of Ti content,the tensile strength decreased,the elongation first increased and then decreased at 800?¹000?,5×10^-5s^-11×10^-3s^-1.10%Ti alloys have the highest elongation at 1000?,5×10^-5s^-1.Its elongation reached 105%and intensity is maintained at 72.36MPa.Its elongation was 9.9%higher than that of Ti-48Al-2Cr-2Nb alloy,while its intensity was only reduced by 14.93MPa.The softening mechanism of materials is mainly dynamic recovery.3.Compared with Ti-48Al-2Cr-2Nb alloy,the core-shell structure?-TiAl based alloys formed by TC4 has not only higher elongation but also higher tensile strength.The high temperature strength of the alloy increases with the content of TC4 increases at800?¹000?,5×10^-5s^-11×10^-4s^-1.In the range of 6%¹0%TC4,the elongation first increases and then decreases with the increase of TC4 content.The 8%TC4 alloys obtained the best elongation.Its elongation reached 92%at 800?,5×10^-5s^-1.And the tensile strength remained at a high level of 426.17MPa.Compared with Ti-48Al-2Cr-2Nb alloy,the elongation and strength increased 68.4%and 21.47MPa.The softening mechanism of materials is mainly dynamic recovery.4.The tensile structure of the alloy containing Ti is obviously deformed.The high temperature deformation mechanism are dislocation slipping and twins in?lamellar grain.Large numbers of dislocation lines are produced by deformation in the?-Ti phase.In the lamellar grain of the core of core-shell?-TiAl based alloys,the?phase and_—?₂ phase always have a fixed orientation relationship that is?111??//?0001??₂,[110]?//[1_—120]?₂._—Th_—e step dislocation and{111}stacking fault which is generated by 1/6[112]+1/6[121]dislocation moving on{111}plane coordinate the deformation of the alloy.5.The deformation mechanism of alloy with TC4 is dislocation slipping and twins in?lamellar grain.In the high temperature deformation structure,the shell structure?TC4?of the core-shell structure has a large deformation and can coordinate the deformation of the core structure.The core-shell structure provides a high elongation and tensile strength for the?-TiAl based alloys.In the high temperature deformation structure,obvious deformation can be observed at the grain boundaries of?-Ti and?-TiAl.From[111]?//[1120]?direction observed the orientation relationship of?-Ti and?-Ti satisfies the Burgers orientation relationship that is?0001??//?01^—1??,[111]?//[112^—0]?.6.The high temperature plasticity and strength of the alloys are considered comprehensively,8%TC4 alloy has the best comprehensive properties at 800?.The alloy can be hot-machined at this temperature and used in the environment at this temperature.