Finite Elemental Simulations On Crack Healing Of TC11 Alloy Induced By Electromagnetic Pulsing Treatment

TC11 alloy is a typical two-phase thermal strength titanium alloy,which has good high temperature mechanical properties and thermal stability.It is also widely used in the manufacture of key components such as compressor disc and blade of aero-engine.However,titanium alloy products are often affected by high temperature,high pressure and transient load in use,which leads to defects such as fracture and fatigue crack and endangers the use safety.It has important value and practical significance in engineering application to treat the crack of material by pulsed electromagnetic.The main research contents are as follows:The macroscopic finite element model of TC11 alloy containing cracks was established.The thermal and structural coupling method was used to numerically simulate the temperature and stress fields of cracks under different pulsed electromagnetic treatment conditions.Combined with the observation of microstructure of TC11 alloy before and after pulsed electromagnetic treatment,the reason of crack healing promoted by pulsed electromagnetic treatment was analyzed.The results show that in the process of pulsed electromagnetic treatment,a significant compressive stress appears in the crack region,which pushes the metal in the crack region to migrate towards the geometric center of the crack,and reduces the crack width gradually.Based on the theory of crystal plasticity and the method of equal-stress homogenization,the constitutive relation of crystal plasticity of TC11 alloy was established.The finite element numerical model of crystal plasticity of TC11 polycrystalline was established by Voronoi algorithm and grain orientation distribution characteristics.Combining with the tensile tests of TC11 alloy at different temperatures,the material parameters at corresponding temperatures were optimized.The tensile deformation simulation results of TC11 poly crystalline are in good agreement with the experimental results,which indicates that the model established in this study can accurately describe the plastic deformation behavior of TC11 alloy.Based on the established plastic model of TC11 polycrystalline crystals,geometrical models of TC11 polycrystalline crystals containing intra-and intragrain microcracks were constructed to simulate the effect of pulsed electromagnetic treatment on the plastic behavior of the alloy containing microcracks at mesoscale.The simulation results show that the contribution of basal plane slip system Ba(0001)[1210]to the equivalent shear strain is greater than 60%of the total accumulated shear strain in α-phase grains with microcracks under pulsed electromagnetic field and tensile loading.For β-phase grains with microcracks,the main slip activated at the initial stage of plastic deformation is(101)[111],and the contribution of(110)[111]and(101)[111]slip systems to the equivalent shear strain is greater than 60%of the total cumulative shear strain.With the increase of pulsed electromagnetic processing time,the number of slip systems started in α or βphase increases gradually.At the same time,the driving force to start the slip system is greater.In the grain containing microcracks,the shear stress in the cracked region is greater than that in the non-cracked region,and the shear stress is applied to the dislocation in the cracked region,which promotes the activity of dislocation motion and the nucleation of new dislocation,thus improving the plasticity of the plastic zone in the cracked region.