| Gamma-TiAl based alloy is a kind of high-quality alloy with high specific strength,good corrosion resistance and high temperature resistance,which is widely used in aerospace field.However,the defect of poor plasticity of gamma-TiAl-based alloys is an important factor restricting its development.Therefore,it is meaningful to study the plastic deformation mechanism of gamma-TiAl based alloy.Grain boundary is an important factor affecting the plasticity of gamma-TiAl based alloys.In this paper,the effect of relative orientation grain boundaries on the plastic deformation behavior of gamma-TiAl based alloys is studied by crystal plasticity finite element simulation.In this paper,the constitutive relation of crystal plasticity based on ordinary slip system and super-slip system is established,the corresponding UMAT subprogram is compiled,and the geometric model of gamma-TiAl polycrystals based on Voronoi algorithm is constructed,and the finite element compression simulation of gamma-TiAl polycrystals is carried out.The effects of three different deformation rates,grain number and grain size parameters on the plastic deformation of polycrystals were studied.The results show that the higher the deformation rate,the higher the strength of polycrystals.The order of strength of the three models from large to small is:1×10-1s-1>1×10-2s-1>1×10-3s-1;while the grain number is 27,the model has converged.The smaller the grain size,the higher the yield strength of the material.The single grain boundary and the mixed grain boundary were studied separately:?3<111>60°,?5<100>36.9°,?9<221>90°,?11<110>50.5°,?13a<100>22.6°polycrystalline compression deformation behavior,the simulation results show that the more the dislocation slip starts,the greater the yield strength of the polycrystal.The order of the yield strength of the five grain boundaries from high to low is:?9<221>90°>?11<110>50.5°>?3<111>60°>?13a<100>22.6°>?5<100>36.9°,start with slip system Corresponding to the situation,the strength of?9<221>90°and?11<110>50.5°is good,and the plasticity of?5<100>36.9°is poor,the plastic hinge of?3<111>60°is good.The compression deformation of?-TiAl-based alloy was studied by thermal simulation compression test combined with electron backscatter diffraction?EBSD?technique.The results were compared with the finite element simulation results.The stress-strain fitting curve proved the reliability of the finite element model..The observation of the thermal simulated compression specimens shows that during the compression deformation process,the crystal layer structure is bent and deformed,and the grain orientation ins ide the crystal changes.The overall trend is changed from[101]crystal orientation to[001]crystal orientation,there are some grain orientations or grain boundaries which are not conducive to dislocation slip,which will be transformed into grain orientation and grain boundaries which are favorable for transferring dislocations under the action of force,grain interior and grain boundary A significant slip band appeared.In this paper,the role of grain boundaries in plastic deformation is studied by analyzing the plastic deformation mechanism of these five grain boundaries in?-TiAl polycrystals.The results show that some grain boundaries hinder the movement of dislocation slip.It is prone to cross-slip and multi-slip phenomenon near the grain boundary,so that stress concentration occurs;some grain boundaries can play the role of transferring dislocations,and adjacent grains are also easy to rotate together.Such grain boundary stress is generally small. |
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