Study On Processing Technology And Strengthening And Toughening Mechanism Of New Multi-component Cobalt-Based Superalloy

The new multi-component cobalt-based superalloy has excellent comprehensive high-temperature properties and good processability at the same time,and its comprehensive performance has reached the level of commercial wrought nickel-based superalloy,showing a good prospect of engineering application.However,in order to become a new generation of commercial wrought superalloy,a reasonable production and processing route must be established to realize the engineering application of the new cobalt-based alloy,and the mechanical properties of the new cobalt-based alloy still need to be optimized and improved.Based on the above considerations,this paper makes a comprehensive and in-depth study on the hot deformation characteristics and the strengthening and toughening mechanism of a new multi-component cobalt-based superalloy.The hot deformation processing characteristics of the new cobalt-based alloy were systematically explored by processing map technology and electron backscatter diffraction(EBSD)analysis technology,the microstructure evolution mechanism of the new cobalt-based alloy under different processing deformation conditions was revealed,and the quantitative relationship among flow stress,processing deformation conditions and microstructure was successfully established.Solid solution heat treatment and aging heat treatment were carried out through different heat treatment processes,and the effects of different heat treatment processes on the microstructure and mechanical properties of the new cobalt-based alloy were comprehensively studied by means of various observation and analysis.The mechanism of heat treatment process on the strengthening and toughening of the new cobalt-based alloy was deeply explained.The engineering practicability and mechanical properties of the new cobalt-based alloy were topologically optimized by alloying with Ta and Ti.The effect mechanism of alloying with Ta and Ti on the strengthening and toughening of the new cobalt-based alloy was expounded,and the effect of alloying with Ta and Ti on the hot deformation properties of the new cobalt-based alloy was discussed systematically.The main conclusions are as follows:The hot deformation behavior of the new cobalt-based alloy belongs to the typical dynamic recrystallization(DRX)type,which is similar to the flow behavior of commercial wrought nickel-based superalloy,and the constitutive relationship between peak stress,strain rate and deformation temperature can be described by Arrhenius-type Sellars-Tegart hyperbolic sine function equation.The hot deformation processing map shows that when carrying out the hot deformation processing of the new cobalt-based alloy,the true strain should be controlled within the range of 0.2?0.5(i.e.,the engineering strain is 22%?65%)in order to restrain the defects of the hot deformation processing structure;the best processing parameters of the new cobalt-based alloy should be selected in the flow peak zone in the hot deformation processing map to obtain a more complete recrystallized grain structure.During the solid solution heat treatment,the DRX nucleation and growth of the new cobalt-based alloy is continued by means of grain boundary protrusion.With the migration of grain boundaries,DRX grains continue to consume dislocation defects caused by work hardening and grow.The grain boundary plays a strengthening role at room temperature and medium temperature,but it becomes a weak link at high temperature.For the new cobalt-based alloy products with higher performance at high temperature,the higher solution temperature should be selected for solid solution heat treatment in order to obtain coarse grain structure.After aging heat treatment,the new cobalt-based alloy forms a typical ?/?' two-phase structure,and the ?' strengthening phase is approximately spherical and dispersed on the ? matrix phase.The nucleation and growth process of the ?' precipitated phase is very consistent with the classical Lifshitz-Slyozov-Wagner(LSW)theoretical model,and the contribution of precipitation strengthening caused by ?' precipitated phase to the strength increase of the alloy can be accurately described by the weak pair-coupling model and the strong pair-coupling model in the dislocation cut-through mechsanism.After alloying with Ta and Ti,the mass density of the new cobalt-based alloy decreases,and the shape of the ?' phase changes from approximately spherical to approximately square,greatly increasing the lattice misfit between the ? phase and ?'phase,which can effectively improve the strength of the new cobalt-based alloy,but also hinder the plastic deformation.Alloying with Ta and Ti improves the hot deformation resistance of the new cobalt-based alloy at low temperature or high rate,and pushes the optimal hot deformation processing region to the high temperature and low rate region,greatly improving the hot deformation activation energy of the new cobalt-based alloy,which makes the hot deformation processing of the new cobalt-based alloy more difficult.