Research On Dimensional Stability Mechanism Of Beryllium

As a reliable high performance material,beryllium plays an important role in instrument grade structural materials in the inertia guidance systems and primary satellite applications due to its excellent dimensional stability.In this paper,the elastic properties and electronic properties of the impurity phases Be O and Be-Fe in beryllium and their effects on the stability of beryllium were studied by means of TEM microstructure observation and first-principle simulation calculation.The vertical thermal expander was used to test the dimensional change rule under the condition of constant temperature aging and thermocycling,and the stability of beryllium was improved by vacuum annealing heat treatment later.The microcreep constitutive equation of beryllium was established by using dynamic fatigue testing machine to test the creep properties.The results showed that:Microscopic observation indicated that the impurity phase was distributed in the grain and grain boundary of beryllium,and there was a stable dislocation structure in the original beryllium material.The first principle analysis showed that the impurity phases Be O,FeBe₅ and AlFeBe₄ were all brittle phases and stable in beryllium with the elastic modulus above 300 GPa.The thermal mismatch between the impurity phase and the beryllium matrix and their aggregation in grain boundary affect the microplastic deformation of beryllium.The sizes of beryllium shrunk during thermocycling with temperature range 80?,120? and 160?,and the shrinkage amount increases with the increase of the temperature range.Moreover,the shrinkage amount of beryllium after constant temperature aging was smaller than that after thermocycling.With the increase of annealing temperature,the dimensional shrinkage of beryllium material decreases and increases.Vacuum annealing treatment has no significant effect on the size change of beryllium.Microcreep behavior of beryllium within 60??80? and 60 MPa?80 MPa illustrated that at a certain load,the higher the temperature was,the higher the total creep strain was,as well as the steady-state creep rate.At a certain temperature,the higher the load was,the greater the total creep strain and steady creep rate were.The apparent stress index was 3-4 and the creep activation energy of microcreep was about 38.93 k J/mol.According to above parameters,the constitutive equation of microcreep was established.The microcreep mechanism is dominated by dislocation slip mechanism under low stress and dislocation climbing plays a leading role under high stress.