Dynamic Mechanical Properties And Annealing Of The Extruded Fine-grained Tungsten Heavy Alloy

The dynamic mechanical properties and failure behavior of fine-grained93W and93W+0.03%Y alloys after rapid hot extrusion were investigated under different strain rates at elevated temperatures by using Split Hopkinson Pressure Bar. Meanwhile, we also investigated the effect of annealing on the mechanical properties and microstructure evolution of the alloys. Some main experimental results are obtained as follows:(1)The quasi-static mechanical properties of fine-grained tungsten heavy alloy are significantly enhanced after rapid hot extrusion. The ultimate tensile strength (UTS), elongation of the as-extruded fine-grained alloy reached1570MPa,6.5%, respectively. While, the ultimate tensile strength (UTS), elongation of the as-extruded coarse-grained alloy were1260MPa,5.6%. Microhardness of tungsten phase of the as-extruded tungsten heavy alloys is severely decreased with annealing temperature increasing. Microstructure observation shows that annealing treatment is preferential to the tungsten contiguity reduction and tungsten grain refinement. After high temperature annealing, the matrix is distributed more homogeneous and the volume fraction of the matrix of fine-grain tungsten heavy alloy is increased.(2) Dynamic strain-stress test show that the peak flow stress of the as-extruded tungsten heavy alloy at different high strain rates was kept at a constant, of the order of2000MPa, indicating that rapid hot extrusion was helpful to decrease the strain rate sensitivity. Microstructure observation shows that the as-extruded fine-grained tungsten heavy alloy formed adiabatic shear band (ABS) then fractured by adiabatic shearing. The critical strain for adiabatic shearing was decreased, showing the rapid hot extrusion is preferential to reduce the critical strain for adiabatic shearing of fine-grained tungsten alloy.(3) The initial testing temperature has a profound effect on the constitutive response of the as-extruded tungsten alloy. Dynamic stress-strain curve exhibits that the peak flow stress and the amount of plastic deformation of specimens tested at higher temperatures is larger than that of specimens tested at relatively lower temperatures. In addition, the width of adiabatic shear band and the shear strain amount in tungsten grains of the specimens tested at higher temperatures(350℃) is greater than those of tested at relatively lower temperatures.