Research On Heat-treatment And Dynamic Mechanical Properties Of Tungsten Heavy Alloys

W-Ni-Fe alloys are typical two pahse composites widely used in military and civilian fields,especially used as kinetic energy penetrator material in defence industry,owing to their outstanding physical and mechanical properties.W-Ni-Fe alloys with high relative density and excellent mechanical properties can be fabricated by traditional liquid-phase sintering,and studying the mechanical properties and adiabatic shear phenomenon under dynamic loading is important to evaluate the penetration performance.Heat-treatment can improve the phase distribution and integrated properties of sintering W-Ni-Fe alloy.93W-4.9Ni-2.1Fe,95W-2.8Ni-1.2Fe-1Al2O3 and 93W-4.9Ni-2.1Fe/95W-2.8Ni-1.2Fe-1Al2O3 alloys are fabricated by mixing of original powders,cool isostatic pressing forming,liquid-phase sintering and quenching heat-treatment in this study,and study the microstructure and mechanical properties under quasi-static and dynamic loading.Besides,we also study the influence of SPS cyclic heat-treatment on the microstructure and mechanical properties of sintering 93W-4.9Ni-2.1Fe and 95W-2.8Ni-1.2Fe-1Al2O3 alloys.Relative density of 93W-4.9Ni-2.1Fe alloy is 99.4%,whereas relative lower densitys of 95W-2.8Ni-1.2Fe-1Al2O3 and 93W-4.9Ni-2.1Fe/95W-2.8Ni-1.2Fe-1Al2O3 alloys are 98.7% and 98.3%,respectively.Under quasi-static loading,the ultimate tensile strength and elongation of 93W-4.9Ni-2.1Fe alloy are 967 MPa and 27.25%.The ultimate tensile strength and elongation of 93W-4.9Ni-2.1Fe/95W-2.8Ni-1.2Fe-1Al2O3 alloy are 846 MPa and 4.75%.For 95W-2.8Ni-1.2Fe-1Al2O3 alloy,770 MPa and 2.25% are obtained.W transgranular cleavage fracture and matrix ductile tearing are dominant in the fracture morphologies of 93W-4.9Ni-2.1Fe alloy,but for the other two alloys,the fracture is mainly characterized as W-W interface fracture with a little W transgranular cleavage fracture and matrix ductile tearing.93W-4.9Ni-2.1Fe/95W-2.8Ni-1.2Fe-1Al2O3 and 95W-2.8Ni-1.2Fe-1Al2O3 alloys have the highest and lowest compression yield strength,respectively.The hardness of 95W-2.8Ni-1.2Fe-1Al2O3 alloy is higher than 93W-4.9Ni-2.1Fe alloy.Dynamic tensile and compression tests are carried out for three prepared alloys.Under dynamic tensile loading,the change of the properties for three prepared alloy is similar,when the strain rate is under 1000 s-1,tensile strength increases with the increase of the strain rate.Plastic deformation stage is shown in 93W-4.9Ni-2.1Fe alloy,but the other two alloys are characterized as brittle fracture of W-W interface separation.The tensile strength decreases significantly and the strain is double for all of the alloys when the strain rate is 2000 s-1,and W-W interface fracture is the main fracture model,only with a little W transgranular cleavage fracture.Under dynamic compression loading,the change of the properties for three alloys is similar and sensitive to strain rate.When the strain rate is 1000~3000 s-1,the yield strength and maximum stress increase first,and then decrease.The maximum value is shown in 2000 s-1.With the increasing of strain rate to 4000~5000 s-1,the properties improve obviously,and then decrease when zhen strain rate is 5500~6000 s-1,which maybe is revelated to the forming of the adiabatic shear band(ASB).The influence of train rate for 93W-4.9Ni-2.1Fe alloy is the ASB depth while for 95W-2.8Ni-1.2Fe-1Al2O3 alloy is the ASB width,and ASBs are easily formed in 93W-4.9Ni-2.1Fe alloy.The effect of vacuum cyclic heat-treatment based on spark plasma sintering(SPS)technique on the as-sintered 93W-4.9Ni-2.1Fe and 95W-2.8Ni-1.2Fe-1Al2O3 alloys has been studied.The results show that the matrix penetration into W-W grain boundaries enhances significantly,and the W-W contiguity and dihedral angle decrease gradually with the cycle index increasing.SPS cyclic heat-treatment does not obviously change the grain size.The content of tungsten increases with the cyclic times,and then decrease.The change of the hardnedss of the alloy is similar to the tungsten content.The bending strength of the alloy increases with the cyclic times.When the cycles go up to 20,the average bending strength reaches the maximum.The maximum deflection of the alloy is shown after 10 cycles.The proportion of W transgranular cleavage fracture is improved with the increase of the cyclic time,especially after 5 cycles for 93W-4.9Ni-2.1Fe alloy,and the proportion of matrix ductile tearing first increases,and then decreases in line with the maximum deflection.