Effect Of Microstructures On Mechanical Properties And Spall Characteristics Of TC21 Alloy

Titanium alloy has great potential in the field of armor protection for its excellent properties.This paper formulates the different heat treatment systems,obtain with different fine structure characteristics of the organization.The various microstructures of TC21 titanium alloy under static tensile tests,dynamic impact tests and plate impact tests,are studied by optical microscope and scanning electron microscope,and revealed the effects of the phase content of transformed β matrix and width of α plates on dynamic mechanical properties,adiabatic shear sensitivity and spall characteristics of TC21 titanium alloy.The main research conclusions are as follows:Equiaxed microstructure and bimodal microstructure of TC21 alloy are obtained when the solution treatment is under β phase transition point.While the solution treatment is above the point,lamellar microstructures with different width of α plates are obtained.The width of α plates increases as decreasing of the cooling rate.In the quasi static tests,the strength and hardnessof the bimodal microstructures are higher than that of the equiaxed microstructure,while the elongation and the percentage reduction of area are lower than that of the equiaxed microstructure.It also can be found that the strength and hardness of lamellar microstructures decrease as the width of α plates increased,accompany with enhanceing of the elongation and the percentage reduction of area.In the dynamic compression tests,the dynamic compressive strength of the bimodal microstructures is higher and the strain and energy absorbed is lower than equiaxed microstructure.The dynamic compressive strength of lamellar microstructure decreases with the increasing of the width of α plates.Meanwhile,as the increasing of the width of α plates,the strain increases when the samples are not under shear failure.All of the three kinds of the microstructures are strain rate sensitive material.In the forced shear tests,the adiabatic shear sensitivity of the equiaxed microstructure is higher than that of the bimodal microstructure.With the increasing of width of α plates,the adiabatic shear sensitivity of lamellar microstructure is increased.In the plate impact tests,the spall strength of the equiaxed microstructure is lower than that of the bimodal microstructure and lamellar microstructure.Microvoids are observed at the α/β phase boundaries in equiaxed microstructure,then the coalescence of the microvoids would cause the spall of the samples.Most of the microvoids of the bimodal microstructure are found nucleated at the α/β phase boundaries while few in α phase.After that,microvoids grow up and coalesce with each other,which led to the formation of microcracks.As for lamellar microstructure,microvoids nucleate and grow at grain boundaries and α/β phase boundaries.The failure mechanism of three kinds of microstructures are microcrack’s propagation to macrocracks combined and the formation of adiabatic shear bands.