Research On Plastic Deformation Behavior Of New High-density DT740 Alloy

For a long time,materials for warheads in the defense field have always been a difficult point for military new materials,in order to meet the needs of the future development of high-end materials in the field of defense,the research team designed a new high-density DT740alloy with high density,high toughness,excellent impact toughness and excellent dynamic mechanical properties.In this thesis,in order to effectively improve the mechanical and adjust the microstructure of the alloy,the effects of different pre-deformation on the mechanical properties and microstructure of DT740 alloy were studied systematically,and the deformation strengthening and precipitation strengthening mechanism were also analyzed,thereby,which provides a theoretical basis for optimizing the cold plastic forming process parameters of the alloy.In addition,in order to solve the problem that the alloy is easy to crack and scrapped during the forging process,the high temperature plastic deformation law of the alloy is also studied in this thesis,and analyzing its dynamic recrystallization behavior,which provide theoretical reference and experimental basis for the hot extrusion process of the alloy.Through experimental research,the work hardening curve of DT740 alloy conforms to the Ludwigson model and has linear hardening stage and parabolic hardening stage,when the pro-deformation is 35%,the alloy's strong plasticity is the best;And the mathematical model between the strength,hardness and pre-deformation of the alloy has good fitting and predictability,which has certain guiding significance for the engineering production practice of the alloy.In addition,the deformation strengthening of DT740 alloy mainly comes from the increase of dislocation density,and the precipitation strengthening mainly comes from the precipitation of nanoscale Ni₄W phase.When the pre-deformation is 0%and 15%,the dislocation pattern in the alloy is mainly low-density dislocation-dislocation line,the dislocation density is low,the volume fraction of the precipitated phase is small and the distribution is uneven;When the pre-deformation is 0%and 15%,the dislocations form high-density dislocation-cell structure,the dislocation density is high,the volume fraction of the precipitated phase is larger and the distribution is more uniform,and the deformation strengthening and precipitation strengthening of the alloy are enhanced.According to the EBSD analysis,after the pre-deformation treatment of DT740 alloy,the grains in the alloy are gradually elongated,the grains have a preferred orientation,and the relative content of small-angle grain boundaries and substructures in the alloy and the KAM value and Taylor value increased.During axial compression deformation of DT740 alloy,the flow stress increases with the decrease of deformation temperature and strain rate,the rheological curve shows typical dynamic recrystallization characteristics.The thermal deformation activation energy Q of DT740 alloy is546.87 KJ/mol,the thermal deformation constitutive equation of the peak stress of the alloy is:?=1.5428×10²⁰[sinh?0.0026_p?]^6.064exp?-546870/R?In addition,the hot working diagram of DT740 alloy was established,and combining with the microstructure analysis,the optimum forging hot working temperature range of DT740 alloy was determined to be:1150¹250°C.In this temperature range,the DT740 alloy can obtain uniform and fine fully dynamic recrystallized structure,and the energy dissipation rate?value is high,about 44%.