The Dynamic Mechanical Properties Of The U-0.75ti Alloy And The Deformation And Fracture,

When facing study of these problems,for example,Engineering dynamite,exploding process,nuclear exploding,resisting compacting,and so on,the materials are in the state of high strain rate,high pressure,so much as high temperature.So the properties of the materials are different from the quasi-static state.As an important material of armor-piercing bullet, U-0.75Ti alloys stand above the strain rate of 10⁴s^-1 in the armour-piercing process.Studying the dynamic mechnical performance,distortion,shear fracture in the strain rate of 10²ï½ž10⁴s^-1, would avail to the nuclear materials optimizing.Through the process flow of induction smelting→water quenching at 800℃→aging treatment,the nominal U-0.75Ti alloys of three aging state were fabricated.The dynamic compression mechanical properties of U-0.75Ti alloys aged at 200℃,380℃,500℃for 4h were studied by Split Hopkinson Pressure Bar(SHPB) at the strain rates of 10²ï½ž10⁴s^-1.The microstructures before and after compression were observed by optical microscope(OM), scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffractometer(XRD).The main conclusions are reported as following:The micro-analysis of results indicate that microstructre of the U-0.75Ti alloys aged at 200℃were relief acicular martensites.The main metastructures of martensites were layered twinnings.With increasing of temperature the twinnings component became fluctuation and the boundaries corrosion resistant decreased.Grain bounaries of the U-0.75Ti alloys aged at 500℃decomposed two phasesα-U and U₂Ti,and U₂Ti with the nano-diameter were found in the grain inner.In the acicular martensites of the U-0.75Ti alloys aged at 500℃were parallel arranged thin strips(Φ＜50nm) with orientation as the twinning direction.The aging decomposition of the U-0.75Ti alloys initiated at the grain boundaries,then the interfaces of acicular martensites,the twinning boundaries in the end.The strength of the U-0.75Ti alloys increased as the strain rate.The mecchnical properties of U-0.75Ti alloys became dissimilarity with the different strain rate range.The strength sequencing of three aging state U-0.75Ti alloys was the same with quasi-state at the strain rate of 1000s^-1～3600s^-1.The strength of U-0.75Ti alloys aged at 500℃were higher than the other two aging state.The stress-strain curves fitted by the Johnson-Cook of the U-0.75Ti alloys matched with experiment curves at the strain rate of 3000s^-1～5000s^-1.Througth the tracer test indicated the deforming process of the U-0.75Ti alloys.The mian slip bands appeared on the surface after the first compression,sub-slip bands emerged and distributed denseness after the second compression,The mian and sub-slip bands overlapped, simultaneity the micro-cracks came into being after the third compression.The fourth compression would cause shear fracture at 45°included angle with the surface.The plastic properties of the fracture decreased and rheological areas increased with aging temperature going up.Impact compression caused grain tropism change at the low strain rate.