Investigation Into The Dynamic Mechanical Properties Of Laser Additive Manufacturing Ti-6Al-4V Alloy

Ti-6Al-4V(TC4)titanium alloys,asα/βtitanium alloys with medium strength and outstanding comprehensive properties,have a great number of applications in the aerospace industry and military equipment industry.However,these materials are often impacted by external objects in the process of use,resulting in failure and damage of materials.Therefore,it is necessary to study the dynamic mechanical properties of materials.In this paper,TC4 titanium alloy samples were manufactured by laser selective melting for research.The effect of laser scanning speed and building angle on the forming quality was studied.The microstructure of the material was controlled by heat treatment.Dynamic mechanical properties of samples with different process parameters were studied by using split Hopkinson pressure bar.To explore the ways to improve the microstructure of laser selective melting forming TC4 alloy and improve the comprehensive mechanical properties of the material.The main research results and conclusions are as follows:1.Flow stress and energy absorption increased firstly and then they dropped sharply as the scanning speed increased from 1.0m/s to 1.6m/s,but no one sample was ruptured.When the scanning speed was 1.2m/s,the maximum flow stress and energy absorption were obtained,which were 1480MPa and 58 J/cm~3,respectively.While they were almost proportional to the building angle,but only sample manufactured at 45°ruptured completely with shearing fracture pattern.In addition,the flow stress and energy absorption increase with the increase of strain rate.SLMed TC4 alloy showed obvious strain rate hardening effect and the sample ruptured at 2100/s finally,which can be characterized by mixed ductility/brittle fracture pattern.2.After solid solution treatment,theα’phase of TC4 sample was decomposed intoα+βphase by laser selective melting.After observation XRD that solution treatment,detected in 40°and 57.5°respectively(110)βand(200)β.With the increase in solid solution temperature,the grain size increases gradually.The intensity of LAGBs first increases and then decreases from the increase in solid solution temperature.When the solid solution temperature exceeds the transition temperature of beta,the intensity of LAGBs decreases sharply due to the formation of widmanstatten structures.At the same strain rate,the flow stress and energy absorption are inversely proportional to the solid solution temperature.3.After the solid solution+aging treatment at different temperature and time,the alloy is a basket-wave morphology,indicating that the aging treatment would not change the structure morphology of the material,but a large number of fine secondary phase particles were distributed in theβphase.With the increase in aging temperature and aging time,grain size first increases and then decreases.With the increase in aging temperature and aging time,the intensity of LAGBs first increases and then decreases,which is directly proportional to the size of grain.TEM observation showed that the number of dislocations in the samples increased after aging treatment and dislocation cells formed.Under the impact on the same strain rate,the flow stress and strain of the aging sample are bigger than those of the untreated sample.The possible reason is that the precipitated phase is generated after the aging treatment,which improves the mechanical properties of the material.The flow stress is inversely proportional to the grain size.Through above the research,the evolution of microstructure and dynamic mechanical response of samples with different process parameters under high strain rate were revealed.The effects of different heat treatment processes of microstructure were revealed.The dynamic mechanical properties of heat treated samples were studied.The results provide a theoretical basis of further optimizing process parameters and further improving the performance of TC4 titanium alloy.