Influences Of Hydrogenation On Microstructural Evolution Of Ti6Al4V Alloy And Molecular Dynamics Simulation Of Edge Dislocation In β-Ti

Thermo Hydrogen Treatment (THT) is a potential approach, which, by the use of hydrogen as a reversible alloying element, can strongly modify the microstructures and enhance the mechanical properties of titanium alloys. The application of titanium alloys on national defence industry and country construction will be impelled with the development of THT.The microstructures of Ti6A14V alloy after hydrogenation at different temperatures have been investigated and analysed by optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrogenation on the microhardness of a and P phases as well as macrohardness has been analysed by hardness testing, and electron probe microanalysis (EPMA) has been used to study the influence of hydrogenation on alloying elements diffusion. Moreover, the edge dislocation in (3-Ti was simulated and calculated by molecular dynamics simulation method. The results obtained in this paper will be a reference to investigate the influence mechanisms of hydrogenation and then modify the synthetic property of Ti6A14V alloy. The main results are summarized as following:(1) Martensite existed in the specimens after hydrogenation at 750℃. Lamellar hydrides with FCC structure as well as large number of dislocations and twins were found in the specimens with hydrogen content beyond 0.278%. The hardness values ofαandβincrease synchronously with increasing of hydrogen, and the hardness increment ofβis obviously larger than that of a. It is considered that solution strengthening and element diffusion are the main factors causing the hardness of a phase increase with the increasing of hydrogen, and formation of 8 hydrides, lattice defects, solution strengthening and alloying element diffusion jointly cause the hardness ofβincrease with the increasing of hydrogen.(2) The microstructures changed obviously after hydrogenation at 850℃. The specimen with 0.278% hydrogen mainly consisted of basket structure, however, when the hydrogen content reached 0.503%, the specimen mainly consisted of Widmanstaten structure. Hydrides precipitated not only fromβphase but also from a phase at the hydrogenated temperature of 850℃, and special orientation relationship was followed when the hydrides precipitated. The macrohardness of Ti6A14V alloy increased after hydrogenation, and solution strengthening, formation ofδhydrides, interaction between hydrogen and dislocation and martensitic transformation are the main factors causing the hardness of Ti6A14V alloy increases with the increasing of hydrogen.(3) Combined the embedded atom method (EAM) with molecular dynamics (MD) simulation method, the structure of edge dislocation core inβ-Ti was simulated on atomic scales. The energy and location of each atom in the dislocation zone after relaxation were caculated, which could derive the radius of dislocation core rc=5.8847 A and the distortion enengy of dislocation core Ecore=1.598×108eV/cm.