A Study Of Thermo Hydrogen Processing Of TA15 Alloy After Welding

The effect of hydrogen treatment on microstructure and mechanical properties of TA15 alloy weld specimen was studied in this paper. The microstructure was observed by an optical microscope (MS) and a transmission electron microscope (TEM). The surface morphology of tensile fracture was observed by a scanning electron microscope (SEM). The change of phase compositions before and after hydrogenizition and eutectoid treatment was analyzed using X-ray diffraction (XRD). The room temperature tensile properties were carried out on an Instron Series IX automatic testing machine.The results showed thatδ-hydride formed after hydrogenising at 600℃for 3h~700℃for3h, and it has a face-centered cubic structure. And these hydrides brought a strong fuzzy effect on microstructure. Completeα+H→β(H) transmission occurred in the process of hydrogenizition at 800℃for 30min. Using water quenching at the cooling stage, a lot of metastable phaseβ(H) and rhombic martensite phaseα" generated by the effect of a high cooling rate. The phaseα" are parallel to each other and have needle morphology, but have different orientation in different grains. Metastable phaseβ(H) and phaseα" would gradually decompose toαandδphase with eutectoid treatment. The decomposition effect became heavier by the rising of eutectoid treatment temperature.Hydrogen was removed and recrystallization accured in the process of annealing at 750℃for 8h in vacuum. Many small needle phaseαappeared after vacuum annealing. They are parallel to each other and their number and size rised with the temperature of hydrogenization. After annealing at 750℃for 8h in vacuum, the refinement effect to big grains in the fusion area was very obviously. But the big grain boundary wasn't broken completely. The refinement effect only occurred in zhe big size grain. The microstructure of base metal changed little, when the temperature of hydrogenization ranged from 600℃to 700℃, but the grain size grew bigger when hydrogenization at 800℃for 30min and. eutectoid at 300℃for 8h .After anneaning in vacuum, with the increasing of hydrogen content tensile strength and plasticity decreased when the temperature of hydrogenization was 650℃. Though after hydrogenising at 800℃and quenching into water, and then eutectoid at 300℃for 8h, and annealing at 750℃for 8h in vacuum, tensile strength decreased and plasticity increased a little.