Of Sc On The Titanium Alloy Microstructure And Properties Of Impact

In this paper, a series chemistry of Ti-Sc binary alloys . Ti-Al-(Sc) alloys and Ti-6Al-4V-(Sc) alloys were prepared by vacuum arc melting method. The as-cast microstructure and microhardness , microstructure and microhardness after annealing-water quenching treatment , phase analysis of as-cast alloys and annealing-water quenching alloys were performed by optical microscopy (OM), scanning electric microscopy (SEM) , microhardness tester and X-ray diffraction technique. The microstructure evolution of every alloys were discussed in this paper. The influence of Sc on microstructure and micohardness of as-cast alloys and microstructure evolution of alloys were elementarily discussed. Through the study, the following conclusions were obtained:In as-cast Ti-Sc binary alloys, with Sc content decreasing, the feature of microstructure changed from helix , lameller colony to typical bi-model microstructure; small content of Sc (2%~5%) refined the microstructure of alloys significantly; most of Sc soluted in Ti and formed Ti-Sc mutual solid solution, Ti-Sc intermetallics didn't form; with 2% content of Sc, the microhardness of alloys reached the highest value. Treated by annealing-water quenching under the temperature of different phase region, the microstructure of alloys were refined, the size of 3 grains decreased and acicular a martensite phase appeared in microstructure; with the annealing temperature decreasing, the volume fraction of acicular a martensite phase decreased and the opposite tendency for bulk a phases was observed.In as-cast Ti-Al-(Sc) alloys, the addition of metal Sc decreased the volume fraction of Widmanstaten and refined the microstructure of alloys; phases in the alloys were mainly a -Ti and hexagonal Ti3Al and cubic Al3Sc; after annealing-water quenching treatment, the microstructure were refined significantly, acicular a martensite phase and bulk a phase appeared in alloys; with the annealing temperature decreased, the volume fraction of a phase increased; after annealing-water quenching treatment under phase region temperature, the additions of Sc retained highvolume fraction of acicular a martensite phases at this temperature. Sc played a role of stabilizing a phases. After heat-treatment, the microhardness values of alloys were higher than that of as-cast alloys, the highest value was about 651(HV0.01). Alloys with higher content of Al can obtain higher microhardness value after heat-treatment under + phase region temperature; alloys with lower content of Al can obtain higher microhardness value after heat-treatment under phase region temperature.Sc refined the microstructure of as-cast Ti-6Al-4V alloys significantly. The main phase in as-cast alloys was a. -Ti and Ti3Al with hexagonal structure. With the additions of Sc, the diffraction peak of a -Ti in low 2 angles became weaker, while the high 2 9 angles peak of a -Ti became stronger. The solid solution strengthen of Sc increased the microhardness of a plate phases, the highest value was about 513(HV0.01) with 0.3% Sc; the highest microhardness value of phase was about 446(HV0.01) with 0.1% Sc. After annealing-water quenching treatment, the microstructure was refined evidently. Sc played a role of stabilizing a phases in alloys. After heat-treatment strengthen and position of some a -Ti diffraction peaks changed, further more some peaks disappeared, instead of structural extinction, the reason should relate to the different morphology of microstructure , volume fraction of a phase and different orientation of grains. After annealing -water quenching treatment at 700 C, in Ti-6Al-4V-0.5Sc alloy the microhardness value of a phase reached 690(HV0.01).