Grain refinement of œ/ß Phase Ti-6Al-4V Alloy by ...

M13After 4 hours annealing, the grain conversion wascompleted and near equiaxed-α grain was occurred withgrain-aspect-ratio is 1.2.frequency807060504030201000 5 10 15 20 25 30 35grain size (micron)after TMTbefore TMTFig. 3.4 α grain distribution of Ti-6Al-4V before TMTwith 20 micron mean grain size andafter TMT (T-64) with 8 micron mean grain sizetensile/yield strength (MPa)2000180016001400120010008006004002000As-recievedEquiaxed, 8 micronEquiaxed, 20 micronWidmanstattengrain shape, sizeMartensitetensile strength yield strength elongationFig. 3.5 tensile properties of Ti-6Al-4V3.3 Influence of microstructures on tensile propertiesThe tensile properties of Ti-6Al-4V were depended onmicrostructures. Tensile and yield strength increase withdecrease in α grain size, from Hall-Petch equation (1).Fig. 3.5 indicated the increase of tensile strength from957.38 to 989.85 MPa and yield strength from 918.18 to942.12 MPa with decrease of α grain size from 20 to 8micron. However, the different grain shapes may affect thedifferent properties. Tensile and yield strength are1604.20 and 1543.82 MPa respectively for Widmanstätenstructure, and are 1741.56 and 1704.10 MPa respectively181614121086420elongation (%)for martensite structure. The differences are resulted bydislocation density and grain orientation change [10].4. Conclusion1. The two processes for grain refinement by TMTare dynamic recrystallization and globularization.2. Dynamic recrystallization was occurred during hotrolling below transus temperature, the temperature ofα/β phase equilibrium, with higher reduction per pass.The dynamically recrystallized grain were equiaxedand refined.3. Globularization was occurred after annealingbelow transus temperature, the material was hot rolledwith lower reduction per pass. The primary-α grainwas produced at the edge, kinking, of flow α structure.4. The tensile properties of Ti-6Al-4V are stronglyinfluenced by the α grain size and shape, because of thedifference in dislocation density and grain orientation.5. AcknowledgementDivision of Materials Technology, School of Energyand Materials, King Mongkut’s University ofTechnology Thonburi and National Metal and MaterialsTechnology Center (MTEC).6. References[1] Ari-Gur, P., Semiatin, S. L., Materials Scienceand Engineering A, A257 (1998) 118.[2] Humphreys, F. J, Prangnell, B. P., Priestner, R.,Solid State and Materials Science, 5 (2001) 15.[3] American Society for Metal, Metal Handbook Vol.9,Ninth Ed, ASM, 1989.[4] Boyer, R., Welsch, G., Collings, E. W., MaterialsProperties Handbook : Titanium Alloys, ASMInternational, 1994.[5] Seshasharyulu, T., Medeiros, S.C., Frazier, W.G.,Prasad, Y.V.R.K., Materials Science and Engineering A,A325 (2002) 113, 117.[6] Elagina, L. A., Gorgienko, A. I., Evmenov, O. P.,Titanium and Titanium Alloys, 2 (1989) 1789.[7] Leica Microsystems Imaging Solutions, Cambridge,United Kingdom, 2001.[8] Ding, R., Guo, Z.X., Computational MaterialsScience, 23 (2002) 209.[9] Miller, R.M., Bieler, T.R., Semiatin, S.L, ScriptaMaterialia, 40 (1999) 1392.[10] Nishimura, T., Tsumori, Y., Shimizu, K., Titaniumand Titanium Alloys, 2 (1987) 1987.