EFFECT OF AL ON OMEGA-PHASE-TRANSFORMATION BEHAVIOR IN TI-8V-5FE-(1-3) AL-ALLOY

Changes of microstructure by aging Ti-8V-5Fe-(1.3-3.3)Al alloy system were studied to clarify the effect of chemical compositions on omega t ransformation of these titanium alloys. Three different alloys whose a luminum content varies from 1.3 to 3.3 mass% were prepared by are reme lting method. The materials used were hot rolled in beta phase region and solution treated at 1223K, followed by water quenching. Vickers ha rdness were measured for the materials which were as-quenched and aged at 623K. Based on hardness data, X-ray diffraction and TEM experiment s were conducted. A slight difference in hardness for as-quenched samp les was dependent upon aluminum content. This indicated that aluminum suppresses a formation of athermal omega phase in Ti-8V-5Fe-(1.3-3.3)A l alloy system. Relative intensity of diffuse scattering measured from digitized electron diffraction patterns, increased with decreasing al uminum content. X-ray diffraction pattern did not changed drastically within 0.6 ks aging, nevertheless isothermal omega and alpha transform ations also occurred over 3.6 ks aged samples. Within the aluminum con tent for this study, these transformations seemed to be suppressed by increasing aluminum. Isothermal omega particles in over aged samples r anged from 10 to 50nm in size, and these fine precipitants were though t to be a main factor for age hardening in this alloy system.