Relationships between Texture, Microstructure and Properties in Titanium and some Titanium Alloys

摘要

According to the processing route involving thermomechanical treatments and/or phase transformations, titanium alloys including titanium aluminides exhibit microstructures with different crystallographic and/or morphological textures that can influence use properties. In addition to X-ray and neutron diffraction which allow characterization of the bulk texture, the local texture determination by Electron Back Scattered Diffraction, EBSD, has permitted the texture-microstructure coupling and therefore a better understanding of the "microstructure-texture-properties" relationships. Another important aspect deals with the control of the microstructure during the processing route. However, in many cases the use of Transmission Electron Microscopy, TEM, remains necessary to study substructure and microtexture of highly deformed or slightly recovered materials. The automatic or semiautomatic indexing of diffraction patterns: spot patterns or Kikuchi lines, allows orientation mapping of the microstructure. Some examples of the evolution of the texture-microstructure couple in some titanium and titanium alloys for the main stages of a processing route will be presented and discussed. In a first, step evolution of texture and microstructure in a γ/α_2 titanium aluminide according to the heat treatment conditions after solidification and forging will be discussed. Then the experimental rolling texture formation will be presented and compared to the simulated textures in the case of α titanium and a TA6V4 alloy, recrystallisation texture formation will be also discussed. Influence of local texture on fatigue resistance will be presented in the case of a TA6V4. Finally, polycrystalline modeling in the β field of a Ti17 alloy will be presented.