Deformation modes and size effect in near-gamma TiAl alloys

作者：Monchoux, Jean-Philippe^*; Luo, Jiangshan; Voisin, Thomas; Couret, Alain

来源：Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2017, 679: 123-132.

DOI：10.1016/j.msea.2016.09.092

• Size effects
• Titanium aluminides
• Mechanical properties
• Twinning
• Dislocations

This paper presents a study of a size effect in TiAl alloys. Spark Plasma Sintering is used to sinter several alloys with a near-gamma microstructure. Both the effect of boron as an inhibitor of grain growth and the rapidity of this powder metallurgy process are used to control the grain size. Following a comparison between EBSD-SEM (Electron Backscatter Diffraction by Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy), the grain size is measured by TEM. Tensile tests are performed at room temperature to measure the yield stress. The deformation microstructure is studied by TEM. In a delimited area, activated deformation systems are identified in every grain. Then, for every system, the Schmid's factors as well as the defect nucleation sites are determined. A size effect leading to a high Hall-Petch constant of k=0.98 MPa m(1/2) is measured. The deformation is found to be due to ordinary dislocations and twinning, which are mainly satisfying Schmid's law. Ordinary dislocations are more frequently observed than twins. Twins are found to form pile-ups and to cross the boundaries under the effect of stress concentration. These results are discussed and interpreted on the basis of the pile-up model applied to the Shockley dislocations involved in twinning.

• 出版日期2017-1-2
• 单位中国工程物理研究院激光聚变研究中心; 中国工程物理研究院