Luo Liangshun

Directional Solidification of TiAl-Based Alloys: Determination of the Primary Phase in Ti-50Al-5Nb Alloy

Abstract In order to obtain excellent comprehensive mechanical properties, it is important to control the lamellar orientation of TiAl-based alloys by directional solidification technology. The control of the lamellar orientation is related closely with the primary phase during the directional solidification of TiAl-based alloys. The identification of the primary phase in directionally solidified TiAl-based alloys is insufficient only according to an isolated two-dimensional micrograph of the lamellar orientation. In this paper, we identified accurately the primary phase according to the quasi three-dimensional micrograph of the lamellar microstructure. The results indicate that the primary phase with various lamellar orientations is β phase during the directional solidification of Ti-50Al-5Nb alloy.

Influences of Fe and B on the Columnar Structure of Ti-46Al Alloys

Abstract The microstructures of Ti-46Al, Ti-46Al-0.3B, Ti-46Al-0.5B, Ti-46Al-2Fe, Ti-46Al-2Fe-0.3B, and Ti-46Al-2Fe-0.5B alloys solidified on water-cooled copper crucible were investigated. It is found that the as-cast alloys possess a typical columnar structure, and the mean diameters of the columnar grains decrease significantly as the addition of Fe or B. The mean columnar diameter in Ti-46Al-2Fe-0.5B is found to be the smallest among these alloys. B addition can increase the constitutional supercooling in front of the solid-liquid interface, which refines the columnar structure and the dendritic structure. Moreover, Fe addition can enhance the refining effect of boron on the columnar structure of TiAl-based alloys.

A Mathematical Model for Determination of Lamellar Spacing in Materials of Poly-Grain Microstructures

Abstract Based on the assumption of spherical grains in polycrystalline materials and the theory of metallography, a mathematical model was developed to calculate the quantitative relationship between apparent and true values of the lamellar spacing cutting through the grain randomly. The results indicate that the grain sizes of most polycrystalline materials are much larger than their lamellar spacings, the ratio of an average apparent value to a true one can be characterized by the corrected coefficient k. The ratio of the apparent lamellar spacing to the grain size reduces from 0.05 to 0.0001, and k increases from 1.5391 to 1.5707, which gradually tends to be π/2. When the ratio of the apparent lamellar spacing to the grain size is smaller than 0.001, value k can be considered as a constant of π/2. The amount of work will be decreased adopting the present model to get the true value of lamellar spacing compared with the conventional methods.