Refinement of lamellar microstructures by boron incorporation in GE-TiAl alloys processed by Spark Plasma Sintering

The aim of this study is to check the efficiency of boron in refining lamellar microstructures of TiAl alloys densified by Spark Plasma Sintering. Boron-containing TiAl47Cr2Nb2B0.6 and boron-free TiAl47Cr2Nb2 alloys were consolidated at varying temperatures. Their microstructures were studied by both scanning and transmission electron microscopies and their tensile properties were measured at room temperature. The structures and chemical composition of borides were analyzed. With the formation of borides, this addition of boron reduces the final grain size and promotes the formation of an unusual quasi-lamellar microstructure during cooling. Borides act as obstacles to the growth of the α grains at high temperature. They are also nucleant of the γ lamellae during cooling, thus increasing the temperature of lamellar transformation. Due to this high temperature nucleation, the quasi-lamellar microstructure is mainly formed by wide γ lamellae. Boron containing alloys exhibit both an interesting ductility and very reproducible mechanical properties, even when sintered at different temperatures.

The addition of boron in alloys processed by Spark Plasma Sintering leads to the formation of an unusual quasi-lamellar microstructure, which exhibits good ductility and reproducible properties (a). It has been studied by SEM (b) and TEM (c).Figure optionsDownload as PowerPoint slideHighlights
► Boron is successfully used to refine the microstructure of TiAl alloys processed by SPS.
► The boron addition leads to the formation of an unusual quasi-lamellar microstructure.
► The quasi-lamellar microstructure exhibits a high ductility and very reproducible properties.