The beneficial effects of boron addition on microstructure transformations and
mechanical properties of γ-TiAl alloys were investigated. Two growth mechanisms of boride (TiB2)
in γ-TiAl alloy were confirmed, the curved flaky borides are products of irregular eutectic reaction
growing coupled with matrix, while some faceted blocky borides in boron-rich alloy are primary
TiB2 phase growing directly in melt. The core of flaky TiB2 is ultra-fine B2 phase and there has an
orientation relationship [1210] TiB2//[001]B2, (1010) //(010)B2. In addition to the well-known
grain refinement effect, boron addition can suppress the formation of metastable feathery and
Widmastätten structure and broadens cooling-rate-range for the formation of fully lamellar structure,
consequently, it improves thermal stability of the lamellar structure and accordingly prolongs the
creep rupture life significantly. Another beneficial effect of boron addition is that boride can
restrain discontinuous coarsening on lamellar grain boundary by pinning action and accelerates
recrystallization of γ grain by introducing TiB2/matrix interfaces as nuclear sites during
homogeneous treatment at 1150°C. Therefore, compared with boron-free alloy more homogeneous
and refined near γ microstructure can be obtained in boron modified alloy.