A new short flow technique combining in situ reaction and rapid solidification has been developed and used to prepare Cu-TiB2 (0.45, 1.6 and 2.5 wt% TiB2) alloys. The effects of in situ reaction conditions, cooling rate and solute concentration on the microstructure change of Cu-TiB2 alloys were systematically investigated and analyzed by modeling. It is shown that the size and distribution of TiB2 particles are strongly dependent on the choice of reactor shape, in situ reaction conditions and solute concentration, specifically, the size and aggregation level of TiB2 particles tend to increase as increasing normal volume percent of TiB2 particles when the same in situ reaction condition is used. Some different in situ reaction mechanisms, based on the microstructure change and TiB2 particle distribution under different conditions, were also established and analyzed, which can be used to quantitatively predict the size of melt micelles needed for synthesizing uniformly distributed TiB2 particles with different sizes in the copper matrix. (C) 2011 Elsevier B.V. All rights reserved.