Competitive precipitation behavior of hybrid reinforcements in copper matrix composites fabricated by powder metallurgy

Copper matrix composites reinforced by in situ-formed hybrid titanium boride whiskers(TiB_(w))and titanium diboride particles(TiB_(2p))were fabricated by powder metallurgy.Microstructural observations showed competitive precipitation behavior between TiB_(w) and TiB_(2p),where the relative contents of the two reinforcements varied with sintering temperature.Based on thermodynamic and kinetic assessments,the precipitation mechanisms of the hybrid reinforcements were discussed,and the formation of both TiB_(w) and TiB_(2p) from the local melting zone was thermodynamically favored.The precipitation kinetics were mainly controlled by a solid-state diffusion of B atoms.By forming a compact compound layer,in situ reactions were divided into two stages,where Zener growth and Dybkov growth prevailed,respectively.Accordingly,the competitive precipitation behavior was attributed to the transition of the growth model during the reaction process.

In situ TiB2/Cu composites fabricated by spray deposition using solid-liquid and liquid-liquid reactions

In situ TiB2/Cu composites were fabricated by both solid-liquid(S-L)and liquid-liquid(L-L)reactive spray deposition in combination with cold rolling and annealing.The microstructure and properties of the fabricated TiB2/Cu composites were investigated.The results show that the reactive mode and rolling treatment are the main factors affecting the microstructure and properties of the TiB2/Cu composite.The in situ reaction in the L-L reaction can be carried out more completely.By controlling the rolling and annealing process,the relative density and the properties of the as-deposited composites are optimized.The comprehensive performance of the deformed TiB2/Cu composite prepared by L-L reactive spray deposition(401 MPa and 83.5%IACS)is better than that by S-L reactive spray deposition(520 MPa and 20.2%IACS).

Analytical Description for Solid-State Phase Transformation Kinetics:Extended Works from a Modular Model, a Review

Solid-state phase transformation plays an important role in adjusting the microstructure and thus tuning the properties of materials. A general modular, analytical model has been widely applied to describe the kinetics of solid-state phase transformation involving nucleation, growth and impingement; the basic conception for iso-kinetics which constitutes a physical foundation for the kinetic models or recipes can be extended by the analytical model. Applying the model, the evolution of kinetic parameters is an effective tool for describing the crystallization of enormous amorphous alloys. In order to further improve the effectiveness of this kinetic model, recently, the recipes and the model fitting procedures were extended, with more factors （e.g., anisotropic growth, soft impingement, and thermodynamic driving force） taken into consideration in the modified models. The recent development in the field of analytical model suggests that it is a general, flexible and open kinetic model for describing the solid-state phase transformation kinetics.