Reactive pressureless infiltration technique for Cu-alloy/TiB₂ and other in situ composites: processing, modeling and analysis

Victoriya Shtessel

doi:10.17918/00009972

Reactive Pressureless Infiltration (RPI) was achieved successfully by the in situ synthesis of Cu-Mn/TiB₂ composite materials. RPI-processed Cu-Mn/TiB₂ composite materials with 7 to 40 v/o TiB₂ exhibit microstructures with fine (0.5-5 [mu]m) and evenly dispersed reinforcement and high room temperature strength and hardness. Infiltration occurs spontaneously at relatively low temperatures (980-1050°C), and does not require complex processing equipment. Primary factors which alter phase composition and microstructure of the MMCs are enthalpy and relative free energy of reinforcement formation, initial powder size, processing temperature and matrix wettability of the reinforcement. Employment of the matrix assisted displacement reaction between the Cu-Ti liquid and MnB₂: MnB₂ + Cu-Ti [yields] TiB₂ + Cu-Mn ensures in situ formation of fine TiB₂ particulates in the Cu-Mn matrix. The reaction also provides for the spontaneous infiltration of the solid MnB₂ preform by Cu-Ti liquid due to wettability. The process can be carried out below the melting point of the Cu because alloying Cu with Mn decreases the liquidus temperature of the alloy and causes diffusional melting of the infiltration front. Possible mechanisms for the evolution of the microstructure during processing are proposed and analyzed. The study demonstrates that TiB₂ is formed by interfacial reaction: Ti + MnB₂ = TiB₂ + Mn. A detailed kinetic model of the reactive pressureless infiltration is proposed. The model evaluates the diffusion, infiltration and reaction processes and predicts the infiltration rate, the thickness of the reacted layer as a function of time, the rate of reaction of TiB₂ formation and the concentration profile of each component in the reactive layer. The model establishes the effects of processing parameters such as reaction time and temperature, wetting of the preform by the melt, preform porosity, preform composition and volume fraction of reinforcement on the infiltration kinetics. It also establishes the limiting stages of infiltration. The proposed model shows good agreement with experimental results and provides a tool for analysis of infiltration kinetics in reactive systems. It may be applied to other systems for different chemistries, properties and geometries to establish process feasibility.

Reactive pressureless infiltration technique for Cu-alloy/TiB₂ and other in situ composites: processing, modeling and analysis

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Reactive pressureless infiltration technique for Cu-alloy/TiB₂ and other in situ composites: processing, modeling and analysis

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