A synthetic route for metal–ceramic interpenetrating phase composites

A novel synthetic route for metal–ceramic interpenetrating phase composites (IPCs) is proposed. The method excludes infiltration operations and eliminates the problem of closed pores and low wettability between ceramic and metal phase. We suggest using two-stage processing including preparation of composite powder precursors by reaction in a metal matrix and subsequent compaction of as-synthesized nanostructured powders. The appropriate choice of compaction technique allows obtaining dense nanostructured bulk IPCs. Bulk interpenetrating phase TiB₂–Cu nanocomposites were fabricated by Spark Plasma Sintering (SPS) and shock wave compaction of powder precursors.     

Structural and Phase Transformations in Alloys during Spark Plasma Sintering of Ti + 23.5 at % Al + 21 at % Nb Powder Mixtures

We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α₂ and Nb₂Al phases and small precipitates of the O-phase (intermetallic compound Ti₂AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.     

Detonation Spraying of Ti–Al Intermetallics: Phase and Microstructure Development of the Coatings

The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti₃Al, TiAl, and TiAl₃ intermetallics. The O₂/C₂H₂ ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl₃ essentially retains in the coatings or partially decomposes forming TiAl and Ti₃Al as minor phases. Detonation sprayed Ti₃Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti₂N and titanium oxynitrides TiN_xO_y. TiAl partially decomposes forming Ti₃Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. The in situ formed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings.     

Control of interfacial interaction during detonation spraying of Ti3SiC2-Cu composites

Changes in the phase composition of the 20 vol % Ti₃SiC₂-Cu composite during detonation spraying as well as corresponding microstructure formation processes in the sprayed coatings have been studied. It was demonstrated that when the amount of the explosive acetylene+oxygen mixture is kept constant (under the constant filled volume fraction of the barrel of the detonation gun of a CCDS2000 facility), the phase composition of the coating depends on the composition of the explosive mixture. The Ti₃SiC₂-Cu system is prone to interfacial interaction; therefore, in order to produce a dense coating preserving the phase composition, oxygen-depleted explosive mixtures should be used and small filled fractions of the barrel. As the temperature of the sprayed particles increases with increasing oxygen content in the explosive mixture, titanium silicon carbide reacts with copper, which results in the formation of the titanium carbide phase and dissolution of the de-intercalated silicon in the copper matrix leading to the formation of TiC _x -Cu〈Si〉 coatings.