Characterization of nanocrystalline monolithic copper, titanium, titanium diboride and composite copper/titanium diboride particles and consolidate

Nanocrystalline materials have received considerable attention due to their novel properties. Their refined microstructures lead to high strengths and toughnesses relative to their coarse-grained counterparts. Properly designed nanostructured metal-matrix composites should maintain high strengths at elevated temperatures. Nanocrystalline powders of titanium diboride, titanium, copper and composite copper-coated titanium diboride were produced with two methods in the present research: low temperature solution phase synthesis and high temperature gas phase combustion synthesis. Powders from the two methods were fully characterized, primarily with electron microscopy, electron diffraction and X-ray diffraction to determine size, morphology, crystal structure and phase purity. Nanostructured powders varying in size from 1 nm to greater than 100 nm, have been produced by both methods. Due to extremely fine size of the powders, they have been observed to be unstable in air and subject to oxidation and other transformations. Convergent beam single crystal electron diffraction studies have characterized the crystal structure of the particles as it relates to external particle morphology. The effects of extremely large surface to volume ratios were observed as morphology variations in powders as were the effects of the two synthesis methods on the evolution of particle morphology. Powders have been consolidated by vacuum hot pressing and hot isostatic pressing, to produce compacts. Consolidates were observed to retain refined microstructures at high densities but were subject to impurities. Composite compacts with high volume fractions of nano-reinforcements were attained which would not be feasible with conventional processing methods. Deformation studies via electron microscopy and mechanical testing were performed on Cu compacts and revealed very high strengths and high recrystallization temperatures which were attributed to incorporated boron. Characterization provided feedback throughout the production process to develop production methods and improve the powders and bulk materials.