Nanostructural states in Nb-Al mechanocomposite after conbined deformation treatment

Nanostructural states were investigated, that were formed in Nb-Al system-based mechanocomposite after combined deformation treatment that includes mechanical activation in a planetary ball mill and subsequent consolidation by torsion under pressure on Bridgman anvils. The formation of the layered structure, consisting of Nb and Al nanobands with width from several to several tens of nanometers was revealed. The structural states with high elastic curvature of crystal lattice and high level of local internal stresses found in Nb and Al subgrains were investigated by transmission electron microscopy

Formation of TiC-Cu nanocomposites by a reaction between Ti25Cu75 melt-spun alloy and carbon

In this work, Ti25Cu75 melt-spun partially amorphous alloy was used as a source of Ti and Cu to synthesize in-situ TiC-Cu nanocomposites. The reaction between the alloy and carbon started during ball milling and continued during Spark Plasma Sintering. At the same time, during ball milling, the alloy experienced phase transformations: crystallization of the amorphous phase was followed by decomposition of TiCu3. Copper crystallites formed during the alloy transformations were the reason for the presence of copper regions 0.5–1 µm in size free from TiC nanoparticles in the sintered composites. The Ti-Cu intermetallics transformed into non-agglomerated TiC 10–20 nm in size distributed in the copper matrix. The hardness of the synthesized TiC-Cu nanocomposites exceeded that of composites obtained by conventional sintering of ball-milled Ti-C-Cu powders

Crystallization of Ti33Cu67 metallic glass under high-current density electrical pulses

We have studied the phase and structure evolution of the Ti33Cu67 amorphous alloy subjected to electrical pulses of high current density. By varying the pulse parameters, different stages of crystallization could be observed in the samples. Partial polymorphic nanocrystallization resulting in the formation of 5- to 8-nm crystallites of the TiCu2 intermetallic in the residual amorphous matrix occurred when the maximum current density reached 9.7·108 A m-2 and the pulse duration was 140 μs, though the calculated temperature increase due to Joule heating was not enough to reach the crystallization temperature of the alloy. Samples subjected to higher current densities and higher values of the evolved Joule heat per unit mass fully crystallized and contained the Ti2Cu3 and TiCu3 phases. A common feature of the crystallized ribbons was their non-uniform microstructure with regions that experienced local melting and rapid solidification

Thermal explosion in mechanically activated low-calorific-value compositions

The effect of preliminary mechanical activation of low-calorific-value powdered formulations in a planetary ball mill on the main parameters of the subsequent thermal explosion has been studied. It has been found that in mechanically activated compositions, the initiation temperature of thermal explosion is reduced by hundreds of degrees. The maximum decrease (1300°C) is observed for the Ti + 4 wt.% C system. Regimes of preliminary mechanical activation of reaction mixtures and the subsequent thermal explosion conditions producing Ti3Al and Ni3Al single-phase intermetallic compounds with nanometer grain size were determined. For the 3Ni + Al composition, the energy accumulated during mechanical activation was evaluated. It is shown that the initiation temperature of thermal explosion in the MA compositions studied can be used to estimate the temperature that develops in the mill drums

Thermal explosion in mechanically activated low-calorific-value compositions

The effect of preliminary mechanical activation of low-calorific-value powdered formulations in a planetary ball mill on the main parameters of the subsequent thermal explosion has been studied. It has been found that in mechanically activated compositions, the initiation temperature of thermal explosion is reduced by hundreds of degrees. The maximum decrease (1300°C) is observed for the Ti + 4 wt.% C system. Regimes of preliminary mechanical activation of reaction mixtures and the subsequent thermal explosion conditions producing Ti3Al and Ni3Al single-phase intermetallic compounds with nanometer grain size were determined. For the 3Ni + Al composition, the energy accumulated during mechanical activation was evaluated. It is shown that the initiation temperature of thermal explosion in the MA compositions studied can be used to estimate the temperature that develops in the mill drums

The influence of TiC particles on the structure and mechanical properties of Ni3Al manufactured by spark plasma sintering

Using precursors, prepared by a preliminary mechanical activation of the 3Ni–Al powder mixture in the energy-intensive ball mills with and without a subsequent addition of the TiC powder, Ni3Al and Ni3Al+TiC samples are consolidated by spark plasma sintering. By the methods of structure characterization and measurement of mechanical properties a comparative study of the influence of TiC is performed. After consolidation, no influence of the introduced particles on the intermetallic matrix structure parameters is found out. Under the synthesis conditions and during the subsequent high-temperature annealing, TiC does not interact with the intermetallic matrix. The presence of coarse-disperse TiC particles favors an additional embrittlement of the Ni3Al+TiC composite at room temperature, while at elevated temperatures a considerable increase in strength and plasticity is observed compared to pure Ni3Al. It is shown that an increase in the tension temperature gives rise to a change in the fracture mechanisms of the intermetallic matrix and coarse-disperse TiC particles