Structure and Phase Composition of a W-Ta-Mo-Nb-V-Cr-Zr-Ti Alloy Obtained by Ball Milling and Spark Plasma Sintering.

In this paper, the structural characteristics of a W-Ta-Mo-Nb-V-Cr-Zr-Ti non-equiatomic refractory metal alloy obtained by spark plasma sintering (SPS) of a high-energy ball-milled powder mixture are reported. High-energy ball milling resulted in the formation of particle agglomerates ranging from several tens to several hundreds of micrometers. These agglomerates were composed of micrometer and submicrometer particles. It was found that, during ball milling, a solid solution of A2 structure formed. The grains of the sintered material ranged from fractions of a micrometer to several micrometers. During SPS, the phase transformations in the alloy led to the formation of a Laves phase of C15 structure and ZrO and ZrO2 nanoparticles. The microhardness of the ball-milled alloy and sintered material was found to be 9.28 GPa ± 1.31 GPa and 8.95 GPa ± 0.42 GPa, respectively. The influence of the processing conditions on the structure, phase composition, and microhardness of the alloy is discussed.

Combustion of Titanium-Carbon Black High-Energy Ball-Milled Mixtures in Nitrogen: Formation of Titanium Carbonitrides at Atmospheric Pressure.

In this work, titanium carbonitrides were synthesized by self-propagating high-temperature synthesis (SHS) in nitrogen. For the first time, the synthesis of titanium carbonitrides by combustion was realized in nitrogen at atmospheric pressure. The synthesis was carried out by subjecting high-energy ball-milled titanium-carbon black powder mixtures to combustion in a nitrogen atmosphere. The influence of the ball milling time on the phase composition of the products of SHS conducted in the Ti+0.3C reaction mixture was studied. It was found that the titanium-carbon black mixtures need to be milled for a certain period of time for the combustion synthesis to yield a single-phase carbonitride product.

Interaction of a Ti⁻Cu Alloy with Carbon: Synthesis of Composites and Model Experiments.

Titanium carbide (TiC), is the most thermodynamically stable compound in the Ti-C-Cu system, which makes it a suitable reinforcement phase for copper matrix composites. In this work, the interaction of a Ti-Cu alloy with different forms of carbon was investigated to trace the structural evolution leading to the formation of in-situ TiC-Cu composite structures. The reaction mixtures were prepared from Ti25Cu75 alloy ribbons and carbon black or nanodiamonds to test the possibilities of obtaining fine particles of TiC using ball milling and Spark Plasma Sintering (SPS). It was found that the behavior of the reaction mixtures during ball milling depends on the nature of the carbon source. Model experiments were conducted to observe the outcomes of the diffusion processes at the alloy/carbon interface. It was found that titanium atoms diffuse to the alloy/graphite interface and react with carbon forming a titanium carbide layer, but carbon does not diffuse into the alloy. The diffusion experiments as well as the synthesis by ball milling and SPS indicated that the distribution of TiC particles in the composite structures obtained via reactive solid-state processing of Ti25Cu75+C follows the distribution of carbon particles in the reaction mixtures. This justifies the use of carbon sources that have fine particles to prepare the reaction mixtures as well as efficient dispersion of the carbon component in the alloy-carbon mixture when the goal is to synthesize fine particles of TiC in the copper matrix.

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.PACS: 81; 81.05.Bx; 81.05.Kf.