Performance Comparison of Al–Ti Master Alloys with Different Microstructures in Grain Refinement of Commercial Purity Aluminum
Three types of Al–5Ti master alloys were synthesized by a method of thermal explosion reaction in pure molten aluminum. Performance comparison of Al–5Ti master alloy in grain refinement of commercial purity Al with different additions (0.6%, 1.0%, 1.6%, 2.0%, and 3.0%) and holding time (10, 30, 60 and 120 min) were investigated. The results show that Al–5Ti master alloy with blocky TiAl3 particles clearly has better refining efficiency than the master alloy with mixed TiAl3 particles and the master alloy with needle-like TiAl3 particles. The structures of master alloys, differing by sizes, morphologies and quantities of TiAl3 crystals, were found to affect the pattern of the grain refining properties with the holding time. The grain refinement effect was revealed to reduce markedly for master alloys with needle–like TiAl3 crystals and to show the further significant improvement at a longer holding time for the master alloy containing both larger needle–like and blocky TiAl3 particles. For the master alloy with finer blocky particles, the grain refining effect did not obviously decrease during the whole studied range of the holding time.
Specificity of the titanium-powder alloying tablets usage in aluminium alloys
An issue of improving the extruded titanium alloying elements with the purpose of the components dilution speed and completeness enhancing is discussed in the paper. Investigation of titanium alloying tablet obtained by cold extrusion has been fulfilled. Problems of the powdered titanium densing are listed and discussed. Determined were chemical compositions of titanium alloying elements from different suppliers, implemented was an estimation of mechanical strength subject to the density of tablets, obtained were the data on absorption and dilution in aluminium solutions, studied was the flux and titanium powder distribution in alloying tablet. Сomparative analysis of the alloying tablet porosity has been carried out by means of the ImageJ image analysis and processing software. Molasses has been used in the produced alloying tablet as a binder, which guarantees the flux uniform distribution throughout tablet volume with homogeneous pores formation after annealing, as distinct from the tablets of other manufacturers. The flux uniform distribution throughout tablet volume assures forming the aluminium alloy structure with the given composition of intermetallic compounds. The obtained alloying tablet possesses higher mechanical properties and demonstrates rate of dissolution in aluminium solution 15–20% higher than that of analogues. It was found that titanium powders should have improper (irregular) form and advanced surface of particles to allow pressing them at low pressures in rigid matrices and obtain products in tablets with the required porosity and strength. It was revealed that improvement of flux adhesion with titanium powder and powders compressibility is achieved by means of introducing a binder, molasses, which envelops particles and provide and additional strength of tablets on extrusion.
Anomalous Annealing Behavior of Arsenic Implanted Silicon as a Function of Dose and Energy
Anomalous annealing behavior of damage in As implanted Si has been investigated by channeling effect measurements. Room temperature As implants with doses from 1014 to 2 × 1016cm-2 at energies ranging from 50 to 250 keV into Si were annealed over the range of 600°C to 1100°C. Anneal temperatures ≥ 950°C reduce the disorder for ion doses of 0.5 to 1 × 1016 cm-2 at energies between 50 and 250 keV. Anomalously high residual disorder was found for the intermediate doses of 2 × 1014 to 2 × 10/cm2 implanted above 100 keV. For this intermediate dose, annealing of implants performed at liquid nitrogen temperatures did not show significant reduction in this damage. However implants at 200° to 300°C indicate a lower amount of damage compared to the room temperature implants.