High-energy Ball Milling Of Elemental Powders Research Articles

Formation of Nano-Sized Y2O3 Dispersoids in Mechanically Alloyed Ni–(Cr, Y2O3, Y) Alloys During Heat-Treatments

In the present work, the evolution of nanoparticles during annealing and hot-consolidation in mechanically alloyed Ni-22Cr-1.5Y, Ni-22Cr-1.5Y2O3 and Ni-3% Y2O3 was examined. The high-energy ball-milling of elemental powders resulted in the complete dissolution of the constituent Cr, Y, or Y2O3, forming a Ni-based solid solution. During the subsequent annealing, however, oxide particles precipitated from the solid solution. In the case of mechanically alloyed Ni-22Cr-1.5Y2O3, over-grown Cr2O3 precipitated at a temperature as low as above approximately 500 degrees C and ternary YCrO3 particles precipitated at 1100 degrees C. In the case of mechanically alloyed Ni-22Cr-1.5Y, on the other hand, the binary Y2O3 phase precipitated at 1100 degrees C during spark plasma sintering. The presence of Cr in the alloy composition facilitated the formation of Cr2O3 or YCrO3, and the precipitated oxides were highly prone to grain growth during hot-consolidation, sometimes reaching several micrometers. In Cr-exempt Ni-3%Y or Ni-3% Y2O3, however, the growth of nanodispersoids was restrained even at temperatures as high as 1000 degrees C and the resulting dispersoid was only nano-sized Y2O3.

Synthesis of single-phase Al–Cu–Fe quasicrystals using high-energy ball-milling

Due to their unique combination of physical, thermal and mechanical properties, aluminium-based quasicrystals are of great interest for many applications such as low friction hard coatings. Nevertheless, as quasicrystalline phases are usually stable only within narrow composition domains, their production on an industrial scale meets some difficulties.Alloys with nominal composition Al67Cu23Fe10 were prepared by high-energy ball-milling of elemental powders. The as-milled powder specimens consist of a nanocrystalline Al(Cu,Fe) solid solution. The structural phase transitions of the ball-milled Al–Cu–Fe nanopowders during constant rate heating were investigated by in situ X-ray diffraction at the B2 beamline at desy-hasylab (Hamburg, Germany). High-quality single-phase quasicrystalline (QC) powders were obtained from nanocrystalline precursors by slow heating to temperatures above 750°C. The QC phase is preserved upon quenching and is stable during subsequent heating runs up to 800°C.

Formation mechanism of titanium silicide by mechanical alloying

The syntheses of five titanium silicides (Ti3Si, TiSi2, Ti5Si4, Ti5Si3, and TiSi) by mechanical alloying (MA) have been investigated. Rapid, self-propagating high temperature synthesis (SHS) reactions were involved in producing the last three materials during room temperature high-energy ball-milling of elemental powders. Such reactions appeared to occur through ignition by mechanical impact in the fine powder mixture formed after a critical milling period. From in-situ thermal analyses, each critical milling period for the formation of Ti5Si4, Ti5Si3, and TiSi was observed to be 22, 35.5 and 53.5 minutes, respectively. However, the formation of Ti3Si and TiSi2 did not occur even after 360 minutes of milling of as-received Ti and Si powder mixture, due to the lack of homogeneity of the powder mixture. Other ball-milling procedures were employed for the syntheses of Ti3Si and TiSi2 using different sizes of Si powder and milling medium materials. Ti3Si was synthesized by milling a Ti and 60 minutes premilled Si powder mixture for 240 minutes. α-TiSi2 and TiSi2 were produced by high energy partially stabilized zirconia (PSZ) ball-milling for 360 minutes in a steel vial followed by jar-milling of a Ti and 60 min premilled Si powder mixture for 48 hr. The formation of Ti3Si and TiSi2 occurs through a slow solid state diffusion reaction, and the product(s) and reactants coexist for a certain period of time. The formation of titanium silicides by MA and the reaction rate appeared to depend on the homogeneity of the powder mixture, milling medium materials, and heat of formation of the product involved.

Phase transformation in Nb—16 at.% Si processed by high-energy ball milling

Evolution of phases during high-energy ball-milling of elemental powders of Nb and Si of composition Nb—16 at.% Si were studied as a function of milling time and milling power. Powders obtained were characterized by X-ray diffraction and calorimetry. Milling can result either in NbSi supersaturated solidsolution or in a very fine partially amorphized mixture. Further milling of the amorphous mixture can result in mechanical crystallization and transformation that leads to formation of Nb, and Nb 5Si 3 and Nb 3Si intermetallic compounds.