Synthesis of nanocrystalline α-Al₂O₃ from nanocrystalline boehmite derived from high energy ball milling of gibbiste

Dry milling of gibbsite has been carried out for 5 h in planetary ball mill to study the effect of mechanical activation on α-Al2O3, formation. Gibbsite undergoes phase transformation during milling and has resulted nanocrystalline boehmite after 5 h of milling. The average crystallite size and the BET surface area of the nanocrystalline boehmite resulted by 5 h milling of gibbsite are 8 nm and 140 m2/g, respectively. The nanocrystalline boehmite has shown reduction in the α-Al2O3 formation temperature as well as in the activation energy of α-Al2O3, formation. The average crystallite size of nanocrystalline boehmite derived α-Al2O3 is measured to be 100 nm by TEM analysis and the BET surface area of resulted nanocrystalline α-Al2O3 is 12 m2/g

Synthesis of in-situ NiAl-Al<SUB>2</SUB>O<SUB>3</SUB> nanocomposite by reactive milling and subsequent heat treatment

NiAl-30 vol.% Al2O3 nanocomposite has been synthesized from the NiO-Al-Ni powder mixture by carrying out reactive milling in toluene medium and subsequent heating. The NiO reduction and the ordered NiAl phase formation occur simultaneously during milling. The unreacted NiO present in as milled powder is reduced by Al/NiAl at 420 ° C on heating. Subsequent heating leads to the formation of a small amount of Ni3Al phase before it transforms completely to NiAl phase above 900 ° C. Amorphous alumina is formed as the product of NiO reduction and it transforms to stable α -Al2O3 at 1000 ° C via the formation of metastable transition γ -Al2O3. After heating to 1120 ° C, the 20 h milled powder consists of nanocrystalline NiAl phase and α -Al2O3 with a crystallite size of 115 ± 40 nm size and 11 ± 3 nm, respectively

Development of in situ NiAl-Al<SUB>2</SUB>O<SUB>3</SUB> nanocomposite by reactive milling and spark plasma sintering

NiAl-10 vol.% Al2O3 in situ nanocomposite has been synthesized by reactive milling and subsequent spark plasma sintering. The synthesized nanocomposites have ~96% of theoretical density after sintering at 1000 °C for 5 min. Microstructural analysis of consolidated samples using TEM has revealed the presence of α-Al2O3 particles of 10-12 nm size in NiAl matrix of submicron grain size. Consolidated NiAl-10 vol.% Al2O3 nanocomposite has shown very high hardness of 772 HV0.3 and compressive strength of 2456 MPa with ∼14% plastic strain. The high hardness and compressive yield strength are attributed to the presence of nanocrystalline α-Al2O3 particles and the appreciable plastic strain is attributed to the submicron grains of NiAl

Influence of heat of formation of B2/L1<SUB>2</SUB> intermetallic compounds on the milling energy for their formation during mechanical alloying

In this paper an attempt has been made to arrive at a relation between the heat of formation of an intermetallic and the milling energy required for its formation during mechanical alloying. This has been demonstrated in case of B2 intermetallic compounds, namely, NiAl, FeAl, CoAl and MnAl. The milling energy corresponding to the start of formation of the compounds during mechanical alloying of the elemental blends is found to decrease linearly with the heat of formation of the intermetallics, calculated using the Miedema's model. Al<SUB>3</SUB>Zr, Ni<SUB>3</SUB>Al, Ni<SUB>3</SUB>Mn, CoFe, NiTi, Zr<SUB>3</SUB>Co are also synthesized in an attempt to test the strength of the hypothesis over a wider range of compounds as well as enthalpy of mixing. An attempt has been made to understand the mechanism of the compound formation

Development of Ni-Al<SUB>2</SUB>O<SUB>3</SUB>in-situ nanocomposite by reactive milling and spark plasma sintering

In the present study, Ni-30 vol pct Al2O3 in-situ nanocomposite was developed by reactive milling of NiO-Al-Ni powder mixture followed by spark plasma sintering (SPS). During milling, fcc to hcp transformation was observed in Ni(Al) phase and it transformed back to fcc phase around 773 K (500 &#176;C). The hardness and yield strength of Ni-30 vol pct Al2O3 nanocomposite are approximately two times higher than that of pure Ni of similar grain size. The improved mechanical properties of nanocomposite are attributed to the presence of alumina particles of nanometer size

Microstructure and mechanical property of Fe-Al₂O₃ nanocomposites synthesized by reactive milling followed by spark plasma sintering

The in-situ Fe based nanocomposite containing Al2O3 particle is synthesized by reactive milling of Fe2O3-Al-Fe powder mixture in toluene medium followed by consolidation of powders using Spark Plasma Sintering process. Transmission electron microscopy investigation of consolidated Fe- Al2O3 nanocomposites has shown heterogenous grain structure of Fe consisting of nano, submicron and micron size grains together with nanometer Al2O3 particles. The hardness of Fe- Al2O3 nanocomposites consolidated at 800°C is 795 MPa