Mechanically alloyed nanocomposites

Solid state and liquid phase sintering of mechanically activated W–20 wt.% Cu powder mixture

Effect of particle size and ratio of B4C reinforcement on properties and morphology of nanocrystalline Al2024-B4C composite powders

article i nfo Article history: Received 16 June 2012 Accepted 27 August 2012 Available online xxxx Sintering and cyclic oxidation behavior of nanostructured W-Cr alloys having 30, 50 or 60 at% Cr, prepared through mechanical alloying of elemental blends have been investigated Relative density of 96-975% could be achieved by sintering at 1700 °C X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy have shown the presence of W-rich and Cr-rich phases in sintered alloys The oxidation resis- tance during exposure at 800 °C is found as the highest in the W04Cr06 alloy, while that at 1000 °C and 1200 °C appears to be the best for the W05Cr05 alloy Relatively finer and more uniform distribution of the Cr-rich phase in microstructure of the W05Cr05 alloy appears to be responsible for its superior oxidation resistance The Cr2O3 is found to be primarily responsible for protection against oxidation at 800 °C, while

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Microstructure and cyclic oxidation behavior of W-Cr alloys prepared by sintering of mechanically alloyed nanocrystalline powders

W-20 wt%Cu alloy, with a high sintering density of 99.2% theoretical density (%TD), ultrafine grain size of 500 nm, and hardness of 310 HV, was fabricated by mechanical alloying and high pressure sintering (HPS). The changes of morphology and structural evolution of W-Cu powders during mechanical alloying process were observed and studied, and the effects of temperature and pressure on the density of sintered compacts were studied. Results showed that nanostructured (NS) mechanical alloyed (MA) W-Cu powders were obtained after a 40 h milling at a milling speed of 400 rpm, and the W-Cu alloy had nanocrystalline structure and shape retention with nearly full densification when the HPS of NS MA W-Cu powders was carried out at 1050 °C with a pressure of 40 MPa. The densification behavior of NS MA W-Cu powders during HPS was also studied, including a nanosintering within the MA powders during heating and a global rearrangement and sintering when an external pressure was applied.

Preparation of W-Cu alloy with high density and ultrafine grains by mechanical alloying and high pressure sintering

In the present investigation, attempts have been made to synthesize W–Cu nanocomposites by mechanical alloying (MA) and the results show that MA is a very good processing technique in making these nanocomposites. Elemental tungsten and copper are also milled. Characterization techniques like XRD, TEM and SEM have been used to study the crystallite size, r.m.s. strain and their morphology changes on milling. Crystallite size of tungsten was found to 15 nm and that of copper as 40 nm after 20 h of milling. Tungsten being brittle has lower crystallite sizes than copper on milling. Copper being ductile has good cushioning effect and tungsten crystallite sizes are relatively higher in the as-milled W–Cu samples when the fraction of copper is higher in W–Cu system. Elemental tungsten, elemental copper and W–Cu nanocomposites obtained after milling for 20 h were subjected to annealing at 400, 600, and 800 °C for 2 h and the phase transformation in these powders was studied.

Syed Nasimul Alam

Papers

Synthesis and characterization of W–Cu nanocomposites developed by mechanical alloying