研究目的
To synthesis and consolidation of nanocrystalline Nb2C–Al2O3 composite within two min from mechanically activated powders using the pulsed current activated sintering, and to evaluate microstructure and mechanical properties of the composite.
研究成果
Nanopowder mixture of Nb2C and Al2O3 was successfully fabricated and densified to 99.7% relative density using PCAS within 2 minutes, resulting in nanograins (24 nm for Nb2C, 40 nm for Al2O3) with improved fracture toughness (5.5 MPa·m1/2) compared to previous studies, though hardness was slightly lower due to inverse Hall-Petch effects at nanoscale.
研究不足
The study does not explicitly mention limitations, but potential areas include the short sintering time possibly limiting full densification or property optimization, and the use of specific equipment and materials that may not be universally applicable.
1：Experimental Design and Method Selection:
The study uses high-energy ball milling to synthesize nanopowder mixture of Nb2C and Al2O3 from Al4C3 and Nb powders, followed by pulsed current activated sintering (PCAS) for rapid consolidation. Thermodynamic feasibility is assessed via Gibbs free energy calculations.
2：Sample Selection and Data Sources:
Powders of 99% pure Al4C3 (-325 mesh) and
3：8% pure Nb (-325 mesh) from Alfa, Inc. are used as starting materials. List of Experimental Equipment and Materials:
High-energy ball mill (Pulverisette-5 planetary mill), tungsten carbide balls (10 mm diameter), stainless steel vial, graphite die (35 mm OD, 10 mm ID, 40 mm height), pulsed current activated sintering system (made by Eltek), pyrometer, X-ray diffraction (XRD) with Cu target, scanning electron microscopy (SEM) with EDAX, Vickers hardness tester.
4：Experimental Procedures and Operational Workflow:
Mix Al4C3 and 6Nb powders by ball milling at 250 rpm for 10 h under air atmosphere with ball-to-powder ratio of 30:
5：Place milled powders in graphite die, evacuate system, apply 80 MPa pressure, heat to 1400°C at 12000°C/min using pulsed current with no holding time under vacuum of 15 Pa, then cool. Measure density by Archimedes method, analyze microstructure with XRD and SEM/EDAX, measure hardness and fracture toughness. Data Analysis Methods:
Grain size calculated using Suryanarayana and Grant Norton's formula from XRD data, hardness measured with Vickers indentation at 20 kg load and 15 s dwell time, fracture toughness calculated using Niihara et al.'s equation from crack lengths.
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