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Field Assisted Sintering Technique Compaction of Ultrafine-Grained Binderless WC Hard Metals

100%

Dopita M., Salomon A., Chmelik D., Reichelt B., Rafaja D.

Acta Physica Polonica A

2012

vol. 122

issue 3

639-642

Tungsten carbide (WC) powder having a crystallite size around 55 nm and the Brunauer-Emmett-Teller specific surface area 2.75 m^2/g was sintered using the field assisted sintering/spark plasma sintering technique. Sintered samples were investigated using different analytical methods providing detailed information on the microstructure and mechanical properties of materials. Density and porosity of specimens were determined using the Archimedes principle and optical and scanning electron micrographs. The X-ray diffraction investigations provided the information on the crystal real structure and crystallite sizes. The electron backscatter diffraction measurements yielded the details about the grain size, frequency, and distributions of grain boundaries. Finally, the essential mechanical properties of sintered samples were obtained from the hardness and fracture toughness measurements. The influences of individual sintering conditions: sintering temperature and sintering time especially, on the microstructure and mechanical properties of sintered specimens were derived. Fully compact samples having the Vickers hardness HV10 around 29 GPa and fracture toughness K_{Ic} approximately 7.2 MPa m^{1/2} were sintered from temperatures of 1800C and holding times 1 min. Specimens sintered at lower temperatures showed lower density which resulted in a significant drop in the sample hardness.

Microstructure and Properties of Spark Plasma Sintered Al-Zn-Mg-Cu Alloy

86%

Becker H., Dopita M., Stráská J., Málek P., Vilémová M., Rafaja D.

Acta Physica Polonica A

2015

vol. 128

issue 4

602-605

The microstructure of an aluminum alloy containing 53 wt% Zn, 2.1 wt% Mg and 1.3 wt% Cu as main alloying elements has been studied with the focus on the precipitation behavior during the spark plasma sintering process. The starting material was an atomized Al-Zn-Mg-Cu powder with the particle size below 50 μm. The particles showed a solidification microstructure from cellular to columnar or equiaxed dendritic morphology with a large fraction of the alloying elements segregated in form of intermetallic phases, mainly (Zn,Al,Cu)₄₉Mg₃₂ and Mg₂(Zn,Al,Cu)₁₁, at the cell and dendrite boundaries. The microstructure of the sintered specimens followed the microstructure of the initial powder. However, Mg(Zn,Al,Cu)₂ precipitates evolve at the expense of the initial precipitate phases. The precipitates which were initially continuously distributed along the intercellular and interdendritic boundaries form discrete chain-like structures in the sintered samples. Additionally, fine precipitates created during the sintering process evolve at the new low-angle boundaries. The large fraction of precipitates at the grain boundaries and especially at the former particle boundaries could not be solved into the matrix applying a usual solid solution heat treatment. A bending test reveals low ductility and strength. The mechanical properties suffer from the precipitates at former particle boundaries leading to fracture after an outer fiber tensile strain of 3.8%.

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2 Acta Physica Polonica A

1 2015

1 2012

2 Dopita M.

2 Rafaja D.

1 Becker H.

1 Chmelik D.

1 Málek P.

1 Reichelt B.

1 Salomon A.

1 Stráská J.

1 Vilémová M.

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Field Assisted Sintering Technique Compaction of Ultrafine-Grained Binderless WC Hard Metals

Microstructure and Properties of Spark Plasma Sintered Al-Zn-Mg-Cu Alloy