Institute of Fundamental Technological Research

The presented paper concerns the technological aspects of the interface evolution in the nickel-silicon carbide composite during the sintering process. The goal of our investigation was to analyse the material changes occurring due to the violent reaction between nickel and silicon carbide at elevated temperatures. The nickel matrix composite with 20 vol pct SiC particles as the reinforcing phase was fabricated by the spark plasma sintering technique. The sintering tests were conducted with variable process conditions (temperature, time, and pressure). It was revealed that the strong interaction between the individual components and the scale of the observed changes depends on the sintering parameters. To identify the microstructural evolution, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy were used. The silicon carbide decomposition process progresses with the extension of the sintering time. As the final product of the observed reaction, new phases from the Ni-Si system and free carbon were detected. The step-by-step materials evolution allowed us to reveal the course of the reaction and the creation of the new structure, especially in the reaction zone. The detailed analysis of the SiC decomposition and formation of new components was the main achievement of the presented paper.

This paper presents the results of studies concerning the production and characterization of Al-SiC/W and Cu-SiC/W composite materials with a 30% volume fraction of reinforcing phase particles as well as the influence of corrosion and thermal shocks on the properties of selected metal matrix composites. Spark plasma sintering method (SPS) was applied for the purpose of producing these materials. In order to avoid the decomposition of SiC surface, SiC powder was coated with a thin tungsten layer using plasma vapour deposition (PVD) method. The obtained results were analysed by the effect of the corrosion and thermal shocks on materials density, hardness, bending strength, tribological and thermal properties. Qualitative X-ray analysis and observation of microstructure of sample surfaces after corrosion tests and thermal shocks were also conducted. The use of PVD technique allows us to obtain an evenly distributed layer of titanium with a constant thickness of 1.5 μm. It was found that adverse environmental conditions and increased temperature result in a change in the material behaviour in wear tests.

metal-matrix composites, silicon carbide, wear resistance, corrosion, thermal shocks

The study presents a detailed analysis of the impact of the coating type of silicon carbide particles and its share by volume on the microstructure and micromechanical properties of Cu-SiC composites. In order to protect the carbide from decomposition during the manufacturing of the composites, the surface of SiC was modified via a plasma vapour deposition technique with a layer of metals (W, Cr, Ti and Ni). Composites with a variable share of the ceramic phase (10–50 %vol.) were obtained at a temperature of 950 °C using spark plasma sintering. An analysis of the structures of the composites, especially in the metal-ceramic boundary region, was conducted with the use of scanning and transmission electron microscopy. The mechanical properties of the composites in the Cu-interface-SiC system were studied via a nanoindentation technique. The comparison of the results of hardness and Young's modulus studies were completed in relation to the actual structures of the materials, which in turn made it possible to determine the impact of the interfacial structure on the global properties of the composite materials.

copper-silicon carbide composites, nanoindentation, SPS, interface study

In the present study, we report a detailed investigation of the unusual size effect in single crystals. For the experiments we specified the hardness in single crystalline copper specimens with different orientations ((001), (011) and (111)) using Oliver-Pharr method. Our results indicates that with decreasing load, after the value of the hardness reached its maximum, it starts to decrease for very small indentation depths (<150 nm). For the sake of accuracy of hardness determination we have developed two AFM-based methods to evaluate contact area between tip and indented material. The proposed exact measurement of the contact area, which includes the effect of pile-up and sink-in patterns, can partially explain the strange behaviour, however, the decrease of hardness at low loads is still observed. At higher loads range the specified hardness is practically constant.

Copper, Single crystal, Nanoindentation, AFM, Size effect

W pracy opisane zostały pomiary emisji akustycznej EA generowanych podczas badania mikrotwardości wgłębnikiem Vickersa, na próbkach krzemowej i stalowej 3 l6L z warstwą węglową. Otrzymane wyniki w postaci wykresów w dziedzinie czasu są porównywane z obserwacjami mikroskopowymi. Za pomocą analitycznego elektronowego mikroskopu skaningowego SEM zobrazowano powierzchnie odcisków, z uwidocznieniem powierzchniowych pęknięć i uszkodzeń. Odcisk mikrotwardości został przecięty z użyciem systemu FIB, zapewniającego odsłonięcie rzeczywistej struktury wewnętrznej materiału w otoczeniu odcisku. Wykonanie sekwencji przekrojów pozwoliło na zobrazowanie SEM przestrzenne uszkodzeń, zwłaszcza typu pęknięcia i rozwarstwienia, a także usytuowanie elementów warstwy wierzchniej i podłoża oraz zasięg odkształceń plastycznych. Zastosowanie obu metod pomiarowych: emisji akustycznej oraz obrazowania mikroskopowego, wzajemnie uzupełniających się, daje wnikliwą diagnostykę do analizy właściwości mechanicznych materiału.

emisja akustyczna, badanie twardości, uszkodzenia, warstwa węglowa RF PACVD, FIB