Search

In recent decades, spark plasma sintering (SPS) has become a widespread technique in the production of high-quality intermetallic-based materials. In this study, we used SPS to fabricate multilayer metal-intermetallic (MIL) composites from pure nickel and aluminum foils. The effect of sintering temperature and pressure on the structure and properties of the fabricated MIL composites is discussed. The sintering temperature was changed from 900 to 1100 °C, the pressure varied from 10 to 40 MPa. The structure of the materials was investigated using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy-dispersive spectroscopy (EDX), and X-ray diffraction (XRD). Depending on the sintering regimes the intermetallic layers in the composites consisted of Ni2Al3, Ni3Al, and NiAl of cubic and tetragonal modifications. Tetragonal NiAl appeared in the form of microtwinned lamellar martensite. A change in SPS temperature from 900 to 1100 °C led to an increase in the volume fraction of nickel-enriched intermetallic compounds, which was accompanied by improving composites strength. With an increase of the SPS pressure from 10 to 30 MPa, the number of pores and cracks in composites decreased. At the same time, their bending strength increased by 2 times (from 450 to 900 MPa). Fractographic studies showed that the fracture mechanism of the intermetallic layers depends on their elemental composition and varies from brittle transcrystalline to wavy “feathery”.

In this study, the non-vacuum electron beam (EB) technology was used to clad commercially pure (CP-) Ti with Ta and Nb. The microstructure of the samples was characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The cladded layers were 1.7–2.7 mm thick and had a dense defect-free structure. Compositional inhomogeneity caused by dendritic liquation was observed in the cladded layers. High cooling rates during non-vacuum EB cladding led to the formation of the α’, α”, β, and ω metastable phases in the samples. The nanoscale ω phase was found in the regions with a high amount of Ta and Nb. Due to the increase in the Nb and Ta content, the microstructure of the samples was refined, and the microhardness increased from 330 HV to 400 HV. The impact toughness of the materials with cladded layers remained at a sufficiently high level (180–250 J/cm2). Corrosion tests carried out in hot nitric acid revealed that the addition of 15% Ta and 11.3% Nb to Ti decreased the corrosion rate from 0.104 mm/year to 0.004 mm/year, which was related to an increase in the fraction of Ta and Nb oxides in the oxide film. The produced materials can be recommended as a relatively cheap alternative for nuclear waste recycling when a hot solution of nitric acid is used.

Titanium and titanium alloys are highly important structural materials for many industries where low density in combination with high mechanical strength and corrosion resistance are required. However, titanium is not applicable for tribological or high temperatures purposes due to its interaction with atmospheric gases and friction seizure during the contact with most metallic materials. To protect the surface of titanium and improve its wear resistance intermetallic coatings can be applied. In this study, the Ti-Al intermetallic layers were fabricated on Ti surface by electron beam melting of Al and Ti powders. By variation of Al/Ti ratio in the initial powders it was possible to control elemental and phase composition of the layers. The formation of TiAl, Al2Ti and Ti3Al phases was observed in the layers. Independently on Al content the layers had lamellar type of structure. Microhardness, wear resistance and oxidation resistance were measured to evaluate the quality of the layers. The microhardness and wear resistance were in good agreement with each other. The coating, consisted of pure Ti3Al phase, demonstrated the highest level of these properties. Oxidation resistance of the coatings increased proportionally to the aluminium content due to formation of alumina in oxide scale.

In this study, the effect of copper on the structure and properties of cast iron is discussed. The experimental samples, with copper content from 0.09 wt% to 14.2 wt%, were synthesized in an induction furnace. The structure of the samples was characterized using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of copper on the volume fraction of graphite and pearlite, and its interlamellar spacing and the tendency of the composites to form a white iron structure are discussed. In particular, precipitation of e-copper was investigated. For a better understanding of the structural evolution, the isoplethal section of 3 wt% C in the Fe-Cu-C phase diagram was calculated. The hardness, tensile strength, friction coefficient and wear resistance of the composites were measured. The addition of copper leads to hardening and strengthening of the composites. However, at a high copper content, the strength of alloys decreases due to the formation of a brittle white iron structure. Copper has a positive effect on the friction coefficient and reduces wear resistance by promoting the formation of ledeburite.