Single-layer graphene on epitaxial FeRh thin films

Graphene is a 2D material that displays excellent electronic transport properties with prospective applications in many fields. Inducing and controlling magnetism in the graphene layer, for instance by proximity of magnetic materials, may enable its utilization in spintronic devices. This paper presents fabrication and detailed characterization of single-layer graphene formed on the surface of epitaxial FeRh thin films. The magnetic state of the FeRh surface can be controlled by temperature, magnetic field or strain due to interconnected order parameters. Characterization of graphene layers by X-ray Photoemission and X-ray Absorption Spectroscopy, Low-Energy Ion Scattering, Scanning Tunneling Microscopy, and Low-Energy Electron Microscopy shows that graphene is single-layer, polycrystalline and covers more than 97% of the substrate. Graphene displays several preferential orientations on the FeRh(0 0 1) surface with unit vectors of graphene rotated by 30 degrees, 15 degrees, 11 degrees, and 19 degrees with respect to FeRh substrate unit vectors. In addition, the graphene layer is capable to protect the films from oxidation when exposed to air for several months. Therefore, it can be also used as a protective layer during fabrication of magnetic elements or as an atomically thin spacer, which enables incorporation of switchable magnetic layers within stacks of 2D materials in advanced devices

Microstructure based strengthening model of a biocompatible WE54 alloy reinforced by SiC.

A large number of magnesium alloys and magnesium-based composites are nowadays used as biocompatible light metallic materials. Example of their applications include bone-tissue screws, cardiac valves, orthodontic screws and components. In this sense, the biocompatibility, durability, and corrosion resistance and blood compatibility are key factors for the full availability of magnesium based alloys in the bioengineering field. On the other hand, minimal necessary mechanical properties necessary for their potential application in such a filed were investigated in the last three decades. With this respect, not only magnesium based alloys, but also magnesium composite alloys were tested for their biocompatibility. Oxides such TiO2, MgO, ZnO, ZrO2, TiB2, Al2O3, and also SiC showed sufficient biocompatibility and in addition, composite magnesium alloys added with such oxides or SiC are known to possess higher mechanical properties compared to their magnesium alloy counterparts. Among the different available metallurgical technologies to produce magnesium alloys, the powder metallurgy (PM) is surely one of the most promising one. With this regard, squeeze casting is one of the most reliable and cost-effective PM technique of production of magnesium based alloys and composites. In the present work, the microstructure and mechanical properties of WE54+15vol.%SiC under various compression temperature conditions, up to 300°C, were investigated by transmission electron microscopy (TEM). Microstructure inspections revealed the formation of stable cuboid secondary phase particles, and lamellae and irregular-shaped intermetallic phases. A microstructure-based strengthening model was proposed and compared to the experimentally obtained compression stress carried out at temperatures ranging 50-to-300°C. The most effective strengthening term was found to be the one coming from the refined grain structure. A further important strengthening contribution was constituted by the secondary phase particle precipitation within the Mg-matrix

Role of Si on lamellar formation and mechanical response of two SPS Ti-15Al-15Si and Ti-10Al-20Si intermetallic alloys

Two TiAlSi intermetallic compounds produced by Spark Plasma Sintering (SPS) adding different Si content were tested by nanoindentation, toughness and wear resistance. Microstructure differences between the two alloys were characterized by TEM and a strengthening model was proposed. The microstructure-based strengthening model well agreed with alloys stress obtained from the nanoindentation hardness. It resulted that as Si content increases, the TiAl phase started to form lamellar structure and inter-lamellar twinning. Al reduction in favour of an equal amount of Si was found to slightly promote Ti5Si3 silicide formation and eventually a TiAl phase coarsening. Ti-15Al-15Si alloy showed submicrometric equiaxed TiAl grains. On the other hand, Ti-10Al-20Si alloy was characterized by a lamellar TiAl phase which was identified as responsible for the different mechanical responses of the two alloys

Microstructure-based alloy compression strengthening model of an equiatomic high-entropy alloy CoCrFeNiNb

High-entropy alloys within the scientific community was promoted due to their exceptionally high mechanical and physical properties, namely compression strength, toughness, plasticity, hardness, wear, corrosion resistance, and thermal stability. In the present study, an equiatomic CoCrFeNiNb HEA was prepared by a sequence of conventional induction melting, powder metallurgy, and compaction via spark plasma sintering. The as-cast HEA showed an ultimate compression strength (UCS) of ~1400 MPa. After sintering and compaction at 1273K the UCS increased considerably up to ~2400 MPa. After compaction at 1273K the fcc phase was characterized by a diffuse presence of nano-size twinning. Extensive TEM quantitative analyses were carried out to model the UCS by the most significant microstructure strengthening features. A quite good agreement between the microstructure-strengthening model and the experimental UCS was found

Compression stress strengthening modelling of a ultrafine-grained equiatomic SPS CoCrFeNiNb high-entropy alloy

High-entropy alloys are known to show exceptionally high mechanical properties, both compression and tensile strength, and unique physical properties, such as their phase stability. These quite unusual properties are primarily due to the microstructure generated by mechanical alloying processes, such as conventional induction arc melting, powder metallurgy, or mechanical alloying. In the present study, an equiatomic CoCrFeNiNb high-entropy alloy was prepared by a sequence of conventional induction melting, powder metallurgy, and compaction via spark plasma sintering. The high-entropy alloys showed uniform sub-micrometer grain microstructure consisted by a mixture of an fcc solid solution strengthened by a hcp Laves phase and a third intergranular oxide phase. The as-cast high-entropy alloys showed an ultimate compression strength (UCS) of ∼1400 MPa, which after sintering and compaction at 1273 K increased up to ∼2400 MPa. Extensive transmission electron microscopy quantitative analyses were carried out to model the UCS. A quite good agreement between the microstructure-strengthening model and the experimental UCS was found

Microstructure and Mechanical Properties of Spark Plasma Sintered CoCrFeNiNbX High-Entropy Alloys with Si Addition

Three mechanically alloyed (MA) and spark plasma sintered (SPS) CoCrFeNiNbX (X = 5, 20, and 35 at.%) alloys with an addition of 5 at.% of SiC were investigated. The face-centered cubic (FCC) high-entropy solid solution, NbC carbides, and hexagonal Laves phase already developed during MA. In addition, the SPS compacting led to the formation of oxide particles in all alloys, and the Cr7C3 carbides in the Nb5 alloy. The fraction of the FCC solid solution decreased with increasing Nb concentration at the expense of the NbC carbide and the Laves phase. Long-term annealing at 800 °C led to the disappearance of the Cr7C3 carbide in the Nb5 alloy, and new oxides—Ni6Nb6O, Cr2O3, and CrNbO4—were formed. At laboratory temperature, the Nb5 alloy, containing only the FCC matrix and carbide particles, was relatively strong and very ductile. At a higher Nb content (Nb20 and Nb35), the alloys became brittle. After annealing for 100 h at 800 °C, the Nb5 alloy conserved its plasticity and the Nb20 and Nb35 alloys maintained or even increased their brittleness. When tested at 800 °C, the Nb5 and Nb20 alloys deformed almost identically (CYS ~450 MPa, UTS ~500 MPa, plasticity ~18%), whereas the Nb35 alloy was much stronger (CYS of 1695 MPa, UCS of 1817 MPa) and preserved comparable plasticity