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Open AccessArticle

Electrical Discharge Machining of Alumina Using Ni-Cr Coating and SnO Powder-Mixed Dielectric Medium

by Anna A. Okunkova, Marina A. Volosova, Elena Y. Kropotkina, Khaled Hamdy and Sergey N. Grigoriev

Metals 2022, 12(10), 1749; https://doi.org/10.3390/met12101749 - 18 Oct 2022

Cited by 11 | Viewed by 3791

Aluminum-based ceramics exhibit excellent wear resistance and hot hardness that are suitable for various responsible applications allowing products to work under extreme mechanical and thermal loads (up to 1000 °C). The problem of high-precision forming complex-shaped parts is a known engineering challenge due to the insulating properties of aluminum-containing ceramics and the formation of chemically active carbides in a hydrocarbon medium. The alternative approach for electrical discharge machining non-conductive sintered Al₂O₃ in the water-based medium using nickel-chrome plasma-vapor-deposed coating of 12 mm, SnO powder suspension (particle diameter of ⌀10 µm, concentration of 150 g/L), and brass wire-tool is proposed. The productivity was evaluated by calculating the material removal rate and discharge gap for various combinations of pulse frequency and duration. The maximal material removal rate of 0.0014 mm³/s was achieved for a pulse frequency of 30 kHz and pulse duration of 1.7–2.5 μs. The recommended value of the interelectrode gap is 48.0 ± 4.9 µm. The possibility of electrical discharge machining aluminum-containing insulating ceramics without using hydrocarbons, carbon and copper-group assisting measures was proposed and shown for the first time. The chemical content of the debris in the interelectrode gap between components of the materials was thermochemically analyzed. Full article

(This article belongs to the Special Issue Machining of Advanced Cutting Materials: Fundamentals, Modeling and Applications)

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10 pages, 1929 KB

Open AccessArticle

Synthesis and Characterization of Nanostructured Multi-Layer Cr/SnO₂/NiO/Cr Coatings Prepared via E-Beam Evaporation Technique for Metal-Insulator-Insulator-Metal Diodes

by Sana Abrar, Muhammad Bilal Hanif, Abdulaziz Salem Alghamdi, Abdul Khaliq, K. S. Abdel Halim, Tayyab Subhani, Martin Motola and Abdul Faheem Khan

Materials 2022, 15(11), 3906; https://doi.org/10.3390/ma15113906 - 31 May 2022

Cited by 4 | Viewed by 3023

Abstract

Enhanced non-linearity and asymmetric behavior of the Cr/metal oxide diode is reported, with the addition of two insulator layers of SnO₂ and NiO to form the metal-insulator-insulator-metal (MIIM) configuration. Such an MIIM diode shows potential for various applications (rectifiers and electronic equipment) which enable the femtosecond fast intoxication in MIIM diodes. In this work, nanostructured multi-layer Cr/SnO₂/NiO/Cr coatings were fabricated via e-beam evaporation with the following thicknesses: 150 nm/20 nm/10 nm/150 nm. Coatings were characterized via Rutherford backscattering (RBS), scanning electron microscopy (SEM), and two-probe conductivity testing. RBS confirmed the layered structure and optimal stoichiometry of the coatings. A non-linear and asymmetric behavior at <1.5 V applied bias with the non-linearity maximum of 2.6 V⁻¹ and the maximum sensitivity of 9.0 V⁻¹ at the DC bias point was observed. The promising performance of the coating is due to two insulating layers which enables resonant tunneling and/or step-tunneling. Based on the properties, the present multi-layer coatings can be employed for MIIM application. Full article

(This article belongs to the Topic Synthesis, Characterization and Performance of Materials for a Sustainable Future)

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13 pages, 6828 KB

Open AccessArticle

Microstructure Investigation on Metal Hydride Alloys by Electron Backscatter Diffraction Technique

by Yi Liu and Kwo-Hsiung Young

Batteries 2016, 2(3), 26; https://doi.org/10.3390/batteries2030026 - 1 Aug 2016

Cited by 17 | Viewed by 8614

Abstract

The microstructures of two metal hydride (MH) alloys, a Zr₇Ni₁₀ based Ti₁₅Zr₂₆Ni₅₉ and a C14 Laves phase based Ti₁₂Zr_21.5V₁₀Ni_36.2Cr_4.5Mn_13.6Sn_0.3Co_2.0Al [...] Read more.

The microstructures of two metal hydride (MH) alloys, a Zr₇Ni₁₀ based Ti₁₅Zr₂₆Ni₅₉ and a C14 Laves phase based Ti₁₂Zr_21.5V₁₀Ni_36.2Cr_4.5Mn_13.6Sn_0.3Co_2.0Al_0.4, were studied using the electron backscatter diffraction (EBSD) technique. The first alloy was found to be composed of completely aligned Zr₇Ni₁₀ grains with a ZrO₂ secondary phase randomly scattered throughout and a C15 secondary phase precipitated along the grain boundary. Two sets of orientation alignments were found between the Zr₇Ni₁₀ grains and the C15 phase: (001)_Zr7Ni10A//(110)_C15 and [100]_Zr7Ni10A//[0

\bar{1}

1]_C15, and (01

\bar{1}

)_Zr7Ni10B//(

\bar{1}

00)_C15 and [100]_Zr7Ni10B//[313]_C15. The grain growth direction is close to [313]_Zr7Ni10B//[

\bar{1}

11]_C15. The second alloy is predominated by a C14 phase, as observed from X-ray diffraction analysis. Both the matrix and dendrite seen through a scanning electron microscope arise from the same C14 structure with a similar chemical composition, but different orientations, as the matrix with the secondary phases in the form of intervening Zr₇Ni₁₀/Zr₉Ni₁₁/(Zr,Ni)Ti needle-like phase coated with a thin layer of C15 phase. The crystallographic orientation of the C15 phase is in alignment with the neighboring C14 phase, with the following relationships: (111)_C15//(0001)_C14 and [1

\bar{1}

0]_C15//[11

\bar{2}

0]_C14. The alignments in crystallographic orientations among the phases in these two multi-phase MH alloys confirm the cleanliness of the interface (free of amorphous region), which is necessary for the hydrogen-storage synergetic effects in both gaseous phase reaction and electrochemistry. Full article

(This article belongs to the Special Issue Nickel Metal Hydride Batteries)

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