Mechanical alloying (MA) is a high-energy ball milling process results in the obtaining of simple and stable microstructures having increased homogeneity compared to other non-equilibrium synthesis methods. The aim of this paper was to develop a high entropy alloy with an improved hardness value suitable for coating turbine blades working in geothermal steam. CoCrFeNiMo high entropy alloy was processed in solid state, using mechanical alloying. After 40h milling time in a planetary ball mill the alloyed sample was consolidated using spark plasma sintering process. The samples obtained were investigated with the aid of optical and electron microscope, X ray diffraction and the hardness value was determined. The results obtained revealed that the powder was completely alloyed after 40 hour milling and the mixture between BCC and FCC phases resulted in 34% improved hardness value in comparison with a stainless steel usually used for turbine blades working in geothermal environment.
The aim of the present paper is to investigate an innovative high corrosion resistance coating realized by electrospark deposition. The coating material was fabricated from HfNbTaTiZr high-entropy alloy. HEA was produced by the mechanical alloying of Hf, Nb, Ta, Ti, and Zr high-purity powders in a planetary ball mill, achieving a good homogenization and a high alloying degree, followed by spark plasma sintering consolidation. The electrodes for electrospark deposition were cut and machined from the bulk material. Stainless steel specimens were coated and electrochemically tested for corrosion resistance in a 3.5% NaCl saline solution.
This work investigates the alloying degree of HfNbTaTiZr high entropy alloy in equimolar percentages from raw, high purity powder, using solid state processing, for further uses in coating work components in harsh environments like marine, geothermal or oil and gas industry. The combination of elements was chosen according their properties, tailoring the composition for the final purpose. The alloying has been performed in a planetary ball mill with stainless steel vial and balls in a protective argon atmosphere to prevent oxidation, contamination or ignition and N-heptane as a process control agent to improve the material’s behavior during welding and re-welding in mechanical alloying process. Samples were taken at regular periods of time and analyzed to check the alloying degree evolution and to establish the optimum parameters for milling, best results being obtained at a speed of 300 rpm for 180 min (effective time) providing an alloying degree over 50% was achieved.
Al0.5CoCrFeNi high entropy alloy was processed by mechanical alloying and investigated in term of powders characteristics and microstructures. The obtained power was pressed and sintered resulting in a bulk material that will be further processed to obtain electrodes that will be deposited on the substrate by electro spark deposition process, in an attempt to obtain a corrosion resisting coating. High Entropy Alloys are known due to their corrosion and wear resistant properties, which makes them the perfect candidates in numerous domains as marine, geothermal, oil and gas industries, where the aggressive environment tends to corrode the in work components of the equipment. The cocktail effect is characteristic to the high entropy alloys, where every component concurs in an alloy with predetermined properties.
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