This study investigates the directional recrystallization behavior of Ni based oxide dispersion strengthened (ODS) alloy according to the zone annealing velocity. The zone annealing temperature is set as 1390°C, while the zone velocities are set as 2.5, 4, 6, and 10 cm/h, respectively. The initial microstructure observation of the as-extruded sample shows equiaxed grains of random orientation, with an average grain size of 530 nm. On the other hand, the zone annealed samples show a large deviation in grain size depending on the zone velocities. In particular, grains with a size of several millimeters are observed at 2.5-cm/h zone velocity. It is also found that the preferred orientation varies with the zone annealing velocity. On the basis of these results, this study discusses the role of zone velocities in the directional recrystallization of Ni base ODS alloy.

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• Directional recrystallisation processing: a review
  Chao Yang, Ian Baker
  International Materials Reviews.2021; 66(4): 256.     CrossRef

Ni(OH)₂ hollow spheres have been prepared by solvent displacement crystallization using a micro-injection device, and the effect of process parameters such as concentration and the relative ratio of the injection speed of the precursor solution, which is an aqueous solution of NiSO₄·6H₂O, to isopropyl alcohol of displacement solvent have been investigated. The crystal phases after NaOH treatment are in the β-phase for all process parameters. A higher concentration of NiSO₄·6H₂O aqueous solution is injected by a micro-injection device and bigger Ni(OH)₂ hollow spheres with a narrower particle size distribution are formed. The crystallinity and hardness of the as-obtained powder are so poor that hydrothermal treatment of the as-obtained Ni(OH)₂ at 120°C for 24 h in distilled water is performed in order to greatly improve the crystallinity. It is thought that a relative ratio of the injection speed of NiSO₄·6H₂O to that of isopropyl alcohol of at least more than 1 is preferable to synthesize Ni(OH)₂ hollow spheres. It is confirmed that this solution- based process is very effective in synthesizing ceramic hollow spheres by simple adjustment of the process parameters such as the concentration and the injection speed.

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• The Effects of Hexamethylenetetramine Concentration on the Structural and Electrochemical Performances of Ni(OH)₂ Powder for Pseudocapacitor Applications
  Dong Yeon Kim, Young-Min Jeong, Seong-Ho Baek, Injoon Son
  Journal of Korean Powder Metallurgy Institute.2019; 26(3): 231.     CrossRef