Mechanical Engineering Journal (Sep 2020)

Fabrication of functionally graded rods with three cylindrical layers made by spark plasma extrusion (SPE) process and characteristics of each layer

  • Hiroshi IZUI,
  • Keisuke KANAZAWA,
  • Takuto WATANABE,
  • Hideki SHIODA,
  • Koichiro ABE

DOI
https://doi.org/10.1299/mej.20-00071
Journal volume & issue
Vol. 7, no. 5
pp. 20-00071 – 20-00071

Abstract

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Functionally graded (FG) rods with three layers in the radial direction were fabricated by a spark plasma extrusion (SPE) process. The FG rods consisted of a pure Ti compact in the center, a 15TiB/Ti composite layer in the middle, and a 25TiC/Ti composite layer on the outside. Extrusion was carried out at a temperature of 1000 °C, at a pressure of 50 MPa with extrusion ratios (cross-sectional area before extrusion/cross-sectional area after extrusion) of 2.3 (from di = 15 mm to do = 10 mm) and 3.5 (from di = 15 mm to do = 8 mm). An FG rod with a length of over 40 mm and a high relative density could be obtained by the SPE process. The cross-sectional area ratio of the pure Ti layer after extrusion significantly decreased compared to the 15TiB/Ti and 25TiC/Ti composite layers due to the higher ductility of the pure Ti. On the contrary, the cross-sectional area ratio of the 25TiC/Ti composite layer increased after the extrusion, because the 25TiC/Ti composite layer had quite low ductility. Due to the sufficient material flow during the extrusion, the TiC particles in the 25TiC/Ti composite layer of the FG rod were uniformly distributed along the extrusion direction. Furthermore, during the SPE process, the TiB clusters in the TiB/Ti composite layer were transformed into TiB whiskers, and the TiB whiskers were mainly oriented parallel to the extrusion direction. The tensile strength of the TiB/Ti composite layer fabricated by the SPE process improved due to the transformation of the TiB whiskers and their orientation along the extrusion direction.

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