Formation of hard metal borides via novel molten salt electrolysis

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Abstract

In this study, the new boriding method called CRTD-Bor (cathodic reduction and thermal diffusion boriding) was introduced for different substrates namely titanium,Ti6A14V, 60-NitinoI, Inconel 600 and steels (AISI 1018, 440C, and AISI 4140).The main benefits of this novel boriding technique are not only its eco-friendly nature but also its ability to provide high growth rates of borides. By playing process parameters, the desired composition of boride phases is possible to be grown on any conductive substrates which have stable boride structures. The presence of TiB2 phase onTi andTi6A14V substrates were confirmed by the X-ray diffraction techniques. The cross-sectional examination of borided Ti samples verified the boride layers consisted of a homogeneous TiB2 phase on the top and TiB whiskers toward the substrate. Cross-sectional SEM investigates of borided Ti6A14V revealed the existence of V in the TiB2 layer, whereas A1 moved away from the grown boride structure. After 35 min of H6A14V boriding at 1100 °C, approximately 7.5 μm thickTiB2 layer was grown. Interestingly, during the boriding of 60-Nitinol, the mixed boride formations with the constituents of NiB, TiB2 and Ni2B were detected where Ni-borides were the predominant structure with their high growth rates (i.e., 60 |im and 270 μm boride layer thicknesses were achieved after 5 min and 120 min of boriding at 950 °C, respectively). Similarly, the boriding of Inconel 600 was very fast and 30 μm Ni2B layer was formed after 5 min of boriding at 950 °C. The formation of a single phase Fe2B layer is very critical for industrial applications of boridcd steels. With the developed new procedure called "phase homogenization (PH)" and by changing process parameters such as current density and temperature, the single phase Fe2B was possible to be grown on alloyed steels with its perfect adhesion on to the substrates. Additional cross-sectional hardness tests confirmed the significant hardness improvements on different base materials after CRTD-Bor; for instance, 3500 HV, 2500 HV,2000 HV, 1600 HV were measured on boridedTi, 60-Nitinol, Inconel, steels, respectively.

Original languageEnglish
Pages (from-to)162-170
Number of pages9
JournalWorld of Metallurgy - ERZMETALL
Volume70
Issue number3
Publication statusPublished - 1 May 2017

Keywords

  • (Fe
  • Boriding
  • Cr)B
  • CRTD-Bor
  • FeB
  • NiB
  • NiB
  • TiB
  • TiB
  • Transition metal borides

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