The effects of ZrB2 (and other di-borides) additions on the free-iron content in ingots with the initial composition of Nd2.2Fe14B1.1

Ken Kirby, Azizah Shaaban, Allan Walton, David Kennedy, Andrew Williams, Richard Sheridan, Ivor Harris

Research output: Contribution to journalArticlepeer-review


Additions of zirconium diboride (ZrB2), to small scale (~1 g)
arc-melted (AM) and larger scale (5kg) book mould (BM) cast alloy with
the composition Nd2.2Fe14B1.1 (near to stoichiometric Nd2Fe14B) have
been shown to be a very effective means of eliminating the free iron
content, which is present as a result of the peritectic nature of the
Nd2Fe14B phase. The composition Nd2.2Fe14B1.1 has been selected for these
experiments to ensure that the practical process of alloy melting and
casting did not result in a composition below stoichiometric levels of Nd
and B in the hard magnetic phase Nd2Fe14B. The effect of zirconium boride
in reducing free iron content has been determined (1) magnetically by
means of the Honda-Owen method on the BM alloys and (2) by image analysis
using scanning electron microscopy for both AM and BM alloys. Generally,
for the BM alloys, both sets of measurements exhibited good agreement
with a progressive reduction in the free iron content with increasing
additions of ZrB2. Without any subsequent homogenisation treatment, zero
free iron was achieved in the AM and BM cast condition, after an addition
of just 1 mole% of ZrB2. Closely similar behaviour was observed with up
to 1 mole% additions of the other Group 4 diborides, TiB2 and HfB2. A
common feature of these (and other diborides) is their great stability,
as evidenced by their very high congruent melting points, and the
microstructures observed in the present studies for the 1 mole% additions
indicate the presence of a possible eutectic mixture between the
diboride, the Nd-rich phase and Nd2Fe14B and this could provide an
explanation for the eventual disappearance of the high temperature
peritectic reaction and hence free iron content in the book mould cast
material. High resolution scanning electron microscopy indicated that the
diborides were embedded largely within the areas of Nd-rich material.
Original languageEnglish
JournalJournal of Alloys and Compounds
Publication statusSubmitted - 2 Dec 2018


  • Metals and alloys
  • Permanent magnets
  • rare earth alloys and compounds
  • Mechanical alloying
  • Microstructure
  • phase diagrams


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