DETERMINATION OF THIN FILM'S MECHANICAL PROPERTIES

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2.9 Heat Treatment after Boriding
Borided parts can be quench hardened in air, oil, and salt bath or polymer
quenchant and subsequently tempered. Heating to the hardening temperature should
be carried out in an oxygen-free protective atmosphere or in a neutral salt bath
(R.Chatterjee-Fischer, 1989)
.
2.10 Boriding of Nonferrous Materials
Nonferrous materials such as nickel, cobalt and molybdenum based alloys as well
as refractory metals and their alloys and cemented carbides can be borided. Copper
cannot: therefore, it provides a good stopping-off material. Of special interest is the
boriding of nickel alloys and titanium and its alloys. Usually, boriding of nickel plate
is done in gaseous BCl 3 -H 2 -Ar mixture in the temperature range of 500 to 1000 o C
(S. Motojima et al, 1981), whereas Permalloy is pack borided with 85% B 4 C and
15% Na 2 CO 3 , or 95 % B 4 C and 5 % Na 2 B 4 O 7 powder mixture at 1000 o C for 6 h in
H 2 atmosphere.
Boriding of titanium and its alloys is carried out preferably between 1000 and
1200 o C. Here pack boriding in oxygen-free amorphous boron in combination with
high vacuum (0.0013 Pa, or 10 –5 torr) and high purity argon atmosphere or gas
boriding with H 2 -BCl 3 -Ar gas mixture is preferred. The microhardness readings of
boride layers formed on titanium and refractory metals are very high compared to
those formed on cobalt and nickel (see Table 2.1). The wear properties of sintered
carbides can be increased by boriding because of the acceptance of boron by soft
cobalt and nickel binders (Lindberg heating treating company, “Boroalloy Process”).
Boride layers formed on tantalum, niobium, tungsten, molybdenum and nickel do
not exhibit tooth-shaped morphology as with titanium. When cemented carbides such
as WC-Co are commercially pack borided with a powder mixture containing 40%
B 4 C, 45% SiC and 5% KBF 4 , three distinct zone are found to be formed in the boride