Page 26 - Annual Report_21-22

Fig. 5: As-cast microstructure of TiTaNbMoZr RHEA.

Fig. 6: (a) Lattice strain and dilatometric strain of TiTaNbMoZr RHEA as a function of temperature, and (b) the variation
of the concentration of thermal vacancies with respect to temperature.

Thermal expansion behaviour of NiB modified W-Ni-Co heavy alloys

The liquid phase sintered tungsten heavy alloys (WHAs) 1.5) system has been chosen as a base composition for
are composed of ~88–98 wt.% W and their microstructure this work as this alloy offers an excellent combination of
reveals that tungsten spheroids are encapsulated by the high hardness, yield strength and compressive strength.
the ductile austenitic matrix phase. WHAs find enormous It is needless to mention that the thermal expansion
applications in strategic sectors since they exhibit a behaviour of material needs to be critically evaluated
combination of excellent physical as well as mechanical for any prospective strategic application. Accordingly, in
properties. In general, fully dense, net-shaped WHAs this work, the role of NiB is investigated in the thermal
are processed by the powder metallurgy route, which expansion characteristics of NiB-modified 90W-6Ni-4Co
involves successive processing steps like blending of heavy alloy, keeping the (Ni+NiB)/Co ratio constant at
powders, compaction and liquid phase sintering (LPS). 1.5. The base composition of 90W-6Ni-4Co is henceforth
Studies reveal that the formation of brittle intermetallic referred to as A1, while the partially Ni substituted
formation can be avoided by maintaining Ni/Co ratio in (90W-3Ni-3NiB-4Co) and fully Ni substituted (90W-6NiB-
the range of 1 to 9 in W-Ni-Co ternary system. Amongst 4Co) WHAs are termed as A2 and A3, respectively.
various combinations, the ternary 90W-6Ni-4Co (Ni/Co =
24 ANNUAL REPORT 2021-22