Advances in Sintering
JOM
Advances in Sintering
M. QIAN 0
0 1.-Centre for Additive Manufacturing, School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University , Melbourne, VIC , Australia. 2.-
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The global powder metallurgy market has
continued to benefit from the revival in the automotive
industry while emerging applications are expected
to further drive demand for powder metallurgy
(PM) components in the near future. Sintering is
the mainstay of a typical PM process in the
production of various types of PM components, whether
they are pore-free, nearly pore-free, or porous. At
the committee meeting held in March 2015, the
TMS Powder Materials Committee decided to
choose sintering as the committee’s technical
emphasis for JOM 2016. Six papers were selected
for the JOM March 2016 topic following a thorough
review process.
In the first article entitled ‘‘Sintering Trajectories:
Description on How Density, Surface Area, and
Grain Size Change,’’ German discusses the ways
how the sintering process has been treated by
researchers in the PM community. As pointed out
by the author, an alternative approach to the
theoretical treatment using a matrix of
mathematical relationships is to track the sintering trajectory
using relatively simple relationships based on bulk
measures, including density, surface area, and
grain size. These relationships, although they often
largely ignore mechanistic details, are applicable to
a wide variety of materials and consolidation
conditions, including hot pressing and spark sintering.
It is suggested that, over a broad array of metals
and ceramics, the sintering trajectories follow a
characteristic trajectory, where specific surface
area, grain size, and fractional density are
interrelated.
The second article, ‘‘Sintering in Laser Sintering’’
by Bourell, offers an informative discussion of the
term ‘laser sintering’ and its accuracy in the broad
context of powder metallurgy including additive
manufacturing. It seems clear from this
contribution that the PM community might consider laser
‘‘sintering’’ to be a historical term and a misnomer.
Ma Qian is the JOM advisor for the Powder Materials Committee of the
TMS Materials Processing & Manufacturing Division, and guest editor for
the topic Advances in Sintering in this issue.
Should ‘‘laser sintering’’ be called something else?
In the interests of accuracy, this is probably so
according to the author.
The third article in this sequence, by Wang et al.,
deals with the ‘‘Fabrication of High Strength and
Ductile Stainless Steel Fiber Felts by Sintering.’’
Stainless steel fiber felts are important porous
stainless steel products, which have found wide
applications for high-volume filtration or
separation, sound absorption or noise control, heat
transfer, and energy absorption, as well as being used in
catalytic converters and surface combustion. This
original research article presents a comprehensive
experimental study of the fabrication of stainless
steel fiber felts by sintering. The critical sintering
conditions for the formation of undesired
bamboolike grain structures in the fiber ligaments are
defined and an innovative sintering process is
proposed and demonstrated.
The fourth article, by Liu and co-workers, reports
on the development of ‘‘Ultrahigh Strength and
Ductile Lamellar-Structured Powder Metallurgy
Binary Ti-Ta Alloys.’’ Ti-Ta alloys are expected to
offer better biocompatibility and corrosion
resistance than titanium, especially when the Ta content
exceeds about 15 at.% or 40 wt.%. The binary
Ti20at.%Ta alloy fabricated by the authors via
sintering from elemental Ti and Ta powders and
subsequent hot-swaging and annealing achieved ultimate
tensile strength of 1600 MPa and tensile elongation
of greater than 25%. The microstructure of the
asfabricated Ti-20at.%Ta alloy is featured by aligned
Ta-enriched and Ti-enriched phases, which
originated from the insufficient diffusion of Ta during
isothermal sintering, an interesting approach
adopted by the authors.
In the fifth article in this compilation, Dvilis and
co-workers investigate the consolidation by spark
plasma sintering (SPS) of multi-phase metal matrix
(Al/Mg) powder composites. The research focuses on
modeling and experimental verification of the
consolidation process of powder composites consisted of
aluminium-magnesium alloy AMg6 (65 wt.%), B4C
powder (15 wt.%), and W nano-powder (20 wt.%), as
well as the optimization of both the composite
content and SPS conditions for improved
consolidation.
For most metal powders (titanium powder is an
exception), the oxide film has an important effect on
their sintering behaviors including the selection of
sintering temperature. In the sixth and final article
in this collection, Gierl-Mayer and co-authors
provide an informative review of ‘The Role Of
Oxygen Transfer In Sintering Of Low Alloy Steel
Powder Compacts’ and discuss in detail the
influence of alloying elements which have higher oxygen
affinity than iron. Several imp (...truncated)