Journal of
MATERIALS RESEARCH
Fabrication of cellular NiTi intermetallic compounds
Bing-Yun Li, Li-Jian Rong, and Yi-Yi Li
Institute of Metal Research, Chinese Academy of Sciences,
Shenyang, 110015, People’s Republic of China
V.E. Gjunter
V.D. Kuznetsov Siberian Physical Technical Institute, Tomsk, 634050, Russia
(Received 10 August 1999; accepted 1 November 1999)
Self-propagating high-temperature synthesis (SHS) has been successfully developed for
the fabrication of cellular NiTi intermetallic compounds, which have an open cellular
structure with about 60 vol% porosity and more than 95% open-porosity ratio. The
SHS reactions lead to the formation of TiNi, Ti2Ni, Ni3Ti, and Ni4Ti3 intermetallics.
The SHS process can be controlled by regulating the preheating temperature, which
has effects on the phase amount and the shape as well as macrodistribution of pores in
the products.
There is a growing need for fabrication of artificial
hard-tissue replacements. The biomaterials industry
worldwide has an annual turnover of $2.3 billion in the
field of hard-tissue repair and replacement (total of $12
billion). There is currently an increasing growth rate
of 7–12% per annum for biomaterials in clinical appli-
cations.1 Several nonmetallic materials have been pro-
posed as candidates for artificial bones and/or teeth, but
none has found wide applications. Due to their low
reliability, especially in wet environments, materials
such as hydroxyapatite-based biomaterials cannot pres-
ently be used for heavy load-bearing applications (like
artificial bones or teeth).2 Metals have been widely
used for major load-bearing applications. There are,
however, various problems related to normal metallic
materials in the human body due to physical properties,
corrosion, wear, and/or negative tissue reaction.3 Ap-
propriate hard-tissue replacement implants should
achieve a match of mechanical behavior with the tissue to
be replaced.4
It is almost certain that cellular materials permit the
simultaneous optimization of stiffness, strength, and
overall weight in a given application. Cellular materials
are naturally load-bearing materials; for example, nature
often uses cellular materials such as wood, bone, and
coral as load-bearing materials. Recently, cellular NiTi
intermetallic compound has been acknowledged as a
most promising biomaterial for use as artificial bones or
teeth roots because of its special pseudoelasticity, which
can accommodate the deformation behavior of hard tis-
sue, and its attractive combination of properties such as
excellent mechanical properties, good corrosion resis-
tance, biocompatibility, and shape-memory effect.5–6
Moreover, its cellular structure allows the ingrowth of
bone tissue and is favorable for the fixation of the im-
plant as well as the transport of body fluids. In addition,
by obtaining different porosity and pore sizes through
controlling the synthesis conditions, it is easy to adjust
the mechanical behavior of cellular NiTi alloys to match
that of replaced hard tissue.
The engineering potential of cellular NiTi alloys in
medicine is considerable as aforementioned, but its
realization requires new and innovative methods of de-
sign, unfamiliar to traditional engineers. Self-propagating
high-temperature synthesis (SHS) is used to synthesize
many ceramics and intermetallics,7–11 including NiTi inter-
metallic compounds. Compared with the conventional
process, the SHS method provides advantages with respect
to time and energy savings and easier processing.
The main aim of this study is to synthesize cellular
NiTi intermetallic compounds by SHS. By changing
preheating temperature, we expect to control the SHS
process and get products with high porosity and well-
distributed pores.
Reactant powders of Ti and Ni were mixed at the
equiatomic Ni/Ti composition. The blended powders
were pressed into cylindrical pellets with a diameter of
26 mm. The relative density of the pellets was about 42%
of the theoretical value. The pellets were ignited in an
SHS reaction chamber. X-ray diffraction (XRD) was
conducted to identify the phases in the products. Optical
metallography and scanning electron microscopy (SEM)
were performed for microstructural characterization
analysis.
Figure 1 shows an XRD trace for the blended powders.
As can be seen, the Ni and Ti powders have been only
mechanically blended and no alloying has occurred.
Because of the low exothermic character of the reac-
tions of Ti and Ni to synthesize Ni–Ti intermetallic com-
pounds by SHS, preheating is needed.12 It is reported that
10
J. Mater. Res., Vol. 15, No. 1, Jan 2000
© 2000 Materials Research Society
Downloaded: 27 Jan 2015
IP address: 131.156.157.31