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Sintering of Incorporated Shape Memory Alloys into Functionally Graded Materials

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24/03/2018 13:46:16
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Research Article Open Access
Khafaji et al., Ind Eng Manage 2018, S:3
DOI: 10.4172/2169-0316.S3-002
Ind Eng Manage ISSN: 2169-0316, IEM an open access journal
Industrial Engineering & Management
Industrial Engineering & Management
ISSN: 2169-0316
Materials with Compositional Variations
Keywords: SMA; Functionally graded NiTi materials; Biocompatibility;
XRD
Introduction
Functionally graded materials (FGM) contain of a gradual change
in the volume fraction or mechanical properties of the ingredient in
a direction. Functionally graded materials are ideal for applications
include sharp thermal gradients, ranging from thermal structures in
advanced aircraft and aerospace engines to computer circuit boards
[1]. The conception of Functionally Graded Materials (FGMs) was
basically advanced in the early 1980s in Japan, where this new material
notion was proposed to increase adhesion and minimize the thermal
stresses in metallic-ceramic composites advanced for reusable rocket
engines [2].
Design of FGM
A main problem in the design of an FGM, aside from this materials
selection, lies in determining the optimum spatial dependence for the
composition. This can be regarded by as that composition profile which
best accomplishes the intended purpose of the material while preserve
other thermal, physical, and mechanical properties within limits that
ensure favorable performance. Another problem lies in prophesy the
characteristics of an FGM, for a given composition profile, during
manufacturing and under in service conditions. Use of theoretical
models to aid in FGM design and to predict FGM fabrication and inservice
behavior is of crucial importance. Once decided, a model can
readily be used to conduct a wide variety of computer “experiments”
in which effects of changing input parameters, such as thermo physical
properties of the constitutive phases, or the composition profile along
the graded direction, is systematically evaluated [3].
The fact that the composition of an FGM cans vary over such a wide
range means that a variety of fundamentally different microstructures
can exist across the graded direction. This, in turn, means that the
thermo physical properties, which are generally substantially dependent
on the microstructure, will also vary with position within the material.
*Corresponding author: Khafaji NSL, Department of Metallurgy Engineering,
Collage of Materials Engineering, Babylon University, Iraq, Tel: 7801006256;
E-mail: dr.nabbaa@gmail.com
Received November 23, 2017; Accepted December 28, 2017; Published January
08, 2018
Citation: Khafaji NSL, Hafiz MH, Atiyah AA (2018) Sintering of Incorporated Shape
Memory Alloys into Functionally Graded Materials. Ind Eng Manage S3: 002. doi:
10.4172/2169-0316.S3-002
Copyright: © 2018 Khafaji NSL, et al. This is an open-access article distributed
under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the
original author and source are credited.
Abstract
Shape Memory Alloys (SMAs) have been investigated as one of the most full of promise smart materials in multi
applications. Among the commercially obtainable Shape Memory Alloys, nickel–titanium (Nitinol or NiTi) ones are
wonderful due to their outstanding performance and reliability. In addition to strain recovery, (Ni-Ti) be an attraction
in several medical applications due to its biocompatibility, corrosion resistance and fatigue behavior. Low range of
transition temperature was the main challenges in the fabrication of these materials. A novel method was introduced
to improve the range of transition temperatures by incorporating the shape memory effect into functionally graded
materials concept. Therefore, industrialization and implementing of NiTi functionally graded materials made by a powder
metallurgy method were carried out through the current work. Two samples with different seven layers of NiTi/NiTi
functionally graded materials were compacted using steel die and punch at the same compacted pressure and different
sintered temperature. After inspect the different samples of NiTi/NiTi functionally graded materials under different
fabrication conditions, the suitability fabrication regime was determined with the aid of microscopic observations. These
materials are designed to have gradual or abrupt Microstructural or compositional variations within the body in one piece
of material, these samples have been produced by powder metallurgy approach and the effect of composition for each
layer studied on the XRD.
Sintering of Incorporated Shape Memory Alloys into Functionally Graded
Materials
Khafaji NSL1*, Hafiz MH2 and Atiyah AA2
1Department of Metallurgy Engineering, Collage of Materials Engineering, Babylon University, Iraq
2Department of Materials Engineering,Technology University, Iraq
A realistic model must appropriately enough account for this fact.
According to the FGM model, the dimensions and composition of each
layer will be determined using the following formula [4]:
( ) ( )
( )
N X2 X
V1 x
X2 X1
? ? ?
= ?? ?? ? ? ?
(1)
Where, V1 (x) represents the local volume fraction of Ni, while the
volume fraction of Ti is being according to the formula:
V2(x) = 1 – V1( x ) X1 (2)
X1 and X2 are the border regions of pure (NiTi) and (NiTi)
respectively, (N) is a variable parameter, where its magnitude
determines the curvature of V1(x). The solution of equations above at
different values of N (i.e., 1, 2 and 0.5) is represented schematically in
the following figure and curve.
With higher values of (N) the plate tends to be toward layer 1 and
7 (the lower and upper layers) that lower values of (N) tend toward
layer 4 (the core layer) (Figure 1). Designers can vary the (N) value to
tailor made the FGM to specific applications at N=0, the curve would
really be a vertical line corresponding to a volume fraction of layer 7=1.
Additionally higher values of (N) push the curve toward layer 1 and 7.
At N=?, a straight line would stay at a layer 1 and 7 volume fraction
of 0 indicate layer 4 It is apparent that structural designers requiring
Citation: Khafaji NSL, Hafiz MH, Atiyah AA (2018) Sintering of Incorporated Shape Memory Alloys into Functionally Graded Materials. Ind Eng
Manage S3: 002. doi: 10.4172/2169-0316.S3-002
Page 2 of 4
Ind Eng Manage Materials with Compositional Variations ISSN: 2169-0316, IEM an open access journal
important thermal protection should consider low values of (N) which
will yield layer 4. Designers that wish corrosion protection with high
load carrying capability should belive higher values on (N) which yield
layer 1 and 7 [5].
In the present work, (N) is taken as 1 as model special distribution
of SMA-FGM. As shown in Figure 2; the model has (15 mm) length and
(15 mm) diameter, for z1=(0.5 mm) thickness of layer 1, z2=(4.53 mm)
thickness of medium layer and the graded layers lies between them.
Fabrication and Characterization
The elemental powders used in this study to prepare (SMA–FGMs)
layers with an average particle size as 33 ?m for Nickel powder and 165
?m for Titanium powder. Preparation of SMA–FGM layers according
to pre designed model profile as indicated in Tables 1 and 2 includes;
wet mixing of the powders for (7 h), filling of powders into the die
cavity by stepwise controlled manner, compacting of powders with
pressure at (300 MPa). Sintering of all prepared samples was in vacuum
furnace with Argon inert gas to (7 h.) at (950°C). X-ray diffraction used
extensively to ensure the development of Martensitic phases during
sintering.
Phase’s analysis of prepared alloys is based upon X-ray diffraction
technique. As a first, mixture of blended powders from each layer and
functionally graded samples has been identified by X-ray diffraction
technique in order to achieve compare these diffraction patterns with
sintered diffraction patterns for the samples. All X-ray diffraction tests
are carried out at S.C. of Geological survey and Mining. Low angle
X-ray diffraction is performed. X-ray generator with Cu K? radiation
at 40 kW and 20 mA is used. The target used in the X-ray tube was Cu,
therefore cu=1. 54060°A was used in obtaining the XRD patterns.
The X-ray is generated by general electric diffraction type Shimatzo
(PW 1840) operating system at scanning speed of 5°(2?) per minute.
The specimen has been held at a fixed angle of ?=5 degrees relative to
the case X-ray beam while the detector has motioned through an angle
of 2(20-90) degrees.
Results and Discussion
X-Ray diffraction patterns
To improve the experimental fabrication of (NiTi) SMA-FGMs, X–
ray diffractions were made to ensure, that the fabricated alloys in each
of SMA-FGMs were transformed homogeneously during the sintering
practices. After sintering the samples at (950°C) for (7 hrs.) under
controlled by argon atmosphere, an X-ray diffraction test was done for
the sintered SMA-FGMs layer samples as well as whole SMA-FGMs.
The transformation mechanism of shape memory alloys (i.e.,
layers) is shown in Figure 3. Three specific phases of NiTi are identified
for characterization: Martensite (M), Austenite (A), and Ni3Ti.
Nitinol are very sensitive to phase transition temperature according to
the compounds of Ni and Ti. They can have cubic, Monoclinic and
Rhombohedral phases according to temperature. It can observe that
All Ni and Ti are transformed to NiTi Monoclinic phase and hexagonal
Ni3Ti phase. The construction of Ni3Ti might be referred to the slow
cooling of samples inside the furnace [6]. The suggested reactivity
during the process are as follows [7].
Ni + Ti ? NiTi ?G : ? 67 KJ / mol (3)
Ni + Ti ? Ni3Ti ?G : ? 1 40 KJ / mol (4)
The diffraction patterns obtained from the tested samples which
the phases, as a result of sintering, could be exposed. From these
figures, the Monoclinic phase peaks are observed between (2?=40–50
degree). Generally, Nitinol was strongly dependent on composition
and thermal treatment, so Ni-Ti alloys can have either a one-step
Martensite phase transition from high temperature or a two-step
Martensite phase transition.
The sintering temperature applied (950°C) was about 0.8 of the
melting temperature of the NiTi intermetallic component (Tm=1310°C),
and stock at that temperature for 7 hours under controlled by argon
atmosphere will result in complete sintering reaction due to the
increase of the inter-diffusion between Ti and Ni which in turn leads to
Figure 1: Plot of V1(z) vs. Z (eqn. 1) for selected values of N.
Figure 2: Design of seven layers SMA-FGMs: (a) SMA-FGM1, (b) SMA-FGM2.
Layers Chemical composition Thickness (mm)
1st 50% at Ti-50%at Ni (45% wt Ti-55% wt Ni) 0.5
2nd 49.3% at Ti-50. 7%at Ni (44.2% wt Ti-55.8% wt Ni) 1.78
3rd 48.5% at Ti-51. 5%at Ni (43.5% wt Ti-56.5% wt Ni) 3.07
4th 47.8% at Ti-52. 2%at Ni (42.7% wt Ti-57.3% wt Ni) 4.35
5th 48.5% at Ti-51. 5%at Ni (43.5% wt Ti-56.5% wt Ni) 3.07
6th 49.3% at Ti-50. 7%at Ni (44.2% wt Ti-55.8% wt Ni) 1.78
7th 50% at Ti-50%at Ni (45% wt Ti-55% wt Ni) 0.5
Table 1: Model of SMA-FGM1 profile.
Layers Chemical composition Thickness (mm)
1st 47.8% at Ti-52. 2% at Ni (42.7% wt Ti-57.3% wt Ni) 0.5
2nd 48.5% at Ti-51. 5% at Ni (43.5% wt Ti-56.5% wt Ni) 1.78
3rd 49.3% at Ti-50. 7% at Ni (44.2% wt Ti-55.8% wt Ni) 3.07
4th 50% at Ti-50% at Ni (45% wt Ti-55% wt Ni) 4.35
5th 49.3% at Ti-50. 7% at Ni (44.2% wt Ti-55.8% wt Ni) 3.07
6th 48.5% at Ti-51. 5% at Ni (43.5% wt Ti-56.5% wt Ni) 1.78
7th 47.8% at Ti-52. 2% at Ni (42.7% wt Ti-57.3% wt Ni) 0.5
Table 2: Model of SMA-FGM2 profile.
Citation: Khafaji NSL, Hafiz MH, Atiyah AA (2018) Sintering of Incorporated Shape Memory Alloys into Functionally Graded Materials. Ind Eng
Manage S3: 002. doi: 10.4172/2169-0316.S3-002
Page 3 of 4
Ind Eng Manage Materials with Compositional Variations ISSN: 2169-0316, IEM an open access journal
an increase the amount of produced NiTi phase which a major shape
memory effect [8].
In other hand, there might have some sort of oxides, which are
lower than disclosure ability of the used XRD apparatus when they are
less than 5%. The formation of Ni3Ti might be refer to the slow cooling
of the samples inside furnace whereas, in the sintering conditions used
through this work, the Gibbs free energies for Ni3Ti was less than that
for NiTi and it seems difficult to obtain a final equilibrium structure of
NiTi alone just by solid-state diffusion [9].
There are four (NiTi) alloys have been studied (first, second, third
and fourth layers). First layer (55 wt% Ni, 45 wt% Ti), its chemical
composition is close to that show in Tables 1 and 2, and the other alloys
have different chemical composition which is shown also in Tables 1
and 2.
Otherwise, the peaks conformable to Ni3Ti might correspond to
that view is based on an XRD pattern for a mixture of 50 at% Ni (50
at%Ti) which shows that the 2?s (in degrees) in a agreement to angles
as shown in Figure 3 [10]. Comparing these angles to those of Ni3Ti
(Figure 3) one can see that they have nearly the same angles, which
makes it difficult to judge (the phases are determined manually, by
indicate to reference cards and literatures [11].
Second layer (55.8 wt% Ni, 44.2 wt% Ti), its chemical composition,
the XRD results can be shown in Figure 3. Third layer (56.5wt% Ni,
43.5 wt% Ti), its chemical composition, the XRD results can be
shown in Figure 3. Forth layer (57.3wt% Ni, 42.7wt% Ti), its chemical
composition, the XRD results can be shown in Figure 3.
The XRD results for SMA-FGM can be shown in Figure 4. The
phases of alloys were specified by calculating d - spacing (using Brag’s
law) liken with standard XRD cards. The range of the diffraction angle
was (20°-90°). All (Ni-Ti) alloys studied have some phases dependent
on chemical composition, the main two phases are (M-NiTi) and
?2 (Ni3Ti), and the other two phases are (Ni2Ti) and(NiTi4) [12].
These phases can be detected according to their wt% used in binary
equilibrium phase diagrams for (Ni-Ti) systems.
Acknowledgments
The financial support Mr Sattar Radhi Al- Khafaji and the Ministry of Higher
Education, is gratefully acknowledged. This research was carried out in the
laboratory at Babylon University.
References
1. Falvo A (2008) Thermomechanical characterization of Nickel-Titanium shape
memory alloys. PhD thesis Department of Mechanical Engineering, University
Della Calabria. Italy.
2. Koizumi M, Niino M (1995) Overview of FGM research in Japan. Mrs Bulletin
20: 19-21.
Figure 3: XRD patterns of FGM layers.
Figure 4: XRD patterns of SMA-FGM1 and SMA-FGM2.
Citation: Khafaji NSL, Hafiz MH, Atiyah AA (2018) Sintering of Incorporated Shape Memory Alloys into Functionally Graded Materials. Ind Eng
Manage S3: 002. doi: 10.4172/2169-0316.S3-002
Page 4 of 4
Ind Eng Manage Materials with Compositional Variations ISSN: 2169-0316, IEM an open access journal
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  • SMA; Functionally graded NiTi materials; Biocompatibility; XRD