U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding
С использованием метода, основанного на ультрамалоугловом рассеивании нейтронов, выполнен анализ размеров пор диаметром 100 нм ... 25 мкм в полученных инжекционной формовкой образцах из никель-титанового сплава (с памятью формы) до и после обработки импульсным электрическим током. При обработке обра...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2010
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| Назва видання: | Проблемы прочности |
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irk-123456789-1120172017-01-17T03:02:52Z U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding Giuliani, A. Calbucci, V. Fiori, F. Imgrund, P. Babutskiic, A.I. Научно-технический раздел С использованием метода, основанного на ультрамалоугловом рассеивании нейтронов, выполнен анализ размеров пор диаметром 100 нм ... 25 мкм в полученных инжекционной формовкой образцах из никель-титанового сплава (с памятью формы) до и после обработки импульсным электрическим током. При обработке образцов поры диаметром меньше 4 мкм коалесцируют, а поры диаметром больше 4 мкм уменьшаются в размерах. Із використанням методу, що базується на ультрамалокутовому розсіянні нейтронів, проаналізовано розміри пор діаметром 100 нм...25 мкм в отриманих інжекційним формуванням зразках нікель-титанового сплаву (із пам’яттю форми) до і після обробки імпульсним електричним струмом. При обробці зразків пори діаметром, який менше за 4 мкм, зливаються, а більше за 4 мкм, зменшуються в розмірах. 2010 Article U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding / A. Giuliani, V. Calbucci, F. Fiori, P. Imgrund, A.I. Babutskiic // Проблемы прочности. — 2010. — № 6. — С. 137-145. — Бібліогр.: 19 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/112017 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Giuliani, A. Calbucci, V. Fiori, F. Imgrund, P. Babutskiic, A.I. U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding Проблемы прочности |
| description |
С использованием метода, основанного на ультрамалоугловом рассеивании нейтронов, выполнен анализ размеров пор диаметром 100 нм ... 25 мкм в полученных инжекционной формовкой образцах из никель-титанового сплава (с памятью формы) до и после обработки импульсным электрическим током. При обработке образцов поры диаметром меньше 4 мкм коалесцируют, а поры диаметром больше 4 мкм уменьшаются в размерах. |
| format |
Article |
| author |
Giuliani, A. Calbucci, V. Fiori, F. Imgrund, P. Babutskiic, A.I. |
| author_facet |
Giuliani, A. Calbucci, V. Fiori, F. Imgrund, P. Babutskiic, A.I. |
| author_sort |
Giuliani, A. |
| title |
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding |
| title_short |
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding |
| title_full |
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding |
| title_fullStr |
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding |
| title_full_unstemmed |
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding |
| title_sort |
u-sans analysis of as-sintered and pec-treated niti sma produced by metal injection moulding |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2010 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/112017 |
| citation_txt |
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA Produced by Metal Injection Moulding / A. Giuliani, V. Calbucci, F. Fiori, P. Imgrund, A.I. Babutskiic // Проблемы прочности. — 2010. — № 6. — С. 137-145. — Бібліогр.: 19 назв. — англ. |
| series |
Проблемы прочности |
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2025-07-08T03:11:35Z |
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2025-07-08T03:11:35Z |
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| fulltext |
UDC 539.4
U-SANS Analysis of As-Sintered and PEC-Treated NiTi SMA
Produced by Metal Injection Moulding
A. Giuliani,
a
V. Calbucci,
a
F. Fiori,
a
P. Imgrund,
b
and A. I. Babutskii
c
a Marche Polytechnic University, Ancona, Italy
b Fraunhofer Institute of Manufacturing and Advanced Materials, Bremen, Germany
c Pisarenko Institute of Problems of Strength, National Academy of Sciences of Ukraine,
Kiev, Ukraine
ÓÄÊ 539.4
Àíàëèç èñõîäíîãî è îáðàáîòàííîãî èìïóëüñíûì ýëåêòðè÷åñêèì
òîêîì íèêåëü-òèòàíîâîãî ñïëàâà, ïîëó÷åííîãî ìåòîäîì èíæåêöèè,
ïðè èñïîëüçîâàíèè óëüòðàìàëîóãëîâîãî ðàññåèâàíèÿ íåéòðîíîâ
À. Äæóëèàíè
à
, Â. Êàëáó÷÷è
à
, Ô. Ôèîðè
à
, Ô. Èìãðóíä
á
, À. È. Áàáóöêèé
â
à Ïîëèòåõíè÷åñêèé óíèâåðñèòåò îáëàñòè Ìàðêå, Àíêîíà, Èòàëèÿ
á Ôðàóíãîôåðñêèé èíñòèòóò ïðîìûøëåííîñòè è ñîâðåìåííûõ ìàòåðèàëîâ, Áðåìåí,
Ãåðìàíèÿ
â Èíñòèòóò ïðîáëåì ïðî÷íîñòè èì. Ã. Ñ. Ïèñàðåíêî ÍÀÍ Óêðàèíû, Êèåâ, Óêðàèíà
Ñ èñïîëüçîâàíèåì ìåòîäà, îñíîâàííîãî íà óëüòðàìàëîóãëîâîì ðàññåèâàíèè íåéòðîíîâ, âû-
ïîëíåí àíàëèç ðàçìåðîâ ïîð äèàìåòðîì 100 íì ... 25 ìêì â ïîëó÷åííûõ èíæåêöèîííîé ôîðìîâ-
êîé îáðàçöàõ èç íèêåëü-òèòàíîâîãî ñïëàâà (ñ ïàìÿòüþ ôîðìû) äî è ïîñëå îáðàáîòêè èìïóëüñ-
íûì ýëåêòðè÷åñêèì òîêîì. Ïðè îáðàáîòêå îáðàçöîâ ïîðû äèàìåòðîì ìåíüøå 4 ìêì êîàëåñ-
öèðóþò, à ïîðû äèàìåòðîì áîëüøå 4 ìêì óìåíüøàþòñÿ â ðàçìåðàõ.
Êëþ÷åâûå ñëîâà: ìåòîä óëüòðàìàëîóãëîâîãî ðàññåèâàíèÿ íåéòðîíîâ, èíæåê-
öèîííàÿ ôîðìîâêà, èìïóëüñíûé ýëåêòðè÷åñêèé òîê.
Introduction. The study of the electromagnetic field effects on dislocations
and other defects involved in the deformation process of polycrystalline solids is
still a challenge in material science. In fact, according to the review of the present
work authors, the influence of specific electric fields was clarified just in a few
conventional materials like steels, cast iron and the principal aluminum and
titanium alloys [1]. On the other hand, it is assessed that an electric field offers an
additional parameter in metal processing with the potential of increasing the
efficiency and effectiveness of the process, improving the final resulting thermo-
mechanical properties.
For instance, high density (103–106 A/cm2) electropulsing influences the
flow stress of metals at 78–300 K during their tensile deformation, significantly
reducing the flow stress (or increasing the strain rate) [2–5].
© A. GIULIANI, V. CALBUCCI, F. FIORI, P. IMGRUND, A. I. BABUTSKII, 2010
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6 137
The effects of an external electric field (surface charge) on the superplastic
deformation of the 7475 Al alloy were investigated and it was found that the field
produced the following effects [6–10]: (a) reduced the flow stress by 10–20%,
(b) slightly increased the strain rate hardening exponent m�� � � �ln ln , (c) slightly
increased the width of the dispersoid-free zone at the grain boundaries. In the case
of 7475 Al alloy, the field also changed the chemical composition and enhanced
the formation of whiskers; therefore: (d) retarding grain growth and (e) significantly
reducing cavitation.
The effects of electric fields were also tested during the superplastic
deformation of 3Y-TZP. Even in this case, the electric field reduced the flow stress
and increased the elongation. Along with its effect on the stress–strain curve, the
field retarded grain growth and cavitation [11].
For the first time in the present work, pulse electric current (PEC) treatment
was applied to NiTi SMA specimens produced by metal injection moulding (MIM).
Ultra-small angle neutron scattering (U-SANS) analysis was performed on
NiTi specimens in order to verify if defect (pore) size varies after the PEC treatment
in the dimensional range between 100 nm and 25 �m. U-SANS technique is in fact
a suitable characterization method in order to get such answer in this range.
1. Materials and Methods.
1.1. NiTi Specimens Preparation by MIM. MIM was first used for NiTi
processing by Bram et al. [12]. In the present process, prealloyed NiTi powder with
a powder particle size d� � 11.3 �m and an atomic ratio of 50.7% Ni–49.3% Ti
was mixed with an organic binder of waxes and polymers to obtain the feedstock.
Specimens were moulded as in conventional injection moulding. The binder was
then retracted from the part and sintered at 1250�C under high vacuum (10 4 mbar).
Density measurements by the Archimedes method showed that a density of
91–94% of theoretical density was obtained after sintering. The process and some
of the obtained moulded parts are depicted in Fig. 1.
1.2. PEC Treatment of NiTi Specimens. PEC treatment was fulfilled using a
pulse electric current generator consisting of a high voltage power supplier,
capacitor banks and discharge switch. Registration of the pulse electric current
Fig. 1. MIM process (left) and NiTi green parts (right).
138 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6
A. Giuliani, V. Calbucci, F. Fiori, et al.
parameters was realized using Rogovsky coil, high frequency A/D converter and
PC where data were stored and processed. The treatment was carried out by direct
current passage through the NiTi specimen. Three short sequential pulses of the
electric current with the maximum amplitude of 52 kA – 56 kA – 52 kA were
passed through the specimen, here the specimen sectional area was near 80 mm2.
2. Experimental Methods.
2.1. Preliminary Characterization by Scanning Electron Microscopy and
Energy Dispersive X-ray Analysis. As-sintered NiTi specimens were characterized
by means of scanning electron microscopy (SEM) and energy dispersive X-ray
(EDX) analyses for a preliminary determination of pore size, Ni–Ti ratio and phase
compositions. The microstructure, as revealed by SEM, is shown in Fig. 2.
Concerning composition, two different phases were detected by EDX
analyses. The light grey matrix phase was found to be NiTi: the atomic ratio
detected was 50.3 Ni–49.7 Ti, which was in good accordance with the base
material composition. The slightly darker phase revealed a Ni/Ti ratio of 33/67,
indicating the presence, after sintering, of a very low amount of NiTi2 secondary
phase. Figure 2 shows such multi-phase microstructure along with some irregular
porosity. In fact, together with large irregularly shaped pores, different fine,
spherical pores were detected, demonstrating the necessity to investigate the PEC
treatment effects on NiTi by U-SANS, such technique being sensitive at a scale
range comparable with the latter pore dimensional group.
2.2. Characterization by the U-SANS. U-SANS analysis was performed at the
double crystal diffractometer (DCD) instrument at the Geesthacht Neutron Facility
(Geesthacht, Germany) on NiTi specimens produced by MIM before and after the
PEC treatment. The DCD, in the chosen set-up, was equipped with triple-bounce
channel-cut perfect Si crystals [13]. Using the (111) reflection, the full width at
half-maximum (FWHM) of the rocking curve (RC) is about 2 6 10 4.
nm 1 at a
wavelength of �� 0.44 nm.
When compared with single-bounce crystals, the instrumental background at a
scattering vector Q � 10 3 nm 1 is decreased by two orders of magnitude: this
Fig. 2. SEM micrograph of NiTi after MIM and sintering at 1250�C under high vacuum.
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6 139
U-SANS Analysis of As-Sintered and PEC-Treated ...
leads to enormous progress involving the possibility to detect small volume
fractions of inhomogeneities in the size range from 100 nm up to about 25 �m
[14].
Because of this, DCD was selected and used in the present work to analyze
shape, size distribution and volume fraction of pores and the effects of the PEC
treatment on them.
Pore size distribution N R( ) shall be defined in the radius interval [Rmin ,
Rmax]: it can be written as a linear combination of m basic size distributions n Ri ( )
with coefficients x i :
N R x n Ri i
i
m
( ) ( ).�
�
�
1
(1)
Cubic B-splines are chosen for the basic size distributions n Ri ( ). With such a
set of basic functions, an arbitrary smooth function can be approximated [15, 16].
We numerically treated the data obtained on both PEC-treated and untreated
specimens with a model based on two phases coexistence: the NiTi phase and
another phase corresponding to pores. This model is called two-phase model and is
based on the assumption of the presence of pores with a size distribution N R( ),
embedded in a homogeneous matrix (polidispersion). The Master equation of such
model is the following [17, 18]:
d
d
N R V R F QR dR
�
�
��
�
( ) ( ) ( ) ( ) ,
2 2 2
0
(2)
where d d� � is the macroscopic cross section of pores (the measured quantity),
( )�
2 is the nuclear contrast between the pores and the matrix, V R( ) is the pore
volume, and F QR( ) is the pore form factor. In our case, on the basis of
preliminary SEM analysis (Sec. 2.1), we considered a sphere-like form factor,
corresponding pores approximately spherical in shape.
Under these conditions it is also possible to estimate pore volume fraction f
by means of the following equation:
f N R V R dr� ( ) ( ) . (3)
An estimate of the pore size can also be obtained by means of the Guinier
approximation. As far as this is valid, that is for QRG �15. (approximately), Eq. (2)
can be written as
d
d
nV
Q RG�
�
��
�
�
�
�
�
�
�
�( ) exp ,
2 2
2 2
3
(4)
where n is the number density of pores and RG is the Guinier radius. For
spherical pores with radius R, R RG � 3 5 ; in the case of polydispersion, RG
depends on the size distribution:
140 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6
A. Giuliani, V. Calbucci, F. Fiori, et al.
R
R N R dR
R N R dR
G
2
8
0
6
0
�
�
�
�
�
( )
( )
, (5)
RG is usually determined by the slope, at low Q values, of the linear plot
ln( )d d
� vs. Q 2 . Anyway an alternative (and even more direct) method is by
plotting Q d d2 ( )
� vs. Q. In fact, from Eq. (4), it is easy to verify that this
function has a maximum for Q RG� 3 .
3. Results. The Q d d2 ( )
� vs. Q plots for the untreated and PEC-treated
specimens are shown in Fig. 3. In the untreated profile, two peaks corresponding to
two pore families are detected, one with RG �2 37. �m and the other with
RG �8 75. �m. In the PEC-treated case, only the peak corresponding to the biggest
family is clearly visible, with a Guinier radius smaller than the one for the
untreated specimen (RG �5 83. �m); on the contrary, the peak corresponding to the
smaller family is not detectable.
In Fig. 4 the DCD scattering curves from the PEC-treated (dotted line) and the
untreated (solid line) NiTi specimens are shown, superimposed to the best fit
curve obtained by writing N R( ) as a linear combination of cubic B-spline
functions � i R( ):
N R c R
d
d
c R V R F QR dRi i
i
N
i i
s
( ) ( ) ( ) ( ) ( ) ( ) .� � �
�
� � � �
1
2 2 2
�
�
01
�
�
��
i
N s
(6)
The coefficients ci are the parameters optimized by the least-square fit and
resulting in the pore size distribution N R( ) shown in Fig. 5.
Fig. 3. Q d d2 ( )
� vs. Q plots for the PEC-treated (dot-line) and the untreated (solid line) specimens.
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6 141
U-SANS Analysis of As-Sintered and PEC-Treated ...
The N R( ) size distribution is four-modal (4 peaks in each curve) (Fig. 5). In
the untreated specimen there is a first big family of pores (I-F) with a main pore
radius slightly bigger than 400 nm, another family (II-F) with average radius close
to 800 nm, a third group (III-F) with a radius close to 2.5 �m and the last family
(IV-F) with a radius close to 10 �m.
It is visible from the results presented in Fig. 5 that after PEC treatment the
redistribution of the pores numbers took place: the total pores’ number in the
former I-F and III-F families was reduced; in the II-F family, the pores’ number
with smaller dimension was reduced and the pores’ number with bigger dimension
was increased; and vice versa for the last IV-F family, the share of pores with
smaller dimension was increased against the reduction of the big pores’ number.
The volume fractions for each pore family can be calculated as the integral of
the curves N R V R( ) ( ) vs. R , where N R( ) is the size distribution, V R( ) is the
volume of the pore, and R is its radius, i.e., applying (2) and (3) and extrapolating
the results shown in Fig. 6.
Fig. 4. DCD scattering curves for the PEC-treated (dot-line) and the untreated (solid line) specimens.
Fig. 5. Pore size distribution in the PEC-treated specimens (dot-curve) and in the untreated ones
(solid curve).
142 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6
A. Giuliani, V. Calbucci, F. Fiori, et al.
In the untreated specimen (solid-line) the I-F (R close to 400 nm) exhibits a
small volume fraction. This is justified by very small volume of such pores. The
second family, with the average radius close to 800 �m has a quite high volume
fraction close to 2/3 of the third group (that one with R close to 2.5 �m). The
fourth family with an average pore radius close to 10 �m has a very small volume
fraction: this is due to the almost negligible amount of pores of such size, as it is
detectable by SEM (Sec. 2.1). After the PEC treatment the volume fraction of the
first family of pores is reduced, the volume fraction of the second family
significantly increased and that of the third family significantly reduced. In
contrast to the other three families, the trend of the last group (with a radius close
to 10 �m before PEC treatment), after the treatment exhibit at the meantime an
increasing of its volume fraction and significant reduction of its pore radius from
10 �m to less than 8 �m. These results (at least for what concerns the III-F and
the IV-F) are in good agreement with the ones previously obtained by the Guinier
approximation.
Analysis of the results obtained shows substantial redistribution of pore
numbers depending of their sizes due to PEC treatment. This is takes place via
coalescence of pores and reduction of their sizes. In addition, an annihilation of
small pores is possible. The reason of these processes can be a vacancy movement
generated by the pores under passage of electric current through the material [19].
At least two mechanisms of stimulation of vacancy generation exist: the first one is
related to entrainment of the vacancies by conductivity electrons and the second
one is related to nonhomogeneity of temperature distribution in the material caused
by inhomogeneous Joule heat release in the defects of material structure (e.g., in
pores). Generated temperature gradients cause local thermal stresses contributing
pores coalescence and emission of vacancy-type dislocation loops. It causes the
reduction of pore sizes and, as extreme case, results in pores’ annihilation.
Conclusions. U-SANS was successfully applied for microstructural analysis
of NiTi shape memory alloys submitted to PEC treatment. In particular, quantitative
information about structure in the size range between 100 nm and a few tens of �m
were obtained. This technique gave us a possibility to investigate parameters such
as cavity density and dimensions, before and after the PEC treatment.
Fig. 6. Pore volume fraction (integrated area) in the PEC-treated specimens (dotted curve) and in the
untreated ones (solid curve).
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6 143
U-SANS Analysis of As-Sintered and PEC-Treated ...
The phase morphology of the material (presence of pores) before and after PEC
treatment has yielded data required for the optimization of the processing routes.
The results described in the previous chapter corroborate that, while pores
with diameter smaller than 4 �m undergo coalescence phenomena after the PEC
treatment, with a reduction of pores number but a crucial increase of their
dimensions, in pores with diameter bigger than 4 �m the PEC treatment causes
pore size reduction.
Redistribution of pores numbers demands a more precise definition of
physical mechanisms through further microstructure investigations.
Acknowledgments. The authors acknowledge the help of Dr. K. Pranzas for
the technical support during the U-SANS experiment at GKSS. This research has
been supported by the European Commission under the 6th Framework
Programme through the Key Action: Strengthening the European Research Area,
Research Infrastructures. Contract No.: RII3-CT-2003-505925 (NMI3).
This work was also supported by the EU Network of Excellence project
Knowledge-based Multicomponent Materials for Durable and Safe Performance
(KMM-NoE) under the contract No. NMP3-CT-2004-502243.
Ð å ç þ ì å
²ç âèêîðèñòàííÿì ìåòîäó, ùî áàçóºòüñÿ íà óëüòðàìàëîêóòîâîìó ðîçñ³ÿíí³
íåéòðîí³â, ïðîàíàë³çîâàíî ðîçì³ðè ïîð ä³àìåòðîì 100 íì...25 ìêì â îòðè-
ìàíèõ ³íæåêö³éíèì ôîðìóâàííÿì çðàçêàõ í³êåëü-òèòàíîâîãî ñïëàâó (³ç ïà-
ì’ÿòòþ ôîðìè) äî ³ ï³ñëÿ îáðîáêè ³ìïóëüñíèì åëåêòðè÷íèì ñòðóìîì. Ïðè
îáðîáö³ çðàçê³â ïîðè ä³àìåòðîì, ÿêèé ìåíøå çà 4 ìêì, çëèâàþòüñÿ, à á³ëüøå
çà 4 ìêì, çìåíøóþòüñÿ â ðîçì³ðàõ.
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144 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6
A. Giuliani, V. Calbucci, F. Fiori, et al.
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Received 22. 04. 2009
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 6 145
U-SANS Analysis of As-Sintered and PEC-Treated ...
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