Transcript Bez tytułu slajdu

On
the
Track
Invar is Fe-Ni, 65-35% alloy.
Ab-initio calculations [1] showed that magnetic
moments of nickel (blue here) are aligned, while
those of iron (red) seem to be chaotic. And this
disorder-in- order assures the minimum volume
(and energy)
Read below.
Physics
USAF Aircraft Pictures -
INVAR Effect- after 100 years finally understood
http://psi-k.dl.ac.uk/TMR1/summary_report.htm
The result on INVAR has been obtained within EU TMR Network
Ab-Initio Calculations of Magnetic Properties of Surfaces, Interfaces and Multilayers
guided by prof. Walter Temmerman from Daresbury Laboratory, Warrington, UK
We thank for the permission.
Modern
Do you remember old spring-moved clocks?
Their pendulum was attached to thin, highprecision spings, made of INVAR.
Old material, but new discoveries!
Nature 400 (1999) 46
In 1897 the Swiss physicist Charles Edouard Guillaume discovered that
fcc Fe-Ni alloys with a Ni concentration around 35 atomic %, now called
INVAR, exhibit anomalously low, almost zero, thermal expansion over a wide
temperature range. This discovery immediately found widespread application
in the construction of calibrated, high-precision mechanical instruments, such as
seismographs and hair springs in watches. Today, Invar alloys are used in
temperature-sensitive devises, such as shadow masks for television and
computer screens. In 1920 Guillaume was awarded the Nobel Prize in Physics
for the discovery of these Fe-Ni alloys.
It was realized early on that the explanation of the Invar effect is related
to magnetism. Yet, though it has been 100 years since this effect was discovered,
it was not understood. In a recent article published in Nature ''Origin of the
Invar effect in iron-nickel alloys (Nature 400, 46 (1999)), I. Abrikosov and B.
Johansson from Uppsala node of the Network, in collaboration with Mark van
Schilfgaarde from Sandia National Laboratories, Livermore, USA, presented
results of ab initio calculations of volume dependences of magnetic and
thermodynamic properties for the most typical Invar system, a random fcc FeNi Invar alloy, where they allowed for noncollinear spin alignments, i.e. where
the spins may be canted with respect to the average magnetization direction.
They have found that the evolution of the magnetic structure already at zero
temperature is characterized principally by a continuous transition from the
ferromagnetic state at high volumes to a disordered noncollinear configuration
at low volumes, and that there is an additional, comparable contribution to the
net magnetization from the changes in the amplitudes of the local magnetic
moments. The noncollinearity gave rise to an anomalous volume dependence of
the binding energy curve, and this allowed Mark van Schilfgaarde, I. Abrikosov
and B. Johansson to explain the well-known peculiarities of Invar systems.
of
http://sun.vmi.edu/hall/afpics.htm
Some material shrink with temperature,
another come back to their old shape.
We call them “shape-memory” alloys.
The most common shape-memory metals are Nickeltitanium 50-50 alloys or copper alloys, like CuZnAl,
and CuAlNi, but even Pt is used.
The wire, twisted at low temperature, when heated
will come back to the original shape.
And the “original” shape? It is fixed bending the wire
at 500ºC. It can be bent and unbent a million times.
stress
stress
plastic deformation
plastic deformation
Memory-shape flaps do not require huge
hydraulic actuators but only heating
wires. They are used in USA military
aviation from sixties
deformation
“Normal” material are subject to a permanent plastic
deformation, once stress exceeds the limit of elasticity. In
shape-memory alloys, a thermal treatment, after the stress has
been removed, brings the object to the original dimensions.
0.6
Germanium
After: K. Ireland, University of Wollongong, Material Engineering
http://www.uow.edu.au/eng/mm/matl/ShapeMemoryAlloys.pdf
0.4
0.2
In shape-memory alloys
two sub-phases coexist:
hard, high-T austenite and
low-T, plastic martensite.
Cooling brings all austenite
to martensite. Subsequent
deformation keeps the
martensite structure intact.
It return to the original
austenite after heating.
-6
-1
loading
loading
Shape memory
Thermal expansion coefficient
 (10 K )
unloading
unloading
deformation
Other applications of memory-shape
alloys span from robot actuators,
hydraulic fittings to medical protesis.
Some material do not expand with temperature,
some of them even shrink, like Germanium at low
temperatures. Sometimes, they expand in one
dimension but shrink in another direction.
Hook’s law
Hook’s law
Negative expansion is often connected to the
presence of some sub-crystal structures,
moving and rotating independently.
An axample is silver-copper oxide, of the cuprite
symmetry structure [2].
0
-0.2
-0.4
0
20
40
60
80
T(K)
x
Nitinol Devices and Components
http://www.nitinol.com/images/3slide3.gif
www.fz-juelich.de/iwv/iwv1/datapool/page/9/fgl2.jpg
Forschungszentrum Jülich
http://www.ifm.eng.cam.ac.uk/people/sc444/
Innovative Manufacturing Research Centre
Cambridge University Engineering Department
Photon energy h 
Ag2O & Cu2O
We can see these tiny changes of interatomic distances with an even
smaller sonde (X-rays). One of the techniques is called
“Extended Fine Structure X-Ray Absorption”
This (left) picture from Transmission Electron Microscopy shows
coexistence of martensite (long needles) and austenite (patches)
phases. In pure titanium only one phase exists (Scanning EM).
It works in the following manner:
1. X-ray (synchrotron radiation) is tuned to the energy of an
internal-electron level of the probe atom.
2. An absorbed X-ray quantum releases an electron from this atom.
3. This electron (i.e. the quantum wave objects) interfers
with itself, getting scattered on neighborourhood atoms.
Two inter-penetrating networks of corner sharing
M4O tetrahedra with O-M-O linear coordination
4. A fine structure, depending on the interatomic diustances is
observed in the X-ray absorption. In this mode the neighbourhood
of the X-ray absorping atom is exploited.
[1] M. van Schilfgaarde, I. A. Abrikosov, B. Johansson, Origin of the Invar effect in iron–nickel alloys, Nature 400 (1999) 46
[2] S. a Beccara, G. Dalba, P. Fornasini, R. Grisenti, A. Sanson, and F. Rocca,
Local thermal expansion in a cuprite structure: the case of Ag2O, Phys. Rev. Lett. 89, 25503 (2002)
Figures are from prof. P. Fornasini,
University of Trento, Physics Department,
Thanks!
This Fe-Cr-Ni-Mo dual-phase stainless
steel elongates better than the chewing gum
And this “cosmic” rubber is soft,
if torn slowly, but springs, if hit.
The Material Science
came to the playground!