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SUMMARY:Magnetic shape-memory alloys replace machines
DTSTART:20120608T110000
DTSTAMP:20260407T055250Z
UID:28824853397ef3033e4c32fd4edea76db98bf0337fd32e40236a04ae
CATEGORIES:Conferences - Seminars
DESCRIPTION:Peter Müllner\, Boise State University\, Idaho\nIn the movie 
 “Terminator 2” with Arnold Schwarzenegger as good guy T-800\, Robert P
 atrick played the villain\, a more modern T-1000 terminator. The T-1000 ou
 tperformed the T-800 because it was made of a liquid metal with the fabulo
 us property of remembering shapes. The material replaced all the little ma
 chines which were built into the old T-800 terminator. Magnetic shape-memo
 ry alloys do exactly that: they enable the replacement of machines by mate
 rials and introduce a new paradigm for mechanical engineering\, particular
 ly useful for the miniaturization of mechanical devices. A pump no larger 
 than 2 x 10 x 25 mm delivers tiny volumes at unprecedented speed and preci
 sion. This pump is an enabling technology of the lab-on-a-chip. The magnet
 ic-field-driven migration of a cavity on a Ni-Mn-Ga single crystal rod tra
 nsports the fluid. The cavity moves via the motion of twin boundaries at s
 tresses well below 1 MPa. This very low twinning stress makes the material
  susceptible to internal and external constraints such as grain boundaries
  and clamping mechanisms. Clamping stresses generate cracks and trigger fr
 acture upon dynamical loading. I will discuss twinning mechanisms from the
  atomistic to the macroscopic length scale with an emphasis on manipulatin
 g the twin microstructure via training and surface treatments. Ni-Mn-Ga al
 loys with optimized twin microstructures overcome internal and external co
 nstraints and perform consistently over extended life times.
LOCATION:MXG312
STATUS:CONFIRMED
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