Sections
Personal tools
 

NiMnGa-polymer-composite

 

← back to Main Page / MSM

 

Single-crystals, usually needed for the MSM effect, are generally difficult and expensive to prepare. There are two alternative approaches for bulk MSM material, polycrystalls and MSM-polymer-composites. Textured polycrystals are capable to work, but especially the stresses along grain boundaries need to be dealt with in order to avoid fracture. Another possibility here is to assume a polycrystal, but in order to avoid a rigid interface between grains, i.e. the grain boundaries, a thin polymer layer is added between grains. These MSM-polymer-composites are prepared by embedding single-crystalline MSM particles (easy to prepare) in a stiffness matched matrix, which is soft enough to allow the particles to deform. On the other hand, the matrix needs to be stiff enough to maintain a coupling of the MSM particles with each other and the matrix. I general, this gives of coarse a somehow diluted system, as only a certain volume fraction of these composites is active MSM material. But further advantages are the easy preparation (textured and in desired shape) and the possibly enhanced fatigue behavior (composite still works when some MSM particles fracture). As MSM alloys are usually good electric conductors, a problem of both single and polycrystalline MSM material is the generated loss in high frequency application due to eddy currents. The polymer matrix in MSM-polymer-composites is insulating, thus eddy currents and corresponding losses are reduced.

In these composites, the orientation of MSM particles within the matrix can be controlled by an applied magnetic field during curing of the polymer matrix. The MSM particles we have used so far are single/oligo crystalline fractions of melt-extracted Ni50.9Mn27.1Ga22.0 (at.%) fibres (figure A). The matrix material has been either polyester or polyurethane. Mechanical compression of the composites leads to easy magnetisation behaviour in the compressed direction and harder magnetisation behaviour in the perpendicular directions of the composites (figure B). This behaviour is attributed to stress-induced twin boundary motion within the MSM particles. Magnetic field controlled damping applications could therefore be envisaged. On the other hand, as the MSM particles used show also the MSM effect, composite actuators are possible.

 

Composite

Electron microscopy (SEM) image of Ni-Mn-Ga fibre fractions (A) and magnetization versus applied field curves for a MSM-polymere-composite (B).


Related publications

  • N. Scheerbaum, O. Heczko, J. Liu, D. Hinz, L. Schultz, O. Gutfleisch: Magnetic field-induced twin boundary motion in polycrystalline NiMnGa fibres, New Journal of Physics 10 (2008) 73002/1-8. URL
  • N. Scheerbaum, D. Hinz, O. Gutfleisch, K.-H. Mueller, L. Schultz: Textured polymer bonded composites with NiMnGa magnetic shape memory particles, Acta Materialia 55 (2007) 2707-2713. URL
  • N. Scheerbaum, D. Hinz, O. Gutfleisch, W. Skrotzki, L. Schultz: Compression-induced texture change in NiMnGa-polymer composites observed by synchrotron radiation, Journal of Applied Physics 101 (2007) 9C501/1-3. URL
  • D. Hinz, N. Scheerbaum, O. Gutfleisch, K.-H. Mueller, L. Schultz: Polyester-bonded textured composites with single-crystalline shape memory NiMnGa particles, Journal of Magnetism and Magnetic Materials 310 (2007) 2785-2787. URL

 

 

 back to main page