Ni-Ti AND Ni-Mn-Ga NANOCRYSTALLINE SHAPE MEMORY ALLOYS AND COMPOSITES FOR NEXT GENERATION SENSORS AND ACTUATORS Teodor M. Breczko Lab of Functional Materials and Nanotechnology of University of Warmia and Mazury, Olsztyn, Poland

SHAPE MEMORY ALLOYS (SMA) Rapidly quenched melt-spun ribbons of Ti-Ni, Ti 50 Ni 50-x Fe x, Ti 50 Ni 50-y Co y and Ti 50 Ni 50-z Cu z shape memory alloys were obtained and studied with the aid of X-ray diffraction, TEM and magnetic susceptibility and resistivity measurements. The formation of amorphous, nanocrystalline, and submicron-grained structures was demonstrated.

The X-ray diffraction studies show that, depending on the composition and the cooling rate, the melt- quenched Ni-Ti-Cu alloys can be prepared in the amorphous (curves 1,2), mixed amorphous- nanocrystalline (3), and submicrocrystalline states (4,5).

Experimental results Changes in RMS micro-strains   2  1/2 *10 -3 with number of thermal and mechanical loading.

High mechanical strength and plasticity of rapidly quenched ribbons may be obtained alongside with narrow temperature hysteresis of the shape memory effect and high durability necessary for a number of applications. The Cu-doped melt-spun ribbons are found to be most promising for sensors and actuators operating in the vicinity of room temperature. Temperature sensor on the base of Ti-Ni-Cu melt-spun ribbon ring actuator with a diameter D = 2 mm (movable contact not shown). Operation temperature T = 70 o C.

FERROMAGNETIC SHAPE MEMORY HEUSLER ALLOYS (FSMA) Ferromagnetic Ni-Mn-Ga and Co-Ni-Ga Heusler alloys attract attention due to their unique combination of thermoelastic martensitic transformation and ferromagnetism as well as potential applications in new types of sensors and actuators. Rapidly quenched ribbons (RQR) of these alloys with nano- and microcrystalline structure controlled by annealing are of interest in connection with the possibility of their shape memory control with the aid of magnetic field.

FERROMAGNETIC SHAPE MEMORY HEUSLER ALLOYS Ni 2+x Mn 1-x Ga Partial substitution of Mn with Ni increases the temperature of structural transition T M and decreases the Curie temperature T C resulting in their coincidence at x ~ 0.19 TMTM TCTC TPTP

Observations in polarized light provide new dimensions to the analysis of the martensite structure. The optical contrast originates from anistropic reflectance of martensite and depends on the orientation of the crystal c-axis with respect to the plane of light polarization. Martensite structure at the surface of a mechanically polished polycrystalline Ni 2.16 Mn 0.84 Ga sample as observed in polarized light

Video showing the appearance and disappearance of martensite phase in Ni 2.16 Mn 0.84 Ga alloy in the course of cooling and heating

Microstructure of Ni 2.16 Mn 0.84 Ga at RT and at Т = 370 К Arrows and letters indicate the points of intersection of martensite boundaries with a rectangular reference grid on the sample surface and their inflection on transition to the austenite state Combined optical measurements of the deformation and microstructural observations provide information on the details of material behaviour during phase transition martensite austenite

OBSERVATION OF DS REALIGNMENT DURING MARTENSITE- AUSTENITE TRANSFORMATION IN Ni-Mn-Ga ALLOY (video film fragments) Sample size 200x800  m Initially the Ni 2.16 Mn 0.84 Ga microcrystal is in the martensitic state characterized by 180-degree magnetic DS. On heating the alloy transforms into a cubic magnetically soft austenite phase with negligible stray fields on the sample surface

Melt-spun Ni-Mn-Ga ribbons thickness 30  m, length mm

initial shape after heating SHAPE MEMORY EFFECT IN NANOCRYSTALLINE Ni-Mn-Ga RIBBON

Simultaneous observation of the martensite and magnetic domain structure of polycrystalline texturized sample having elongated grains

Displacement 0,6 – 5 mm, Force – up to 1000 Newtons, Frequency 300 – 1000 Hz MAGNETICALLY CONTROLLED ACTUATORS BASED ON Ni-Mn-Ga ( ADAPTAMAT) A5-2 A06-3 A1-2000

RESULTS 1. The new trend in magnetic shape memory control is developed on the basis of “classical’ shape memory. The reversible martensitic transition by magnetic field at constant temperature is demonstrated. 2. One- and two way shape memory control of Ni- Mn-Fe-Ga nanocrystalline samples is shown. The recoverable strain 3% for one-way and 1,4% for two way shape memory is measured. 3. The results can be applied to MEMS, NEMS and MAGMAS devices design.

IMEM-CNR, Magnetic Materials Department, Parma, Italy (Dr Franca ALBERTINI) - magnetic properties of nanocrystalline materials Laboratoire d'Electrotechnique de Grenoble, France, (Dr. Orphee CUGAT) - application of nanocrystalline materials in MAGMAS Lab of Functional Materials and Nanotechnology of University of Warmia and Mazury, Olsztyn, Poland (Prof. T. BRECZKO) - X-ray, MFM A.F.Ioffe Institute, Russian Academy of Sciences (Prof. V.I. BETEKHTIN) - structural studies Institute of Powder Metallurgy, Minsk, Belarus ( Dr. N.M. CHIGRINOVA) - multilayered structures Institute of Radioelectronics, Russian Academy of Sciences, Moscow (Prof. V.G. SHAVROV) – composite structures Tver State University, Russia (Prof. R.M. GRECHISHKIN), domain structure studies Dept. Fisica Unversitat de Girona, Spain (Dr. Joan Josep SUNOL) - mechanical alloying of nanocrystalline materials Institute of Metal Physics of Ural Division of Russian Academy of Sciences in Ekaterinburg (Prof. V.G. PUSHIN) - electron microscopy) THE TEAM C.V.Kurdyumov Institute for Metal Physics and Functional Materials, Moscow (Prof. A.M. GLEZER) - thin film preparation St Petersburg State Technical University (prof.. A. I. MELKER) - computer simulations