Search results for "Diffusionless transformation"
showing 7 items of 7 documents
Wavelets Image Analysis for Friction Stir Processed TiNi Functional Behavior Characterization
2015
Abstract A key topic regarding Ti Ni Shape Memory materials concerns the possibility to attain welded junctions that preserves the shape memory properties of material. Other research topic for SMAs regards the retention of the shape memory effect cyclic stability; in fact, good shape memory properties frequently decrease during SME cycling of material. A method able to improve the cyclic stability of TiNi shape memory effect is the grain refinement. Considering these above mentioned research topics, a solid state welding process, as the Friction Stir Welding, is thus attractive for SMA joining and it exhibits potentials for achieving welded joints affected by microstructural changes that pr…
Shape memory NiTi thin films deposited at low temperature
1999
Abstract NiTi shape memory alloy (SMA) thin films have the potential to become high performance actuators for micro-electromechanical systems. Low temperature crystallized NiTi films would ensure a good compatibility with microelectronic processes and polymers. To avoid the drawbacks induced by annealing, we have tried to obtain low temperature crystallized RF sputtered NiTi films by optimising deposition parameters. We have found that NiTi films containing an excess of Ti (∼52%) were crystallized when deposited on Si(100) substrates heated up to only 473 K. NiTi/Si(n) Schottky diodes I–V characteristics showed a temperature dependence indicating structural transition in the NiTi electrode.…
Martensitic phase transformation cubic-orthorhombic of NaCN and (NaCN)0.98 (KCN)0.02
1990
The ferroelastic cubic-orthorhombic transition of single crystals NaCN and (NaCN)0.98 (KCN)0.02 has been studied by x-ray diffraction. The domain configuration obtained is consistent with the Wechsler, Lieberman, Read-model for martensitic transformations.
Effects of pressure and of thermal history on the structural phase transition of KCN
1992
The cubic-noncubic structural phase transition of a KCN single crystal is studied as a function of thermal history and of hydrostatic pressure up to 2 kbar. The standard sequence of phases is cubic-monoclinic-orthorhombic on cooling and orthorhombic-cubic on heating. The monoclinic phase is also absent in first cooling runs at low pressures (p≦250 bar). The width of the monoclinic field inp, T phase diagram is increased in second cooling runs. The effects are discussed in terms of a martensitic transformation behavior and random strain fields.
Friction Stir Processing of NiTi Shape Memory Alloy: Microstructural Characterization
2010
Shape Memory Alloys (SMA) are metal materials that, after being strained, come back to their original shape at a designated temperature. Welding NiTi alloys is not simple because when the material is melted, due to the high reactivity of the alloy elements, the typical shape memory properties may disappear. The solid state welding process, such as friction stir welding, is thus attractive for SMA joining and it exhibits potentials for achieving welded joints affected by microstructural changes that preserve the shape memory properties. The present study investigates the feasibility of friction stir welding process to join NiTi shape memory alloys; in order to analyse the welding process, it…
Structural and Magnetic Properties of Epitaxial Ni<sub>2</sub>MnGa Thin Films
2009
We report on the preparation and investigation of epitaxial thin films of the magnetic shape memory alloy Ni2MnGa. For samples close to the stoichiometric composition we find that the phase transformation temperature is affected by the crystallographic orientation. Changes in the crystal structure due to the transformation are observed using temperature-dependent X-ray diffraction. Films with higher manganese content are in the martensitic state at room temperature. Those samples on Al2O3(11-20) reveal the 7-layered orthorhombic structure that allows strains up to 10 %. To avoid blocking of magnetostrictive effects by the substrate, free-standing films are prepared using water-soluble NaCl(…
Crystal polymorphism of (μ4–O)-body centered adamantanoid Cu(II) complexes
2016
Abstract Two novel polymorphs of [Cu4(μ4–O)(μ–Cl)6(DASO)4], (DASO = diallyl sulfoxide; C6H10OS), rhombic (C) and triclinic (D), were obtained and examined by single crystal X-ray diffraction analysis at two temperatures, 295(2) and 100(1) K. This study, in addition to our recent work on the tetragonal (A) and trigonal (B) forms of the title compound, allowed determining the nature of polymorphism and temperature-induced phase transitions. It is stated that both the packing arrangement and the displacive transformation integrate these structures, forming the symmetrically and thermodynamically related series: A,B → C → D. The C3h → C4 distortion of Cu(II) trigonal bipyramidal coordination ge…