Hanuš Seiner

Shape recovery mechanism observed in single crystals of Cu–Al–Ni shape memory alloy

Micromechanism of the shape recovery process is optically observed in single crystals of the Cu–Al–Ni shape memory alloy. Formation of X and λ-interfaces (interfacial microstructures with two intersecting habit planes) is documented, both in a thermal gradient and during a homogeneous heating. The observed growth mechanisms (i.e. mechanisms of nucleation and growth of the twinned structures) are described and analysed. Weakly non-classical boundaries between austenite and two crossing twinning systems are also documented.

Anomalous lattice softening of Ni2MnGa austenite due to magnetoelastic coupling

Elastic constants of the cubic Ni2MnGa austenite phase and corresponding mechanical damping were determined in the temperature range from 220 K to 400 K and magnetic field up to 2 T using ultrasound pulse-echo method and resonant ultrasound spectroscopy. The shear coefficient c′ increases from 3.6 GPa in the demagnetized state to 5.9 GPa at magnetic saturation, whereas the damping decreased nearly six times. The changes of other elastic constants, c11 and c44 with an applied field were less than 1%. In the ferromagnetic state, the c′ was proportional to the square of magnetization. Above the Curie point, the coefficient c′ and damping were field-independent. The anomalous shear softening is attributed to strong magnetoelastic coupling enhanced by low magnetic anisotropy.

Linearized forward and inverse problems of the resonant ultrasound spectroscopy for the evaluation of thin surface layers

In this paper, linearized approximations of both the forward and the inverse problems of resonant ultrasound spectroscopy for the determination of mechanical properties of thin surface layers are presented. The linear relations between the frequency shifts induced by the deposition of the layer and the in-plane elastic coefficients of the layer are derived and inverted, the applicability range of the obtained linear model is discussed by a comparison with nonlinear models and finite element method (FEM), and an algorithm for the estimation of experimental errors in the inversely determined elastic coefficients is described. In the final part of the paper, the linearized inverse procedure is applied to evaluate elastic coefficients of a 310 nm thick diamond-like carbon layer deposited on a silicon substrate.

The relation between lattice parameters and very low twinning stress in Ni50Mn25+xGa25-x magnetic shape memory alloys

In search for the origins of the extraordinary low twinning stress of Ni-Mn-Ga magnetic shape memory alloys we studied the thermally induced changes of structure in Ni

Nucleation and growth of hierarchical martensite in epitaxial shape memory films

_{50}

Anisotropic elasticity of DyScO3 substrates

Mn

Sensitivity of the resonant ultrasound spectroscopy to weak gradients of elastic properties

_{25+x}

Temperature dependence of twinning stress – Analogy between Cu–Ni–Al and Ni–Mn–Ga shape memory single crystals

Ga

An ultrasonic internal friction study of ultrafine-grained AZ31 magnesium alloy

_{25-x}

The effects of microstructure on crackling noise during martensitic transformation in Cu-Al-Ni

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