Quantitative Transmission Electron Microscopy Analysis Research Articles

Cyclic softening of the Ti-10V-2Fe-3Al titanium alloy

The β-metastable Ti-10V-Fe-3Al alloy is studied in low cycle fatigue (LCF) at room temperature. An acicular and two equiaxed αp structures aged at different temperatures were produced and specimens were tested under plastic strain control. The experimental results show that the Ti-10V-2Fe-3Al alloy softens cyclically. The amplitude of the softening is not affected by the microstructure and it decreases as the applied plastic strain increases. The investigations show that this phenomenon proceeds from a decrease in both the isotropic and the kinematic components of the stress. The deformation modes have been analyzed by transmission electron microscopy (TEM) after the cyclic softening stage. Homogeneous prismatic slip is mainly observed in the α-phase. Furthermore, abundant cross-slip of <a> dislocations and <c+a> slip are also observed. The kinematic decrease is associated with a process of grain-to-grain homogenization of yielding through the microstructure, and the isotropic softening with dislocations annihilation enhanced by cross-slip in the α-phase. Quantitative TEM analysis with regard to the crystallographic orientation of α, particles indicates that the decrease in the softening amplitude at high levels of the applied plastic strain must be related to the occurrence of 〈c+a〉 slip.

The influence of niobium supersaturation in austenite on the static recrystallization behavior of low carbon microalloyed steels

This work describes the effect of Nb supersaturation in austenite, as it applies to the strain-induced precipitation potential of Nb(CN), on the suppression of the static recrystallization of austenite during an isothermal holding period following deformation. Four low carbon steels, microalloyed with Nb, were used in this investigation. Three of the steels had variations in Nb levels at constant C and N concentrations. Two steels had different N levels at constant C and Nb concentrations. The results from the isothermal deformation experiments and the subsequent measurement of the solution behavior of Nb in austenite show that the recrystallization-stop temperature (TRXN) increases with increasing Nb supersaturation in austenite. Quantitative transmission electron microscopy analysis revealed that the volume fraction of Nb(CN) at austenite grain boundaries or subgrain boundaries was 1.5 to 2 times larger than Nb(CN) volume fractions found within the grain interiors. This high, localized volume fraction of Nb(CN) subsequently led to high values for the precipitate pinning force (FPIN). These values forFPIN were much higher than what would have been predicted from equilibrium thermodynamics describing the solution behavior of Nb in austenite.

Kinetics of crystallization in a Fe 90Zr 10 amorphous alloy

The crystallization kinetics of amorphous Fe 90Zr 10 have been investigated by transmission electron microscopy (TEM), initial susceptibility and differential scanning calorimetry (DSC) measurements. A quantitative TEM analysis of the early stage of crystallization corresponding to primary crystallization of α-Fe led to much lower values. The activation enthalpies for nucleation, crystal growth and overall crystallization (1.6, 2.5 and 2.6 eV) are very close to the values found in the same alloy for self-diffusion of Fe and Zr in amorphous FeZr. From the decrease of the initial magnetic susceptibility which occurs during crystallization an activation enthalpy of 1.5 eV was found; this is in agreement with TEM data. The results indicate that post-critical nuclei with a size distribution are present in the as-quenched state.

Morphological studies of micelle formation in block copolymer/homopolymer blends

The micellar structure of poly(styrene-butadiene) diblock copolymer/polystyrene homopolymer blends has been investigated by small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) as a function of copolymer concentration, copolymer block molecular weights, and homopolymer molecular weight. The SAXS from blends exhibiting spherical micelles, as evidenced by TEM, has been modeled using a polydisperse Percus–Yevick hard sphere fluid model to obtain the interparticle interference contribution to the scattered intensity. By combining this modeling with quantitative TEM and SAXS invariant analysis, the structure of the micelles as a function of the molecular parameters can be completely characterized. In addition, a transition from liquid-like to an ordered simple cubic arrangement of micelles has been observed upon increasing the copolymer concentration.