Tensile tests were performed in situ in a transmission electron microscope to investigate the twinning mechanism in non-modulated Ni–Mn–Ga martensite. The reorientation of the twin variants occurs via twinning dislocations. Their generation and movement were followed; the glide plane and Burgers vector were verified. Individual twinning dislocations were visualized.

Stress-induced martensitic transformations and twinning processes were studied in thin foils of CuAlNi single crystals strained in situ in a transmission electron microscope. The nucleation and growth of the martensite plates were monitored for three transformation processes known from bulk experiments: (i) the transformation of austenite into 2H martensite at low-stress levels; (ii) the twinning/detwinning processes in 2H martensite; and (iii) the transformation between austenite and 18R martensite at higher stress levels. The morphology of the austenite/martensite habit planes was examined, and the existence of planar interfaces between a single variant of 2H martensite and austenite on the microscopic level was proven.

Stress-induced martensitic transformations and twinning processes were studied in thin foils of CuAlNi single crystals strained in-situ in a transmission electron microscope. A detailed structure analysis comprised identification of phases existing under stress and determination of their mutual crystallographic orientation. Three transformation processes were detected: i) transformation of austenite into 2H martensite at low stress levels; ii) twinning/detwinning processes in 2H martensite, and iii) transformation between austenite and 18R martensite at higher stress levels. Nucleation and growth of martensite plates were followed, and morphology of the austenite/martensite habit planes was examined. Existence of planar interfaces between a single variant of 2H martensite and austenite on microscopic level was proved.

Structural observations by transmission electron microscopy were performed and analyzed on in situ strained foils of a Cu–Al–Ni shape memory alloy. The experiments were carried out at room temperature. Two stress-induced transformation processes are described in this paper. (i) Transition between two variants of γ′1 (2H) martensite. Both variants coexisted at low stresses. With increasing stress, one variant was replaced by the other one and appeared again during unloading. (ii) Transformation between β1 (D03) austenite and β′1 (18R) martensite. Nucleation and behaviour of the β′1 needles under stress were followed.

The stress distribution in a foil strained in situ in a transmission electron microscope is strongly affected by the polished depression and the hole. In the present study, this effect has been investigated in detail on a Fe–Si foil plastically deformed under uniaxial straining in transmission electron microscopy. The slip-trace direction varied considerably around the hole, indicating local changes of the macroscopic slip plane. Since non-crystallographic slip occurs in Fe–Si under conditions used in the experiment and the crystallographic relation between the macroscopic slip plane and the tensile stress direction is known, the local tensile axes could be established. It was found that the deviations of the local tensile stress axis from the external stress axis may be as large as ±60°. The stress distribution determined experimentally is compared with an analytical solution as well as a finite element analysis of the problem.

The transfer of the common slip system across grain boundaries was examined. Bicrystals of alloys Fe-Si with Si content 4 and 5.5 at% were used for both tension and compression straining. The progress of the deformation was followed by synchrotron radiation diffraction topography after straining and under increasing external stress. An x-ray sensitive camera was used for recording the topographs in addition to the classical technique using photographic plates. Three slightly different settings with different sensitivities to interplanar spacing (deformation) and orientation variations of the adjacent crystal regions were applied. The movement of the slip bands was followed. A distortion of the image appeared at the grain boundary when the slip bands stopped there and decreased or nearly disappeared when the slip bands crossed it after an increase in the applied stress. The distortion is explained by elastic deformation around the heads of the slip bands stopped at the boundary. True slip transfers are differentiated from the false ones by observing elastic deformation in early deformation stages and by optical observation of slip pattern after deformation. The transfer of the common slip system across a twin boundary, whereas expected to be direct, required stress accumulation. The twin boundary proved to be a real barrier. The results obtained for specimens with different Si content were compared.

Specimens for in situ TEM straining were prepared from Fe-5.5 at.%Si Σ 3 bicrystals with {112} grain boundary plane. They were strained under three different directions of the stress at the boundary with respect to the orientation of the grains. Transfer of slip across the boundary was analysed. In one case, the transfer of slip was realized by a transformation of the slip dislocation in one grain into the slip dislocation in the other grain. Low energy dislocation was created in the GB in accordance with general transfer criteria. In the second case, the incoming and outgoing slip systems were in direct contraction to the general transfer criteria. In the third case, oriented for common slip system in both grains, the trapped incoming slip dislocations dissociated into twinning dislocations which created twins on the other side of the boundary.

Bulk bicrystals of Fe–4at.% Si of Σ9 or Σ15 type, oriented for single slip and deformed in compression were studied by conventional transmission electron microscopy. The deformation was limited to early stages. In both bicrystals, the deformation proceeded by independent slip in both grains. In the Σ9 bicrystal, a small fraction of deformation was attributed to the transfer of slip from one grain to the other leaving residual grain boundary dislocations. In the Σ15 bicrystal, dislocations of both signs of Burgers vectors were observed in the grains. The movement of dislocations from the boundary was initiated by dislocation sources formed in the boundary. Jogs on screw dislocations may support the formation of sources.

This work describes carbides present in the tool steel containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W, prepared by the powder metallurgy (PM) process. The influence of thermal treatment conditions on carbide behavior is investigated. During austenitization, some dissolution Of M7C3 occurs, while MC carbides are thermally stable. So, the quenched steel is composed of two types of carbides: chromium rich M7C3 and niobium rich MC, besides martensite and retained austenite. During tempering of the hardened steel at the temperatures above 480degreesC, the precipitation of very fine carbides and martensite recovery occur, which results in secondary hardening. Precipitated particles are predominantly vanadium and molybdenum rich MC, M2C, and M6C carbides.

In situ X-ray diffraction topography using synchrotron radiation (SRXRT) observation of deformation of Fe–4at.% Si bicrystals Σ3, Σ9 and Σ15 was completed by TEM observation of deformed samples. The results were discussed from the viewpoint of the criteria allowing prediction of slip accommodation at the grain boundary. The common slip system in a Σ3 bicrystal is impeded by dissociation of slip dislocations into grain boundary dislocations. In Σ9 bicrystals, the transfer with highest probability appears simultaneously with independent deformation in both grains. In Σ15 bicrystals, no residual dislocations were observed in the boundary. The slip dislocations contribute to creation of dislocation sources in the boundary.

The work is aimed at describing the influence of thermal treatment on the properties of a tool steel containing (in wt.%) 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W prepared by the powder metallurgy process. Alloying with niobium positively affects the microstructure, the mechanical properties and the performance of the steel. The microstructure of the hardened steel is composed of a martensitic matrix, retained austenite and various types of carbide. During tempering of the hardened steel at the temperatures above 480°C precipitation of very fine carbides occurs, which results in secondary hardening. The optimum thermal treatment of the steel is austenitisation at 1050–1100°C, nitrogen cooling and tempering at 540°C (3×1 h).

In-situ straining experiments have been performed to study the mechanisms of propagation of deformation at grain boundaries (GB) in symmetrical Σ3 Fe–4 at.% Si bicrystals with common primary slip system in both grains. Three different orientations of tensile axis with respect to the {112} GB plane were studied and three different effects were observed. In no case was the propagation of primary-slip dislocations across the GB observed. When the tensile axis lies in the GB plane, the slip dislocations of the tertiary slip system enter the GB, interact with GB dislocations, and the dislocations of the secondary slip system are generated in the second grain. When the angle between the primary slip plane and the GB is about 20°, the primary-slip dislocations whose Burgers vectors belong to the GB plane, cross slip and follow the GB plane. Primary-slip dislocations are formed in one grain and a new sub-grain boundary is formed in the other grain when the angle between the primary slip plane and the GB is about 49°.

Rigid-body displacement perpendicular to a symmetrical {112} grain boundary in a Sigma = 3 Mo bicrystal was measured using the x-fringe method. The grain boundary contained a set of parallel intrinsic dislocations accommodating the deviation from the exact coincidence. The observed images were compared with theoretical image simulations. This procedure enabled us to eliminate the influence of dislocations on the measurement of the displacement. The result was compared with the expansion previously determined by high-resolution electron microscopy and by theoretical atomic simulations.

Layered core−shell bimetallic silver−gold colloids in the size range of 10−16 nm have been prepared by the seed-growth method. Silver nuclei were covered by gold shells of various thicknesses without any stabilization agent. Interfacial (Ag)Au colloid−2,2‘-bipyridine films were prepared from these bimetallic colloids and used for the purpose of analysis of transmission electron microscopy (TEM) images and electron diffraction. Both observed and calculated TEM images were used to characterize the prepared nanoparticles. On the basis of the analysis of TEM images, the calculated TEM image contrast, and results obtained by electron diffraction, energy-dispersive X-ray analysis, and other experiments, the core−shell structure of the prepared (Ag)Au nanoparticles was revealed. Particles were found to consist of a silver core and a gold shell enriched with silver.

SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.

Dislocation interaction with a Sigma = 3 grain boundary in bce Fe-4at% Si was investigated by in-situ TEM. The dislocations, whose Burgers vector belongs to the grain boundary plane, cross slip out of their slip band, and do not form stress concentrations. No slip transfer through the grain boundary has been observed yet.