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.

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.

The paper reports on a detailed investigation of microstructure and phase composition of rapidly solidified and annealed AlNi18.5 and AlNi17Zr1.8 ribbons. The ribbons were prepared by the melt spinning (planar flow casting) technique. The microstructure and phase composition have been studied by TEM and XRD. The specimens were annealed and subsequently subjected to microstructure investigations to asses their thermal stability. Rapidly solidified alloys are composed of a-Al and Al3Ni phase grains. No significant difference in the shape between Al and Al3Ni grains was found. The Al9Ni2 metastable phase was identified in the rapidly solidified AlNi17Zr1.8 alloy and the Al3Zr phase precipitates from the a-Al solid solution in the AlNi17Zr1.8 alloy after the high temperature annealing.

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 the present paper, microstructure, phase composition and elevated temperature behaviour of two rapidly solidified (RS) AlCr6Fe2Ti(0–1.5)Si1 (in wt.%) powder alloys are described. Rapidly solidified powders were composed of α(Al) solid solution matrix and finely dispersed intermetallic phases of spherical or irregular shapes. XRD and TEM investigations revealed the presence of quasi-crystalline icosahedral Al84.6Cr15.4, Al82Fe18, Al95Fe4Cr, Al74Cr20Si6 and crystalline Al, Al13Cr2, Al13Fe4, Al3FeSi phases. The fraction of quasi-crystalline phases in the form of spheroids was reduced as the powder particle size increased. The presence of titanium significantly increases the fraction of icosahedral phases. DTA measurement revealed an exothermic reaction at 450–500°C in the fine powder fraction (size 25–45μm) of the AlCr6Fe2Ti1.5Si1 alloy. This fraction also exhibited a hardening after annealing at 350°C/50h. The hardening, as well as the exothermic effect were due to a decomposition of the icosahedral phases described by the reaction Al95Fe4Cr(Ti, Si) + Al84.6Cr15.4(Ti, Si) + Al74Cr20Si6(Fe, Ti) → Al13Cr2 + Al3FeSi + TiSi.

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.

Complete structural analysis of a Mo bicrystal containing a Σ = 3, [101](121)A grain boundary (GB) was achieved by means of transmission electron microscopy from the microscopic to the nanoscopic level. Secondary GB dislocations compensating a small deviation from the exact Σ = 3 concidence were observed and their character was determined. Rigid-body displacements (RBDs) were determined directly from high-resolution electron microscopy images using samples with surface normal parallel and perpendicular to the tilt axis. Measured values of RBDs are compared with recent theoretical calculations.

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.