In Situ Study of γ‐TiAl Lamellae Formation in Supersaturated α2‐Ti3Al Grains

In situ heating transmission electron microscopy (TEM) was used to investigate the initial stage of γ‐TiAl lamellae formation in an intermetallic Ti–45Al–7.5Nb alloy (in at.%). The material was heat treated and quenched in a non‐equilibrium state to consist mainly of supersaturated, ordered α₂‐Ti₃Al grains. Subsequently, specimens were annealed inside a TEM up to 750 °C. The in situ TEM study revealed that ultra‐fine γ‐TiAl laths precipitate in the α₂‐matrix at ≈730 °C which exhibit the classical Blackburn orientation relationship, i.e. (0001)α₂//(111)γ and [$11{\bar {2}}0$ ]α₂//<110]γ. The microstructural development observed in the in situ TEM experiment is compared to results from conventional ex situ TEM studies. In order to investigate the precipitation behavior of the γ‐phase with a complementary method, in situ high energy X‐ray diffraction experiments were performed which confirmed the finding that γ‐laths start to precipitate at ≈730 °C from the supersaturated α₂‐matrix.     

Processing and Applications of Intermetallic γ‐TiAl‐Based Alloys

Development and processing of high‐temperature materials is the key to technological advancements in engineering areas where materials have to meet extreme requirements. Examples for such areas are the aerospace and spacecraft industry or the automotive industry. New structural materials have to be “stronger, stiffer, hotter, and lighter” to withstand the extremely demanding conditions in the next generation of aircraft engines, space vehicles, and automotive engines. Intermetallic γ‐TiAl‐based alloys show a great potential to fulfill these demands.     

Effects of Thermally Induced Cyclic γ ↔ ε Transformation on Shape Memory Effect of a Quenched FeMnSiCrNi Alloy

The effects of thermally induced cyclic γ ? ε transformation on microstructures and shape memory effect (SME) are investigated in a quenched Fe14Mn5.5Si8.0Cr5.0Ni alloy. The results show that the annealing at 773 K remarkably improves the SME in the quenched alloy. One thermal cycling between 290 and 773 K remarkably increases the SME, but the further thermal cycling hardly improves the SME. The reason is that the amount of thermal ε martensite remarkably reduces after annealing at 773 K, but it hardly changes with the further increase of thermal cycling between 290 and 773 K. The pre‐existing thermal ε martensite not only prevents the occurrence of stress‐induced ε martensitic transformation but also promotes the formation of α′ martensite.     

In Situ Characterization of a Nb and Mo Containing γ‐TiAl Based Alloy Using Neutron Diffraction and High‐Temperature Microscopy

In recent times, novel titanium aluminides containing the bcc β‐phase at high temperatures are being developed for improved hot‐working capabilities, however, predictions of the phase diagrams are merely uncertain. Here we present in‐situ neutron studies, which are particularly sensitive to the atomic disorder in the ordered phases. Complementary laser scanning confocal microscopy is employed for in‐situ microstructural investigations.     

High‐Performance Field‐Effect Transistors Based on αP and βP

The electronic properties of black and blue phosphorus nanoribbons are investigated, which enables the proposal of junction‐free field‐effect transistors that comprise metallic armchair nanoribbons as electrodes and, in between, a semiconducting zigzag nanoribbon as channel material (cut out of a single sheet of monolayer black or blue phosphorus). Using first‐principles calculations and the nonequilibrium Green's function method, the proposed field‐effect transistors are characterized. It is found that it is possible to achieve outstanding performance, with high on/off ratios, low subthreshold swings, and high transconductances.     

Facile Synthesis of γ‐In2Se3 Nanoflowers toward High Performance Self‐Powered Broadband γ‐In2Se3/Si Heterojunction Photodiode

An effective colloidal process involving the hot‐injection method is developed to synthesize uniform nanoflowers consisting of 2D γ‐In₂Se₃ nanosheets. By exploiting the narrow direct bandgap and high absorption coefficient in the visible light range of In₂Se₃, a high‐quality γ‐In₂Se₃/Si heterojunction photodiode is fabricated. This photodiode shows a high photoresponse under light illumination, short response/recovery times, and long‐term durability. In addition, the γ‐In₂Se₃/Si heterojunction photodiode is self‐powered and displays a broadband spectral response ranging from UV to IR with a high responsivity and detectivity. These excellent performances make the γ‐In₂Se₃/Si heterojunction very interesting as highly efficient photodetectors.     

Notch stress analyses of high‐frequency mechanical impact‐improved welds by using ρf = 1 mm and ρf = ρ + 1 mm approaches

This paper presents further assessments of the previously reported round‐robin fatigue data obtained from high‐frequency mechanical impact (HFMI)‐improved longitudinal welds. A detailed statistical analyses of geometry measurements of HFMI‐treated weld toe profiles are presented. The fatigue analyses based on notch stress as defined by the International Institute of Welding are performed using the finite element method. Notch stresses are assessed based on both the fictitious weld toe radius and the addition of measured actual notch radius to the fictitious radius. While no large differences are observed between the results of methods, the former one is found to be more practical and faster to implement from the end‐user point of view.