No abstract

Mitigation of embrittlement caused by recrystallization and radiation is the key issue of tungsten (W) based materials for use in the advanced nuclear system such as fusion reactor applications. In this paper, our nanostructured W materials development performed so far to solve the key issue is reviewed, including new original data. Firstly, the basic concept of mitigation of the embrittlement is shown. The approach to the concept has yielded ultra-fine grained, recrystallized (UFGR) W(0.251.5) mass%TiC compacts containing fine TiC dispersoids (precipitates). The UFGR W(0.251.5)%TiC exhibits favorable as well as unfavorable features from the viewpoints of microstructures and various thermo-mechanical properties including the response to neutron and ion irradiations. Most of the unfavorable features stem from insufficient strengthening of weak random grain boundaries (GBs) in the recrystallized state. The focal point on this study is, therefore, to develop a new microstructural modification method to significantly strengthen the random GBs. The method is designated as GSMM (GB Sliding-based Microstructural Modification) and has lead to the birth of toughened, fine-grained W1.1%TiC in the recrystallized state (TFGR W1.1TiC). The TFGR W1.1TiC exhibits much improved thermo-mechanical properties. The applicability of TFGR W1.1TiC to the divertor in ITER is discussed.

No abstract

Transformations from austenite to martensite or bainite in ferrous alloys have great technological importance, but some aspects remain elusive. The orientation relationship (OR), morphology and habit plane can vary considerably from one system to another. Much published work considers these OR in terms of their variation from named relationships such as Kurdjumov-Sachs and Nishiyama-Wassermann. We discuss here, instead, the use of a set of angular parameters based on the classic work of Kurdjumov and Sachs in the 1930s, that provide a unified and elegant description facilitating extraction and detailed statistical treatment of OR from large electron backscatter diffraction datasets, as well as straightforward comparison with named OR and with the predictions from the phenomenological theory. Spatially correlated mappings of OR parameters obtained using this approach suggest that the observed variations in OR are related to the martensitic morphology rather than being an experimental artefact.

No abstract

No abstract

Improvement of the hot stamping process is important for reducing processing costs and improving the productivity and tensile properties of final components. One major approach to this has been to conduct all or part of the process at lower temperatures. The present paper reviews the state of the art of hot stamping techniques and their applications, considering the following aspects: (1) conventional hot stamping and its advanced developments; (2) warm stamping approaches in which complete austenitisation is not attained during heating; (3) hot stamping with a lower forming temperature, i.e., low-temperature hot stamping (LTHS); (4) advanced medium-Mn steels with lower austenitisation temperatures and their applicability in LTHS. Prospects for the further development of LTHS technology and the work required to achieve this are discussed.

High‐resolution characterization techniques are combined with thermodynamic calculations (CALPHAD) to rationalize microstructural features of single crystal Ni‐base superalloys. Considering the chemical compositions of dendritic and interdendritic regions one can explain differences in γ′‐volume fractions. Using thermodynamic calculations one can explain, why γ‐nanoparticles are observed in the central regions of large cuboidal γ′‐particles and why tertiary γ′‐nanoparticles form in the γ‐channels. The chemical compositions of the γ‐channels and of the newly formed γ‐particles differ because of the Gibbs–Thomson pressure which acts on the small particles. With increasing size of secondary γ′‐particles, their shape changes from spherical to cuboidal. Some general thermodynamic aspects including the temperature dependencies of the Gibbs free energy G, the enthalpy H, and the entropy S and site occupancies in the ordered L12 (γ′) phase are considered. The importance of cooling rate after homogenization is discussed.