Impact Properties of TiC Dispersed Molybdenum Alloys Exposed to 2273 K Heating

Ultra-fine grained molybdenum alloys with fine TiC particles at grain boundaries that were recently developed by the authors are very promising for the application to divertor components in advanced fusion devices. In order to examine the impact toughness and microstructural change of the alloys which were exposed to high temperature heating, miniaturized flat specimens, 1 mm by 1 mm by 20 mm, of both the alloys with TiC additions to 1.0 wt% and TZM alloy were subjected to vacuum heating up to 2273 K for 3.6 ks. The impact toughness was evaluated by three-point bending tests. It is shown that the developed alloys exhibit much improved toughness (lower ductile-to-brittle transition temperature and higher yield and maximum strengths) and the toughness increases both by increasing TiC content and by using mechanical alloying (MA) treatment for fabrication : the ductile-to-brittle transition temperature of the MA treated alloy with 1 wt% TiC is 75 K lower than that of TZM. In addition, the alloy with 1 wt% TiC shows no significant grain growth, though TEM observation indicate the occurrence of recrystallization

Development of Nanostructured Tungsten Based Materials Resistant to Recrystallization and/or Radiation Induced Embrittlement

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–(0.25–1.5) mass%TiC compacts containing fine TiC dispersoids (precipitates). The UFGR W–(0.25–1.5)%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 W–1.1%TiC in the recrystallized state (TFGR W–1.1TiC). The TFGR W–1.1TiC exhibits much improved thermo-mechanical properties. The applicability of TFGR W–1.1TiC to the divertor in ITER is discussed

Plasma Membrane and Nuclear Localization of G Protein–coupled Receptor Kinase 6A

G protein–coupled receptor (GPCR) kinases (GRKs) specifically phosphorylate agonist-occupied GPCRs at the inner surface of the plasma membrane (PM), leading to receptor desensitization. Here we show that the C-terminal 30 amino acids of GRK6A contain multiple elements that either promote or inhibit PM localization. Disruption of palmitoylation by individual mutation of cysteine 561, 562, or 565 or treatment of cells with 2-bromopalmitate shifts GRK6A from the PM to both the cytoplasm and nucleus. Likewise, disruption of the hydrophobic nature of a predicted amphipathic helix by mutation of two leucines to alanines at positions 551 and 552 causes a loss of PM localization. Moreover, acidic amino acids in the C-terminus appear to negatively regulate PM localization; mutational replacement of several acidic residues with neutral or basic residues rescues PM localization of a palmitoylation-defective GRK6A. Last, we characterize the novel nuclear localization, showing that nuclear export of nonpalmitoylated GRK6A is sensitive to leptomycin B and that GRK6A contains a potential nuclear localization signal. Our results suggest that the C-terminus of GRK6A contains a novel electrostatic palmitoyl switch in which acidic residues weaken the membrane-binding strength of the amphipathic helix, thus allowing changes in palmitoylation to regulate PM versus cytoplasmic/nuclear localization