46 research outputs found

    FAST-DB: A novel solid-state approach for diffusion bonding dissimilar titanium alloy powders for next generation critical components

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    Titanium alloy components are subjected to challenging conditions in high performance applications, consisting of complex loads and thermal gradients. To improve the performance and efficiency of such components, it is desirable to introduce different microstructures into subcomponent regions which cannot be achieved by the conventional melt-wrought processing route. Instead, a solid-state consolidation route using dissimilar titanium alloy powders is proposed. In this study commercially pure Ti (CP-Ti), Ti-6Al-4V (Ti-6-4), and Ti-5Al-5Mo-5V-3Cr (Ti-5553) have been diffusion bonded using field assisted sintering technology (FAST) for dwell times of 10, 20, and 60 min. The effectiveness of FAST for diffusion bonding (DB) of dissimilar alloy powders has led to the authors terming this hybrid process as "FAST-DB". Excellent bond integrity was produced with no cracking, unbonded regions or voids in the dissimilar bond combinations, at all dwell times. Furthermore, reliable control and prediction of the bond characteristics and degree of elemental diffusion was demonstrated through commercial thermodynamic software. Elemental diffusion was characterised across the bonds and the chemical diffusion bond width increased linearly with dwell time. Peak hardness values occurred directly on the interface for Ti-5553 and CP-Ti bonds, whilst slightly into the Ti-6-4 alloy for the Ti-5553 and Ti-6-4 bonds, which can be attributed to fine scale alpha at the interface. In Ti-6-4 with CP-Ti bonds, a smooth transition was observed. Mechanical testing demonstrated that the FAST-DB interface had excellent structural integrity, with necking and fracture occurring in the lower strength alloy

    Novel high strength titanium-titanium composites produced using field-assisted sintering technology (FAST)

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    To increase the strength of titanium alloys beyond that achievable with α-β microstructures, alternative reinforcing methods are necessary. Here, field-assisted sintering technology (FAST) has been used to produce a novel Ti-5Al-5Mo-5V-3Cr (Ti-5553) metal-matrix-composite (MMC) reinforced with 0-25 wt.% of a ∼2 GPa yield strength TiFeMo alloy strengthened by ordered body-centred cubic intermetallic and ω phases. The interdiffusion region between Ti-5553 and TiFeMo particles was studied by modelling, electron microscopy, and nanoindentation to examine the effect of graded composition on mechanical properties and formation of α, intermetallic, and ω phases, which resulted in a > 200 MPa strengthening benefit over unreinforced Ti-5553

    Search for the associated production of the Higgs boson with a top-quark pair

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    A search for the standard model Higgs boson produced in association with a top-quark pair t t ¯ H (tt¯H) is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb −1 and 19.7 fb −1 collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H → hadrons, H → photons, and H → leptons. The results are characterized by an observed t t ¯ H tt¯H signal strength relative to the standard model cross section, μ = σ/σ SM ,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is μ = 2.8 ± 1.0 for a Higgs boson mass of 125.6 GeV

    Measurement of prompt Jψ\psi pair production in pp collisions at \sqrt s = 7 Tev

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    Production of prompt J/ ψ meson pairs in proton-proton collisions at s s√ = 7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 fb −1 . The two J/ ψ mesons are fully reconstructed via their decays into μ + μ − pairs. This observation provides for the first time access to the high-transverse-momentum region of J/ ψ pair production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/ ψ transverse momentum ( p T J/ ψ ) and rapidity (| y J/ ψ |): | y J/ ψ | 6.5 GeV/ c ; 1.2 4.5 GeV/ c . The total cross section, assuming unpolarized prompt J/ ψ pair production is 1.49 ± 0.07 (stat) ±0.13 (syst) nb. Different assumptions about the J/ ψ polarization imply modifications to the cross section ranging from −31% to +27%
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