Thickness Of Deposited Material Research Articles

Residual stresses and fatigue crack growth in friction surfacing coated Ti-6Al-4V sheets

The relation between the translational stud speed and the residual stress (RS) state of Friction Surfacing (FS) coated 2 mm thick Ti-6Al-4V sheets was studied using synchrotron diffraction. The influence of the RS state on fatigue crack propagation (FCP) was studied using C(T)-100 samples.It was shown that an active zone of tensile RS is present in the coated region, inducing compressive stresses in the remaining sheet. Higher depositing stud translational speeds show a tendency towards high RS peak values. The deposited material thickness has an influence on the RS distribution.FCP tests have shown branching cracks deflecting away from the coating, possibly due to the compressive RS around it. Cracks have propagated significantly slower than in uncoated samples. RS measurements on cracked samples have revealed tensile RS peaks at the crack tips with high values of 350 MPa in the direction parallel to the intended crack propagation, which prevent the cracks from reaching the coated region.

Integration of GaN Crystals on Micropatterned Si(0 0 1) Substrates by Plasma-Assisted Molecular Beam Epitaxy

We present an innovative approach to integrate arrays of isolated, strain-free GaN crystals on patterned Si substrates. First, micrometer-sized pillars are patterned onto Si(0 0 1) substrates. Subsequently, 2.5 μm Si substrates are deposited by low-energy plasma-enhanced chemical vapor deposition, forming crystals mostly bounded by {1 1 1}, {1 1 3}, and {15 3 23} facets. Plasma-assisted molecular beam epitaxy is then used for GaN deposition. GaN crystals with slanted {0 0 0 1} facets having a root-mean-square surface roughness of 0.7 nm are obtained for a deposited material thickness of >3 μm. Microphotoluminescence measurements performed at room and cryogenic temperature show no yellow luminescence and a neutral donor-bound A exciton transition at 3.471 eV (10 K) with a full width at half-maximum of 10 meV. Microphotoluminescence and micro-Raman spectra reveal that GaN grown on Si pillars is strain-free. Our results indicate that the shape of GaN crystals can be tuned by the pattern periodicity and that ...

Plasma deposition by a coaxial discharge in powder

Different types of material powder have been placed at the breach of a coaxial discharge for impulse plasma deposition. The coaxial discharge is powered with a 46.26 μF, 24 kV capacitor bank. When the discharge takes place at the breach, the powder is evaporated and ionized to form a sheath of its material. The plasma sheath is ejected from the discharge zone with a high velocity to be deposited on a glass substrate. It has been found from scanning electron microscopy analysis that the deposited material is almost homogeneous for ceramic and graphite powders. The grain size is estimated to be of the order of a few microns. To measure the deposited material thickness, a microdensitometer, a laser interferometer and an optical microscope are used. It has also been found that the deposited material thickness depends on the discharge number of shots and the capacitor bank energy.

Nanodimensional whisker growth by the generalized vapor-liquid-crystal mechanism

A theoretical model describing the growth of a nanodimensional whisker (NW) according to the generalized vapor-liquid-crystal mechanism is proposed. According to this model, atoms are supplied to a supersaturated liquid drop both directly from the gas phase and by diffusion from the substrate surface and from the side face of the crystal. An expression for the NW length L as a function of the drop radius R and the deposited material thickness H is obtained. In the general case, the growth law L(H) is linear at large H but exhibits curvature in the intermediate growth stage. The length of a thin NW is inversely proportional to its radius. The proposed approach generalizes theoretical models developed previously for the description of NW growth by methods of vapor phase epitaxy and molecular beam epitaxy.