A new method for notching ceramics was developed using a picosecond laser for fracture toughness testing of alumina samples. The test geometry incorporated a singleedge-V-notch that was notched using picosecond laser micromachining. This method has been used in the past for cutting ceramics, and is known to remove material with little to no thermal effect on the surrounding material matrix. This study showed that laser-assisted-machining for fracture toughness testing of ceramics was reliable, quick, and cost effective. In order to assess the laser notched single-edge-V-notch beam method, fracture toughness results were compared to results from other more traditional methods, specifically surface-crack in flexure and the chevron notch bend tests. The results showed that picosecond laser notching produced precise notches in post-failure measurements, and that the measured fracture toughness results showed improved consistency compared to traditional fracture toughness notching methods.
PACS 61.43.Dq -Amorphous semiconductors, metals, and alloys PACS 62.50.-p -High-pressure effects in solids and liquids PACS 61.05.C--X-ray diffraction and scattering Abstract -Ge0.15Sb0.85 is a phase change material that undergoes a transition from a semiconducting glass to a crystalline metal when being densified. In this work, we investigate some parameters controlling the crystallization pressure Pc in related compounds by conducting highpressure experiments on initially amorphous, germanium-and silicon-doped antimony. We find that the amorphous phase is stabilized to higher pressures when the dopant size is decreased. This result can be easily rationalized under the assumption that in the glass, Ge and Si atoms occupy tetrahedral or related small coordination shells. When pressure increases, the larger Ge atoms move sooner into the larger octahedral shells, which are characteristic for the crystal, than the smaller Si atoms do. We also find that Pc increases quickly with Ge and Si concentrations. This observation implies that the pressure-induced change of coordination cannot be a local, elementary event, but that the four-coordination of the group-14 atoms is stabilized by the presence of other four-coordinated atoms.
Optical emission spectroscopy and charge collector time-of-flight measurements have been used to study interaction of laser ablation carbon plasma with grid screens in vacuum under conditions typical for pulsed laser deposition of thin diamondlike films. The effect of velocity distribution transformation of the ion flow has been observed and studied in a variety of experimental conditions. Our results indicate that the observed phenomenon is due to interaction of two plasma flows, the initial expanding one and the fraction of that flow scattered by the substrate or the screen. Three typical modes of velocity distribution function transformation have been observed depending on the plasma density: linear attenuation of the flow density, nonlinear attenuation of the slow ‘‘tail’’ of the velocity distribution function, and nonlinear transformation of the entire velocity spectrum. The latter regime occurs when plasma is throttling through the fine mesh screen. Our observations show that the reported phenomenon may substantially affect deposited film properties.
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