Metallographic Specimen Preparation for Electron Backscattered Diffraction

Electron backscattered diffraction (EBSD) is performed with the scanning electron microscope (SEM) to provide a wide range of analytical data; e.g., crystallographic orientation studies, phase identification and grain size measurements. The quality of the diffraction pattern, which influences the confidence of the indexing of the diffraction pattern, depends upon removal of damage in the lattice due to specimen preparation. It has been claimed that removal of this damage can only be obtained using electrolytic polishing or ion-beam polishing. However, the use of modern mechanical preparation methods, equipment and consumables does yield excellent quality diffraction patterns. The experiments discussed here covered a wide variety of metals and alloys prepared mechanically using three to five steps, based on straightforward methods that generally require less than about twenty-five minutes

Mitigating the susceptibility to intergranular corrosion of alloy 625 by friction‑stir welding

In this work, friction-stir welding (FSW) was employed to alloy 625 grade I (soft annealed) sheets. Therefore, solid-state based welding was undertaken with a tool rotational speed of 200 rpm and a welding speed of 1 mm/s. Microstructural features were analyzed by light optical and scanning electron microscopy (LOM and SEM). Moreover, microhardness measurements were performed. The susceptibility to intergranular corrosion was verifed by the double-loop electrochemical potentiokinetic reactivation (DL-EPR) test. Complementary, intergranular corrosion was also evaluated by the ASTM G28 Method A. FSW promoted grain refnement, increased microhardness, and reduction in the degree of sensitization. Finally, the mean corrosion rate observed in the ASTM G28 Method A test was 0.4406 mm/year, which suggests a good weld quality

Spatially resolved acoustic spectroscopy for rapid imaging of material microstructure and grain orientation

Measuring the grain structure of aerospace materials is very important to understand their mechanical properties and in-service performance. Spatially resolved acoustic spectroscopy is an acoustic technique utilizing surface acoustic waves to map the grain structure of a material. When combined with measurements in multiple acoustic propagation directions, the grain orientation can be obtained by fitting the velocity surface to a model. The new instrument presented here can take thousands of acoustic velocity measurements per second. The spatial and velocity resolution can be adjusted by simple modification to the system; this is discussed in detail by comparison of theoretical expectations with experimental data

Photogrammetric measurement of 3D freeform millimetre-sized objects with micro features: an experimental validation of the close-range camera calibration model for narrow angles of view

The measurement of millimetre and micro-scale features is performed by high-cost systems based on technologies with narrow working ranges to accurately control the position of the sensors. Photogrammetry would lower the costs of 3D inspection of micro-features and would be applicable to the inspection of non-removable micro parts of large objects too. Unfortunately, the behaviour of photogrammetry is not known when photogrammetry is applied to micro-features. In this paper, the authors address these issues towards the application of digital closerange photogrammetry (DCRP) to the micro-scale, taking into account that in literature there are research papers stating that an angle of view (AOV) around 10° is the lower limit to the application of the traditional pinhole close-range calibration model (CRCM), which is the basis of DCRP. At first a general calibration procedure is introduced, with the aid of an open-source software library, to calibrate narrow AOV cameras with the CRCM. Subsequently the procedure is validated using a reflex camera with a 60mm macro lens, equipped with extension tubes (20 and 32mm) achieving magnification of up to 2 times approximately, to verify literature findings with experimental photogrammetric 3D measurements of millimetresized objects with micro-features. The limitation experienced by the laser printing technology, used to produce the bi-dimensional pattern on common paper, has been overcome using an accurate pattern manufactured with a photolithographic process. The results of the experimental activity prove that the CRCM is valid for AOVs down to 3.4° and that DCRP results are comparable with the results of existing and more expensive commercial techniques.Percoco, G.; Sánchez Salmerón, AJ. (2015). Photogrammetric measurement of 3D freeform millimetre-sized objects with micro features: an experimental validation of the close-range camera calibration model for narrow angles of view. Measurement Science and Technology. 26(9):1-9. doi:10.1088/0957-0233/26/9/095203S19269Mitchell, H. L., Kniest, H. T., & Won‐Jin, O. (1999). Digital Photogrammetry and Microscope Photographs. The Photogrammetric Record, 16(94), 695-704. doi:10.1111/0031-868x.00148Chen, Z., Liao, H., & Zhang, X. (2014). Telecentric stereo micro-vision system: Calibration method and experiments. Optics and Lasers in Engineering, 57, 82-92. doi:10.1016/j.optlaseng.2014.01.021Stamatopoulos, C., & Fraser, C. S. (2011). Calibration of long focal length cameras in close range photogrammetry. The Photogrammetric Record, 26(135), 339-360. doi:10.1111/j.1477-9730.2011.00648.xYang, X., & Fang, S. (2014). Effect of field of view on the accuracy of camera calibration. Optik, 125(2), 844-849. doi:10.1016/j.ijleo.2013.07.089Strobl, K. H., Sepp, W., & Hirzinger, G. (2009). On the issue of camera calibration with narrow angular field of view. 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems. doi:10.1109/iros.2009.5354776Ricolfe-Viala, C., & Sanchez-Salmeron, A.-J. (2010). Lens distortion models evaluation. Applied Optics, 49(30), 5914. doi:10.1364/ao.49.005914Ricolfe-Viala, C., Sanchez-Salmeron, A.-J., & Valera, A. (2013). Efficient Lens Distortion Correction for Decoupling in Calibration of Wide Angle Lens Cameras. IEEE Sensors Journal, 13(2), 854-863. doi:10.1109/jsen.2012.2229704Zhang, Z. (2000). A flexible new technique for camera calibration. IEEE Transactions on Pattern Analysis and Machine Intelligence, 22(11), 1330-1334. doi:10.1109/34.888718Percoco, G., Lavecchia, F., & Salmerón, A. J. S. (2015). Preliminary Study on the 3D Digitization of Millimeter Scale Products by Means of Photogrammetry. Procedia CIRP, 33, 257-262. doi:10.1016/j.procir.2015.06.046Ricolfe-Viala, C., & Sanchez-Salmeron, A.-J. (2011). Camera calibration under optimal conditions. Optics Express, 19(11), 10769. doi:10.1364/oe.19.010769Guidi, G. (2013). Metrological characterization of 3D imaging devices. Videometrics, Range Imaging, and Applications XII; and Automated Visual Inspection. doi:10.1117/12.2021037Herráez, J., Martínez-Llario, J., Coll, E., Rodríguez, J., & Martin, M. T. (2013). Design and calibration of a 3D modeling system by videogrammetry. Measurement Science and Technology, 24(3), 035001. doi:10.1088/0957-0233/24/3/03500

Hot nanoindentation in inert environments

An instrument capable of performing nanoindentation at temperatures up to 500 °C in inert atmospheres, including partial vacuum and gas near atmospheric pressures, is described. Technical issues associated with the technique (such as drift and noise) and the instrument (such as tip erosion and radiative heating of the transducer) are identified and addressed. Based on these considerations, preferred operation conditions are identified for testing on various materials. As a proof-of-concept demonstration, the hardness and elastic modulus of three materials are measured: fused silica (nonoxidizing), aluminum, and copper (both oxidizing). In all cases, the properties match reasonably well with published data acquired by more conventional test methods.United States. Office of Naval Research (Contract No. N00014-08-1-0312)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie

Corrosion of cast Stellite-3 analogue in simulated PWR conditions

Wear resistant alloys are required for deployment of pressurised water reactor primary circuits and in this context, the corrosion behaviour of a cast cobalt-based alloy following exposure for 30 days in lithiated water at 300°C was investigated. Corrosion of the surface was observed, resulting in the formation of a ~100 nm thick chromium and silicon-rich oxide. Preferential corrosion of the matrix at its interface with just one of the carbide types was observed to a depth of ~1 μm; for the first time this was found not due to any inhomogeneity in the matrix but was instead an electrochemical effect