For example if you command the probe to be shifted by x units in the X

For example if you command the probe to be shifted by

This preview shows page 13 - 16 out of 16 pages.

For example, if you command the probe to be shifted by x units in the X-direction, there is generally a significant displacement in the Y and Z directions. Any such movement of the cantilever in Z-direction is undesired and adds the errors to the data. Modern AFM instruments therefore use an alternative set of scanners wherein Z-scanner is separated from the X-Y scanner (Figure 14B).
Image of page 13
Figure 13 Piezoelectric scanners used in AFM: A piezoelectric tube (A) and a scanner having decoupled X-Y and Z piezoelectric elements (B). A laser beam is focused on the cantilever that has a highly reflective surface. The laser beam reflected off the cantilever is focused on a position sensitive photodiode quadrant. The cantilever is scanned over the sample surface in a raster pattern. Any deflection in the cantilever because of sample interaction causes displacement in the laser spot on the photodiode; this displacement signal is analyzed to calculate the deflection in the cantilever. Imaging can be performed in either constant-force mode (distance between the tip and the specimen can change) or constant-height mode (force between the tip and the specimen can change).
Image of page 14
2.4 Macroscopy: 2.4.1 Sulphur Print: Serves for detection of increased sulfur concentration (segregations) in steel and counts therefore as etching process. If a bromide paper that was soaked in 5 % sulfuric acid is pressed on the metallographic specimen of a steel sample, the sulfur-containing sections of the paper turn dark. The sulfuric acid reacts with the sulfide inclusions and forms hydrogen sulfide. This again reacts with the bromide paper to dark silver sulfide. This indicates the distribution of the sulfide inclusions in the material. The print is secured, watered, dried and can thus be archived. 2.4.2 Flow line observation: Grain flow is a directional orientation of metal grains and any non-metallic inclusions that have been deformed due to forging. Individual grains are elongated in the direction of the metal flow or plastic deformation. More importantly, non-metallic inclusions, particles and other impurities inherited during the casting process are elongated in the direction of grain flow. Grain flow occurs to some extent in all metal-forming processes, and not just forging. 2.4.3 How to observe flow-lines? The forging needs to be ground and polished, after sectioning, similar to a metallographic sample. Then, macro-etching is carried out. 2.4.4 Why flow lines are visible? One can observe grain flow-lines due to the presence of particles and inclusions. The etchant attacks the interface region between these inclusions as well as the base metal. The metal is corroded due to acid and the unaffected inclusions are visible as flow lines. 2.4.5 Significance of flow lines: Mechanical properties vary with respect to orientation relative to grain flow. Properties like impact toughness, ductility and fatigue strength, which are measures of a material’s resistance to cracking, can be improved significantly by proper alignment of the direction of crack propagation and the grain flow. The optimum alignment occurs when the maximum principal stress (perpendicular to a potential crack or fracture) is aligned with the grain-flow lines.
Image of page 15
Image of page 16

You've reached the end of your free preview.

Want to read all 16 pages?

  • Two '17
  • Electron, Scanning Tunneling Microscope, Scanning electron microscope, Scanning probe microscopy, Atomic force microscopy

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors