Slip traces

Fig. 8.3. Slip traces on crystal surface. Slip traces are a microstructural consequence of the onset of plastic deformation (courtesy of C. Coupeau).

After initial deformation, examination of the crystal surface, again by optical means, reveals a novel feature already discussed in fig. 8.3, namely, slip traces. These slip traces are the debris left in the wake of dislocations that have made their way to the crystal surface, leaving behind a jump across the relevant slip plane at its point of intersection with the crystal s surface. These slip traces bear a precise geometrical relation to the underlying crystalline geometry and thereby provide a central clue in ferreting out the microscopic origins of plastic deformation. 

A second example of the way in which deformation can be examined using surface microscopy is shown in fig. 13.2. What this figure reveals is a series of snapshots of the surface profile fhat attends a series of points on the stress-strain curve once plastic deformation has commenced. In keeping with our discussion of the emergence of slip traces, it is clear that with increasing deformation, both the number of active slip planes and the number of dislocations per slip plane increase. 

Figure 8-14. Slip traces in a frictional system with compliant restraint. (a) Woods metal on babbit. (b) Constantan on steel. Load 2.45 N. Tractive velocity 0.025 cm/s. Data by Morgan, Muskat and Reed [19].

Fig. 4.33 Slip traces in grains of polycrystalline MgO specimen shortened 3.5 % at 8 kbars pressure. Compression axis horizontal, a Uniformly distributed slip in group of grains (xl50), b nonuniform slip in grain (xl50), c kinked grain (xl50), and d extension fracturing associated with kinking (x200). All specimens unetched [40]. With kind permission of John Wiley and Son...

Fig. 4.36 Slip traces on specimens deformed at high temperatures under 5 kbars confining pressure, a Kinking in specimen shortened 11 % at 400 °C (xl25), b wavy noncrystallographic deformation bands in specimen shortened 6 % at 400 °C (x55), and c diffuse deformation bands and fine slip in specimen shortened 10 % at 750 °C (x 125) [40]. With kind permission of John Wiley and Sons...

When deactivation occurs rapidly (in a few seconds during catalytic cracking, for instance), the fresh activity can be found with a transport reac tor through which both reac tants and fresh catalyst flow without slip and with short contact time. Since catalysts often are sensitive to traces of impurities, the time-deac tivation of the catalyst usually can be evaluated only with commercial feedstock, preferably in a pilot plant. 

The differing malleabilities of metals can be traced to their crystal structures. The crystal structure of a metal typically has slip planes, which are planes of atoms that under stress may slip or slide relative to one another. The slip planes of a ccp structure are the close-packed planes, and careful inspection of a unit cell shows that there are eight sets of slip planes in different directions. As a result, metals with cubic close-packed structures, such as copper, are malleable they can be easily bent, flattened, or pounded into shape. In contrast, a hexagonal close-packed structure has only one set of slip planes, and metals with hexagonal close packing, such as zinc or cadmium, tend to be relatively brittle. 

Chose a sturdy notebook, one that will survive your need to open and close it on innumerable occasions and one that will not burst when you have taped or pasted in chart paper tracings, scintillation counter output, chemical manufacturer s product information slips, graphs, etc. (Even superbly constructed laboratory notebooks can be damaged through normal use so protect your notebook out of respect for its archival value.)... 

T1he adsorption of metal ions from aqueous solutions is a phenomenon of immediate interest to workers in many diverse disciplines. The incorporation of metals into geological sediments, removal of metal ions from industrial and civic effluent, interference of trace metal ions in analytical and electroanalytical chemistry, ore flotation, metallurgical leaching processes, and the stability of ceramic slips are all processes which are controlled to a large extent by interaction of metal ions with solid-liquid interfaces. 

Three procedures for determining dynamic friction are given, the initial friction, friction after repeated movement between the surfaces and friction in the presence of lubricants or contaminants. The presentation of results gives considerable detail on the interpretation of the friction traces, including dealing with slip stick. 

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