A general program for interpreting electron diffraction patterns
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Fig. 4 - - D i s l o c a t i o n b o u n d a r i e s o b s e r v e d in ( l i l ) thin foils of
compression creep crystal of Cu 6 wt pct A1 crystal oriented 10 deg from [111] on [111]-[101] symmetry line. Conditions: t = 25 h, T = 750~ r = 340 g-mm -2. served are shown in Fig. 3, and this evidence in conjunction with the etch pit results shows that only (110) {1[1} slip occurs. In particular, there is no evidence of cube slip, while there ts extensive secondary {111} slip activity. With the above in mind, an alternative explanation favored by the authors suggests that a sub-boundary system can develop In (110) through glide alone. Speefflcally, if the conjugate system, y-DA, Interacts with the ertttcal system, 6-AC, Lomer-Cottrell locks are formed along [il0], the ltne of Intersection of the two planes. The reaction is: ( D y + y A ) +(A6 +6C) ~ Dy+y6 + 6 C Tilt boundaries composed of these locks can subsequently form in regions of the c r y s t a l where there is simultaneous activity on both systems. According to Amelinckx's analysis of two dislocation tilt boundaries formed by glide, the contact plane normal is given by: =
(a~ x a~)
x ~
x
b~)
Letting al = [ i i l ] , as = [111], bl = [101] and b2 = [01i], the result/~ = [110] is obtained, as observed. The configuration of boundaries so formed would resemble those produced by p r i m a r y ot-DC dislocations undergoing cube c r o s s slip. Also, if the p r i m a r y ot-DC disl o c a t i o n s attached themselves to these tilt boundaries, the resultant configuration would be indistinguishable from genuine cube c r o s s slip followed by L o m e r - C o t trell dissociation. Fig. 4 c o r r o b o r a t e s the above interpretation. The plane of the foil is parallel to the prim a r y slip plane, ( l i l t . Dislocations on 6(111) and y ( i i l ) intersect the foil along [101] and [011] r e s p e c tively. Where these dislocations have intersected, they have reacted to produce a diffuse boundary in (110) which intersects the foil plane along [i12]. Dislocations lying in the p r i m a r y slip plane have also attached themselves to the resultant boundary in the manner described. The various possible origins of the (110) boundary unfortunately must remain conjectural b e c a u s e Burgers vector determinations were not performed. One of the authors (DLK) acknowledges the support METALLURGICAL TRANSACTIONS
A General Program for Interpreting Electron Diffraction Patterns M. BOOTH, M. GITTOS, AND P. WILKES The interpretation of electron diffraction patterns which approximate closely to plane sections of the r e ciprocal lattice, requires a knowledge of the interplanar distances (d-spacings) and angles for the given structure. The electron microscopist usually comp a r e s the ratios of measured distances from the pattern with those calculated from the proposed structure and when a tentative indexing system is chosen, checks it by measuring the interplanar angle and comparing it with a calculated value.* *The International Union of Crystallography has programs availa
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