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crease in flow s t r e s s from the first cycle to saturation, is 12.1 MN.m -~ for copper-cobalt as compared to 28.4 MN. m -z for the copper single crystals. The cumulative strain at which the saturation s t r e s s is reached is l a r g e r for copper-cobalt than for pure copper. The effect of orientation on fatigue hardening of copper-cobalt single c r y s t a l s is quite marked as shown in Fig. 1. The fatigue hardening is 35.1 MN 9m -2 for the copper-cobalt single crystals of duplexslip orientation as compared to 12.1 MN. m -2 for the crystals of single-slip orientation. The cumulative strain at which the saturation s t r e s s is reached is an order of magnitude smaller for copper-cobalt single crystals of duplex-slip orientation as compared to that for crystals of single-slip orientation. An examination of the surface of the fatigued specimens by optical m i c r o s c o p y revealed uniformly spaced fine slip lines on all the surfaces within the gage length. While crystals of single-slip orientation r e vealed only the p r i m a r y slip traces, crystals of duplexslip orientation showed a c r i s s - c r o s s pattern of prim a r y and conjugate slip. The spatial and Burgers vector distribution of the dislocations was studied after fatigue deformation into the saturation stage. The dislocation m i c r o s t r u c t u r e was studied on sections parallel to the p r i m a r y and conjugate planes, i.e., (111) and (111) planes r e s p e c tively. Single-slip orientation: The dislocation m i c r o s t r u c ture in the saturation stage of fatigue deformation of copper-cobalt single crystals is shown in Fig. 2. A detailed study of the Burgers vector of dislocations showed that almost all the dislocations were in the r t

7.0

101

102

70

Cu-Co Duplex

Stip)

6.0

50

5.0

50 =•

~

~o~

~" 4.0 E E

z 7

03

@

3.0

2.0

_~0

/ Pure Cu' / //(Duplex slip) ./'Pure Cut' / ." (Single slip) /

/

11

I0

1.0 t""

r K e m s t e y & P o t e r s o n (6 ) t~ K u p c i s et al (2)

"" i,,

t

|11t111

......1

I

I

I 1

101 102 N (Cycles)

|

0 ,103

I ! !

Fig. l--Fatigue hardening curve. VOLUME6A, OCTOBER 1975-1957

p r i m a r y plane and had either the p r i m a r y Burgers vector, a/2 [I01] or the coplanar Burgers vectors a/2 [0~1] and a/2 [lI0]. There were v e r y few forest dislocations. A prominent feature is the alignment of p r i m a r y edge dipoles in the trace directions of the conjugate and critical planes on the p r i m a r y plane.

Duplex-slip orientation. The dislocation m i c r o structure in the saturation stage of fatigue d e f o r m a tion of copper-cobalt single crystals oriented for duplex-slip is shown in Figs. 3 and 4. The cell s t r u c ture is well-developed and an equiaxed closed-cell distribution is seen on the (111) or primary plane.

Fig. 2--Single-slip orientation: Dislocation microstructure on the (111) plane.

Fig. 3--Duplex-slip orientation: Dislocation microstructure on the primary plane.

1958-VOLUME 6A, OCTOBER 1975

METALLURGICALTRANSACTIONSA

m i n a p a r t i c l e s . 1 The p r