Effect of cold work on recrystallization behavior and grain size distribution in titanium
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I.
INTRODUCTION
IN a recent paper, Rhines and Patterson Lreported the effect of degree of prior cold work on grain volume distribution and its consequent effect on grain growth in recrystallized aluminum. The grain volume distribution was found to be log-normal and remained constant during grain growth, in agreement with earlier studies by Okazaki and Conrad 2'3 on titanium. Further, it was shown that the standard deviation of the distribution, In o-v, which is a measure of the spread in the size of the grains, depends on the degree of cold work 9 preceding annealing, being smaller the greater the degree of cold work. Moreover, it was found that the number of faces F per grain, and of edges E per face are also log-normal and that In erF and In ere increase in a linear fashion with In o-v. The corresponding increase in relative number of threeedged faces with In err was considered to account for the generally observed increase in rate of grain growth with reduction in degree of cold work. In view of the importance of the results of Rhines and Patterson with respect to the dependence of rate of grain growth on In O-v, and in turn on the degree of cold work, it was felt that a further study into these relationships was desirable, especially on a metal in addition to aluminum. Since detailed studies on the grain size distribution of annealed titanium had been carried out previously, 23 it was decided to employ this metal in the present investigation. The previous studies 2'3 on the grain size distribution in titanium were carried out on annealed specimens following a fixed amount of cold work, namely, 93 pct reduction in area by swaging. Conventional planar metallographic analysis 3 revealed that the linear intercept grain size 1 distribution is log-normal and that for a given mean grain size 7 the distribution is relatively independent of the combination of annealing time and temperature used to obtain it. Serial H. CONRAD is Head, Materials Engineering Department, North Carolina State University, Raleigh, NC 27695-7907. M. SWINTOWSKI, formerly a Graduate Student at The University of Kentucky, is with Timken Research Laboratory, Canton, OH 44706. S. L. MANNAN is on leave at NCSU from the Reactor Research Centre, Kalpakkam, India. Manuscript submitted July 14, 1984. METALLURGICAL TRANSACTIONS A
sectioning 2 established that the distributions of the mean intercept grain size 1, the grain area A, and the grain volume V were all log-normal and that the slopes of plots of cumulative frequency vs log grain size were independent of the mean grain size in each distribution, i . e . , the distributions remained constant during grain growth. Comparison of these slopes gives In er/ = a In
O- A
=
b In Ov
[1]
w h e r e a = 1.17 a n d b = 1.429 It was also found that the mean values o f / , A, and V were related through 7 = a(A) ''2 = /3(V) '/3
[2]
where c~ and/3 are approximately equal to one. Further, the number of faces, vertices, and edges of a polyhedral grain were found to increase as its size became larger. Worthy
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