Cyclic deformation behavior of high-purity titanium single crystals: Part I. Orientation dependence of stress-strain res
- PDF / 186,768 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 88 Downloads / 225 Views
I.
INTRODUCTION
NUMEROUS investigations of the fatigue mechanism have been conducted on metals and alloys which possess a cubic crystal structure; however, information on metals having a hexagonal close-packed (hcp) crystal structure is still limited due to a lack of experimental results. Titanium is one of about 20 hexagonal metals, and it plays an important role in high-technology structures. It is now established that slip with an ^a& Burgers vector in atitanium occurs on {1010} prismatic planes, {1011} firstorder pyramidal planes, and the (0001) basal plane.[1–7] Also, the first-order pyramidal planes {1011} and the second-order pyramidal planes {112 2} with a ^c 1 a& Burgers vector are available for slip.[8–12] Among these slip systems, prismatic slip is usually preferred as the deformation mode. It has been observed to be activated even at a Schmid factor less than 0.02.[2] Six different twining planes reported in titanium include {1011}, {1012}, {1122}, {1124}, {1123}, and {1121}.[1,2,11–14] The complex slip and twinning behavior produced by competition between these systems makes it difficult to understand the deformation mechanism of titanium, especially under cyclic loading. It is widely recognized that the most developed understanding of fatigue mechanism has been obtained on highpurity materials; in particular, single crystals of face-centered cubic (fcc) metals. To the authors’ knowledge, almost all the available studies on a-titanium single X. TAN, Postdoctoral Fellow, formerly with the Research Institute for Strength of Metals, Xi’an Jiaotong University, is with the Hemispheric Center for Environmental Technology, Florida International University, Miami, FL 33199. H. GU, Professor, is with the Research Institute for Strength of Metals, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China. C. LAIRD, Professor, is with the Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104. N.D.H. MUNROE, Associate Professor, is with the Hemispheric Center for Environmental Technology, Florida International University. Manuscript submitted April 23, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
crystals are limited to plastic deformation under monotonic loading.[2–6,9–12,15] Only in a few newly published articles[16,17] has the cyclic deformation behavior of titanium single crystals been reported. It is very difficult to obtain large titanium single crystals with high crystalline perfection for fatigue testing. Akhtar and Teghtsoonian[3] found that attempts at seeding always resulted in failure. The seed crystal invariably recrystallized due to the allotropic transformation. For this reason, titanium single crystals have been grown with random orientations using strain annealing in the present study. In this article, we report results on the geometric theory of cyclic slip and twinning in titanium, which is believed to be the basis for an understanding of the cyclic stress-strain response of titanium single crystals and the orientation dependence of
Data Loading...
