Workability of commercial-purity titanium and 4340 steel during equal channel angular extrusion at cold-working temperat
- PDF / 2,233,358 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 153 Views
I. INTRODUCTION
INVENTED in the former Soviet Union by Segal, the equal channel angular extrusion (ECAE) process[1,2] offers an attractive alternative for the primary breakdown as well as secondary working of conventional and advanced alloys. In the process, an ingot (or prior-worked billet) is extruded through a channel consisting of two continuous sections situated at an angle 2f to each other (Figure 1). The imposed strain per pass is a function of the channel angle.[1,3] Much larger strains can also be imposed in a given set of tooling through the use of multipass extrusion, which is possible because the cross-sectional area of the workpiece is not changed. The ability to impart large deformations without a change in cross section permits much smaller ingots to be melted to obtain a given size of semifinished product. Hence, the process is especially useful for materials prone to macrosegregation during the casting of large ingots. Other advantages of ECAE are moderate working pressures (compared to conventional extrusion through converging or shear dies) and the ability to control crystallographic and mechanical texture during multipass ECAE by judicious rotation of the workpiece between passes. Having been introduced to the West by Segal in the early 1990s, ECAE has become the subject of considerable interest, and research on the process has greatly increased. A number of investigations relating to metal flow[4,5,6] and microstructure/dislocation substructure evolution (primarily in aluminum and copper alloys) during ECAE[7–10] and to subsequent superplastic or service properties[11,12,13] have been conducted. On the other hand, relatively little research S.L. SEMIATIN, Senior Scientist, Materials Processing/Processing Science, and D.P. DeLo, Visiting Scientist, Processing Science Group, are with the Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLM, Wright-Patterson Air Force Base, OH 454337817. V.M. SEGAL, Principal Research Scientist, is with Johnson Matthey Electronics, Spokane, WA 99216. R.E. GOFORTH, Associate Professor, is with the Mechanical Engineering Department, Texas A&M University, College Station, TX 77843-3123. N.D. FREY, Vice President, is with E.T. Concepts, Inc., London, OH 43140. Manuscript submitted May 11, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
has been performed to establish workability criteria. The only effort addressing workability issues appears to be that of Semiatin et al.,[14] who investigated failure during hot ECAE of a gamma titanium aluminide alloy. Such considerations may be important for difficult-to-work alloys especially in view of the simple shear nature of metal flow during ECAE, which may give rise to shear localization or shear cracking. The present effort was undertaken as a follow-on to previous work on flow localization during hot working via ECAE.[14] The objective of the current research was to establish the failure mode of several typical difficult-to-work alloys, commercial-purity titanium and AISI 4340 steel, during c
Data Loading...
