Influence of temperature transients on the hot workability of a two-phase gamma titanium aluminide alloy
- PDF / 7,914,588 Bytes
- 18 Pages / 598 x 778 pts Page_size
- 96 Downloads / 211 Views
I.
INTRODUCTION
TWO-PHASE titanium aluminide alloys containing TiA1 (y) and Ti3A1 (0/2) phases have received considerable attention from the aerospace as well as automotive industries. These alloys are characterized by low density, high stiffness, excellent tensile and creep strength to about 800 ~ and moderate oxidation resistance. One of the major challenges encountered in the development and potential application of near gamma titanium aluminides relates to the cost-effective processing of the alloys via the ingot-metallurgy and wrought-processing approach. In this context, several studies have been conducted to evaluate the hot workabilityt~ of near gamma titanium aluminides as well as to develop special processing practices such as isothermal forging, canned extrusion/forging, pack rolling, and isothermal rolling.iS ~3~ While the microstructural development occurring in near gamma alloys during ingot breakdown processes has been very well documented,t',3 ~0,~3~the microstructural evolution during secondary processing such as pack rolling or closed-die forging has been studied only to a limited extent. As the section size/thickness becomes relatively small, severe temperature transients and gradients develop across the workpiece during pack rolling[~,~41 and conventional or hot die forging.[8) The kinetics and morphological aspects of phase transformations that occur dur-
V. SEETHARAMAN, Senior Scientist, is with the Materials and Processes Division, UES, Inc., Dayton, OH 45432. S.L. SEMIATIN, Senior Scientist, is with the Metals and Ceramics Division, Wright Laboratory Materials Directorate, Wright-Patterson Air Force Base, OH 45433-7817. Manuscript submitted April 7, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS A
ing such pronounced nonisothermal deformation processing methods are interesting not only from a fundamental point of view, but also because these features exert a profound influence on the susceptibility of the gamma titanium aluminides to undergo cracking and/or fracture during hot working. The objective of the present work was to assess the influence of temperature transients on the deformation resistance, the microstructural development, and the fracture characteristics of a Ti-45.5A1-2Nb-2Cr alloy during hot working. The experiments were designed so that the information and knowledge obtained from this work could be used to interpret the microstructures obtained in pack-rolled or hot-die forged parts of near gamma titanium aluminides.
II.
EXPERIMENTAL PROCEDURE
A. Materials and Testing Procedures
The chemical composition of the near gamma TiA1 alloy used in the present work was 45.45 at. pct A1, 2.20 at. pct Cr, 2.05 at. pct Nb, and the balance titanium. The alloy was obtained in the form of induction skull melt ingots measuring - 7 0 mm in diameter. The ingots were hot isostatically pressed ("hipped") and then isothermally forged at 1175 ~ with a nominal height reduction of 6:1. The resuiting pancakes, measuring - 2 0 mm in thickness, were heat treated at 1227 ~ for 8 hours to obtain
Data Loading...
