The effect of hydrogen on mechanical properties in Ti-10V-2Fe-3Al
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I.
INTRODUCTION
H Y D R O G E N has long been known to have deleterious effects on the physical and mechanical properties of titanium and titanium alloys. J-4 While the effect of hydrogen on and a + /3 titanium alloys has been well studied, far less is known about the specifics of hydrogen in/3 alloys. 5 For/3 alloys, present understanding suggests that there are multiple effects due to hydrogen. An added complication is that, with the larger concentrations of alloying additions necessary to stabilize the/3 phase, hydrogen effects in a/3 alloy may also depend upon the alloying elements present. A major difference between/3 alloys and other titaniam alloys is that hydrogen has a high solubility in the/3 phase; thus high hydrogen concentrations can be present without the formation of a hydride. 5 Hydride formation in/3 alloys has been observed only when the alloy was heat treated to precipitate a phase. For microstructures without a phase, it is suggested that hydrogen effects are the result of factors other than hydride effects. ~ As hydrogen is a potent/3 stabilizer it can affect properties by modifying microstructure. Hydrogen, however, may also affect properties by more intrinsic mechanisms, akin to what is observed as hydrogen embrittlement in Fe and Ni alloys. Metastable /3 alloys are of particular interest due to the formation of the w and deformation-induced martensite phases. In Ti-10V-2Fe-3A1 these two phases have been previously well characterized so as to provide a starting point for understanding hydrogen effects on the alloy. The metastable nature of the alloy also allows for easy manipulation of the microstructure. This work focuses on the effect of hydrogen on mechanical properties of Ti-10V-2Fe-3A1 in the /3 annealed and
J.E. COSTA, formerly at Carnegie Mellon University, IS Member of Techmcat Staff, Sandla NaUonal Laboratories, Livermore, CA 94550. J.C. WILLIAMS and A. W THOMPSON are, respecnvely, Dean, Carnegie Insutute of Technology, and Professor, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted June 9, 1986. METALLURGICAL TRANSACTIONS A
water quenched condition. The resulting microstructure is sufficiently lean in /3 stabilizing elements to render the /3 phase metastable with respect to subsequent thermal or mechanical treatments. This alloy provides an important link between the a + /3 alloys and the more heavily stabilized all-/3 alloys.
II.
EXPERIMENTAL
The material used in this study was obtained from a TIMET commercial purity ingot of Ti- 10-2-3,/3 and a + /3 forged to 216 mm diameter round billet sections. Further processing was performed to yield 12.7 mm and 25.4 mm thick plate from which specimens were machined. The chemical composition of the starting material is listed in Table I. The material used in this research contained a high density of Ti4P(S, Si) inclusions. These inclusions, on the order of 1 micrometer in diameter, were equiaxed and homogeneously distributed throughout the material. Th
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