Comparison of the Microstructure, Tensile, and Creep Behavior for Ti-24Al-17Nb-0.66Mo (Atomic Percent) and Ti-24Al-17Nb-
- PDF / 460,028 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 85 Downloads / 162 Views
INTRODUCTION
TITANIUM-ALUMINUM-NIOBIUM (Ti-Al-Nb) alloys differ from conventional a and a + b Ti alloys in that their constituent phases may include the ordered intermetallic orthorhombic (O) phase, based on Ti2AlNb, the ordered hexagonal-close-packed (hcp) intermetallic a2 phase, based on Ti3Al, and the bodycentered-cubic (bcc) phase whose ordering is dependent upon composition.[1–5] This class of alloys has exhibited greater elevated-temperature strength and creep resistance than conventional a + b Ti alloys and Ti3Albased alloys.[1,6–14] In particular, a Ti-24Al-17Nb (at. pct) alloy has exhibited an attractive balance of elevated-temperature tensile, creep, and fatigue strength while maintaining adequate room-temperature (RT) strength, toughness, and elongation-to-failure (ef).[15–23] Improvement in creep resistance may result from altering the microstructure through heat treatment or compositional changes. The addition of molybdenum (Mo), a beta-phase stabilizer, affects the grain size and the constituent phase volume fractions. Molybdenum acts as a solid-solution strengthener and also tends to reduce diffusion-controlled reactions.[24] Small Mo additions of 1 at. pct have resulted in significant creep property improvements.[14,25–27] In fact, a Ti-24Al17Nb-1Mo (at. pct) alloy has proven to be significantly more creep resistant than several other Ti-Al-Nb alloys, including Ti-24Al-17Nb (Figure 1) and TiMetal 21S, J.P. QUAST, Graduate Student and C.J. BOEHLERT, Assistant Professor, are with the Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824-1226, USA. Contact e-mail: [email protected] Manuscript submitted July 27, 2006. Article published online March 27, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS A
Ti-24Al-11Nb (at. pct), Ti-1100, Ti-22Al-23Nb (at. pct), and Ti-6Al-2Sn-4Zr-2Mo-1Si (wt pct) at a stress of 172 MPa and temperature of 650 C.[14] However, relatively few studies have focused on investigating the effects of Mo additions on the microstructure and mechanical properties of Ti-Al-Nb alloys or determining the range of Mo compositions which are beneficial to the mechanical behavior. Recently, researchers have focused on developing more cost-effective processing methods, such as powder metallurgy, for O-based titanium alloys.[28–30] Tape casting is one such fabrication technique that is advantageous over casting and hot working (forging or rolling) because of its versatility in shape and composition control along with greater material utilization. Previous studies have shown that the properties of alloys produced via powder metallurgy compare favorably to those that were produced using more conventional processes.[31] The primary objective of this study was to examine the microstructure and mechanical performance of tapecast O-based quaternary Ti-Al-Nb-Mo alloys. A second objective was to determine the effect of varying Mo additions, between 0.66 and 2.3 at. pct, on the microstructural features and the impact this causes on the creep deformation be
Data Loading...
