Cooling Rate Effects on Ti-6Al-4V and Beta III Titanium Alloys
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COOLING RATE EFFECTS ON Ti-6AI-4V AND BETA III TITANIUM ALLOYS
T. F. BRODERICKa, F. H. FROESa, AND A. G. JACKSONb aAir Force Wright Aeronautical Laboratories, Materials Laboratory, Structural Metals Branch, Wright-Patterson AFB, OH 45433; bsystems Research Laboratories, 2800 Indian Ripple Road, Dayton,
OH 45440
ABSTRACT The titanium alloys Ti-6A1-4V and Ti-11.5Mo-6.OZr-4.5Sn (Beta III) were produced at cooling rates of 103*C/sec and IO50C/sec using the Rotating Electrode Process (REP), and the Electron Beam Splat Quenching (EBSQ) process, respectively. Material from both alloys examined in the as-produced, heat treated, and vacuum hot pressed (VHP) conditions exhibited an order of magnitude decrease in beta grain size with increasing cooling rate ("'135 pm and 7 pm in the Ti-6A1-4V alloy; 1u40 pm and 2-4 pm in the Beta III alloy), and a difference in aging response between REP powder and EBSQ flakes. After heat treatment the Ti-6AI-4V developed an alpha morphology which was lenticular in REP powder and equiaxed in EBSQ flakes. Three possible mechanisms are proposed to explain this change involving an increased dislocation density and a tendency for grain boundary allotriomorphic alpha in the EBSQ case. Heat treatment of the Ti-11.5Mo-6.OZr-4.5Sn materials showed a change in the location of alpha precipitation from interdendritic to grain boundary in going from REP to EBSQ. It is suggested that this change may relate to the decreased solute redistribution which occurs in the more rapidly cooled material.
INTRODUCTION Titanium and titanium alloys are widely used in the aerospace industry because of their high strength-to-density, fracture behavior, and general corrosion resistance [1-3]. However, with the requirement for higher performance system; the demands for materials with increased levels of mechanical property behavior has grown. These increased mechanical properties have largely been met with improved aluminum, superalloy, and organic composite materials, with only small improvements in titanium alloys [4-7]. Recently, the U.S. Air Force recognized that quantum improvements in titanium alloy behavior were possible using rapid solidification (RS) techniques and initiated programs to develop new titanium alloys with higher use temperature [8], higher usable strength (strength combined with enhanced damage tolerance) [9], and lower density [10]. At the same time it has been recognized that RS can also offer advantages in conventional titanium alloys because of microstructural refinement. It is the purpose of this paper to report preliminary results obtained by rapidly solidifying an alpha-beta alloy (Ti-6AI-4V) and a metastable beta alloy (Beta III [Ti-11.5Mo-6.OZr4.5Sn]). EXPERIMENTAL The Ti-6AI-4V and Ti-11.5Mo-6.OZr-4.5Sn alloys examined in this work were produced to cover a range of estimated cooling rates from 103,C/sec, considered a lower limit of RS, to 105°C/sec. Mat. Res.Soc.Symp.Proc.Vol. 28 (1984) Published by Elsevier Science Publishing co., Inc.
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Spherical powder with an average particle s
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