L. Zeng, Alcoa Fastening Systems, Carson, CA; L. Haylock, Alcoa Fastening Systems, Torrance, CA; J. Fanning, TIMET-R&D, Henderson, NV; S. Sweet, Perryman Co.,, Houston, PA; A. Zenke, Alcoa Fastening Systems, Hildesheim, Germany; M. March, Alcoa Fastening Systems, Carson operation, Carson, CA
Ti-6Al-4V has been the most commonly used titanium alloy for aerospace fasteners for almost 50 years. However, the need to increase the strength of Ti-6Al-4V fasteners combine with the inherent limitation in through hardenability of Ti-6Al-4V, has created interest in other alloys. In addition, there is also a need to eliminate cadmium plating associated with alloy steel and Cres fasteners, and high strength titanium is viewed as an alternative to these materials. Over the past few years, Alcoa Fastening System (AFS) evaluated the capabilities of many emerging titanium alloys for their potential application as high strength fastener materials. Recently, AFS had successfully developed high-strength titanium fasteners using Timetal 555 (Ti-5Al-5Mo-5V-3Cr-0.5Fe). The Ti555 is a newly developed near b titanium alloy introduced by Timet. High strength Ti-555 fasteners were manufactured using conventional fastener manufacturing processes. Detailed qualification tests, including non-destructive, mechanical, and metallurgical tests as revealed that the newly developed Ti555 fasteners demonstrated excellent properties, meeting or exceeding the typical specification requirements of 1250MPa (180ksi) cadmium plated alloy steel fasteners. Non-destructive testing, including dimensional verification and identification, met product specifications. Metallurgical testing, including discontinuities, hydrogen contents, and grinding burns, were within specification limits. Mechanical properties evaluation showed a tensile strength of 1309 MPa (190 ksi) with more than 10% elongation. Double shear testing showed a minimum strength of 779 MPa (113 ksi) for uncoated parts and 744 MPa (108 ksi) for coated fasteners. Further microstructural evaluation revealed finely distributed secondary a phase within primary b matrix after aging.
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