Notched Tensile and Impact Fracture of Ti-15-3 Laser Welds
- PDF / 2,650,327 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 82 Downloads / 165 Views
I.
INTRODUCTION
BETA titanium alloys offer an attractive combination of strength, toughness, and fatigue resistance in heavy sections.[1] Among metastable b titanium alloys, Ti-15V-3Cr-3Sn-3Al (Ti-15-3) is one of the most widely used materials. For example, Ti-15-3 is used throughout the aircraft industry as an alternative to Ti-6-4.[2] Several studies have shown that the strength and ductility of Ti-15-3 can be enhanced through thermo or thermomechanical treatment.[3–5] The strength of Ti-15-3 and the volume fraction of the a phase decrease with an increase in the aging temperature.[6] In direct aging at higher temperature 673 K to 1023 K (400 C to 750 C) after solution treatment, a precipitation occurs first at b grain boundaries, followed by intragranular a precipitation.[3] At lower aging temperature 573 K to 673 K (300 C to 400 C), fine a precipitates are formed uniformly within b grains by nucleating at precursory isothermal x particles.[3] Moreover, an increase in b grain size from 15 to 200 lm in the Ti-15-3 alloy results in a strength increase and a ductility decrease.[4] Additionally, it was reported that the notched tensile strength (NTS) decreases but the fracture toughness increases as the b grain size increases.[6] Laser welding is performed in many fields to weld titanium alloys for various applications.[7,8] It is well known that the presence of sharp notches in a material increases the likelihood of cracking or sensitivity under tensile straining.[9,10] In previous studies, sharp notch specimens were used to investigate the effect of microstructure on the notch sensitivity of titanium alloys and LEU-WEN TSAY, Professor and YAN-JIE WU, Graduate Student, are with the Institute of Materials Engineering, National Taiwan Ocean University, Keelung 202, Taiwan, Republic of China. Contact e-mail: [email protected] CHUN CHEN, Professor, is with the Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, Republic of China. Manuscript submitted September 16, 2010. Article published online July 14, 2011 3778—VOLUME 42A, DECEMBER 2011
welds.[11–13] However, little information regarding the mechanical properties of Ti-15-3 welds is available in the literature.[14,15] Accordingly, the objective of the present study was to investigate the NTS and impact toughness of Ti-15-3 laser welds aged at temperatures ranging from 590 K to 866 K (317 C to 593 C). The mechanical properties and microstructure of the laser welds were then compared to those of unwelded Ti-15-3 plates aged at the same temperature. In addition, the notch sensitivity, impact toughness, and fracture behavior of the welded and unwelded specimens are related to the microstructures.
II.
MATERIAL AND EXPERIMENTAL PROCEDURES
Annealed Ti-15-3 sheets with a thickness of 3.0 mm were purchased from Hwa-Chu Co. The chemical composition of the alloy in weight percent was as follows: 3.05Al, 2.92Cr, 2.99Sn, 15.1V, 0.071Fe, 0.12O, 0.016C, 0.014N, 0.021S, and balance Ti. A Rofin–Sinar RS 850 CO2 laser (Hamburg, Ger
Data Loading...
