Microstructural Evolution of the Interface Between Pure Titanium and Low Melting Point Zr-Ti-Ni(Cu) Filler Metals
- PDF / 2,272,603 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 107 Downloads / 186 Views
razing of Ti alloys is a useful technology for expanding their usage in new civil application areas that require properties of high strength-to-density ratio and strong corrosion resistance, such as aircraft turbine engines, chemical apparatuses, and heat exchangers.[1] The most important aspect of titanium brazing is the filler metals. A number of filler metals have been tested for titanium alloys. Filler metals used for Ti brazing can be divided into Ag-, Al-, and Ti-Zr-based filler metals.[1– 3] In particular, Ti-Zr-based filler metals in which Cu and Ni are added as melting point depressants (MPDs) exhibit excellent properties, such as high corrosion resistance and joint strength.[1,3,4] When the MPDs in the Ti-Zr-based filler metals diffuse into the parent Ti metals during the brazing process, both the joint and base metals can become homogenized, which makes the
DONGMYOUNG LEE, Research Associate, is with the Department of Materials Science & Engineering, College of Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7204, USA. JUHYUN SUN, Researcher, DONGHAN KANG, Graduate Student, and SEUNGYOUNG SHIN, Principal Researcher, are with the Department of Heat Treatment Technology R&BD Group, Korea Institute of Industrial Technology, 7-47, Songdo-Dong, Yeonsu-Gu, Incheon 406-840, Korea. Contact e-mail: branchross@ gmail.com JUHWA HONG, Professor, is with the Department of Advanced Materials Engineering, Chungbuk National University, 410, Sungbong-Ro, Heungduk-Gu, Cheongju 361-763, Korea. Manuscript submitted December 23, 2013. Article published online October 1, 2014 5914—VOLUME 45A, DECEMBER 2014
tensile strength levels of the joint close to those of the base metals. This also means that a joint having thermal and corrosion resistance levels similar to those of the base metals can be obtained.[3] In titanium brazing, Ti-Zr filler metals should have a lower melting point than the beta transus temperature of the base metals because a lower brazing temperature provides and preserves the high mechanical properties of Ti-brazed assemblies.[1] Another important aspect should be considered when choosing a filler metal. New phases formed as the result of a reaction between base and filler metals are important in terms of metallurgy. MPDs for Ti-Zr filler metals tend to form brittle intermetallics, such as TixNiy and TixCuy, and their formation negatively affects joint integrity.[1–3] Botstein et al. reported that a Ti joint brazed with Ti25Zr-50Cu filler metal could form many intermetallic phases such as c-(Ti,Zr)2Cu and/or k-Cu2(Ti,Zr) laves phases.[3,4] Their effect on the corresponding mechanical properties strongly depends on the brazing time, temperature, and filler metal composition. This intermetallics formation can occur if the Cu concentration in the center of a joint after brazing is 7 to 14 wt pct.[4] They also reported that the intermetallic phases originated from the equilibrium phases of the filler metals. Chang et al. reported that Ni diffuses into the Ti-base metal faster than Cu along
Data Loading...
