• PDF / 1,547,917 Bytes
• 10 Pages / 584.957 x 782.986 pts Page_size
• 76 Downloads / 298 Views

DOWNLOAD

REPORT

---

u Takaku, Ikuo Ohnuma, and Kiyohito Ishida Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan (Received 12 March 2009; accepted 22 April 2009)

The phase equilibria at 300, 400, 500, and 600
C in the Ag–Bi–Ni system and 300, 400, and 500
C in the Cu–Bi–Ni system were experimentally determined by metallography and electron probe microanalysis on equilibrated alloys and diffusion couples. Differential scanning calorimetry was used to measure the temperatures of phase transformations. All the experimental results show that the solubilities of the ternary elements of the binary intermetallic compounds in the Ag–Bi–Ni system are limited. However, the binary intermetallic compounds have some solubilities of the ternary elements in the Cu–Bi–Ni system. No ternary intermetallic compound was found in the Ag–Bi–Ni and Cu–Bi–Ni systems. On the basis of the determined results, the phase equilibria in the Ag–Bi–Ni and Cu–Bi–Ni systems were thermodynamically assessed, and reasonable agreement between the calculated results and experimental data was obtained.

I. INTRODUCTION

Because of the prohibition of Pb in electronic materials, a great effort has been placed on the development of new Pb-free soldering and brazing materials.1–5 The phase diagram provides a basic information to design new Pb-free soldering materials. Recently, the present authors developed a thermodynamic database for phase diagrams in microsoldering alloys, including the elements Pb, Bi, Sn, Sb, Cu, Ag, Zn, Ni, and Au,6–8 using the calculation of phase diagrams (CALPHAD) method, which provides an extremely useful tool for the design of materials because it significantly decreases the amount of required experimental work.9 On the basis of thermodynamic calculation, information on the melting temperature range for solder, the solidification path, and the susceptibility to intermetallic formation with various substrates is available. The Ag–Bi–Ni and Cu–Bi–Ni systems are the two basic ones in this database, but there are no ternary thermodynamic parameters of those two systems in the prior database. It is necessary to carry out the thermodynamic assessments of these two ternary systems. No experimental data on the phase equilibria in the Ag–Bi–Ni system were reported. A few experimental data regarding the phase equilibria in the Cu–Bi–Ni a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0302

2644

http://journals.cambridge.org

J. Mater. Res., Vol. 24, No. 8, Aug 2009 Downloaded: 25 Mar 2015

system were published in 1922,10 where some mistakes in the solubilities of the binary intermetallic compounds and the miscibility gap of the face-centered cubic (fcc) phase in the Cu–Ni binary system were found.11 The purpose of this work is to experimentally determine the phase equilibria in the Ag–Bi–Ni and Cu–Bi– Ni systems, and to carry out the thermodynamic assessments of these two ternary systems on the basis of the experimental data and the assessed binary systems.