Microstructures, Mechanical and Chemical Properties of TLP-Bonded Joints in a Duplex Stainless Steel with Amorphous Ni-B

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INTRODUCTION

TRANSIENT liquid-phase (TLP) bonding, which is feasible for the fabrication of the sound joints in materials with multifunctional structures and combines the beneficial features of the liquid-phase joining and diffusion bonding techniques, has been especially successful for joining Ni-base alloys.[1–10] Recently, this bonding process has been used as the preferred option for joining steels,[11,12] stainless steels,[13,14] and duplex stainless steels.[15–20] Prior work investigated in detail the microstructural developments on the TLP-bonded joints in duplex stainless steels with Ni-based amorphous alloys by means of cross-sectional and layer-by-layer characterization methods.[18–20] The recent investigations on the effects of cooling rates and fillers (namely, Ni- and Fe-based insert alloys and copper foils) on the microstructure and properties of TLP-bonded, duplex stainless steels have been reported.[16,17] When the Ni- and Fe-based alloys are employed as the insert alloys, B and/or Si are used as the major melting-point depressant element(s). However, the effects of brittle borides formed in the bonds on microstructures and properties were not involved in the investigations.[16,17] It has been reported that the temperature range of 1293.15 K (1020 C) to 1353.15 K (1080 C) is appropriate for the solution treatment in duplex stainless XINJIAN YUAN, Doctor, formerly with Pusan National University, Busan 609735, Republic of Korea, is now with the College of Materials Science and Engineering, Chongqing University, Chongqing 400045, P.R. China. MYUNG BOK KIM and YOUNG HO CHO, Graduate Students, and CHUNG YUN KANG, Professor, are with the Department of Materials Science and Engineering, Pusan National University. Contact e-mail: [email protected] Manuscript submitted June 10, 2011. Article published online December 21, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A

steels to dissolve secondary-phase precipitates without affecting the balance of matrix phases.[21] Ni-based amorphous insert alloys are usually suitable for bonding in the preceding temperature range. Furthermore, these amorphous metals with good corrosion resistance have excellent intersolubility with stainless steel system and remarkable homogeneity in microstructure and property. Thus, in this article, Ni-based amorphous foils were used as the interlayer. Compared with other reports, two novel aspects of the work were discussed in the current study. First, the influences of microstructural features with particular emphasis on the boride precipitates on mechanical properties of TLP-bonded joints in a duplex stainless steel were studied at various times and using Ni-based filler metals with and without Cr. The mechanisms governing the fracture were also interpreted in detail. Second, an in-depth examination on the relations between microstructures and corrosion properties was conducted.

II.

EXPERIMENTAL PROCEDURE

The nominal chemical composition of a nitrogencontaining duplex stainless steel used as the base metal was given in Table I. The ulti

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