Transient Liquid Phase Bonding of Cu-Cr-Zr-Ti Alloy Using Ni and Mn Coatings: Microstructural Evolution and Mechanical P
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JMEPEG DOI: 10.1007/s11665-017-2830-4
Transient Liquid Phase Bonding of Cu-Cr-Zr-Ti Alloy Using Ni and Mn Coatings: Microstructural Evolution and Mechanical Properties T. Venkateswaran, K.R. Ravi, D. Sivakumar, Bhanu Pant, and G.D. Janaki Ram (Submitted October 23, 2016; in revised form June 14, 2017) High-strength copper alloys are used extensively in the regenerative cooling parts of aerospace structures. Transient liquid phase (TLP) bonding of a Cu-Cr-Zr-Ti alloy was attempted in the present study using thin layers of elemental Ni and Mn coatings applied by electroplating. One of the base metals was given a Ni coating of 4 lm followed by a Mn coating of 15 lm, while the other base metal was given only the Ni coating (4 lm). The bonding cycle consisted of the following: TLP stage—heating to 1030 °C and holding for 15 min; homogenization stage—furnace cooling to 880 °C and holding for 2 h followed by argon quenching to room temperature. Detailed microscopy and electron probe microanalysis analysis of the brazed joints were carried out. The braze metal was found to undergo isothermal solidification within the 15 min of holding time at 1030 °C. At the end of TLP stage, the braze metal showed a composition of Cu17Ni-9Mn (wt.%) at the center of the joint with a steep gradient in Ni and Mn concentrations from the center of the braze metal to the base metal interfaces. After holding for 2 h at 880 °C (homogenization stage), the compositional gradients were found to flatten significantly and the braze metal was found to develop a homogeneous composition of Cu-11Ni-7Mn (wt.%) at the center of the joint. In lap-shear tests, failures were always found to occur in the base metal away from the brazed region. The copper alloy base metal was found to undergo significant grain coarsening due to high-temperature exposure during brazing and, consequently, suffer considerable reduction in yield strength. Keywords
brazing, Cu-Cr-Zr-Ti alloy, electroplating, transient liquid phase bonding
1. Introduction Attractive thermal properties coupled with good strength make copper alloys well suited for launch vehicle engine components and allied sub-systems (Ref 1-3). Cu-Cr-Zr-Ti alloy is commonly used in regeneratively cooled structures in liquid propulsion engines of launch vehicles (Ref 4). Joining of this copper alloy in complex shapes and varied thicknesses using brazing is a critical manufacturing step in realizing functional hardware. The braze filler is chosen based on the thermal and mechanical requirements of a given application. Braze fillers based on Cu-X systems (X: Ag, Zn, Ag-P, Ag-Sn, Ag-Mn, Mn-Ni, etc.) are widely used for brazing of copper alloys (Ref 5). Conventionally, the braze filler is introduced in T. Venkateswaran, Materials and Mechanical Entity (MME), Vikram Sarabhai Space Centre, ISRO, Trivandrum, India and Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, India; K.R. Ravi, Structural Nanomaterials Laboratory, PSG Institute of Advanced Studies, Coimbatore, India and
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