Experimental procedure of Combustion joining of C/C composites to tial intermetallics

C/C composite were obtained from CFCCARBON ltd, China, which was 2D entwined and 3D punctured. C/C substrates were sliced into 8mm-8mm-5mm pieces. The applied TiAl intermetallics had a nominal composition of Ti-46Al-2Cr-2Nb, which were also cut into 8mm-8mm-5mm pieces for metallographic observation and 30-10-5mm for the shear test. All of the joined surfaces on the TiAl samples were polished using SiC paper of <1000 grit prior to joining.

Ti powder, Al powder and C powder were dry-mixed in a ball mill for 120 min and cold pressed at a pressure varying from 20 to 50 Mpa into disc specimens of a diameter of 10mm and a thickness of 0.4-2.0 mm. the resultant variation in the green density ranged from 60% to 70% of the theoretical density. Commercial Ag-Cu-Ti filler metal that had a composition of Ag-26.4Cu-4.5Ti and a thickness of 100um was used.

The joining apparatus schematic is shown in Fig.1. The joining process was carried out in induction heating equipment with an Ar flow atmosphere. The joining assembly was heated to ignite the self-sustaining reaction in the Ti-Al-C interlayer. After the reaction was initiated, the induction heating was stopped, and then the assembly was cooled to room temperature. The combustion temperatures of the powder compact interlayer were measured using two fine-wire Pt/Pt-13%Rh thermocouples in which one thermocouple was inserted into the center of the powder compact interlayer and the other one was inserted adjacent to the interlayer- C/C interface.

After the joining process, the joint microstructure were characterized using X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. For EDS analysis, 10 tests were carried out for a given phase. Shear strength tests were performed at a constant speed of 0.5 mm/min using a universal testing machine. Ten shear samples were examined for the joints brazed at a certain parameter, and the average values and the deviations of the shear strengths were obtained.

 

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