The Effects of Filler Types on the Microstructure and Mechanical Properties of Ti-6Al-4V/316L Stainless Steel Joints Produced with Vacuum Brazing

This study investigates the effects of three brazing fillers, including AgCuTi, amorphous Ti-based, and amorphous Zr-based fillers, on the various properties of the joints between Ti-6Al-4V and 316L stainless steel. In this regard, the brazing was conducted at two temperatures of 900 degrees C and 950 degrees C for 30 min. The microstructure and the mechanical properties of the samples were analyzed using optical microscopy, scanning electron microscopy, x-ray diffraction, shear strength, and microhardness tests. Results showed that using AgCuTi filler at 900 degrees C, the microstructure of the brazed area included the layers of Ti2Cu, an Ag-based solid solution, and Fe3Ti. However, increasing the brazing temperature to 950 degrees C eliminated the Ag-based solid solution and increased the thickness of the Ti2Cu reaction layers. In contrast, the brazed joints produced with Ti- and Zr-based fillers displayed almost similar microstructure when the temperature increased. The reaction layer thickness for these fillers was notably less than that of AgCuTi samples (2 vs. 8-12 mu m). The joints produced with AgCuTi fillers showed the lowest microhardness of 154 HV at 900 degrees C. Moreover, the corresponding value for all samples increased with temperature, and the highest hardness of 793 HV was achieved with Ti-based fillers at 950 degrees C. The highest shear strength value of 218.8 MPa was also obtained for the samples brazed with Ti-based filler at 950 degrees C which was about 8.04% and 2.8 times higher than the corresponding values calculated for the samples brazed with Zr-abased filler (202.5 MPa) and AgCuTi (78.6 MPa) at 950 degrees C.