EFFECT OF COOLING RATE ON TITANIUM AND STAINLESS STEEL JOINTS PERFORMED WITH COPPER INTERLAYER

Microstructure and mechanical response of joints of titanium and AISI 304 stainless steel performed using copper foil as an interlayer was evaluated in the study. The process was carried out in vacuum in the temperature range of 850 to 900 degrees C for 60 min. The effect of temperature and cooling rate after processing stage on the microstructure and mechanical properties of the joints were analyzed by means of optical and scanning electron microscopy (SEM), electron probe microanalyses, microhardness measurements and tensile and shear strength tests. The maximum values of tensile and shear strengths were obtained for the joints processed at 900 degrees C for 60 min. The cooling rate after bonding stage had significant influence on the microstructure and composition of the copper/titanium interface that could contain the eutectoid mixture of alpha-Ti+CuTi2 or the undercooled beta-Ti solid solution. The difference in mechanical properties of joints slowly and rapidly cooled reached up to 25 MPa and increased with lowering joining temperature. Observation of fracture surfaces of the joints slowly and rapidly cooled demonstrated that failure took place through the eutectoid mixture or stainless steel/copper interface, respectively.