Multiple Microstructure Evolution and Mechanical Properties of Gh4169/Tc4 Brazed Joint

Abstract

Given that the brittleness of Ti-Cu intermetallic compounds (IMCs) was less than that of Ti-Ni IMCs, a copper-based filler was employed to braze GH4169 and TC4 at temperatures ranging from 920 °C to 980 °C for 30 minutes. The research investigated the influence of brazing temperatures on the microstructure at interfaces, mechanical properties, and fracture patterns. A multilayer structure (layer I, II and III) formed in the GH4169/TC4 brazed joint was showed. The interface microstructure was GH4169/TiNi3 + (Cr, Ni, Fe)ss/Ti(Cu, Ni)/Ti2(Cu, Ni)/α-Ti/TC4. The layer I primarily composed of dendrites by solid-solid diffusion, and the grains grew mainly along the <0001> direction. The Ti2Cu grain in layer II grew mainly along the direction of the <010>, and the α-Ti in the layer III grew mainly along the direction of <0001> when the temperature was 940 °C. As the temperature increased, the grains size decreased, and the number of low angle grain boundaries (LAGBs) in layer I and layer III increased. The shear strength of the joints first increased and then decreased as the temperature rose. The maximum shear strength was 174.1 MPa, reached at 940 °C after 30 minutes. The hardness and elastic modulus of the TiNi3 + (Cr, Ni, Fe)ss and Ti(Cu, Ni) phases were 15.85 GPa and 306.5 GPa, 9.06 GPa and 184.4 GPa, respectively. The abrupt changed in hardness and elastic modulus primarily caused majority of the joints to fracture at the interface between the TiNi3 + (Cr, Ni, Fe)ss and Ti(Cu, Ni) phases.

Keywords: TC4, GH4169, Ti-Cu IMCs, Copper foil, Shear strength, Nano-hardness