# Brazing Ti-48 Al-2 Nb-2 Cr Alloys with Cu-Based Amorphous Alloy Filler
## 1 Introduction  
Due to their low density, high specific strength, excellent creep strength, and good oxidation resistance at elevated temperature, the TiAl alloys are considered ideal materials for high-temperature applications in aerospace vehicles, automotive engines, and airframes. However, the practical application of TiAl alloys is mainly limited by their intrinsic brittleness and poor workability, which makes it very difficult to prepare complicated and large components [1; 2; 3; 4]. In order to expand the applications of TiAl alloys, it is necessary to join individual and small components into complex and large components. So far, several techniques, such as fusion welding [5; 6; 7], diffusion bonding [8; 9; 10], and brazing [11; 12; 13], have been applied to join TiAl alloys. Despite their partial successes, these techniques are not practical in large-scale applications. For instance, the fusion welding of TiAl alloys suffers from stringent conditions such as preheating and postheating, and inevitable solidification crack. As for diffusion bonding, a long-time exposure of TiAl alloys at high bonding temperature and high pressure canchange their microstructure. Alternatively, vacuum brazing is widely used to brage TiAl alloys with good joint mechanical properties. Such a method is facile and economical, and can be performed at low temperatures. So far, several kinds of filler metals have been employed for brazing TiAl alloys, such as Ag-based [14; 15], Al-based [16], and Ti-based eutectic brage alloys [17; 18; 19]. Although Ag-based and Al-based filler metals have low liquidus temperature and excellent wettability, the formed joints have low joining strength and working temperature, which severely limit their practical applications. High joining strength can be realized via Ti-based fillers due to their good compatibility with TiAl alloys. [PERSON] et al. [19] brazed TiAl alloy using TiNi eutectic alloy, and the maximum room temperature shear strength reached up to 196 MPa. However, the high melting point of the TiNi eutectic brage alloy demands a rather high brazing temperature of more than 1453 K. [PERSON] et al. [11] brazed TiAl intermetallics with Ti-Cu-Ni filler metal, which has a liquidus temperature of 1233 K. The obtained excellent bonding strength was achieved with a brazing temperature of 1473 K, which was higher than the liquidus temperature. Recently, some Ti-based amorphous filler metals have been developed for brazing TiAl alloys, owing to their advantage of superior wettability, accelerated atomic diffusion, enhanced surface reaction, etc. This advantage is ascribed to the instantaneous melting and homogeneous features of these amorphous fillers. In addition, adding Zr into the Ti-based alloy filler can effectively decrease the brazing temperature and reduce the residual stress developed in the joint, causing an enhanced joint strength [20; 21; 22]. [PERSON] et al. studied the weldability of Ti-48 Al-2 Nb-2 Cr (at. %) alloys by TiZrCuNiCo amorphous ribbon, and the maximum tensile strength at room temperature reached 316 MPa [23]. [PERSON] et al. brazed TiAl and TC4 alloys with TiZrCuNi(Mo) and obtained the maximum shear strengths of 351 MPa and 437 MPa with the Mo-free and 8 wt % Mo filler metals, respectively [24]. [PERSON] et al. reported that the Ti-45 Al-2 Mn-2 Nb-1B (at. %) alloys were joined using amorphous Ti-37.5 Zr-15 Cu-15 Ni (wt %) ribbon, and a tensile strength of 468 MPa was obtained. The results shown that the mechanical behavior of joints is highly dependent on the feature of the interface, especially the content of (Ti, Zr)\({}_{2}\)(Cu, Ni) [25]. From the above analysis, it can be concluded that the Ti-based and Ag-based filler alloys are useful for achieving the sound joint of TiAl alloys. It is worth noting that the Cu-based filler owns a lower brazing temperature than the Ti-based counterpart. Therefore, the cheaper copper filler may bring in unique mechanical properties along with its facile brazing requirements.