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The solid-state diffusion bonding experiments of the high Nb containing TiAl alloy were successfully carried out at the 1100°C under a uniaxial pressure of 30MPa for 45min, and the microstructure as well as the shear strength of the diffusion bonding interface with different surface roughness were investigated. The surface roughness was measured by AFM, and the microstructure characterization of interfaces was taken by SEM, EDS, AES. In addition, the bond qualities were evaluated by shear testing at room temperature. The results indicated that the surface roughness is of importance to improve the quality of diffusion bonding joint. Moreover,the white layer microstructure at the bonding interface was found in some samples which was caused by the oxygen content about 2%~3%. Furthermore, the shear teat showed that the shear strength of the joints can achieve 383MPa with the surface roughness is 0.062μm. Meanwhile, the recrystallization phenomenon at the diffusion bonding interface could improve the shear strength. Introduction The titanium aluminide alloy is considered to be a potential material for high-temperature structural applications in aerospace and automotive industry. Compared to conventional superalloy, titanium aluminide alloy have several advantages, such as high specific strength, high specific stiffness, good creep and oxidation resistance at elevated temperature[1-6].The operating temperature can enhance to more than 900°C, especially when the element of niobium was added into the conventional titanium aluminide alloy. However, low plasticity and low formability at room temperature restrict the extensive application of the high niobium containing titanium aluminide alloy. Diffusion bonding (DB) technology is one kind of efficient connectivity technology for the high niobium containing titanium aluminide alloy. By choosing appropriate process parameters,the defects of voids and the hot crack can be avoided, hence we can obtain a sound joint through the DB technology. [7-11]. DB technology has been used in many advanced materials, such as ceramics, 2nd Annual International Conference on Advanced Material Engineering (AME 2016) © 2016. The authors Published by Atlantis Press 635 intermetallic compound (IMC) and stainless steel etc. Cao et al. [12] successfully diffusion bonded the TiAl intermetallics and Ti3AlC2 ceramics using Ti-Ni interlayer. They found that the sound joint can be obtained at 920°C/ 60 min due to the interdiffusion of Ti and Al elements. And the highest shear strength of the joint was 151.6MP. Duarte et al. [13] studied the diffusion bonding of the gamma-TiAl alloy using modified Ti-Al nanolayer. Their study indicates that the joining of gamma-TiAl using modified Ti-Al alloy nanolayer doped with Cu at 900°C/50MPa/1h can be obtained without defects due to the ternary TiCuAl phase produced. NAKAO et al. [14] successfully joined the Ti-38Al binary cast alloy using the solid state diffusion bonding method. According to their results, the Time-Temperature-Bonding (TTB) and Time-Temperature-Oxide (TTO) diagrams showed how to make a sound joint at different bonding conditions. Moreover, their tensile result indicated that the tensile strength of the joint at room temperature was about 225MP and the bonding joints fractured at the base metal. Meanwhile, the recrystallization at diffusion bonding interface has improved the joint performance at 1273K with post-bonding heat-treatment. Cam et al. [15] found that the surface roughness was an important factor to the connection of γ-TiAl sheet and the sound bonds could be achieved in primary annealed gamma sheets with ground surface at 1000°C/5MPa/8h.However,they could not evaluate the surface roughness with the professional instruments. These studies mainly focus on the welding parameters and the joint properties of the titanium aluminide alloy. The influence of surface roughness on bonding surface of high niobium containing titanium aluminide alloy is scarcely reported and lucubrated. A newly developed high niobium containing titanium aluminide alloy, named Ti-45Al-8.5Nb-0.2W-0.1B-0.1Fe-0.1Y was investigated in this paper, which has promising application in aerospace industry. This alloy was bonded by the solid-state diffusion bonding at1100 °C under a uniaxial pressure of 30MPa/45min.The surfaces of the bonding specimens were characterized by atomic force microscope (AFM).And the bonding interfaces were characterized using scanning electron microscope (SEM) together with Energy Dispersive Spectrometer (EDS) and Auger electron spectroscopy (AES).The bonding shear qualities were evaluated by a mechanical testing machine at room temperature. Materials and Experimental Procedures Materials The chemical composition (at.%) of high Nb containing TiAl alloy used in this paper is listed in Table1 This alloy was processed as follows: vacuum arc re-melting (VAR)for three times → Hotisostatic -pressed (HIP) under the conditions of 1280°C/140MPa/240min →canned-forging at 1250°C with the stain of 10/s(deformation is 60%) → heat-treatment at 1320°C and hold for 20min.The final microstructure is near lamellar which is shown in Fig.1.

The Influence of Surface Roughness on Diffusion Bonding of High Nb Containing TiAl Alloy