Transient Liquid Phase bonding of γTiAl using Al films and SPS method

摘要

Purpose: Investigation of joining γ-titanium aluminides using Al interlayers. Design/methodology/approach:: In order to achieve a proper joining of TiAl elements, a method known as Transient Liquid Phase (TLP) bonding was combined with Spark Plasma Sintering (SPS). All the experiments were performed under a uniaxial pressure of 7.4 MPa in a vacuum to prevent possible oxidation of liquid Al in the interlayer. The study analyzed the difference in microstructure of joints achieved with Al film thicknesses of 50, 100, 200 and 300 μm, as well as two different bonding temperatures of 900 and 1100°C. After bonding the samples were cross-sectioned, polished using 220-1200 mesh SiC paper, and 1/4 μm diamond dispersion, and analyzed using OM, SEM, EDS and EBSD, while Vickers hardness tests were performed to compare the hardness of the joint to that of the base material. Findings: The analysis of the microstructures revealed that a joint has been created between the two starting γTiAl elements. The bond consisted of Ti_xAl_y phases, with some presence of Ti_2AIC and TiC. The Vicker's hardness tests reviled in some cases similar results to those of base material. Research limitations/implications: Presence of carbon rich phases within the joint, are the result of graphite mold and filling what react with molten Aluminum. This can be counteracted by replacing graphite with prefabricated TiAl powder after SHS. That however results in increasing the amount of phases such as Ti_3AI, TiAI_2 and TiAI_3, different from the original γTiAl within the joint. An increase in bonding time and temperature could allow for faster homogenization in the joint, but would make the process more expensive and time-consuming. Practical implications: The process allows for creation of strong joints, showing signs of homogenization. Low temperature and short time makes it a possible candidate for joining γTiAl elements. Originality/value: The use of Al instead of commonly used Cu or Ni, allows minimalization of introduce impurities into the joint, while Al is still cheap and common and thus doesn't increase the cost of the process.