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

Szastak K., Matsuura K., Kata D., Ohno M.

Journal of Achievements in Materials and Manufacturing Engineering

2014

Vol. 67, nr 1

5--13

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 TixAly phases, with some presence of Ti2AlC 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 Ti3Al, TiAl2 and TiAl3, 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.

Odporność na korozję wysokotemperaturową stopu na osnowie fazy γ-TiAl podczas utleniania w środowisku zawierającym chlorowodór

Małecka J.

Ochrona przed Korozją

2013

nr 2

44--49

W pracy przedstawiono wyniki utleniania izotermicznego stopu Ti-46Al-7Nb-0,7Cr-0,1Si-0,2Ni na osnowie fazy międzymetalicznej γ-TiAl w atmosferze 9% O2 + 0,2% HCl + 0,08% SO2 + N2. Podstawą doboru takiego składu atmosfery utleniającej jest występowanie w środowisku przemysłowym związków siarki z chlorowodorem i ich współudział w procesie korozyjnym. Utlenianie przeprowadzono w temperaturze 700ºC. Stwierdzono, iż badany stop wykazuje zadowalającą odporność na korozję wysokotemperaturową.

Test results of isothermal oxidation of γ-TiAl-based Ti-46Al-7Nb-0,7Cr-0,1Si-0,2Ni alloy in an atmosphere of 9% O2 + 0,2% HCl + 0,08% SO2 + N2 are presented. Oxidation was carried out at 700º. It was found that Ti-46Al-7Nb alloys show good high-temperature corrosion resistance.