Diffusion bonding between a commercial pure tantalum and an austenitic stainless steel SUS304 was performed in a vacuum of 8 mPa at temperatures ranged from 600 to 1200°C. The direct bonding of the tantalum to the stainless steel, resulted in extremely low joint strength and formed intermetallic compounds such as FeTa, Fe7Ta3, NiTa2, NiTa, Ni2Ta, Ni3Ta, Ni8Ta and Cr2Ta in the bond zone of the joint. To examine the influence of Cr, C, Fe and Ni of alloying elements of the stainless steel to the joint strength, the diffusion bondings were carried out between the tantalum and a pure chromium, the tantalum and a carbon steel (C: 0.42 mass%), the tantalum and a pure iron and the tantalum and a pure nickel. The effect of the insert metals of Fe, Ni and Cu foil on the joint strength between the tantalum and the stainless steel has been also studied. Main results obtained are as follows :
(1) The joint of the tantalum to the chromium was not enough to machine to tensile test pieces due to the forming of the intermetallic compound of Cr2Ta in the bond zone.
(2) The joint of the tantalum to the carbon steel and the joint of the tantalum to the iron formed intermetallic compounds such as FeTa, Fe7Ta3, TaC and Ta2C, and FeTa and Fe7Ta3 in the bond zone, respectively. These joint strength, however, increased with the bonding temperature and attained to about 150 MPa at maximum the bonding temperature of 900°C. The joint strength was found to decreased at the higher bonding temperature than 1000°C. The joints could not be machined to tensile test pieces at the bonding temperature than 1100°C.
(3) The intermetallic compounds such as NiTa2, NiTa, Ni2Ta, Ni3Ta and Ni8Ta in the bond zone were formed in the bond zone of the joints of the tantalum to the nickel. The maximum joint strength of 225 MPa was obtained at the bonding temperature of 900°C.
(4) The joint strength of the tantalum to the stainless steel with Cu foil as an insert metal increased with the bonding temperature. The maximum value of 265 MPa was obtained at the bonding temperature of 1050°C, which was almost the same as that of the tantalum base metal.