The Paton Welding Journal, 2015, №09



2015 №09 (09)

DOI of Article 10.15407/tpwj2015.09.01

2015 №09 (02)

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The Paton Welding Journal, 2015, #9, 5-12 pages
 

Structure of γ-tial joints in resistance butt welding with application of interlayers

S.I. Kuchuk-Yatsenko, I.V. Zyakhor, S.V. Chernobaj, A.A. Nakonechny And M.S. Zavertanny

E.O. Paton Electric Welding Institute, NASU. 11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua
 
 
Abstract
The paper deals with the features of producing joints of an alloy based on γ-TiAl intermetallics at resistance butt welding with application of interlayers in the form of foil, differing by thickness, composition and structural state. Investigations were performed on samples of Ti-47Al-2Cr-2Nb (at.%) alloy, produced by electron beam remelting, both in as-delivered (cast) condition, and after heat treatment (1250 °C, 6h). Used as interlayer was titanium foil with microcrystalline structure 100, 200 and 400 mm thick, and nanostructured multilayered foils Ti/Al (52Ti-48Al, at.%) and Ti/Co (75Ti-25Co, at.%) of 30-160 mm thickness. Experiments were performed in K802 system, welding mode parameters were varied in the following ranges: 5-20 MPa pressure at heating, 20-100 MPa upset pressure, hand 5-15 mm upset value. Joint microstructure and composition were studied by optical and scanning electron microscopy and X-ray microprobe analysis. Metal strength properties in the joint zone were assessed by microhardness distribution and rupture testing. It is established that the zone of Ti-47Al-2Cr-2Nb alloy joints made with application of solid titanium foil demonstrates structural inhomogeneity in the form of a continuous titanium interlayer and diffusion zone between the interlayer and alloy being welded, containing linear porosity. Application of nanostructured Ti/Al and Ti/Co foils ensures formation of defect-free joints. Metal structure in the joint zone is fine-grained bimodal γ/γ + α₂, irrespective of base metal initial structure. Remains of nanostructured foils of Ti/Al system are present in the joint zone in the form of an interlayer of dispersed γ-TiAl intermetallic, not containing any chromium or niobium. At application of foil of Ti/Co system of eutectic composition, no chemical inhomogeneity in the form of foil transformation products is found in the butt. At rupture testing of the joints, fracture runs through the base metal of Ti-47Al-2Cr-2Nb alloy. Joint region of higher hardness in all the considered cases coincides with the zone of structural changes resulting from thermodeformational impact of the welding process. 21 Ref., 11 Figures.
 
Keywords: resistance butt welding, titanium aluminide, interlayer, nanostructured multilayer foil, welded joint
 
 
Received:                21.04.15
Published:               26.10.15
 
 
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