Effect of microstructure on mechanical properties of friction-welded joints between Ti and AISI 321 stainless steel

Abstract

The microstructures and mechanical properties of the friction welded pure Ti/AISI 321 stainless steel have been investigated. From the Ti side from the interface to the Ti base metal, the sequence of recrystallized grain, elongated grain and many twin embedded grain structures were observed. The reaction layers were formed within 0.2 μm thickness at the interface under the conditions of relatively longer friction time (t1) and lower upset pressure (P2). These reaction layers formed at the central interface were identified as (Fe, Cr)2Ti, FeTi2 or Fe2Ti 4O and β-Ti, while those of the peripheral interface were identified as FeCr (σ phase), (Fe, Cr)2Ti, FeTi and β-Ti. The σ phase was restrictedly formed at the peripheral interface. Higher mechanical properties were acquired under higher upset pressure condition due to higher compressive force between bonded materials, smaller grain size and narrower thickness of reaction layer. Therefore, maximum ultimate tensile strength of these joints was approximately 420 MPa with the conditions of 400 MPa of P2 and 0.5 s of t1.