Interface characteristics and performance of additively manufactured steel-titanium bimetals prepared through composition gradient layers

Abstract

In this study, laser-directed energy deposition (LDED), a powder-feeding laser additive manufacturing technique, was utilized to fabricate bimetals comprising high-strength steel (HSS) and Ti6Al4V (TC4). Through meticulous compositional control, four distinct regions (labeled Areas 1 through 4) comprising Fe-Ti intermetallics with varying sizes and morphologies were obtained at the LDEDed HSS/TC4 interface. These zones exhibited thicknesses of approximately 190 μm, 210 μm, 525 μm, and 205 μm, respectively. The effect of these intermetallics on the performance of LDEDed HSS/TC4 bimetals was investigated. The results indicated that most Fe-Ti intermetallics, characterized by reticular/granular morphologies or fine precipitates, were dispersed at the bonded interfaces (Areas 1, 3, 4). Nevertheless, irregular and long-striped C14_Laves phases were observed in Area 2, indicating the presence of a pure Fe2Ti region. Performance testing revealed that fractures predominantly occurred within a hard and brittle Fe2Ti region (Hardness: 891.5HV) during mechanical grinding or tensile clamping, highlighting the formidable challenge of achieving high-quality LDEDed HSS/TC4 bimetals through a component-regulated building strategy. The difficulty arises from the high Fe content in HSS and high Ti content in TC4, resulting in the formation of a pure Fe2Ti region at the interface. Thermodynamic calculations suggest that the composition-gradient-layer strategy may not be optimal for the integrated laser additive manufacturing of HSS and TC4. These findings provide valuable insights into the design of steel-titanium functional gradient materials and other multi-material components.