Comparative study of coatings with different molybdenum equivalent on titanium alloy forged plate for laser cladding: Microstructure and mechanical properties

Abstract

In this study, three types of titanium alloy powders (TA15, TC11 and TB2) with distinct molybdenum equivalent ([Mo]eq = 1.6, 3.4, 18.6, respectively) were deposited on the forged TC4 (Ti-6Al-4V, wt%) plates by laser cladding. The microstructure and mechanical properties of laser cladded samples were studied. The results show that coatings with fully martensitic α' phase (TA15 coating), fully lamellar (α + β) (TC11 coating), and fully β phase (TB2 coating) were obtained in the coating zone (CZ) under as-clad state. Compared with the ultimate tensile strength (UTS ~ 975 MPa) and elongation (EL ~ 14 %) of forged TC4 substrates, laser cladded samples under as-clad (D) and heat treatment (HT) states exhibited the comparable UTS (955–1180 MPa). The poor elongation (EL < 5 %) was obtained in the cladded samples with TC11 coating and heat treated TB2 coating, which was ascribed to the higher microhardness (440–460 HV) and more α/β interface led to the brittle tendency of coatings. The laser cladded samples of TA15 coating and TB2 coating under as-clad state respectively exhibited the elongation of 8.5 % and 14 %, which were acceptable for attaining 60 % and 100 % of the elongation of forged TC4 substrates. The improved elongation of laser cladded samples was mainly attributed to the decreased strength mismatch and relieved stress concentration at the interface of coating and heat affected zone (HAZ). This study provides a guidance for selecting appropriate alloy powder to achieve the better mechanical properties for repair of wrought Ti-alloys components by laser additive manufacturing.