Powder heat treatment for cold spray additive manufacturing: role of athermal omega and omega assisted α precipitation in β-Ti-5553 alloy

• Ti-5553 As-received powder develops athermal omega after one-cycle powder heat treatment. • Embrittlement of the thermal omega phase hinders dislocation movement during cold spray additive manufacturing deposition. • A two-cycle heat treatment powder produces omega-assisted fine alpha, improving deformability. • The porosity of the deposit decreases from around 14% to approximately 7% by using the two-cycle powder heat treatment. • After a two-cycle powder heat treatment, nano-hardness increases by around 34% compared to the As-received powder. Cold spray additive manufacturing (CSAM) enables sustainable repair by minimising thermal degradation. In this study, Ti-5553 powder was heat-treated to examine how nanoscale ω-phase precipitates and their role in promoting fine α precipitation within the β matrix affect its cold sprayability. In a one-cycle heat treatment (HT-1: 900 °C/3h), athermal ω precipitates (ω ath ) developed within the β matrix, as identified by selected-area electron diffraction (SAED). A two-cycle heat treatment (HT-2: 900 °C/3h + 665 °C/1h) dissolved ω ath and generated ω-assisted fine α precipitates, which are Widmanstätten intragranular α (α WM ). Splat morphologies and deposits were characterised by electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and electron channelling contrast imaging (ECCI). The HT-1 powder showed reduced deformability due to the presence of ω ath , while the HT-2 powder showed enhanced deformation, attributed to facilitated slip transmission by fine α WM precipitates. HT-2 powder deposits had reduced porosity (7%) compared to those from as-received (AR) powder (14%). The HT-2 powder showed increases in nanohardness of approximately 33.7% and 35.2% compared to the AR and HT-1 powders, respectively. This work highlights that precipitation engineering can optimise β titanium alloys for CSAM by uncovering how ω-assisted α WM precipitation governs deposition behaviour in Ti-5553.