Coupled effects of particle flux and post-deposition hot isostatic pressing on the consolidation of cold-sprayed Ti-5553 alloy

Cold spray (CS) enables the fabrication and repair of components with minimal thermal exposure and negligible oxidation. Cold-sprayed β‑titanium Ti-5Al-5 V-5Mo-3Cr (Ti-5553) alloy has a strong potential in the aerospace industry due to its superior specific strength to Ti6Al4V. The study firstly focuses on process optimisation, evaluating how different powder feed rates and sample traverse speeds affect deposition behaviour such as deposit porosity and thickness. Then, CS was performed with 10 different process conditions, which have different powder feed rates and sample traverse speeds. The porosity ranges from 12.5% to 22.1%, and the thickness varies from 0.9 mm to 8.1 mm, indicating the critical role of the varied powder feed rate and traverse speed in controlling the particle flux and its effect on the porosity and thickness. The second part of the study investigates the effects of post-deposition treatments on deposit densification, including hot isostatic pressing (HIP) and vacuum heat treatment (VHT). A single-step hot isostatic pressing treatment (HIP-1: 800 °C at 200 MPa for 4 h), a stepwise HIP treatment (HIP-2: 200 MPa at 320 °C for 1 h, 770 °C for 6 h, and 820 °C for 4 h), and a VHT, which followed the same schedule as HIP-2 but without applied pressure and with a faster cooling rate of 170 °C/min, were applied to the cold-sprayed deposits. The post-deposition processes enable investigation of densification mechanisms and microstructural evolution, including pore closure via diffusion-assisted deformation and the β → α phase transformation. The HIP processes show a significant reduction in the porosity of the Ti-5553 cold-sprayed deposition, with decreases of 45.6% and 51.8% for HIP-1 and HIP-2, respectively, compared to the as-received (AR) sample, whereas the reduction was moderate at 29.9% for the VHT process. This work shows that the powder feed rate and sample traverse speed significantly affect the porosity and thickness of deposits by altering particle impact and flux conditions. Moreover, the superior densification in the cold-sprayed Ti-5553 deposition was achieved via HIP processing, attributed to pore closure and microstructural refinement. • The effect of different feed rates on impact velocity was quantified and modelled via Accuraspray and CFD for Ti-5553. • The coupled effects of feed rate and traverse speed on the porosity of cold-sprayed Ti-5553 samples were examined. • Porosity ranged from 12.5 to 22.1% with changes in feed rate and traverse speed. • HIP and VHT were applied to decrease the porosity of the AR Ti-5553 deposit. • Porosity decreased from 12.5% to 6.2% through the stepwise HIP process.