Additive manufacturing of nickel-microalloyed titanium alloy: The significant impact of precipitation of Ti2Ni on mechanical properties

Abstract

Nickel (Ni) is rarely utilized as an alloying element in conventional titanium (Ti) alloys since the active eutectoid reaction can induce severe elemental segregation and microstructural inhomogeneity, resulting in undesirable mechanical properties. In this work, we adopted selective laser melting (SLM) method to fabricate Ni-microalloyed titanium alloys (Ti-0.4 wt%Ni) effectively addressing the above issues. Nano-scale α′-laths with Ni supersaturation, rather than eutectoid lamellae, were obtained in the as-printed samples since the ultra-fast cooling rate (10⁵–10⁸ K/s) can effectively suppress Ni diffusion. Therefore, the microstructural inhomogeneity was improved and the grain size was refined, resulting in an exceptional strength enhancement. Furthermore, we investigated the precipitation behavior of Ti₂Ni precipitates from α-matrix during aging. Ni tended to segregate near the boundaries of α′-laths, facilitating the formation of Ti₂Ni precipitates at lath boundaries. Ti₂Ni precipitates can produce a significant precipitation strengthening effect, but their size and distribution need to be reasonably controlled to avoid the deterioration of mechanical properties. The study developed a novel Ti-Ni binary alloy with homogeneous microstructure and excellent mechanical properties, and demonstrates that only trace additions of Ni can significantly enhance the strength of Ti alloys, providing a useful approach and insights to improve the performance of Ti alloys.