Microstructure and Mechanical Properties Evolution during Solution and Ageing Treatment for a Hot Deformed, above β-transus, Ti-6246 Alloy

Abstract

The present study investigates the influence of hot-deformation, above β-transus and different thermal treatments on the microstructural and mechanical behaviour of a commercially available Ti-6246 titanium-based alloy, by SEM (scanning electron microscopy), tensile and microhardness testing techniques. The as-received Ti-6246 alloy was hot-deformed—HR by rolling, at 1000 °C, with a total thickness reduction (total deformation degree) of 65%, in 4 rolling passes. After HR, different thermal (solution—ST and ageing—A) treatments were applied in order to induce changes in the alloy’s microstructure and mechanical behaviour. The applied solution treatments (ST) were performed at temperatures below and above β-transus (α → β transition temperature; approx. 935 °C), to 800 °C, 900 °C and 1000 °C respectively, while ageing treatment at a fixed temperature of 600 °C. The STs duration was fixed at 27 min while A duration at 6 h. Microstructural characteristics of all thermomechanical (TM) processed samples and obtained mechanical properties were analysed and correlated with the TM processing conditions. The microstructure analysis shows that the applied TM processing route influences the morphology of the alloy’s constituent phases. The initial AR microstructure shows typical Widmanstätten/basket-weave-type grains which, after HR, are heavily deformed along the rolling direction. The STs induced the regeneration of α-Ti and β-Ti phases, as thin alternate lamellae/plate-like structures, showing preferred spatial orientation. Also, the STs induced the formation of α′-Ti/α″-Ti martensite phases within parent α-Ti/β-Ti phases. The ageing treatment (A) induces reversion of α′-Ti/α″-Ti martensite phases in parent α-Ti/β-Ti phases. Mechanical behaviour showed that both strength and ductility properties are influenced, also, by applied TM processing route, optimum properties being obtained for a ST temperature of 900 °C followed by ageing (ST2 + A state), when both strength and ductility properties are at their maximum (σUTS = 1279 ± 15 MPa, σ0.2 = 1161 ± 14 MPa, εf = 10.1 ± 1.3%).

Alloy Design and Fabrication of Duplex Titanium-Based Alloys by Spark Plasma Sintering for Biomedical Implant Applications

“…Interestingly, with the gradual change in Sn content, the morphology of the equilibrium phases in the alloys changed from the elongated sheet-like structure to a cross-lamellar structure to micron-scale, very fine-width pointed characteristics, as labeled in Figure 1 . The major features of the α precipitate formed in all specimens are typically very diverse, and they can be subdivided into a typical thin-grain-boundary α phase (α GB ), lamellar α colonies, and an acicular α s -type precipitate phase [ 46 , 47 ]. In our case, it is plausible that the burst increase in the precipitate could be attributed to the continuous furnace cooling after HFIHS.…”

“…In our case, it is plausible that the burst increase in the precipitate could be attributed to the continuous furnace cooling after HFIHS. Since all specimens were cooled normally to room temperature, the distribution of the alpha phase is mainly dependent on our processing method [ 47 , 48 ]. Typically, when comparing the microstructural morphologies of Alloy-A (having 4 wt.% Sn) and Alloy-C (having 8 wt.% Sn), it is evident that Alloy-4 exhibits diverse and composite morphological characteristics ranging from a thin-rain-boundary α phase (α GB ) and lamellar α colonies to acicular αs precipitates, as shown in Figure 1 .…”

Evolution of Microstructural and Mechanical Properties during Cold-Rolling Deformation of a Biocompatible Ti-Nb-Zr-Ta Alloy

“…Mechanical characterization by micro-hardness testing was performed using an INNOVATEST Falcon 500 (INNOVATEST Europe BV, Maastricht, Netherlands) equipment with a 200 gf testing force and a 30 s dwell time. The mechanical testing procedure is presented in detail in a previous paper [ 52 ]. The following mechanical characteristics were measured: ultimate tensile strength (σ UTS ), yield strength (σ 0.2 ), fracture strain (ε f ), elastic modulus (E) and microhardness (HV0.2).…”

Laser Powder Bed Fusion of Ti-6Al-2Sn-4Zr-6Mo Alloy and Properties Prediction Using Deep Learning Approaches

“…Ti-6Al-2Sn-4Zr-6Mo is an α+β alloy with α-phase of a hexagonal closed packed crystal structure, in addition to its body-centred cubic β-phase. Ti-6Al-2Sn-4Zr-6Mo is characterised by its high fatigue strength and toughness properties at intermediate temperature level in the range of 315–400 °C, which makes it ideal for compressor disks, turbine blisks, spacers, and seals [ 31 , 32 ]. Ti-6Al-4V is one of the most researched titanium alloys using AM, which can be considered a benchmark because it is used in many applications, including aerospace and biomedical industries.…”