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%).

Highlights

  • In the past decades, the demand for structural materials possessing high strength, high plasticity and high corrosion resistance increased due to the rapid development in modern industries, where such combination of properties is demanded, i.e., automotive and aeronautical industry [1,2,3,4,5,6,7]

  • Titanium alloys can be classified according to their component phases in: α-class alloys, possessing a mono-phase microstructure consisting of α-Ti phase such as: CP-Ti Grade 1 to CP-Ti Grade 4, β-class alloys, possessing a mono-phase microstructure consisting of β-Ti phase

  • The Ti-based shape-memory alloys, especially those belonging to Ti-Ni system, possess an interesting combination of strength, superalesticity and shape memory effects, properties which are largely influenced by the alloying elements [10]

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Summary

Introduction

The demand for structural materials possessing high strength, high plasticity and high corrosion resistance increased due to the rapid development in modern industries, where such combination of properties is demanded, i.e., automotive and aeronautical industry [1,2,3,4,5,6,7]. Ti alloys showed an excellent combination of strength/ductility and corrosion resistance properties in comparison with α and β classes [8,9]. The Ti-based shape-memory alloys, especially those belonging to Ti-Ni system, possess an interesting combination of strength, superalesticity and shape memory effects, properties which are largely influenced by the alloying elements [10]

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