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We used selective laser melting (SLM) to produce a three-dimensional specimen of pure Ti and found that an equiaxed grain structure and weak crystallographic texture could be achieved simultaneously via subsequent heat treatment. These traits have never been attained simultaneously in pure Ti prepared by traditional methods such as casting and rolling. This remarkable achievement was possible because recrystallization occurred during heat treatment without plastic deformation; such deformation introduces stored energy that drives recrystallization but inevitably causes a strong texture to develop. The occurrence of recrystallization was attributed to unique features of the SLM process including a very high cooling rate and repetitive layer stacking. These features generated considerable stored energy by affecting solidification and the β → α phase transformation. Steep in-grain orientation gradients and a fine lath structure also contributed to the activation of recrystallization by facilitating recrystallization nucleation. The heat-treated specimen showed tensile properties with significantly reduced anisotropy. This finding will provide new strategies for developing isotropic metallic materials and may introduce new applications of SLM.

Bimodal grain structures are often produced in a metal by employing severe plastic deformation followed by low-homologous-temperature annealing (≤0.4Tm, where Tm is melting temperature). Here, a bimodal grain structure was achieved in a Co–20Cr–15W–10Ni–C superalloy via moderate cold rolling (strain ≈0.3) and ultrahigh-homologous-temperature annealing (≥0.8Tm). During annealing, carbide-assisted heterogeneous static-recrystallization played a key role in forming the bimodal grain structure. A 40% increase in combined strength and ductility was observed.

The present study describes the influence of β stabilizers (namely Fe and Cr) on the microstructural evolution and mechanical behavior of Ti–6Al–4V alloy fabricated by direct energy deposition. As the β stabilizer content increases from 1 to 4 wt%, the coarse columnar-grained morphology typical of additively manufactured Ti–6Al–4V is significantly refined, with a columnar-to-equiaxed transition. Furthermore, reheating of the deposited layers by the deposition of overlaying layers during fabrication induces an element partitioning effect, resulting in the formation of fine-grained α and isothermal ω. Hence, the heat profile during direct energy deposition resembles conventional solution and aging treatments. In addition, increasing the amount of β stabilizer steadily increases the room temperature strength of the Ti–6Al–4V alloy. The alloy with 4 wt% Fe showed the maximum strength, of ∼1.5 GPa.

The effect of aging treatment on the microstructures and hardening behavior of a metastable beta Ti–9.2Mo–2Fe alloy, which is new designed on the basis of Bo–Md molecular orbital method (Bo, the bond order; Md, the metal d-orbital energy level), has been investigated using hardness measurement, X-ray diffraction, optical microscopy and TEM characterization. The results reveal that, the athermal ω phase with the size of 2–5 nm is found in Ti–9.2Mo–2Fe alloy when solution-treated at 860 °C followed by water quench. The isothermal ω phase is also found when Ti–9.2Mo–2Fe alloy aged at temperatures from 300 °C to 500 °C, although the ω phase has a limited time of stability at 400 °C and 500 °C. The athermal ω phase does not lead to attractive hardening due to its too small size and volume fraction, so the hardness of the solution-treated alloy is about 370 Hv. However, the isothermal ω phase with the size of 5–10 nm shows a moderate hardening (470 Hv), while the ω phase with the size of 50–100 nm contributes the best hardening (∼500 Hv). As well, the hardening due to isothermal ω phase precipitation hardly exhibits over-aging response as long as ω phase exists.

A study on the microstructural characteristics and tensile properties of a new high strength Ti–6Cr–5Mo–5V–4Al alloy were investigated. Both the α/β and β solution treatment and subsequent aging at temperatures ranging from 460 °C to 560 °C were introduced to investigate the microstructural characteristics and microstructure–property relationships. The results show that the primary α phase formed during the α/β solution treatment can increase the stability of the β matrix and then restrain the size of secondary α phase during subsequent aging. In the α/β solution plus aging condition, the secondary α phase with the size of about 1 μm results in a high strength above 1500 MPa with −6% of elongation. The β solution treatment leads to the least stable β matrix and the greatest driving force for secondary α phase, so coarser α phases tend to form during aging. The β solution plus aging does not lead to attractive high strength because of the coarser and non-uniform α phase. And it also leads to a poorer combination of strength and ductility than the α/β solution plus aging. Direct aging exhibits the best strengthening. The ultimate strength of the alloy is about 1600 MPa with acceptable elongations of 6.5–7.5% when direct aged at 500 °C for 2–8 h. It benefits from the mixed microstructure with nano-scale and micron-scale α phases. However, more detailed investigations are needed to improve the ductility. As a whole, the alloy can be heat treatable to obtain an excellent balance of strength and ductility, and provide abundant stress levels with optional ductility (900–1600 MPa in ultimate strength and 6–20% in elongation).