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Metallic structural components made from dissimilar titanium alloys are playing important roles in high-end industries such as aerospace and aviation. In this paper, a Ti-5Al-2.5Sn/Ti-6Al-4V dissimilar titanium alloy material was additively manufactured by the selective laser melting (SLM) process. Interface characteristics, microstructure, and mechanical properties of the SLM-deposited samples before and after complete annealing treatment were researched to provide some technical basics for the integral fabrication of dissimilar titanium alloy components. The results demonstrated that a defect-free metallurgical bonded interface with a ~ 70-μm-wide element inter-diffusion region could be obtained between the Ti-5Al-2.5Sn and Ti-6Al-4V layers under both the as-deposited and the complete annealing states. The interfacial bonding strength between the dissimilar titanium alloys was always higher than the strength of the Ti-5Al-2.5Sn layers. Microstructure evolution and element inter-diffusion mechanisms of the SLM-produced Ti-5Al-2.5Sn/Ti-6Al-4V samples were also revealed and related to the change in mechanical properties.

Mg-Zn binary alloys with seven distinctive compositions (Zn (wt.%) = 1, 2, 4, 6, 8, 10 and 12) were prepared using a selective laser melting (SLM) additive manufacturing technology. Densification behaviors and microstructure of the SLM-processed alloys were analyzed using quantitative metallography analysis, XRD, SEM, and EDS. The mechanical property characterizations were carried out through microhardness and uniaxial tensile tests. The results showed that the increase of Zn content had a significantly deteriorating effect on the densification response of the SLM-processed Mg-Zn alloys. At 1 wt% Zn content, near full-dense products could be obtained. At 2–10 wt% Zn contents, SLM-processed alloys suffered from solidification cracking and the crack density showed an approximate “Λ-shaped” variation trend with the increase of Zn content. At 12 wt% Zn content, solidification cracks were eliminated but lots of micro-pores formed within the SLM sample. All the SLM samples exhibited a duplex microstructure composed of α-Mg matrix and Mg7Zn3 eutectic phase. With the increase of Zn content, the quantity of Mg7Zn3 increased continuously whilst its morphology gradually transformed from granular shape to nearly reticular structure. The hardness and tensile tests showed that only the Mg-1Zn sample has comparable mechanical properties with the as-cast counterpart. At higher Zn contents, mechanical properties of the SLM-processed alloys became significantly degraded, mainly because of the deterioration of the densification degree.

Laser remelting (LR) is often used during selective laser melting (SLM) processes to improve the densification degree and top surface quality of the products. However, researches regarding its effects on side surface quality, residual stress, microstructure, and mechanical property are still quite lacking. The influence of the repeated usage of LR on a solidified layer is also not very clear. To address these issues, LR treatments with the cyclic numbers of 1–3 on every solidified layer have been employed during the SLM processes of a Ti-5Al-2.5Sn alloy in this study and their influences on deposition quality, residual stress, microstructure, and mechanical property were researched. The results first indicated that although the improvement in top surface quality and densification degree would be more and more notable with the increase of LR cycles, the side surface quality could not be improved through all the LR treatments. Then, it was shown by the hole-drilling tests on the surface centers of several 15 × 15 × 3 mm3 thin-plate specimens that when 1 cycle of LR was conducted on every solidified layer, the principal residual stress at the hole bottom of the SLM sample could be far beyond that of the non-treated one. In contrast, when 2 or 3 cycles of LR were conducted, the measured principal residual stresses could be reduced to lower than that of the non-treated ones. It was also proved that unlike the non-treated sample which presented a martensite-dominated microstructure with a very weak texture, all the LR-treated samples exhibited two kinds of preferential orientations. Finally, tensile properties of the stress-relieved samples were tested and it was seen that under the combined influence of the densification and the microstructure factors, the elongations of the LR-treated samples became slightly higher than that of the non-treated one whereas the tensile strengths were nearly identical. In summary, this paper demonstrates that there is still limitation in using LR as an auxiliary process of the SLM production of titanium products. The possible increase in residual stress and the formation of strong textures should be particularly considered.

Selective laser melting (SLM) technology was employed for the additive manufacturing of Ti-5Al-2.5Sn α titanium alloy in this work and the influences of laser energy input on densification behavior, microstructure evolution and mechanical performances of the as-deposited products were investigated. It was found that the relatively high volumetric energy densities (VEDs) of 167–417 J/mm3 resulted in large quantities of keyhole-induced spherical pores whereas the relatively low VEDs of 51–83 J/mm3 led to notable lack-of-fusion defects. At the proper VED of 125 J/mm3, highly densified products with internal porosity of merely 0.05% were obtained. At the relatively high VEDs of 167–417 J/mm3, as-built samples presented duplex microstructures composed of acicular α′ martensites and bulk αM massive grains. In contrast, overwhelmingly martensitic microstructures were formed at lower VEDs of 51–125 J/mm3. The martensitic microstructure exhibited a unique hierarchical feature, which could be explained using the theory of athermal martensitic transformation kinetics. With the decrease of VED from 417 J/mm3, the average size of α′ needles increased first, then came to its plateau at the VEDs of 167–208 J/mm3, and decreased again at the VEDs of 51–167 J/mm3. At the VEDs of 167–417 J/mm3, the formation of spherical pores and bulk αM grains resulted in relatively poor tensile properties. At the VEDs of 51–83 J/mm3, the formation of lack-of-fusion defects masked the enhanced fine-grain strengthening effect provided by the much refined α′ needles and the decrease in the fraction of bulk αM, thus also leading to very limited tensile properties. At the proper VED of 125 J/mm3, as-built tensile properties reached to their peak with ultimate tensile strength of 1173 MPa, yield strength of 1061 MPa, and elongation of 7.7%. This can be attributed to the high densification degree, the almost complete vanish of bulk αM grains, and the moderate size of α′ needles.

In the present work, selective laser melting technology (SLM) has been used to produce Ti-5Al-2.5Sn α titanium alloy and the influence of post-deposition heat treatments on microstructure and mechanical properties of the as-deposited alloy has been in-depth analyzed for the first time. As-deposited Ti-5Al-2.5Sn exhibits a columnar prior-β microstructure with martensitic α′ needles filled inside and a small amount of grain-boundary α (αGB) stripes precipitated at the prior-grain boundaries. After subtransus heat treating at 600 °C to 750 °C for 2 h, incomplete recrystallization of the as-deposited microstructure occurs and the recrystallized α grains with equiaxed morphology nucleate mainly through grain boundary migration of the stripe-like αGB, leading to a duplex microstructure composed of the soft recrystallized α and 75.1–97.6% high-strength α′. After subtransus heat treating at 850 °C to 950 °C for 2 h, complete recrystallization of the as-deposited microstructure occurs and the coarsening of recrystallized α grains becomes more pronounced at 950 °C. By contrasting, an excessively coarsened widmanstatten microstructure composed of α laths with lengths up to several hundred micrometers has been obtained after supertransus heat treating at 1100 °C for 2 h. Both of the as-deposited and heat-treated samples exhibit relatively weak textures, resulting in very little mechanical anisotropies. Because of the dominant α′ microstructure, as-deposited possesses ultrahigh tensile strengths but also a poor elongation (7.7–8.2%) in comparison to the conventionally-fabricated Ti-5Al-2.5Sn. After the heat treatments, tensile strengths gradually decrease whereas elongation increases first and then decreases with the elevating annealing temperature, reaching its peak at 750 °C (14.4–15.2%). Finally, it has been proved that both elongations and tensile strengths of the 650–850 °C/2 h heat-treated samples can exceed those of the conventionally-fabricated Ti-5Al-2.5Sn. These findings provide some basis for the rapid fabrication of high-strength α titanium alloy products with a satisfactory ductility.

In the present work, selective laser melting of Ti-5Al-2.5Sn α-Ti alloy has been carried out on a self-developed system. First of all, optimized processing parameters for 3D Ti-5Al-2.5Sn components were determined through single track and single layer formation processes. After that, near full-dense parts with different sizes were successfully built up and their microstructures as well as texture features were in-depth analyzed employing optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer and electron back-scattered diffraction. Because of the rapid cooling rate inherent to selective laser melting technology and the absence of β-stabilizing elements, as-deposited Ti-5Al-2.5Sn possesses an overwhelmingly acicular α′ martensitic structure with a small amount of α grains discontinuously precipitated at the prior-β grain boundaries, making it exhibit higher strength/hardness but poorer elongation/impact toughness in comparison to the deformed and as-cast Ti-5Al-2.5Sn. The overall texture is found to be nearly random after SLM. As a result, mechanical behaviors of the as-built Ti-5Al-2.5Sn are isotropous. Under the interaction between the residual pores and the overwhelmingly martensitic microstructure, as-deposited sample presents better fatigue performance than the forged Ti-5Al-2.5Sn at a high peak cyclic stress of beyond 700 MPa. Nevertheless, the opposite situation occurs when the peak cyclic stress is lower than 700 MPa.

In the present work, a Fe–11Cr–9Ni–6Co–3Mo (wt.%) maraging stainless steel was successfully fabricated by selective laser melting (SLM). The SLM process parameters were optimized and the influence of heat treatment on microstructure and mechanical properties of the SLMed Fe–11Cr–9Ni–6Co–3Mo samples was systematically explored. The results show that the optimized laser volume energy density with the relative density ≥99.5% for the SLMed samples is 83.33–200 J/mm3. For SLMed samples, the phase analysis reveals predominantly martensite with some retained austenite, and the microstructure is characterized by the prior austenite grains and fine martensite laths. After subsequent heat treatments (solution + cryogenic cooling + aging), the microstructure results in the formation of nanosized CrMoC carbide precipitates, uniformly dispersed in the martensite laths and retained/reverted austenite. Compared with the SLMed samples, the microhardness and tensile strengths are significantly improved after subsequent heat treatments. The effects of heat treatment parameters (solution temperature, aging temperature and aging time) on mechanical properties primarily depend on the size and fraction of carbide precipitates as well as the content of retained/reverted austenite. The microhardness of 439–444 HV, yield strength of 1325–1355 MPa and ultimate strength of 1365–1374 MPa are obtained with the optimal heat treatment regime (solution treatment at 750–850 °C for 1 h + cryogenic cooling at −73 °C for 2 h + aging treatment at 450 °C for 7 h).

As an emerging additive manufacturing technology, multi-laser powder bed fusion (ML-PBF) can be used for the rapid fabrication of large-size Ti–6Al–4V components with complex shapes. However, researches regarding the overlap quality control of the relevant products are insufficient. In this study, a self-developed ML-PBF system was used to produce a series of Ti–6Al–4V samples. The defect, microstructure, and mechanical property of the overlap regions obtained from different process conditions were researched. It is demonstrated that the overlap region can be nearly fully dense regardless of whether the scanning paths of the corresponding two lasers are the same or different. However, if the two lasers scan the overlap region simultaneously and their incident points encounter with each other, a large number of keyhole defects may form. All the overlap regions possess an acicular martensite microstructure, which is essentially the same as that of the single-laser PBF material. However, crystallographic texture intensities of the overlap regions are relatively stronger compared with that of the single-laser PBF material. When the encounter of two different laser incident points is avoided during the ML-PBF process, basic mechanical properties of the overlap region such as microhardness and tensile strength can be comparable to those of the single-laser PBF material. The results can help to improve the performance consistency of large-size Ti–6Al–4V components fabricated by ML-PBF.