Additive manufacturing (AM), often termed 3D printing, has recently emerged as a mainstream means of producing metallic components from a variety of metallic alloys. The numerous benefits of AM include net shape manufacturing, efficient use of material, suitability to low volume production runs, and the ability to explore alloy compositions not previously accessible to conventional casting. The process of AM, which is nominally performed using laser (or electron) based local melting, has a definitive role in the resultant alloy microstructure. Herein, the corrosion of alloys prepared by AM using laser and electron-based methods, relating the corrosion performance to the microstructural features influenced by AM processing, are reviewed. Such features include unique porosity, grain structures, dislocation networks, residual stress, solute segregation, and surface roughness. Correlations between reported results and deficiencies in present understanding are highlighted.

Additive manufacturing (AM) is gaining increasing popularity in various fields, including biomedical engineering. Although AM enables fabrication of tailored components with complex geometries, the manufactured parts typically feature several internal issues, such as unpredictable distribution of residual stress and printing defects. However, these issues can be reduced or eliminated by post-processing via thermomechanical treatment. The study investigated the effects of combinations of AM and post-processing by the intensive plastic deformation method of rotary swaging (variable swaging ratios) on microstructures, residual stress, and corrosion behaviors of AISI 316L stainless steel workpieces; the corrosion tests were performed in an ionized simulated body fluid. The results showed that the gradual swaging process favorably refined the grains and homogenized the grain size. The imposed swaging ratio also directly influenced the development of substructure and dislocations density. A high density of dislocations positively affected the corrosion resistance, whereas annihilation of dislocations and formation of subgrains had a negative effect on the corrosion behavior. The first few swaging passes homogenized the distribution of residual stress within the workpiece and acted toward imparting a predominantly compressive stress state, which also favorably influenced the corrosion behavior. Lastly, the presence of the {111}||swaging direction texture fiber (of a high intensity) increased the resistance to pitting corrosion. Overall, the most favorable corrosion behavior was acquired for the AM sample subjected to the swaging ratio of 0.8, exhibiting a strong fiber texture and a high density of dislocations.

The corrosion of additively manufactured (AM) metallic materials, such as stainless steels (SS), is a critical factor for their qualification and reliable use. This review assesses the emerging knowledgebase of powder-based laser AM SS corrosion and environmentally assisted cracking (EAC). The origins of AM-unique material features and their hierarchal impact on corrosion and EAC are addressed relative to conventionally processed SS. The effects of starting material, heat treatment, and surface finishing are substantively discussed. An assessment of the current status of AM corrosion research, scientific gaps, and research needs with greatest impact for AM SS advancement and qualification is provided.

Inconel 718 alloy is a popular material used for additive manufacturing. Corrosion involvement is crucial for its application. The corrosion behaviors of the additive manufacturing Inconel 718 alloy in neutral NaCl solution and acidic solution have been thoroughly investigated and documented. However, information available in the literature regarding the corrosion behaviors of additive manufacturing Inconel 718 alloy in alkaline solution is insufficient. In this paper, the corrosion behavior of Inconel 718 alloy fabricated through selective laser melting (SLM Inconel 718) in NaOH solution was studied using open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostats polarization, Mott-Schottky analysis, and X-ray photoelectron spectroscopy (XPS). The results were compared with a commercial rolled Inconel 718 alloy (R Inconel 718). Pitting corrosion was observed in both SLM Inconel 718 alloy and R Inconel 718 alloy. SLM Inconel 718 alloy has lower activity and corrosion rate compared with R Inconel 718 alloy. Because the passive film formed on the surface of SLM Inconel 718 alloy has a lower content of porous NiO and a higher content of compact Cr2O3, the passive film is more compact; however, the donor/acceptor density is lower in the passive film.

采用开路电位、动电位极化、电化学阻抗、恒电位极化、Mott-Schottky和X射线光电子能谱等测试技术研究了激光选区熔化增材制造Inconel 718合金(SLM Inconel 718)在0.1 mol/L NaOH溶液中的腐蚀行为，并与商用轧制Inconel 718合金(R Inconel 718)进行对比。结果表明，SLM Inconel 718合金与R Inconel 718合金均发生点蚀，SLM Inconel 718合金的点蚀优先发生在熔池边界和孔隙部位。相比R Inconel 718合金，SLM Inconel 718合金的活性更低、腐蚀速率更小、耐蚀性能更优，其主要原因在于：SLM Inconel 718合金表面生成的钝化膜中多孔NiO的含量更低，致密Cr₂O₃的含量更高，钝化膜更加致密，并且钝化膜的载流子密度更低，因此，SLM Inconel 718合金的钝化膜保护性能更好，耐蚀性能更优。

Stress corrosion cracking (SCC), as an important research direction in the interdisciplinary of material mechanics and corrosion electrochemistry, is one of the main failure modes of stainless steel components. Compared with traditional wrought technology, additive manufacturing (AM) 316L stainless steel has complicated microstructure and inherent defects including pores and lack of fusion places (LOF) caused by additive manufacturing process, resulting in more complex SCC behavior. Herein, the basic SCC behavior of 316L stainless steel was discussed in detail on the basis of the researches of AM316L stainless steel at home and abroad. The main contents include two stress corrosion mechanisms of hydrogen induced cracking and anodic dissolution. Two behavior of transgranular cracking and intergranular cracking were described. The effects of microstructure on SCC behavior of AM316L, including twins, different crystal interface, pores, LOF, and element segregation were summarized. The current situation and advantages of three <i>in-situ</i> characterization methods, including electrochemical noise, high-resolution neutron diffraction and three-dimensional morphology characterization were introduced, which are of great significance to explore the SCC behavior of AM316L. Finally, the prospective future of the research directions of SCC behavior of additive manufacturing stainless steel were proposed, including the research of SCC characteristics under high temperature irradiation environment and the principle of stress distribution and restructuration at crack tips.

应力腐蚀开裂是不锈钢零部件失效的主要形式之一,是材料力学和腐蚀电化学交叉领域的重要研究方向。与传统工艺制备相比,增材制造技术制备的316L不锈钢内部微观组织复杂,存在增材制造工艺引起的气孔、未熔合区等固有缺陷,导致其应力腐蚀行为更为复杂。本文基于国内外关于增材制造316L不锈钢的研究实例,综述了应力腐蚀行为特征及主控机制,包括氢致开裂和阳极溶解两种应力腐蚀机理、穿晶断裂和沿晶解理两种作用形式,并归纳了孪晶、异种晶相交界处、气孔及未熔合处、元素偏析等组织结构缺陷等对增材制造316L不锈钢应力腐蚀的影响。针对电化学噪声、高分辨中子衍射、三维形貌表征等三种原位测试方法在不锈钢应力腐蚀行为研究方面的现状和技术优势进行了总结。最后提出了高温辐照等严苛环境下的应力腐蚀行为特征研究,以及裂纹尖端应力分配模型及重构准则等增材制造不锈钢应力腐蚀未来的研究方向。

Laser additive manufacturing (LAM) of titanium (Ti) alloys has emerged as a transformative technology with vast potential across multiple industries. To recap the state of the art, Ti alloys processed by two essential LAM techniques (i.e., laser powder bed fusion and laser‐directed energy deposition) will be reviewed, covering the aspects of processes, materials and post‐processing. The impacts of process parameters and strategies for optimizing parameters will be elucidated. Various types of Ti alloys processed by LAM, including α‐Ti, (α + β)‐Ti, and β‐Ti alloys, will be overviewed in terms of microstructures and benchmarking properties. Furthermore, the post‐processing methods for improving the performance of LAM‐processed Ti alloys, including conventional and novel heat treatment, hot isostatic pressing, and surface processing (e.g., ultrasonic and laser shot peening), will be systematically reviewed and discussed. The review summarizes the process windows, properties, and performance envelopes and benchmarks the research achievements in LAM of Ti alloys. The outlooks of further trends in LAM of Ti alloys are also highlighted at the end of the review. This comprehensive review could serve as a valuable resource for researchers and practitioners, promoting further advancements in LAM‐built Ti alloys and their applications.

The 24CrNiMo alloy steel powder was used as experimental material. The microstructure and mechanical properties of as-deposited, quenched and tempered (QT) and stress-relief annealed (SR) specimens were analyzed. The X-ray diffraction (XRD) analysis showed that the specimens in the three states were mainly ferrite (α-Fe), in which the as-deposited samples had puny face-centered cubic (FCC) structure Fe (γ-Fe). The microstructure observation showed that the as-deposited specimens were made up of ferrite, granular bainite, a small amount of cementite and residual austenite. The tensile test results indicated that the tensile strength and yield strength of the as-deposited specimens were 1199 MPa and 1053 MPa respectively, and the elongation at break was 10.7%. The elongation of QT and SR specimens increased to 11.6% and 12.8%, respectively. The electron backscattered scattering detection (EBSD) analysis results showed that the small-angle grain boundary content of the as-deposited samples was 58%, and large-angle grain boundary content was 15%. After QT and SR, small-angle and large-angle grain boundaries were obtained than those in the as-deposited specimens. The high-temperature friction and wear properties and thermal fatigue performances of the QT and SR specimens were improved significantly. The QT specimens had the smallest wear and thermal fatigue crack lengths, excellent resistance to friction and wear performance and prevention of crack growth, with an ideal comprehensive properties.

Porous titanium and its alloys have been considered as promising replacement for dense implants, as they possess low elastic modulus comparable to that of compact human bones and are capable of providing space for in-growth of bony tissues to achieve a better fixation. Recently, the additive manufacturing (AM) method has been successfully applied to the fabrication of Ti-6Al-4V cellular meshes and foams. Comparing to traditional fabrication methods, the AM method offers advantages of accurate control of complex cell shapes and internal pore architectures, thus attracting extensive attention. Considering the long-term safety in the human body, the metallic cellular structures should possess high fatigue strength. In this paper, the recent progress on the fatigue properties of Ti-6Al-4V cellular structures fabricated by the AM technique is reviewed. The various design factors including cell shapes, surface properties, post treatments and graded porosity distribution affecting the fatigue properties of additive manufactured Ti-6Al-4V cellular structures were introduced and future development trends were also discussed.

This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent β phase, martensite (α’) and newly generated β phase that formed in the present experiments were elucidated. The primary X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile test were combined to discuss the relationship between α’, β phase and mechanical properties. The average width of each coarse β columnar grain is 80–160 μm, which is in agreement with the width of a laser scanning track. The result revealed a further relationship between β columnar grain and laser scanning track. Additionally, the high dislocation density, stacking faults and the typical ( 10 1 ¯ 1 ) twinning were identified in the as-built sample. The twinning was filled with many dislocation lines that exhibited apparent slip systems of climbing and cross-slip. Moreover, the α + β phase with fine dislocation lines and residual twinning were observed in the stress relieving sample. Furthermore, both as-built and stress-relieved samples had a better homogeneous density and finer grains in the center area than in the edge area, displaying good mechanical properties by Feature-Scan. The α’ phase resulted in the improvement of tensile strength and hardness and decrease of plasticity, while the newly generated β phase resulted in a decrease of strength and enhancement of plasticity. The poor plasticity was ascribed to the different print mode, remained support structures and large thermal stresses.

Laser powder bed fusion (L-PBF) is an additive manufacturing technology that is gaining increasing interest in aerospace, automotive and biomedical applications due to the possibility of processing lightweight alloys such as AlSi10Mg and Ti6Al4V. Both these alloys have microstructures and mechanical properties that are strictly related to the type of heat treatment applied after the L-PBF process. The present review aimed to summarize the state of the art in terms of the microstructural morphology and consequent mechanical performance of these materials after different heat treatments. While optimization of the post-process heat treatment is key to obtaining excellent mechanical properties, the first requirement is to manufacture high quality and fully dense samples. Therefore, effects induced by the L-PBF process parameters and build platform temperatures were also summarized. In addition, effects induced by stress relief, annealing, solution, artificial and direct aging, hot isostatic pressing, and mixed heat treatments were reviewed for AlSi10Mg and Ti6AlV samples, highlighting variations in microstructure and corrosion resistance and consequent fracture mechanisms.

采用激光选区熔化成形技术（Selective Laser Melting，SLM）制备TC4钛合金试样，观察其显微组织，并用电化学腐蚀实验测试不同成形面以及粗糙度对TC4钛合金耐蚀性能的影响，并与传统轧制态进行对比。结果表明：成形方式、成形面和粗糙度均影响TC4钛合金的耐蚀性能。激光选区熔化成形技术制备的TC4钛合金纵截面由原始柱状&beta;晶粒和与生长方向成&plusmn;45&deg;针状&alpha;'马氏体组成，横截面上的晶粒呈棋盘状。传统轧制态由片状&alpha;+&beta;相以及等轴&alpha;相组成。传统轧制态的耐腐蚀性要强于SLM成形的试样，且SLM成形的纵截面的耐腐蚀性要强于横截面。表面粗糙度小的试样耐腐蚀性要强于表面粗糙度大的试样。激光选区熔化成形态试样腐蚀表面都出现明显的腐蚀坑，腐蚀形态均为点蚀。

This paper evaluates the corrosion behavior of Ti-6Al-4V alloy parts produced by laser-based powder bed fusion additive manufacturing (AM). The effect of post annealing heat treatment on the corrosion resistance of AM parts is studied by comparing the heat treated samples with cold rolled commercial titanium alloy samples. The results obtained via corrosion tests show that the corrosion rate of as-fabricated AM parts is almost sixteen times worse than the commercial grade samples. The accelerated rate was due to the presence of non-equilibrium phases and can be ameliorated by a proper post heat treatment process at 800 degrees C for 2 h. The proposed heat treatment makes the corrosion behavior of AM parts comparable to the commercial grade samples, due to the stress relief of the martensitic phase and formation of BCC phase of beta Ti-6Al-4V which has a higher corrosion resistance. CALculation of PHAse Diagrams (CALPHAD) method was used to identify the equilibrium phases.

Additive manufacturing (AM) has shown the ability in processing titanium alloys. However, due to the unique thermal history in AM, the microstructure of AM-fabricated parts is metastable and non-equilibrium. This work was aiming to tailor the microstructure and to improve the mechanical properties of α+β Ti-6Al-4V alloy and metastable β Ti-5Al-5Mo-5V-1Cr-1Fe alloys by manipulating the post-process heat treatment. The results showed that Ti-6Al-4V exhibited a metastable α’ martensite microstructure in the as-fabricated condition, while a metastable β structure was formed in as-printed Ti-5Al-5Mo-5V-1Cr-1Fe. After post-process heat treatment, both lamellar and bimodal microstructures were obtained in Ti64 and Ti-5Al-5Mo-5V-1Cr-1Fe alloys. Especially, the Ti-6Al-4V alloy subjected to 950 °C annealing showed the lamellar structure with the highest fracture toughness of 90.8 ± 2.1 MPa.m1/2. The one cyclically heat-treated has excellent combined strength, ductility and fracture toughness attributed to the bimodal structure. In addition, similar observations of lamellar and bimodal microstructure appeared in the post-process heat-treated Ti-5Al-5Mo-5V-1Cr-1Fe alloy. This study demonstrated that heat treatment is an effective way to tackle the non-equilibrium microstructure and improve the mechanical properties of selective laser melting (SLM)-fabricated titanium alloys.

Selective laser melted (SLM) IN 718 alloy specimens are subjected to heat treatment and shot peening to assess the effect of post processing on the corrosion performance of the alloy in a 3.5 wt % NaCl solution. The four conditions used in this analysis are as-built material (AB), heat-treated as-built material (HT), shot-peened as-built material (SP), and heat-treated and shot-peened as-built material (HTSP). Microstructural studies revealed the presence of a 500 nm sized cellular structure with a γ matrix surrounded by the Laves phase in the AB material. Shot-peening reduced the surface roughness of the AB and HT samples to almost 80%. The potentiodynamic experiments revealed a highest Icorr value of 0.21 µA/cm2 for the AB material and the lowest Icorr value of 0.04 µA/cm2 for the HTSP material. In the Electrochemical Impedance Spectroscopy (EIS) analysis, the Nyquist plot substantiated the increasing corrosion resistance in the same order of decreasing corrosion rate. The Bode plot exhibited two resistance–capacitance (RC) time constants for all four conditions. The solution resistance measured around 30 Ω, with the HTSP specimen exhibiting the highest passive film resistance of 676 kΩ cm2 and the AB specimen exhibiting the lowest passive film resistance of 234 kΩ cm2. This study has shown that elimination of the network of the Laves phase in SLM material through heat treatment and smooth surface morphology achieved through shot peening improves the corrosion resistance of Inconel 718 alloy.

The manufacturing route primarily determines the properties of materials prepared by additive manufacturing methods. In this work, the microstructural features and mechanical properties of 316 L stainless steel prepared by the selective laser method have been determined. Three types of samples, (i) selective laser melted (SLM), (ii) selective laser melted and hot isostatic pressed (HIP) and (iii) selective laser melted and heat treated (HT), were characterized. Microstructural analysis revealed that SLM samples were formed by melt pool boundaries with fine cellular–dendritic-type microstructure. This type of microstructure disappeared after HT or HIP and material were formed by larger grains and sharply defined grain boundaries. The SLM-prepared samples contained different levels of porosity depending on the preparation conditions. The open interconnected LOF (lack of fusion) pores were observed in the samples, which were prepared with using of scanning speed 1200 mm/s. The blowhole and keyhole type of porosity were observed in the samples prepared by lower scanning speeds. The HIP caused a significant decrease in internal closed porosity to 0.1%, and a higher pressure of 190 MPa was more effective than the usually used pressure of 140 MPa, but for samples with open porosity, HIP was not effective. The relatively high yield strength of 570 MPa, tensile strength of 650 MPa and low ductility of 30–34% were determined for SLM samples with the lower porosity content than 1.3%. The samples after HIP showed lower yield strengths than after SLM (from 290 to 325 MPa) and relatively high ductility of 47.8–48.5%, regardless of the used SLM conditions.