Additive Manufacturing Post-Processing Treatments, a Review with Emphasis on Mechanical Characteristics

Gruber K., Szymczyk-Ziółkowska P., Dziuba S., Duda S., Zielonka P., Seitl S., Lesiuk G.

• LPBF fabricated Inconel 718 is heat treated in HIP (H) and non-HIP (A) variants. • Fatigue crack growth rate (Paris regime) is tested at stress ratios R=0.1 and R=0.5. • The variants A and H show similar FCGR and similar fracture modes. • The variants A and H show better FCGR compared to the literature results at R=0.5. Numerous studies were conducted on the tension-compression fatigue behavior of Inconel 718 (IN718) fabricated with laser powder bed fusion (LPBF). Contrary, only a few fatigue crack growth rate (FCGR) studies are available in the literature. Considering the above, LPBF manufactured IN718 is heat treated in variants including (H) and excluding (A) hot isostatic pressing. FCGR tests are performed at stress ratios R=0.1 and R=0.5. Both variants show similar FCGR and fracture modes at both stress ratios, despite a significant difference in ductility. Furthermore, A and H show similar FCGR at R=0.1 and better performance at R=0.5 compared to wrought IN718.

Zhang S., Zhang Y., Qi J., Zou Z., Qian Y.

Ti-6.5Al-2Zr-1Mo-1V (TA15), widely used in the aerospace industry, is a medium- to high-strength, near-α titanium alloy with high aluminium equivalent value. The TA15 fabricated via laser powder bed fusion (L-PBF) normally presents a typical brittle appearance in as-built status, with high strength and low ductility. In this study, the microstructure and properties of L-PBF TA15 were engineered by various heat treatments below the β-transus temperature (1022 °C). After heat treatment, the original acicular martensite gradually transforms into a typical lamellar α + β dual-phase structure. Withannealing temperature increases, the lamellar α phase thickened with a decreased aspect ratio. Globularisation of the α grain can be noticed when annealing above 800 °C, which leads to a balance between strength and ductility. After heat treatment between 800–900 °C, the desired combination of strength and ductility can be achieved, with elongation of about 12.5% and ultimate tensile strength of about 1100 Mpa.

Muñoz J.A., Elizalde S., Komissarov A., Cabrera J.M.

Large gains in strength and ductility are of little significance if the material’s anisotropy is high. Therefore, improving the mechanical properties and reducing the anisotropy of Al alloys obtained by additive manufacturing is a topic of growing interest. This manuscript examines the effect of distinct heat treatments on the mechanical, anisotropic, and microstructural behavior of a hypoeutectic, almost eutectic, AlSi11Cu alloy obtained by laser powder bed fusion (L-PBF). The microstructural characterization revealed an Al matrix surrounded by a Si-rich network, forming a coral-like pattern with a heterogeneous combination of columnar and equiaxed grains. The texture indicated that the columnar grains were preferentially oriented towards the building direction with strong Cube and Goss components. Different strength-ductility ratios were obtained following the annealing and solution heat treatments at different temperatures (200 °C–550 °C) with a holding time of 1 h. In terms of grain size and dislocation density, no significant changes were found in the microstructure, suggesting that grain size and dislocation strengthening mechanisms are not highly affected by the heat treatments. In addition, the Si-enriched network remained interconnected until 300 °C. At higher temperatures, this interconnection was lost, giving rise to large Si particles depleting the Si content in solid solution in the Al matrix. Digital image correlation maps revealed that deformation fields were more homogeneous when the cellular structure disappeared. The visco-plastic self-consistent model showed that when applying the load at 30° in the building direction (BD), the largest tensile strength was generated, whereas the lowest strength was obtained when the load was parallel to the BD. Heat treatments for 1 h holding time were found to be efficient in reducing the Lankford coefficients dispersion, suggesting improvements in formability and reducing the alloy’s planar anisotropy. These results revealed that annealing up to 400 °C or higher temperatures followed by water quenching leads to good strength and ductility ratios while reducing anisotropy.

Arana M., Ukar E., Rodriguez I., Aguilar D., Álvarez P.

• WAAM of 2319 aluminium alloy is investigated. • Deposition strategy, geometry and heat treatment affects mechanical properties. • Without interlayer dwell time, fine equiaxed microstructure is obtained. • Low anisotropy is achieved if proper artificial aging is applied. There is an increasing interest in additive manufacturing of high strength aluminium alloys built with wire and arc additive manufacturing (WAAM) technologies. Al-Cu alloys are susceptible to hot cracking, however, pulse advanced cold metal transfer (CMT-PADV) welding process ensures a low heat input that avoids this defect while reducing the part porosity. This study has demonstrated that porosity below 1 % does not affect mechanical properties of 2319 WAAM walls, whereas the as-built microstructure and applied heat treatment highly influence the properties obtained. Without interlayer dwell time, a fine uniformly distributed equiaxed microstructure is obtained, however, if an interlayer arc stop period is applied, columnar dendritic grains in the interlayer zone is obtained. Heat treatment with low aging temperature and time demonstrated not to be suitable to ensure high mechanical properties and low anisotropy. Instead, if 190 °C and 26-hour aging heat treatment is used, properties up to 324 MPa for yield stress, 452 MPa tensile strength and 8 % elongation can be achieved perpendicularly to the building direction with anisotropy of 1 %, 2 % and 46 %, respectively, for the manufacturing conditions that avoided columnar grains. This fact was critical to ensure highest strength and ductility values and low anisotropy.

Zhang Y., Roch A.

We demonstrate in this paper that Fused Filament Fabrication (FFF) is a reliable and rapid technology for manufacturing complex parts made with 17-4PH stainless steel. We printed, sintered, and evaluated the performance of FFF manufactured 17-4PH stainless steel. Our results show that FFF is competitive and even superior to other manufacturing technologies. It turned out that the mechanical properties are highly dependent on the post-treatment and hardening procedure. The elongation changed from 5 % − 9.5 % due to annealing treatments. We found yield strength of 1007 MPa, ultimate strength of 1212 MPa, and density > 99 % after hardening.

Zhang W., Chabok A., Kooi B.J., Pei Y.

• Critical overview on recent progresses of additive manufactured high entropy alloys (HEAs). • Selective laser melting, laser melting deposition, electron beam melting and recently emerging wire arc additive manufacturing are comparatively studied. • The microstructure characteristics and mechanical properties of additive manufactured HEAs are comprehensively summarized. • Emerging functional properties of additive manufactured HEAs are discussed. • The future prospects of HEAs fabricated by additive manufacturing are presented. High entropy alloys (HEAs) are promising multi-component alloys with unique combination of novel microstructures and excellent properties. However, there are still certain limitations in the fabrication of HEAs by conventional methods. Additive manufactured HEAs exhibit optimized microstructures and improved properties, and there is a significantly increasing trend on the application of additive manufacturing (AM) techniques in producing HEAs in recent years. This review summarizes the additive manufactured HEAs in terms of microstructure characteristics, mechanical and some functional properties reported so far, and provides readers with a fundamental understanding of this research field. We first briefly review the application of AM methods and the applied HEAs systems, then the microstructure including the relative density, residual stress, grain structure, texture and dislocation networks, element distribution, precipitations and the influence of post-treatment on the microstructural evolution, next the mechanical properties consisting of hardness, tensile properties, compressive properties, cryogenic and high-temperature properties, fatigue properties, creep behavior, post-treatment effect and the strengthening mechanisms analysis. Thereafter, emerging functional properties of additive manufactured HEAs, namely the corrosion resistance, oxidation behaviors, magnetic properties as well as hydrogen storage properties are discussed, respectively. Finally, the current challenges and future work are proposed based on the current research status of this topic.

Carrozza A., Aversa A., Mazzucato F., Bassini E., Manfredi D., Biamino S., Valente A., Fino P.

This work deals with the effect of different heat treatments on directed energy deposition (DED)-produced Ti-6Al-4V samples. Annealing treatments at 1050 °C followed by different cooling rates were conducted to allow a complete recrystallization of the microstructure and remove the columnar prior-β grains, thus increasing the overall isotropy of the material. An agine treatment at 540 °C was also performed for further microstructural stabilization. The microstructures, textures and mechanical properties were then assessed. Due to the heat treatments, greatly differing microstructures were achieved in an equiaxed grain morphology. However, a “grain memory” effect was detected which resulted in the grains size increasing along the height of the samples. This effect was correlated to the intrinsic prior-β grain width variation along Z on the as-printed specimens, typical of the DED technology. Electron backscatter diffraction analyses proved that the intensity of the preferential directions increased after the heat treatments, likely due to the crystallographic variant selection mechanisms taking place when the samples cool down from the annealing temperature. This effect is also influenced by the significant difference in terms of prior-β grains sizes between the heat-treated and the as-printed specimens. To sum up, a complete homogenization of the material via heat treatment above the β-transus temperature proved to be challenging. In fact, the data suggest that the intrinsic texture-related anisotropy granted by the manufacturing process is very difficult to be eliminated. • The post-annealing cooling mean has a great impact on the final microstructure. • “Grain memory” effect prevents full prior-β grains homogenization. • Comparing the texture of different microstructures is hard due to the dissimilar sizes. • Crystallographic variant selection mechanisms take place during the heat treatment.

Funch C.V., Somlo K., Christiansen T.L., Somers M.A.

The effects of different thermochemical post-processing treatments on the microstructure and properties of additively manufactured austenitic stainless steel were investigated. If the nitrogen content in the as-built condition is high, austenitization in vacuum causes a reduction in nitrogen content near the surface. This can be remedied by applying a small amount of nitrogen in the gas during austenitization. Using high temperature solution nitriding, the surface hardness could be effectively raised by deliberate nitrogen ingress, while maintaining a very fine structure inside the primary austenite grains. The excellent combination of strength and ductility of the as-built condition is accompanied by a low degree of work-hardening. This condition showed elastic and plastic anisotropy. The vertically built condition exhibits a lower strength and an early initiation of yielding as compared to the horizontally built conditions. High temperature treatments were able to efficiently reduce the mechanical anisotropy exhibited in the as-built condition. A combination of high- and low temperature surface hardening was investigated using nitriding, carburizing and nitrocarburizing. In all cases expanded austenite developed on the surface, which created a strong hardness increase. • Austenitization in vacuum will cause denitriding, so nitrogen atmosphere is needed. • Mechanical plastic and elastic anisotropy of the as-built condition. • Anisotropy is reduced by high temperature treatments to remove cell structure. • Low temperature surface hardening produces a hard case of expanded austenite.

Navickaitė K., Nestler K., Böttger-Hiller F., Matias C., Diskin A., Golan O., Garkun A., Strokin E., Biletskiy R., Safranchik D., Zeidler H.

In this paper, a comparison of two surface polishing techniques suitable for additive manufactured titanium alloy parts is presented. The symmetrically branched parts designed by the Israel Aerospace Industries (IAI) for high fatigue resistance under cyclical loading were polished using plasma electrolytic polishing (PEP) and powder blasting combined with PEP. Surface roughness data and micrographs were obtained before and after polishing. The polished parts were tested under cyclical tension loading in order to compare the influence of two surface treatments on fatigue resistance. The tension loading results obtained on the analysed parts were compared to those obtained on parts loaded in as-built condition.

Khosravani M.R., Božić Ž., Zolfagharian A., Reinicke T.

• Overview of the process parameters in FDM technique. • Design and fabrication of intact and defected 3D-printed parts. • Accelerated thermal ageing on intact and defected components. • Fracture studies of polymeric additively manufactured structural components. • Influence of raster orientation and thermal ageing on the failure behavior of parts. The significant increase in applications of additive manufacturing has led to various investigations in this field. Three-dimensional (3D)-printed parts might be subjected to different environmental conditions during their service life. Therefore, a profound knowledge on this subject can significantly help to increase structural performance of these parts. In the present study, effects of accelerated thermal ageing on the mechanical behavior of 3D-printed parts has been investigated. To this aim, a natural environment has been simulated and the related effects are investigated by means of accelerated thermal ageing with temperature in the range of −5 °C to 35 °C. Moreover, the current study describes influence of manufacturing defect on the fracture behavior of 3D-printed components. Since defects and anomalies might be occurred during 3D printing process, fabricated parts can show different mechanical behaviors. In the present investigation, intact and defected test coupons with different raster orientations were printed and examined. In detail, polylactic acid material was used in fabrication of the specimens based on the fused deposition modeling process. These groups of specimens were also aged and subjected to tensile load. The documented results indicate effects of thermal ageing on the structural integrity of intact and defected specimens. The outcome of this study can be utilized for future design and next computational modeling of 3D-printed polymer parts.

Zhang L., Cao W., Zhang Y., Jiang R., Li X.

Porosity defects are difficult to overcome in Al-Zn-Mg-Li alloys, despite their high potential for application in the military and aerospace industries. Multidirectional forging and aging treatment were applied to tune the microstructure and mechanical properties of wire arc additive manufacturing Al-Zn-Mg-Li alloy. The grains were elongated along the forging direction attributed to the severe extrusion stress, accompanied by a great density of equiaxed recrystallized grains. As the forging reduction expanded from 30% to 50%, the average grain size was evidently reduced from 23.1 μm to 16.9 μm. A considerable number of porosities were heat-welded during the forging deformation process. The Al 2 CuMg, Al 7 Cu 2 Fe, and Al 5 CuLi 3 phases were severely fragmented and agglomerated in the form of condensed clusters. Furthermore, numerous needle-shaped Al 3 (Li, Mg) phases were stochastically distributed. As the forging reduction increased from 30% to 50% and the aging temperature/time increased (from 140 °C/5 h to 170 °C/10 h), the rod like η′-MgZn 2 phase was obviously coarsened, which considerably deteriorated the properties. The ultimate tensile strength was dramatically increased from 386 MPa to 473 MPa when comparing the specimens with 30% and 50% forging reduction. Both the yield strength and hardness exhibited a similar trend. The elongation was greatly enhanced with a higher forging reduction. Ultimately, the aging behavior was thoroughly investigated and the relationship between the strength η′-phase and yield strength was theoretically discussed.

Chmielewska A., Wysocki B., Kwaśniak P., Kruszewski M.J., Michalski B., Zielińska A., Adamczyk-Cieślak B., Krawczyńska A., Buhagiar J., Święszkowski W.

The use of elemental metallic powders and in situ alloying in additive manufacturing (AM) is of industrial relevance as it offers the required flexibility to tailor the batch powder composition. This solution has been applied to the AM manufacturing of nickel-titanium (NiTi) shape memory alloy components. In this work, we show that laser powder bed fusion (LPBF) can be used to create a Ni55.7Ti44.3 alloyed component, but that the chemical composition of the build has a large heterogeneity. To solve this problem three different annealing heat treatments were designed, and the resulting porosity, microstructural homogeneity, and phase formation was investigated. The heat treatments were found to improve the alloy’s chemical and phase homogeneity, but the brittle NiTi2 phase was found to be stabilized by the 0.54 wt.% of oxygen present in all fabricated samples. As a consequence, a Ni2Ti4O phase was formed and was confirmed by transmission electron microscopy (TEM) observation. This study showed that pore formation in in situ alloyed NiTi can be controlled via heat treatment. Moreover, we have shown that the two-step heat treatment is a promising method to homogenise the chemical and phase composition of in situ alloyed NiTi powder fabricated by LPBF.

Hu Y., Chen H., Jia X., Liang X., Lei J.

Excellent mechanical properties, including residual stress, ductility and strength, are important requirements for bone implants. In order to achieve this effect, titanium samples were manufactured by selective laser melting, and the prepared parts were subsequently subjected to three different heat treatment, which were 550 °C, 650 °C and 750 °C for 2 h, respectively. The results show that for as-built sample, relatively short lath-shaped α grains and a few needle-shaped α′ grains were present. After heat treatment, the α grains became thicker and longer, and the α′ grains became more. As the heat treatment temperature increases from 550 °C to 750 °C, the size of the lath-shaped α grains gradually decreases, and the small-sized needle-shaped α′ grains become denser. Moreover, the tensile strength, elongation and shrinkage of specimens increased as the heat treatment temperature increased. The fine microstructure of heat-treated samples also significantly promoted the improvement of tensile properties. The fracture mechanism of the specimens changed from brittle fracture to a mixed mode including ductile and brittle fracture, so that the tensile strength and ductility of the heat-treated specimens were well combined.

Zhang B., Wei W., Shi W., Guo Y., Wen S., Wu X., Gao K., Rong L., Huang H., Nie Z.

The Al–7Si–0.6 Mg alloy with added rare earth erbium (Er) was prepared by laser powder bed fusion (LPBF) technology, and the effect of heat treatment on the microstructure and mechanical properties was studied. The addition of Er introduces Al 3 Er to the molten pool, which can effectively hinder the epitaxial growth of the columnar crystal. The effect of rapid cooling and the addition of Er can also modify eutectic Si particles, resulting in an ultrafine eutectic network cellular structure. Moreover, the as-built samples have an excellent tensile strength exceeding 438 MPa and a ductility of over 8%; furthermore, such excellent mechanical properties are associated with small grains, a continuous Si network, and extremely oversaturated solid solubility. After heat treatment, LPBF-processed alloy samples exhibit superior mechanical properties, especially after direct age treatment, which can mainly be attributed to the precipitation strengthening effect introduced by nanosized precipitates.

Zhang Z., Wang L., Zhang R., Yin D., Zhao Z., Bai P., Liu B., Wang F.

Recently, wire and arc additive manufacturing (WAAM) technique has been used to fabricate the Mg alloy parts, and the solution annealing was generally employed to eliminate the residual stress and homogenize the microstructure of WAAM Mg alloy. Due to the microstructure differences between the WAAM and cast Mg alloys, the effect of solution annealing on the microstructures and corrosion behavior of cast and WAAM Mg alloy was theoretically different. Unfortunately, there is no research on the effect of solution annealing on the corrosion behavior of WAAM Mg alloys. In this study, the effect of solution annealing (415 °C for 8 h) on microstructures and corrosion behavior of wire and arc additive manufactured (WAAM) AZ91 magnesium (Mg) alloy in 0.1 M NaCl was investigated by microstructure analysis and electrochemical measurements. It was found that solution annealing coarsened the grain, eliminated non-basal grain orientation and dissolved the Mg 17 Al 12 phase of the as-received WAAM AZ91 Mg alloy. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) results revealed that solution annealing improved the corrosion resistance of WAAM AZ91 Mg alloy evidenced by the decreased corrosion current density, increased the pitting potential and impedance. EN results indicated that the WAAM AZ91 Mg alloy in two states underwent totally different corrosion mechanisms in 0.1 M NaCl, and the heat treated WAAM AZ91 Mg alloy had lower pit initiation rate and lower pit growth ability. The relationship between the microstructures and the improved corrosion resistance after solution annealing is discussed.

Bouchareb S., Doufnoune R.

Lin X., Yang J., Lin J., Dai P., Huang Y., Che C.

Alazzawi S., Ali N.H., Shihab S.K., Hanon M.M.

Lea A., Matalgah K., Yudhanto A., Fleck T.J.

Sanusi K., Malatji N., Jeje S., Kanyane R., Shongwe M.

Abstract This review paper provides a comprehensive overview of the heat treatment processes applied to laser additive manufactured medium-entropy alloys (MEAs), focusing on their impact on microstructural evolution and material properties. MEAs, characterized by their high compositional complexity and exceptional mechanical performance, have garnered significant attention in materials science due to their potential for advanced engineering applications. The paper begins by outlining the fundamental concepts of MEAs, including their composition, properties, and applications. It then explores various laser additive manufacturing (LAM) techniques, such as selective laser melting (SLM) and laser metal deposition (LMD), and their associated challenges, including issues related to microstructure, porosity, and residual stresses. A detailed examination of heat treatment processes follows, covering methods such as solutionizing, aging, annealing, and quenching, and their effects on MEAs. The review highlights how these heat treatment techniques influence microstructural changes, such as phase transformations and grain refinement, and their subsequent impact on mechanical properties, including hardness, tensile strength, and ductility. Additionally, the paper addresses the effects of heat treatment on thermal stability and corrosion resistance, emphasizing the importance of optimizing these processes for enhanced performance in various industrial applications. Recent advancements in LAM and heat treatment technologies are discussed, alongside emerging trends and future research directions. Key areas for further investigation include the development of novel heat treatment techniques, the need for standardized testing and evaluation methods, and the exploration of sustainable practices. The review concludes with recommendations for future research efforts aimed at addressing current knowledge gaps and advancing the field of MEAs in both academic and industrial contexts. This review provides valuable insights for researchers, engineers, and industry professionals seeking to optimize the performance of MEAs through effective heat treatment strategies and advanced manufacturing techniques.

Martins M.F., Olmo Martínez R.D., Revilla R.I., Graeve I.D.

Awd Allah M.M., Abd El‐Halim M.F., Sebaey T.A., Mahmoud S.F., Saleh D.I., Abd El‐baky M.A.

AbstractThis work investigates the effect of printing parameters on the crashworthiness performance of square tubes made with polyethylene terephthalate glycol reinforced with carbon fiber (PETG‐CF). This was accomplished by analyzing three printing parameters, infill pattern structure, infill density, and layer height, each of which changed across four levels. The specimens' structural performance was then assessed using quasi‐static axial compression testing. In addition to carefully documenting failure histories, data on crash load, absorbed energy, and displacement responses were methodically recorded during the testing. Several critical performance measures, including the initial peak crash load (), the total energy absorbed (U), the mean crash load (), the specific absorbed energy (SEA), and the crash force efficiency (CFE), were used to evaluate crashworthiness. A complex proportional assessment (COPRAS) method, was employed to determine the optimal configuration. The results indicate that the honeycomb structure achieves the highest values for , U, , and SEA, with measurements of 5.57 kN, 250.54 J, 4.64 kN, and 15.27 J/g, respectively. Meanwhile, the Schwarz P attains the maximum CFE, with a value of 1.585. The COPRAS results further indicated that the HC‐30‐0.20 configuration exhibited the best crashworthiness performance.Highlights The designed configurations were created using FDM. The tubes were exposed to axial compression loads. The crashing load and energy absorption curves against displacement were computed. Besides, the crashing histories were detected. Furthermore, the COPRAS method is used to catch the optimal structure.

Veres C., Tănase M.

Functionally graded materials (FGMs) are a class of advanced materials characterized by spatially varying properties, offering significant advantages in aerospace, automotive, and biomedical industries. The integration of additive manufacturing (AM) has revolutionized the fabrication of FGMs, enabling precise control over material gradients and complex geometries. This review presents a comprehensive bibliometric and content analysis of 3D-printed FGMs, focusing on materials, processing techniques, mechanical properties, and application trends. The findings highlight the growing research interest in FGMs since 2016, with a peak in 2021, and the dominant contributions from the USA and China. Key research trends include advancements in selective laser melting and direct energy deposition techniques, which have enhanced mechanical performance by improving wear resistance, tensile strength, and elasticity. Despite these advancements, challenges such as residual stresses, interfacial bonding weaknesses, and material anisotropy persist. Future research should focus on optimizing AM processes to enhance material homogeneity, developing eco-friendly materials to align with sustainability goals, and establishing standardized testing methods for FGMs to ensure their reliability in industrial applications.

Alzyod H., Kónya G., Ficzere P.

Devito F., Natalicchio A., Lavecchia F., Dassisti M.

Ali M.Y., Rao G.K., Prasad B.A.

Kantaros A., Douros P., Soulis E., Brachos K., Ganetsos T., Peppa E., Manta E., Alysandratou E.

This study explores the use of advanced 3D imaging and printing technologies to digitally document and physically replicate cultural artifacts from the Archaeological Museum of Alexandroupolis. By employing structured light scanning and additive manufacturing techniques, detailed digital models and precise physical replicas of two significant artifacts were created—a humanoid ceramic vessel and a glass cup. A handheld 3D scanner was utilized for capturing intricate surface details, with post-processing methods to refine and colorize the digital models. Regarding 3D printing, both Fused Deposition Modeling (FDM) and Stereolithography (SLA) were employed, tailored to the artifacts’ unique requirements for resolution and material properties. This dual approach supports heritage preservation by generating tangible educational resources and providing alternative exhibits to safeguard original artifacts. Our results demonstrate that integrating 3D scanning and printing effectively enhances the accessibility, durability, and educational utility of cultural heritage assets, offering a sustainable model for artifact preservation and study.

Evdokimov D., Sangines Lezama F.A., Filinov E., Chertykovtsev P.

The stress level of a rotating component is of vital importance in order to ensure its safe operation. The primary source of stress for this type of component is the induced centrifugal stress, which depends on the material, rotational speed, and the distribution of the mass. The reduction of stress has been a topic of study for some time; however, the advent of additive technologies has prompted a new wave of research into the design and manufacture of centrifugal impellers for gas turbine engines, incorporating internal lattice structures (LSs). These structures offer benefits in terms of material savings and load reduction by decreasing the centrifugal force. The present work analyzes the stress–strain state of a turbine centrifugal impeller for six different designs, distinguished by the presence or absence of LSs of various geometries, achievable only through additive technologies. The analysis was conducted on a turbine impeller, which serves as an example of a promising small-scale gas turbine engine (SSGTE). The effectiveness of LSs was assessed through their unloading effect; furthermore, an approach to identify their optimal location within the impeller was demonstrated.

Johnson J., Kujawski D.

Inconel 718 is one of the most used alloys within the aerospace gas turbine industry. The acceptance of Inconel 718 within the aerospace gas turbine industry has largely been due to its high strength and fatigue capabilities up to 677 °C (1250 °F). This alloy is traditionally produced through conventional manufacturing methods, such as casting, wrought, and sheet forming. The various traditional manufacturing methods of this alloy have been well understood and characterized for use in critical components. However, Inconel 718 can also be produced with non-traditional manufacturing methods, such as by additive manufacturing. Producing Inconel 718 by additive manufacturing has the opportunity to design more complex components that provide distinct advantages over conventionally produced components. However, prior to implementing additively manufactured Inconel 718 within the aerospace gas turbine industry, there needs to be a complete understanding of the material’s performance. In an effort to completely characterize additively manufactured Inconel 718, this study focuses on the characterization of the alloy’s low-cycle fatigue performance. Specimens were produced via the laser powder bed fusion process in a vertical orientation. Both as-printed surfaces and fully machined surface specimens were evaluated at 24 °C (75 °F) and 538 °C (1000 °F). Fractography analysis was then completed on the specimens to understand differences in the crack initiation and propagation with respect to test temperatures and surface conditions. Based on these tests, it was shown that the fatigue life knockdown due to the as-printed surface conditions was 62.8% at 538 °C (1000 °F) versus only 8.5% at 24 °C (75 °F). These findings are discussed in detail within this article, and future work is proposed.

Yadav A., Srivastava M., Jain P.K.