With respect to process and resource efficiency, semisolid casting processes, such as rheocasting, represent promising technologies for processing lightweight materials in the automotive industry. The reduced temperature of the melt during the casting process allows longer service life for the molds and less production rejects in industrial applications. However, up to now process-microstructure-property correlations have not been investigated in detail. Most studies focusing on these processes are producing simple geometries without a reduction in the cross section. Moreover, mechanical properties are only tested in the quasistatic regime. The present study investigates specimens taken from application-oriented parts. These specimens are examined comprehensively, i.e., from microstructure to the fatigue properties, and are compared to high pressure die cast counterparts. Based on the main findings, the following conclusion can be drawn: Although some differences can be found with respect to the microstructure appearance, under quasistatic loading the results are similar for the die cast and rheocast material (with a yield strength of 125 MPa and ultimate tensile strength of 240 MPa); however, with respect to fatigue properties in the low-cycle fatigue regime, the rheocast material shows reduced scatter: Thus, rheocasting is found to be the method of choice when improved fatigue properties are required.

Laser‐based powder bed fusion of metals (PBF–LB/M) represents a manufacturing technique enabling the production of application‐adapted components. The process is influenced by multiple factors that interact during fabrication. Eventually, these lead to complex cooling conditions, resulting in microstructures strongly affecting the mechanical properties. Understanding the process‐microstructure‐property relationships is therefore crucial. The present study investigates microstructurally graded components made of austenitic steel 316L. Focus is on microstructural differences and residual stress evolution. Components are manufactured by utilizing a dual‐laser system, consisting of a 400 W Gaussian and a 1 kW top‐hat laser. Strengthening is strongly promoted by sub‐structures, i.e. specific dislocation arrangements, decorated with chromium and molybdenum segregations. As a result, PBF–LB/M processed 316L demonstrates superior quasi‐static properties compared to conventionally manufactured 316L. Differing cooling rates prevailing in areas processed either with the 400 W or the 1 kW laser significantly influence the substructure size, eventually resulting in distinctive strength and hardness. The incremental hole drilling method, considering local crystallographic orientation for data evaluation, was used to analyze changes in the residual stress distribution at different specimen‐handling stages and lateral residual stress depth distributions. Results obtained pinpoint a pronounced in‐depth gradient and a rather homogeneous lateral residual stress depth distribution.

Directed energy deposition (DED) as an additive manufacturing (AM) technique with its high productivity is a promising technology with respect to rapid repair applications. Although process characteristics like the layer‐wise built‐up are similar in all AM processes, the microstructure and resulting properties are unique for all primary shaping technologies. In the present study, metastable CrMnNi steels with varying chemical compositions and a concomitantly altered stacking fault energy are processed via DED and afterwards tested via tensile tests at different temperatures. Depending on the specific stacking fault energy of the alloy and deformation temperature, the microstructure is dominated either by martensitic phase transformation, twinning, or slip. The resulting characteristic curves are compared to results from literature focusing on other primary shaping technologies such as laser‐based powder bed fusion of metals and casting. Depending on the manufacturing technology, the shape of the stress–strain curves varies. This can be rationalized based on initial dislocation densities as well as chemical homogeneity. The prevailing microstructural features influence the work hardening behavior as well as the homogeneity of deformation due to locally varying chemistry and stacking fault energy.

In this study, the alloying of stainless steels with various sulfur contents is investigated to obtain steel powders with significantly reduced mean diameters without changing the operational parameters of the atomizing unit. The steels are produced in a VIM12 furnace and atomized on a VIGA-1B setup with high-pressure argon. The desired reduction in the mean diameter is attributed to the decrease in surface tension with increasing sulfur content, which is in good agreement with previous findings. A transition from a positive to a negative thermal gradient of the surface tension is observed, along with a shift to higher temperatures with increasing sulphur concentration. In addition, the chemical assessment of the powders reveals a lower evaporation of manganese and a reduced increase in nitrogen content with increasing sulfur content. The sphericity and flowability are not affected by the addition of sulfur. Viscosity and density measurements are also conducted to characterize the steels thoroughly. Scanning electron microscopy reveals the presence of manganese sulfide, which was submicron in size and well distributed. Iron sulfides, mostly attributed to hot shortness, were not observed, which was also confirmed by thermodynamic modeling using Thermo-Calc software. The atomization of stainless steels can be greatly influenced by alloying with sulfur. Sulfur addition effectively reduces the surface tension (ST) of the researched steels and subsequently the mean diameter of the resulting powders. A transition of the thermal gradient of ST is also observable. Changes in manganese and nitrogen content dependent on sulfur are monitored and discussed as well.image (c) 2024 WILEY-VCH GmbH

Additive manufacturing processes have attracted broad attention in the last decades since the related freedom of design allows the manufacturing of parts with unique microstructures and unprecedented complexity in shape. Focusing on the properties of additively manufactured parts, major efforts are made to elaborate process-microstructure relationships. For instance, the inevitable thermal cycling within the process plays a significant role in microstructural evolution. Various driving forces contribute to the final grain size, boundary character, residual stress state, etc. In the present study, the properties of commercially pure iron processed on three different routes, i.e., hot rolling as a reference, electron powder bed fusion, and laser powder bed fusion, using different raw materials as well as process conditions, are compared. The manufacturing of the specimens led to five distinct microstructures, which differ significantly in terms of microstructural features and mechanical responses. Using optical and electron microscopy as well as transmission electron microscopy, the built specimens were explored in various states of a tensile test in order to reveal the microstructural evolution in the course of quasistatic loading. The grain size is found to be most influential in enhancing the material’s strength. Furthermore, substructures, i.e., low-angle grain boundaries, within the grains play an important role in terms of the homogeneity of strain distribution. On the contrary, high-angle grain boundaries are found to be regions of strain localization. In summary, a holistic macro-meso-micro-nano investigation is performed to evaluate the behavior of these specific microstructures.

Gas-atomized (GA, spherical) and water-atomized (WA, spattered) commercially pure iron (cp-Fe) powders were processed using laser-based powder bed fusion, resulting in a slightly higher porosity of the WA condition. In addition to characterization of quasi-static mechanical properties, fatigue tests, which are known to be detrimentally affected by porosity, were finally considered, revealing good properties even for the WA condition. In terms of microstructure stability, the GA and WA specimens significantly differ; effects seen can be rationalized based on the actual chemical compositions. While the GA specimens show an obvious yield phenomenon and softening under cyclic loading, the WA specimens reveal microstructure stability in cyclic tests.

To obtain steel powders with significantly reduced density and improved corrosion resistance, stainless steels were alloyed with aluminum at various contents (0.1–6 mass%), and the technological and metallurgical implications and consequences of alloying were discussed. Steels were produced using a VIM-12 furnace and atomized using a VIGA-1B Ar inert gas atomizer. The obtained powders were chemically assessed, revealing small losses of aluminum during atomization. These losses are directly associated with oxide formation during the process. Changes in the minor alloying elements were also observed and discussed. The particle size distribution of the atomized steels decreased as aluminum content increased. The influence of the metal mass flow rate on the atomization results was also examined, revealing smaller median particle sizes (d50) at a lower mass flow rate. To investigate the influence of the particle size on the microstructure of the produced powders, secondary dendrite arm spacing (SDAS) measurements were conducted using optical microscopy. The cooling rate, which is directly associated with the particle diameter, had a significant influence on the SDAS. Aluminum addition had no apparent influence on the SDAS. The cast and atomized materials of different particle sizes were subjected to magnetic saturation and metallographic and electron backscatter diffraction (EBSD) examinations to investigate and compare the phase distribution and microstructures in both states with respect to the particle size. For up to 4.5 mass% aluminum, the ferrite content continuously increased, whereas the behavior was different for the alloy with 6 mass% Al.

In light of the steadily increasing importance of resource efficiency, powder recycling represents one of the major prospects in additive manufacturing. The present study focuses on Ti6Al4V parts manufactured by electron beam-based powder bed fusion using blends of virgin and recycled powder. The latter powder was gained by mechanical comminution of support structures and, thus, addresses a novel topic beyond the well-known reuse of un-melted powder. Microstructure analysis is conducted by scanning electron microscopy and micro-computed tomography, mechanical properties are analyzed by quasi-static tensile and fatigue tests. Thereby, the applicability of recycled powder is assessed, eventually revealing that mechanically recycled powder can be qualified to partially substitute virgin powder in powder bed additive manufacturing.

To reduce production time and decrease production cost, the increase of layer thickness is an adequate option in powder bed fusion. In order to determine the relationships between process parameters in laser powder bed fusion (PBF-LB/M) and final porosity in AlSi10Mg, samples were processed following a space-filling experimental design in the present study. A total of 144 samples were fabricated considering layer thicknesses of 30 mu m, 45 mu m, 60 mu m, and 90 mu m. Afterwards, porosity was assessed using image analysis and computed tomography. Different types of defects were found as expected, however, fully dense parts were realized in case of every considered layer thickness. Predictive models were developed using data-driven approaches, eventually enabling multi-variate analysis of the correlations and determination of appropriate processing conditions resulting in both low porosity of parts and high build rates.

Two additively manufactured (AM) materials, i.e., stainless steel 316 L (SS316L) and Ni-base superalloy Inconel 718 (IN718), have been exposed to MgCl2-KCl-NaCl (47.1-22.7-30.2 mol%) salts at 700 ? to investigate their corrosion behavior. Corrosion tests were conducted using SS316L processed by laser metal deposition (LMD), IN718 by laser powder bed fusion (PBF-LB) as well as conventionally processed counterparts. The obtained results reveal that LMD SS316L is characterized by inferior corrosion resistance, mainly due to the segregation of 8-ferrite at grain boundary (GB). Two different types of corrosion morphologies, uniform corrosion and GB -driven corrosion, are observed in both AM and the conventionally processed IN718 samples. The GB-driven corrosion is accelerated by the evolution of 8-phase in case of IN718.

The novel combination of friction stir processing (FSP) and additive manufacturing (AM) is studied herein. Laser‐based powder bed fusion of metals (PBF‐LB/M) is used to establish 316 L stainless steel with a bimodal microstructure. Upon FSP, the as‐built bimodal microstructure with an average grain size of 179 μm is transformed into the unimodal microstructure containing ultrafine grains with an average grain size of 1.2 μm. Results obtained by mechanical testing reveal that after FSP; the hardness, the yield point, and the ultimate strength of additively manufactured 316 L are enhanced by 45%, 77%, and 62%, respectively. Microstructure assessment reveals that such a unique improvement in the mechanical properties is due to considerable structural refinement leading to grain boundary strengthening. Energy‐dispersive X‐Ray diffraction analysis reveals that phase transformation does not occur upon FSP. Fracture analysis further indicates that severe plastic deformation (SPD) during FSP can promote the transformation of coarse voids to fine voids and, hence, densification of as‐built parts.

Metallic material concepts associated with the sustainable and efficient use of resources are currently the subject of intensive research. Al addition to steel offers advantages in view of lightweight, durability, and efficient use of high-Fe scrap from the Al industry. In the present work, Al was added to Fe-12Cr-(9,12)Ni-3Mn-0.3C-xAl (x = 0.1–6) (wt.%) stainless steels to assess its influence on microstructure and mechanical properties. According to density measurements based on Archimedes’ principle, densities were between 7.70 and 7.08 g/cm3. High-energy X-ray diffraction estimations of the lattice parameter indicated that nearly 31% of density reduction was caused by the lattice expansion associated with Al addition. Depending on Al concentration, austenitic and duplex matrix microstructures were obtained at room temperature. In the presence of up to 3 wt.% Al, the microstructure remained austenitic. At the same time, strength and hardness were slightly enhanced. Al addition in higher quantities resulted in the formation of duplex matrix microstructures with enhanced yield strength but reduced ductility compared to the austenitic alloys. Due to the ready formation of B2-(Ni,Fe)Al intermetallics in the ferrite phase of the present alloy system, the increase in strength due to the presence of ferrite was more pronounced compared to standard duplex stainless steels. The occurrence of B2 intermetallics was implied by dilatometry measurements and confirmed by electron microscopy examinations and high-energy X-ray diffraction measurements.

The complex thermal history imposed by the laser-based powder bed fusion of metals (PBF-LB/M) process is known to promote the evolution of unique microstructures. In the present study, metastable CrMnNi steels with different nickel contents and, thus, different phase stabilities are manufactured by PBF-LB/M. Results clearly reveal that an adequate choice of materials will allow to tailor mechanical properties as well as residual stress states in the as-built material to eventually redundantize any thermal post-treatment. The chemical differences lead to different phase constitutions in as-built conditions and, thus, affect microstructure evolution and elementary deformation mechanisms upon deformation, i.e., twinning and martensitic transformation. Such alloys designed for additive manufacturing (AM) highlight the possibility to tackle well-known challenges in AM such as limited damage tolerance, porosity and detrimental residual stress states without conducting any post treatments, e.g., stress relieve and hot isostatic pressing. From the perspective of robust design of AM components, indeed it seems to be a very effective approach to adapt the material to the process characteristics of AM.

Due to its high cost and demanding characteristics, Tantalum requires unique processing techniques and is restricted to small parts. In the present work, Ti65Ta was additively manufactured as a new potential material for small biomedical implants. Assessment of the effects of a remelt scanning strategy was solely accomplished by testing of small mechanical specimens. Yield strength was achieved superior to either L-PBF pure Ti or Ta and low-cycle fatigue behaviour was similar to that of L-PBF Ti-6Al-4 V. The Ti65Ta alloy is a good candidate for a new gold standard alloy for small bone interfacing implants.

In the present study, a novel austenitic stainless Cr-Mn-Ni steel was processed using laser-based powder bed fusion of metals (PBF-LB/M) at substrate plate temperatures ranging between 20 °C and 500 °C. Microstructure evolution was analysed by means of electron backscatter diffraction (EBSD). Different substrate plate temperatures lead to differences in microstructure evolution due to the prevailing cooling conditions and overall thermal history, eventually resulting in different hardening behavior under quasi-static tensile loading even if the general mechanical performance of the different conditions is very similar. From the results shown, it is deduced that the prevailing microstructures are a result of different internal stress states evolved during solidification, cooling and intrinsic heat treatment, respectively. The different internal stress states promote increased local orientation deviations within the grains, which can be rationalized by different dislocation densities. The monotonic strength of the steel in focus is outstanding compared with cold-rolled counterparts and data available in literature.

In recent decades additive manufacturing (AM) for years has been in focus of academia and industry as its underlying production principle allows for the realization of designs of unprecedented geometrical complexity. However, often such structures are not realized due to the lack of understanding of structural and mechanical properties, this fact amongst others related to the unique microstructures established by the related processes. In this context, residual stresses, highly affected by the scan strategy and process parameters used, play an essential role. Generally, various methods and approaches can be used to determine residual stress states experimentally. However, especially in case of the unique microstructures formed by AM, most standard procedures cannot be applied reliably. Commonly used methods based on X‐ray diffraction rely on laboratory X‐ray sources and synchrotron radiation. In present work, a novel method is proposed for robustly calculating residual stresses based on the linear regression method (similar to the sin 2 ψ approach in reflection mode). Data obtained by use of synchrotron radiation in transmission mode are applied. To assess the reliability of the novel procedure, results are validated using simulations and in situ tensile tests. For these tests the well‐known Ni‐base alloy INCONEL 718 processed by laser powder bed fusion (LPBF), being characterized by a complex microstructure, and a conventionally manufactured 100Cr6 steel sample are used.

Additive manufacturing has gained increasing attention in recent years in numerous industrial sectors due to its inherent characteristics, e.g. tool-free production and unprecedented freedom of design. However, in some applications such as heat exchangers the design has to follow certain restrictions, e.g. to allow for the removal of unfused powder, which can be enclosed in cavities. Moreover, in case multi-material parts are considered, the use of different powders during processing is often uneconomical since powder recycling is highly challenging. Therefore, the production of complex structures being characterized by limited accessibility and components made of different materials often require a subsequent joining process. Based on an analysis of state-of-the-art joining technologies employed for additively manufactured metal components, research gaps related to adhesive bonding are deduced. In light of the prevailing gaps, the influence of selective laser melting process parameters like laser power and build direction on the surface topography and, thus, on the bondability of the substrates are investigated. The mechanical tests reveal a high bond strength for the vertically oriented samples and the samples manufactured with a laser power of 400 W. Furthermore, a laser post-treatment of the SLM samples lead to an improvement of lap shear strength. Finally, results reporting on the ageing behaviour of these joints and an outlook on further research activities are given.

The process of laser-based powder bed fusion of metals (PBF-LB/M) is one of the most promising technologies in the field of additive manufacturing. The high freedom of design enables the integration of functionality and production of customized parts. Main drawbacks of this technology are related to relatively low build rates and reliability. The reliability of parts can be derogated due to various process instabilities leading to process-induced defects and process errors, where the latter can even lead to an interruption of the process. Due to limited build rates, a continuation of the process would be highly desirable, however, data reporting on the structural integrity of such interruptedly built parts are hardly available in literature so far. To tackle this research gap, the current study investigates the influence of process interruptions on the properties of AlSi12 processed by PBF-LB/M. The influence of the interruption on microstructure evolution is examined by electron backscatter diffraction. Mechanical properties of these specimens under monotonic and cyclic loading ranging from low-cycle fatigue up to very high-cycle fatigue regimes are investigated and compared to data obtained from counterparts built without interruption.

CuCrZr parts were fabricated by laser beam powder bed fusion (LB-PBF) technique and subjected to different heat treatments. As a result, four different conditions were considered for further investigations, that is, the as-built condition, conditions of maximum hardness (MH) and maximum electrical conductivity (MC), and a condition representing a compromise between hardness and conductivity (H&C). Microstructural evolution and performance under monotonic and cyclic loading were studied. Fracture surfaces revealed significant volume fractions of process-induced defects such as lack-of-fusion (LoF) and pores, irrespective of the condition considered. The effect of these defects on the tensile behavior was found to be marginal, whereas the fatigue performance was noticeably affected due to multiple crack nucleation promoted by large LoF defects. Assessment by computed tomography (CT) revealed a strong influence of the geometry and therefore, of the scan path length, on resulting microstructure and defect population eventually rationalizing obvious discrepancies to the initial process parameter and material density optimization study.

For the first time, the novel combination of multi-pass equal channel angular extrusion/pressing (ECAE/P) and selective laser melting (SLM) was investigated. Herein, four passes of ECAP via route Bc at 150 degrees C were applied as a severe plastic deformation (SPD) technique on the SLM as-built AlSi12 to promote superior mechanical properties. The microstructure and mechanical behavior of AlSi12 fabricated by SLM were studied before and after ECAP, applying several mechanical and microstructural characterization techniques. Results of the tensile experiments revealed that the yield point, the ultimate strength, and the ductility of the as-built sample were improved by 56%, 11%, and 55% after 4 passes of ECAP, respectively. This enhancement is attributed to the effective grain refinement and the persisting silicon phase network after SPD as evidenced by electron backscatter diffraction and elemental mapping results. Moreover, micro-computed tomography analysis disclosed that ECAP considerably reduces the remnant porosity of the post-treated SLM AlSi12 samples eventually further affecting the strength of the ultra-fine grained AlSi12 in a positive way. Findings presented herein indicate that it is viable to utilize ECAP as a post-AM processing tool for mechanical property improvement of laser powder bed fused microstructures with the virtue of enhanced densification. Even if geometrical restrictions exist in ECAP, results obtained herein are transferrable to other SPD techniques with suitable processing windows, which would pave the way to advanced properties of adequately post-treated conditions.