Duplex stainless steels offer a wide range of application due to good mechanical properties and high corrosion resistance. Only duplex stainless steel with microstructure consisting of equal ferrite and austenite contents meets this requirement and other secondary phases deteriorate the properties. Microstructural and uniaxial tensile properties of the SAF 2507 duplex stainless steel (SDSS) prepared via spark plasma sintering are reported in this work. The SAF 2507 SDSS powder was consolidated via spark plasma sintering at 900 degrees C and 1100 degrees C. The microstructure of the samples sintered at the temperature of 900 degrees C contained numerous pores (volume porosity of 16 %), significant fraction of the sigma-phase and the strength and plastic properties of this sample are low. The good mechanical properties. Post-manufacturing solution annealing resulted in a uniform austenite-ferrite microstructure for both spark plasma sintering temperatures. In the case of the sample sintered at 1100 degrees C, only minor changes occurred in microstructure , mechanical properties during post-manufacturing heat treatment. Properties of spark plasma sintered material were compared with the same alloy prepared by additive manufacturing.

The AZ91 magnesium alloy was subjected to a complex treatment involving age hardening (supersaturation and artificial aging) and simultaneous surface layer modification. The specimens were supersaturated in contact with a mixture containing varying concentrations of zinc chloride, followed by cooling either in air or water. After supersaturation, the specimens were subjected to artificial aging and then air-cooled. This process resulted in the formation of a surface layer made of zinc-rich phases. The thickness and microstructure of the surface layer were influenced by the process parameters, namely, the zinc chloride content in the mixture and the cooling rate during supersaturation. The treated specimens exhibited favorable tensile strength and greater elongation compared to the as-cast AZ91 alloy, with values comparable to those of the alloy subjected to standard T6 tempering. No cracking of the layer was observed under moderate deformation, though greater deformation resulted in the formation of cracks, primarily in the areas containing the Mg5Al2Zn2 intermetallic phase. The produced layer demonstrated strong metallurgical bonding to the AZ91 substrate.

Additive manufacturing (AM) has revolutionised the production of complex components with custom mechanical properties. However, as-deposited AM-ed materials often exhibit inferior mechanical behaviour compared to conventionally manufactured counterparts because of defects generated during the deposition. In this study, the effects of equal channel angular pressing (ECAP) on fracture toughness and fatigue endurance of Ti-6Al-4V titanium alloy manufactured by direct energy deposition (DED) are investigated. The aim of this study is to compare the mechanical performance of the material in the as-deposited and ECAP-ed states, exploiting the potential benefits of ECAP in improving the properties of additively manufactured components. ECAP processing is used to induce severe plastic deformation (SPD) and create a unique microstructure in Ti-6Al-4V specimens. As-deposited and ECAP-ed specimens were evaluated using stress intensity factor (SIF) analysis, fatigue crack growth, and high cycle fatigue tests using miniaturized specimens. Fractographic analysis was performed using scanning electron microscopy (SEM) to examine the fracture surfaces and identify the underlying failure mechanisms. The results revealed that while ECAP led to a slight increase in porosity, it significantly reduced fracture toughness and had a negligible effect on the rate of propagation of fatigue cracks. In addition, the ECAP-ed specimens showed reduced fatigue endurance of the material.

Additive manufacturing (AM) is an innovative technology allowing faster and cheaper production of complex -shaped parts in comparison to conventional methods. On the other hand, equal channel angular pressing (ECAP), belonging to severe plastic deformation (SPD) methods, induces large amounts of strain and dislocations to the material, which cause its strengthening and densification. In this study, the unique combination of directed energy deposition (DED) and four-pass ECAP processing was investigated. The experimental material is DED-processed titanium alloy Ti-6Al-4 V in as-deposited and ECAP-ed states. The material in both states was sub-jected to microstructure investigation using light (LM) and scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD), porosity and hardness measurement and mechanical testing, which included evaluation of tensile properties. The fracture surfaces of the specimens after testing were observed using SEM. The ECAP processing led to significant deformation of original grains and refinement of microstructure. In the case of ECAP-processed specimens, a significant improvement of mechanical properties in terms of strength and elongation was observed.

In recent years, much attention has been directed towards multi-material systems produced using additive manufacturing technologies. Especially directed energy deposition-based systems provide a powerful tool for relatively simple production of components with controlled chemical composition in certain directions and locations. In this contribution, the potential of bimetallic material manufacturing based on the combination of nickel alloy Inconel 625 and 42C steel using direct laser deposition process was investigated. The monolithic single material blocks as well as graded blocks with alternate material deposition order were produced and investigated via light and scanning electron microscope. In addition, the miniaturized tensile tests at ambient and high temperatures were performed. It was observed that the character of two-material joint changed with the order of deposited materials. Based on the maps of chemical composition, it was shown that joint Inconel 625 to 42C was rather gradual, while 42C to Inconel 625 had sharp distribution of the main elements around the fusion line. The tensile test results demonstrated that the location of preferential failure was the joint itself in the case of gradual interface regardless of the test temperature. On the other hand, the sharp joint failed within Inconel 625 material at room temperature, while at elevated temperature the failure was observed in 42C steel region.

Functionally graded materials manufactured by additive manufacturing technologies reached high interest in additive manufacturing community over the last decades. High potential of additively manufactured multimaterials was demonstrated by many studies over the last 10 years. Most of the studies dealing with functionally graded materials had one common sign, which is the chemical composition gradient being controlled in the building direction of the final product. Hence, the multi-material interface is mostly situated in horizontal plane (XY) of the product. However, due to a complex geometry of the product, it is not always possible or desirable to achieve certain interface orientation and multi-material interface might incline from the ideal horizontal plane. Typically, corner zones, where interface orientation changes suddenly from horizontal to vertical orientation, are the most critical locations. Therefore, investigation of the interface orientation is important in order to establish the additive manufacturing limitation for certain applications. The current study revealed that the interface inclination has significant influence on the amount and distribution of formed defects at the materials interfaces. Furthermore, it was shown that the interface surface quality in terms of as-deposited surface or machined surface can significantly affects the defects formation. The effect of defects on the tensile specimen's elongation was significant, which based on the interface angle dropped over more than 70%.

Functionally graded materials (FGMs) are materials distinguished by gradual variation in structure and composition within their volume. Nowadays, the development of FGMs is also accelerated by development and expansion of additive manufacturing (AM) technology, which represents a tool for their relatively easy and precise production. This contribution is focused on the characterization of mechanical performance of SS316L-IN718 interface in terms of local tensile behavior that was investigated using miniaturized tensile test (MTT). The tensile behavior of single material zones (SS316L and IN718) as well as two-material interface zones were examined in parallel and perpendicular orientations with respect to the direction of deposition. The strain maps of MTT specimens were compared and used as a tool for failure process evaluation. Beside the sharp two-material interface observed using scanning electron microscope (SEM), a diffusion zone of certain elements was detected via wavelength-dispersive spectroscopy (WDS) line scan. The specimen orientation at the interface is a decisive factor considering the material failure location. The fractographic analysis of MTT specimen machined in vertical orientation showed that the fracture process was observed preferably in the SS316L zone. The strain within IN718 zone was very limited until the end of the test. Contrary to that, in the case of the specimen oriented horizontally, the failure process was initiated in the zone of IN718, which was characterized by higher strength but the plastic capacity was depleted earlier. The recorded stress level yielded the values above these of vertical specimen (SS316L) but below IN718. This suggests that the stress was carried preferably by the IN718 part of horizontally-oriented specimen.

The present work aimed to study the properties of medium-carbon steel during tempering treatment and to present the strength increase of medium-carbon spring steels by strain-assisted tempering (SAT). The effect of double-step tempering and double-step tempering with rotary swaging, also known as SAT, on the mechanical properties and microstructure was investigated. The main goal was to achieve a further enhancement of the strength of medium-carbon steels using SAT treatment. The microstructure consists of tempered martensite with transition carbides in both cases. The yield strength of the DT sample is 1656 MPa, while that of the SAT sample is about 400 MPa higher. On the contrary, plastic properties such as the elongation and reduction in area have lower values after SAT processing, about 3% and 7%, respectively, compared to the DT treatment. Grain boundary strengthening from low-angle grain boundaries can be attributed to the increase in strength. Based on X-ray diffraction analysis, a lower dislocation strengthening contribution was determined for the SAT sample compared to the double-step tempered sample.

The AZ91 magnesium alloy was subjected to a complex treatment consisting in age hardening (supersaturation and artificial aging) and simultaneous modification of the surface layer. The specimens were supersaturated in contact with the mixture containing zinc chloride and then cooled in the air or in the water. The mixtures with various content of ZnCl2 were used. The specimens after supersaturation were subjected to artificial aging followed by air cooling. The process resulted in the formation of the surface layer containing phases rich in zinc. The thickness and microstructure of the surface layer were dependent on the process parameters, i.e. content of a zinc chloride in the mixture and cooling rate during supersaturation. The specimens were characterised by favourable tensile strength and higher elongation compared to as-cast AZ91 alloy (similar values to the alloy subjected to standard age hardening to T6 temper). No cracking of the layer was observed for a moderate deformation of the specimen. Greater deformation resulted in the formation of cracks, located mainly in the areas composed of the Mg5Al2Zn2 intermetallic phase. The produced layer was strongly metallurgically bonded to the AZ91 substrate.

In recent years, cold spray process is increasingly used for additive manufacturing of metallic components, referred to as cold spray additive manufacturing (CSAM). Unlike the fusion-based AM processes, CSAM is achieved in a solid-state, bringing several advantages such as the absence of severe oxidation or phase composition changes. At the moment, the main limitation of CSAM is the generally low ductility of the as-sprayed deposits. In this paper, using Cu as a model material, we demonstrate a way to overcome this limitation. Importantly, a high ductility of the deposits in their as-sprayed state is achieved without a trade-off in mechanical strength. Furthermore, we show that without any post-heat treatment, the properties of CSAM Cu are comparable to bulk, non-AM Cu.

The design freedom in Laser Metal Deposition provided by the absence of a powder bed enables the fabrication of Functionally Graded Materials through Additive Manufacturing. For the first time, two suitable γ-TiAl alloys (TiAl48Cr2Nb2, TiAl45Nb4C) are combined in direct and gradual transitions to generate different microstructure morphologies and, consequently, different mechanical properties within a component after an identical heat treatment. The influence of alloy composition, microstructure type, and material transition on the tensile properties and fracture toughness is analyzed through miniature testing. Miniature tensile tests show no orientation dependency in regard to the build direction and the composition/microstructure transition is not found to be a preferred fracture site. The miniature fracture toughness tests reveal that already small composition changes—insufficient to alter the microstructure configuration—can have a significant effect on the cracking behavior. Graphical abstract

Functionally graded materials (FGM) are a very promising group of technical materials. The potential of FGM was increased recently by Additive manufacturing (AM) techniques. This is due to the possibility of automatisation of the entire process and achievable variable material structure by controlled deposition parameters. The defects and unexpected structure formation are crucial for the performance of additively manufactured components. Conventional compositionally graded multi-material systems are characterised by horizontally oriented interfaces located within the XY plane of the deposition system. This paper deals with the fabrication of a graded material based on 316L and IN718 in combination with vertically oriented interfaces between single materials zones. Critical defects were observed in the microstructure as a result of solidification cracking. Mini tensile test results showed that the 316L/IN718 interface and 316L in ZYX (vertical) orientation are the weakest points of the produced material. Fractographic analysis revealed that all specimens in the YZX testing direction exhibit the solidification cracking propagated along the grain boundaries with a detrimental effect on the strength of the 316L/IN718 interface. Results of the current study were confronted with previous results obtained for horizontally deposited combination of materials.

Additive manufacturing (AM) becomes a more and more standard process in different fields of industry. There is still only limited knowledge of the relationship between measured material data and the overall behaviour of directed energy deposition (DED)-processed complex structures. The understanding of the structural performance, including flow curves and local damage properties of additively manufactured parts by DED, becomes increasingly important. DED can be used for creating functional surfaces, component repairing using multiple powder feeders, and creating a heterogeneous structure with defined chemical composition. For thin parts that are used with the as-deposited surface, this evaluation is even highly crucial. The main goal of the study was to predict the behaviour of thin-walled structures manufactured by the DED process under static loading by finite element analysis (FEA). Moreover, in this study, the mechanical performance of partly machined and fully machined miniaturized samples produced from the structure was compared. The structure studied in this research resembles a honeycomb shape made of austenitic stainless steel AISI 316L, which is characterized by high strength and ductility. The uncoupled damage models based on a hybrid experimental-numerical approach were used. The microstructure and hardness were examined to comprehend the structural behaviour.

Super duplex stainless steel SAF2507 is characterized by good mechanical properties and corrosion resistance. However, the combination of high strength and corrosion resistance requires the balanced ratio of austenite and ferrite in microstructure. At the same time, the presence of other secondary phases such as intermetallic phases (sigma, chi), carbides (M7C3, M23C6) and nitrides (pi, CrN, Cr2N) is strongly undesirable. Additive manufacturing of duplex stainless steel has not been described in detail yet and the existing studies deal with the duplex stainless steels deposited by powder bed methods primarily. This study investigates the properties of steel SAF2507 prepared by the directed energy deposition (DED) method in the as-built state and after post-manufacturing solution annealing at 1100 degrees C for 60 min followed by water quenching and compares them with the duplex stainless steel additively manufactured by powder methods and conventional ways of preparation. Microstruc-ture, phase composition and mechanical properties of both materials were studied in detail. The material after DED contains of about 28 wt% austenite, which is much more compared to additively manufactured duplex stainless steels by powder bed. The as-built state contained allotriomorphic grain boundary austenite (GBA), Widmansta center dot tten austenite (WA) and intragranular austenite (IGA). Coarsening of austenite occurred during so-lution annealing, while ferrite's grains size decreased. The solution annealed material achieves approximately the desired ratio of austenite-ferrite 50:50. Yield strength decreased slightly during solution annealing from 680 MPa to 540 MPa, whereas elongation and notch toughness increase. The ductile to brittle transition temperature (about-100 degrees C) did not change significantly during solution annealing.

After severe plastic deformation (SPD) processing, aluminum alloys show increased strength but low ductility. However, the ductility of the materials obtained during tensile tests does not reflect the full plastic deformation ability of the materials. This work presents the results of a more comprehensive plasticity analysis, which is applied first time to material after SPD processing. The current study considers an aluminum alloy 5083 before and after equal channel angular pressing (ECAP). The plasticity analysis was implemented based on the fracture locus, which was plotted in the space of the equivalent strain to fracture, the stress triaxiality parameter, and the Lode angle parameter using the Hosford-Coulomb (H-C) model. The parameters of the H-C model were determined using a combined experimental-numerical approach. It was found that the plasticity of the 5083 alloy strongly depended on a combination of the stress triaxiality and Lode angle parameter. However, the fracture locus of the material after ECAP processing showed slightly higher values of equivalent strain to fracture than that of the initial material. This approach makes it possible to estimate the ultimate plasticity of the materials after ECAP processing for a wide range of stress-strain states and can be used to predict fracture in plastic deformation processes. (c) 2021 Elsevier B.V. All rights reserved.

In most cases, the components (U-profiles, Ω-profiles, box-beams) are used to validate the material model generated from the measurement of individual sheet metal parameters. The validation process consists of comparing the resultant force vs displacement from the experiment to the simulation. The loading conditions during testing are predominantly chosen based on the final application the material, and a component manufactured from it. Taking an example, the U-profiles or Ω-profiles are usually loaded in three-point-bending mode, and the so-called box-beams are loaded axially in compression mode. In mechanical testing for automotive industry, the application of dynamic loading is necessary for observation of the material behaviour under high strain rates. The machine used for this purpose can be a drop weight tower, which is usually instrumented by a crosshead displacement measurement and one load cell. However, such an instrumentation is insufficient for precise description of the component behaviour during dynamic events. The solution is offered by the high-speed 3D DIC measurement of deformation. Nevertheless, there are still many parameters that can be obtained from these tests, which can lead to much more accurate validation of the material model. In addition to the DIC measurement, a local deformation measurement by means of strain gauges and continuous temperature measurement in the notch area were proposed in this study. The result is a complex set of the material properties in a given loading conditions.

Fracture toughness of automotive-grade dual-phase steel (DP450) and interstitial free (IF) steel is determined using essential work of fracture (EWF) methodology. Geometrical constraints of standard fracture toughness tests made the EWF method an alternative for thin sheets. Double edge notched tension (DENT) specimens are used for the EWF tests. The two steels have different mechanical and microstructural properties, which helps test the applicability of the EWF methodology to different materials. The effect of notch-tip radius on the EWF test results is analyzed for both the steels. The sensitivity of fracture toughness to notch-tip radius is not the same for both steels. During the EWF test, the digital image correlation (DIC) technique is used to determine the local strain variation of DENT specimens. The hole expansion ratio is determined for the two steels to compare against the EWF test results. The IF steel, despite lower strength, has better fracture toughness and hole expansion capability against the DP450 steel.

Additive manufacturing is a one of the most promising technology nowadays that offers the advantages not only in building products of complex shapes but also of complex materials. A complex structure is characteristic for Functionally Graded Composites, which basics, principles and applicability have been widely investigated over the last years. The present study is focused on the detailed investigation of mechanical and structural properties of FGC consisting of stainless steel 316L and Inconel 718 processed by Blown Powder Directed Energy Deposition system. Mechanical properties within single layers and over layers transitions were investigated with the use of tensile tests and fracture toughness tests. Metallographic and fractographic investigations were carried out. Metallographic investigation revealed the differences in the interfaces between single material layers, nucleation processes and subsequent growth of the grains of the used materials. It has been shown that the formation of transition region between deposited single material layers is dependent on the order of material deposition since different deposition parameters are used for certain material. Evaluation of the tensile properties showed that the mechanical properties of a single material layers are in very good agreement regardless of the deposition height. However, the types of interfaces considering to the results of fractographic observations affect the tensile performance of the Functionally Graded Composite. The fracture toughness test results demonstrate changes in the mechanism of crack propagation at the interface between materials with respect to the type of transition. Furthermore, the material layers interfaces turned out to be the weakest points of the Functionally Graded Composite.

The aim of the study was to determine the effect of specimen geometry, strain rate and a cooling medium on the flow curves of steel. Cubic and cylindrical specimens made of low-carbon nonalloyed steel were tested in the study. The stress concentration in the different specimen geometries was analysed by the numerical simulation. The uniaxial compression tests were carried out at the following strain rates: 0.01, 0.1, 1.0 and 10.0 s(-1) . The deformation was recorded using the optical and mechanical extensometers. The temperature field was monitored by the thermographic method and using thermocouple. During the tests at the highest strain rates, the characteristic decrease of stress value on the compression curve was observed which is related to the temperature increment due to the thermomechanical coupling effect. This phenomenon can affect the results of the test and complicate the further evaluation of material model using numerical simulation. Therefore, some methods of cooling samples during testing were proposed in the article, such as comparison of cooling effectivity of air, water, ethanol and oil.

Due to the nature of the Electron Beam Powder Bed Fusion (EB-PBF) process, it offers an opportunity to produce parts with desired localized mechanical properties by influencing the microstructure evolution of built components through process parameters adjustment. This research demonstrated this potential, not only producing IN718 components with custom grain structures but also successfully produced IN718 single crystal components. At this moment, EB-PBF is widely associated with low volume manufacturing when compared to conventional manufacturing processes. For this reason, small scale testing (SST) is also utilized in this research as an efficient and practical approach to assess fracture behavior of EB-PBF manufactured components.