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The combination of precipitation-hardening stainless steels (PH-SS) and laser powder bed fusion (LPBF) enables the manufacturing of tools for plastic injection moulding with optimised geometry and conformal cooling channels, with potential benefits in terms of productivity, part quality, and tool duration. Moreover, the suitability of LPBF-manufactured PH-SS in the as-built (AB) condition to be age-hardened through a direct aging (DA) treatment enables a great heat treatment simplification with respect to the traditional solution annealing and aging treatment (SA). However, plastic injection moulding tools experience severe thermal cycles during their service, which can lead to over-aging of PH-SS and thus shorten tool life. Therefore, proper thermal stability is required to ensure adequate tool life and reliability. The aim of the present work is to investigate the aging and over-aging behaviour of a commercially available PH-SS (AMPO M789) manufactured by LPBF in the AB condition and after a solution-annealing treatment in order to evaluate the effect of the heat treatment condition on the microstructure and the aging and over-aging response, aiming at assessing its feasibility for plastic injection moulding applications. The AB microstructure features melt pool borders, oriented martensite grains, and a cellular solidification sub-structure, and was retained during aging and over-aging. On the other hand, a homogeneous and isotropic martensite structure was present after solution annealing and quenching, with no melt pool borders, cellular structure, or oriented grains. The results indicate no significant difference between AB and solution-annealed and quenched specimens in terms of aging and over-aging behaviour and peak hardness (in the range 580–600 HV), despite the considerably different microstructures. Over-aging was attributed to both the coarsening of strengthening precipitates and martensite-to-austenite reversion (up to ~11 vol.%) upon prolonged exposure to high temperature. Based on the results, guidelines to aid the selection of the most suitable heat treatment procedure are proposed.

In the present work, the mechanical and magnetic properties of pure iron manufactured by laser-powder bed fusion (L-PBF) were investigated both in the as-built (AB) and stress relieved (HT) conditions, with the aim of elucidating their relationship with the microstructure and evaluating whether and to what extent it can be suitable for industrial applications. The L-PBF process was optimized to obtain high density, crack-free components. Specimens for microstructural analyses, tensile and magnetic tests were manufactured under the optimized conditions and tested both in the as-built and annealed (850 °C for 1 h, to relieve the residual stresses) conditions. Tensile tests showed high tensile strength in both AB and HT conditions (larger than those of conventionally produced pure iron), with higher ductility and lower strength after stress relieving. The magnetic study indicated a not optimal magnetic softness although the heat treatment enhanced the permeability and reduced the coercivity with respect to the as-built condition. The high mechanical strength and low magnetic softness came from the very fine grain size (about 5 μm) of L-PBF pure iron. Instead, the improvement of magnetic softness and ductility after heat treatment was attributed to the possible reduction of dislocation density and consequent stress relief. The results indicated the possibility to achieve a considerably high mechanical strength, in pure iron manufactured by L-PBF, although the fine grain size limits its magnetic softness.

Stainless steel (SS) alloys produced by laser-based powder bed fusion (LPBF) offers comparable and sometime superior mechanical properties compared to conventionally processed materials. Some of these steels have been extensively studied over the last decade; however additively manufactured martensitic SS, such as AISI 420, need further research in characterizing their post-built quality and mechanical behaviour. This lack of information on martensitic SS is not consistent with their growing demand in the automotive, medical and aerospace industries due to their good corrosion resistance, high hardness and good tensile properties. Selection of the appropriate process parameters and post treatments plays a fundamental role in determining final properties. For this reason, the effect of LPBF process parameters and different heat treatments on density, defect characteristics and locations, roughness and mechanical properties of AISI 420 were investigated in this paper. A first experimental campaign was carried out to establish a set of suitable process parameters for industrial applications. Starting from this result, detected defect properties were investigated by computed tomography (CT) scans. Dimensions, sphericity and distributions of defects inside the volume were analysed and compared between samples manufactured with different parameters. In the second part of the paper, the influence of process and post-process conditions on mechanical properties was investigated. The final presented results establish a correlation between the employed production cycle and the resulting properties of LPBF AISI 420 specimens.

Laser welding of dissimilar aluminum alloys has gained interest over recent years, especially for the production of lightweight components. Pore and crack formation is one of the most critical factors to be taken into consideration for such applications, in particular when one or more parts are produced by die casting or additive manufacturing (AM). Current laser systems offer several methods for defect reduction and process control, while optimized process strategies must be correlated to key factors influencing welding outcomes. In light of these aspects, the current paper investigates the welding of AA6082 sheets with AlSi10Mg parts produced by AM in a lap-joint configuration typical of battery housings in the e-mobility industry. Both laser welding with and without filler wire are investigated, along with the potential advantages of using a wobbling scanning strategy, in order to understand the impact of process strategies on weld bead quality. The importance of process parameter optimization is highlighted for all of the employed strategies, with special emphasis on defects, weld bead chemical composition, joint morphology, and dilution between the materials involved. The findings demonstrate that by introducing filler wire and employing active wobbling, highly reflective alloys can be welded correctly (porosity below 1%, equivalent ultimate strength up to 204 MPa) with good tolerance to variations in process parameters, while filler wire can be excluded in high-productivity welding where linear scanning is employed and detailed optimization of process parameters is performed (porosity below 2%, equivalent ultimate strength up to 190 MPa).

Despite ongoing optimization, selective laser melting (SLM) technology still cannot guarantee the production of completely defect-free components. This work investigates hot isostatic pressing (HIP) in a nitrogen environment and solubilization heat treatment as methods for improving the quality of 316L stainless steel components produced by SLM. The characteristics of HIP-treated specimens are firstly correlated with the initial density of samples obtained with different SLM process parameters, showing that HIP is effective at eliminating pores in components with high initial density (above 99%) but not in those with low initial density (approximately 94%). Subsequently, the mechanical properties and microstructure of 316L stainless steel specimens produced by SLM are examined in the as-built state and after various post-process conditions including solubilization heat treatment and HIP at pressures from 50 to 2000 bar. The observed effects of post-processing on the porosity and microstructure of each specimen are consistent with hardness and tensile test results, with the benefits and limitations of HIP clarified for future implementation.

Additive manufacturing processes based on the local fusion of a powder bed, such as selective laser melting (SLM), are a valid alternative to conventional technologies and a growing number of industrial sectors are currently relying on these processes for the production of different components. However, there are still some limits in using SLM and they are often related to the feedstock material. For this reason, in the present work, the effects of powder properties and pre-treatments, as well as process parameters, on the fabrication of aluminum alloy A357 samples were investigated. Two different batches of powder were considered in order to evaluate the effects of particles shape and size in the as-received condition and after two different pre-treatments: 60 °C for 3 h and 200 °C for 1 h. Selective laser-melted samples were produced in the conditions described above and were then characterized in terms of density, phase and chemical composition, defects, and hardness. The results showed a correlation between powder conditions in terms of morphology and pre-treatment on the properties of SLM A357 aluminum alloy components.

Wire arc additive manufacturing (WAAM), also known as Arc-DED, possesses great potential for efficient production using various materials and wire types. This study utilized gas metal arc (GMA) and plasma transferred arc (PTA) variants of WAAM to deposit 2.25Cr-1Mo steel employing a metal-cored wire (MCW) and a solid wire counterpart having the same chemical composition for the comparative study. Initially, bead-on-plate trials were conducted with both WAAM processes and different shielding gas combinations in GMA-WAAM using the cored wire. The heat input versus deposition ratio was analysed to assess the heat input and the effects of shielding gases in GMA-WAAM. Arc behaviour was monitored with a process camera, and bead morphologies and dilutions were compared. Furthermore, test walls were deposited under the two WAAM processes and the shielding gas conditions, employing the cored and solid wire. Detailed microstructural study was conducted through optical microscopy, and hardness tests were performed to determine the mechanical properties. Energy dispersive X-ray spectroscopy (EDS) was used to examine the elemental composition and potential segregation in walls deposited with cored and solid wires. Results indicated a lower heat input when using cored wire and variable heat input due to shielding gases. A bainitic/martensitic microstructure was observed in test walls deposited with cored and solid wires with comparable microstructural features. The PTA process produced higher hardness than GMA, and solid wire exhibited slightly higher hardness than cored wire. Selection of shielding gas also influenced the hardness. Finally, the EDS maps and elemental study revealed comparable results for both wires. The results show good performance and outcome for cored wire.

This paper presents an experimental study of milling operations performed on 18Ni(300) maraging steel components produced by selective laser melting (SLM). The aim was to identify the manufacturing process chain to obtain the best properties of finished 18Ni(300) molds produced by a combination of additive and subtractive manufacturing methods. The SLM process variables taken into consideration were the build direction and post-build heat treatment, while cutting speed was considered as the only process variable for the milling phase. Surface roughness and hardness, cutting forces and tool wear were considered for the evaluation of the optimal manufacturing process parameters.

Grinding represents an indispensable phase in a manufacturing route because it allows to obtain the final required features in terms of dimensions and roughness. Although the grinding technology has always been applied with lubricants, nowadays, oil application becomes more and more limited to reduce the environmental pollution. In dry finishing technologies, heat control represents the main problematic of the process; indeed, grinding usually reaches relevant temperatures causing thermal defects. Therefore, process temperature prediction represents a challenge allowing to prevent thermal defects on the working material. But the final results are influenced by the kinematics parameters and also by the grinding wheel specifications. This paper aims to predict thermal defects in the material also considering the wheel specification. A hierarchical FEM model which considers both the microscopic and macroscopic aspects of the grinding process was developed. Starting from the mechanical action of a single grain on the material, a moving heat source was built to represent the interaction of the grinding wheel with the workpiece. A single grain grinding model is followed by a thermal model which considers the process parameters and the grinding wheel specification. Tangential grinding tests were developed to validate the model by adopting embedded thermocouples and grinding wheels with different structures were used. To further validate the model, metallographic and micro-hardness analyses were developed to verify the microstructural change due to the grinding cycle. A maximum average percentage difference of 10.8% was detected between calculated and measured temperatures and good agreement with the microstructural analysis was found.

Additive processes like Laser Beam Powder Bed Fusion (PBF-LB) result in a distinctive microstructure characterized by metastability, supersaturation, and finesse. Post-process heat treatments modify microstructural features and tune mechanical behavior. However, the exposition at high temperatures can induce changes in the microstructure. Therefore, the present work focuses on the analyses of the tensile response at room and high (200 °C) temperature of the A357 (AlSi7Mg0.6) alloy processed by PBF-LB and subjected to tailored T5 (direct aging) and T6R (rapid solution treatment, quenching, and aging) treatments. Along with the effect of microstructural features in the as-built T5 and T6R alloy, the role of typical process-related defects is also considered. In this view, the structural integrity of the alloy is evaluated by a deep analysis of the work-hardening behavior, and quality indexes have been compared. Results show that T5 increases tensile strength at room temperature without compromising ductility. T6R homogenizes the microstructure and enhances the structural integrity by reducing the detrimental effect of defects, resulting in the best trade-off between strength and ductility. At 200 °C, tensile properties are comparable, but if resilience and toughness moduli are considered, as-built and T5 alloys show the best overall mechanical performance.