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Precipitation hardening (PH) stainless steels, such as 15-5PH, have a high strength combined with excellent corrosion resistance. These properties make them valuable in critical industries such as defence, construction, aerospace, energy and maritime. Recent advancements in additive manufacturing (AM) technology enable the rapid and cost-effective production of components. In the case of 15-5PH components manufactured using wire arc additive manufacturing (WAAM), the as-deposited mechanical properties are not suitable at present for industrial applications. This paper explores the mechanical properties of this process and alloy combination without post weld heat treatment with the aim of eventual adoption in this condition by industry. The impact of weld heat input on the microstructure and mechanical properties of stainless steel 15-5PH produced using WAAM was investigated. The microstructure was examined using hardness testing in addition to optical and electron microscopy. Furthermore, mechanical properties were measured with tensile and impact testing. Investigations were conducted on material produced using weld heat inputs of 0.223 kJ/mm and 0.565 kJ/mm. These results indicate that reducing the weld heat input leads to a minor decrease in strength but an 80% increase in impact toughness. This reduction in weld heat input is correlated with a 50% reduction in volume fraction of δ-ferrite while also noting a 55% increase in carbide precipitates. In addition, the fracture surfaces were predominantly cleavage or quasi-cleavage in morphology. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) of 1.4614 and 1.4543 maraging stainless steels is characterized with fine structural TEM-ASTAR, hydrogen electrochemical permeation, thermodesorption and tensile testing (with slow strain rate during H cathodic charging) experiments. Both solutions annealed and 550 °C aged states are studied. When aged, 1.4614 grade contains nanometric hexagonal Ni3Ti precipitates whereas 1.4543 grade contains three families of nanometric precipitates, namely, hexagonal Ni3Ti, non fcc-rich Cu and G-phase rich in Si, Ti and Ni with cube-cube relations with martensite. From the permeation and thermodesorption results, it appears that austenite and nanometric precipitates seem to constitute deep traps for hydrogen in both grades. From tensile tests with in situ H charging, 1.4614 and 1.4543 maraging grades show a high susceptibility to HE with relative reduction of area (RRA) strictly superior to 80% for both metallurgical states. The presence of retained austenite does not seem to bring any HE resistance because of its transformation into martensite during deformation. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) of 1.4614 and 1.4543 maraging stainless steels is characterized with fine structural TEM-ASTAR, hydrogen electrochemical permeation, thermodesorption and tensile testing (with slow strain rate during H cathodic charging) experiments. Both solutions annealed and 550 °C aged states are studied. When aged, 1.4614 grade contains nanometric hexagonal Ni3Ti precipitates whereas 1.4543 grade contains three families of nanometric precipitates, namely, hexagonal Ni3Ti, non fcc-rich Cu and G-phase rich in Si, Ti and Ni with cube-cube relations with martensite. From the permeation and thermodesorption results, it appears that austenite and nanometric precipitates seem to constitute deep traps for hydrogen in both grades. From tensile tests with in situ H charging, 1.4614 and 1.4543 maraging grades show a high susceptibility to HE with relative reduction of area (RRA) strictly superior to 80% for both metallurgical states. The presence of retained austenite does not seem to bring any HE resistance because of its transformation into martensite during deformation.

Precipitation hardening stainless steels have attracted extensive interest due to their distinguished mechanical properties. However, it is necessary to further uncover the internal quantitative relationship from the traditional standpoint based on the statistical perspective. In this review, we summarize the latest research progress on the relationships among the composition, microstructure, and properties of precipitation hardened stainless steels. First, the influence of general chemical composition and its fluctuation on the microstructure and properties of PHSS are elaborated. Then, the microstructure and properties under a typical heat treatment regime are discussed, including the precipitation of B2-NiAl particles, Cu-rich clusters, Ni3Ti precipitates, and other co-existing precipitates in PHSS and the hierarchical microstructural features are presented. Next, the microstructure and properties after the selective laser melting fabricating process which act as an emerging technology compared to conventional manufacturing techniques are also enlightened. Thereafter, the development of multi-scale simulation and machine learning (ML) in material design is illustrated with typical examples and the great concerns in PHSS research are presented, with a focus on the precipitation techniques, effect of composition, and microstructure. Finally, promising directions for future precipitation hardening stainless steel development combined with multi-scale simulation and ML methods are prospected, offering extensive insight into the innovation of novel precipitation hardening stainless steels. [ABSTRACT FROM AUTHOR]

3D-printed components have potential applications in the fabrication of complex parts because of their advantages such as low wastage and cost-effectiveness. However, the durability of additively manufactured metallic components is not comparable to that of conventionally fabricated components, owing to the defects introduced during fabrication. The effect of inclusions on the fatigue strength of additively manufactured metallic components has been extensively investigated using the Murakami model. However, the interaction between the defects and the typical microstructure fabricated by additive manufacturing is yet to be revealed, although the unusual heating history during the fabrication process considerably affects the microstructure. This study aims to reveal the synergistic effect of defects and microstructure on the fatigue strength of additively manufactured precipitation-hardened 17-4PH stainless steel. Fatigue tests were conducted on additively manufactured precipitation-hardened 17-4PH stainless steel. The fatigue limit estimated using Murakami's model revealed that the summed area of the defects with the surrounding aggregation region could provide a better prediction. The carbide aggregates, produced via heating/cooling during Powder Bed Fusion (PBF), promoted microcrack propagation. • The localized microstructure surrounding defects has carbide aggregation. • Heat treatment exaggerated carbide aggregation and reduce enhance element in matrix. • Brittle microcracks propagated from the defect promoted fatigue crack initiation. [ABSTRACT FROM AUTHOR]

Precipitation hardening stainless steels have attracted extensive interest due to their distinguished mechanical properties. However, it is necessary to further uncover the internal quantitative relationship from the traditional standpoint based on the statistical perspective. In this review, we summarize the latest research progress on the relationships among the composition, microstructure, and properties of precipitation hardened stainless steels. First, the influence of general chemical composition and its fluctuation on the microstructure and properties of PHSS are elaborated. Then, the microstructure and properties under a typical heat treatment regime are discussed, including the precipitation of B2-NiAl particles, Cu-rich clusters, Ni3Ti precipitates, and other co-existing precipitates in PHSS and the hierarchical microstructural features are presented. Next, the microstructure and properties after the selective laser melting fabricating process which act as an emerging technology compared to conventional manufacturing techniques are also enlightened. Thereafter, the development of multi-scale simulation and machine learning (ML) in material design is illustrated with typical examples and the great concerns in PHSS research are presented, with a focus on the precipitation techniques, effect of composition, and microstructure. Finally, promising directions for future precipitation hardening stainless steel development combined with multi-scale simulation and ML methods are prospected, offering extensive insight into the innovation of novel precipitation hardening stainless steels.

In the present study, effects of blade and shroud thickness profiles on the stress distribution and fatigue life of centrifugal compressor impellers are investigated. Impeller geometry is generated based on an available data of a single-stage centrifugal compressor and is simulated in actual operating conditions. Pressure distribution on the impeller blades is obtained using Computational Fluid Dynamics (CFD) simulation which is then incorporated into Finite Element (FE) structural analysis. Equivalent stress and total deformation contours on the impeller are employed to pinpoint critical areas and maximum stress values. Simulations are performed for multiple cases with various shroud and blade thickness values to capture the role of these important parameters in aeromechanical behavior of the structure. Furthermore, fatigue stress amplitude limit and fatigue-life are evaluated based on the results of the FE analyses. It will be demonstrated that semi-open configuration is the most desirable design from mechanical stress and fatigue-life viewpoints. For shrouded impellers, it is shown that the mechanical stress increases and fatigue life decreases with increasing the blade thickness while for the shroud thickness, there exist an optimal point with minimum stress level and maximum fatigue life. The methodology and results of this paper can be employed for other impellers with different geometries and operating conditions to find the optimal design points from the structural mechanics perspective. • A centrifugal compressor impeller is simulated in actual operating conditions using combination of CFD and FE analyzes • Stress and deformation distribution are obtained for various blade and shroud thickness cases. • Effects of shroud and blade thickness profiles is investigated on maximum equivalent stress and maximum total deformation. • Stress amplitude limit and fatigue-life are calculated for the impeller under different geometrical conditions. • An optimal shroud thickness is found which leads to the smallest maximum stress and highest fatigue-life. [ABSTRACT FROM AUTHOR]

In order to investigate the recrystallization behavior of peened surface deformation layer of precipitation hardening stainless steel, a classic x-ray diffraction line profile analysis, Voigt method, was carried out on peened 17-4PH with different isothermal annealing temperatures. The activation energy of domain boundary migration (Qa) and the activation energy of microstrain relaxation (Qb) were calculated by regression analysis in different annealing temperature conditions. The results show that the value of Qa decreases with annealing temperature increasing, which is due to the influence of precipitation (ε-Cu) size on the movements of grain and subgrain boundaries. The maximum growth rate of ε-Cu particles occurs during 400 to 500 °C interval. Compared with growth behavior of domain size, microstrain relaxation behavior is less sensitive to precipitation particle size. The effects of annealing temperature and time on dislocation density are both significant when annealing temperature is lower than 500 °C. However, the effect of annealing temperature on dislocation density becomes insignificant when annealing temperature is higher than 500 °C. 300 °C annealing temperature only leads to the microstrain relaxation but nearly cannot lead to the domain size growth even if prolonging annealing time. Microstructure enhancement effect still exists in plastic deformation layer when 300 °C annealing temperature lasts for 60 min but nearly disappears when 600 °C annealing temperature lasts for 20 min. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of a duplex plasma nitriding followed by an oxidizing stage process (which is also referred as oxy-nitriding) on the corrosion behavior of a 17-4PH precipitation hardening stainless steel. The formation of both, expanded martensite (b.c.t. α′-phase) and chromium oxide (type CrO) in the subsurface of oxy-nitrided samples at specific controlled conditions, leads in a noticeable increasing in the time-to-rupture during the sulfide stress cracking test, in comparison with an untreated reference sample. Oxy-nitriding improves the corrosion performance of the alloy when it is immersed in solutions saturated by sour gas, which extends the application potential of this type of steel in the oil and gas extraction and processing industry. The presence of the oxy-nitrided layer inhibits the corrosion process that occurs in the near-surface region, where hydrogen is liberated after the formation of iron sulfides, which finally produces a fragile fracture by micro-crack propagation; the obtained results suggest that oxy-nitriding slows this process, thus delaying the rupture of the specimen. Moreover, oxy-nitriding produces a hard, sour gas-resistant surface, but do not significantly affect the original chloride ion solution resistance of the material. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the tribological behavior and adhesion of SiNx films deposited by PACVD on nitrided and non-nitrided Corraẍ PH stainless steel were evaluated. The films were characterized by FTIR and EDS, hardness was assessed with a nanoindenter and the microstructure was analyzed by Optical Microscopy, SEM and FIB. To evaluate the tribological behavior, fretting and linear sliding tests were performed using WC and alumina balls as counterparts, and the adhesion of the SiNx films was characterized using the Scratch Test and Rockwell C indentation methods. Erosion tests were conducted in sea water and sand flux. Corrosion behavior was evaluated by the Salt Spray Fog Test. The film reached a hardness of 2300 HV and a thickness of about 1.4 microns. The duplex coated sample had a better tribological behavior than the simple coated sample, the nitrided layer allowed a graded interlayer which improved the wear resistance. Regarding the film adhesion, the duplex coating had an acceptable adhesion; the nitrided layer reduced the interface stress and enhanced the adhesion. Additionally, the films evidenced good corrosion resistance in a saline environment. [Copyright &y& Elsevier]