PH Stainless Steel Research Articles

Smoothed Particle Hydrodynamics Approach for Simulation of Non-Newtonian Flow of Feedstocks Used in Powder Injection Molding

The present work aims to explore the ability to simulate flow patterns and the velocity field in the powder injection molding (PIM) process using the smoothed particle hydrodynamics (SPH) method. Numerical simulations were performed using the DualSPHysics platform. A feedstock formulated from 17-4 PH stainless steel powder (60 vol. % of powder) and a wax-based binder system was prepared to experimentally obtain its rheological properties that were implemented in DualSPHysics using two different viscosity models. The numerical simulations were calibrated, and then validated with real-scale injections using a laboratory injection press. During the calibration step, the feedstock flow momentum equation in the DualSPHysics code was modified and boundary friction coefficients at different injection rates were adjusted to create a frictional effect. During the validation step, these calibrated conditions were used to simulate the flow behavior into a more complex shape, which was compared with experimental measurements. Using an appropriate boundary friction factor, both the frictional effect of the boundaries and the stability of the numerical solution were taken into account to successfully demonstrate the ability of this meshless SPH method. The flow front length and feedstock velocity obtained in a complex cavity were satisfactorily predicted with relative differences of less than 15%.

A Review of the Mechanical Properties of 17-4PH Stainless Steel Produced by Bound Powder Extrusion

17-4PH Stainless Steel is a mechanically high-performing alloy that is widely used across chemical and mechanical processing industries. The alloy is conventionally fabricated by cast methods, but emerging additive manufacturing techniques are presently offering an economic, efficient, and environmentally friendly alternative. Bound Powder Extrusion (BPE) is a relatively new additive manufacturing technique that is used to fabricate three-dimensional, free-form components. Investigation into the mechanical properties and behavior of 17-4PH stainless steel fabricated by BPE is vital to understanding whether this technique proposes a competitive substitute to the cast alloy within industry. Published literature has investigated the as-fabricated mechanical properties, microstructure, porosity, and post-processing heat treatment of the BPE alloy, with limited comparison evident among the papers. This paper, therefore, aims to review published findings on the mechanical properties of 17-4PH stainless steel produced by additive manufacturing techniques, with a key focus on BPE. It is important to highlight that this review study focuses on the MetalXTM 3D printer, manufactured by Markforged. This printer is among the widely utilized BPE 3D printers available in the market. The key results, together with the impact of post-heat treatments, were discussed and compared to provide a more comprehensive picture of the patterns that this alloy presents in terms of its microstructure and mechanical properties. This enables the manufacture of components relative to desired material performance, improving overall functionality. A comparison of yield strength, ultimate tensile strength (UTS), Young’s modulus, ductility, and hardness was made relative to microstructure, porosity, and density of published literature for the as-fabricated and post-heat-treated states, identifying areas for further research.

Moisture Effects on Qualities and Properties of Laser Powder Bed Fusion (LPBF) Additive Manufacturing of As-Built 17-4PH Stainless Steel Parts

Laser powder bed fusion (LPBF) has the advantages of high resolution and geometric freedom but can be susceptible to process failures and defects caused by inappropriate process parameters and powder conditions. This study aims to reveal and quantify the moisture effect on the qualities and properties of as-built parts with various process parameters. The results showed that the density was decreased by 7.86% with humid powder (60.0% relative humidity (RH)) compared to dry powder (3.4%RH). Expectedly, the observed low density led to the property degradation in the hardness, yield strength (YS), and ultimate tensile strength (UTS) of the humid powder by 11.7, 15.02, and 21.25%, respectively, compared to that of dry powder (3.4%RH). Interestingly, the elongation at break of the parts fabricated with humid powder (60.0%RH) was increased by 2.82%, while their YS and UTS were decreased significantly. It seems that the water molecules on the powder surface hindered the reaction between the N2 shielding gas and melted powder, which resulted in the reduction in the austenite (γ) phase by up to 4.05 wt.%. This could be mainly responsible for the decrease in both the YS and UTS of the humid powder by approximately 100 and 150 MPa, respectively. This study demonstrates that the moisture of the metal powder used for LPBF should be carefully controlled to ensure desirable as-built qualities and properties.

Effect of heat treatment on microstructure and mechanical properties of 17-4PH stainless steel manufactured by laser-powder bed fusion

The 17-4 precipitation-hardened (PH) stainless steel was prepared by laser-powder bed fusion (L-PBF), and the effects of different aging temperatures on the microstructures and properties of 17-4PH stainless steel were systematically studied. The results show that the 17-4PH stainless steel prepared by laser powder bed fusion requires a solid solution treatment in order to obtain the lath martensite structure, and then the niobium carbides and ε-Cu phase nanoparticles were precipitated by aging treatment to improve the strength of 17-4PH stainless steel. When the aging heat treatment parameter is 450 °C/5 h, the mechanical properties of the 17-4PH stainless steel are better, and the ultimate tensile strength (UTS) and elongation (El) are 1387 MPa and 7.3%, respectively. Compared with the as-printed 17-4PH stainless steel, the ultimate tensile strength of aging heat treatment exhibits an increase of 25.2%, and then, as the increase of aging temperature, the niobium carbides and ε-Cu precipitation phase become coarser, resulting in a decrease in the strength of 17-4PH stainless steel and an increase in plasticity.

Analysis of Cracks in Solution-Treated AISI 17-4PH Stainless Steel Observed During Machining of Aerospace Component

Analysis of Cracks in Solution-Treated AISI 17-4PH Stainless Steel Observed During Machining of Aerospace Component

Microstructure and Defect Analysis of 17-4PH Stainless Steel Fabricated by the Bound Metal Deposition Additive Manufacturing Technology

Metal additive manufacturing (AM) technologies can be classified according to the physical process involving the raw material as fusion-based and solid-state processes. The latter includes sintering-based technologies, which are aligned with conventional fabrication techniques, such as metal injection molding (MIM), and take advantage of the freeform fabrication of the initial green part. In the present work, 17-4PH stainless steel samples were fabricated by material extrusion, or rather bound metal deposition (BMD), a solid-state AM technology. The powder-based raw material was characterized together with samples fabricated using different angular infill strategies. By coupling different characterization technologies, it was possible to identify and classify major properties and defects of the raw material and the fabricated samples. In addition, microstructural modifications were found to be linked with the mesostructural defects typical of the BMD solid-state additive manufacturing technology applied to metals.

Development of Multiple Ceramic Coatings on Porous Tubular Metal Support

Micro-tubular metal supported Solid Oxide Fuel Cell (MS-SOFC) has many advantages over traditional ceramic supported SOFC, such as greater mechanical robustness, better thermal and redox cycling along with low cost of starting material. Among the multiple MS-SOFC fabrication methods, the one involving sequential dip-coating followed by co-sintering has the potential to reduce the fabrication cost further, making it attractive from a commercial production standpoint. However, the co-sintering route is challenging because it requires constrained sintering conditions, high temperatures, and inert atmosphere. Other challenges with the co-sintering route are delamination and cracking of layers, warping of cell, diffusion of Fe and Cr away from metal support, diffusion of Ni from anode, coarsening of Ni in the anode, and lack of complete densification of YSZ electrolyte even at temperatures as high as 1350 °C.In this work, we developed a new ceramic multilayer design on a porous tubular 3D-printed metal support. Scandia Stabilized Zirconia (SSZ) and, Ni and SSZ (Ni-SSZ cermet) were used as electrolyte and anode, respectively. Stainless steel 17-4 PH was identified as the metal support material due to its matching coefficient of thermal expansion with SOFC ceramic materials, low cost and corrosion resistance nature. The dip coating steps and the co-sintering process were optimized so that they could be adopted for a cost-effective fabrication of MS-SOFC. The binder-burnout step was optimized to prevent cracking of the multilayers during the co-sintering process. To avoid delamination and to impede the inter-diffusion of elements, a coating of an intermediate layer made of 17-4 PH stainless steel+Ni+YSZ was introduced between the metal support and the succeeding layers. Preliminary results suggest that the intermediate layer has a potential to prevent delamination and inter-diffusion. Introduction of the debinding step and optimized sintering profiles resulted in the formation of the uniform and dense electrolyte coating. However, certain cell warping was observed after electrolyte sintering, suggesting further improvement is still needed in the support design and ceramic processing.

Thermo-hydraulic performance evaluation of a NACA 63-015 heat exchanger with shark denticles as surface textures

In this study, the effect of using bio-inspired surface texturing as a technique to further enhance the efficiency of a single Plate Fin Heat Exchanger (PFHX) was investigated experimentally. By using biomimicry across disciplines, the denticle, which is a body adaptation from shark skin for enhanced hydrodynamics, was identified as a surface texture to be used on the fin of a PFHX. A smooth NACA 63-015 PFHX (HX0) was used as baseline for thermo-hydraulic performance comparisons. Initially, three PFHXs (HX1, HX2 and HX3), consisting of arrays of denticles upscaled to different scale factors, were designed and printed in ABS plastic to evaluate Additive Manufacturing (AM) limits. By analysing optical images and pressure drop results, HX2 was found to be the best performing array in terms of printing quality and pressure drop performance. Both HX0 and HX2 were then printed in stainless steel 17-4PH by using a Markforged Metal X printer, and then experimentally compared to evaluate their flow and heat transfer behaviours. Results demonstrate that the addition of shark denticles as surface textures on HX2 shifted the onset of turbulence from a fully turbulent to a transitional regime compared to HX0. For Re < 5.7×104, the friction factor for HX2 was less than that of HX0, while at higher Re values the trend was reversed due to increases in skin friction drag. At Re = 3.9×104, the friction factor for HX2 was 56% lower than that of HX0. Overall, a mean improvement of 14% in Nusselt number was noted for HX2 compared to HX0. Further, a mean thermo-hydraulic performance of 1.11 was noted for HX2 for the range of tested Re values, which demonstrated that the addition surface textures in the form of shark denticles to a NACA 63-015 profile yielded a more efficient PFHX compared to a smooth one.

Heat treatments of 17-4 PH SS processed by SLM to improve its strength and biocompatibility in biomedical applications

This research investigates the impact of heat treatment on the microstructure, hardness, and corrosion resistance of 17-4 PH SS (stainless steel) processed by Selective Laser Manufacturing (SLM) in Phosphate Buffer Solution (PBS) and compared to its commercial wrought counterparts. The SLM process produced a segregated microstructure with significant variations in composition and phases. Post-process heat treatment resulted in a uniform and reproducible microstructure in the SLM samples with a significant improvement in corrosion resistance in the solubilised samples and a remarkable hardening in the solubilised and aged samples. Additionally, heat-treated SLM samples showed no relevant release of metallic elements to PBS electrolyte after 75 days of immersion, indicating its potential use as a biomaterial. The study concludes that the manufacturing process used to produce SS have a significant impact on its properties, moreover, post-build treatment improve microstructure providing uniformity which positively impact in the corrosion resistance. The electrochemical results also suggest that, after homogenization, the additively produced 17-4 PH SS shows a better behaviour in biological environment than the wrought 17-4 PH SS.

Effect of laser energy density on surface morphology, microstructure and mechanical behaviour of direct metal laser melted 17-4 PH stainless steel

Abstract The surface and microstructural characteristics of 3D printed parts play a significant role under mechanical loading. The authors have explored the effect of laser energy densities on the surface morphology, microstructure and mechanical behaviour of 17-4 precipitation hardened stainless steel fabricated under the direct metal laser melting technique. The considered processing parameters were laser energy density and its technical parameters: laser power, layer thickness, hatch spacing and scanning speed. The mechanical and metallurgical properties of the as-printed samples appeared better than the wrought counterpart due to the higher densification level (99.74 %) induced by the rotating scanning strategy. X‐ray diffraction revealed the presence of both the martensitic α phase and austenitic γ phase in the as-printed sample. There is no significant anisotropy in the mechanical behaviour as the build direction has a random texture with a fine columnar grain structure. The high laser energy density with low layer thickness results in an excellent surface finish. The tensile strength (1180 MPa) and the elongation for the as-printed sample (45.0 %) were considerably more significant than that for the wrought sample (1160 MPa and 26.0 %), which is attributed to the combination of low and high-angle boundaries, as confirmed by the electron backscatter diffraction results.

Variability in mechanical properties of additively manufactured 17-4 PH stainless steel produced by multiple vendors: insights for qualification

Variability in mechanical properties of additively manufactured 17-4 PH stainless steel produced by multiple vendors: insights for qualification

In Situ Characterization of 17-4PH Stainless Steel by Small-Angle Neutron Scattering.

17-4PH martensitic steel is usually used as valve stems in nuclear power plants and it suffers from thermal aging embrittlement due to long-time service in a high-temperature and high-pressure environment. Here, we characterized the evolution of microstructures at the nano-scale in 17-4PH steel by in situ small-angle neutron scattering (SANS) with a thermo-mechanically coupled loading device. The device could set different temperatures and tensile so that an in situ SANS experiment could dynamically characterize the process of nanoscale structural changes. The results showed that with increasing thermal aging time, the ε-Cu phase precipitates and grows as the temperature is 475 °C and 590 °C, and the ε-Cu phase is spherical at 475 °C but became elongated cylinders at 590 °C. Moreover, the loading stress could aid in the growth of the ε-Cu phase at 475 °C.

3D printing of magnetostrictive property in 17/4 ph stainless steel

Additive manufacturing (AM) of metallic alloys significantly advances diverse areas of science/engineering with a prosperous future trend. Although this technology is also very attractive for smart materials development, the creation of a pre-programmed “4th dimension” property to appear in response to external stimuli represents an important challenge. Here we report on 3D printing of stainless steel based magnetic alloy and detail the ways to optimize the magnetisation and magnetostriction to be used for actuation and sensing. By controlling the printing parameters and sintering process, we are able to tune the magnetic and magnetoelastic properties of the 17/4 ph stainless steel, demonstrating material fabrication multi-function with a cost effective advantage. The stainless steel 17/4 ph samples in the as-printed (AP) and sintered steel (SS) stages are compared. In the developed SS sample, a remarkable increase of 18% in saturation magnetisation yet with 12.6 % lower coercivity was achieved. Moreover, the 54% higher magnetostriction was developed for the SS sample compared to the AP sample. Plus, the difference in anisotropy energy K1 was also lower for the SS sample. The structural and magnetic properties control are reported at each stage of the printing process, demonstrating development and optimization prospects of 3D printable metallic sensors and actuators.

Investigation of Evolution of Inclusions in 15-5PH Stainless Steel During Hot Compression Using 3D X-Ray Microscopy

Investigation of Evolution of Inclusions in 15-5PH Stainless Steel During Hot Compression Using 3D X-Ray Microscopy

Onto the role of copper precipitates and reverted austenite on hydrogen embrittlement in 17-4 PH stainless steel

High strength materials are of interest for hydrogen powered mobility where structural components can be exposed to high pressure (350–700 bars) of dihydrogen. However, high strength stainless steels such as 17-4 PH grade with a martensitic matrix are known to be more prone to hydrogen embrittlement (HE). The mechanisms affecting this type of grade have not been completely elucidated yet. In particular, in this work, the role of copper rich precipitates (Cu-pp) and reverted austenite (γrev) on mechanical behavior in presence of hydrogen was investigated. At first, advanced structural characterizations (Synchrotron-XRD, ACOM/TEM) were performed on different metallurgical conditions. Then, hydrogen trapping ability of Cu-pp and γrev was investigated using thermal desorption spectroscopy (TDS). Hydrogen embrittlement susceptibility was qualified through slow strain rate tensile testing. The results showed that the formation of tiny Cu-pp (< 10 nm) during ageing was deleterious for the HE resistance of the steel, since it increased the ultimate tensile strength. In addition to their role in the steel hardening, tiny Cu-pp actively trapped hydrogen at the Cu-pp/matrix interfaces. The nature of Cu-pp/matrix interfaces, which affects their surface energy and therefore the binding energy of hydrogen, impacted clearly the HE resistance. In particular, TDS experiments showed that tiny ‘slightly coherent’ Cu-pp acted as a low energy hydrogen trap contrary to tiny ‘incoherent’ fcc Cu-pp which strongly trapped hydrogen. The former was found to have a deleterious effect while the latter had a rather beneficial effect. Besides, a high fraction of reverted austenite was beneficial for the HE resistance since it softened the material, and trapped rather strongly hydrogen at the γrev/matrix. The fcc (Cu-pp or γrev)/martensitic matrix interfaces seemed to play a major role in hydrogen trapping in 17-4-PH stainless steel. When hydrogen is tightly bound to these interfaces, it happens to reduce the hydrogen embrittlement susceptibility of the material, 17-4 PH that is generally ‘H fragile’ because of its martensitic matrix.

Investigation of machinability indicators during sustainable milling of 17-4PH stainless steel under dry and MQL environments

17-4PH steel, which has the perfect combination of corrosion resistance and high mechanical properties, is especially preferred in defense and aerospace applications, but its machinability is poor. Thus, an extensive research has been conducted on its milling under sustainable cutting regimes (dry and minimum quantity lubrication_MQL) to contribute to both more efficient use and sustainable machining. First, the changes in resultant cutting force ( Fr), the average surface roughness ( Ra), the mean roughness depth ( Rz) and total energy consumption ([Formula: see text]) were investigated after the experiments performed by applying the L18 orthogonal array. Subsequently, machining conditions were optimized for the minimization of machinability indicators with the Taguchi-based grey relational analysis technique. Finally, the predictive models for these indicators were developed by regression analysis. The order of importance for Fr and [Formula: see text] was the depth of cut and feed, while for Ra and Rz this ordering was found to be feed rate and cutting regime. Short curved chips formed in MQL cutting regime contributed positively to the minimization of the considered machinability indicators. Although the energy consumption due to spindle speed increased with increasing cutting speed in dry cutting environment, the decrease in material strength resulted in a decrease in [Formula: see text]. Since the cooling effect of MQL reduces the cutting temperature, material softening and thus the expected decrease in cutting resistance could not be achieved, so the decrease in [Formula: see text] was not as much as dry cutting. Optimum machining conditions were determined as MQL cutting regime, the cutting speed of 120 m/min, the cutting depth of 0.5 mm and feed rate of 0.05 mm/rev. The determination coefficients of the predictive models developed by regression analysis showed that these models can be used safely in up milling.

Suppressing the deformation of as-built parts by optimizing the structure of boss bottom in material extrusion of metals

Compared to other metal additive manufacturing technologies, material extrusion (ME) of metals offer several advantages, including low investment cost, safety, simpleness and so on. However, part deformation caused by material shrinkage will reduce its productivity. To address this issue, a method was provided to suppress the deformation by optimizing the boss bottom. The stress field of the model was analyzed using finite element model (FEM), and self-made equipment was used to print the as-built part using 17-4PH stainless steel powder and polymer. The result revealed that the bottom structure could effectively change the stress field of the model and prevent deformation. The optimized structure of the boss bottom could widen the process window and save up to 61.82 % of materials. In conclusion, it provided a new perspective for forming as-built parts without deformation in ME of metals.

Influence of bio-inspired surface texture of additively manufactured 17-4 PH stainless steel adherends on the strength of adhesively bonded joints

The bonding potential of as-printed additively manufactured stainless steel is largely unknown, and the use of additional hierarchical bio-inspired surface texture has not yet been explored or characterized. In this study, it is demonstrated with the use of Selective Laser Melting (SLM) that a hierarchy of three surface features at different length scales can greatly improve the shear strength of metal-metal adhesive joints. The intrinsic stochastic texture of the SLM as-printed surface showed a high contact angle and a mixed failure with a dominance of adhesive failure. However, enhancing the as-printed surface with the Tree Frog (TF) and Fish Scale (FS) bio-inspired textures produced super-wetting surfaces, significantly improving the shear strength due to the synergistic effect of mechanical interlocking and physical adsorption adhesion mechanisms, resulting in mixed failure. The results indicated that the interfacial bonding performance was in line with the super-wetting behavior and was higher for the samples with a hierarchy of three surface features. The highest increase in bond strength was found for the tree frog hierarchical hexagonal texture (+70% compared to the as-printed texture). In contrast, abrasion of the as-printed surface with P1000-grit paper significantly reduced the surface roughness and increased the water contact angle, resulting in the lowest shear strength.

Localized corrosion of 15–5 PH and 17–4 PH stainless steel in NaCl solution

Localized corrosion of 15–5 PH and 17–4 PH stainless steel in NaCl solution

Selective Laser Melting Process Parameter Optimization on Density and Corrosion Resistance of 17-4PH Stainless Steel

Selective Laser Melting Process Parameter Optimization on Density and Corrosion Resistance of 17-4PH Stainless Steel