Key Engineering Materials Vol. 982

Abstract: Surface and sub-surface related degradation of steels can be minimized using suitable surface coatings. High entropy alloys (HEA) are prominent and emerging materials among many coating materials. The current study investigates the effect of heat treatment of HEA coating on mechanical, metallurgical, and corrosion properties. The HEA coatings on SS304 steel were deposited using a High-Velocity Oxy-Fuel (HVOF) thermal spray process. The developed coatings were furnace heat treated at 700 °C, 900 °C, and 1100 °C, respectively, and their performance was benchmarked with the as-sprayed coatings. The metallurgical, mechanical, and microstructural analyses were performed using X-ray diffraction (XRD), Nanoindentation, Scratch test, and Field Emission Scanning Electron Microscope (FESEM) techniques. The corrosion response of the as sprayed and heat-treated coatings were recorded using a Potentiostat. The results indicated that as-sprayed coatings consisted of a single-phase BCC solid solution; however, the single-phase changed to a dual dual-phase system after heat treatment (BCC+FCC). The 900 °C heat-treated HEA coating exhibited superior mechanical and corrosion properties. But those characteristics started diminishing when the heat treatment temperature exceeded 900 °C. The introduction of the new FCC phase softened the coating, thereby leading to the evolution of microcracks in the coating. These micro-cracks acted as channels for electrolyte diffusion and further corroded the coatings. The current study surmised that HVOF-sprayed HEA coating should not be heat treated at above 900 °C.

Abstract: Titanium alloys are highly valued in various industries due to their exceptional qualities. This study examines how the build orientation affects the mechanical and fatigue properties of Laser Powder Bed Fusion (PBF-LB) produced Ti6Al4V, without heat treatment. The research shows mechanical properties vary based on build orientation with vertically oriented specimens exhibiting the highest yield and tensile strengths, while vertical orientation excels in ductility, measured through elongation at break. Impact toughness sees variations with horizontal orientation performing the best. However, build orientation has minimal influence on flexural bending fatigue performance. Both diagonal and vertical orientations show similar fatigue limits at around 40 MPa. Dry electropolishing proves to be an effective technique, significantly enhancing fatigue performance with limits stabilizing at about 150 MPa. This study underscores the importance of considering build orientation in PBF-LB manufacturing for specific mechanical and impact properties and the potential of dry electropolishing in improving the fatigue performance of Ti6Al4V components. These findings offer valuable insights for the additive manufacturing industry, aiding in the optimization of Ti6Al4V component production.

Abstract: The study investigates the impact of severe shot peening on the fatigue strength of wire arc additively manufactured carbon steel. Initial characterization revealed a material with prominent equiaxed grains and large grain sizes. However, the application of SSP induced a considerable reduction in grain size, particularly on the surface, consequently enhancing the surface's strength and hardness, yet leading to an inhomogeneous structure within the WAAM CS SSP part. Hardness measurements demonstrated a substantial impact on surface hardness, reaching a depth of approximately 0.4 mm, with a 64% increase observed due to SSP, elevating it from an average of 165 HV to a maximum of 270 HV near the surface. Tensile tests on WAAM CS and WAAM CS SSP displayed notable improvements in mechanical properties following SSP treatment. Yield strength increased by approximately 5%, and ultimate tensile strength rose by 2.5%, resulting in a peak tensile strength of 513 MPa. However, this enhancement was accompanied by reduced ductility, evidenced by decreased elongation from 44% in WAAM CS to 35% in WAAM CS SSP. Bending fatigue tests highlighted a significant enhancement in fatigue resistance due to SSP treatment. The fatigue limit increased by 21% from 190 MPa for WAAM CS to 230 MPa for WAAM CS SSP, indicating improved resistance in both low-cycle and high-cycle fatigue regimes. This enhancement in fatigue resistance is attributed to the heightened mechanical strength post-SSP treatment, suggesting a trade-off between increased strength and reduced ductility. The results demonstrate that SSP significantly enhances surface attributes, strength, and fatigue resistance of WAAM CS. This advancement bears implications for engineering applications where enhanced mechanical properties and fatigue resistance are vital, despite the induced trade-offs in material characteristics.

Abstract: The aim of this work is to evaluate the characteristics of continuous precipitates (CP) developed within the grain and grain boundary precipitates through statistical analysis of the number density and size (i.e., length and width) at varying aging conditions of AZ80 Mg alloy. Scanning electron microscopy illustrates the characteristics and features of precipitates, distinctively. The results reveal an increment of number density, whereas the reduction in the size of precipitates with decrease in the aging temperature for the varying aging times. The variation in hardness values at different aging conditions has been ascribed to this.

Abstract: IIn a geothermal environment, cathodic protection is employed to improve resistance against corrosion fatigue. However, during the cathodic reactions under applied potential, hydrogen is generated and assimilated, leading to a reduced lifetime expectancy of high-alloyed steels. The corrosion fatigue mechanism of a standard duplex stainless steel X2CrNiMoN22-5-3 (1.4462) specimen loaded with hydrogen was studied in a corrosion chamber specifically designed for the purpose, surrounded by the electrolyte of the Northern German Basin at 369 K. The microstructural reactions resulting in hydrogen incorporation significantly decrease the number of cycles to failure of the specimen. This reduction is attributed to hydrogen enhancing crack propagation and causing early failure, primarily due to the deterioration of the mechanical properties of the ferritic phase rather than corrosion reactions or corrosive degradation.

Abstract: This study investigates the impact of varied heat treatment parameters on the mechanical and metallurgical characteristics of 9254 steel. Different cylindrical specimens underwent controlled heat treatments targeting three different phases. The interplay of time and temperature was systematically explored to understand their influence on bending strength, bending deflection, hardness, and microstructural evolution. The results revealed that a partially tempered martensitic structure exhibiting an exceptional ultimate strength of 4308 MPa. Achieving this involved a heat treatment, starting at 900°C for 30 minutes, followed by rapid cooling in an oil bath, quenching at 165°C for 5 minutes, annealing at 180°C for 60 minutes, and gradual air-cooling. This treatment regimen produced a specimen with a desirable combination of mechanical properties, showcasing its potential significance in advanced engineering applications.

Abstract: Additive manufacturing, specifically Laser Powder Bed Fusion (PBF-LB), has gained prominence for its capability to produce complex near-net-shaped components. While PBF-LB offers advantages such as lightweight construction and cost-effectiveness, post-processing remains crucial to meet specific design requirements. This study investigates the post-processing technique of severe shot peening (SSP) on PBF-LB-manufactured 316L stainless steel, a material widely used for its favorable mechanical properties and corrosion resistance. The research focuses on the enhancement of bending fatigue properties through SSP treatment, examining the influence of material thickness on fatigue behavior. Comparative analysis reveals the effectiveness of SSP in significantly improving fatigue strength irrespective of variations in material thickness. Mechanical properties are explored for different thicknesses subjected to SSP treatment. Electron Backscatter Diffraction (EBSD) is employed to scrutinize the surface properties of the samples, providing knowledge on the microstructural changes induced by SSP. The study contributes to the understanding of the role of material thickness in the context of SSP treatment, offering a comprehensive exploration of the mechanical and fatigue characteristics of PBF-LB-manufactured 316L stainless steel.

Abstract: Stainless steel SS304 is extensively used in dental applications for its high strength, hardness, and corrosion resistance. However, Conventional dental joining techniques such as soldering and fusion welding, reliant on elevated temperatures and toxic fluxes, present substantial oral health risks, leading to potential health deterioration due to toxic emissions. The study proposes the utilization of a microwave hybrid heating process (MHH) for joining stainless steel SS304 (15mm × 7.9mm × 0.2mm) and pure zinc metal powder (44 µm, 99% purity), citing its enhanced efficiency, speed, precision, and diminished environmental footprint as key characteristics without fume. It explores heat processing between 30°C to 60°C and cold temperature processing from 0°C to 10°C to analyze alterations in hardness properties and microstructures. The study identified a direct correlation between temperature and microhardness, observing an increase in microhardness with rising temperatures. Optimal microhardness of 208.6 HV was achieved at 60°C during a 3 min heat treatment. Cold temperatures induced slight deformation and grain transformation, while heat treatment enhanced grain density and hardness, particularly in the strongly bonded boundary layer, with experimental and predicted values using Fuzzy logic showing promising outcomes and errors below 10%. In conclusion, the study demonstrates that achieving a specific hardness value in stainless steel joints is highly desirable for dental applications, alongside the observation of favorable microstructures. These findings underscore the potential of MHH to propel dental technology forward and promote sustainable practices while addressing environmental concerns.

Abstract: Copper (Cu) foam is a promising material that owns a high surface area that can be utilized in a thermal application. In this research, the brazing of Cu substrate to Cu foam in the sandwich configuration using Cu alloy filler foil was carried out. The foam at different pore per inch (PPI) of 15, 25 and 50 are brazed at different brazing temperatures. Mechanical and microstructure analysis were conducted to investigate a suitable brazing temperature and the best pore density of foam. The compressive strength of brazed 50 PPI foam has yielded the highest due to the highly dense interconnected branches. While the highest shear strength of brazed interface using 15 PPI foam has been recorded. The large branch size of 15 PPI foam has contributed to the sound joint between the brazed joint interface of Cu substrate and foam. Both mechanicals analysis above exhibits a highest strength at 660 °C as a brazing temperature The shear stress-strain curve of Cu substrate and foam brazed joint interface shows a brittle behaviour which accordance with the discoverable brittle phases of Cu₃P and Ni₃P using X-ray diffraction (XRD). Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX) have presented the formation of Cu₃P and Ni₃P at the brazed joint interface of Cu substrate and foam.