Key Engineering Materials Vol. 833

Abstract: Metal powder is used in the Powder Metallurgy (PM) application process. Most of the metals used in the PM are stainless steel made by the gas atomization process. This study uses the free fall gas atomizer. The material was used to produce the metal powder from various forms of stainless steel 304 raw material, which is melted in an electric induction furnace. This method is very practical to be applied in the large-scale metal processing industries. While the gas pressure variation results show that metal powder with a smaller size will be produced more using high gas pressure. The free fall gas atomizer has successfully produced stainless steel 304 metal powder with the size <40 μm and have a spherical shape. The well-rounded sphericity for 8 bar pressure, 10 bar pressure, and 12 bar pressure are 61.1%, 41.7%, and 37.5% respectively. It can be concluded that 12 bar pressure produces the smallest size range of powder about <40 µm with the most quantity about 1.11%wt, followed by 10 bar pressure about 0.41%wt and 8 bar pressure about 0.07%wt.

Abstract: The objective of this study is to investigate and determine the effect of the stand-off distance (distance between the welded plates) on the mechanical properties of the Tungsten Inert Gas (TIG) welded joints. Butt TIG welding was performed for 316 stainless steel (SS) by using different pre welding stand-off distances with fixing the other parameters (thickness of welded plates, voltage, current, groove shape, and scanning speed). The influence of the stand-off distance parameter was examined by using tensile test, hardness test in the three different regions (base metal, heat effected zone, and molten zone), non-destructive testing (including visual inspection, liquid pentrant and X – ray) and microscopic examinations. Results show that the stand-off distance is one of the most important geometrical parameters of the Butt welded joints to end by good mechanical properties. It is found that the optimum stand-off distance was about 1 mm (shows the highest hardness results), but still there were some defects in some spots in the molten metal zone which caused a decrease in the hardness values in these locations. The 2 mm stand-off distance shows reasonable results, and the worst case was recorded for the 0 mm stand-off distance condition. Generally the hardness values of the heat affected zone in all conditions were the highest when compared to both metal welding zone and the base metal zone.

Abstract: The present work is aimed at developing superhydrophobic coatings on AA 7075 using two different fatty acids namely Stearic acid and Myristic acid. The coating was developed by initially etching the substrate in 1 M NaOH solution at a temperature of 70 °C for 10 hours, followed by passivating in 0.01 M ethanolic stearic acid and 0.01 M ethanolic myristic acid for different durations of passivation time. The coated samples were further investigated for their surface morphology, wettability and corrosion resistance. The contact angle and surface morphology of the developed coatings were assessed by contact angle goniometer and scanning electron microscopy (SEM) respectively. The corrosion behavior of the coatings was studied in 3.5 Wt. % aqueous NaCl solution by potentiodynamic polarization test (PDP). Passivation using fatty acids resulted in alteration of the surface morphology, which resulted in the increase of the contact angle exhibiting superhydrophobic nature, which also enhanced the corrosion resistance of the alloy.

Abstract: The effects of Cu addition of 0.38, 3.82, and 6 wt. % in Al-7Si-4Mg alloy on hardness and age hardening response were discussed. Samples were solution treated at 495 °C for 2 h, quenched, and aged at 130 °C for 0 to 498 h. Characterization included hardness test, microstructural observation by an optical microscope (OM) and Scanning Electron Microscope (SEM) combined with Energy Dispersive X-Rays Spectroscopy (EDX), as well as Simultaneous Thermal Analysis (STA) testing. The results showed an increased in as-cast hardness along with addition of Cu. Peak hardness increased to 64.47, 65.8, and 70.1 HRB by addition of 0.38, 3.82, and 6 wt. % Cu, respectively. The addition of Cu promoted the formation of Al₂Cu and Al₅Cu₂Mg₈Si₆ which contributed to higher as-cast hardness. Formation of GP-zone, θ”, and θ’ was observed after ageing at 48, 240, and 290 °C, respectively and no effects of Cu was detected on the formation temperatures of the precipitates.

Abstract: Thermal spray is often applied on steam turbine blade leading edge to increase abrasion resistance. Stellite 1 is one of the commonly used material as it is known to wear protection against abrasion, oxidation, and corrosion at elevated temperature. This paper evaluated microstructure, hardness, and surface cracks of HVOF-sprayed Stellite-1 coating applied to the steam turbine blade. Optical microscopy reveals that all cracked and no-cracked coating have similarity in the microstructure. Typical 1.89% porosity was found on the specimen. The unbonded interface between the coating and substrate was also located to about 38% in length. All samples have 4.1% different in coating hardness with an average value of 718 HV. Coating thickness has a relation with the amount of porosity produced. Analysis of variance showed that both of the thickness and the hardness of coating are influencing the coating in making the penetrant indication. The microstructure showed a less dense coating with apparent porosity and unbonded interface when compared with other HVOF experiment. Blasting with excessive pressure and or the improper angle have made an alumina deposit at and below interface which may interfere with coating adhesion. Chromium Carbide and Silicon Oxide are formed near the porosity of coating.

Abstract: ASTM T22 (Fe-2.25Cr-1Mo), 347HFG (Fe-18Cr-11Ni), and 310H (Fe-25Cr-19Ni) steels were reacted with CO₂-0.3SO₂-6O₂ mixed gas. During corrosion at 700-800 °C for 20-100 h, 347HFG (Fe-18Cr-11Ni), and 310H (Fe-25Cr-19Ni) steels had good protective Cr₂O₃ oxide scale. Corrosion rates increased progressively as the corrosion temperature and time increased. Corrosion resistance increased in the order of T22, 347HFG, and 310H, suggesting that the alloying elements of Cr and Ni beneficially improved the corrosion resistance of steels. Basically, Fe oxidized to Fe₂O₃, and Cr oxidized to Cr₂O₃, some of which further reacted with FeO to form FeCr₂O₄.

Abstract: The article presents the results of numerical and experimental studies of stress-strain curves of 1D-reinforced polymer composite materials based on hollow porous fibers and epoxy matrix. The two-scale nature of the composite under research was taken into account. A surrogate easily parameterized model based on Bezier curves was developed and used to approximate the stress-strain curve of ductile material. The calculations were performed using reversible homogenization and finite element methods, which were implemented in computational subsystem of DCS GCD. Representative volume elements of the investigated materials were created using the geometry generating subsystem of DCS GCD. Test samples were made using three-axis milling machine and compression tests were carried out. Computational results of effective stress-strain curves determination were obtained and compared with experiments.

Abstract: The paper presents a mathematical model of a finite element for modeling imperfect interface conditions for two contacting surfaces. The element is used in the numerical implementation of the Asymptotic Averaging Method (AAM) for the determination of effective elastic properties of composite materials under investigation. Numerical experiments are carried out to calculate the elastic properties taking into account the adhesion layer using a displacements field jump condition at the phase boundary. Results are compared with adhesion modeling using an additional bulk phase.

Abstract: This study focused on the physical properties of latex extracted from five species of Artocarpus J.R.Forster & G.Forster, namely: A. altilis (Parkinson) Fosberg, A. blancoi Merr, A. camansi Blanco, A. heterophyllus Lam., and A. ovatus Blanco as potential natural adhesives. Surface morphology showed that all five Artocarpus spp. have no specific forms, but otherwise flexible and viscoelastic. Contact angle measurements showed that all samples of Artocarpus spp. were hydrophilic with low contact angle values owing to the contents of natural source of the latex. FTIR analysis matched all Artocarpus latex samples to that of Polyvinyl acetate. Highest resin content was found on A. ovatus with all the species containing natural resin. It was also confirmed that out of the three stress strain analyses, A. camansi had the highest values for tensile strength, A. ovatus had the highest values for Young’s modulus of elasticity and the highest percentage elongation values belonged to A. heterophyllus. Adhesive shear strengths with maximum force values were highest in A. ovatus. Through cluster analysis, out of the eight variables tested A. heterophyllus was the outgroup being attributed to its latex gum-like property. All the above tests and analyses suggested that latex of all five Artocarpus spp. were similar in characteristics to polymer adhesive. Among which A. camansi and A. ovatus exhibited high results on adhesive strength tests.

Abstract: The objective of this paper is to study the mechanical, physical, and wear properties of the 3D printed Polylactic acid (PLA) materials. Tensile Strength, Modulus, and Ductility are investigated as a function of the infill percentage and the printing direction. Shioe D hardness versus infill percentage was investigated. Weight loss versus rolling contact time was investigated to measure the wear properties of the parts. The 3D printed parts have shown a great influence by the infill percentage. Such observation was not found in terms of printing direction. The weight loss due to rolling contact was a function of rolling contact time.