Key Engineering Materials Vol. 856

Abstract: Ti-based coating has been used for biomaterials to improve biocompatibility, mechanical and corrosion properties. Each coating shows unique performance depending on a variety of factors such as coating microstructure and properties as well as in-service conditions. In this study, the microstructure, surface topography, hardness, adhesion and corrosion properties of Ti and TiN films on stainless steel 316L coated by cathodic arc physical vapor deposition process (PVD) were studied. The results showed that the surface roughness of 316L increased after being coated with Ti and TiN film as evidenced by the numerous particles and voids observed on the surface of both films. The hardness of 316L coated with Ti and TiN was increased by approximately 50% and 85%, respectively. Ti and TiN coated samples showed good adhesion strength with the first critical load (LC1) of approximately 10N and 15N, respectively. However, the types of film failure for Ti and TiN were found to be different. Partial delamination with a high degree of plastic deformation was observed for Ti coating, whereas surface cracks were found for TiN coating. This finding is likely attributable to the difference in flow resistance and the amount of particles and voids observed. All samples showed a stable passive region during 7 days of immersion in Ringer’s solution. Ti film showed better corrosion resistance than TiN, which may have been caused by the effect of more voids on TiN surfaces formed by PVD coating.

Abstract: Fe-Ni based superalloys have been widely used in land-base gas turbine application. The turbine blade was in service for 50,000 h at high temperature and stresses. When subjected to long-term exposure at high temperature, the microstructure lost its best mechanical properties due to the microstructural instability. The aim of this research is to understand the effect of cooling rate on gamma (γ) grain size and gamma prime (γ’) particle size, morphology, and its volume fraction in rejuvenated Fe-Ni based superalloys. The alloys were solutionized above the γ’ solvus temperature at 1125 °C for 2 h for homogenization and cooling to room temperature at different cooling rates. The alloys were experienced with furnace cooling, air cooling, oil quenching, and water quenching. Microstructural analyses were investigated. Grain size, morphology, volume fraction of γ’ precipitates were investigated. Preliminary mechanical properties such as microhardness was conducted.

Abstract: Nickel-base superalloys are used as a land-base turbine engine due to its excellent properties at elevated temperatures. Nickel base superalloy, grade IN-738. Laser welding is commonly chosen for the refurbishment of the turbine blade. This paper aims to focus on understanding welding speed parameters in laser welding method. With constant power at 400 watts, welding speeds were varied from 1, 3, 5, and 8 mm/s. All of these alloys have no cracks found in fusion zone, HAZ, and bulk area. Increasing welding speed results in less heat energy input, reduces the penetration depth and weld pool area. The 1mm/s, which were subjected to the highest heat energy input, results in very small size of the γ’ precipitates in the fusion zone due to re-precipitation of the γ’ precipitates during the solidification process. The fusion zone also exhibits the highest hardness. The size of the γ’ precipitates in HAZ area are much larger, compared to the fusion zone The bulk areas have no effect from the heat and showed much larger size of the γ’ precipitates, which was caused by microstructural degradation during service, leads to the lowest hardness value among the three zones.

Abstract: The purpose of the study was to inspect microstructure, mechanical properties and impact toughness of ductile cast iron grade FCD450 produced by austempering process. The study focused on austempering parameter, which effected impact toughness of material at low temperature. The FCD450 was initially temperature austenized at 885°C (1625˚F) for 2 hours. Austempering was carried out at three different temperatures of 271°C (520˚F), 313°C (560˚F) and 357°C (675˚F). The austempering temperature were varied at 1.5, 2.5 and 3.5 hours. X-ray diffraction was showed that the austempered ductile cast iron (ADI) microstructure consists of austenite and ferrite. The results showed that when austempered at 357°C (675˚F) for 2.5 hours has highest hardness and impact energy at low temperature. The dimple ductile fracture of ADI fracture surfaces was revealed by scanning electron microscope (SEM).

Abstract: The research focuses on investigating different types of steel confinements around a clustered large-size stud shear connector using in full-depth precast concrete bridge deck panel. The tests were based on Push-off test of two main groups of specimens: (1) the specimens with 4-stud shear connector where three different types of confinement were adopted including of O-ring confinement, Wire-mesh confinement, and L-angle confinement), and (2) the specimens with 8-stud shear connector where two different types of confinement were investigated including of Plate-ring confinement and L-angle confinement. The test results concluded that L-angle confinement type of the group of specimens with 4-Stud is the most sufficient type comparing between the different types of confinement in the same group. The maximum resistance was found at 41-ton, while as the displacement was found to be the most expansible and gradually reduced until the failure point. This means that the sign of failure can be noticeable prior to a collapse of the structure. For the group of specimens with 8-Stud, the resistance of this group was higher than the group of specimens with 4-Stud about 50 - 100% increase depending on each type of confinement. The maximum resistance was found for Plate-ring confinement type at 70-ton, which was agreed with the increment of the displacement about 20 - 50%. In comparison between specimens with 8-Stud, the Plate-ring confinement showed greater resistance and more relative displacement about 15% than the L-angle confinement.

Abstract: This research presented the surface oxidation of stainless steel grade 304 (S304) welded by a gas tungsten arc welding (GTAW) process. The welded S304 was inspected by visual and penetrant testing methods. The surface of the welded specimen was oxidized by the chromic solution to an obtained oxide film on S304 welded specimen. After that, the structural phase and crystallite size of the oxide film were investigated by X-ray diffractometer (XRD). The thickness of the obtained film was analyzed by an atomic force microscope (AFM). Furthermore, the effects of the oxide film on hardness and corrosion properties of specimen were analyzed by Vickers hardness tester and potentiostat instrument to study the correlation between the property of oxide film and the surface properties of the welded pipe S304 after oxidation.

Abstract: This work presented the hardfacing process of high-strength structural steel based on JIS G3106 standard grade SM490YA by semi-automatic flux-cored arc welding with a dual shielding process of flux-cored self-shielded and protective gas-shielded (FCAW-G). In the welding process, the surface of SM490YA specimen was hardfacing welded by metal cored wire based on chromium carbide which was in standard of 8555: E10-MF-65-G. The hardfacing welds from FCAW-G and traditional self-shielding FCAW (FCAW-S) with and without preheat were inspected by visual and penetrant tests for evaluating the welding quality. The macrostructure of the deposited layer was investigated by optical microscope and image analysis for analyzing the weld penetration and weld dilution. In addition, the hardness of the hardfacing welded specimens was tested for the evaluation of the surface durability of the welded SM490YA.

Abstract: The objectives of this research is developed the fuel briquette compression machine and studied the properties of fuel briquette of palm residue from a community palm oil production process in Thailand. The palm residue from a community palm oil production process had a palm meat and a mixed fiber. It was a material for testing. The fuel briquette has the standard shape. Because palm meat and fiber are tough to make fuel therefore the design and building of fuel briquette compression machine were hydraulic system. The fuel briquette compression machine was developed to be easy to use and increase production rate of fuel briquette. The fuel briquette compression machine from palm residue was divided of 3 Hp motor, hydraulic pump, cylinder, and forming mold set. The ratios of ingredients for testing of fuel briquette extrusion (palm residue : water : cassava starch) were 1:1:1, 2:1:1, 3:1.5:1, and 4:1.5:1 kg. The experimental pressures were 108, 147 and 196 N/cm². From the result, it was found that the production rate of fuel briquette was higher than S. Wannapakhe (2018)’s. The properties of fuel briquette were passed the standard except the property of density value that was near the standard. The highest of production rate by using pressure, was 20 kg/cm² at the ratio of ingredients of 4:1.5:1 kg.

Abstract: Hydraulic bulge test or biaxial test is a well-known mechanical test used to determine a flow stress of material because of the large level of effective strains and not interfered by the necking unlike in uniaxial tensile test. However, the flow stress obtained is influenced by the anisotropy effect. That flow stress needs to be corrected by the anisotropic values (r-values) obtained from the uniaxial tensile test which limited by the necking. Therefore, to obtain the accurate flow stress the r-values should be determined directly from the biaxial test. The elliptical tests with ratio of 2 (the ratio between major and minor axis) at different sheet orientations (0^๐ and 90^๐ from the rolling direction) and the equibiaxial test were proposed. In this research, the effect of the sheet orientations upon the flow stress (K and n values) under biaxial tests was investigated by experiment and equation of material grade SPCD with the thickness of 0.8mm. The results showed that the flow stress without correcting r-values gave more variations than those with correcting one with the r-values obtained from the uniaxial test. Therefore, the r-values used to correct the flow stress under biaxial test should be directly determined from the biaxial test.

Abstract: This paper investigates the effect of fiber laser surface modification of AISI 316L austenitic stainless steel on corrosion behavior. In the experiments, the fiber laser with center wavelength of 1062 nm was employed with various laser parameters of beam velocity and laser frequency. The laser-treated has performed on the specimen surface in order to form the melted layer with an argon gas shielding. The electrochemical tested results showed that the laser-treated increases 40% pitting potential. Moreover, the results also exhibited corrosion potential shift to more positive potential. On the basis of the findings on the corrosion improvement, it can be concluded that the pitting potential of the material can be improved by a corrosion protective layer from the new laser-treated surface.