Papers by Keyword: Microstructure

Abstract: Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these parts is very important to prolong their lifetime in a economical point of view. In this study, Inconel 718 filler metal was welded with GTAW method in the cast steel which would be generally used with piston crown material. And the corrosion properties of weld metal zone, heat affected zone and base metal zone were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H₂SO₄ solution. The weld metal and base metal zones exhibited the highest and lowest values of hardness respectively. Furthermore, the corrosion current density of the weld metal zone indicated the lowest value, having the highest value of hardness. The corrosive products with red color was more or less observed in the base metal zone, while the weld metal zone exhibited the general corrosion without corrosive products of red color. The microstructure of the pearlite with black color was predominantly observed in the base metal zone, however, the microstructure of ferrite with white color increased increasingly in the heat affected zone, and the microstructure of ferrite with white color was significantly observed in the weld metal zone. In particular, the polarization characteristics such as impedance, polarization curve and cyclic voltammogran associated with corrosion resistance property were well in good agreement with each other. Keywords : Repair welding, Inconel 718 filler metal, GTAW, Weld metal zone, Electrochemical method, Corrosion current density, Hardness. Microstructure

Abstract: The objective of the present study was to find the influence of laser beam shape on macroscopic morphology and microstructure of single Ni60 laser clad tracks. Laser cladding of Ni60 alloy powder can be used to manufacture and remanufacture backup rollers for the steel industry. Controlling temperature distribution can assist with achieving favorable macroscopic morphology and microstructure. Five different beam profiles were used in our experiment to prepare clad tracks. The beam profiles varied in terms of the ratio of energy densities between the internal and external parts. The macroscopic morphology and microstructure was tested using SEM. The study founds decreasing the ratio is possible to achieve wider clad tracks with a larger cross section area. It was found that microstructure in upper region tended to form net-like dendrite microstructure at low energy density ratios.

Abstract: The deformation behavior of a Udimet720Li superalloy under hot compression tests was characterized in the temperature range of 1060~1160°C and strain rate range of 0.001~20s^-1. Processing maps were conducted at a series of strains to calculate the efficiency of hot working and to recognize the instability regions of the flow behavior. A Zener-Hollomon parameter is given to characterize the dependence of peak stress on temperature and strain rate. The efficiency of power dissipation of the Udimet720Li superalloy obtained in a strain range of 0.1~0.7 are essentially similar, which indicates that strain does not have a significant influence and the instability region shown in high strain and high strain rates at all temperatures. The regions for the full recrystallization can be divided by the dissolution beginning temperature of primary γ'which are the optimum hot working parameters.

Abstract: In this research, influence of annealing process on microstructure and mechanical performance of Nb-Ti-stabilized 430 ferritic stainless steel were investigated. In order to obtain the optimal annealing process, metallographic observation, SEM detection and tensile test were carried out. It is found that the microscopic structure is composed of fine and uniform isometric recrystallization grain after annealing. Optimum microstructure and mechanical properties can be achieved while annealed at 950 °Cfor 90 seconds. The annealed sample can obtain the optimum microstructure and mechanical properties under such annealing process. The yield platform is eliminated and the average plastic strain ratio is further improved to 1.269, which reflected a well deep drawability of the Nb-Ti-stabilized 430 ferritic stainless steel compared to SUS 430 stainless steel.

Abstract: The article studies on sections microstructure of 430ferritic stainless steel after tension, the tensile temperatures are the 1073K, 1173K, 1223K, 1273K, 1323K and 1423K. The transverse sections (vertical tensile direction) of fractured specimens microstructure of 430ferritic stainless steel were observed and compared with those of longitudinal sections (parallel tensile direction). Moreover, we compare microstructure of transverse section specimens with the salt water-cooled condition and air-cooled condition. The optical micrograph of fractured tensile specimens of 430stainless steel after cooling to room temperature indicated that the volume fraction of the martensite is gradually increased and then declined from 1073K to 1423K. At 1223K, the martensite content is highest. At 1423K, martensite is sharply reduced and disappeared, the microstructure of 430ferritic stainless steel is almost all of ferrite and grain boundary obviously observed. Due to tensile deformation, the morphology of martensite is massive in the transverse section specimens. Whereas, the strip-type morphology of martensite was observed in the longitudinal section specimens. The cooling rate impact on the microstructure was also discussed.

Abstract: Nickel-cobalt alloy deposits were prepared on copper substrate by electrochemical deposition at various cobalt concentrations in electrolytic solution of 0, 6, 12, 18 and 24 g l^-1. The deposition was performed at current density of 30 mA/cm². X-ray diffraction measurements confirmed that all nickel-cobalt alloy films formed have face-centered cubic structure. EDS studies showed that Co content in Ni-Co alloys increased with the increase of cobalt sulfate concentration in the solution. It can be suggested that increasing concentration of co sulfate is the reason for an increase in activity of cobalt ion. The investigations on the electrodeposited Co-Ni alloys have been shown that their microstructure and surface morphology were found to depend strongly on the Co content in the Ni-Co alloy deposited.

Abstract: In this paper, the influence of heat treatment temperature on the microstructure and mechanical properties of cast steel (ZG25MnNi) was investigated. The results showed that normalizing treatment can effectively refine cast microstructure of ZG25MnNi and maximum hardness achieved at 900°C. After normalized at 900°C, the sample tempered at 500°C,530°C,560°C, 590°C, 620°C, 650°C respectively. With the tempering temperature increasing, the samples tensile strength increased gradually and elongation decreased gradually. When tempered at 530-590°C, the sample had a relatively high strength plastic product. The results showed that the best normalizing temperature is 900°C and the optimum tempering temperature is 530-590°C.

Abstract: This paper prepared Cu-ZrO₂ composite by a modified internal oxidation in order to improve the high temperature strength of resistance Spot-welding electrode. The results showed that with the increasing of the cold deformation, Hardness increased while electrical conductivity decreases. Hardness reached 100HV and electrical conductivity was up to 86%IACS after cold drawn in 56%. With the increasing of annealing temperature and annealing time, Hardness of the composite decreased more slowly compared with the conventional Cu-Cr-Zr alloy and was higher than that of the Cu-Cr-Zr alloy after annealed above 700°C for 2h and at 600°C for 5h , which was attributed to the dispersion strengthening effect of the Zirconia particles. Thus, the Cu-ZrO₂ composite has good high-temperature stability and can be used for the electrode

Abstract: For the further research of 3D tubular woven carbon fiber composite, a unit cell division method and a mechanical model were put forward to predict the engineering elastic constants. The model adopted raceway shape as the yarns cross-section, and prediction methods of volume fractions and elastic modulus were established based on the micro structure and geometric parameters of the yarn. Then the finite element method was used to analysis the mechanical behavior under the circumstances of axial-tensile load, and the stress state was revealed. The results shows that the predicted values using finite element method agree well with the theoretical calculation values, thus the model and analysis method of elastic constants is verified.

Abstract: The microstructures of the Mg-6Zn-2Y alloy solidified under high pressures were investigated using scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The room-temperature compression behavior was analyzed through experiments, showing that the microstructures of the alloys are consisted of α-Mg and quasicrystal I-Mg3Zn6Y phases. With solidification pressure increasing, the microstructures were refined, and the morphologies of the inter-dendritic secondary phase were improved from continuous networks into long-island and granule. The compression strength, yielding strength and compressibility were increased significantly corresponding with solidification pressure, from 259.02 MPa, 230.39 MPa and 18.3% under ambient pressure to 361.43 MPa, 272.25 MPa and 33.1% under high pressure of 6 GPa. The cleavage planes are flat, and the cleavage steps are straight under ambient pressure. However, the cleavage planes are small and rough under 4-6 GPa; tearing dimples occur in the tearing area, indicating that the degree of cleavage fracture decreases under high pressure.