Materials Science Forum Vols. 809-810

Abstract: Solar grade silicon and modified Al-Si alloys are widely used in the world. These two favored materials are expected to obtain by the electromagnetic directional solidification of hypereutectic Al-Si melts. The segregation of hypereutectic Al-Si alloy is feasible with respect to the process of either pull-up or drop-down in electromagnetic directional solidification. To explore the segregation efficiency, experiments have been conducted in a high-frequency induction furnace with different pulling conditions of hypereutectic Al-Si melts. The results show that the segregation efficiency of dropping-down is higher than that of pulling-up; the slower dropping-down rate lead to higher segregation efficiency in the electromagnetic directional solidification; increasing the temperature gradient may promote the separation efficiency. A separation mechanism model responsible for the formation of the distribution of primary silicon in the cross-sections is also proposed. Wish to provide theoretical basis for the more efficiency of the segregation of hypereutectic Al-Si melts.

Abstract: Steel 30CrMnSiNi2A slices were irradiated by a continuous wave fiber laser beam with the intensity of 14.5W/cm². Alloy samples with various temperature processes were obtained by changing the laser irradiation time, irradiation times and atmosphere environment. X-ray diffraction, scanning electron microscope, energy dispersive spectrometer and nanoindentation system were employed to characterize their microstructure morphology and mechanical properties. Three layers were observed in the samples fracture, namely oxide film, hard brittle layer and alloy substrate. The hard brittle layer had a higher hardness and a lower toughness compared with the base metal. Referring to the temperature history, we deemed that the surface oxidation and the solid phase transformation were the main factors which changed laser coupling efficiency. The results also illuminated the correlation between the microstructure morphology and the response to laser irradiation of the samples.

Abstract: Ni_50-xMn₃₇In₁₃Co_x (x=0,5) alloy powders were obtained by ball-milling from the corresponding ribbon precursors. The as-milled Ni₅₀Mn₃₇In₁₃ and Ni₄₅Mn₃₇In₁₃Co₅ powders show disordered fct and fcc structures respectively, due to the larger lattice distortion in Ni₄₅Mn₃₇In₁₃Co₅. DSC and XRD results show that the high-temperature annealing will lead to a one-step ordering process from fct to Heusler structure in Ni₅₀Mn₃₇In₁₃, and a two-step ordering process, including fcc to bcc and bcc to Heusler phase transitions in Ni₄₅Mn₃₇In₁₃Co₅. After annealed at 400°C and 650°C, the martensitic transformation behavior is gradually and partially restored in Ni₅₀Mn₃₇In₁₃ powders. As modulated by the annealing temperatures, the martensitic transformation temperatures increase with the grain sizes of Ni₅₀Mn₃₇In₁₃ powders. However, the martensitic transformation is almost completely suppressed in 650°C annealed Ni₄₅Mn₃₇In₁₃Co₅ powders with only some weak reflection peaks from 7M martensitic phase observed in XRD pattern.

Abstract: High temperature thermoplastic of 50Mn2V casting slab was tested by Gleeble-1500 thermal simulator machine. The morphology, microstructure and composition of fracture surfacewere observed and analyzed by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).The results show that, there are two brittle temperature zones of 50Mn2V casting slab at the temperature of 600~950°C and 1300~1465°C, respectively, The section shrinkaging rate is less than 60%. The fracture mode changes from mixed one dominated by intergranular to toughness transgranular one with the increase of temperature at the range of 600~1250°C. However, the fracture is along with the solid-liquid phase at the range of 1300°C~ melting point.

Abstract: The intergranular corrosion (IGC) behaviors of welded joints of 316LN stainless steel with different welding heat input were investigated in this study. The boiling nitric acid method was chosen to provide the IGC environment. The corrosion rates of different specimens were studied and the micro-structures of each zone (base material, heat affected zone and weld zone) were analyzed in detail. The results show that welding heat input affects IGC resistance remarkably and low welding heat input can reduce the IGC tendency. The IGC test can be divided into three stages, i.e. the initial corrosion stage, stable corrosion stage and rapid corrosion stage. The IGC resistance of WZ for 316LN stainless steel is better than that of BM and HAZ due to the beneficial role of delta ferrite.

Abstract: This paper analyzed the morphology and reasons of pitting corrosion perforation of 0Cr18Ni9 stainless steel cooling water pipes in a power plant and pointed out the measures to prevent the pitting corrosion under this condition. The results showed that: the reason of pitting corrosion of 0Cr18Ni9 stainless steel cooling water pipes was the existence of multiple Cl^-and easily fouling Ca²⁺ and Mg²⁺ in water, with the corrosion products mainly the oxides of Fe and Cr; the economic measures to prevent pitting corrosion were to increase the pH of water and decrease the content of Ca²⁺ and Mg²⁺.

Abstract: The acoustic emission (AE) response of 316LN welded joint during intergranular corrosion (IGC) was investigated in this study. The boiling nitric acid method was chosen to provide the IGC environment and AE signals were detected by Macro-SAMOS AE testing system. The metallographic structures and AE results were studied and analyzed in detail. The results show that the IGC process of 316LN welded joint can generate many AE signals and the AE activity is high. The AE amplitude is below 35dB and mainly ranges from 25dB to 34dB. Two types of AE signals are obtained and both the frequency peaks are 50 kHz. It is believed that grain boundary corrosion, ferrite corrosion and separation of grains are the possible AE sources.

Abstract: The bond length, average binding energy, magnetic moment per atom and the ionic potential of Ni_n (2-13) clusters were calculated in detail. The variations of magnetic moment per atom and the ionic potential agree well with experimental data. Theoretical results show that BPW91/Lanl2dz method is the best method and basis set for nickel clusters research, respectively. The ground state configurations and electronic structure properties of Ni_n (2-13) clusters were investigated using the BPW91/LanL2DZ level of DFT method. Through the molecular orbital, we could explain the paramagnetic and diamagnetic to the influence of the magnetic moment after different nickel cluster molecular hybridization.

Abstract: Aluminium alloy is difficult to be plated because of high chemical activity. In order to obtain electroless nickel plating with excellent adhesion to the substrate, the key lines is the pretreatment process. This study introduces several significant pretreatment processes of aluminium alloy surface at home and abroad for these years, and describes the principles of pretreatment processes. Finally, the development direction of pretreatment processes for aluminium alloy is forecasted.

Abstract: The structural properties, elastic properties, and heat of formation of a high entropy alloy (HEA) of AlCoCrCuFeNi containing different mole fraction of Ni. The calculated results indicate that the lattice parameter decreased and the mass density increased as the mole fraction of Ni increased. The high entropy solid solutions AlCoCrCuFeNi_x using the FCC model are mechanically stable. The elastic properties have been deduced by Voigt-Reuss-Hill (VRH) approximations, and the calculated ratio of shear modulus to bulk modulus indicated that When the mole fraction of Ni was 0 in the FCC model, or 0.5 in both the BCC and FCC models, the high entropy solid solutions were considered ductile materials. All the HEAs are thermodynamically stable due to their negative heats of formation.