Advanced Materials Research Vol. 772

Abstract: In this paper, a formula for the calculation of carbon content during austenitizing of cast iron was deduced, considering the effect of silicon content on the heat treatment parameter. According to this formula, the carbon content of the austenite in a certain austenization temperature for a cast iron with given components can be easily calculated, and the austenization temperature for getting the expected carbon content in the austenite can also be determined. Besides, according to the relationship between austenization temperature Tx and the according carbon content Cax, and considering the effect of silicon content, the diagram of Cax, Tx and silicon content during the austenitizing process of cast iron was made.

Abstract: Room-temperature ferromagnetism has been found in AlN grown by direct arc discharge method using the direct reaction of Al powder with N₂ gas. The observed room-temperature ferromagnetism which arises from the aluminum vacancy is intrinsic properties in AlN. The results could rule out oxygen impurities as the main cause of magnetic origin in AlN. First-principles calculations reveal that spontaneous spin polarization creates with a 3.0 u_B local moment for AlN and magnetic originate from the polarization of the unpaired 2p electrons of N surrounding the Al vacancy. The aluminum vacancy induced may be applicable to other Ш-V nitride semiconductors in turning their magnetism.

Abstract: The deformation twinning leads to a reduction of the coefficient of strain hardening, i.e. twinning plays an important role in deformation of steel. The contribution of twinning to the total deformation is significant (up to 1/3 of the overall deformation). The final effect of twinning on strain hardening rate depends on the number of factors introduced by the twinning itself in the process of sliding. Calculated Schmid factors for slip systems operating in the matrix and in the twin. The analysis of the twinning geometry in particular grains showed that twinning is primarily developed for systems with the highest Schmid factor. However, twinning was also observed with a minimum and even zero Schmid factor. The obtained results indicate the importance of the orientation of slip planes in the newly formed micro-twins and Schmid factors for twinning. The important role of crystallographic texture in the physics of strain hardening was also shown.

Abstract: Solar grade silicon (SoG-Si) is the basic material of photovoltaic industry. Metallurgical method as a way of purification isconsidered to reduce the cost of polysilicon production unanimously based on its low cost, short production cycle, relatively simple process, lowpollution and controllable scale size, and it has become a hot topic in the subject research around the world.In this paper Al-Si-Sn alloy is used to purifypolysiliconand influence on the purification efficiency of polysilicon with different compositions of Al-Si-Sn alloy is analyzed. In order to study the segregation of impurity B in purification process, we introduce final segregation coefficient k_B,final and analyze the relation between k_B,final and the content of Al,Snin Al-Si-Sn alloy thermodynamically.

Abstract: Two as-cast Al-Zn-Mg-Cu alloys with different alloying element contents have been studied in terms of precipitation phases and properties. The modeling results show that different composition of the alloy has a significant effect on the microstructure and the tensile properties, while the electrical conductivity is not affected by the variation of the alloy composition.

Abstract: Finite element method to analyze the fretting wear characteristics based on Hertz theory, Coulomb friction law and a modified Archard wear equation, has been applied to a cylinder-on-flat configuration for typical steam generator tube material Inconel 690 alloy and typical anti-vibration bar material Inconel 600 alloy (Cr plating) in the nuclear power plant, under gross slip and partial slip conditions. The evolutions of contact profile, surface contact variables with increase in wear cycles are predicted. The slip regime is predicted to have significant effects on the fretting wear behavior. Under the gross slip regime, it is found that the peak contact pressure occurs at the center of the contact scar, and the actual relative slip is slightly smaller than the applied value. The contact width increases, and the peak pressure decreases gradually with increase in wear cycles. Whereas under the partial slip regime, the peak contact pressure occurs at the stick-slip boundary, the actual relative slip is much smaller than the applied value, and no relative slip occurs in the stick zone. The contact width increases gradually, and the peak pressure increases rapidly with increase in wear cycles.

Abstract: The resistance associated with temperature and magnetic field is a crucial parameter in researching the physical properties of the Perovskite-type manganites. To find out a suitable method to predicting the resistance of La_0.65Ca_0.35MnO₃ and La_0.8Sr_0.2MnO₃ in the process from paramagnetic phase to the ferromagnetic phase via the temperature and the magnetic field was the aim of this paper. By the nonlinear fitting, an appreciated analytic expression showing the temperature-dependence resistance both less or higher than the metal-insulator transition temperature,T_c, at different magnetic field was put forward. All of the nonlinear fitting between the measured and the calculated data were so satisfied that the minimum correlation coefficient is below 0.9997, the average relative errors do not exceed 1.0%.

Abstract: Procedures for welding duplex stainless steel conventional arc welding methods were studied by several authors and nowadays and recently they are well handled. Todays practice requires application of processes providing excellent weld joint quality, quick production and possibility of automation. Therefore the application of laser beam welding has a great potential of application. This research paper describes weldability of DSS 2205 by laser beam. The main factor examined in the process of welding duplex steel is the shielding gas and his effect on weld joint properties. Welding was performed with gaseous CO₂ laser machine Ferranti Photonics AF 8 having 8 kW max. output power and wave length 10.6 µm. Microstructure of weld joint specimens was analysed in order to observe the phase composition ratio. Samples are welded with same process parameters except of shielding gas. Helium and nitrogen were applied as a shielding gas to examine their influence in comparison to weld joints welded without shielding gas. Since the nitrogen promotes the austenite formation, its application brought the best results having almost same phase composition as base material.

Abstract: Microstructural and mechanical properties of friction stir welded 4mm7075-T6 aluminum alloy were investigated in this paper. The microstructures in WAZ,TMAZ and HAZ were analyzed. The results show that with the rotating speed at 1500 rpm and welding speed at 60mm/min, a defect-free welding joint was obtained. The tensile strength was 362 MPa, which is 65% of base metals; Weld nugget is composed of equiaxed grains; The lowest hardness between the TMAZ and HAZ of advancing side. The fractography revealed that samples failed in ductile mode and the strain fracture appears in advancing side of weld zone.

Abstract: Microstructuresand electrochemical properties of La0.73Ce0.27Ni3.25+xMn0.35Al0.15Cu0.75Fe0.25 alloys are investigated. XRD results indicate that all alloys are identified with LaNi5 phase with CaCu5 type hexagonal structure, and lattice parameter a, c and cell volume V decrease with increasing x value. Maximum discharge capacity first increases from 286.4 mAh/g (x = 0) to 313.2 mAh/g (x = 0.25), and then decreases to 308.9 mAh/g (x = 0.75). High-rate dischargeability of the alloy electrodes increases when x increases from 0 to 0.75. HRD1200 increases with the increase in the I0 and D, and shows a linear relationship with the I0 and D.