Narrow Results

The recovery behavior of 20% plastically deformed AlSi_11.35Mg_0.23 in various stages of isochronal annealing is investigated by positron lifetime (LT). Experimental results show that the positron mean lifetime is a function of annealing temperature. The lifetime of the positron annihilating in a perfect lattice is 187.3 ps. It is 229.8 ps in a 20% deformed one. There are two regions in the isochronal annealing, one of them is related to the point defect and the other to the dislocation. The activation enthalpy for the dislocation is calculated from the isothermal study in the dislocation region from 575–675 K by slow and fast cooling and it is 0.16 ± 0.02 and 0.53 ± 0.06 eV, respectively.

The Fe–C–H interaction near defects in iron structures was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalization molecular orbital. Calculations were performed using three Fe clusters to simulate an edge dislocation, a divacancy; both in bcc iron and a stacking fault in an fcc iron structure. In all cases, the most stable location for C atom inside the clusters was determined. Therefore, H atom was approximated to a minimum energy region where the C atom resides. The total energy of the cluster decreases when the C atom is located near the defects zone. In addition, the presence of C in the defects zone makes no favorable H accumulation. The C acts as an expeller of H in a way that reduces the hydrogen Fe–Fe bonds weakening.

The defects induced by a spike rapid thermal annealing (RTA) process in crystalline silicon (c-Si) solar cells were investigated by the photoluminescence (PL) technique and the transmission electron microscopy (TEM), respectively. Dislocation defects were found to form in the near-surface junction region of the monocrystalline Si solar cell after a spike RTA process was performed at 1100${}^{\circ }$C. Photo J–V characteristics were measured on the Si solar cell before and after the spike RTA treatments to reveal the effects of defects on the Si cell performances. In addition, the Silvaco device simulation program was used to study the effects of defects density on the cell performances by fitting the experimental data of RTA-treated cells. The results demonstrate that there was an obvious degradation in the Si solar cell performances when the defect density after the spike RTA treatment was above $1\times 10^{13}$cm${}^{-3}$.

Owing to the advancement in the field of materials, different range of grades have been developed. The machinability examination of these newer grades must be carried out for future applications. One such newer grade of magnesium with AZ31 is deemed for study during the drilling process. The independent parameters considered are spindle speed (SS), feed rate (FR) and drill bit diameter (DBD). The dependent parameters considered are burr height (BH), burr thickness (BT), drilling time (DT) and surface roughness (SR). Improving hole accuracy is essential for manufacturing superior products, which is discussed in this work. At the same time, the machining time has also to be minimized to increase the production rate. With these objectives, the experimental investigation is made. Further, an analytical model for predicting the responses is developed; later, optimization is carried out to obtain the desired responses through the desirability function approach. The multi-objective optimization suggests the SS of 1100rpm, the FR of 0.198mm/rev., and the DBD of 6mm for reducing the entire dependent is reckoned.

To improve the corrosion resistance of X70 pipeline steel in seawater, nickel coating was prepared on the surface of X70 steel by electroplating method. The corrosion properties of the samples in simulated seawater were studied by macroscopic electrochemical experiment and micro-scanning electrochemical experiment. The systematic characterization of the samples was conducted using a scanning electron microscope (SEM), energy disperse spectroscopy (EDS), and X-ray diffractometer (XRD) techniques. The time-dependent model was established to simulate the localized corrosion by COMSOL Multiphysics. The characterization results show that the nickel coating prepared at 0.045 A is compact and thickest. In the macroscopic electrochemical results, the impedance value of the nickel layer prepared at 0.045 A is 34% and 36% higher than that of the other two coatings, and the current density is 25% and 66% lower than that of the other two coatings. In the micro-scanning electrochemical results, the impedance value of the nickel layer prepared at 0.045 A is 5% and 40% higher than that of the other two coatings, and the current density is 14% and 26% lower than that of the other two coatings. Therefore, 0.045 A is the best electroplating current for preparing nickel coating. The simulation results show that the micropores on the surface of nickel-plated X70 are easy to induce localized corrosion, and the degree of localized corrosion decreases with the increase of micropore diameter.