Journal of advanced materials and processing
Volume:10 Issue: 2, Spring 2022

In the current study, the effect of colloidal copper nanoparticles on the deposition rate and hardness of Ni-Cu-P coating deposited by electroless method on L80 steel substrate was investigated. Copper particle size, microstructure, chemical composition, and hardness of the coating before and after heat treatment at different temperatures were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDS) analysis, and microhardness. The microstructure study by XRD showed that the Ni-Cu-P coating has an amorphous structure. The heat treatment at 400 °C transformed the structure from amorphous to crystalline and formed Niα, Ni3P, and Ni3.8Cu phases. The amount of copper nanoparticles in the coating 4.58 wt% was measured. The deposition rate of the Ni-Cu-P coating was 11 µm/h. Furthermore, the hardness of the coating increased from 738HV to 1300HV by performing heat treatment.

In this work, the bilayer NiO/Fe thin films compared with single-layer Fe film were deposited on Si (100) substrate using the sputtering technique at deposition angles of 0° and 31.5°. Structure, the static magnetic properties, and the temperature dependence of the dynamic magnetic properties in the range from 300 K to 420 K have been investigated. The results show that the nanocrystalline BCC phase of Fe with the average crystallite size of 11-12 nm and (110) preferred orientation is formed during the deposition process. The resonance frequency is found to rise from 1.03 GHz to 1.13 GHz by employing the NiO sublayer for the typically deposited Fe film. Moreover, the resonance frequency increases for the NiO/Fe films from 1.13 GHz to 1.67 GHz as the deposition angle increases from 0° and 31.5° as a result of the increase in the magnetic anisotropy from 16 Oe to 45 Oe. The permeability values decrease for both as-deposited films with increasing temperature; however, the higher values of the permeability are observed for the film obtained at a deposition angle of 31.5°.

In this study, the microstructure, tensile, and fatigue behavior of the copper matrix composites reinforced by steel particles are investigated. The composite grades containing 2.5, 5.2, and 7.4 wt% steel particles up to 90 µm in size are manufactured by the casting method. The microstructure of the composite samples is studied by scanning electron microscopy. The tensile and fatigue test samples are prepared and tested based on the ASTM standard. Adding 2.5 wt% steel particles to the copper matrix increases the yield strength, tensile strength, and elongation of the pure copper by about 48, 21, and 4.8%, respectively. The fatigue test results show that reinforcing the pure copper with 2.5 wt% steel particles improves the fatigue life of the pure copper by 67, 31, and 86 percent in 60, 80, and 100 MPa amplitude stresses, respectively. On the other hand, further increasing the reinforcement particle content to 5.2 and 7.4 wt% causes unusual fatigue behavior and adversely affects the mechanical strength of the composite. Therefore, the fatigue life of the composite samples reinforced by more than 5.2 wt% steel particles is not a function of the stress level and does not increase with the decrease of the stress.

The purpose of this study is to investigate the effects of withdrawal rate on the dendrite microstructure and its formation mechanism, the porosity, and the interaction between them in Rene 80 superalloy. So, Rene 80 Ni-base superalloy was directionally solidified on a laboratory scale using the Bridgman method. The cylindrical rods were grown at withdrawal rates of 2, 4, 6, 8, and 10 mm.min-1. Dendritic structure and solidification microporosities were evaluated in transverse and longitude sections. The results showed that when the withdrawal rate was increased, the primary and secondary dendritic arm spacing decreased. With an increasing withdrawal rate, which causes to decrease in the dendritic arms spacing, the volume fraction of inter-dendritic gamma prime was first decreased until the rate of 6 mm.min-1, and after that, its volume fraction increased. This structure results from peritectic and eutectic transformations with checkerboard-like and fan-like morphology, respectively. Moreover, the volume fraction of microporosities was minimal at the rate of 6 mm.min-1, while their average size decreased from 13.2 to 8.7 μm. The specimens were given a two-stage heat treatment followed by a stress rupture test at 191 MPa and 980˚C. It was shown that at R=6 mm.min-1, directionally solidified rods with a less solidification microporosity and well-orientated dendritic structure give higher rupture life of 25.43 hrs.

The present work evaluates the mechanisms that cause the weld geometry to change in activating flux TIG (A-TIG) welding. For this purpose, an austenitic 316 stainless steel and ferritic A516 steel in conventional TIG and A-TIG welding were compared and evaluated under the same process parameters. Al2O3, Fe2O3, MnO2, SiO2, and TiO2 powders were used as activating fluxes. The depth of penetration and width of the beads were measured metallographically. In conventional TIG, the welds of carbon steel and stainless steel had a thickness of about 2.2 mm and 1.7 mm, respectively. A-TIG welding of 316 SS using TiO2, MnO2, and Fe2O3 led to a 75% increase in the weld depth. In the case of Al2O3 and SiO2 the weld depth increased 50% and 9%, respectively. However, in A516 steel, less thermodynamically stable oxide fluxes such as MnO2, and Fe2O3 had a smaller effect i.e., 9-22% increases. More stable oxides like Al2O3, SiO2, and TiO2 caused a decrease of about 30% in the weld depth compared to the conventional TIG weld. It was proposed that when the penetration increases, reverse Marangoni is dominant. This mechanism is mainly associated with viscosity and surface tension that vary by the dissolution of oxygen in the melt. Regarding penetration reduction, as in the case of more stable oxides like SiO2, the energy dissipation by the flux through heating and dissociation of the oxide and barrier effect of the undissolved oxide dominate.

In this study, for the first time, thermoplastic polyurethane granule (TPU) is used as a reinforcing phase and self-healing agent in a polymer composite epoxy resin (ER) to exhibit mechanical properties recovery. When the polymer composite is damaged or cracked, TPU granules are released at the site of damage and cause auto-repair of surfaces. Therefore, TPU granules with different composition percentages were mixed in silicon molds containing epoxy resin polymer composite. 4 samples with different TPU granules percentages were selected (A= 0 Wt.% TPU, B=10 Wt.% TPU, C=20 Wt.% TPU, and D=30Wt.% TPU). At first, making a deep cut in 4 polymer composite samples, the self-healing process and mechanical properties improvement are investigated by mechanical tests. In the self-repairing behavior of self-healing samples, it is observed that polymer composite samples with self-repairing agents of ER+20 Wt.% TPU granules had the highest self-healing efficiency (60.2%) compared to other specimens. A mechanical test shows that Sample C has a higher Young’s modulus (4.837 MPa) and higher tensile strength (9.46 MPa). Also, the impact test illustrated Sample C has a higher impact energy of 7.1 (J/m). Therefore, sample C has the highest mechanical properties among self-healing samples.