Key Engineering Materials Vol. 835

Abstract: Nanocrystalline spinel zinc ferrite ZnFe₂O₄ thin film has been studied and synthesized via the electrodeposition-anodization process. Electrodeposited ZnFe₂ alloys were obtained from aqueous sulphate bath. The resulted alloys were electrochemically oxidized in strong alkaline solution (1 M KOH) at room temperature to the analogous hydroxides. The electroanodized ZnFe₂ alloy film was annealed in air at 400 °C for 2 h to get the required zinc ferrite. The electrochemical factors controlling of the electrodeposition of ZnFe₂ alloys such as the bath temperature, agitation, the current density were studied and optimized. The crystal structure, crystal size and microstructure of the produced ferrites were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The deposited film was mainly composed of ZnFe₂O₄ based on XRD studies. The produced film had a spinel structure and the crystallite size was 4.9 nm. SEM micrograph of the resulted zinc ferrite particles shows compact crystallites shapes and agglomerated chains with smallest semicircular particles like morphology.

Abstract: Direct melt foaming method was used to fabricate 7075 Al-SiO₂ composite foams from recycled beverage aluminum cans and SiO₂ waste particles. The microstructures of the produced composite foams revealed typical characteristic features of the conventional foams, where large dark areas (pores), curved cell walls, cell edges, nodes on the cell edges, cell walls and plateau regions were observed. The microstructures of the composite foams showed fine and irregular shape of SiO₂ particles, which were uniformly distributed in the cell wall and plateau region of composite foams. The grain size of α-Al was reduced by the addition of SiO₂, indicating that the refining effect of the SiO₂ is due to heterogeneous nucleation of the α-Al grain by SiO₂ particles or restriction of the α-Al grain growth by the SiO₂ particles, or both. SEM and EDX indicated that the SiO₂ particles reacted with the molten 7075 Al during melting and foaming process, forming MgAl₂O₄, MgO, Al₂O₃ and Mg₂Si.

Abstract: Secondary phase carbides in term of type and morphology are considered as the most challenge facing the applications of hot work tool steel. AISI H13 tool steel is one of the most applicable hot work tool steel grades. M₂₃C₆, M₆C and MC are the common secondary carbides that are forming throughout the martensite matrix of H13 tool steel. In this research, nanoinoculant silicon nitride was added to the molten H13 tool steel to act as an inoculant for the secondary carbide categories through ladle treatment process. By using OM and SEM, it was observed that nanoinoculant has the great impact in the nucleation of secondary carbides into fine shape, in particular M₂₃C₆ type. In addition, mechanical tests proved that the nucleation of secondary carbides promotes the mechanical properties of hot work H13 tool steel to its ultimate. Impact toughness of the inoculated H13 tool steel was observed with higher value than that was done at the ordinary H13 tool steel. At the meantime, wear resistance of inoculated H13 tool steel was multiplied two times higher than as delivered H13 tool steel.

Abstract: Shape memory alloys are programmed to memorize original trained shape. Ni-Mn-Ga is one of the ferromagnetic shape memory alloys. It is used as actuator, and sensor due to large output strain at high frequencies. This work presents a study on enhancing magnetic properties of thermally treated alloy by using new method of training in which alloys are exposed to different hydrostatic pressures using pressing die. Single near stoichiometric composition was produced. Elemental analysis showed homogeneity of the alloy. XRD pattern revealed Martensitic phase peaks. Transformation temperature was found to be below 100 OC. Training was applied by hydrostatic pressing die. Different training pressures were obtained using hydraulic press. After applying hydrostatic pressures starting from 2.5 bar to 10 bar, it was found that pressures up to 7.5 bar will increase the coercivity and saturation magnetization of the alloy, while pressures beyond 7.5 bar lessened these magnetic properties.

Abstract: The separation of fine coal can be improved by pre-desliming, which was significantly enhanced when fine coal was processed using a Falcon concentrator, and <45-μm coal slime was removed. Ultrafine classification tests using Krebs classification cyclone with annular rinse water showed that the increase in feeding concentration negatively affected the efficiency of classification while increasing the classification size because the settling was hindered by the high underflow concentrations. The optimization experiments with response indicators of classification efficiency based on orthogonal design using Design-Expert software indicated that the optimal classification efficiency reached 91.32% with a feeding pressure of 0.03 MPa, a rinse water pressure of 0.02 MPa, and a feeding concentration of 12.5%. Meanwhile, the classification size was 49.99 μm, which agreed well with the predicted value.

Abstract: Background: The most frequently used monomer in commercial composite resins is bisphenol A glycidyl dimethacrylate. Bisphenol A glycidyl dimethacrylate free monomer and the long chain dimer acid based monomer were considered as an alternative method to improve mechanical and physical properties of composite resins. Objective: To study the surface roughness of different nanohybrid composites with different monomer compositions after finishing and polishing with different polishing systems. Materials and Methods: 72 composite disk specimens were prepared and divided into 3 groups (n=24) according to the resin composite that were used (harmonize kerr, venus diamond heraeus kulzer and n'durance septodont). Each group was subdivided into 4 subgroups (n=6) according to the polishing technique that was used (Jiffy natural universal wheels ultradent, sof-lex spiral wheels 3m espe, hiluster kerr or enhance system dentsply). Atomic force microscope was used to measure surface roughness. Results: There was statistical significant difference in surface roughness measuring among different n'durance, venus diamond and harmonize groups (Kruskal Wallis Test p<0.05). Post hock pairwise comparison revealed that venus diamond showed statistically significant higher surface roughness when compared with either n'durance and harmonize. Among the polishing systems, jiffy natural universal wheels produce the least surface roughness. Conclusion: Different monomer compositions may have direct effect on the final surface polish of the restorative materials. Clinical significance: The use of jiffy natural universal wheels may be found to result in the smoothest surface finish with the least clinical steps.

Abstract: This article aims at investigation the effect of partial and total replacement of molybdenum by tungsten in ordinary heat resistance steel, in term of constituent phases. Three steel grades of P91 steel were produced in induction furnace with different molybdenum and tungsten contents. The produced steel were hot forged at 950 °C – 1100 °C, followed by air cooling. The ordinary heat treatment was applied through austenizing at 1050 °C for one hour followed by water quenching and then, they were tempered at 700 °C for 2 hours. Optical microscope, Scanning Electron Microscope (SEM), and EDX were used to investigate the microstructure and precipitated phases after complete heat treatment process. In addition, Thermo-Calc program was used to predict the phases which may be formed. The results showed that replacement of molybdenum by tungsten has an effect on the solubility of different intermetallic phases at high temperature, delaying the deteriorative Z-phase.

Abstract: The effect of chromium content and prior hot deformation of the austenite on the continuous cooling transformation (CCT) diagram of a newly developed low-carbon bainitic steel has been studied using dilatometer measurements conducted on a Gleeble 3800 simulator with cooling rates ranging from 2-80 °C/s. After austenitization at 1100 °C, specimens were either cooled without strain or given 0.6 strain at 880 °C prior to dilatometer measurements. The resultant microstructures have been studied using laser scanning confocal microscopy, scanning electron microscopy and macrohardness measurements. CCT and deformation continuous cooling transformation (DCCT) diagrams were constructed based on the dilatation curves, final microstructures and hardness values. Depending on the cooling rate, the microstructures of the investigated steels after cooling from the austenite region consist of one or more of the following microstructural components: lath-like upper bainite, i.e. bainitic ferrite (BF), granular bainite (GB), polygonal ferrite (PF) and pearlite (P). The proportion of BF to GB as well as the hardness of the transformation products decreased with decreasing cooling rate. The cooling rate at which PF starts to appear depends on the steel composition. With both undeformed and deformed austenite, increasing the chromium content led to higher hardenability and refinement of the microstructure, promoting the formation of BF and shifting the ferrite start curve to lower cooling rates. Prior hot deformation shifted the transformation curves to shorter times and higher temperatures and led to a reduction in hardness at the low cooling rates through the promotion of ferrite formation.

Abstract: Understanding the microstructure evolution of metal thin films on various substrates is essential for developing thin films that need specific requirements. The microstructure of thin films has been identified to be related to the mobility of the adatoms during growth. Recently, the theory of non-classical crystallisation of thin films has been introduced to explain the structure formation in chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes. Much work has been conducted on CVD deposited thin films, while little data appears on PVD techniques. The effect of substrate material on the microstructure of the deposited nickel-titanium (NiTi) thin film and its optical absorbance is studied in this work. Three different substrates with identified surface conditions were used to deposit thin films of NiTi in the same chamber under the same processing conditions. The NiTi thin film was deposited using radio frequency (RF) PVD sputtering process on stainless steel (SS), aluminium (Al) and copper (Cu) substrates. The results were analysed in view of state of art structure models and mechanisms. The microstructure was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical absorbance was measured by spectrophotometery. The results have shown that the structure and morphology of the grown films have varied in all conditions. Amorphous structures were obtained for Al and Cu substrates, while crystalline structures were obtained for the stainless-steel substrate at the same sputtering conditions.