Key Engineering Materials Vol. 835

Abstract: In this work, the corrosion behavior of different grades of cast iron in 3.5% and 5% of NaClsolution was evaluated. The samples used in this work are; Grey cast iron (GI), ductile cast iron(DI), austempered ductile cast iron (ADI), intercritically austempered cast iron (IADI) and Ni-Resist cast iron. The study was carried out using the Open- Circuit technique (OPC),Potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS)measurements and complemented by Scanning electron microscopy (SEM) and Energydispersive X-ray analysis (EDAX). The results obtained showed that the austempering heattreatment and nickel addition improves the corrosion resistance of cast iron. The order ofcorrosion resistance in NaCl solution is as follows: Ni-Resist > ADI > IADI > DI > GI.

Abstract: Accurate determination of piezoelectric properties such as piezoelectric charge coefficients (d₃₃) is an essential step in the design process of sensors and actuators using piezoelectric effect. In this study, a cost-effective and accurate method based on dynamic loading technique was proposed to determine the piezoelectric charge coefficient d₃₃. Finite element analysis (FEA) model was developed in order to estimate d₃₃ and validate the obtained values with experimental results. The experiment was conducted on a piezoelectric disc with a known d₃₃ value. The effect of measuring boundary conditions, substrate material properties and specimen geometry on measured d₃₃ value were conducted. The experimental results reveal that the determined d₃₃ coefficient by this technique is accurate as it falls within the manufactures tolerance specifications of PZT-5A piezoelectric film d₃₃. Further, obtained simulation results on fibre reinforced and particle reinforced piezoelectric composite were found to be similar to those that have been obtained using more advanced techniques. FE-results showed that the measured d₃₃ coefficients depend on measuring boundary condition, piezoelectric film thickness, and substrate material properties. This method was proved to be suitable for determination of d₃₃ coefficient effectively for piezoelectric samples of any arbitrary geometry without compromising on the accuracy of measured d₃₃.

Abstract: Normalizing is an effective heat treatment in improving the microstructure and developing the mechanical properties of micro-alloyed steel. The normalizing parameters such as temperature and holding time are the main keys to microstructure and mechanical properties controlling. Therefore, obtaining an optimum combination of mechanical properties must be subjected to an ideal combination of these parameters. Furthermore, adjusting the optimum normalizing parameters must be considered for every chemical composition depending on the critical transformation temperatures. In this work, four micro-alloyed steel alloys containing V (0.008-0.1wt %) and Ti (0.002-0.072) were held on different normalizing temperatures for 30 minutes. The first holding temperature was carried out just above the Ac3 temperature and the second was carried out above the Ac3 by 100°C (Ac3+100°C). With the controlled normalizing condition, V-Ti-micro-alloyed steel alloy has produced an ultra-fine structure of grain size 2.2 microns and combined high strength of 725 MPa YS, 1058 MPa UTS and good ductility of 20%.

Abstract: Carbon steel containing boron-dual phase was produced by casting and were heated to 1200 °C for hot forging to produce plates of 10 and 6 mm thick. The plates produced were heated to the inter-critical annealing temperature for 15 min. and then water quenched followed by tempering process. The microstructure of the produced steel is ferrite with islands of martensite. Welding was done to the heat treated steel plates (6mm) using SMAW process and applying AWS-E11016 electrode and as a result an over-tempered region in the heat affected zone was formed with a significant reduction of the ultimate tensile strength of the welded joint. Reduction of heat input resulted in an increase in the joint strength. Welding of the hot rolled plates with a subsequent heat treatment resulted in formation of homogenous joint with good mechanical and metallurgical properties. Application of Electron Beam Welding to this dual phase steel resulted in a welded joint with good mechanical properties comparable to that of the base metal. The results were discussed based on microstructure analysis and hardness distribution of the welded joints.

Abstract: TC21 with a composition of Ti-6Al-3Mo-1.9Nb-2.2Sn-2.2Zr-1.5Cr is considered a new titanium alloy that is used in aerospace applications as a replacement for the famous Ti-6Al-4V alloy due to its high strength-to-weight ratio, high operating temperature and corrosion resistance. In this study, two different solution treatment techniques were applied on TC21 samples. Solution treatment was applied using two step heating at 1000/800 °C for 15 min each and then cooled using water quenching or air cooling to see the effect of cooling rate on microstructure as well as mechanical properties. The solution treated samples were divided into two groups; one was tested as solution treated samples without aging. While, the second group was aged at 575 °C for 4 hrs. Maximum hardness of 442 HV was observed for the water quenched and aged samples, while the minimum hardness of 340 HV was obtained for water quenched samples without aging. The lowest wear rate was obtained for water quenched and aged samples. However, the highest wear rate was reported for the samples solution treated and water quenched without aging.

Abstract: The quality of welded joints of FSSW is mainly dependent on the processing parameters while the main disadvantage of this process is the creation of an exit hole. Process parameters, namely tool dimensions, tool rotational speed, and stir time were changed and their impact on bond dimensions and weld strength was investigated using 2024-T3 Al Alloy. Macro- and microstructures of the welded samples were examined; shear fracture loads were measured and the optimum set of operation variables was determined. To decrease the exit hole of the first stage the present paper proposes a modified two-stage weld-refill process employing the same welding machine. In this work, this two-stage process was referred to as reversed friction stir spot welding (ReFSSW). In the second stage, a smaller pin was used and the shoulder diameter was designed such that to force the metal of the upper plate to flow towards the exit hole of the first stage decreasing its dimensions. The metal flow in the second stage was evaluated by examining the microstructure of the metal that filled the exit hole of the first stage. Thin stir zone was found around the pin of the second stage followed by thermomechanically affected zone consisting of grains elongated in the vertical direction. The proposed process resulted in smaller exit hole dimensions and consequently higher mechanical properties compared with the conventional single-stage FSSW.

Abstract: Ti-Mn alloy has a high specific strength, excellent cold workability and good biocompatibility. A cold rolled Ti-7 wt.% Mn was compared to annealed sample at 900°C for 10 min and the corrosion resistance property was tested in artificial saliva solution (AS). The Ti-7 wt.% Mn alloys (cold rolled and annealed) were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and compared to pure Ti. Simultaneously, the alloys tested in the AS solution for up to 28 days mainly by following the open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), SEM and EDX. Annealed Ti-7wt.% Mn showed good corrosion properties similar to that of pure Ti, hence the new Ti-7wt.%Mn alloy have higher specific strength than pure Ti, yet showed same corrosion properties which favor implanted dental applications.

Abstract: Recycling of solid waste generated from metallurgical industries will avoid disposal of wastes, enhance the use of secondary raw material fines and save costs. Numerous hydrometallurgical and pyrometallurgical processes, or a combination of both, have been proposed for the utilization of metallurgical waste. Due to insufficient knowledge of the properties of these wastes, most of these attempts still have some technical difficulties. Investigation the properties of metallurgical waste is needed before choosing the suitable recycling process.The present work describes the chemical, morphological and mineralogical properties of blast furnace sludge (BFS) and basic oxygen furnace sludge (BOFS) produced in steel plants in Finland. The investigations indicated that BFS and BOFS show significant contents of iron and coke. The sludges also contain considerable concentrations of unwanted elements such as Zn. The authors propose that microwave dezincing followed by briquetting or pelletization represent a potential method for sludges recycling. Owing to high Fe and C content it can be utilized as self-reducing material.

Abstract: 316L stainless steel is used in various industrial applications including chemical, biomedical and mechanical industries due to its good mechanical properties and corrosion resistance. Recycling of 316L stainless steel scrap without significantly reducing its value has received recently great attention because of the environmental regulations. In the current work, 316L stainless steel scrap was recycled via casting using Skull induction melting technique. The casted products subsequently subjected to laser surface melting process to improve its surface properties to be used for harsh environment. The results showed defect free surfaces with homogeneous microstructures. Nano size grains were also obtained due to rapid solidification process. Such nano size grains are preferred for extending the usage of the 316L stainless steel in new applications.Corresponding author: E-Mail: elgazzar.ha@gmail.com

Abstract: Nanocrystalline bismuth ferrite BFO; BiFeO₃ and manganese sillenite, BMO; Bi₁₂MnO₂₀ (BMO) powders have been successfully elaborated using a facile co-precipitation approach. The formed materials were examined using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM). Furthermore, the change in the optical properties was performed based on Fourier transform infrared spectroscopy (FT-IR) and UV-visible spectrophotometer. Typical, pure BiFeO₃ and Bi₁₂MnO₂₀ phases were detected for the precursors precipitated at pH 10 based on ammonium hydroxide as a base then annealed at 500°C for 2h. Eventually, the optical band gap energy of BFO and BMO using Kubelka–Munk function based on Tauc’s plot was found to be 2.12 and 2.79 eV, respectively.