Journal of advanced materials and processing
Volume:11 Issue: 2, Spring 2023

The aim of this research is to study the effect of fine grain structure on the mechanical and superplastic properties of cold worked SP700 alloy. Thickness reductions of 20%, 40%, and 60%. were applied during cold rolling. Then the specimens were annealed at 700°C, 750°C, and 800°C for 40 minutes. The tensile test was applied at 25, 700oC, 750°C, and 800°C with strain rates of 0.01s-1, 0.005s-1 and 0.001s-1. The SEM and OM were used to analyze the specimens' microstructures. The alloy cold rolled to 40% reduction and annealed at 700°C exhibited a maximum elongation of 1380% at a stress level of 30 MPa and a strain rate of 0.005 s-1 at 700°C. Microstructural evlauation showed that during the superplastic test, dynamic recrystallization took place. The strain rate sensitivity varied in the range of 0.32 to 0.46. Fundamental equations were also used to determine the mechanism of superplasticity. The activation energy is obtained as 385 kJ.mol-1. Results validated that the Rachinger sliding is the main superplastic mechanism in the SP700 alloy.

Semi-stable β-titanium (Ti-3873) Ti-3Al-8Mo-7V-3Cr alloy with excellent workability properties has been designed based on high demanded aircraft Ti-5Al-5Mo-5V-3Cr alloy according to semi-experimental d-electron approach. The aim of the present research is to investigate the deformation behavior of Ti-3873 alloy via warm compression test. For this purpose, compression test has been conducted in the temperature range of 650-850 °C and strain rates of 0.001,0.1 and 1, 1 s-1 at dual phase α/β and single phase β regions. The test was continued up to plastic strain of 0.7. For establishing the relationship between the microstructure and flow behavior, the initial and subsequent microstructure of the specimens after warm deformation was studied via optical and scanning electron microscopes. The microstructural evaluation and flow curves revealed that dynamic recovery and partial continuous dynamic recrystallization were the dominant restoration mechanisms. The results showed that softening has been increased in the temperature range of 800-850 °C and strain of 0.001 and 0.1 s-1 which is confirmed by the activation energy calculated from the sinus hyperbolic equation. The activation energy for dual phase α/β and single phase β regions are determines as 429 kJ/mol and 353 kJ/mol, respectively. The higher value of activation energy for α/β dual phase region is attributed to dynamic globularization of α lamellas. The preferable regions for hot workability of the alloy were achieved at the temperature range of 800-850 °C and strain rate of 0.01-0.001 s-1 corresponding to the peak efficiency of 39% in the processing map.

Steel slag, as a by-product of the iron industry, is widely produced in the world. In this paper, steel slag from local furnaces is partially replaced as concrete aggregate to compensate for irregular consumption of raw material for concrete and reduce environmental impacts of waste slag. Six mix designs were considered, and three categories of aggregate size were selected to evaluate the aggregate replacement effect in the concrete samples. Sieve analysis, X-ray diffraction (XRD) analysis, aggregate porosity, slump, compressive strength, and microstructure analysis were implemented to investigate aggregates and concrete samples. The results showed that compressive strength and water absorption of the concrete with 20% aggregate replacement were 37.4 MPa and 3%. By 20% aggregate replacement, improvement in the compressive strength and reduction in the water absorption were observed. Increasing aggregate replacement to 40% reduced compressive strength by 62% and increased water absorption. In the concrete containing 62% of the replacement, the required compressive strength of 30 MPa, as design compressive strength, was achieved. However, although the pores in the slag aggregates can affect fresh and hardened properties of concrete, selecting an appropriate range of aggregates from the gradation curve can limit the side effects due to the pores.

In this research, laser cladding of Stellite 6 on the 35CrMo substrate was done. Various parameters of the laser caldding process were studied and after optimization of the parameters, microstructure and microhardness were evaluated. Characterization of the cladded layer was done by scanning electron microscope, X-ray diffraction, and Vickers microhardness. The results show that the clad track height was dependent on the parameters of the powder feeding rate and the laser scanning speed, and the laser power had the minimal effect. Similarly, the clad track width was controlled by the laser power and laser scanning speed. The clad track dilution was proportional to the laser power and had the greatest impact compared to other parameters. The wetting angle was controlled by three parameters: laser power, laser scanning speed, and powder feeding rate. Laser power of 550 W, powder feeding rate of 0.6 g/s, and laser scanning speed of 10 mm/s were chosen as the optimal parameters. The results showed a good metallurgical bonding between the cladding and the substrate. The microstructure of the single clad track was dense and crack- and pore-free, and due to the thermal and concentration gradient changes during solidification, it consisted of three different areas, including planar, columnar dendritic, and equiaxed dendritic microstructures. A significant improvement in the microhardness of Stellite 6 cladding was observed as compared with the substrate. By increasing the overlapping ratio from 30 to 60%, the dilution rate decreased from 31 to 7%. As a result, the microhardness reached 361 HV in the overlapping ratio of 30% and further to 452 HV in the overlapping ratio of 60%. The overlapping ratio of 60% between adjacent passes created the best results.

In this research, HP heat-resistant steel modified by niobium was welded using the GTAW process and ER NiCr-3, ER NiCrMo-3, and MF filler rods. The microstructure of the base metal, weld metals, heat-affected zone, and interface between the base and weld metals was studied using optical and electron microscopes (FESEM) equipped with an EDS point analysis system. The microstructure of HP steel base metal with an austenitic matrix and chromium-rich and niobium-rich precipitates on the grain boundary was observed. All three weld metal microstructures have a fully austenitic matrix that is dendritically solidified. In all weld metal produced by three different weld wires, precipitates rich in chromium (M23C6 carbide) and precipitates rich in niobium and titanium (MC carbide) were observed. The microstructural studies showed that the interfaces between the base metal and weld metals are fully continuous and free of cracks and voids. An unmixed zone (non-homogeneous zone) with a large width was formed at the interface between the base metal and the ERNiCr-3 weld metal. Any unmixed zone was not observed at the interface of the base metal and weld metals of the ERNiCrMo-3 and MF steel. Epitaxial growth was observed at the interface between the base metal and weld metals of ER NiCrMo-3 and MF steel.

Friction Stir Welding (FSW) is a welding technique that has brought significant advancements to the field of metal joining. An innovative variation of this technique is known as bobbin tool friction stir welding (BTFSW). This study aimed to compare various aspects, including force, temperature, and strain, between FSW and BTFSW. For this reason, the finite element method was employed, utilizing the Eulerian technique to model the welding process. The findings revealed that the presence of two shoulders in BTFSW enhances heat generation by increasing the contact area with the workpiece, resulting in improved frictional heat production. The advancing side of the BFSW sample exhibited the highest recorded peak temperature, reaching 532°C. On the other hand, the CFSW sample displayed a comparatively lower peak temperature of approximately 347°C. The elevated temperature in BTFSW enhances material flowability and plasticity, leading to reduced longitudinal forces compared to FSW. In CFSW, the longitudinal force varies between 3500 N and 2500 N, whereas in BTFSW, the longitudinal force is significantly lower, approximately 800 N. Furthermore, analysis of strain distribution demonstrated that BTFSW exhibits an hourglass-shaped strain pattern, indicating a larger area affected by strain when compared to FSW. These results highlight the benefits of BTFSW in terms of enhanced heat generation, reduced forces, and a larger strain-affected area, underscoring its potential as a superior welding technique.