Key Engineering Materials Vols. 622-623

Abstract: The influence of different secondary cooling conditions (air cooling and water cooling) on microstructure, texture and properties of Fe-1.2wt%Si non-oriented silicon strips prepared by twin-roll strip casting were studied. Specimens were examined by OIM, EBSD and X-RD. The microstructures obtained by water cooling are more homogeneous and coarse in grain size than that obtained by air cooling. The dominant {100} texture can be observed in the case of water cooled, while the air cooled strip show a diffuse texture characteristic. The annealed sheets subjected to water cooling than air cooling show higher permeability and lower core loss due to the presence of relatively larger grain size and more ideal fibre components such as Goss and Cube., It seems that rapid secondary cooling of as cast strips can furtherer optimize the microstructure and texture prior to cold rolling and then substantially the final magnetic properties of 1.2wt% Si non-oriented silicon steels.

Abstract: Hypereutectic Al-Si-Cu alloys which are typical light-weight wear-resistant materials, are required to improve the ductility as well as the strength and wear-resistance for the wider applications. Increase in amounts of primary silicon particles causes the modified wear-resistance of hypereutectic Al-Si-Cu alloys, however, it leads to the poor strength and ductility. It is known that dual phase steels composed of hetero-structure have succeeded to bring contradictory mechanical properties of high strength and ductility concurrently. In order to apply the idea of hetero-structure to hypereutectic Al-Si-Cu alloys for the achievement of high strength and ductility along with wear resistance, ultrasonic irradiation to molten metal during the solidification, which is named sono-solidification, was carried out from its molten state to just above the eutectic temperature. The sono-solidified Al-17Si-4Cu alloy is composed of hetero-structure, that is, hard primary silicon particles, soft non-equilibrium α-Al phase and eutectic region. Rheocasting was performed at just above the eutectic temperature with sono-solidified slurry to shape a disk specimen. After the rheocasting with modified sono-solidified slurry held for 45s at 570^oC, the quantitative optical microscope observation exhibits that the microstructure is composed of 18area% of hard primary silicon particles and 57area% of soft α-Al phase, in contrast there exist only 5area% of primary silicon particles and no α-Al phase rheocast with normally solidified slurry. Hence the tensile tests of T6 treated rheocast specimens with modified sono-solidified slurry exhibit the improved strength and 5% of elongation, regardless of more than 3 times higher amounts of primary silicon particles compared to that rheocast with normally solidified slurry.

Abstract: Laser Beam Forming is a flexible manufacturing process with great promise for sheet and metal forming, hence, considered as a novel manufacturing method for forming and shaping of metallic components. Being a thermo-mechanical forming process that enables parts or components to be formed with external heat of a laser beam, it is important to monitor and measure the temperature during the laser forming process in order to ensure the integrity of the processed components. This study reports on the temperature monitoring and measurement during laser beam forming process of steel sheets. The experimental design followed the L-27 Taguchi Orthogonal Array. The temperature of nine sets of samples laser beamed formed at different process parameters were monitored using the thermocouple data logger. The temperature for all the components formed at the nine parameter windows were analysed during the process. Hence, it was observed that the measured temperature increases with the increasing line energy during the laser beam forming process.

Abstract: Many metals, such as titanium and superalloys, are used for a wide range of aerospace applications, which include aircraft gas turbine engine and space launcher propulsion engine. In order to manufacture a stiffened extension with superplastic blow forming at elevated temperature, the structural integrity of the joint part was investigated since the welded or bonded joint of internal channels should maintain its strength during superplastic blow forming process. Various types of joint methods were performed in order to investigate microstructural and mechanical properties of the bonded specimen at elevated temperature. In this paper, the possibility of manufacturing combustion chamber and other aerospace components with superplastic blow forming of titanium and superalloy was demonstrated. An innovative manufacturing method to produce complex configuration from titanium multi-sheets by superplastic forming with low hydrostatic pressure was presented. The result also shows that the manufacturing method with superplastic blow forming of multi-sheets of IN718 alloy has been successfully demonstrated for near net shape forming of subscale nozzle extension cone with internal channels.

Abstract: The processes of spinning and flow forming of hard metal sheets made from nickel superalloy INCONEL can be realized cold or with heating - e.g. by a induction or laser. When metal sheet is heated it is necessary to measure the temperature field on heated area, because its determines the deformation susceptibility. To control the temperature field pyrometers and infrared cameras are used. Due to strong changes in the surface of a formed material, under temperature influence (oxidation) and the action of the forming rolls, it is necessary to determine the emissivity coefficient values as a function of temperature and surface conditions. The paper presents the concept of determining these values, as well as an alternative technique for measuring temperature field, based on the methods of image analysis.

Abstract: Powder metallurgy (PM) of nickel-based superalloys has been used for a wide range of products owing to their excellent special properties in processing and applications. Typical processes for high performance PM superalloys include hot isostatic pressing, hot extrusion and hot isothermal forging. Hot isostatic pressing is normally conducted at a high temperature, by using a low pressure for a long time in a closed vessel, resulting in high cost and low product efficiency. In this paper a novel forming process, i.e. direct powder forging for powder metallurgy of superalloys has been proposed. In this process, the encapsulated and vacuumed powder is heated up to the forming temperature and forged directly to the final shape, by using a high forming load for a very short time. Direct powder forging is a low-cost and energy-saving process compared to conventional PM processes, and in addition, press machines of conventional forging can be used for direct powder forming process. In direct powder forging it is important to control the relative density of the deformed part since the existence of voids could reduce the mechanical strength and fatigue life. In this paper, feasibility tests of direct powder forging are presented. Microstructure, relative density and hardness of the formed specimen were studied.

Abstract: The proposed Ferrite-Bainite Dual Phase (FBDP) steel is suitable for automotive industries. The steel satisfies high specific strength (strength/weight ratio), which is positively reflected on both fuel consumption and crashing resistance.

Abstract: The strengthening mechanisms which are operative in bainite are very well known: small bainite packet, small width of the laths, dislocation density and size and number of carbide particles (Fe₃C), among others. Bainite packet size has been traditionally considered as the value measured by optical microscopy (OM), as electron back scattered diffraction (EBSD) technique is relatively recent. In a V-microalloyed steel with bainitic microstructure of C=0.38%, V=0.12% and N= 0.0214% the average length and width of ferrite laths and of cementite carbides were measured. On the other hand, the bainite packet size was measured by OM and EBSD with a misorientation of 15o. These values of the microstructural units have been taken in account to calculate the effective surface energy γ_p given by Griffith’s model for cleavage fracture. It was concluded that bainite packet size determined by EBSD with a misorientation angle criterion of 15o was the microstructural parameter that controls cleavage crack propagation. Given the relationship between the average unit crack path (UCP) and the bainite packet size, it was concluded that the effective surface energy of cleavage fracture (γ_p) would be between 71.6 and 82.6 J m^-2.

Abstract: Forming of micro-components from powder with fields-activated sintering technology (FAST) renders different forming and sintering mechanisms, comparing to that occurring during the forming of macro-sized components with a similar technology. Establishing a good understanding of these mechanisms would help process design and control aiming at achieving desired quality of the components to be formed. This paper presents a study and the results on the sintering kinetics of the powder during Micro-FAST for the fabrication of micro-gears (the module is 0.2 and the pitch diameter 1.6 mm) from copper powder. The results showed that the densification of copper powder is related largely to the bulk plastic-deformations of the particles and the melting of the particles at contact interfaces. Particularly, it is revealed that plastic deformations of the copper particles mainly occurred at approximately 340 °C and melting of the particle-interfaces at approximately 640 °C. Differently, in a densification process with a traditional powder sintering method, grain growth and neck growth would, normally, be two dominant mechanisms that achieve the densification of powder.

Abstract: To improve mechanical properties of a closed-cell type aluminum foam, the surface pores are filled with aluminum powder by selective laser melting (SLM). The relationship between the laser irradiation conditions and solidification characteristics of aluminum powder is investigated with one-line laser irradiation on the aluminum powder with a thickness of 5 mm. The aluminum powder is continuously melted and solidified with laser spot diameter of 0.6 mm and scanning speed of 10–20 mm/s. According to the successful melting and solidification conditions, the SLM is applied to the surface pores of a closed-cell type aluminum foam supplied with aluminum powder. The supplied aluminum powder is confirmed to be successfully melted and welded to the aluminum foam. As the result, the aluminum foam with nonporous surface layer (sandwich structure) is fabricated by the SLM with aluminum powder. The compressive behavior of the fabricated aluminum foam with nonporous surface layer is investigated.