Papers by Keyword: Spray Forming

Abstract: The present paper describes the Lead dispersion in hypoeutectic Aluminium-Silicon alloys and their microstructural characteristics. The homogeneous dispersion of Lead (Pb) in Aluminium-Silicon alloys (Al-6Si+Pb (=0, 10, 15, 20, 25)) were fabricated by using of spray forming technique (also known as spray casting or spray deposition) in the form of near-net shape disc. The microstructural characterization has been done for different location of spray formed disc by using optical microscopy (OM), Scanning electron microscopy (SEM) and X-Ray Diffraction (XRD) respectively. The results of the optical image were exhibited the equiaxed and globular grain morphology of primary Aluminium with the homogeneous dispersion of extremely fine and malleable particles of Lead and spherical particles of silicon in α–Aluminium matrix. The dispersed Lead has seen clearly in the SEM images of spray formed Aluminium-Silicon alloys and result of XRD pattern confirmed the phases of Aluminium-Silicon and Lead. The grain size of Aluminium has been analyzed by intercept line method. The lattice parameter and lattice strain have been calculated with the help of the XRD pattern to determine the effect of Lead dispersion on Al-Si alloy.

Abstract: Spray forming has attracted considerable attention for the production of high speed steels due to its potential and priority in the microstructure refining and cost saving. In this study, high-quality large billets of 2060 high speed steel were successfully produced by spray forming process using a twin-atomizer facility. As-deposited billet was subsequently processed by hot forging, quenching in oil at 1180 °C and a triple tempering in the temperature range of 500-580 °C. The microstructures and hardness of the deposit and their subsequent development resulting from hot forging and heat treatment were investigated. This paper was designed to provide insight and have a better understanding of such a system for the steel. The results showed that the as-deposited microstructure was composed of the fine equiaxed grains with V-rich MC and W-Mo-rich M₂C carbides non-uniformly distributed along the grain boundaries and inside the grains. M₂C presented rod-like or unconnected net-shaped morphologies in the as-deposited microstructure. Following hot forging, metastable M₂C carbides were completely decomposed into refined MC and M₆C nearly spherical carbides uniformly distributed throughout the microstructure. A hardness value of 31HRC was attained for the spray deposited and hot forged samples. With increasing the tempering temperature, hardness was increased firstly and then decreased. Secondary hardening peak appeared at 540 °C for spray formed 2060 steel austenitized at 1180 °C, and the corresponding peak hardness reached 71HRC.

Abstract: Deposits of the Fe-6.5wt%Si alloy rapidly quenched by spray forming were investigated. The order phase can be either B2 or DO3 depending on annealing treatment conditions. The observation of pairs dislocations indicates the presence of super dislocations and B2 antiphase boundaries (APBs) which affects significantly the soft magnetic properties. The dislocations bound the APBS which yield δ fringes when image 200 superlattice reflections. Samples treated at 700oC for 1 h were oil quenched, this has induced a decreasing of power loss and the TEM micrographs have showed developed 1⁄4 <111> antiphase domain structure in the B2 phase. The magnetic properties were: power loss of 1.59 W/kg and coercive force of 76 A/m, at B=1 T, f=60 Hz. The samples annealed at 1250°C for 1h showed the same interaction between the APBs but better power losses on their magnetic properties. The magnetic properties were: 1.30 W/kg power loss and 40 A/m coercive force, at same conditions described above. This suggests a strong interaction between magnetic properties and antiphase domain structure in the B2 ordered phase. Optical microscopy observations corroborate the magnetic measurement conclusions.

Abstract: Spray forming is a new developed advanced metal-forming process, of which the property benefits from rapid solidification. The porosity produced during the atomization progress can obviously decrease the material performance. In this paper, a self-designed Laval-type atomizer is used to improve atomization efficiency. The atomization results show that the atomizer can obtain well atomization effect at a relative lower atomization pressure, and the mass median diameter d₅₀ is 63.5μm and 43.4μm when the atomization gas pressure P₀=0.4 and 0.8MPa separately. The technological parameters are optimized by overall considering the atomized droplet size, gas consumption, deposition property, and the metal yield. By the designed atomizer, the as-deposited billet with lower porosity content can be obtained with the technological parameters of the melting temperature T=800°C, atomization pressure P₀=0.6MPa, and spray distance h=500mm. Further test with the deposited billet show that the grain size of the spray formed 7055-Al alloy is mainly ranging 10~30μm, which is about one third of that of as-cast billet.

Abstract: The hot deformation behavior of a nickel based P/M superalloy by spray forming and hot isostaticpressingwas investigated by isothermal compression test at Gleeble 3500 thermal mechanical simulator. The compression test was performed in the temperature ranging from 1025°C to 1150°C and in the strain rate ranging from 10^-1/s to 10^-3/s. The results show that the flow curves of true stress and true strain exhibit typical dynamic recrystallization and dynamic recovery. Compression temperature and strain rate have a strong effect on the dynamic recrystallization grain refinement.With higher strain rate the refined dynamic recrystallizationmicrostructure can be obtained at deformation temperature lower thanγ′solution temperature. Grain coarsening occurs at the deformation temperature close to γ′solution temperature, and the grain grows up obviously with decreasing strain rate.

Abstract: Three kinds of master alloys, including scrap material, vacuum induction melting (VIM) ingot and electro slag remelting (ESR) ingot, were spray formed into different billets. The influence of master alloy on the cleanliness of spray formed superalloy was investigated by means of electron beam (EB) button melting and Scanning Electron Microscopy (SEM), on the basis of optimized process of spray forming and EB button melting. The results show that the inclusions in spray formed preform are mainly composed of alumina and magnesia, stem from master alloy and some refractory materials in the process of remelting. The cleaner the master alloy, the lower level of inclusion contents of the billet. Among three kinds of master alloys, the ESR ingot exhibit the cleanest melt surface in the process of re-melting and contains much smaller inclusions in EB button. The cleanliness of spray formed billet is better than ingot stack for deposition. Superclean sprayforming billet with smaller size inclusions (<100μm) can be attained by the ESR ingots.

Abstract: In this paper, Al-Zn-Mg-Cu alloys were produced through spray forming technique. Microstructures of interconnected porosity defects in spray-deposited preforms were characterized by means of field emission scanning electron microscopy (FESEM). The formation mechanisms of different types of interconnected pores were investigated. The densification of deposited alloy preforms with interconnected pores was also analyzed. Interconnected pores in deposited alloys may be classified into four types, interconnected pores between interstices, between gas pores, between interstices and gas pores, and interconnected pores associated with solidification shrinkage, according to morphology and formation mechanism.

Abstract: The computational fluid dynamic (CFD) software was used to calculate the velocity field in atomization chamber of spray forming equipment. The relationship between melt flow rates, gas aspiration of the atomizer and operating pressure are complex, and the above mentioned parameters are closely related to the atomization process. The influences of different delivery chamfers on gas flow field, which is determined by atomizer structure, were analyzed. Using K-epsilon model with a symmetrical domain, the gas dynamic of different delivery chamfer conditions were investigated. The results indicate that the sharp point of delivery tube causes detachment of flow field, and 56°, 45° and 34° chamfer conditions have same diffusion angle. Gas was aspirated from delivery tube when chamfer was 0°, which is beneficial to liquid metal flow in atomization process.

Abstract: In this study, 8009 heat resistant aluminum alloy was synthesized by the spray atomization and deposition technique. The microstructure and mechanical properties of the alloy were studied using transmission electron microscopy, X-ray diffraction, and tensile tests. The secondary phases in the microstructure of the spray-deposited alloy were examined. The tensile test results indicate that the spray-deposited 8009 alloy both at room and elevated temperature displays superior tensile strength due to the presence of the thermally stable Al₁₂(Fe,V)₃Si particles.

Abstract: Heat-resistant Al-8.5Fe-1.3V-1.7Si aluminum alloys were prepared by spray forming technique. The phase transition of deposited alloys from room temperature to 500°C was measured by Differential Scanning Calorimeter. The organization and the second phases of the alloys were observed and studied by transmission electron microscopy. The research results show that No endothermic peak appears in the deposited alloys during heating process, there is no phase transition occur in the alloy during the heating process from room temperature to 500°C. The deposited alloys mainly include α-Al and α-Al₁₂(Fe,V)₃Si phase. Under the transmission electron microscopy, there are also a small amount of slug, fan-shaped, needle-like, block, strip second phases, these phases are Al₁₂Fe₃Si, Al₈Fe₂Si, θ-Al₁₃Fe₄, Al₉FeSi₃, Al₆Fe.