Showing papers on "Spray forming published in 2005"

Microstructure and electrical conductivity of Al-SiCp composites produced by spray forming process

Abstract: Al- SiCp composites have been synthesized by spray forming process with variation in particle flow rate, size of reinforcement particles and their volume fraction. The microstructure of composites and their electrical conductivity have been investigated. The results showed a uniform dispersion of large size particulate phase in the matrix of the primary α- phase with its equiaxed grain morphology. However, clustering of small size particles was observed at the grain boundary and grain junctions. The grain size of the composite materials was observed to be lower than that of the base Al- alloy. The composite materials invariably indicated their lower electrical conductivity compared to that of the monolithic Al- alloy. The electrical conductivity of composites decreased with increase in the volume fraction and decrease in size of the reinforcement particles. A high flow rate of particles during spray deposition resulted in a decrease in its conductivity. These results are explained in the light of thermal mismatch between the matrix and the reinforcement phases resulting in generation of high dislocation density. The droplet- particle interaction and resulting microstructure evolution during the spray deposition of the composites are discussed.

Spray processing of 2014-Al+SiCP composites and their property evaluation

Abstract: Aluminium alloy (2014-Al alloy)-based metal matrix composites containing SiCP particulates were produced by spray co-deposition. The mass median diameter and mass flow rate of SiCP were varied from 6 to 30 μm and from 10 to 30 mass% of the melt flow rate respectively. Spray formed billets of 200 mm diameter and 400 mm height were produced. Porosity and SiC content were measured at different positions in the preform. The mass fraction of reinforcement incorporated in the preform varies from 6 to 15%. Porosity is observed to increase with the increase in the surface area of the reinforcement/matrix interface. Optical microscopy shows a uniform distribution of particulates. Smaller size particles are pushed towards the grain boundaries during solidification of the deposit, in contrast to their large size counterparts. The matrix grain size varies from 15 to 50 μm with the variation in size and content of reinforcement particles. The grain size of the matrix decreases with the increase in the SiCP content. This decrease in the grain size is more sensitive to the size of the reinforced particulates, i.e. smaller size particulates give rise to a better refinement. Microstructural examination of overspray powder particles shows that the collision of melt droplets and SiC particles is the major mechanism for the incorporation of small particles. The ageing behavior of composites was studied at different temperatures for various sizes and volume fractions of particles, and the mechanical properties were evaluated. Composites with smaller particulate size show an early hardness peak than those with larger size particulates. Composites reinforced with intermediate size of SiCP particulates show an increased elastic modulus compared to unreinforced alloy.

High-Speed Steels Produced by Conventional Casting, Spray Forming and Powder Metallurgy

Abstract: Powder metallurgy (PM) and spray forming (SF) have been reported as important alternative routes for tool steel production. The ability to promote refined and more uniform microstructures is their main advantages, leading to improved properties and larger isotropy. While PM application is a completely established technology, the SF process may be considered as a not totally explored field. Therefore, the present work aimed to study the potential of both processes, focusing at high-speed steel (HSS) production. AISI M3:2 highspeed steel was produced by conventional casting, spray forming and powder metallurgy. Conventional ingots and a 400 mm diameter SF billet were rolled to small diameter bars, with cross section around 110 mm. The PM material was evaluated in the as-HIPed condition, in comparative diameters. Large diameter HSS bars are used mainly in cutting tools, but are also applied in cold work tooling when high wear resistance is required. In the present characterisation, microstructures and bend test analysis were used, both in transverse and longitudinal directions. The results show that the as-HIPed PM material presents finer and more uniform carbide distribution, leading to a complete isotropy and higher toughness than conventional steel. In the SF material, carbides are also finer, have good distribution and the isotropy is considerably higher than that for conventional HSS.

Drop-on-demand deposition of superheated metal droplets for selective infiltration manufacturing

Abstract: The deposition of metal droplets is of great engineering interest because of its practical applications to such various fields as spray forming, surface treatments, and solid freeform fabrication (SFF), etc. The objective of this work is to develop a new drop-on-demand generator of superheated metal droplets that is suitable for the selective infiltration manufacturing (SIM), a new SFF process for the direct fabrication of metal parts. The developed generator comprises a solenoid vibrator, a micro-drilled 130 μm diameter nozzle, an impulse-transmitting rod, and a tubular heating element. A parametric study showed that the diameter of droplets was 301 ± 10 μm when the superheating temperature of Sn–37Pb wt% was set at 260 °C, 299 ± 12 μm at 290 °C, and 301 ± 12 μm at 320 °C. Experiments showed that the developed generator is able to deposit superheated metal droplets according to the frequency of the vibrator.

Microstructure and Magnetic Properties of Fe-6.5wt%Si Alloy Obtained by Spray Forming Process

Abstract: Deposits of the Fe-6.5wt%Si alloy produced by spray forming were annealed at temperatures between 900 and 1300oC, during 1h in vacuum and quenched in oil at temperatures between 300 and 700oC, separately. Magnetic properties, singular microstructure and random crystallographic texture were measured. After annealing at 1250°C for 1h under vacuum, the average grain size is of 500 μm, the grain orientation is random and the magnetic properties were: power loss of 1.30 W/kg, maximum permeability of 15400 and coercive force of 40 A/m, at B=1 T, f=60 Hz by using 0.60 mm thick rings for all studied samples. Higher annealing temperatures cause no decreasing of these properties. After quenched at 700°C, an improvement the magnetic properties where detected due to antiphase domain B2 growth. The magnetic properties were: power loss of 1.59 W/kg, maximum permeability of 12300 and coercive force of 76 A/m, at B=1 T, f=60 Hz.

Plasma spray formed near-net-shape MoSi2–Si3N4 bulk nanocomposites—structure property evaluation

Abstract: This article, for the first time, presents the challenges toward the successful consolidation of near-net-shape bulk MoSi 2 –Si 3 N 4 –SiC nanocomposite using plasma spray forming. A detailed characterization of the spray formed bulk nanocomponent has been performed using optical microscopy (OM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and Vickers hardness testing. Vickers hardness (900 Hv) and fracture toughness (∼>5 MPa m 1/2 ) of the nanocomposite showed a little deviation from the expected, which might be due to the difference in the particle (Si 3 N 4 ) size and their distribution in the MoSi 2 matrix as a function of component thickness. Relatively higher hardness is attributed to the retention of the nanostructure in the composite. In addition, the as fabricated bulk nanocomposite showed enhanced oxidation resistance.

Corrosion performance of Al-Si-Cu hypereutectic alloys in a synthetic condensed automotive solution

Abstract: In this investigation the corrosion resistance of four Al-Si hypereutectic alloys in a solution typical of condensate from automotive fuel combustion products, and referred to here as synthetic condensed automotive solution, has been studied. Three commercial alloys that are used for cylinder liners, and a laboratory made alloy, were studied by electrochemical impedance spectroscopy and measurements were taken after increasing times of immersion in this solution. Comparison of the electrochemical response of the four alloys in the corrosive solution was carried out. Although the mechanisms by which the four alloys corroded were similar, the results indicated differences in corrosion resistances of these alloys, and these differences could be related to their microstructures. The laboratory prepared alloy showed increased susceptibility to pitting corrosion compared to the commercial alloys. The surfaces of the alloys were examined, before and after the corrosion test, by scanning electron microscopy and analyzed by energy dispersive spectroscopy. The results indicated preferential attack of the aluminium matrix phase in all the alloys. The alloy with higher copper content and prepared by spray forming was more susceptible to pitting compared to the other alloys. The EIS response at low frequencies indicated a diffusion-controlled process, probably that of oxygen to the alloy interface.

Inhibited coarsening of a spray-formed and extruded hypereutectic aluminum-silicon alloy in the semisolid state

Abstract: The microstructural evolution of a spray-formed and extruded hypereutectic aluminum-30 pct silicon-5 pct copper-2 pct magnesium alloy heated into the semisolid state has been investigated. Liquid is formed initially by a quaternary eutectic reaction and then by a ternary melt reaction. These reactions occur relatively quickly. However, the binary Al-Si eutectic melt reaction takes a significant time—around several hours depending on the temperature. The coarsening rate constants (K) for the growth of the silicon particles are approximately three to four orders of magnitude lower than those for the majority of metal spray-formed alloys. This may be associated with difficulties in addition or removal of atoms from the low index silicon facets. Where growth does occur, agglomeration of silicon particles may play a large role, especially at higher liquid contents. Electron backscatter diffraction (EBSD) gives evidence of agglomeration, and furthermore shows that high-angle silicon-silicon boundaries are not wetted with liquid.

Optimizing material distribution for tool trajectory generation in surface manufacturing

Abstract: Surface manufacturing is widely used in industry. Automatic CAD-guided tool planning has many applications in surface manufacturing, such as spray painting, spray forming and indirect rapid tooling. Generating tool trajectories for freeform surfaces to satisfy the given requirements is still highly challenging due to the complex geometry of free-form surfaces and the spray gun model. A CAD-guided tool trajectory generation system for free-form surfaces has been developed in our previous work. A material distribution model is also presented. Because of the irregular shape of automotive parts, the spray width may not be a constant. Also the path integration for a part with multiple patches may need the spray width to be changed. This will increase the material distribution deviation. In this paper, algorithms are developed to minimize the material distribution deviation because of the change of the spray width. The material distribution requirements can then be satisfied

Spray formed bearing steel insensitive to distortion

Abstract: To minimize the distortion of bearing steel components during manufacturing processes, 100Cr6 steel (SAE 52100) has been produced by spray forming as an alternative approach to conventional continuous casting process Material characteristics and distortion behaviour of the spray formed 100Cr6 steel were investigated in comparison with continuous cast material The investigation showed that the spray formed 100Cr6 steel exhibited lower distortion potential than the conventional material due to much better metallurgical homogeneity

Crystallization behavior of spray-formed and melt-spun Al89La6Ni5 hybrid composites with amorphous and nanostructured phases

Abstract: The crystallization behavior of spray-formed and melt-spun Al 89 La 6 Ni 5 alloys was studied. Spray forming process could produce a bulk scale Al 89 La 6 Ni 5 hybrid composite consisting of amorphous and nanostructured phases directly without the need of an amorphous precursor. The fraction of amorphous phase in the spray-formed composite was determined to be 36% by DSC, which came mostly from supercooled liquid droplets upon spray forming. Amorphous phase partially devitrified to nano-scale fcc-Al secondary crystals during deposition. Two significant primary crystals observed in the spray-formed bulk hybrid composite are Al 3 Ni and Al 11 La 3 (Ni), but their size is reduced to about 1 μm. Contrary to the microstructure of spray-formed deposit, the heat-treated and fully devitrified melt-spun ribbon hybrid composite consists of nano-scale fcc-Al, Al 3 Ni, Al 11 La 3 as well as some metastable Al 6 Ni and Al 4 LaNi phases with sizes of about 200 nm. Deformation twins were found in the Al 11 La 3 (Ni) crystals in spray-formed deposit, but not in the fully devitrified ribbon. Finally, the microstructure structure evolution of spray-formed deposit and heat-treated ribbon are studied and proposed.

Spray Forming and Post Processing of Superalloy Rings

Abstract: Spray forming as a technology to produce near net shape components or preforms for additional forming operations with defined microstructural properties is well known for several alloys and applications. The production of spray formed superalloy rings made of IN718 and U720 for aero engine components in order to reduce production cost is the goal of the current EU-research project. Several spray runs were carried out at University of Bremen to optimize the process parameters regarding a low porosity, low segregation and a high yield. Macro and microetchings were prepared to analyze the influence of the parameter variations on before mentioned structural properties. Several optimized rings were used to examine the influence of thermomechanical processing on porosity and microstructure of spray formed superalloy rings. Hot isostatic pressing and forging processes were performed separately as well as in combination in order to obtain the ideal post processing route, which was determined via microstructure analysis. As a result of this project, it became clear that HIPping is an integral part of the postprocessing of as-sprayed material, due to the fact that it was not possible to produce as-sprayed material without porosity. The development of micro- and macro structural properties through all these processes and their variations will be shown. Another paper presented here will focus on the final properties and applications of this material.

Spray Forming and Thermal Processing for High Performance Superalloys

Abstract: A unique pilot low-pressure spray forming plant was established and its spray atomisation and deposition process developed to study the new processing methods for high performance materials and to develop spray forming technology suitable for making sound superalloy preforms The results indicated that high density (>99%) preforms (billets and rings) with little gas pick-ups and with the microstructural features of rapidly solidified superalloys, ie refined equiaxed grains and uniform microstructure, could be achieved after the optimisation of the spray atomisation and deposition process The effects of subsequent thermal processing on the density, microstructure and mechanical properties of the spray formed superalloy were investigated Compared to the turbine disks and rings made by wrought superalloys, the spray formed superalloys with identical chemistry showed significantly improved metallurgical quality, higher mechanical properties, and better hot workability

Crystallographic orientation-spray formed hypereutectic aluminium-silicon alloys

Abstract: Aluminium-silicon alloys have been wide accepted in the automotive, electric and aerospace industries Preferred orientation is a very common condition for metals and alloys Particularly, aluminium induces texture during the forming process The preparation of an aggregate with completely random crystal orientation is a difficult task The present work was undertaken to analyse the texture by X-ray diffraction techniques, of three spray formed hypereutectic Al-Si alloys Samples were taken from a billet of an experimental alloy (alloy 1) and were subsequently hot-rolled and cold-rolled (height reduction), 72% and 70%, respectively The other used samples, alloys 2 and 3, were taken from cylinders liners The results from the Laue camera showed texture just in the axial direction of alloy 3 The pole figures also indicated the presence of a typical low intensity deformation texture, especially for alloy 3 The spray formed microstructure, which is very fine, hinders the Al-Si texture formation during mechanical work

Spray Forming of AZ91 Magnesium Alloys with and without Si Addition

Abstract: ray forming was employed to refine the microstructures of AZ91 and AZ91-3.34wt%Si Mg alloys during solidification by means of rapid solidification generated at atomization and droplet flight stages. The process parameters of spray forming were varied to reduce the porosity level and improve the morphology of the billet preforms. As-spray-formed microstructures were characterized using OM, SEM/EDS, and XRD, which were compared with as-cast microstructures. The significant differences of grains, Mg2Si and Mg17Al12 in morphology and in size between as-spray-fromed and as-cast materials are mainly due to fast cooling and solidification rates of spray forming process. Supersaturated matrix is found in as-spray-formed materials due to rapid solidification generated by spray forming. Overall, spray-formed materials are shown to have four characteristics, which are much finer microstructures, uniformly distributed phases, equiaxed-shaped phases, and supersaturated matrix.

Research on Ultra-High Strength Al-11Zn-2.9Mg-1.7Cu Alloy Prepared by Spray Forming Process

Abstract: An ultra-high strength Al-11Zn-2.9Mg-1.7Cu alloy has been prepared by spray forming process. The microstructures of as-cast and as-deposited alloys have been studied. XRD analysis result shows that the phases of spray formed Al-11Zn-2.9Mg-1.7Cu alloy consist of a-Al, MgZn2, Al2Cu and Al2CuMg. T6 heat treatment process is used to strengthen the alloy. The ultimate tensile strength reach up to 810MPa, and the elongation is about 9~11%. This kind of aluminum alloy is an ideal structural material for the aerospace and automobile industries.

Preparation of heat-resistant aluminium alloy

Abstract: The invention was involved in spray forming method, especially for preparation of 8009 alloy ingots. On the base of existing method, the powder of same alloy (the diameter is less than 43um) in the atomizing air to change the atomizing medium. The controlled temperature was 860-950deg.C and extrusion coefficient was 16-30.The melt temperature was 950-1250deg.C and the injection temperature wad 900-1200deg.C . The atomizing pressure was 0.4-0.8MPa and the pressure of sending powder was 0.1-0.2MPa. The chassis speed was 200-600r/min and the drop speed was 200-600r/min. The cooling velocity in the process of coagulation of preparation of 8009 alloy ingots was increased and the educt of Al3Fe4 phase was inhibited, so the mechanical property of 8009 alloy was improved totally. Increasing the recovery rate of powder was in favor of recovery of alloy powder and protection of environment.

Effect of processing parameters on physical properties of spray formed and stir cast Al–2Mg–TiO2 composites

Abstract: In the present study, a modified spray forming set-up has been used to prepare Al–2Mg–TiO2 composites. Up to 6 and 11% by weight of the rutile particles have been successfully incorporated in Al–2Mg matrix using the modified spray forming technique. The density measurement reveals that the optimum nozzle-to-substrate distance is 30 cm and the optimum speed of rotation of the substrate is 8 rpm. The electrical resistivity measurement shows that resistivities of composites are marginally greater than the base alloy. The cold rolled alloy shows a wider hump in the resistivity variation, due to the recrystallization of the matrix. Similar observations are made in case of both stir cast and spray formed Al–2Mg–TiO2 composites. The kinetics of recrystallization of composites is faster than the matrix alloy. This is evident from relatively small hump in resistivity variation with temperature of composites. The fast recrystallization kinetics in composites is due to the generation of dislocations owing to the thermal mismatch between the Al matrix and the rutile particles. In addition to the hump at lower temperature, resistivity measurement of Al–2Mg–TiO2 composites shows a peak at temperature between 350 and 400 °C. The peak is due to the formation of the TiAl3 phase at TiO2 particle–matrix interface. Thermal conductivity of spray formed Al–2Mg–TiO2 composite is greater than the base alloy.

Modelling Shape Evolution and Heat Flow of Spray-Formed Ring Preforms

Abstract: A finite element model has been developed to simulate the coupled effects of deposit shape evolution and heat flow inside spray formed ring-shaped deposits. The shape model was developed using Matlab and included the features of: (1) atomiser scanning; (2) substrate movement relative to the atomiser; and (3) sticking efficiency. Atomiser scan and various substrate horizontal travel speeds were studied to optimise the ring shape in terms of useful materials suitable for downstream processing. The heat flow model was developed using the commercial finite element code Femlab. A data mapping technique was developed to transfer thermal data between different domains when the computational domains are subject to changing geometry and therefore the coupled effects of shape evolution and heat flow were addressed. Spray forming of ring deposits was performed on the large spray forming unit at Oxford University. In-situ temperature measurements were carried put for acquisition of boundary conditions and validation of the heat flow model. Heat flow modelling revealed that edge effects had a strong influence on the ring thermal history and the porosity distribution inside the deposits is closely related to the local solidification time.

Microstructural Characterisation by Scanning Electron Microscopy of Spray Formed Al/SiCp Matrix Composite

Abstract: The material used in this work was produced by spray forming AA7475 aluminium alloy and co-depositing silicon carbide particles (20% volume fraction). The spray formed composite billets were hot extruded into round bars. The microstructure was examined in the as received and heat treated (annealed, aged, and overaged) conditions by scanning electron microscopy. Scanning electron microscopy revealed an extensive Mg2Si phase precipitation at the Al/SiCp interface due probably to Mg segregation from the matrix to the interface, during the heat treatments.

Effect of Warm Rolling on Microstructure and High Temperature Mechanical Behavior of a Nano-Structured Al-8Fe-2Mo-2V-1Zr Alloy

Abstract: Mechanical properties of a nano-structured Al-8Fe-2Mo-2V-1Zr alloy produced by spray forming and subsequent hot-extrusion at 420°C were investigated in terms of tensile test as a function of temperature. Warm rolling was adapted as an additional process to expect further refinement in microstructure. Well-defined equiaxed grain structure and finely distributed dispersoids with nano-scale in particle size were observed in the spray formed and hot extruded sample (as-received sample). The average grain size and particle size were measured to 500 nm and 50 nm, respectively. While it was found that warm rolling gives rise to precipitate fine dispersoids less than 10 nm without influencing the grain size of matrix phase, in the temperature range of RT∼150°C, distinguishable changes in ultimate tensile strength were not found between the as-received and warm-rolled samples. At elevated temperatures ranging from 350 to 550°C, warm-rolled sample showed a higher value of elongation than as-received one although similar values of elongation were observed between two samples at temperatures lower than 350°C.