Showing papers on "Spray forming published in 2004"

Spray forming high speed steel—properties and processing

Abstract: The potential of spray forming (SF) for microstructural refining can be attractive to the production of high speed steels. The refined as-cast structure may lead to important improvements of material properties, compared to conventionally cast materials. The present work aimed to compare the properties of AISI M3:2 high speed steel produced through spray forming and conventional casting. Also, the processing of SF billet is considered, specifically the hot working conditions and its relation to carbide size. A round 400 mm diameter SF billet was produced using a twin atomiser. Characterisation was performed in the as-cast structure and after hot working to 116 mm squared bars and 11 mm diameter round bars. The results show that, compared to conventionally cast high speed steel, the SF material has higher isotropy in toughness due to its less oriented carbide distribution. Regarding processing procedures, time and temperature employed in heating before hot working also affect the microstructure of SF material.

Consolidation of partially amorphous aluminium-alloy powders by severe plastic deformation

Abstract: The microstructures and properties of Al-based alloys produced by severe plastic deformation under high pressure torsion straining were compared with alloys of the same compositions consolidated by hot extrusion and spray-forming processing. Partially amorphous alloy powders of two systems were studied; Al 90 Fe 7 Z 3 alloy powders were prepared by high-energy ball milling and Al 84 Y 3 Ni 8 Co 4 Zr 1 +SiC composite powder was prepared by gas atomisation. The alloy powders have been cold consolidated by high-pressure torsion straining under a stress of 5 GPa resulting in refined and uniform microstructures, with hardness values well above the measured values for the hot-extruded Al 90 Fe 7 Z 3 alloy and for the spray-deposited Al 84 Y 3 Ni 8 Co 4 Zr 1 +SiC composite alloy.

Spray Simulation: Modeling and Numerical Simulation of Sprayforming metals

Abstract: Spray forming combines the metallurgical processes of metal casting and powder metallurgy to fabricate metal products with enhanced properties. This book provides an introduction to the various modelling and simulation techniques employed in spray forming, and shows how they are applied in process analysis and development. The author begins by deriving and describing the main models. He then presents their application in the simulation of the key features of spray forming. Wherever possible he discusses theoretical results with reference to experimental data. Building on the features of metal spray forming, he also derives common characteristic modelling features that may be useful in the simulation of related spray processes. The book is aimed at researchers and engineers working in process technology, chemical engineering and materials science.

Microstructure and mechanical properties of spray deposited hypoeutectic Al-Si alloy

Abstract: The microstructure and the tensile properties of an Al–8.9 wt.% Si–3.2 wt.% Cu–0.9 wt.% Fe–0.8% Zn alloy processed by spray forming was investigated. The alloy was gas atomized with argon and deposited onto a copper substrate. The microstructure was evaluated by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Small faceted dispersoids observed surrounding equiaxial α-Al matrix were identified by SEM–EDS as silicon particles. Sand cast samples with the same composition showed a columnar dendritic α-Al matrix, Al–Si eutectic, polyhedric α-AlFeSi and needle-like β-AlFeSi intermetallics. In the spray formed material the formation of the Al–Si eutetic was suppressed, and the formation of the α-AlFeSi and β-AlFeSi intermetallics was strongly reduced. The fine and homogeneous microstructure showed an aluminium matrix with grain size ranging from 30 to 40 μm, and particle size of the silicon dispersoids having a mean size of 12 μm. Room temperature tensile tests of the spray formed alloy showed relative increasing of strength and elongation when compared with the values observed for the conventionally cast counterparts. These results can be ascribed to the refined microstructure and the scarce presence of intermetallics of the spray formed material.

Workability of spray-formed 7075 Al alloy reinforced with SiCp at elevated temperatures

Abstract: Macrostructures of spray-formed 13 vol.% SiC reinforced 7075 aluminum metal matrix composites (MMCs) were studied. The workability of spray-formed MMCs was studied, which was compared with that of conventional continuously-cast 7075 aluminum alloy. Upset forming was employed to study the workability, for which the strain, strain rate, and temperature were varied. The effects of lubrication were studied. The evolving morphologies during upsetting were investigated together with the surface defects. The relationships between true strain and true stress were studied, and the strain rate sensitivities, m, were calculated. Macrostructural evolution during upset forming was characterized. The forming limit diagram of strain paths during deformation were plotted and analyzed.

Hot workability of spray-formed AISI M3:2 high-speed steel

Abstract: Axisymmetric hot compression tests (900–1100 °C) on spray-formed AISI M3:2 high-speed steel were performed in order to establish suitable parameters for hot forging of this material. Special attention was paid to establish the deformation conditions that lead to the breakdown of the carbide network, present after spray forming, and to avoid fracture of the material as a result of deformation. By a combination of microstructural analysis and finite element modelling, values for fracture stresses in this temperature range and critical strains for the breakdown of the carbide network are given. The activation energy for hot deformation was also determined.

Ultrasonic spray coating system

Abstract: Disclosed is an ultrasonic spray coating system comprising an ultrasonic transducer with spray forming head, integrated fluid delivery device with air and liquid supply passage ways, support brackets and an ultrasonic power generator

Spray forming of Al–Si–Pb alloys and their wear characteristics

Abstract: A modified spray forming process is described to synthesize liquid immiscible alloys based on Al–Si–Pb system. The atomization of the melt was carried out at a gas pressure of 1.0 MPa and the nozzle to substrate distance was varied from 0.35 to 0.55 m. The microstructure and wear characteristics of the spray-deposits were investigated. The results invariably exhibited an equiaxed grain morphology of the primary α-phase with variation in grain size from 10 to 25 μm in addition to a uniform dispersion of ultra-fine particles of lead and globular silicon particles in Al-matrix. The size of Si particles varied from 0.5 to 5 μm and that of Pb particles from 0.1 to 25 μm with variation in deposition distance. The microstructural variation was also observed in different regions of the deposit. The atomized powder particles revealed two different types of microstructures, the one showing a cellular-dendritic morphology of the primary α-phase whereas the other exhibited fine spherical Al-particles dispersed in the matrix of Pb-rich phase. The wear rate and the coefficient of friction of Al–Si–Pb alloy were observed to be lower than that of Al–Si alloy at loads varying from 10 to 90 N at a sliding velocity of 1.0 ms −1 . The possible reasons for this behaviour are discussed in the light of microstructural features of the alloy and the nature of the worn out surfaces of the wear test specimens.

Spray forming of silicon added AZ91 magnesium alloy and its workability

Abstract: Si was added to AZ91 Mg alloy to improve the mechanical properties of the AZ91 Mg alloy. Spray forming was employed to refine the primary phases 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 optical microscope (OM), scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and X-ray diffraction (XRD), which were compared with as-cast microstructures. Workability of spray-formed materials was studied, which was compared with that of cast materials. In the workability study, cylindrical specimens were extruded by simple direct extrusion with various ram speeds at various temperatures. Extrusion pressure and ram displacement were recorded and analyzed. Material flow patterns and macrostructures of extrusion, and surface conditions and microstructures of extruded specimens were analyzed using stereoscope, OM, and SEM. The effects of extrusion temperatures and ram speeds on the workability of spray-formed and cast materials were studied and compared. The extrusion operating conditions of spray-formed and cast materials were determined.

Spray rolling aluminum alloy strip

Abstract: Spray rolling combines spray forming with twin-roll casting to process metal flat products. It consists of atomizing molten metal with a high velocity inert gas, cooling the resultant droplets in flight and directing the spray between mill rolls. In-flight convection heat transfer from atomized droplets teams with conductive cooling at the rolls to rapidly remove the alloy’s latent heat. Hot deformation of the semi-solid material in the rolls results in fully consolidated, rapidly solidified product. While similar in some ways to twin-roll casting, spray rolling has the advantage of being able to process alloys with broad freezing ranges at high production rates. This paper describes the process and summarizes microstructure and tensile properties of spray-rolled 2124 and 7050 aluminum alloy strips. A Lagrangian/Eulerian poly-dispersed spray flight and deposition model is described that provides some insight into the development of the spray rolling process. This spray model follows droplets during flight toward the rolls, through impact and spreading, and includes oxide film formation and breakup when relevant.

Modeling of the solidification of gas-atomized alloy droplets during spray forming

Abstract: In order to describe the microstructure evolution of a supercooled droplet under the situation that the nucleation and the growth of the grains occur concurrently during spray forming, a model has been developed based on the population dynamics method. This model is solved numerically to investigate the solidification behaviors of the gas atomized Al–4.5 wt.% Cu droplets. The results show that the nucleation takes place under a critical supercooling for a given droplet. The grain sizes are significantly different during the period of nucleation and recalescence, but become uniform with the progress of the solidification. In addition, a smaller droplet has a higher cooling rate and a finer microstructure at the end of the solidification.

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract: The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmiss...

Microstructure and wear resistance of spray formed high chromium white cast iron

Abstract: A 2.9% C–22% Cr white cast iron was processed by spray forming (SF) aiming to investigate the resulting microstructure and the wear resistance of this alloy. Two gas to metal flow rate ratios (GMR) of 0.12 and 0.23 were used. The samples were characterized by wear resistance tests, X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM), in both as-sprayed condition and after heat treatments. The as-sprayed microstructure showed M7C3 carbides embedded in a matrix of austenite and martensite and after heat treatments the matrix became a mixture of pearlite and austenite, which presented a better performance in dry sand/rubber wheel wear resistance tests, particularly when associated with a fine distribution of carbides at the higher GMR.

Microstructure and wear characteristics of spray formed and hot extruded Al–Si alloys

Abstract: The microstructural and wear properties of spray formed Al–6.5Si, Al–18Si and Al–18Si–5Fe–1.5Cu (wt-%) alloys have been investigated. The microstructure of the Al–6.5Si alloy exhibits the equiaxed grain morphology of the primary a-Al phase with eutectic Si at the grain boundaries. The size of the primary Si particulates in the Al–18Si alloy varied from 3 to 8 mm embedded in the eutectic matrix. Complex intermetallic phases such as b-Al5SiFe and d-Al4Si2Fe are observed to co-exist with primary Si in the spray formed Al–18Si–5Fe–1.5Cu alloy system. The periphery of the preforms invariably showed pre-solidified particles with a large amount of interstitial pores. An extrusion ratio of 6 : 1 for these alloys led to drastic porosity reduction and extensive breaking of second phase particles. These microstructural features showed distinct variation in the wear behaviour and the coefficient of friction of the alloys. The Al–18Si–5Fe–1.5Cu alloy shows better wear resistance compared with the other two alloys, particularly at higher loads. The coefficient of friction shows a dependence upon the applied load. However, this becomes steady at higher loads. The wear behaviour of these alloys is discussed in light of the morphology of debris particles as well as that of the worn surfaces.

Analysis of deposit growth in spray forming with multiple atomizers

Abstract: In spray forming, multiple atomizers may be used simultaneously to increase the throughput and to spray large size billets. In addition, the advantage of the use of multiple sprays is better control of the distribution of the incoming mass and enthalpy fluxes on the deposit surface. By this, the thermal condition in the top layer of the billet is controlled to ensure steady-state growth and cooling of the deposit. The interaction of two overlapping sprays is described in this paper. The mass flux and the enthalpy distribution have been experimentally investigated for different spray conditions and overlapping angles of the two sprays. Starting from a geometric model, a three-dimensional simulation of the preform geometry and incoming enthalpy flux on the top layer of the deposit has been conducted. The most relevant process parameters and physical properties are taken into account in this model. The model results are in good agreement with experimental preform shapes.

Nitrogen pick-up during spray forming of high-alloyed steels and its influence on microstructure and properties of the final products

Abstract: Spray forming is now getting established as a production route for high-alloyed steels. Tool steels for hot work, cold work and high-speed cutting applications and heat resistant steels generally contain high amounts of numerous elements including chromium, vanadium and aluminium, elements with high affinity for nitrogen. Within the spray forming process nitrogen is usually used as protective atmosphere as well as for gas atomization. The investigation considers nitrogen interaction with steel alloys during the spray forming in a closed vessel. Atmospheres with different nitrogen partial pressure are applied during the process. The microstructure of the spray formed, hot worked and finally heat treated steels is compared. Impact strength, wear resistance and strength at elevated temperature are analysed for the tool steels with respect to the nitrogen content. During melting intensive interaction of the melt with the atmosphere occurs according to the solubility of nitrogen in the alloy and high amounts of nitrogen are picked up. As a general result for the conventional alloys under investigation in spray formed condition this leads to reduction of toughness. This can be explained by additional precipitation of nitrides or carbonitrides. Nitrogen pick-up during spray forming can be avoided primarily by remelting in an argon atmosphere.

Overspray injection in spray forming of CuSn13.5 billets

Abstract: In the conventional spray forming process the yield, i.e. the ratio of the deposited material mass to the atomized melt mass, ranges from 50 to 80%. The feedback of overspray to the process by means of injection into the spray cone has several promising advantages, including increase of the overall yield, decrease of gas consumption, and reduction of segregation. However, overall porosity increases. Several CuSn13.5 billets were spray-formed with varied Powder to Melt mass flow Ratio (PMR) of 0, 0.1, 0.2 and 0.3, varied Gas to Melt mass flow Ratio (GMR) of 0.7 to 0.56 and varied particle sizes of the injected overspray powders (different sieving fractions from 0 to 300 μm). Analyses of the microstructure, porosity, radial segregation of Sn, and the yield were carried out and correlated with the process parameters.

Effect of reactive elements on porosity in spray-formed copper-alloy Billets

Abstract: In spray-formed preforms, porosity is unavoidable. This is because the atomising gas becomes entrapped during the process. Normally, nitrogen is used for atomisation and therefore the voids are filled with this gas, which is not soluble in copper. To obtain a dense material after further forming processes such as extrusion, forging or drawing, porosity has to be limited to a specified level. There are means to influence porosity inside the spray-formed billet. To a certain extent, porosity can be influenced by process parameters. Reactive elements inside the alloy have an additional effect, that is reaction of elements such as Zr, Ti, Al with the entrapped nitrogen. Until now, a detailed explanation has not been given, however, a theory of hot porosity formation is presented in this paper. The calculated content of nitrogen and titanium-nitride is verified using analytical methods. The addition of titanium into the melt can reduce porosity by a factor of three.

Spray forming of the glass former Fe83Zr3.5Nb3.5B9Cu1 alloy

Abstract: The glass former Fe 83 Zr 3.5 Nb 3.5 B 9 Cu 1 (at.%) alloy was processed by spray forming. The aim was to investigate the possibility of forming novel microstructures using this process. The ratio between the gas mass flow rate and the metal mass flow rate used was 0.23, and nitrogen was used as atomization gas. The resulting deposit, weighting about 0.8 kg, as well as the overspray powder with a median particle diameter about 150 μm, were characterized by using X-ray diffratometry, differential scanning calorimetry and scanning electron microscopy with energy dispersive spectroscopy. Saturation induction ( B s ), maximum permeability ( μ max ) and coercive field ( H c ) were measured. The overspray powder showed a microstructure consisting of amorphous and α-Fe phases. The volume fraction of the amorphous phase decreased as the granulometric size range increased. The deposit presented fully crystalline structure with α-Fe, Fe 3 Nb, Fe 2 Zr and Fe 2 B phases. The formation of amorphous phase in the overspray and its absence in the deposit indicates that the deposit was formed by the impacting of a high volume fraction of fully liquid droplets, providing temperature and time enough for complete crystallization of the deposit.

Spray forming of 2014-Al alloy based composites with injection of SiC particulates

Abstract: Aluminium alloy (AA2014) based metal matrix composites were produced by spray atomization and co-deposition. The mass median diameter and mass flow rate of SiC were varied between 6 and 58 mum and between 10 and 30 wt.% of the melt flow rate, respectively. Microstructures of deposits and overspray powder particles were examined. Porosity and SiC content were measured at different positions in the preform. The fraction of SiC particulates incorporated in the preform varies between 4 and 11 vol.%, which is caused by the low compaction efficiency lying within the range of 30 to 50 % of injected secondary particulates. Porosity is observed to increase with increase in deposited SiC content. Optical microscopy shows a uniform distribution of particles in the microstructure. Microstructural examination of overspray powder particles shows that the basic reason for the incorporation of smaller particles is the collision between reinforcement particles and the liquid droplets during flight. The results are presented and discussed in light of process parameters used.

Control of cooling during spray forming of bearing steel billets

Abstract: In an effort to minimize the distortion of bearing steel rings during the production process, 100Cr6 steel billets are spray formed with a unique cooling control system to control the cooling and solidification behavior of the deposits. Effects of heating around the deposits, gas cooling at the substrate bottom and the gas flow over the deposits are investigated both by numerical simulation and experiment. Porosity profiles and microstructures of spray formed bearing steel are examined and evaluated. The investigation results show that the thermal boundary conditions of the deposits play important roles on the cooling and solidification behavior of the deposits, especially at the deposit periphery. Porosity in the 100Cr6 bearing steel deposit can be reduced significantly with the special cooling control system.

Microstructure and mechanical properties of spray formed ultrahigh-carbon steels

Abstract: The microstructure and mechanical properties of the spray formed 1.25C–3.0Si–1.5Cr ultrahigh-carbon steel (UHCS) were described. The 1.25C–3.0Si–1.5Cr UHCS was processed by spray forming to break up carbide networks. The fine pearlites with average interlamellar spacing of 0.20 μm was observed in the as-sprayed microstructure. The ultimate tensile strength and the pearlite spacing can be related by the Hall–Petch equation. The as-sprayed 1.25C–3.0Si–1.5Cr UHCS consisting of fine lamellar pearlites has been shown to exhibit superplastic behavior at elevated temperature. The dramatic change of microstructure from fine lamellar pearlites to equiaxed grains stabilized by spheroidized particles during superplastic deformation has been observed. The estimation on the basis of thermodynamics shows that the content of chromium of 1.54 wt.% is needed to inhibit graphite formation in the 1.25C–3.0Si–1.5Cr UHCS.

Production, microstructural and mechanical characterization of spray formed Al-6 wt.% Fe alloy and pre-mixed Al-6 wt.% Fe/SiCp composite

Abstract: Different batches of Al–6 wt% Fe and of pre-composite Al–6 wt% Fe/SiC powders were produced, via melting of aluminum followed by iron addition in the induction furnace of a gas atomizing unit, eventually adding in situ a suitable amount of SiC particulate The inclusion of the reinforcing particles in the melt was enhanced by means of stirring under an argon shielding atmosphere Gas atomization via sonic close-coupled discrete jet nozzles was thereafter performed, and a part of the spray cone was intercepted by a still substrate The microstructural characterization of both the pre-composite powder and of the spray deposited samples was carried out by microscopy, image analysis and X-ray diffraction The high viscosity of the matrix allowed to achieve a maximum volumetric fraction of reinforcement of around 10% By means of X-ray stress analysis the residual stresses in the spray formed specimens were determined, and resulted to be compressive, and higher in the composite material The elastic properties of the spray formed samples were determined by the flexural resonance test, carried out on prismatic samples cut from the spray formed samples, while their transverse strengths were determined by three points bend test

Spray forming of tubular bearing steel preforms

Abstract: For the manufacture of bearing rings with enhanced performance, 100Cr6 tubular preforms have been spray formed on austenitic steel bars. Porosity profiles and attendant microstructures of the tubular deposits have been characterized in this study. The deposits show refined equiaxed microstructures reflecting the benefits of rapid solidification. Significant porosity is present both in the inner and outer surface regions of the spray deposits. Preheating of the substrate before spraying does not eliminate pores at the base of the deposit due to cooling by the atomizing gas. A high-enthalpy input is predicted to reduce the level of porosity at the surfaces, and to improve material homogeneity.