Showing papers on "Spray forming published in 2007"

Solidification in Spray Forming

Abstract: Solidification in spray forming takes place in two distinct steps: typically half of the alloy latent heat is removed rapidly from the droplet spray created by gas atomization; the droplets are then constituted into a billet at deposition where the remaining liquid fraction solidifies relatively slowly. However, within the droplet spray, individual droplets have different thermal and solidification histories and depositing droplets may be solid, mushy, or liquid. Despite many studies of solidification behavior in spray forming, uncertainties and some misconceptions remain on how the solidification conditions in the spray and billet interact to give rise to the characteristic spray-formed microstructure comprising refined, polygonal/equiaxed primary grains with low levels of microsegregation. This article presents a simple numerical model for the spray-formed grain size arising from the deposition of the various droplets in the spray and combines insights provided by the model with previous investigations of the phenomena occurring during and immediately after deposition to propose a comprehensive description of the important solidification behavior during spray forming. Remelting, grain multiplication, thermal and elemental equilibration, and microstructural coarsening are proposed to play a critical role in the evolution of the spray-formed microstructure.

Magnetic properties evaluation of spray formed and rolled Fe–6.5 wt.% Si–1.0 wt.% Al alloy

Abstract: The Fe–6.5 wt.% Si alloy is an excellent soft magnetic material. However, it is too brittle to be hot/cold-rolled since its ordered structure induces the formation of dissociated superlattice dislocations and correlated high stress concentrations leading to premature fracture. The addition of aluminum to high silicon electrical steels, combined with high solidification rates of the spray forming process, can alter the kinetics of these ordering transformations offering the possibility to obtain thin sheets through the hot/cold rolling process. The aim of this work was to determine the magnetic properties of spray-formed Fe–6.5 wt.% Si–1.0 wt.% Al alloy in the “as-sprayed” condition and after hot/cold rolling. After annealing at 973 K for 1 h, the best magnetic properties were observed in the rolled samples. This result is due to the elimination of microstructural defects and porosity and the formation of DO 3 ordered structure.

Carbon nanotube reinforced aluminum nanocomposite via plasma and high velocity oxy-fuel spray forming.

Abstract: Free standing structures of hypereutectic aluminum-23 wt% silicon nanocomposite with multiwalled carbon nanotubes (MWCNT) reinforcement have been successfully fabricated by two different thermal spraying technique viz Plasma Spray Forming (PSF) and High Velocity Oxy-Fuel (HVOF) Spray Forming. Comparative microstructural and mechanical property evaluation of the two thermally spray formed nanocomposites has been carried out. Presence of nanosized grains in the Al-Si alloy matrix and physically intact and undamaged carbon nanotubes were observed in both the nanocomposites. Excellent interfacial bonding between Al alloy matrix and MWCNT was observed. The elastic modulus and hardness of HVOF sprayed nanocomposite is found to be higher than PSF sprayed composites.

Laser Shock Flier Impact Simulation of Particle-Substrate Interactions in Cold Spray

Abstract: Coating-substrate adhesion in cold spray is a paramount property, the mechanisms of which are not yet well elucidated. To go into these mechanisms, due to the intrinsic characteristics of the cold spray process (particle low-temperature and high velocity) direct observation and control of inflight particles and related phenomena cannot be done easily. For this reason, an experimental simulation of the particle-substrate reactions at the particle impingement was developed. This simulation is based on original flier impact experiments from laser shock acceleration. Relevant interaction phenomena were featured and studied as a function of shearing, plastic deformation, phase transformation primarily. These phenomena were shown to be similar to those involved in cold spray. This was ascertained by the study of the Cu-Al metallurgically reactive system using SEM, TEM, EPMA, and energy balance and diffusion calculations. This simulation could also be used to feed finite element modeling of cold spray and laser shock flier impact.

Microstructural modifications induced during spray deposition of Al–Si–Fe alloys and their mechanical properties

Abstract: In the present investigation, different Al alloys such as Al–6.5%Si, Al–18%Si, Al–5%Fe and Al–18%Si–5%Fe–1.5%Cu (wt.%) were spray deposited and the over-spray powder particles were collected. The spray formed materials as well as their as-cast counterparts were extruded at 480 °C using an area reduction ratio of 6:1. The microstructural features of alloys and the over-sprayed powder particles were examined. The extruded alloys were tested for the tensile properties at a cross-head speed of 0.5 mm min−1. The alloys showed drastic refinement of primary phase and modification of the second phase after spray deposition. Over-spray powder particles showed varied microstructure depending upon the size. Powder microstructures suggested high undercooling experienced by the droplets. The Al–5Fe alloy exhibited partitionless solidification in over-sprayed powder particles. In some cases, non-twinned dendrites were also observed. The mechanical properties of the spray deposited and extruded alloys showed considerable improvement in strength and ductility compared to their as-cast counterparts. This property enhancement is attributed to the unique microstructural features generated during spray deposition process. The results of this investigation have been discussed in light of the microstructural features of the alloys.

Microstructure and mechanical properties of spray deposited and extruded/heat treated 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 porosity level, the conditions of the heat treatment applied and the presence/addition of certain alloying elements to this alloy is known to greatly affect its mechanical properties. In this work, the alloy was gas atomized with argon and deposited onto a copper substrate, extruded at 623 K and heat treated to the T6 temperature Mg was added to some heats. Room temperature tensile tests of the spray formed and extruded alloy showed significant increase of elongation when compared with the values observed for the as-spray formed deposits. This result can be ascribed to the decrease of porosity promoted by the extrusion process. The spray formed and extruded, T6 heat-treated samples showed significant increase of strength without lowering the elongation results. The addition of 0.3 wt.% Mg increased the response to the heat treatment process.

Spray forming of glass former Fe63Nb10Al4Si3B20 alloy

Abstract: In this study the Fe63Nb10Al4Si3B20 (at.%) alloy was processed by spray forming with the aim of investigate the formation of amorphous phases and novel microstructures by the high cooling rate involved in this process. The gas/metal mass flow rate used was 0.25, and nitrogen was used as the atomization gas. The resulting deposit of a mass of about 1.2 kg, as well as the overspray powder, with a median particle diameter about 120 μm, were characterized by using X-ray diffractometry, differential scanning calorimetry and scanning and transmission electron microscopy with energy of dispersive spectroscopy. Magnetic properties were measured through hysteresis loop tracer equipment. The overspray powder presented a mass median diameter of d50 ≅ 120 μm and an increasing of amorphous phase volume fraction with decreasing of particle size. The microstructure of the deposit was heterogeneous varying with the thickness, presenting at center region 20 mm and at border 1 mm with different porosities 5 and 10%, respectively. The thicker region presented fully crystalline microstructure whereas the thinner presented about 75% amorphous phase. The phases identified in both deposit and overspray powder were: amorphous, α-Fe, Fe23B6, FeB and FeNbB. Amorphous phase formation in the thinner region of the deposit and the absence in the thicker region indicates that the resulting amorphous phase depend on the maintenance of amorphous phase formed during atomization that might be controlled by process parameters. Spray forming of Fe-based amorphous alloys followed by hot consolidation in T

Investigation on the microstructure and mechanical properties of the spray-formed Cu-Cr alloys

Abstract: Cu–1.2 wt.%Cr and Cu–3.2 wt.%Cr alloys were prepared by spray forming. The as-deposited alloys were subsequently warm rolled at 300 °C with a 40% reduction and then two types of thermo-mechanical treatments were adopted to enhance the mechanical properties of the Cu–Cr alloys. The microstructural features of the Cu–Cr alloys in different thermo-mechanical processing conditions were characterized using optical, scanning electron and transmission electron microscopy techniques. The results show that the spray-formed Cu–Cr alloys exhibit a better response to heat treatment compared to the conventional casting alloys. The chromium content has a great effect on the aging behaviors of the Cu–Cr alloys. Although a higher chromium content leads to a larger volume fraction of chromium precipitates generated during the solidification, it does not cause an increase in the mechanical properties. The chromium content should be lower than 1.2 wt.%.

Analysis of Twin-Nozzle-Scanning Spray Forming Process and Spray Formed High Speed Steel (HSS)

Abstract: The process characteristics of the twin-nozzle-scanning spray forming were introduced in the paper briefly. Additionally, the microstructure of high-speed steels produced by spray forming was inspected using scanning electron microscopy (SEM, back diffraction morphology) and energy dispersive spectroscopic analyses (EDS). Without thermal isotropic pressure (HIP) and hot forge, at some position of spray deposited HSS billet some porosity was found, the forming reason of porosity was analyzed.

Shape memory effect and superelastic behavior of TiNi shape memory alloy processed by vacuum plasma spray method

Abstract: Machining of TiNi shape memory alloy into a complicated three-dimensional (3D) shape is quite difficult, thus a near-net shape forming of 3D shaped TiNi alloy is attractive and cost-effective. Vacuum plasma spray (VPS) process is one of such near-net shape forming processes. In this paper, two kinds of thick TiNi layer, Ni-rich and Ti-rich compositions, were fabricated by VPS process and their shape memory effect (SME) and superelastic (SE) behaviors were characterized. As-VPS processed Ni-rich TiNi which was subjected to homogenization at 1163 K for 7.2 ks and subsequent aging at 773 K for 18 ks exhibited good martensitic transformation behavior. The recoverable strain of the TiNi alloys due to SME and SE behavior were measured to be 2.4% and 5.0%, respectively. The Ti-rich TiNi alloy also exhibited good martensitic transformation behavior and SME in the as-homogenized state.

Three-Dimensional Mathematical Modeling and Numerical Simulation of Billet Shape in Spray Forming Using a Scanning Gas Atomizer

Abstract: A three-dimensional shape model, tracing the coordinates of the moving surface of a growing billet spray formed by a scanning gas atomizer, has been developed in this study. New mesh generation and surface smoothing algorithms for the growing billet, as well as shading algorithms, are incorporated into the model for accurate prediction of the shape and dimensions of the billet during spray forming. Mass flux distribution profiles of the spray generated by the scanning atomizer under different spraying conditions have been revealed for the shape modeling. Geometrical evolution of the billet in spray forming has been investigated based on analysis of the scanning mechanism of the atomizer. The shape modeling has been validated by different numerical algorithms and experimental investigations. Finally, the influence of processing conditions on the shape and dimensions of spray-formed deposits have been simulated and discussed. Near-net-shaped preforms with triangular or square cross section, other than the usual circular cross section, are expected to be produced under appropriate spray forming conditions.

Modeling the Spray Forming of H13 Steel Tooling

Abstract: On the basis of a numerical model, the temperature and liquid fraction of spray-formed H13 tool steel are calculated as a function of time. Results show that a preheated substrate at the appropriate temperature can lead to very low porosity by increasing the liquid fraction in the deposited steel. The calculated cooling rate can lead to a microstructure consisting of martensite, lower bainite, retained austenite, and proeutectoid carbides in as-spray-formed material. In the temperature range between the solidus and liquidus temperatures, the calculated temperature of the spray-formed material increases with increasing substrate preheat temperature, resulting in a very low porosity by increasing the liquid fraction of the deposited steel. In the temperature region where austenite decomposition occurs, the substrate preheat temperature has a negligible influence on the cooling rate of the spray-formed material. On the basis of the calculated results, it is possible to generate sufficient liquid fraction during spray forming by using a high growth rate of the deposit without preheating the substrate, and the growth rate of the deposit has almost no influence on the cooling rate in the temperature region of austenite decomposition.

Spray Forming of Mg2Si Rich Aluminum Alloys

Abstract: Aluminium Alloys with a 22 wt.-% Mg2Si content were spray formed. This alloy features a low density and is therefore a superior material for lightweight applications. The main problem in the spray forming of this type of alloy was the occurrence of high porosities. First process optimizations have been performed to decrease porosity under a certain level, so that it can be closed by an extrusion process.

Influence of processing technology on phase transformations in a rare-earth-containing Mg–Zn–Zr alloy

Abstract: An investigation was carried out into the effect of annealing on the precipitation processes and stability of the microstructure in the magnesium alloy Mg-3 wt.% Zn-1 wt.% Nd-0.5 wt.% Zr produced by various solidification conditions. The alloy was produced by squeeze casting and spray forming with and without subsequent extrusion. The phase transformations were studied by means of relative electrical resistivity changes during isochronal annealing in the temperature range from 293 to 783 K. The microstructure of selected states was analyzed by transmission electron microscopy.

Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al89La6Ni5 Metallic Glass Matrix Composites

Abstract: A spray-formed Al89La6Ni5 metallic glass matrix composite plate was obtained in thickness of 1 mm and diameter of 200 mm, comprising over 64% primary crystals (e.g. Al11La3) uniformly dispersed in the glass matrix. The microstructure can not be achieved by annealing corresponding amorphous precursor. The crystals existing in the glass matrix were found to increase the hardness of the composite. Through nanoindentation test, the hardness and modulus of the composite at ambient temperature were found superior than its amorphous ribbon counterpart. The hardness of the composite was estimated with the rule of mixture from the constituents to be 4.4 GPa, which agreed well with the nanoindentation results. From loss modulus measurement and TMA test at elevated temperatures, a weak Tg signal in the range of 213– 240 � C was revealed in the as-spray-formed composite. Furthermore, the dimension shrinkage of the composite was only 0.5% during the TMA test, which is much smaller than that of amorphous ribbon counterpart by up to 20%. The enhanced hardness by constituent second phases and the dimension stability of the composite are associated with their inherent microstructure, the primary crystals in particular. [doi:10.2320/matertrans.MJ200767]

Spray Forming of Al-Fe-Cr-Ti and Al-Si-Li Alloys

Abstract: This work presents an investigation of the spray forming and downstream processing of Al alloys that are difficult to produce in bulk by conventional solidification processing: Al-Fe-Cr-Ti alloys for intermediate temperature applications and Al-Si-Li alloys for high stiffness, low density applications in fast moving machinery. For the Al-Fe-Cr-Ti alloys, spray forming is being investigated to allow the scale-up of alloy compositions previously explored only as ribbons or powders in traditional rapid solidification routes. For Al-Si-Li alloys, spray forming is used to provide globular primary AlLiSi in a fully divorced AlLiSi/α-Al eutectic structure. For both alloys, the as spray formed and downstream processed microstructure of 20kg billets has been investigated by scanning electron microscopy, electron probe microanalysis, and X-ray diffractometry. Preliminary mechanical properties have also been investigated.

Aluminum based alloy preform, aluminum based alloy dense body, method for producing them and sputtering target

Abstract: PROBLEM TO BE SOLVED: To provide a technique, where the variation in the density of an aluminum based alloy preform by a spray forming process is reduced, and the preform can be produced in a high yield. SOLUTION: In the aluminum based alloy preform, the average of relative density is 50 to 65%, and the difference between the part showing the maximum value of the relative density and the part showing the minimum value of the relative density is ≤30%. The method for producing the preform includes: a stage where an aluminum based alloy is melted within the range of (liquidus temperature+100°C) to (liquidus temperature+400°C), so as to obtain the molten metal of the aluminum based alloy; a stage where the molten metal of the aluminum based alloy is subjected to gas atomizing under the conditions in which the gas/metal ratio is ≥4 Nm 3 /kg, and, provided that the angle made by the central axis of the confronted gas atomizing nozzle is defined as 2α, α satisfies 1 to 10°, so as to be atomized; and a stage where the atomized aluminum based alloy is deposited on a collector under the conditions in which spray distance is 700 to 1,200 mm and the collector angle is 20 to 45°, so as to obtain the preform. COPYRIGHT: (C)2007,JPO&INPIT

Spray forming of Si-Al alloys for thermal management applications

Abstract: N.B. For copyright reasons two figures have been removed from this thesis prior to making it available in ORA.

Spray forming of Si-Al alloys for thermal management applications

Abstract: This thesis describes the processing and characterisation of Al-70Si alloys manufactured by gas atomised spray forming at Sandvik-Osprey (Neath, UK) and Oxford University using a newly commissioned spray forming pilot-plant facility. Spray formed Al-70Si (CE7) provides an attractive balance of thermophysical properties making it suitable for thermal management applications. Microstructural characterisation of CE7 was conducted using optical microscopy, image analysis, electron probe micro analysis (EPMA) and electron backscatter diffraction (EBSD). Microscopy revealed an interpenetrating network microstructure consisting of fine, randomly oriented polycrystalline primary Si interpenetrated by large, α-Al grains devoid of eutectic Si. Mechanical testing and thermal cycling simulated a service environment and revealed for the first time crack initiation, growth and blunting mechanisms, the effect of intermetallic phases on the bulk mechanical properties, and anisotropy effects resulting from macrosegregation of Al during solidification. A relationship between the inter-phase interface length and the fracture toughness has been proposed and methods of interface length refinement have been investigated, including chill casting and spray forming. Spray formed CE7 modified with separate additions of B, P, P+Ce and Sr have been microstructurally and mechanically characterised and compared with binary CE7. While alloy additions were effective in refining primary and eutectic Si in chill cast alloys, spray formed alloys showed little change in interface length. Particle injection of Si-Al powder was effective in refining the scale of the spray formed microstructure, and improving mechanical properties. The deleterious effect of intermetallic phases on bulk mechanical properties has been demonstrated and highlighted the importance of melt cleanliness and materials control during manufacturing.

Optimisation of Spray Forming Ni Superalloys via Process Modelling and On-Line Monitoring

Abstract: The optimisation of spray forming IN718 alloy rings for aeroengine applications was investigated using both modelling and experimental approaches. A multiphysics numerical model has been developed and implemented to assist in the optimisation of the spray forming process. IN718 alloy ring preforms were spray formed at University of Oxford (UK) and The University of Bremen (Germany). A variety of on-line monitoring facilities were integrated onto spray forming units to (1) investigate the dynamics of alloy melt atomisation and droplet deposition at a sprayed surface; and (2) acquire ring preform thermal history and various thermal boundary conditions for the numerical model. Modelling and experiments were performed iteratively to investigate the effects of key spray forming parameters including gas metal flow ratio, atomiser scan, substrate heating schemes on the resulting ring preform shape, internal heat flow and solidification. It was found that preform top surface temperature and alloy liquid fraction inside the preform during spray forming were critical factors in governing the formation of macro/microporosity and the grain size of as-sprayed preforms. In the optimised conditions, IN718 alloy ring preforms were characterised by a microporosity of less than 1.5% and randomly oriented equaxied grains of 20-50 μm.

Characteristics of hot compression deformation and microstructure evolution of spray formed nickel base superalloy

Abstract: The hot compression test of the spray formed plus hot isostatic pressed(HIP)nickel- based superalloy was conducted on Gleeble-1500D thermal mechanical simulator at a temperature range of 1050—1140℃,and strain rate range of 001—100 s~(-1)with engineering strain 50%The processing map and activation energy map of the alloy were established by using tested data,and mi- crostructure evolution of deformed samples was also examinedThe results show that the grain size of spray formed alloy does not significantly increase after HIPDue to the variations of dislocation move- ment and density in deformation,the yield drop was observed only at higher temperatureProcessing map and activation energy map indicate that the instability domain of the alloy is at the temperature range of 1050—1110℃and strain rate of 001s~(-1),and the highest efficiency of power dissipation(η) appeared at 1110—1140℃and 10—100 s~(-1),and a platform region was also observed at 1140℃and 10—100 s~(-1)So,the optimum conditions for thermomechanical processing correspond to theηmaximum region and activation energy platform region,at which the full dynamic recrystallization (DRX)occurred

Spray-Formed High-Tin Bronze—A Homogeneous Pre-Material for ${\rm Nb}_{3}{\rm Sn}$ -Based Superconductor Wire

Abstract: The advantages of high-tin bronze which is produced by the innovative process "spray forming" and its commercial application in Nb3Sn superconductor wire are presented. An important decision in the processing of Nb3Sn superconductor wire after the bronze method is the choice of pre-material. As the bronze, together with the niobium, is subjected to hot and cold forming processes, homogeneous bronze pre-material is required. High-tin bronze produced by spray forming exhibits a high degree of homogeneity. Advantages of spray-formed bronze are the very fine, equi-axed grains, the homogeneous grain structure, the reduced delta phase particle size, the minimized delta phase volume fraction and the homogeneous element distribution. These advantages are given in all spray-formed bronze qualities with tin contents up to 20%. Spray-formed bronzes with tin contents of 14.5%, 15.5% and 16.0% and an additionally titanium content up to 0.3% are commercially produced and supplied to different superconductor wire manufacturers. The processing results show that the production process stability is excellent and the results of superconducting properties are reproducible. Bronzes with tin contents of 17% and 20% have also been successfully spray-formed and formed into tubes and rods. These bronzes are now subject of investigations regarding the use in future Nb3Sn superconducting magnets with increased magnetic field strength.