Showing papers on "Spray forming published in 1995"

Science and technology of rapid solidification and processing

Abstract: Grain Boundary Deformation and Fracture of a Fine Grained, High Purity AL-2per cent MG Alloy at 150C (423K) H.C. Chang, N.J. Grant. Growth Parameters in Formation and Stability of Rapidly Solidified Microstructure H. Jones. Synthesis and Properties of Bulk Metallic Glass W.L. Johnson, A. Peker. Synthesis, Fabrication and Properties of Bulk Amorphous and Nanocrystalline Alloys S.J. Poon, Y. He, G.J. Shiflet, G.M. Dougherty. Aluminum-Rich Metallic Glasses G.S. Shiflet, Y. He, G.M. Dougherty, H. Chen. Numerical and Experimental Study of Porosity Evolution during Plasma Spray Deposition of W H. Liu, W. Cai, R.H. Rangel, E. Lavernia. Spray Processing of Ti Metal Matrix Composites P.S. Grant, Y.Y. Zhao, J.H. Li, M.L. Jenkins, B. Cantor. Spray Forming with Uniform Droplets C.A. Chen S. Sahu, J.-H. Chun, T. Ando. Microstructure and Mechanical Properties of Alloys and Metal Matrix Composites (MMCs) Processed by the Spray Forming Technique J.S. Zhang, W.J. Zhang, G.L. Chen. Surface Crystallization and Field Induced Anisotropy of Cobalt-Rich Amorphous Alloys C.K., Kim, R.C. O'Handley, W.K. Ho. A Perspective on the High Resistance to Coarsening and Durability of Silicide Dispersions in RSPM Al-Fe-V-Si Alloys D.M.J. Wilkes, H. Jones. Short-Drop-Tube Experiments on AlCuFe Alloys C. Voltz, B. Vinet, J. Bletry. Solidification of Refractory Materials Processed in the Ultrahigh-Vacuum Drop Tube at the CEREM/Grenoble S. Tournier, B. Vinet, E. Cini. Thixoforming of Spray Cast Materials A. Zavaliangos, A. Lawley. High Temperature Deformation of Rapidly Solidified 7091 P/M Aluminium Alloy H.N. Azari, G.S. Murty, G.S. Upadhyaya. Microstructures, Tensile Properties and Fatigue Crack Growth Behaviour of the Zirconium Modified 2024 Alloys Processed by Liquid Dynamic Compaction X. Duan, A. Farah, I. Ucok, N.J. Grant. Processing and Structure of a Rapidly Solidified Mg-8.5wt.per centLi-1wt.per centCa-1wt.per centY Alloy via Liquid Dynamic Compaction I. Ucok, K. Kubota. Rapid Solidification Processing of Discontinuously-Reinforced Metal Matrix Composites T.S. Srivastan, T.S. Sudarshan, E.J. Lavernia. Processing and Properties of Spray Formed 2xxx Aluminum Alloys A. Kahveci. Self-Diffusion and Relaxation Processes in Amorphous Metallic Alloys H. Kronmuller, W. Frank, P. Scharwaechter. Microscopic Criteria for Glass Formation T. Egami. Magnetic Behavior in Nanocrystalline Fe-Cu-Nb-Si-B Alloys at Elevated Temperatures I. Skorvanek, C.K. Kim, R.C. O'Handley. Diffusion, Oxidation, and Nucleation of Crystalline Phases in the Glass-Forming Systems Zr60Ni25Al15 S. Schneider, X. Sun, M.-A. Nicolet, W.L. Johnson. Non-Contact AC Calorimetry of Undercooled Alloys D.S. Lee, D. Uffelman, W.L. Johnson. Diffraction Studies of the Structure of Amorphous and Nanocrystalline Fe-W Alloys C.N.J. Wagner, E. Yang, M.S. Boldrick. (Part contents).

Gas atomizer with reduced backflow

Abstract: An improved molten metal spray forming atomization ring converter adapted for the spray forming of a refined molten metal from a molten metal refining or melting chamber wherein the molten metal is atomized into tiny molten droplets by gas impingement in a stream of molten metal and to the structure by which the molten metal droplets are preferentially directed to and deposited on a target surface The molten metal spray forming atomization ring converter is adapted to control the flow of liquid metal droplets and to avoid a backflow of such droplets during the gas atomization by providing structure, such as small apertures to the inner diameter of the ring, by providing large holes through the inner diameter and adding a porous metal filter to cover the large holes or by providing a gas supply system independent from the atomization system gas supply, such that a pressure or diffused source of gas is provided at the inner bore These modifications produce a relatively small mass flow of gas sufficient to feed the entrainment requirement of the high speed jets, but sufficiently low enough to avoid preatomization of the liquid metal wherein backsplash of the metal is reduced and/or prevented

Modelling of droplet dynamic and thermal histories during spray forming—III. Analysis of spray solid fraction

Abstract: The complex equations governing droplet dynamic and thermal behaviour during spray forming have been analysed to give an approximate expression for the spray solid fraction as a function of the process parameters of the form f S = a 1 + a 2 Δ T + a 3 υ g i z 2 / 3 M ˙ 1 / 2 where vgi is the initial gas velocity at atomisation, Ṁ is the molten alloy mass flow rate, ΔT is the molten alloy super heat above the liquidus, and z is the axial distance. This expression provides an extremely convenient relationship to indicate the variation of spray solid fraction during spray forming, which is a key variable controlling final as sprayed billet microstructure. Predicted N2 atomised Al-4 wt%Cu spray solid fractions based upon the analytical expression have been compared with equivalent results obtained from a detailed computer model described previously in Parts I and II under a wide range of conditions of vgi, Ṁ, ΔT and z and gave good agreement. Best-fit values of a1, a2 and a3 were 1.9 × 10−1, −1.4 × 10−3 and 1.3 × 10−3 respectively, in good agreement with predicted values.

Methods of recycling oversray powder during spray forming

Abstract: A method for the recycling of overspray powder during spray forming is provided. The method involves providing a refining vessel to contain an electroslag refining layer floating on a layer of molten refined metal. An ingot of unrefined metal is lowered into the vessel into contact with the molten electroslag layer. A current is passed through the slag layer to the ingot to cause surface melting at the interface between the ingot and the electroslag layer. As the ingot is surface melted at its point of contact with the slag, droplets of the unrefined metal are formed and these droplets pass down through the slag and are collected in a body of molten refined metal beneath the slag. The refined metal is held within a cold hearth. At the bottom of the cold hearth, a cold finger orifice permits the withdrawal of refined metal from the cold hearth apparatus. The refined metal passes from the cold finger orifice as a stream. The stream is atomized for spray forming into a preform article on a spray collection station having a solid receiving surface for receiving the atomized metal thereon to form the preform article. The powder produced during the atomization which was not deposited on the solid receiving surface of the spray collection station is recycled onto the top of the molten slag in the electroslag refining station.

Systems for recycling overspray powder during spray forming

Abstract: A system for the recycling of overspray powder during spray forming is provided. The system involves providing a refining vessel to contain an electroslag refining layer floating on a layer of molten refined metal. An ingot of unrefined metal is lowered into the vessel into contact with the molten electroslag layer. A current is passed through the slag layer to the ingot to cause surface melting at the interface between the ingot and the electroslag layer. As the ingot is surface melted at its point of contact with the slag, droplets of the unrefined metal are formed and these droplets pass down through the slag and are collected in a body of molten refined metal beneath the slag. The refined metal is held within a cold hearth. At the bottom of the cold hearth, a cold finger orifice permits the withdrawal of refined metal from the cold hearth apparatus. The refined metal passes from the cold finger orifice as a stream. The stream is atomized for spray forming into a preform article on a spray collection station having a solid receiving surface for receiving the atomized metal thereon to form the preform article. The powder produced during the atomization which was not deposited on the solid receiving surface of the spray collection station is recycled onto the top of the molten slag in the electroslag refining station.

The dynamics of spray-formed billets

Abstract: A model is developed to describe three-dimensional transient growth of spray-formed aluminium billets. Approximation via an averaging method reduces the problem to a single quasilinear partial diff...

Spray forming of Al/SiC metal matrix composites

Abstract: Summary This paper describes the as-sprayed microstructure of a model Al-4wt%Cu/SiC particulate (Al4Cu/SiCp) metal matrix composite (MMC) manufactured by spray forming, and the relationship between microstructure and solidification conditions during manufacture. Injection of SiCp into the melt atomization region during the spray forming of Al4Cu results in significant SiCp incorporation into molten droplets during atomization, and relatively little incorporation during flight to the substrate and at deposition. SiCp clustering is evident in the Al4Cu droplets and results in clustering in the as-sprayed MMC deposit. Matrix dislocation and precipitation microstructures are dependent upon local solidification conditions during spray forming. Increased dislocation density and increased quantity of fine-scale θ′-Al2Cu precipitation is found in the α-Al(Cu) matrix where local deposit cooling rates are high, i.e. in the vicinity of the substrate/deposit interface and when increased spray distances are used in manufacture. Lower dislocation density and increased quantity of grain-boundary θ-Al2Cu is found where deposit cooling rates are relatively low, i.e. distant from the substrate/deposit interface and at decreased spray distances. In all cases, dislocation densities are higher in α-Al(Cu)/SiCp interfacial regions than in the α-Al(Cu) matrix. There is no evidence of α-Al(Cu)/SiCp interfacial reaction in the as-sprayed condition indicating that cooling rates during spray forming are sufficiently rapid to prevent reaction.

SiCp/Mg-Ce and Mg-Ca alloy composites obtained by spray forming

Abstract: SiC particulate dispersed Mg-10%Ce and Mg-5%Ca alloy composites were successfully obtained by using an experimentally constructed spray forming apparatus with simultaneous injection of SiC particles. The spray formed composites showed relative density higher than 95%. The relative density was improved to above 99% by hot extrusion. The uniformity in distribution of dispersed SiC particles was also improved by hot extrusion. It has been shown that fine SiC particles which are even smaller than 1μm in diameter can be dispersed by spary forming technique. The measured Vf of SiC particles in spray formed and hot extruded materials increased with an increase of the average particle size. The obtained Vf of coarse SiC particles which is 12μm in average size was as high as 18.8%. The elastic modulus and hardness were appreciably increased by dispersion of SiC particles. However, improvement in tensile strength was not observed in the composites.

Metallic articles having heat transfer channels

Abstract: Metallic articles (21) having heat transfer channels are produced by solidification of molten metallic material (3, 4, 6) about preformed channel defining means (5) such that a solidified metallic deposit having heat transfer channels is formed. The channel defining means may be in the form of either solid elements (which are subsequently removed to leave the channels), or conduit elements (which may remain permanently embedded in the article). Moulds, dies, cores and other tools for use in moulding or casting of plastics and metals are particularly suitably formed by the process, the heat transfer channels being used for cooling of the respective articles during use. The molten metallic material is preferably deposited by spray forming utilising one or more sprays of molten metallic material.

Effect of processing on microstructure and wear characteristics of an Al-4·5Cu-10Pb alloy

Abstract: An Al-4·5Cu-10Pb alloy was processed by spray forming as well as impeller mixing followed by chill casting methods. The microstructure, mechanical properties and dry sliding wear characteristics of the alloy were evaluated. The spray formed alloy showed an equiaxed grain morphology with a uniform dispersion of lead particles in the matrix phase. In contrast a cellular-dendritic morphology of the primary phase was the characteristic feature of the alloy processed by impeller mixing and chill casting method. The spray formed alloy indicated its superior mechanical properties and low wear rate particularly at higher applied load and sliding velocity. The possible reason for this behaviour is discussed in the light of microstructure of the alloy and the nature of the worn out surfaces of the wear test specimens.

Spray Forming with Uniform Droplets

Abstract: A Sn – 37 wt.% Pb eutectic alloy was spray formed with a uniform-droplet spray generated by a non-gas atomization process based on the controlled break up of a laminar jet. Uniform droplets were produced to have identical thermal history and velocity and were deposited onto a substrate in controlled motion to provide distinctly different thermal states of the droplets and the deposit surface. The spray formed alloy presented fine, equiaxed two-phase microstructures when partially solidified droplets were deposited and expitaxial, columnar microstructures when superheated droplets were deposited, on either a solidified or partially solidified deposit surface. The range of microstructural control possible by uniform-droplet spray forming was illustrated with a process-structure map.

Processing and Properties of Spray Formed 2XXX Aluminum Alloys

Abstract: Spray forming (S/F) process has been commercially used to fabricate large diameter tubes and roll preforms1 Monolithic and metal matrix composite extrusion and forging preforms have also been produced to develop an alternative preform fabrication process to P/M- or I/M-based processes2,3 Furthermore, reduction in the number of manufacturing steps and improvement in microstructure along with extended composition range; the spray forming process has emerged as a serious alternative primary process to I/M process as well as continuous casting processes

Aluminum-silicon alloy pre-compact low in thermal expansion and its compact

Abstract: PURPOSE: To produce a Al-Si alloy pre-compact low in thermal expansion, excellent in suitability as an electric component material, etc., and capable of plastic working by using spray forming method and to produce a compact low in thermal expansion by using the pre-compact. CONSTITUTION: This pre-compact obtained by the spray forming method consists of the Al-Si alloy of 3-45wt.% Si content, and has a density of 95% to true density. Also oxygen, hydrogen and nitrogen incorporated in the inside of the pre-compact is limited to ≤250ppm, ≤0.4ppm and ≤60ppm respectively. COPYRIGHT: (C)1996,JPO

Microstructure and Mechanical Properties of Alloys and Metal Matrix Composites (MMCs) Processed by the Spray Forming Technique

Abstract: In this paper, the recent research activities in the field of spray forming performed at University of Science and Technology Beijing have been briefly reviewed. We have established a spray forming facility recently, and the microstructure and mechanical properties of several alloys (including Ni3Al-base alloys and high speed steels) and particulate reinforced metal matrix composites (MMCs) (including aluminium alloy 2618+SiCp and maraging steel+A12O3) have been evaluated. The results of characterization of the microstructure and mechanical properties of the representing spray deposited materials (Ni3Al-base alloys and Al 2618+SiCp MMC) are given here.

The spray forming of Ni based superalloys

Abstract: The main aim has been to investigate the effect of process parameters on the spray forming of UDIMET 720 and in particular to understand the mechanism of grain size evolution in the deposit using a combination of experimental and computer modelling techniques. Samples of two spray formed Ni superalloys, MAR-M-002 and UDIMET 720, have been re-heated into the solid/liquid region and the fully solid region just below the solidus temperature for a series of times to try and reproduce the situation of grain growth in a spray formed deposit. Grain growth in the solid/liquid region follows the equation: d3=d03 +Kt, where d is the grain size, d0 is the initial grain size, K is the coarsening rate constant and t is the time. Coarsening rate constants have been determined for temperatures in the solid/liquid region and they increase with increasing temperature/decreasing solid fraction. Existing spray forming equipment for Al alloys has been modified to manufacture UDIMET 720 deposits. Process conditions were monitored continually during spray forming, in particular the temperature of the deposit by embedded thermocouples and infra red thermal imaging of the deposit top surface. Above a deposit temperature of ≈1250°C the microstructure consists of equiaxed fine grains (20μm-35μm) and the porosity is low ( A commercial finite difference based fluid dynamics software program, FLUENT, has been used to model the 2-dimensional dynamic and thermal behaviour of UDIMET 720 droplets during gas atomisation and spray forming. The effect of atomising gas pressure, spray distance and melt mass flow rate on the equilibrated droplet spray temperature has been examined and shows similar variations with process parameters as the measured maximum deposit temperature. The predicted spray temperature at the substrate is always higher than the measured maximum deposit temperatures under all conditions, and increases with (i) decreasing gas pressure, (ii) decreasing spray distance and (iii) increasing MFR. Mean droplet temperatures and velocities are strongly dependent on droplet size, the mean droplet temperature decreases and mean droplet axial velocities increases with decreasing droplet size.

Spray-formed tooling and aluminum strip

Abstract: Spray forming is an advanced materials processing technology that converts a bulk liquid metal to a near-net-shape solid by depositing atomized droplets onto a suitably shaped substrate. By combining rapid solidification processing with product shape control, spray forming can reduce manufacturing costs while improving product quality. De Laval nozzles offer an alternative method to the more conventional spray nozzle designs. Two applications are described: high-volume production of aluminum alloy strip, and the production of specialized tooling, such as injection molds and dies, for rapid prototyping.

A study of the spray forming of Al-Li alloys

Abstract: The atomization and spray forming of liquid metals was studied. Melt break up algorithms were developed to predict the size distribution of the spray generated as well as secondary aspects of the atomization phenomena. In the model, which is based on the Surface Wave Formation (SWF) theory, the relative velocity between the gas and melt phase was thought to induce a sinusoidal disturbance on the surface of the melt column. Depending on the flow conditions such a disturbance could grow in amplitude and cause certain parts of the surface to be torn off the liquid column. A number of different approaches to the problem of drop disintegration were also considered. Based on experimental observations of the critical Weber number made by other authors, a criterion was formulated, which allowed the secondary break up of drops to be predicted. In addition, an analytical model originally presented by Wolf and Andersen (1965), which was intended to describe the stripping mode of secondary disintegration, was also revised and incorporated into a computer routine. Finally a comparison of the models was made against the predictions of the empirical Lubanska (1970) equation. High Speed Photography studies of a water column atomized by gas revealed that the formation of a surface wave was the prominent mechanism perturbing and finally disintegrating the column into a fine spray of drops. Phase Doppler Anemometry studies of the water/gas jet produced during the atomization of a water column indicated that there was a gradient of particle sizes across the spray. The finer fragments were found in the close proximity of the centre axis of the conical flow, with particles becoming larger in size as the distance from the centre increased. Vaporization of the water drops near the centre due to the high gas velocities should be taken into account when interpreting these results. The break up algorithms were tested against experimental data for a number of different A1 and Fe alloys with various solute elements, obtained using a close coupled atomization facility. Case studies were made for the effects of gas injection pressure, initial melt stream diameter, initial melt stream exit velocity and number of atomizing gas jets on the mean powder particle size produced. The algorithms could predict the distribution of drop sizes in space, a feature that enabled the simulation of spray forming runs and the direct comparison of the numerical predictions to experimental data. The shapes of the Al-1.6wt%Hf and the Al-1.6wt%Hf-3.2wt%Li alloy preforms and the particle distribution along the radial direction of the Al-1.6wt%Hf preform were calculated and compared favourably with experimental data. Microscopic observation of Al-1.6wt%Hf and Al-1.6wt%Hf-3.2wt%Li preforms indicated that there was a variance of particle size as well as grain size along the radial direction of the spray. The grain size was found to decrease with increasing distance from the central axis of the preform, while the radial distribution of drop diameters did not reveal a distinct trend.

Use and characterization of linear nozzles for spray forming

Abstract: Commercial production of aluminum sheet and plate by spray atomization and deposition is a potentially attractive manufacturing alternative to conventional ingot metallurgy/hot-milling, and to continuous casting processes because of reduced energy requirements and reduced cost. To realize the full potential of this technology the Aluminum Company of America (Alcoa), under a cooperative agreement with the U.S. Department of Energy, has investigated currently available state-of-the-art atomization devices to develop nozzle design concepts whose spray characteristics are tailored for continuous sheet production. This paper will discuss Alcoa`s research and development work on three linear nozzle designs. The effect of geometry and process parameters on spray pattern and particle size distribution will be presented. The discussion will focus on the final spray formed deposit produced by these deposition systems.

Sprühkompaktieren von Kupferlegierungen im industriellen Massstab

Abstract: Following the introduction of the spray forming method for processing aluminium alloys, the method is now also used in the manufacture of semi-finished products of copper alloys. Spray forming of billets measuring up to 2.2 m in length and 300 mm in diameter is described below. The outstanding feature of billets manufactured in this way is their isotropic material behaviour. The wear properties of sliding rails containig graphite and manufactured from various spray-formed copper materials are improved considerably to conventionally produced tin bronze.

Continuous spray forming of functionally gradient materials

Abstract: Researchers at Plasma Processes Inc. have produced a Functional Gradient Material (FGM) through advanced vacuum plasma spray processing for high heat flux applications. Outlined in this paper are the manufacturing methods used to develop a four component functional gradient material of copper, tungsten, boron, and boron nitride. The FGM was formed with continuous gradients and integral cooling channels eliminating bondlines and providing direct heat transfer from the high temperature exposed surface to a cooling medium. Metallurgical and x-ray diffraction analyses of the materials formed through innovative VPS (vacuum plasma spray) processing are also presented. Applications for this functional gradient structural material range from fusion reactor plasma facing components to missile nose cones to boilers.

Spray-forming monolithic aluminum alloy and metal matrix composite strip

Abstract: Spray forming with de Laval nozzles is an advanced materials processing technology that converts a bulk liquid metal to a near-net-shape solid by depositing atomized droplets onto a suitably shaped substrate. Using this approach, aluminum alloys have been spray formed as strip, with technoeconomic advantages over conventional hot mill processing and continuous casting. The spray-formed strip had a flat profile, minimal porosity, high yield, and refined microstructure. In an adaptation to the technique, 6061 Al/SiC particulate-reinforced metal matrix composite strip was produced by codeposition of the phases.