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Session Chairperson: Professor Jose Luis Estrada Haen, Instituto Politecnico Nacional, Unidad Profesional Adolfo Lopez Mateos, Mexico
2:00 pm KEYNOTE
EXPERIMENTAL BASED DETECTION OF THE SPLASH LIMITS FOR THE NORMAL AND OBLIQUE IMPACT OF MOLTEN METAL PARTICLES ON DIFFERENT SURFACES: M. Berg, J. Ulrich, Universitat Bremen, SFB 372,Verfahrenstechnik/FB4, Postfach 330440, D-28334 Bremen, Germany
Understanding of the impact of single molten metal particles contribute to reduce the overspray during the spray deposition processes. The impact of molten Pb- and Sn-particles with a flat solid surface is investigated experimentally. The impact process is monitored by a high speed video system. At each measurement all temperatures (particle, target, and ambient) are taken as the weight of the particle before and after impact. By means of the image processing, the final diameter of the splat is found and evaluated regarding physicla properties, impacting diameter, impact power, and target surface roughness. By the weight difference of a particle before and after the impact, amount of splashing material is detected. The impact diameter, the impact speed, and the spreading diameter are also observed by the high speed, and the spreading diameter are also observed by the high speed video system. The results are presented in the form of diagrams with dimensionless numbers such as the ratio of the maximum spreading diameter, d, to the initial particule diameter, D. Other numbers such as Weber, We, or Reynolds, Re, in connection with d/D ratio give the possibility of comparing all experimental results with each other. A critical dimensionless number above which splashing exists has been discussed.
MICROSTRUCTURE CHARACTERIZATION OF AL-SI AND AL-MMCS PROCESSED BY SPRAY ATOMIZATION AND DEPOSITION: Jose Luis Estrada, Enrique Nicolas, Instituto Politecnico Nacional, Unidad Profesional Adolfo Lopez Mateos, MEXICO; Enrique J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92717
The spray atomization and deposition process is described as applied to Al-Si alloys and Al-Si metal matrix composites. This process shown to be similar to powder metallurgy (P/M) in that advanced alloys can be manufactured. However, many difficulties inherent in P/M are avoided, including oxide film formation and the need for degassing. In the spray atomization and deposition process atomized droplets exist for only a few milliseconds before being deposited to form high density preforms. The primary metallurgical characteristics of Al-12w/oSi, Al-17w/oSi, Al22w/oSi and Al-alloy based MMCs reinforced with SiC particulates preforms are presented. Characterization of the preforms consisted of the description of the production technique, descriptions of the microstructures by light microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Auger electron spectroscopy. The volume percentage of reinforced particles was determined. Both the spray deposited Al-Si alloys and the Al-Si metal matrix composites exhibited a rapid solidified matrix microstructure and the spray deposited MMCs a relatively uniform distribution of reinforcements.
TUNGSTEN BORIDE SYNTHESIS IN BURNING: S.V. Nikolenko, V.V. Gostischev, Institute of Materials, Far Eastern Branch of the Russian Academy of Sciences, Khabarovsk, Russia
Nowadays, a great theoretical and practical interest is observed towards tungsten boride, that can be explained by its' specific physical, chemical and mechanical properties. This paper discusses the process of tungsten boride extraction by alumothermy from the tungsten-containing mineral (sheelite concentrate) derived from the original product by enriching. The experiments were conducted in air and vacuum. The study of the extracted products has shown that their composition differs and depends on the synthesis conditions. For example, if we use B2O3, in relation W:B=1:2; 1:3; 1:4, as a boride element, then we get the lower borides as the synthesis products: W2B, WB and metallic tungsten. The use of boron oxide with coal gives W2C together with W2B5. Including boron carbide guarantees that we shall receive the higher boride W2B5, independently from the environment of the reaction, due to the high speed of the burning. The conducted set of experiments, shows the possibility of synthesizing tungsten boride-base powders from the enriched mineral raw materials, which can be used for electro-spark and laser deposition of wear and heat resistant harding coats on construction and instrumental steels.
POROSITY AND OXIDE DISTRIBUTION IN SPRAY FORMED Al-Cr-Zr ALLOYS: M. Baker, A. Hellwig, A.F. Norman, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK
In spray formed Al alloys porosity is common and typically about 2 to 8% depending on alloy and product form and the oxygen content is typically less than the level of oxygen in commercially produced RS/PM Al alloys. There is no experimental evidence available about the distribution of Al2O3 in spray formed Al alloys. We have studied the size and distribution of pores and the distribution of oxides in spray formed Al-Cr-Zr alloys. The fracture surfaces of the as sprayed and forged deposits were examined by AES and SAM. Cratered regions on the in situ fracture surfaces were identified and a localized 2nm thick Al2O3 film on their surface was measured by high resolution AES. The fracture path followed areas rich in Al2O3.
3:30 pm BREAK
STUDY OF MICROSTRUCTURE AND PROPERTIES OF SPRAY FORMED Al-Cr-Zr ALLOYS: A.F. Norman, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK
The technical problems and cost associated with the multi-step PM processing of RS Al alloys have hindered their successful development. Spray forming can obviate these problems by means of the integral inert gas atomisation and deposition operation in which the alloy exists in particulate form only for a few milliseconds. Spray forming experiments have been performed on Al-Cr-Zr alloys studied previously by the combined RS/PM route. The microstructure and the tensile properties of the forged and heat treated deposits will be compared with the RS/PM alloy. The latter exhibits superior properties, not matched by the spray formed alloy.
ABOUT SELECTION AND DESIGN OF ELECTRODE MATERIALS FOR ELECTRO-SPARK ALLOYING OF STEELS: A.D. Verkhoturo, S.V. Nikolenko, Institute of Materials, Far Eastern Branch of Russian Academy of Sciences, Khabarovsk, Russia
Earlier, we have proposed several parameters of selecting and designing electrode materials for electro-spark alloying (ESA) of metallic surfaces. These parameters were developed according to the necessity of achieving the maximum depth, continuity, the least stress in the alloyed layer (AL), as well as the least roughness. However, the developed principles account only for the "geometrical" characteristics of AL, without accounting for the technological characteristics, and the current manufacturing demands: higher productivity of the ESA process, creating the optimal conditions for the AL forming. Considering all of the above this paper discusses: 1) The scientific principles of designing and selecting the multi-component electrode materials, that account for the electrode space composition, as well as the composition-structure-characteristics relationship of electrode materials on the physical-chemical characteristics of AL and allowing to decrease fragile destruction of electrode material in the total erosion phenomena. 2) "Technological" scheme of AL forming, that accounts for effect of physical-chemical properties of electrodes, parameters of ESA process on physical-chemical and exploitational properties of AL and allowing to receive coatings with given characteristics. According to these principles several new electrode materials have been created, using tungsten carbide and titanium base with self-fluxing and mineral additives that allow to greatly increase wear and heat resistance of construction and instrumental steels.
CHARACTERIZATION OF CONTINUOUS PRODUCTION OF ALUMINUM ALLOYS DURING LINEAR SPRAY ATOMIZATION AND DEPOSITION: Y. Zhou, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92697-2575; S.W. Lee, V.G. McDonell, G.S. Samuelsen, Dept. of Mechanical Engineering and Aerospace, University of California, Irvine, CA 92697-2575; R.L. Kozarek, Processing Design and Smelting Division, Aluminum Company of America, Alcoa Center, PA 15069
The linear spray atomization and deposition is a potential near-net shape technique for continuous production of aluminum alloys. Possible benefits of linear spray atomization and deposition are: a) deposit geometry improvement, b) high productivity, c) high aspect ratio, and d) low overspray yield. In the present study, characterization of metal sprays using phase Doppler particle analyzer (PDPA), such as droplet velocity distribution, droplet size, droplet size distribution and spatial distribution, was carried out. The droplet size distribution of aluminum alloy powders were also studied using the mechanical sieving method to compare with the results obtained using PDPA. The plot of the axial velocity with droplet diameter reveals the relationship that smaller droplets have higher axial velocity than do lager droplets. The results also indicate that the axial velocity exhibit the bimodal behavior when atomization pressure approaches a certain critical value and this bimodal behavior behaves increasingly with higher atomization pressure. The Sauter mean diameter obtained using PDPA and the mass median diameter using the mechanical sieving show a decreasing trend with increasing atomization pressure.
SPRAY ATOMIZATION AND DEPOSITION OF GAMMA TITANIUM ALUMINIDE ALLOYS: B. Li, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California at Irvine, Irvine, CA, 92697-2575
Spray forming of gamma titanium aluminides had been investigated experimentally and numerically. Three different nominal compositions had been successfully spray formed. The microstructure of spray formed Ti-47Al consists of fine, equiaxed fully lamellar 2+ structure, with an average linear grain size of 60 µm and an average interlamellar spacing of 0.3 µm. These microstructural characteristics led to a higher creep resistance, in a temperature-stress regime of 780 to 850°C and 180 to 320 MPa, relative to fully lamellar -TiAl obtained through conventional casting + heat treatment processes. A two dimensional modeling of the momentum and thermal behavior of atomized droplets of -TiAl predicted that the two dimensional droplet size distribution in the spray cone changes from being heterogeneous to being almost homogeneous as axial flight distance increases. The modeling results also indicated that the two dimensional distribution of the fraction solidified in the spray cone is heterogeneous. The fraction solidified in the spray at any given axial distance increases with increasing radial distance from the spray axis.
COARSENING KINETICS OF SOLID PARTICLES IN THE SPRAY-FORMED ALUMINUM ALLOY PREFORMS: Ram B. Bhagat, Maurice F. Amateau, The Pennsylvania State University, Applied Research Laboratory, P.O. Box 30, North Antherton Street, State College, PA 16804
The coarsening kinetics of solid particles in the semi-solid aluminum alloys have been reported to follow a parabolic or a cubic law. Considering the gas-dynamic nature of the spray forming process, the high-velocity impact on the substrate is most likely to cause extensive deformation of the semi-solid and even the fully solidified droplets leading to dendrite fragmentation and grain multiplication followed by homogenization and coarsening both during the solidification and subsequent cooling until the temperature falls to a low value. In this investigation, we have developed a growth kinetics relationship based on our experimental results of the heat treatment of select spray-formed aluminum alloys. The calculated rate constant (as a function of temperature) is used in conjunction with a two-dimensional finite element analysis for transient heat transfer to determine the growth of a solid particle in the semi-solid state at any time. The results of this study are useful in understanding the kinetics of grain growth and in obtaining equiaxed, fine-grained microstructures in the aluminum alloys.
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