Osprey Process Research Articles

Effect of rolling deformation on microstructure and texture of spray-deposited magnesium alloy containing Mg-Nd-Zn typed LPSO

Billets of Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy were produced by spray-deposition (the Osprey process). Effect of rolling deformation (T=350°C, ε=5%, 10%, and 15%, respectively) on microstructure and texture evolution of the Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that at pass reduction of ε=5%, 10% and 15% at 350°C respectively, Mg-Nd-Zn typed 24R-LPSO structure was formed in (Ca, Nd)Al2 phase (C15 Laves phase). With the increase in pass reduction (i.e. 5%, 10% and 15%), the texture pole density level of basal texture (0002) changed little and pyramidal texture (101¯3) were increased. In contrast, those of prismatic texture {101¯0} <112¯0> were increased initially and followed by a reduction, indicating texture randomization in the grain-refined Mg alloy. The combined contribution of LPSO phase and C15 phase was key to randomize the texture of the grain-refined Mg alloy. It was noted that the microcosmic plastic deformation of LPSO phase and nanometer-sized dispersed C15 phase impeded dislocation movement, led to dislocation tangles, and facilitated recrystallization.

EFFECTS OF ROLLING DEFORMATION ON TEXTURE AND LPSO PHASE OF SPRAY-DEPOSITED MAGNESIUM ALLOYS CONTAINING Nd

Mg alloys have been applied widely as structural materials over the past decades, with low density, high specific strength, stiffness, specific elastic modulus, and high recycling rate. However, their features of poor ductility and formability at room temperature have limited their application due to hexagonal close-packed crystal structure with less independent slip systems. Grain refinement and texture randomization are two means to activate other slip systems. In this work, the billets of Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy produced by spraying deposition method (the Osprey process) were studied in order to analyze the effect of rolling deformation at 350 °C and pass reduction e =20%, 25% and 30% on texture and microstructure evolution of an extruded size-asymmetry Mg alloy by SEM, TEM and XRD. The results show that under the condition of reduction of e =20% at 350 °C, a long-period stacking ordered phase with 24R structure was formed in (Ca, Nd)Al2 phase (C15 Laves phase ). All of basal texture (0002), prismatic texture {1010} , and pyramidal texture {1012} were activated, with pole density level weakened while pass reduction increased (e =20% , 25% and 30% ), namely, texture randomization achieved in Mg alloy, with main causes of nanometer-sized dispersed C15 phase impeding dislocation movement 第938-944页 pp.938-944

Spray forming – a promising process for making high-quality steels and alloys

This article examines the technological possibilities for making Al-, Cu-, Si-, and Ni-alloys and high-alloy steels by the Osprey Process: the principle of the process, the equipment, the technology used to form the semifinished product, the properties of the finished product, and areas of application. It is shown that the Osprey Process is superior to conventional refining and powder metallurgy methods in terms of its technical-economic indices.

Modern trends in increasing the quality of the steels intended for cutting and metal-working tools: II. Spray forming of billets

Tools for cold forming of materials are used to produce articles made of metals and ceramic materials by cold drawing, embossing, drifting, forging, knurling a thread, and so on. Apart from a high strength, the tool material in this case must also have high abrasive and adhesive wear resistance. When a tool interacts with high-strength abrasive particles, abrasive wear takes place: it is characteristic of processing of ceramics, when high-strength ceramic particles penetrate into a meat surface and form microgrooves in it. In this case, large carbide particles present in a metal hinder this process better than small carbide particles [1]. Adhesive wear takes place when metal is in contact with a metal: microbonds appear between the tool and processed-metal surfaces at contact microareas because of high pressures, and metallic microparticles are torn out from the tool. Adhesive wear can combine with abrasive wear, which is related to the presence of ceramic particles in the metal to be processed. Therefore, high-hardness carbides (VC etc.) in a tool intended for cold metal and ceramic working without cutting should provide an optimum combination of hardness and abrasive wear resistance. In this case, large carbides in a tool metal are favorable for wear as compared to small carbides. However, as the carbide size increases, the metal hardness decreases. In other words, neither a traditional “ingot” metal with large carbides and a low hardness nor a powdered (granulated) metal with a high hardness and small carbides can provide an optimum combination of the functional properties of a certain tool. Therefore, in the last decade, metallurgists have focused their attention on the production of ingots by a nontraditional spray deposition method [2], namely, a spray forming (SF) process. Specifically, they use spray forming to produce a radically new type of ingots, i.e., deposited ingots. The quality of the SF metal is so high that this process is now one of the most dynamically developed high-quality metallurgy processes all over the world. The SF process is used to produce ingots from various steels and alloys, as well as from nonferrous metals. This process has attracted the particular attention of the manufacturers of tool cold-working metal, since it can form spherical primary carbides whose sizes are smaller than those in the metal of traditional ingots and large than those in the metal of gas-sprayed powders. In other words, the SF metal has the optimum combination of hardness and wear resistance that cannot be achieved by other methods of producing a tool metal. The SF process is an improved Osprey process [2, 3], which was designed at Osprey Metals Ltd. (Great Britain). In the course of the conventional Osprey process, a metal‐gas torch is directed into a mold during gas spraying, where semiliquid metal drops solidify layer-by-layer and form an ingot. The mold is fixed in this process. In the SF process, a mold or a crystallizer is absent. A metal‐gas torch is directed onto a gas-cooled rotating metallic disk, which serves as a seed for freezing (deposition) of an ingot. The seed is rotated and pulled down at a speed so that the distance between the spraying focus and the center of the deposited surface is unchanged. Although the rate of rotation was indicated, we can assume by analogy with a two-electrode VADER process that it ranges from 80 to 120 rpm.

Structure and Property of Nickel-Modified Ultrahigh Strength Al-Zn-Mg-Cu Alloy by Spray Forming

Six kinds of Al-Zn-Mg-Cu alloys, modified with nickel and zirconium, have been produced by rapid solidification using spray deposition(the Osprey process). The effect of nickel on the structures, mechanical properties of ultrahigh strength aluminium alloy is studied, and the probable maximum of mechanical properties is predicted. There are three nickel-rich phases, Al3Ni2, Al7Cu4Ni and MgNi2, forming in 1%Ni alloy, its ultimate tensile strength(UTS) increased with increasing extrusion ratios significantly while maintaining high levels of ductility, Futhermore, the extruded bars show enhancing more clearly than extruded plates in UTS and ductility. The content of Ni should decreased with increasing of Zn and Zr, and the highest properties(UTS=832MPa, Elongation=7.5%)are attained in 0.20Zr＋0.30Ni (wt%)alloy. In addition, the size, the shape and the homogeneous distribution of zirconium-rich phase produced in solidification is the key to effecting the mechanical properties of materials when Zr content is 0.2~0.5％.

Numerical Simulation of Thermal History in a Novel Spray Forming Process

A novel spray forming process was developed to produce large billets, wide plates or thick tubes with excellent microstructures and high cooling rates. Its uniqueness lies in a combination of the wide-range reciprocating movement and the swing scan of a gas atomizer, and the externally forced cooling of substrate during this spray deposition procedure. Its basic concept is that both good sticking and rapid solidification can be achieved if droplets with high liquid fractions impact a cold substrate, spread fully and then deposit on the surface. In order to control and optimize this new process, the thermal histories of droplets and deposits for spray forming of aluminum alloy billets were simulated with a set of new numerical models. Through shortening spray distance and raising melt superheat properly, the liquid fraction of droplets before deposition will increase and their spread on the deposit surface can improve for good sticking. Simulation results show that the optimal liquid fraction of droplets for deposition is about 0.2 higher than that in the conventional Osprey process. Its optimum spray distance is about 0.25m, which is nearly half as that in the Osprey process. In addition, this new process increases the mushy layer area and the specific surface area of heat extraction during deposition. Together with the forced cooling of substrate, it results in higher cooling rates. A high-quality large billet can be obtained by controlling the atomizer movement, the droplet liquid fraction and the deposit surface temperature properly in this new process.

Mesoscopic structure control of spray formed high strength Al–Zn–Mg–Cu alloys

Several high solute, high strength 7xxx series aluminum alloys with solute contents close to equilibrium solid solubility limits of the Al–Zn–Mg–Cu system have been produced by rapid solidification using spray deposition (the Osprey process). This process yields massive preforms directly from the liquid state by combining atomization and consolidation into one step. Various elements, including chromium, manganese and silver are incorporated to produce a variety of microstructures and mechanical properties. The zinc to magnesium ratio is also varied to see the effect on the strength. Superior strengths in excess of 849 MPa are achieved and are attributed to two major substructures with different scale; nanometer sized η′ metastable precipitates and slightly larger, but finely distributed dispersoids which provide a fiber-like reinforcement. The remarkable strengthening is predominantly attributed to precipitation hardening and a large coherency strain.

ALD — Osprey link brings new melt package to market

UK spray-forming specialists Osprey and German vacuum-melting experts ALD have signed an agreement that puts together a unique software/hardware package for customers using the patented Osprey process. This is a short news story only. Visit www.metal-powder.net for the latest powder metallurgy industry news.

Fabrication of spray-formed hypereutectic Al–25Si alloy and its deformation behavior

This article reports the fabrication of hypereutectic Al–25Si alloy, which is expected to be applied to the cylinder liner part of the engine block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, through a spray casting process and the characterization of the microstructural and the mechanical properties of this alloy. The OSPREY process used in this study is one of spray forming techniques, which can produce semi-finished products such as billet, tube, and plate with rapid solidification (RS) structure and density in a single operation from molten metal. The obtained microstructure of the hypereutectic Al–25Si alloy appeared to consist of Al matrix and equiaxed Si particles with average diameter of 5–7 μm. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to 500 °C. The strain rate sensitivity parameter ( m) of this alloy has been found to be very low (≤0.1) below 300 °C and reached maximum value of about 0.2 at 500 °C. During the deformation above 300 °C in compression, remarkable strain softening has been observed. The extrusion has been successfully conducted at the temperatures of 300 °C and above with the ratio of area reduction of 28 and 40 in this study.

Interfacial reactions between a lead borosilicate glass containing CuO and an Al/Si alloy — evidence for galvanic cells

A PbO-rich borosilicate glass with the additions of CuO and Al2O3 has been developed as a thick-film, dielectric coating for a high Si content Al/Si alloy produced by the Osprey process (Al–70Si wt.%). Wetting behaviour and interfacial reactions were investigated using sessile drop experiments at temperatures between 520 and 583°C under air and argon atmosphere. The wetting behaviour of the glass was found to be a function of atmosphere and wetting angle decreased with increasing temperature and time. Coatings applied in air in the range 520–565°C showed <1% porosity, whereas those applied at 583°C in argon exhibited relatively high porosity (∼8%) and both coating and un-wetted substrate surface supported large Al–Si spheres containing ∼21 wt.% Si. Coatings heated in air at 520 and 540°C show good bonding with no interfacial reaction products. However, those samples heated in air at 565°C consistently show evidence of excessive interfacial reactions which are the components of a galvanic process, leading to the oxidation and dissolution of the Al regions (anodic) and the deposition of copper at the glass/Si interface (cathodic). From observations of the rate of copper deposition, the current density arising from the electron flow through the alloy has been calculated to be ∼0.91 A m−2. The galvanic process is suppressed at the periphery of the coating where oxygen diffused from the atmosphere enables interface oxidation. The onset of the galvanic process between 540 and 565°C occurs when dissolution rate exceeds oxidation rate, exposing the fresh Al anode to the glass melt. Under inert atmosphere (at 583°C), air oxidation is not possible and galvanic cell redox reactions generate an excessive copper interlayer as the system attempts to sustain the oxide layer at the Al anode.

Mechanical properties of tungsten carbide-copper composite made by osprey process : R.Palma et al. (University of Chile, Santiago, Chile.)

Mechanical properties of tungsten carbide-copper composite made by osprey process : R.Palma et al. (University of Chile, Santiago, Chile.)

Multipass cold rolling and resultant mechanical properties of a Cr-containing nickel aluminide

The difficulties encountered in fabricating Ni3Al-based intermetallic alloys into final structural components, due to their limited workability as a result of their inherent high yield strength and low ductility at elevated temperatures, are an important issue that have restricted the commercial applications of these materials. The Osprey spray deposition process is capable of delivering near-net-shape preforms, thereby avoiding the technical problems related to the hot working of these materials, e.g. hot rolling of slabs. The present work concerns an investigation of the cold rollability of a chromium-containing Ni3Al intermetallic alloy produced with the Osprey process. The sliced preform with a thickness of 7 mm was successfully cold rolled through multipasses into sheets with a thickness of 0.7 mm and a good surface finish. The material has been found to have a high working hardening rate at room temperature. The maximum total reduction permissible without resulting in rolling defects is 30%. Thus, for larger reductions, intermediate annealing between rolling passes is necessary and it has been optimized to be at 1100°C for one hour. The repeated cold rolling and the recrystallization occurring during intermediate annealing change the initial microstructural features and grain size of the Osprey-spray-deposited material. The cold-worked and annealed intermetallic sheets with a thickness of 0.7 mm have a yield strength of 570 and 730 MPa and a elongation value of 33 and 7%, at room temperature and at 700°C, respectively. Fractography shows a transition from the transgranular fracture mode at low temperatures to the intergranular fracture mode at temperatures above 650°C.

Spray forming of large diameter special steel billets: L.Shaw, C.Spiegelhauer. (Special Melted Products Ltd, Sheffield, UK). Int. J. Powder Metall., Vol 33, No 3, 1997, 31–36

This project is of four years duration and is carried out with the financial aid of the European Coal and Steel Community. It has the fundamental aim of demonstrating the applicability of spray forming as a viable process for industrial scale steel production. The Osprey process has potential for the production of billets in special steels. However, earlier studies had shown that the technology was not developed sufficiently to permit production on an industrial scale. This was because of an absence of the understanding of the process control required for large billets. The objective of the project has been to extend the technology of spray forming steel in the horizontal mode to produce billets up to 400mm diameter and by up to 1200kg in weight. Work conducted within the project is described including the construction of the demonstration plant, commissioning, process development, evaluation and extension of the process from the initial trials on D2 steel to other materials.

Influence of heat treatments on microstructure and mechanical properties of Cu-15Ni-8Sn prepared by spray forming

An alloy of composition (wt-%) Cu-15Ni-8Sn produced by the Osprey process has been examined after a range of thermomechanical treatments with the aim of achieving high strength combined with reasonable ductility. Extensive cold working and an anneal in a two phase region for recrystallisation, followed by spinodal decomposition, leads to a high strength with reasonable tensile elongation because of the small grain size. Yield stresses in excess of 1100 MPa are obtained by contributions of grain size hardening, spinodal hardening by the internal strain amplitudes created during decomposition, and progressive ordering at tin rich sites. Alternatively, very short high temperature anneals or medium short low temperature anneals for recovery or partial recrystallisation of the cold worked state lead to materials with very high yield stresses, between 1250 and 1450 MPa, maintaining similar values of tensile elongation.

Influence of heat treatments on microstructure and mechanical properties of Cu-15Ni-8Sn prepared by spray forming

An alloy of composition (wt-%) Cu-15Ni-8Sn produced by the Osprey process has been examined after a range of thermomechanical treatments with the aim of achieving high strength combined with reasonable ductility. Extensive cold working and an anneal in a two phase region for recrystallisation, followed by spinodal decomposition, leads to a high strength with reasonable tensile elongation because of the small grain size. Yield stresses in excess of 1100 MPa are obtained by contributions of grain size hardening, spinodal hardening by the internal strain amplitudes created during decomposition, and progressive ordering at tin rich sites. Alternatively, very short high temperature anneals or medium short low temperature anneals for recovery or partial recrystallisation of the cold worked state lead to materials with very high yield stresses, between 1250 and 1450 MPa, maintaining similar values of tensile elongation.

Conformado de aleaciones en estado semisólido. Aplicación a aleaciones hipereutécticas de Al-Si

The processing of alloys in the semi-solid state, known as Rheocasting, Thixoforming, Thixoforging or Thixocasting, is within the new technologies used for the production of materials. This work describes the process as well as the phenomena implied in it. As the forming of alloys in the semisolid state requires of a previous material preparation (in order to obtain a non-dendritic structure) the Osprey process or Spray-forming, used in this work, is briefly described. Finally, both the microstructural results obtained from the combination of the two technologies in hypereutectic Al-Si alloys (Al-25%Si-5%Cu, Al-25%Si-5%Cu-2%Mg and Al-30%Si-5%Cu) and comparison with microstructures obtained from similar alloys processed by conventional methods are shown.

Production of large high alloy tool steel billets by osprey process : J. Overgaard et al. (Det Dansk Stalvalsevaerk AS, Denmark)

Production of large high alloy tool steel billets by osprey process : J. Overgaard et al. (Det Dansk Stalvalsevaerk AS, Denmark)

Ni3Al and Ni3Si-based intermetallics produced by the Osprey process

Four NiAlbased and two NiSiTibased intermetallic compounds were spray-deposited using a nitrogen gas for atomization. The impurity contents, relative densities and microstructures of the alloys were investigated in the as-deposited condition.The oxygen content of the alloys varied from 20 to 90 ppm, and the nitrogen content ranged from 10 ppm in a binary Ni 3 AI compound to 90 ppm in NiAlCrFe alloy and to 150 ppm in the case of NiSiTi. No sign of nitrides or oxides was observed. The relative density of the alloys was higher than 99% and the majority of pores located at grain boundaries. The chromium free NiAI alloy had a single-phase, equiaxed and recrystallized structure (γ′), while the chromium containing NiAI alloys had a γ γ′ multiphase structure with 5–20% volume fraction of the disordered γ phase. The γ phase formed a network or a bimodal mixture of network and lamellar structures in the ordered γ′ matrix. The NiSiTi alloys showed a cell structure with cell interiors consisting of γ γ′ network structure and cell borders of the ordered γ′ phase. The mechanical properties were comparable with those of the previously spray-deposited Ni 3 Al-based alloys or with those of the NiSiTi based alloys of the present type.

Spray-cast monolithic and composite materials: distinguishing features in their microstructure and metallurgy—an extended abstract

International 1. Background SPRAY casting via the Osprey process has emerged as a viable near-net shape technique for the processing of monolithic alloys and composites with attendant integrity of microstructure and properties. The process involves sequential gas atomization and consolidation of droplets on a substrate to produce a near-net shape preform in a single processing step, as shown schemati- cally in Fig. 1. Composites are generated by injecting second- phase particulates into the spray of droplets or by reacting the droplet with a suitable gas during flight. This droplet consolida- tion technology is considered a viable alternative to current processing routes because of cost savings from a reduction in the number of processing steps, an improvement in the cleanliness and microstructure relative to powder metallurgy and casting, respectively, and higher pouring rates than with conventional thermal spray processes. The as-sprayed microstructure is com- posed of fine equiaxed grains (<50 lam) with residual porosity of <3% and is devoid of macrosegregation or prior particle boundaries. Composites manifest the same structure, with the reinforcing phase either dispersed uniformly or located at grain boundaries.

Model for Predicting Buildup of Cylindrical Billets in Osprey Preform Process

A detailed numerical model to predict the buildup of cylindrical preforms in the Osprey process is described. A sensitivity study confirmed the importance of chamber design factors such as the direction of spray on to the end of the preform, scanning amplitude, and scanning frequency with respect to preform rotation. The nature of the scanning motion was also found to have a profound influence on the shape of the preform end. PM/0672