Spray formed and rolled aluminium‐magnesium‐scandium alloys with high scandium content

Aluminium‐magnesium‐scandium alloys offer good weldability, high corrosion resistance, high thermal stability and the potential for high strength by precipitation hardening. A problem of aluminium‐scandium alloys is the low solubility of about 0.3 mass‐% scandium when using conventional casting methods. The solution of scandium can be raised by higher cooling rates during solidification. This was realised by spray forming of Al‐4.5Mg‐0.7Sc alloys as flat deposits. Further cooling rates after solidification should also be high to prevent coarse precipitation of secondary Al₃Sc. Therefore a cooling device was designed for the spray formed flat deposits. The flat deposits were rolled at elevated temperatures to close the porosity from spray forming. Microstructures, aging behaviour and tensile properties of the rolled sheets were investigated. Strength enhancements of about 100 MPa compared to conventional Al‐Mg‐Sc alloys were achieved.     

Materials characterization and mechanical properties of graded tool steels processed by a new co‐spray forming technique

In order to meet the requirements of micro cold forming tools, a new co‐spray forming process has been applied to produce graded materials from two different tool steels in this study. The two steel melts were atomized and co‐sprayed simultaneously onto a flat substrate, resulting in a flat graded deposit when the two sprays were overlapped. To eliminate porosity and break up carbide network, the graded deposits were further hot rolled. The resultant graded tool steels were investigated with respect to porosity, element distribution, microstructure, hardness, strength, and toughness. The degree of overlapping of the two sprays determined the concentration gradient of the chemical elements in the deposits. The overlapping of the spray cones also contributed to low porosity in the gradient zone of the deposits. The porosity in the graded deposits could be essentially eliminated by means of hot rolling. The carbides and grain structures of the hot rolled tool steels were fine and homogeneous. By means of combining different tool steels in a single deposit, different microstructures and properties were combined.     

High yield spray forming of small diameter tubes using pressure‐gas‐atomization

The economy of the spray forming process is restricted by the generation of overspray, which in many cases cannot be re‐introduced into the process by re‐melting or co‐injection. Especially for small deposits, such as small diameter tubes (diameter <100 mm), the amount of overspray can become large in conventional spray‐forming processes. In this work, an alternative process with a pressure‐gas‐atomizer operating at low melt flows is presented. Tubes with diameters of 50 mm and 90 mm were spray‐formed and analyzed regarding yield and porosity. It was found that yields up to 96% can be achieved with porosities below 1% if proper process parameters are identified and used. An evaluation of the yield and the corresponding achievable porosity is conducted to identify resource‐efficient sets of parameters.     

Spray forming of high density sheets

Porosity is one of the most important quality criteria of spray‐formed materials in the as‐sprayed condition. Typically, spray‐formed sheets have a porous rim close to the substrate and depending on the spray conditions cold or hot porosity may also be present in the core of the deposit. This porosity has to be removed or minimized to make further processing steps such as rolling, forging or extrusion possible. In this paper, the influence of both substrate temperature and deposit surface temperature on porosity in spray‐formed sheets is studied. For this purpose spray forming experiments (sheet size 1000 mm × 250 mm) were carried out using three different materials: aluminium‐bronze, tin‐bronze and a nitriding steel. For the copper‐base alloys preheated steel‐substrates with different temperatures were moved through a scanning spray cone. In the case of steel a ceramic substrate at room temperature was used. In addition to the variation of the substrate temperature, the gas to metal mass flow ratio (GMR) was varied to achieve different deposit surface temperatures. During the run the surface temperature in the deposition zone was measured using a scanning, multi‐wavelength pyrometer. Samples of the deposits were polished and rasterized by light microscopy. The local porosity was characterized by digital image analysis. The influence of the substrate temperature and the GMR on the porosity in the vicinity of the substrate is evaluated and discussed in detail. The impact of the deposit surface temperature on the porosity was analyzed and is discussed as well. It was found that the deposit surface temperature has a strong impact on porosity for spray‐formed sheets. Finally, experimental results were used to develop a new approach to predict the porosity in spray‐formed sheets. The results clearly show the dependence on material properties. This approach can be used to identify process parameters to generate high density sheets in the future.     

喷射沉积柱状坯形状模型

通过坐标跟踪法建立了沉积坏形状预测模型。该模型不但考虑沉积坯任何表面点身自位置变化对沉积效果的影响，同时考虑了该点温度和其它表面点位置对该点沉积效果的影响，其计算过程严格按照喷射成形的实际过程执行，可实时计算并记录沉积坯的形貌，并验证了计算效果。本文模型可用于多种工艺下喷射沉积坯的形状预测。     

Modeling of the Shape Forming of Composite Roll

1. IntroductionSpray forming is a novel rapid solidification technology capable of manufacturing high quality roll ina single integrated operation. During spray formingprocess, alloy melt is atomized by high-speed gas jetsto form a spray of fine droplets. These droplets arecooled rapidly and sprayed onto a substrate bar in asemisolid state, resulting in a near-net-shape roller.Compared with conventional technologies (e.g., I/Mmethods), this advanced technology has a great dealof advalltages o…     

喷射成形工艺过程数值计算的研究进展

主要介绍了国内外目前对喷射成形过程中3个重要工艺环节(即雾化过程、金属熔滴沉积坯凝固时的热传输以及沉积坯形状控制)数值计算的研究进展,同时简介了喷射成形工艺流程,并对喷射成形数值计算以后的发展提出了一些观点.     

A hybrid arc spray forming technique for the manufacture of nickel superalloy IN617

Spray forming produces cast microstructures with comparatively low macro‐ and micro‐structural chemical segregation and is thus well‐suited for the manufacture of complex chemistry, multi‐component alloys that otherwise show strong elemental segregation. Although spray formed Ni superalloys have shown properties equivalent or superior to their conventionally cast/wrought counterparts, they have not been adopted commercially because of the difficulties in ensuring a high process yield and the complexity and associated cost of large‐scale Ni superalloy melting. In this paper, we describe a hybrid arc spray forming (HASF) process in which costly, large‐scale alloy melting as pre‐cursor to spray forming is avoided by the use of a consumable wire feedstock. To achieve thermal conditions of melt spray forming – essential to produce a refined, polygonal grain structure – a customised secondary atomisation system has been developed. Fe‐0.8 wt%C and Ni superalloy IN617 microstructures and preliminary mechanical properties suggested that hybrid arc spray forming may offer an attractive combination of convenience, low cost and mechanical performance.     

双扫描雾化喷射成形工艺过程优化控制研究

本文采用“反推法”研究了雾化沉积工艺中关键参数的确定原则，并推导了双喷扫描过程中沉积平面上任意一点处金属质量流率与时间的关系。文中采用优化后的工艺参数进行了数学计算，并通过雾化沉积实验对计算结果进行了验证，对比结果证明采用“反推法”确定沉积工艺参数具有很高的计算效率和准确性，同时该结果可推广应用于任意数目喷嘴的雾化沉积工艺。     

Bulk synthesis of amorphous and nano‐crystalline materials by spray forming

Bulk amorphous and nano‐crystalline metallic materials have been observed to possess excellent mechanical and physical properties. The conventional process routes, to synthesize such materials, are restricted by their ability to achieve rapid solidification, which limits the dimensions of the materials produced. In the last 10–12 years, spray forming has been employed to avoid these limitations by using its capability of layer by layer deposition of undercooled droplets. The current literature indicates that the opportunities provided by this process can be effectively utilized to produce bulk materials in a single step. In this paper, an attempt has been made to bring out the developments in the synthesis of bulk amorphous and/or nano‐crystalline materials by spray forming. The effect of process parameters, droplet size distribution in the atomized spray, the thermal conditions of droplets prior to deposition and the deposition surface conditions have been discussed. It has been demonstrate that a layer by layer deposition of undercooled droplets of glass forming alloys on a relatively cold deposition surface is the suitable condition to achieve bulk amorphous/nano‐crystalline materials.     

Design and Atomization Properties for an Inside‐Out Type Effervescent Atomizer

Atomization of aqueous polymer solutions is a key step in the formulation of several pharmaceutical products. Droplet size control is essential in order to produce pharmaceutical products with the desired properties. The purpose of this paper is to investigate design issues for an inside‐out type of effervescent atomizer used to spray water and aqueous solutions of polyvinylpyrrolidone (Kollidon® K‐30) and hydroxypropyl methylcellulose (Pharmacoat® 603). The atomizer was operated at air‐to‐liquid mass ratios of 0.1, 0.3, and 0.5 and a feed pressure of 1172 kPa. Fluid viscosities ranged from 1 to 47 mPa.s. The influence of several atomizer design features was considered, including exit orifice length‐to‐diameter ratio, exit orifice diameter, the total area of the air injection holes, the distance between the air injection point and the exit orifice, the diameter of the mixing chamber, and the orientation of both air and liquid flows. Droplet size distributions were shown to vary significantly with the atomizer's exit orifice diameter, air injector design, and air injector distance to the exit orifice. In all cases air‐to‐liquid mass ratio played a key role in the mean droplet size. The design of the atomizer was shown to have the most pronounced effect on the mean droplet size at the lowest air‐to‐liquid mass ratios. Optimization of the atomizer design is very important in order to obtain small droplet sizes in pharmaceutical processes where the amount of air/gas should be minimized, e.g., closed‐cycle spray drying and agglomeration processes.     

Spray forming

Spray forming is a relatively new manufacturing process for near net shape preforms in a wide variety of alloys. Spray formed materials have a characteristic equiaxed microstructure with small grain sizes, low levels of solute partitioning, and inhibited coarsening of secondary phases. After consolidation to full density, spray formed materials have consistently shown properties superior to conventionally cast materials, and comparable to powder metallurgy equivalents. The reduction of processing steps for spray forming in comparison with powder metallurgy and conventional cast/forge routes offers potential economic advantages. However, serious economic barriers to the widespread commercialisation of spray forming remain. These include the high cost of inert gases for atomization, significant losses from overspray, bounce-off and machining, poor process reproducibility and problems of implementing robust on-line control for metallurgical quality. Extensive model experiments with process monitoring and numerical simulation have been used to understand the underlying process physics and the development of preform shape and microstructure in an effort to enable full process control and so reduce losses. However, despite considerable progress, the cost of spray forming has not yet reduced significantly to compete broadly with existing technologies.     

The stressed-strained state in the chip forming zone during the finish turning of workpieces of hardened steels

The finite element method has been used for modeling the stressed-strained state in the chip forming zone in cutting workpieces of hardened steels by tools equipped with cutting inserts of cubic boron nitride-based polycrystalline superhard material (PCBN). Special features of the stressed-strained state in the chip forming zone when using tools with a flat and a cylindrical rake faces have been discussed.     

Microstructural properties of ZnO:Sn thin films deposited by intermittent spray pyrolysis process

Zinc oxide films have been prepared via spray pyrolysis using a perfume atomizer. ZnCl₂ has been used as precursor. The influence of the precursor solution and dopant concentration has been investigated. Homogeneous films are obtained with a precursor concentration ranging between 0.3 and 0.4 M and a SnCl₂ dopant concentration of 1–2%. The films exhibit broad band gaps and small conductivity. The microstructural properties of these films have been compared with that of films deposited using a classical nozzle. Films deposited by perfume atomizer are rougher, with smaller grain size, compared to films deposited with a classical nozzle.     

Spray Forming of Homogeneous 20MnCr5 Steel of Low Distortion Potential

Spray forming is an advanced technology for the manufacture of homogeneous material from the melt. In this study, 20MnCr5 steel, a typical case hardening steel for gear and shaft production, has been spray formed and hot worked to semi‐finished bars. Shaft‐like specimens have been made from the spray‐formed material for distortion investigation. Material characteristics of the spray‐formed 20MnCr5 steel have been studied. In cooperation with other projects of the Collaborative Research Center SFB570 ‘’Distortion Engineering’’, evaluation of distortion behavior of the shaft specimens after machining and heat treatment has been made in comparison with continuous cast material. Spray‐formed 20MnCr5 steel shows lower distortion potential due to improved material homogeneity.     

Droplet velocity and thermal state from hot gas atomization of steel melt: Impact on the quality of the spray-formed tubular deposit

The velocity and thermal behavior (temperature, enthalpy, solid fraction) of atomized droplets in a metal spray play the most important role in the spray forming process. These properties mainly determine the materials yield and the final product quality (e.g., porosity, microstructure) of the as-sprayed materials. Changing the gas temperature in the atomization process directly influences these droplet properties in the spray. To understand the droplet behavior in the spray at various atomization gas temperatures (i.e., room temperature RT 293 K, 573 K, 873 K), numerical simulations using computational fluid dynamics (CFD) techniques have been performed and validated by experiments. A series of atomization runs (powder production and spray-forming with AISI 52100 steel) has been conducted at different atomization gas temperatures and pressures with a close-coupled atomizer (CCA). The in-situ temperature detection of the deposit surface (pyrometer) and in the substrate (thermocouples) has been performed to observe the effect of particle properties on the deposit. The result shows that hot gas atomization provides smaller droplets with faster velocity in the spray, affecting the droplet impact and deformation time in the deposition zone. A higher solid fraction of the smaller droplets by hot gas atomization also reduces the deposit surface temperature. Increasing the substrate diameter further decreases the deposit surface temperature without compromising the deposit quality (i.e., porosity) and also refines the grain size. Pre-heating of the substrate up to 573 K results in lower porosity in the vicinity of the substrate.     

Herstellung HVOF gespritzter,feinststrukturierter Cermetschichten unter Verwendung von feinen WC‐12Co Pulvern

Manufacturing of HVOF sprayed, finest structured cermet coatings using fine WC‐12Co powders The continuous increase in productivity and performance of modern sheet metal forming processes combined with the employment of novel, high strength materials cause high wear on tool systems. Coating technologies like thermal spraying provide a high potential to functionalize and to protect the surface of forming tools. However, it has to be ensured that the high shape and dimensional accuracy of the tool contour is preserved after the application of a wear protective coating. This aim cannot be achieved using currently applied, thermally sprayed coating systems with conventional, coarse grained microstructure. To solve this problem, novel finest structured coatings have been developed in this study by thermal spraying of fine WC‐12Co powders using the HVOF technique. For this purpose the influence of varying HVOF combustion gas compositions on the spray process as well as on the corresponding coating properties has been investigated. Next to a high surface quality the focus was placed on achieving coatings with high hardness and corresponding high wear resistance, low porosity as well as a good adhesive strength on the substrate material.     

Modelling of billet shapes in spray forming using a scanning atomizer

A numerical method is presented to predict and analyze the shape of a growing billet produced from the ‘spray forming’ which is a fairly new near-net shape manufacturing process. It is important to understand the mechanism of billet growth because one can obtain a billet with the desired final shape without secondary operations by accurate control of the process, and it can also serve as a base for heat transfer and deformation analyses. The shape of a growing billet is determined by the flow rate of the alloy melt, the mode of nozzle scanning which is due to cam profile, the initial position of the spray nozzle, scanning angle, and the withdrawal speed of the substrate. In the present study, a theoretical model was first established to predict the shape of the billet and next the effects of the most dominant processing conditions, such as withdrawal speed of the substrate and the cam profile, on the shape of the growing billet were studied. Process conditions were obtained to produce a billet with uniform diameter and flat top surface, and an ASP30 high speed steel billet was manufactured using the same process conditions established from the simulation.     

喷射沉积坯体特征尺寸的神经网络模型建立与仿真

采用神经网络技术建立了沉积坯特征尺寸模型,该模型描述了喷射成形关键工艺参数对沉积坯尺寸的影响规律,模型输出的相对误差为6.58%,RMS(均方差)为0.372mm.模型的仿真结果给出了沉积坯尺寸的变化规律,其中稳态仿真结果可用于预先确定喷射实验中所采用的合适工艺参数;而动态仿真结果表明,雾化气体压力和沉积器平移速度对沉积坯几何尺寸都有较大影响,其中沉积器平移速度具有调节范围大的优点,成为调节沉积坯几何尺寸较合适的工艺参数.     

On the characterization of bulk copper produced by cold gas dynamic spray processing in as fabricated and annealed conditions

The use of cold gas dynamic spray processing (cold spray), a process known for a coating and repair process for many alloy systems, has been demonstrated for the production of bulk copper deposits exceeding 25 mm in thickness. The microstructure and hardness of the specimens were characterized in as sprayed and annealed conditions. Microhardness was measured in both directions from the spray/substrate interface to assess the effects of cold spray impact on the substrate material and to characterize the properties of bulk “as-sprayed” copper before and after annealing. Microstructure was analyzed via scanning and transmission electron microscopy.