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.     

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.     

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.     

Development of low‐melting‐point filler materials for laser beam brazing of aluminum alloys

In order to develop low‐melting‐point filler materials for laser beam brazing of aluminum alloys, Al–Si–Cu based alloys and Al–Si–Zn based alloys were produced via spray forming and associated deformation processes. The selected alloys were spray formed in the form of billet with a diameter around 160 mm and hot extruded into wire rods with a diameter of 8 mm. The extrusions were further cold worked into thin wires with a diameter of 1.2 mm via rotary swaging. Finally, the filler wires were applied in the laser beam brazing of AA6082 structures. It showed that the newly developed filler materials could meet the requirements of the laser beam brazing of aluminum alloys. Particularly, the laser beam brazing process using the spray‐formed filler materials required a significantly lower energy input and allowed for higher brazing speed as compared to the conventional AlSi12 filler material.     

结构材料喷射成形技术与雾化沉积高温合金

喷射成形是利用快速凝固方法直接制备金属材料坯料或半成品的先进材料制造技术 ,喷射沉积高温结构材料的冶金性能好、生产效率高、成本低 ,因而在近几年得到了迅速发展 .本项研究的主要目的是要通过喷射成形工艺参数的调整、最大限度地直接减少喷射成形坯中的孔隙度 ,进而得到优质坯料 .利用优化的雾化喷射沉积技术制备了多种高温合金沉积坯 ,沉积坯整体致密、晶粒细小、组织均匀、无宏观偏析、含气量低、力学性能提高 .还简要地比较了喷射成形高温合金与用常规铸锭冶金工艺和粉末冶金工艺制备高温合金的异同 ;总结了航空材料研究院喷射成形高温材料近年来的研究状况 ,包括专用高温材料喷射成形装置和技术及其应用 .     

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.     

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.     

Analysis of spray formed tool steels

The technique of atomising liquid metal and compacting the micro‐droplets to a billet on a rotating support combines advantages from cast, wrought and powder metallurgical materials. A production rate of several tons per hour requires precisely controlled processing routines. Important process parameters based on processing, manufacturing and application of spray formed material are now developed by fundamental investigations established in projects focused in a special co‐operative research program (SFB 372) at the University of Bremen which is funded by the Deutsche Forschungsgemeinschaft (DFG). By this method advanced alloys of high hardness can be formed without inhomogeneities like segregations and pores in the center of the ingot. By example of tool steels the influence of spray forming on microstructure and homogeneity of the elemental distribution is shown.     

Microstructure and elevated temperature mechanical properties of Al–8Fe–4RE alloy fabricated by spray forming

Al–8Fe–4Ce alloy is currently manufactured by consolidating the atomized powders. With the aim to reduce the cost, spray forming process was applied in manufacturing with misch metal as raw materials. Spray forming (SF) as well as casting were employed to prepare Al–8Fe–4RE alloy, followed by hot‐press to compact the samples. The mechanical properties of SFed and cast Al–8Fe–4RE alloys are characterized at a temperature of 350 °C. The results show that the Al₃Fe phases contained in SF alloy is comparatively refined, forming needle‐shaped phases embedded in the Al matrix, and the SF alloy also showed lower degree of preferred orientation in (111) plane. Although both factors might explain the superior performance of the SF sample, the fracture appearance after tensile test at 350 °C shows that the contribution from crystallographic feature might be predominant. Spray forming is proved to be a very promising technique for manufacture of Al–Fe–Ce alloys of high strength at an elevated temperature.     

热等静压对喷射成形TiAl基合金孔隙率的影响

着重研究了气体辅助喷射成形和离心喷射沉积形成的Ｔｉ－４８Ａｌ－２Ｍｎ－２Ｎｂ金属间化合物的孔隙率以及热等静压工艺对合金孔隙率的影响，利用Ｑｕａｎｔｉｍｅｔ图象分析仪定量测试了各种状态样品的孔隙率。结果表明，气体雾化成形合金的孔隙率约３．２９％，离心喷射盛开有合金的孔隙率约２．２０％，孔隙率的大小与喷射成形工艺密切相关。     

Vom Lötbruch bis zum Rotbruch – Gemeinsamkeiten und Besonderheiten

The soldering embrittlement is a brazing defect due to local or continuous material separation. It can limit the guarantee and reliability of brazed joints or even render it impossible. Normally this material separation occurs in an intercrystalline way along the grain boundaries or even sub grain boundaries. Thus the liquid metal embrittlement belongs macroscopically to the embrittlements which were influenced by applied procedures on basic materials. The character of liquid metal embrittlement and the kinetic of crack formation can be compared to similar material separations such as reheat cracks next to welding line or red shortness cracks during the metal forming process. In the present article the authors compare these intercrystalline material separations and specify the common similarities and characteristics in which the brazing joints are focused.     

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.     

喷射成形技术及其在钢铁材料上的应用

喷射成形是近年来发展非常迅速的一种近终成形先进冶金工艺技术。与传统铸造工艺及粉末冶金工艺相比,喷射成形设备、工艺简单,能生产偏析小、晶粒细、致密度高的材料。喷射成形技术在铝基合金、铁基合金、高温合金、铜合金及复合材料等方面都得到了广泛的应用。主要介绍该技术的原理及其在钢铁材料方面的应用情况,并讨论了它在钢铁领域的发展趋势,指出喷射成形工艺是一种有望替代粉末冶金工艺生产高合金钢材及一些特殊钢材的崭新工艺。     

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.     

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…     

MICROSTRUCTURAL MODELING AND NUMERICAL ANALYSIS FOR THE SUPERPLASTIC FORMING PROCESS

Superplastic forming is a manufacturing process during which a sheet is blow formed into a die to produce lightweight and strong components. In this paper, the microstructural mechanism of grain growth during superplastic deformation is studied. A new model, which considers grain growth, is proposed and applied to conventional superplastic materials. The relationships among the strain, strain rate, test temperature, initial grain size, and grain growth in superplastic materials are discussed. According to the proposed model, theoretical predictions for superplastic forming processes are presented, and comparison with experimental data is given. The new constitutive equation of superplasticity is introduced into a finite element method program to study superplastic blow forming. The effects of the geometric shape parameters of the die on the superplastic blow forming process are investigated, and the inhomogeneity in the thickness distribution of the specimen is analyzed.     

Microstructure of a recycled AA7050 alloy processed by spray forming followed by hot extrusion and rotary swaging

The aim of this study is to evaluate the microstructure of a recycled AA7050 alloy processed by spray forming followed by hot extrusion and swaging. Machining chips from an aircraft manufacturer were used as raw material. The microstructure was investigated by optical microscopy (MO) and scanning electronic microscopy (SEM). The spray formed deposit was homogenized at 743 K, 8 h, extruded at 693 K with a deformation rate of 0.1 s^–1 and an extrusion rate of 156:1, producing a bar with 8.0 mm in diameter. Due to a specific combination of high extrusion temperature and deformation rate, partial recrystallization occurred and different grain sizes were obtained through the extruded cross section. After extrusion, the 8.0 mm bar was processed by rotary swaging in several steps up to a 2.0 mm final diameter. The resulting microstructure revealed a cold worked structure, with no recrystallization. Tensile tests were performed in both cases and the slant type of fracture reveals that Portevin Le‐Chatelier effect took place in this alloy. Moreover, the efficacy of extrusion and rotary swaging parameters to reduce the porosity, intrinsic to the spray form process, was analyzed, as well the distribution of intermetallic particles.     

An approach for modeling the active transformation of microstructure of two‐phase Alloys in FEM simulation of technological chains in superplastic forming (SPF)

Optimization and broadening of the technological regimes of superplastic forming require more accurate accounting of the transformation of microstructure during all stages of the forming process. On the one hand, it is very important to predict the resultant microstructure in different parts of the formed structure as it determines the operation properties, and on the other hand, active transformation of microstructure can lead to either hardening (grain coarsening) or softening (grain refinement) of the material. These changes in the mechanical behavior of a material can be quite significant and need to be taken into account in the FEM simulation of superplastic forming processes to achieve the required accuracy. One approach for modeling the microstructural transformation in an FEM simulation for a two‐phase alloy is proposed herein. Constitutive model with internal variables is described. The questions of validity of macroscopic and microscopic equations are discussed. The approach for taking into account the transformation of metallographic texture is proposed.     

3-D Simulation of hot forming and microstructure evolution

Stretch rolling is used for the production of a preform for subsequent die-forging of a connecting rod. A fully three-dimensional thermo-mechanically coupled FEM-simulation of a five-pass stretch rolling process has been performed. The influence was studied of various thermal and mechanical boundary conditions on the spatial strain and temperature fields developing. The results for the parameters strain, strain rate and temperature are used to predict the austenite grain size during the hot forming process by use of established recrystallization models. The calculated grain sizes are compared with those of formed components showing good agreement between experiment and numerical prediction.     

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。