Rapid solidification of martensitic stainless steel atomized droplets

The microstructure of martensitic stainless steel powders produced by inert gas atomization was investigated. Depending upon the powder particle size, the microstructure was found to exhibit a cellular, dendritic, or martensitic morphology. Relationships between the microstructure scale and the particle diameter were identified. It was found that at a critical particle diameter of 25 to 30 μm, the structure changed from cellular/dendritic (96.5 vol pct bcc and 3.5 vol pct fcc) to martensite. The solidification path of the powder particles below and above 25 to 30 μm in size was considered. High-temperature X-ray diffraction (HTXRD) measurements revealed that there is a delay in the appearance of the fcc phase for the small particle size. The delay in the appearance of the fcc phase is a result of different nucleation sites for the fcc phase between the large and the small particle size.     

Rapid solidification of a droplet-processed stainless steel

Individual powder particles of a droplet-processed and rapidly solidified 303 stainless steel are characterized in terms of microstructure and composition variations within the solidification structure using scanning transmission electron microscopy (STEM). Fcc is found to be the crystallization phase in powder particles larger than about 70 micron diameter, and bcc is the crystallization phase in the smaller powder particles. An important difference in partitioning behavior between these two crystal structures of this alloy is found in that solute elements are more completely trapped in the bcc structures. Massive solidification of bcc structures is found to produce supersaturated solid solutions which are retained to ambient temperatures in the smallest powder particles. Calculated liquid-to-crystal nucleation temperatures for fcc and bcc show a tendency for bcc nucleation at the large liquid supercoolings which are likely to occur in smaller droplets. The importance of small droplet sizes in rapid solidification processes is stressed. Formerly with Massachusetts Institute of Technology, Cambridge, MA.     

Particle bonding,annealing response,and mechanical properties of dynamically consolidated type 304 stainless steel powders

The nature of interparticle bonding in explosively consolidated, centrifugally atomized (CA), and vacuum gas-atomized (VGA) Type 304 stainless steel powders has been examined. Stress waves with sufficient amplitude to produce full density do not necessarily produce metallurgical bonds between particles; the local strain and strain rate are found to determine the degree of local heating and, in turn, the degree of particle fusion. Particle interaction is found to be limited to nearest neighbors. The as-consolidated CA material has approximately twice the ultimate tensile strength of mill-annealed wrought Type 304 stainless steel. Consolidated CA powder has a higher defect density than VGA powder consolidated under the same conditions; however, the VGA material recrystallizes at a lower temperature due to a lower concentration of carbides. Annealing explosively consolidated material produced from either powder results in sintering, improved particle bonding, and greater ductility.     

Amorphous Phase Formation Analysis of Rapidly Solidified CoCr Droplets

This paper investigates amorphous phase formation and rapid solidification characteristics of a CoCr alloy. High cooling rate and high undercooling-induced rapid solidification of the alloy was achieved by impulse atomization in helium atmosphere. Two atomization experiments were carried out to generate powders of a wide size range from liquid CoCr at two different temperatures. Amorphous fraction and kinetic crystallization properties of impulse atomized powders were systematically quantified by means of differential scanning calorimetry. In addition, different but complementary characterization tools were used to analyze the powders microstructures. The fraction of amorphous phase within the investigated powders is found to be promoted by high cooling rate or smaller powder size. The critical cooling rate for amorphous phase formation, which is influenced by the oxygen content in the melt, is found to be ~3 × 10⁴ K s^?1 and corresponds to a 160-µm-diameter powder atomized in helium. Hardness of the powders is found to follow a trend that is described by the Hall–Petch relation when a relatively high fraction of crystalline structures is present and decreases with the fraction of amorphous phase.     

气雾化Al-Pb系轴瓦合金

采用气雾化技术，制备了应用于工业化ＲＳＰＭ工艺的高质量ＡｌＰｂ系合金粉末。对雾化粉末显微结构的分析表明，第二相（铅相）在基体中分布均匀，其粒径大小取决于凝固过程的冷速；不同粒径的粉末第二相分布随冷速的增加而分布更均匀、细化。对雾化粉末中各元素分布的分析表明，硅、铜等元素在晶界上有富积现象。     

雾化法制备高品质钛合金粉末技术研究

研究了惰性气体雾化法和等离子旋转电极法两种雾化法制备工艺所得TA15钛合金粉末的化学成分、粒度分布、颗粒形貌及微观组织。结果表明,雾化法制备的粉末间隙元素增量低,而且颗粒球形度高,颗粒内部是细小的胞状显微组织;惰性气体雾化法制备的粉末细粉收得率较高,有较多的吸附颗粒,颗粒内部有气孔;等离子旋转电极法制备的粉末粒度分布范围窄,颗粒呈规则的球形,表面光亮、圆滑。     

Al-Fe-Ce alloys based on water-atomized powders for high-temperature applications

The microstructure and mechanical properties of Al-Fe-Ce alloys based on water-atomized powders between 20 and 300 °C are examined in comparison with the properties of similar alloys produced by other rapid crystallization techniques. Changes in atomization parameters vary both the cooling rate (from 10⁴ to 10⁶ K/sec) and powder size distribution (from 5 to 100 µm). The excellent compactability of water-atomized powders facilitates powder consolidation, which is based on hot extrusion and cold pressing of degassed powders. The mechanical properties are examined by tensile tests. The ultimate tensile strength is 500 to 550 MPa at 20 °C and 270 to 300 MPa at 300 °C at adequate plasticity. The properties achieved are comparable with those of similar alloys known from the literature.     

Neutron diffraction study of austempered ductile iron

Crystallographic properties of an austempered ductile iron (ADI) were studied by using neutron diffraction. A quantitative phase analysis based on Rietveld refinements revealed three component phases, α-Fe (ferrite), γ-Fe (austenite), and graphite precipitate, with weight fractions of 66.0, 31.5, and 2.5 pct, respectively. The ferrite phases of the samples were found to be tetragonal,14/mmm, with ac/a ratio of about 0.993, which is very close to the body-centered cubic (bcc) structure. The austenite phase had C atoms occupying the octahedral site of the face-centered cubic (fcc) unit cell with about 8 pct occupancy ratio. A strong microstrain broadening was observed for the two Fe phases of the samples. The particle sizes of the acicular ferrite phase were studied by using small angle neutron scattering. The analysis suggested a mean rod diameter of 700 A. The scattering invariant predicts a ferrite volume fraction consistent with the powder diffraction analysis. A textbook case of nodular graphite segregation, with average diameters ranging from 10 to 20 μm, was observed by optical micrography.     

粉末冶金铜铁合金的组织与性能

分别以元素混合粉、机械合金化粉和水气联合雾化合金粉为原料,结合冷等静压成形、烧结及轧制工艺制备了Cu?5％Fe合金(质量分数),对比了三种原料粉的铜铁合金粉末形貌、微观组织、力学性能及物理性能.结果表明,铁颗粒分布均匀,元素混合、机械合金化和水气联合雾化法粉末烧结体中铁颗粒平均尺寸分别为9.4μm、1.2μm、3.5μ...     

Magnetic contributions to the thermodynamic functions of alloys and the phase equilibria of Fe-Ni system below 1200 K

A generalized approach is proposed to calculate the magnetic contribution to the thermodynamic functions of alloys. This approach is applied successfully to the Fe-Ni binary system. The predicted magnetic specific heat of the fcc phase at 75 at. Pct Ni is in agreement with the experimental data within the accuracies of the data and the predicted values. The magnetic contributions to the Gibbs energies of the fcc and bcc phases for the Fe-Ni alloys obtained from this approach are added to the nonmagnetic portion of the Gibbs energies. The nonmagnetic portion of the Gibbs energy of the fcc phase is obtained from extensive thermochemical data at high temperatures as discussed in the paper immediately following this one. The total Gibbs energies of the fcc, bcc, and the orderedγ′-(FeNi₃) phases are then used to calculate/predict phase equilibria of the Fe-Ni binary at temperatures lower than 1200 K. The calculated equilibria are in agreement with available experimental data. In addition, a irascibility gap of the fcc phase at low temperatures is predicted, resulting in the formation of a monotectoid equilibrium at 662 K as given below: {fx1361-02} The existence of the miscibility gap is due to the magnetic Gibbs energy term of the fcc phase which is composition dependent. Experimental results reported in the literature support the predicted miscibility gap.     

合金Co-Zr-B纳米粉末的相组成及磁性能研究

将硼氢化钠(NaBH4)的水溶液加入到氯化钴(CoCl2·6H2O)和硫酸锆(Zr(SO4)2·4H2O)的混合水溶液中,利用BH-4把混合溶液中的CO2 和Zr4 同时还原出来,首次成功制备出非晶态Co-Zr-B三元纳米合金粉末.用电感耦合等离子体发射光谱(ICP)、X射线衍射(XRD)、选区电子衍射(SAED)、透射电子显微镜(TEM)、差示扫描量热法(DSC)以及振动样品磁强计(VSM)分析了样品的成分、结构和磁性能.发现所制备的不同成分的粉末颗粒呈球形,粒径在20～60nm之间.纳米粉末由非晶相基体和少量晶体相杂质组成,而非晶相基体又由Zr基非晶颗粒和含有Zr的Co基非晶颗粒构成.还原产物中的Co原子和Zr原子的分数之比与金属盐混合溶液中的Co2 与Zr4 离子的分数之比几乎相等.提高NaBH4溶液的加入速度,可增加产物中B元素的含量.样品的晶化温度在765.1～771.3K之间,样品的热稳定性随Zr含量的增加而增加,样品的磁性能也与样品中Co、Zr原子的含量之比有关.当原子数x(Co)/x(Zr)比值从1.94增加到5.14时,饱和磁化强度从4.76emu/g增加到8.87emu/g,矫顽力在1271.66A/m(15.98Oe)到2133.49A/m(26.81Oe)之间不规则变化.     

Processing and microstructure of Powder Metallurgy Al-Fe-Ni Alloys

Prealloyed rapidly solidified Al-Fe-Ni alloy powder with dispersoid volume fractions of 0.19, 0.25, and 0.32 FeNiAl₉ was produced by air atomization. The powder was degassed, canned, and consolidated to full density by vacuum hot pressing and extrusion or by direct extrusion. Microstructures in the alloy powder and consolidated material were characterized by means of optical, scanning (SEM), and transmission electron microscopy (TEM) and constituent phases identified by X-ray diffraction. The coarsening kinetics of the FeNiAl₉ dispersoid were moni- tored by differential scanning calorimetry (DSC) and by quantitative metallography. Atomized powders exhibited two scales of microstructures: optically featureless regions and regions with a coarse dispersoid morphology. Within the featureless regions, there are three morphologies, namely, a fine uniform precipitate microstructure, a cellular microstructure, and an eutectic microstructure. The only dispersoid observed in the atomized powders and consolidated material was FeNiAl₉). The two scales of microstructure were retained after consolidation, and after hot extrusion, the typical microstructure consisted of a recovered matrix structure with a grain size of 0.2 to 0.3 μm and equiaxed intermetallics of average diameter 0.1 μm. The microstructure was resistant to coarsening up to approximately 370 °C. Coarsening kinetics in this alloy system were consistent with a grain boundary diffusion model (activation energy 146 kJ/mol) and were not appreciably affected by dispersoid volume fraction.     

Microstructural transitions during containerless processing of undercooled Fe-Ni alloys

The microstructural development associated with solidification in undercooled Fe-Ni alloys has been reported in different studies to follow various pathways, with apparent dissimilarities existing as a function of sample size and processing conditions. In order to identify the possible hierarchy of microstructural pathways and transitions, a systematic evaluation of the microstructural evolution in undercooled Fe-Ni alloys was performed on uniformly processed samples covering seven orders of magnitude in volume. At appropriate undercooling levels, alternate solidification pathways become thermodynamically possible and metastable product structures can result from the operation of competitive solidification kinetics. For thermal history evaluation, a heat flow analysis was applied and tested with large Fe-Ni alloy particles (1 to 3 mm) to assess undercooling potential. Alloy powders (10 to 150 μm), with large liquid undercoolings, were studied under the same composition and processing conditions to evaluate the solidification kinetics and microstructural evolution, including face-centered cubic (fcc)/body centered cubic (bcc) phase selection and the thermal stability of a retained metastable bcc phase. The identification of microstructural transitions with controlled variations in sample size and composition during containerless solidification processing was used to develop a microstructure map which delineates regimes of structural evolutions and provides a unified analysis of experimental observations in the Fe-Ni system.     

Phase relationships in the iron-rich Fe-Cr-Ni-C system at solidification temperatures

The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich comer of the Fe-Cr-Ni-C system as part of a larger study of the Fe-Cr-Mn-Ni-C system. The investigation consisted of measurements of tie-lines for the liquid-delta (bcc) and the liquid-gamma (fcc) equilibria in the iron-rich corner of the Gibbs tetrahedron bounded by 0 to 25 wt Pct Cr, 0 to 25 wt Pct Ni, and 1.2 wt Pct C (bal. Fe). The temperature ranged from 1811 to 1750 K. Compositions for the tie-lines were obtained from liquid-solid equilibrium couples and the temperatures of the equilibrium, by differential thermal analysis (DTA). A mathematical procedure was employed on the experimental data to obtain parameters for a thermodynamic model of the alloy system. This involved minimization of an error function. The details of this analysis are discussed fully in this paper. Calculations by the model employing the “best-set” parameters are in good agreement with the experimental results. The usefulness of the model is demonstrated by calculation of the three-phase equilibrium in the quaternary system as a function of temperature. Formerly Research Fellow, Massachusetts Institute of Technology, is Senior Research Engineer, Armco Inc., Middletown, OH 45043     

真空雾化CoCrAlTaY热喷涂粉末的特性及其涂层的结合强度

采用真空雾化制备了CoCrAlTaY高温合金粉末。结果表明:该合金粉末呈球形,粉末粒度呈近正态分布,粉末由CoAl、γ、Cr27C3和TaC相组成;合金粉末涂层与基体结合良好,其结合力达到52 MPa。     

紧耦合气雾化参数对3D打印用金属粉末性能的影响

利用自主设计研发的紧耦合雾化制粉装置,采用真空感应熔炼气雾化工艺制备3D打印用Inconel 625合金粉末,通过调整雾化参数研究导液管内径对粉末粒度分布、表面形貌、氧含量(质量分数)及流动性能等特性的影响.结果表明:使用紧耦合雾化制粉装置制备出的粉末粒度范围较广,收得率较高,其中尺寸小于53μm的粉末收得率可达50％...     

粉末粒度和氧含量对HIP态FGH96合金组织的影响

对氩气雾化法制备的高温合金FGH96粉末进行了热等静压(HIP)处理,分析了粉末粒度和氧含量对HIP态合金组织的影响,研究了FGH96合金组织中PPB的类型、相结构和形成机制。结果表明,氩气雾化FGH96粉末的氧含量较低,平均氧含量约为50×10-6,随着粉末粒度降低,颗粒比表面积增大,促进了粉末氧含量的升高;粉末经HIP处理后氧含量具有遗传特征,原始粉末氧含量越高,HIP态合金氧含量也越高,且平均氧含量增至83×10-6;粉末尺寸和氧含量对合金致密化行为无明显影响,HIP态合金密度约为8.33 g·cm-3。小尺寸粉末制备的HIP态合金原始颗粒边界主要析出ZrO2和MC碳化物,而大尺寸粉末制备的HIP态合金原始颗粒边界主要析出大尺寸花瓣状γ’相和少量MC碳化物。粉末粒度和氧含量影响PPB析出,小尺寸粉末因氧含量高经HIP处理时颗粒边界处存在更多、尺寸更大稳定的ZrO2,ZrO2成为MC碳化物析出形核的核心,促进了大量MC碳化物的析出。     

Processing and microstructure of powder metallurgy Al-Fe-Ni alloys

Prealloyed rapidly solidified Al-Fe-Ni alloy powder with dispersoid volume fractions of 0.19, 0.25, and 0.32 FeNiAl₉ was produced by air atomization. The powder was degassed, canned, and consolidated to full density by vacuum hot pressing and extrusion or by direct extrusion. Microstructures in the alloy powder and consolidated material were characterized by means of optical, scanning (SEM), and transmission electron microscopy (TEM) and constituent phases identified by X-ray diffraction. The coarsening kinetics of the FeNiAl₉ dispersoid were monitored by differential scanning calorimetry (DSC) and by quantitative metallography. Atomized powders exhibited two scales of microstructures: optically featureless regions and regions with a coarse dispersoid morphology. Within the featureless regions, there are three morphologies, namely, a fine uniform precipitate microstructure, a cellular microstructure, and an eutectic microstructure. The only dispersoid observed in the atomized powders and consolidated material was FeNiAl₉. The two scales of microstructure were retained after consolidation, and after hot extrusion, the typical microstructure consisted of a recovered matrix structure with a grain size of 0.2 to 0.3 μm and equiaxed intermetallics of average diameter 0.1 μm. The microstructure was resistant to coarsening up to approximately 370 °C. Coarsening kinetics in this alloy system were consistent with a grain boundary diffusion model (activation energy 146 kJ/mol) and were not appreciably affected by dispersoid volume fraction.     

Mechanical properties and fracture behavior of an ultrafine-grained Al-20 wt pct Si alloy

The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder size <26 μm was 322 MPa, while for the coarser powder (45 to 106 μm), it was 230 MPa. The tensile strength of the extruded bar from the fine powder (<26 μm) was also higher than that of the Al-20 wt pct Si-3 wt pet Fe (powder size: 60 to 120 μm) alloys. With decreasing powder size from 45 to 106 μm to <26 μm, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 μm at 3.5 m/s) was larger on the worm surface in comparison to the bars from the fine powders (5 μm at 3.5 m/s), attributed to the lower strength of the bars with coarse powders.     

气体雾化法制备TiB2/Al复合材料粉末及其组织演变

采用氟盐反应法制备TiB₂/Al复合材料铸锭,并以此为原料利用高压气体雾化制粉技术制备TiB₂/Al复合材料粉末。利用金相显微镜、扫描电子显微镜、X射线衍射仪、粒度分布仪等手段对所制备铸锭和粉末的组织及性能进行了表征。结果表明:Al熔体中TiB₂的溶度积远小于TiAl₃和AlB₂的溶度积,TiB₂自Al熔体中沉淀析出导致的体系Gibbs自由能变化量比TiAl₃或AlB₂自Al熔体中沉淀析出导致的体系Gibbs自由能变化量的值更小。TiB₂/Al复合材料铸锭及粉末均主要由α-Al相和TiB₂相组成。气体雾化制备TiB₂/Al复合材料粉末中TiB₂颗粒具有纳米尺度,且均匀弥散地分布于Al基体之中,不存在明显的偏聚现象。TiB₂/Al复合材料粉末的粒度主要分布在10～100 μm之间,呈正态分布,粒径介于10～70 μm粉末占比（质量分数）约为81.1%,粒径大于70 μm粉末收得率为12.6%,粒径小于10 μm粉末收得率为6.3%。