Coarsening Manner and Microstructure Evolution of Al—In Hypermonotectic Alloy during Rapidly Cooling Process

Anumerical model reflecting the real physical processes well has been developed to predict the coarsening manner of the second phase droplets and the microstructural evolution under the common action of nucleation, diffusional growth, colliding coagulation during rapid cooling Al-In hypermonotectic alloys.The model reflects the real physical processes well and is also applicable to other immiscible alloys.     

Heterostructured crystallization mechanism and its effect on enlarging the processing window of Fe-based nanocrystalline alloys

The harsh melt-spinning and annealing processes of high saturation magnetization nanocrystalline softmagnetic alloys are the biggest obstacles for their industrialization. Here, we proposed a novel strategy to enlarge the processing window by annealing the partially crystallized precursor ribbons via a heterostructured crystallization process. The heterostructured evolution of Fe_84.75Si₂B₉P_3C0.5Cu_0.75(at.%)alloy ribbons with different spinning rate were studied in detail, to demonstrate the gradient nucleation and grain refinement mechanisms. The nanocrystalline alloys made with industrially acceptable spinning rate of 25-30 m/s and normal annealing process exhibit excellent magnetic properties and fine nanostructure. The small quenched-in crystals/clusters in the free surface of the low spinning rate ribbons will not grow to coarse grains, because of the competitive grain growth and shielding effect of metalloid elements rich interlayer with a high stability. Avoiding the precipitation of quenched-in coarse grains in precursor ribbons is thus a new criterion for the composition and process design, which is more convenient than the former one with respect to the homogenous crystallization mechanism, and enable us to produce high performance nanocrystalline soft-magnetic alloys. This strategy is also suitable for improving the compositional adjustability, impurity tolerance, and enlarging the window of melt temperature,which is an important reference for the future development of composition and process.     

Highly Improved Gaseous Hydrogen Storage Characteristics of the Nanocrystalline and Amorphous Nd-Cu-added Mg2Ni-type Alloys by Melt Spinning

The nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of （Mg24Ni10Cu2）loo-xNdx （x = 0-20） were prepared by melt spinning. The X-ray diffraction and transmission electron microscopy inspections reveal that, by varying the spinning rate and the Nd content, different microstructures could be obtained by melt spinning. Particularly, the as-spun Nd-free alloy holds an entire nanocrystalline structure but the as-spun Nd-added alloy has a nanocrystalline and amorphous structure, which implies that the addition of Nd facilitates the glass forming in the Mg2Ni-type alloy. Also, the degree of the amorphization in the as-spun Nd-added alloys clearly increases with increasing the spinning rate and the Nd content. The H-storage capacity and the hydrogenation kinetics of amorphous, partially and completely nanocrystalline alloys were investigated and it was found that they are dependent on the microstructure and the phase composition of the alloys. Specially, enhancing the spinning rate from 0 （the as-cast was defined as the spinning rate of 0 m/s） to 40 m/s makes the hydrogen absorption saturation ratio （R5a） （a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity） increase from 35.2% to 90.3% and the hydrogen desorption ratio （R10d） （a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity） rise from 12.7% to 44.9% for the （x = 5） alloy. And the growing of the Nd content from 0 to 20 gives rise to the R5a and R10d values rising from 85.7% to 94.5% and from 36.7% to 54.8% for the as-spun （30 m/s） alloys, respectively.     

Effect of Processing Parameters on Microstructures of Melt—Spun Al—In Immiscible Alloys

Melt spinning rapid solidification technique was employed to fabricate homogeneous Al-In immiscible alloys and their final microstructures and morphologies were investigated.There existed a transition of columnar Al grain→equiaxed grain for the thicker ribbon,but only columnar Al grain for the thinner ribbon throughout the thickness.In the columnar grain field,most of the fine In particles was distributed within the cells,but a minority of bigger In particles or short rods was perpendicularly distributed at the grain boundaries.In the equiaxed grain field,the fine In particles were located in Al grains and coarser particles were situated at the boundaries.The average particle size increased with increasing distance from the chilled surface throughout the ribbon.At the same wheel speed (same cooling rate),the average particle size increased with raising In content.At the same composition condition,the average particle size decreased with increasing wheel speed and/or decreasing ejection temperature.     

Microstructural Features of Spray-Deposited Immiscible Bearing Alloys Al-43Sn and Al-7Sn-1.3Cu-1.3Ni

Two commercial grade aluminum based immiscible bearing alloys were spray-deposited using convergent-divergent type of nozzle. The processing parameters for spray-deposition were adjusted in such a way that most of the droplets arrived on the deposition substrate in either liquid or semi-liquid state. The microstructural features of spray-formed and as-cast alloys are compared. In spray-formed alloys equiaxed grains were observed. The cell boundaries and intercellular regions were observed to be decorated with sub-micron sized particles whereas in normal casting the second phase was observed to be segregated along grain boundaries. The morphology and distribution of second phase were observed to have similarity with those in over-spread and atomized powders produced under similar processing conditions. The microstructural features observed with variation in spray conditions are discussed in detail.     

Modeling and Simulation of the Microstructure Evolution during a Cooling of Immiscible Alloys in the Miscibility Gap

The microstructure development during a cooling period of alloys being immiscible in the liquid state such as Al-Pb or Al-Bi has gained renewed scientific and technical interest during the last decades.Experiments have been performed to investigate the phase transformation kinetics in the liquid miscibility gap and numerical models have been developed to simulate and analyze the solidification process.The recently developed computational modeling techniques can,to some extent,be applied to describe the decomposition,the spatial phase separation and the microstructure evolution during a cooling period of an immiscible alloy through the miscibility gap.This article overviews the researches in this field.     

Effects of Additional Elements on Microstructure and Precipitation Behaviour in Rapidly Solidified Al-Ti Base Alloys

Rapidly solidified Al-Ti base alloys were prepared by melt spinning at the cooling rate about 107 K/s. The melt-spun ribbons were used to observe the dricrostructures after heat treatment.In the supersaturated Al-Tl-Si alloy, age hardening occurred after 1 h anneal in the temperature range of 4000~500℃, which seems to be attributed to the precipitation of metastable Ll2- (Al,Si)3Ti phase. However. the microhardness was relatively low because of the low v/o and the insufflcient stability of precipitates. Thus. Cr was added to Al-Ti-Si alloys in order to stabilize the microstructures and to increase the v/o of precipitate5. As a result. the alIoys containing Cr were evaluated to possess the improved properties at the service temperature.     

Three Dimensional FE Analysis on Flange Bending for TC4 Alloy during Shear Spinning

In this paper, the 3D elastic-plastic simulation was carried out by using finite element （FE） code according to the phenomena of flange keeping straight, bending towards headstock and bending towards tailstock in the shear spinning experiments for TC4 alloy. The simulation results for the three kinds of deformations of the flange agree well with the experimental results. So it is possible to explain the reason of flange bending by analyzing the strain vectors in the flange for the three kinds of deformation, which shows that it is important to apply the FE simulation technology for predicting the defects and optimizing the spinning process of TC4 alloys.     

Influences of Preparation Conditions and Melt Treatment Procedureson Melt Treatment Performance of Al-5Ti-Band Al-10Sr Master Alloys

The influences of preparation conditions of Al-5Ti-B （as-cast and hot-rolled） and Al-10Sr （as-cast and hotextruded） and melt treatment procedures on the grain refinement and modification performance of A356 alloy are experimentally studied. For the two master alloys, the 50% reduction is sufficient to meet the demands of the efficient grain refinement and modification of A356 alloy. When Al-STi-B is introduced into the melt prior to degassing, the grain refinement efficiency of Al-5Ti-B will be greatly increased due to the better dispersity of TiB2 particles. Al-5Ti-B master alloy is less prone to affect the modification effect of Al-10Sr when they are used together.     

Preparation and Structural Characterization of Rapidly Solidified AI-Cu Alloys

Rapidly solidified Al_(100-x)—Cu_x alloys(x = 5,10,1 5,25,35 wt%) were prepared and analyzed.High cooling rate increased the Cu solubility in 9.-AI matrix.The influence of the cooling rate on Cu solubility extension in Al was experimentally simulated.Thus the pouring was performed in metallic die and by melt spinning-low pressure(MSLP) technique.Melt processing by liquid quenching was performed using a self-designed melt spinning set-up which combined the cooling technology of a melt jet on the spinning disc with the principle of the mold feeding from low pressure casting technology.The thickness of the melt-spun ribbons was in the range of30—70 μm.The cooling rate provided by MS-LP was within 10~5—10~6 K/s after the device calibration.The obtained alloys were characterized from structural,thermal and mechanical point of view.Optical microscopy and scanning electron microscopy were employed for the microstructural characterization which was followed by X-ray analysis.The thermal properties were evaluated by dilatometric and differential scanning calorimetric measurements.Vickers microhardness measurements were performed in the study.In the case of the hypereutectic alloy with 35 wt%Cu obtained by MS-LP method,the microhardness value increased by 45%compared to the same alloy obtained by gravity casting method.This was due to the extended solubility of the alloying element in the α-AI solid solution.     

Preparation and properties of iron-boron metallic glass ribbons melt spun in air

The preparation of metallic glass ribbons by melt spinning is a simple technique; however, a researcher often faces many problems when undertaking the preparation of such ribbons. The difficulties encountered are oxidation of the melt, choking of the nozzle by the solidified metal, formation of metal globules or ribbon fragments, oxidation of the ribbons, etc. These problems are particularly severe when working with high melting point alloys. This report describes certain experimental techniques used to overcome problems in preparation of metallic glass ribbons of iron-boron and other high melting point alloys. The ribbons thus produced have been characterized by transmission electron microscopy, mechanical tests and differential thermal analysis. The mechanical strength of the ribbon is comparable to the best recorded strength for ribbons of similar composition. Thedta data support the view that the formation of the phase Fe₂₃B₆ takes place upon crystallization of the eutectic alloy.     

Shape memory characteristics and superelasticity of Ti-Ni-Cu alloy ribbons with nano Ti2Ni particles

Microstructures and deformation behaviour of Ti-45Ni-5Cu and Ti-46Ni-5Cu alloy ribbons prepared by melt spinning were investigated by transmission electron microscopy, thermal cycling tests under constant load and tensile tests. Spherical Ti2Ni particles coherent with the B2 parent phase were observed in the alloy ribbons when the melt spinning temperature was higher than 1773 K. Average size of Ti2Ni particles in the ribbons obtained at 1873 K was 8 nm, which was smaller than that (10 nm) in the ribbons obtained at 1773 K. Volume fraction of Ti2Ni phase in the ribbons obtained at 1873 K was 40%, which was larger than that (20%) in the ribbons obtained at 1773 K. The stress required at temperatures of Af + 10 K for the stress-induced martensitic transformation increased from 93 MPa to 229 MPa and apparent elastic modulus of the B2 parent phase increased from 56 GPa to 250 GPa with increasing the melt spinning temperature from 1673 K to 1873 K in Ti-45Ni-5Cu alloy ribbons. The critical stress for slip deformation of the ribbons increased by coherent Ti2Ni particles, and thus residual elongation did not occur even at 160 MPa, while considerable plastic deformation occurred at 60 MPa in the ribbons without Ti2Ni particles. Almost perfect superelastic recovery was found in the ribbons with coherent Ti2Ni particles, while only partial superelastic recovery was observed in the ribbons without coherent Ti2Ni particles.     

Structural inhomogeneities of AlSi alloys rapidly quenched from the melt

Hypo- and hyper-eutectic AlSi alloys were rapidly quenched from the melt using the melt-spinning technique with two spinning velocities. Structural differences between the wheel (chill) and upper sides of the melt-spun ribbons were investigated by optical and scanning electron microscopy and X-ray diffraction methods (texture- and size-strain analyses). The Al-rich phase of the hypo-eutectic alloys was textured. The textures observed from both sides of the ribbons were different; in neither case was it of fibre type. For the larger spinning velocity applied, the structural imperfection of the wheel side was larger than that of the upper side for both the Al-rich and the Si-rich phases.     

Microstructure of Al-Si Alloys Rapidly Solidified from the Different Temperature Melts

1.IotroductionCoolingratehasasignificanteffectonsolidifyingmicrostructureofAl-Sialloys,ithaJsbeenshownthatthemorphologyofeutecticsiliconchangesfromplatestofiberswhenthecoolingrateisincreased[1'2].Rapidsolidificationprocessingprovidesawaytogreatlyre-finemicrostructure.Inmelt-spinningprocess,alargecircumferentialvelocityoftherotatingwheelisac-companiedbyalargecoolingandsolidificationrate.SoasmallsizeofAl-richandSi-richphaseswasgainedinthespunribbonsofAlSialloysl3].Obviously,themicrostructure…     

La2Fe14B和Ce2Fe14B合金在快淬和热处理过程中相析出行为的比较

研究了溶体快淬三元La_2Fe_(14)B和Ce_2Fe_(14)B合金的相析出行为和磁性能,对不同快淬速度(10~50 m/s)和不同热处理温度下制备的样品进行了系统分析。结果表明,通过直接快淬,La_2Fe_(14)B合金中不能形成2∶14∶1硬磁相,而Ce_2Fe_(14)B合金可以获得2∶14∶1相。La_2Fe_(14)B合金在10m/s快淬时主要由La和α-Fe相组成,而Ce_2Fe_(14)B合金中2∶14∶1硬磁相在10m/s和20m/s快淬时析出。随着辊速的增加,非晶相逐渐增多并成为主相。在热处理过程中,La_2Fe_(14)B合金析出相以α-Fe和La相为主,并且高温下液态的富La相和α-Fe相可以共存;而Ce_2Fe_(14)B合金中先析出α-Fe,后析出2∶14∶1硬磁相,随后析出相长大。结果还表明,La_2Fe_(14)B比Ce_2Fe_(14)B有更高的非晶居里温度和更低的α-Fe相析出温度。由于硬磁相的析出,Ce_2Fe_(14)B合金可以获得较好的硬磁性能,包括一定的矫顽力。此研究对含La、Ce稀土永磁材料的生产具有一定的指导作用。     

Morphology and mechanical properties of melt-spun and conventionally cast aluminium,AlMg and AlSi alloys before and after hot extrusion

Rapidly solidified aluminium, AlMg (0 to 16.5 at % Mg) and AlSi (0 to 20.2 at % Si) alloys were produced by melt spinning. The AlMg ribbons were single-phase, whereas the AlSi ribbons were dual-phase. In the ribbons of both alloy systems the fineness of the microstructure increased with increasing alloying element content. The melt-spun ribbons were consolidated by hot extrusion. For comparison, conventionally cast alloys of corresponding compositions were extruded analogously. During the extrusion process in AlMg (16.5 at % Mg) and in the AlSi alloys precipitation occurred. The consolidation of the ribbons was markedly influenced by the oxide layer on the ribbon surfaces: in the AlSi consolidates a more intimate contact between the ribbons was apparent than in the aluminium and AlMg consolidates. In the extrudates of the conventionally cast alloys the grains and second-phase particles were much larger than in the consolidates. The observed dependence on alloy composition of hardness, ultimate tensile strength and elongation at fracture of both consolidated ribbons and extrudates of the conventionally cast alloys are discussed in terms of matrix grain size, solute content of the matrix, amount and size of second-phase particles and recrystallization behaviour. For all compositions of the alloys the Vickers hardness of the as-melt-spun ribbons was higher than that of the consolidated products, owing to recrystallization and precipitation provoked by the hot consolidation process. The ultimate tensile strength as well as the elongation at fracture of both consolidated ribbons and extruded conventionally cast alloys did not differ significantly for AlMg. However, due to a finer microstructure and a stronger inter-ribbon bonding, for AlSi alloys with a high silicon content the rapid solidification processing route did yield a product with significantly improved mechanical properties as compared with the extruded conventionally cast alloys.     

TITANIUM-NICKEL SHAPE MEMORY ALLOY PROCESSED BY RAPID SOLIDIFICATION

A rapidly solidified equiatomic titanium-nickel alloy for shape memory applications has been produced by melt spinning under an argon atmosphere. The effect of rapid solidification processing and subsequent annealing treatment on the structure and transformation characteristics of the melt spun ribbons have been investigated. Most of the fine grained ribbons have been ground to powder in a vibratory mill and consolidated by a powder metallurgy method to produce bulk shape specimens. In addition, titanium-nickel powder compacts containing varying amount of nickel from 49 to 55 atomic per cent have been examined. The thermoelastic martensitic reaction characteristics are discussed in relation to the refined grain structure and the state of order of the spun products. The quench hardening capability of nickel-rich alloys (≥ 51 at %Ni) is described and related to the supersaturated structure produced by quenching.