Microstructure and Properties of Fe–Cr–B–Al Alloy After Heat Treatment

By means of optical microscope, scanning electron microscope, X-ray diffraction, energy dispersive spectrometer, Rockwell and Vickers hardness tester, and wear tester, the microstructure and properties of Fe–10Cr–1B–4Al alloy quenched in different temperature has been studied. The results show that the microstructure of as-cast Fe–10Cr–1B–4Al are composed of pearlite, ferrite and the eutectic borocarbide which shows a network distribution along grain boundaries. The eutectic borocarbides are composed of M₇(C, B)₃, M₂(B, C) and M₂₃(C, B)₆. As the quenching temperature increases, the network structure of eutectic borocarbide breaks, but the type of eutectic borocarbide has no obvious change, and the matrix structure changes gradually from ferrite to pearlite. As the quenching temperature increases, the macro-hardness and the matrix micro-hardness of Fe–10Cr–1B–4Al alloy increases gradually. The macro-hardness and matrix micro-hardness of alloy reach the highest value of 45.7 HRC and 388.1 HV, respectively when the quenching temperature is 1150 °C. The hardness of alloy decreases slightly when the quenching temperature is too high. While quenching at 1150 °C, the alloy has the highest wear resistance and good comprehensive properties.     

Metastable phases produced by laser melt quenching

A Nd: glass laser has been used to produce and retain metastable phases which are similar to phases obtained by rapid quenching (“splat cooling”) techniques. A single laser pulse of 10 msec duration was focused onto the surface of an alloy specimen to provide a beam intensity of approximately 3.7 × 10⁵ watts per sq cm. A small volume of metal in the relatively large specimen immediately underwent melting. Upon cessation of the laser pulse, the molten metal solidified very quickly. Extremely rapid cooling was achieved due to the presence of nearly ideal conditions for conduction cooling. Laser melting of various alloys of the eutectic Ag-Cu system resulted in a complete series of solid solutions, as verified by X-ray analysis. In addition, the laser melt quenching technique provided a threefold increase in microhardness of the resolidified metal. Formerly Western Electric Engineering Research Center, Princeton, N. J. 08540     

Structure and properties of a splat cooled 2024 aluminum alloy

Pound lots of splat cooled 2024 aluminum flake materials were produced by rapidly quenching the atomized melt against a rotating copper disc. Three flake sizes were selected, cold compacted into aluminum cans, and extruded at 300°C at a reduction ratio of 20 to 1. The extruded rods were reduced 50 pct by cold swaging, solution treated at 495°C, water quenched, and naturally aged. The splat cooled 2024 alloy had constituent particles of 1 fim and finer (compared to 5 to 20 μm for the commercial alloy); further, one of the complex constituent phases (AlCuFeMn) was essentially eliminated by the rapid quench. Compared to commercial 2024-T4, the splat cooled 2024 alloys showed 14 to 17 pct increase in yield and tensile strength (no loss of ductility) a seven-fold increase in fatigue life at 30,000 psi, and a large improvement in the 300°F (150°C) stress rupture life in tests beyond 100 h. The fracture characteristics of the splat alloys, while exhibiting excellent to superior ductility, appear inhomogeneous due to the presence of finely dispersed oxide films scattered in the structure. Formerly Research Assistant, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology     

An integrated model for dendritic and planar interface growth and morphological transition in rapid solidification

Rapid solidification can be achieved by quenching a thin layer of molten metal on a cold substrate, such as in melt spinning and thermal spray deposition. An integrated model is developed to predict microstructure formation in rapidly solidified materials through melt substrate quenching. The model solves heat and mass diffusion equations together with a moving interface that may either be a real solid/liquid interface or an artificial dendrite tip/melt interface. For the latter case, a dendrite growth theory is introduced at the interface. The model can also predict the transition of solidification morphology, e.g., from dendritic to planar growth. Microstructure development of Al-Cu alloy splats quenched on a copper substrate is investigated using the model. Oscillatory planar solidification is predicted under a critical range of interfacial heat-transfer coefficient between the splat and the substrate. Such oscillatory planar solidification leads to a banded solute structure, which agrees with the linear stability analysis. Finally, a microstructure selection map is proposed for the melt quenching process based on the melt undercooling and thermal contact conditions between the splat and the substrate.     

Coarsening kinetics during solidification of Ni-Al-Ta dendritic monocrystals

Several dendritic monocrystals of nickel-rich Ni-Al-Ta alloys were directionally solidified at about 0.25 m/h⁻¹ under a gradient of 8 × 10⁻³ K/m⁻¹. The solid-liquid interface was fossilized at a given moment by rapidly quenching the remaining liquid. In some specimens crystal pulling was interrupted for various lengths of time prior to quenching. The quenched solid-liquid interfaces were used for a convenient and rapid evaluation of: 1) isothermal coarsening kinetics of the dendritic solid at a temperature between the liquidus and the eutectic temperatures and; 2) dendrite coarsening kinetics during solidification. It was found that extension to the ternary Ni-Al-Ta system of a model previously developed for binary systems predicted isothermal dendrite coarsening kinetics in close agreement with experimental results. Agreement for coarsening kinetics during solidification was less good. An increase in tantalum or aluminum contents slowed down coarsening, yielding finer microstructures. At equal atomic percental increase in concentration, the effect of tantalum was more significant than that of aluminum.     

Containerless processing and rapid solidification of Nb-Si alloys of hypereutectic composition

Niobium-silicon alloys from 21 to 27 at. pct Si were rapidly solidified employing a combination of electromagnetic levitation and splat-quenching techniques. Levitated liquid drops were over-heated or undercooled to different temperatures in the electromagnetic lévitation field and sub-sequently released into a splat-quenching apparatus. Some undercooled drops were allowed to solidify in the coil. Analytical scanning (SEM) and transmission electron microscopy (TEM) as well as X-ray diffraction were used to characterize the microstructures of the processed samples. In the range of compositions studied, the splat-quenched drops always formed the tetragonal Nb₃Si phase directly from the liquid. On the other hand, drops solidified in the coil were characterized by the presence of the primary intermetallic Nb₅Si₃ and the absence of both peritectic Nb₃Si and the equilibrium eutectic. In these cases, a metastable α-Nb + Β-Nb₅Si₃ eutectic formed. The cubic A15 Nb₃Si structure was not observed in any of these experiments. The results are discussed in terms of possible metastable configurations of the Nb-Si phase diagram as well as concepts of nucleation and growth kinetics applied to the Nb₃Si and Nb₅Si₃ intermetallics. Formerly Graduate Student, Vanderbilt University.     

Metastable phases in the Tl-Sn alloy system

The structures of metastable Tl-Sn alloys prepared by rapid quenching (splat cooling) to —190°C have been investigated. Over a large part of the total composition range single phase alloys were obtained. Four new metastable phases with relatively simple, elementlike structures were found: α₁ (tetragonal), ω (hexagonal), γ (hexagonal), and γ₁ (not determined in detail); α₁ represents the rarely found transition between the A1 and A2 structure types. Crystalchemically, the new phases are in agreement with previously established general rules for the occurrence of stable and metastable B-metal phases.     

Electron diffraction study of a noncrystalline Zr−Ni phase

Metastable noncrystalline phases were retained by rapid quenching Zr?Ni alloys from the liquid state over the composition range 25 to 70 at. pct Ni. The X-ray and electron diffraction patterns of the metastable phases showed broad diffraction maxima indicating absence of long range crystalline order in them. The pair function of the metastable noncrystalline phase in a splat cooled Zr_0.7Ni_0.3 alloy was determined from the electron diffraction data. The various interatomic distances corresponding to the positions of the peaks in the pair function curve were determined. The nearest-neighbors coordination number was computed from the area under the first peak. The radius of the first near neighbor shell is 2.95 Å and the ratio of the second to the first interatomic distance is equal to 1.41 which is significantly lower than that observed in most metallic liquids. The local atomic arrangement in the non-crystalline Zr_0.7Ni_0.3 alloy was shown to be based on simple fcc coordination.     

快淬对La0.67Mg0.33(NiCo)3贮氢合金电化学性能的影响

测试了AB3型贮氢合金La0.67Mg0.33(NiCo)3铸态与快淬态的电化学性能,用XRD和SEM测试了合金的微观结构,研究了快淬对AB3型贮氢合金电化学性能的影响.结果表明,快淬使合金的放电容量降低,对合金的活化性能没有明显影响;快淬降低了合金的容量衰减率,提高了合金的循环寿命,其主要原因是快淬使合金的晶粒显著细化.铸态和快淬态合金均具有多相结构,包括斜六面体的(La,Mg)Ni3相,六方的LaNi5相及少量的LaNi2相.快淬使合金中的LaNi2相含量增加,这是快淬使合金放电容量下降的一个主要原因.     

Strong and Ductile Martensitic Steels for Automotive Applications

The limits of strength and ductility of a medium‐carbon silicon chromium spring steel are investigated for the case of conventional heat treatment including austenitization, quenching and tempering. The effect of phosphorus and austenite deformation prior to quenching was studied by measuring mechanical properties after quenching and tempering and by microstructural investigation. Strong influence of phosphorus on the ductility is observed for the quenched and tempered martensite without prior austenite deformation. The minimum in ductility found after tempering at 350°C is explained by the formation of cementite and grain boundary segregation of phosphorus. Two thermomechanical treatments were tested involving different austenite conditions produced by variation of the deformation temperature. The deformed conditions, recrystallized or work‐hardened, exhibit higher ductility at all tempering temperatures tested. A combined thermomechanical treatment is proposed that provides the highest ductility after tempering at 300°C independent of the phosphorus content. All thermomechanical treatments described in this study refine or eliminate carbide films at prior austenite grain boundaries. It was found possible to increase the tensile strength and the fatigue limit by deformation of austenite prior to quenching while maintaining or increasing the ductility level.     

Formation of Structure and Magnetic Properties of NdFeB Powders Quenched by Centrifugal Sputtering

This paper describes the structure and magnetic properties of nanocrystalline NdFeB hard magnetic materials and their evolution during quenching of melted alloys by centrifugal sputtering followed by finishing annealing. The investigation covers a range of NdFeB alloys of typical composition of commercial grades. Results of the study of critical parameters defining the formation of rapid quenched particles of optimal sizes are described. As shown, the maximum magnetic properties can be obtained at completed crystallization process, which is featured by the maximum quantity of basic hard magnetic phase Nd2Fe₁₄B and minimum quantity of soft magnetic alpha-iron.     

On the decomposition of β phase in some rapidly quenched titanium-eutectoid alloys

The decomposition of the β phase in rapidly quenched Ti-2.8 at. pct Co, Ti-5.4 at. pct Ni, Ti-4.5 at. pct, and 5.5 at. pct Cu alloys has been investigated by electron microscopy. During rapid quenching, two compctitive phase transformations, namely martensitic and eutectoid transformation, have occurred, and the region of eutectoid transformation is extended due to the high cooling rates involved. The β phase decomposed into nonlamellar eutectoid product (bainite) having a globular morphology in Ti-2.8 pct Co and Ti-4.5 pct Cu (hypoeutectoid) alloys. In the near-eutectoid Ti-5.5 pct Cu alloy, the decomposition occurred by a lamellar (pearlite) type, whereas in Ti-5.4 pct Ni (hypereutectoid), both morphologies were observed. The interfaces between the proeutectoid α and the intermetallic compound in the nonlamellar type as well as between the proeutectoid α and the pearlite were often found to be partially coherent. These findings are in agreement with the Lee and Aaronson model proposed recently for the evolution of bainite and pearlite structures during the solid-state transformations of some titanium-eutectoid alloys. The evolution of the Ti₂Cu phase during rapid quenching involved the formation of a metastable phase closely related to an “ω-type” phase before the equilibrium phase formed. Further, the lamellar intermetallic compound Ti₂Cu was found to evolve by a sympathetic nucleation process. Evidence is established for the sympathetic nucleation of the proeutectoid a crystals formed during rapid quenching.     

Microstructure and mechanical properties of unidirectionally solidified Al-Si-Ni ternary eutectic

Al-10.98 pct Si-4.9 pct Ni ternary eutectic alloy was unidirectionally solidified at growth rates from 1.39μm/sec to 6.95μm/sec. Binary Al-Ni and Al-Si eutectics prepared from the same purity metals were also solidified under similar conditions to characterize the growth conditions under the conditions of present study. NiAl₃ phase appeared as fibers in the binary Al-Ni eutectic and silicon appeared as irregular plates in the binary Al-Si eutectic. However, in the ternary Al-Si-Ni eutectic alloy both NiAl₃ and silicon phases appeared as irregular plates dispersed in α-Al phase, without any regular repctitive arrangement. The size and spacing of NiAl₃ and Si platelets in cone shaped colonies decreased with an increase in the growth rate of the ternary eutectic. Examination of specimen quenched during unidirectional solidification indicated that the ternary eutectic grows with a non-planar interface with both Si and NiAl₃ phases protruding into the liquid. It is concluded that it will be difficult to grow regular ternary eutectic structures even if only one phase has a high entropy of melting. The tensile strength and modulus of unidirectionally solidified Al-Si-Ni eutectic was lower than the chill cast alloys of the same composition, and decreased with a decrease in growth rate. Tensile modulus and strength of ternary Al-Si-Ni eutectic alloys was greater than binary Al-Si eutectic alloy under similar growth conditions, both in the chill cast and in unidirectionally solidified conditions.     

Microstructure and mechanical properties of unidirectionally solidified Al-Si-Ni ternary eutectic

Al-10.98 pct Si-4.9 pct Ni ternary eutectic alloy was unidirectionally solidified at growth rates from 1.39μm/sec to 6.95μm/sec. Binary Al-Ni and Al-Si eutectics prepared from the same purity metals were also solidified under similar conditions to characterize the growth conditions under the conditions of present study. NiAl₃ phase appeared as fibers in the binary Al-Ni eutectic and silicon appeared as irregular plates in the binary Al-Si eutectic. However, in the ternary Al-Si-Ni eutectic alloy both NiAl₃ and silicon phases appeared as irregular plates dispersed in α-Al phase, without any regular repctitive arrangement. The size and spacing of NiAl₃ and Si platelets in cone shaped colonies decreased with an increase in the growth rate of the ternary eutectic. Examination of specimen quenched during unidirectional solidification indicated that the ternary eutectic grows with a non-planar interface with both Si and NiAl₃ phases protruding into the liquid. It is concluded that it will be difficult to grow regular ternary eutectic structures even if only one phase has a high entropy of melting. The tensile strength and modulus of unidirectionally solidified Al-Si-Ni eutectic was lower than the chill cast alloys of the same composition, and decreased with a decrease in growth rate. Tensile modulus and strength of ternary Al-Si-Ni eutectic alloys was greater than binary Al-Si eutectic alloy under similar growth conditions, both in the chill cast and in unidirectionally solidified conditions.     

Influence of Phosphorus on the Nucleation of Eutectic Silicon in Al-Si Alloys

The role of phosphorus (P) in the heterogeneous nucleation of eutectic silicon (Si) and the evolution of eutectic grains in hypoeutectic aluminum-silicon alloys were investigated. Systematic additions of P in the range of 0.5 to 20 ppm to Al-7 wt pct Si alloys of different purities have shown that the morphology of the eutectic Si changes from a fine plate- to a coarse flake-like structure. The growth of eutectic grains was investigated by interrupting the eutectic reaction by quenching experiments. Moreover, the macroscopic growth mode of the eutectic grains was characterized by electron backscatter diffraction. An increase in P concentration from 2 to 3 ppm resulted in a transition of the macroscopic growth mode of the Al-Si eutectic in high purity alloys from growth with a planar front with a strong dependence of the thermal gradient, to nucleation in the vicinity of the primary Al dendrites and subsequent growth of distinct eutectic grains. It is suggested that AlP particles are the key impurities acting as potential nucleation sites for eutectic Si. This is further substantiated as with increasing P concentration nucleation and growth of the Al-Si occurred at higher temperatures close the equilibrium Al-Si eutectic solidification temperature at 850 K (577 °C). In addition, the recalescence undercooling ΔT _R,eu was reduced from 4.5 K (0.5 ppm P) to 1.5 K (20 ppm P) in high purity alloys. This was accompanied by a drastic increase of the nucleation rate of the eutectic grains.     

Study of a splat cooled Cu-Zr-noncrystalline phase

By rapid quenching from the melt, using the splat forming gun technique, a noncrystalline phase has been obtained in a Cu-Zr alloy containing 60 at. pct Cu. Upon heating, rapid crystallization of the samples takes place at 477°C with a heat release of about 700 cal per mol. The variation of the electrical resistivity of the samples with temperature confirms the transformation. Very high resolution electron microscopy studies of the structural changes of the samples, at 3 × 10⁶ magnification, upon heating are presented and show the gradual crystallization of the amorphous structure. A. REVCOLEVSCHI was Visiting Scientist at Massachusetts Institute of Technology on leave from CNRS-Paris, France     

快淬MmNi_(3.5)Co_(0.75)Mn_(0.55)Al_(0.2)合金的电化学性能

应用不同的快淬速度制取成分为ＭｍＮｉ３．５Ｃｏ０．７５Ｍｎ０．５５Ａｌ０．２的贮氢合金，并做了电化学充放电循环实验，比较了它们的电化学活化速度、放电容量、放电电压性能以及电化学循环稳定性。冷却速度越高，合金的电化学循环稳定性越好、放电电压平台越平坦，放电电压也稍高，但导致放电容量下降，初期活化困难。     

An investigation of the effects caused by electromagnetic vibrations in a hypereutectic Al-Si alloy melt

In order to investigate the mechanism by which electromagnetic vibrations affect the solidification structure of metallic alloys, an experimental apparatus which enables the simultaneous application of electric and magnetic fields under different cooling conditions (ranging from rapid to furnace cooling) is developed. The objective is followed by inducing vibrations in a hypereutectic Al-Si alloy melt containing suspended silicon particles and interrupting the process at different temperatures before and after the start of solidification by water quenching. Interrupting the process at temperatures higher than the liquidus has revealed the effects of vibrations independent of the influences of the nucleation and growth phenomena. Establishing the conditions for obtaining identical cooling rates in experiments with different experimental conditions has lead to the exclusion of effects resulting from the differences in cooling rates and recognition of the effects caused only by electromagnetic vibrations. It is found that the application of either of the two fields alone has no significant effect on the solidified structure, while profound effects are observed when the two fields are applied simultaneously. An increase in the number of suspended silicon particles and a reduction in their average size are the effects noticed before the start of solidification. In this research, it has for the first time been clearly verified, through microscopic observation of the quenched samples, that these effects are brought about by the cavitation phenomenon. After the start of solidification, particles are locally agglomerated and expelled toward the surrounding walls under a combined influence of electromagnetic vibrations and pinch force squeezing the liquid. The final structure obtained is composed of an almost completely eutectic matrix surrounded by agglomerates of silicon particles along the outer surface.     

Effect of the liquid phase on the formation of orthorhombic boride during the crystallization of Fe<Subscript>82</Subscript>B<Subscript>18</Subscript> amorphous ribbons

Amorphous Fe₈₂B₁₈ ribbons prepared by melt quenching from different temperatures have been studied during step-by-step heating. Depending on the quenching temperature, the crystallization of the ribbons was shown to occur via different mechanisms, namely, with and without the formation of the orthorhombic Fe₃B^orth boride. This is related to different structural states of the melt used for the preparation of the rapidly quenched ribbons. The appearance of the orthorhombic Fe₃B^orth boride is preceded by the crystallization of the amorphous component with the formation of the Fe₃B^tet boride having a distorted body-centered tetragonal lattice.     

淬火-配分马氏体钢的组织特征

淬火-配分(Quenching and Partitioning,简称QP)工艺是针对马氏体钢提出的热处理新工艺。利用QP工艺处理40Si2Ni2钢,并通过扫描电镜观察其微观组织特征。结果表明,与传统淬火+回火工艺得到的组织不同,QP组织为低碳(回火态)和高碳马氏体(淬火态)共存,其中高碳马氏体呈现为有规则几何形状、边界清晰、无析出物析出的块状组织,淬火温度(QT)对高碳马氏体(淬火态)量有影响。