Effect of micro-additions of Mo,P, Si and Ti on the thermal stability of Ni24Zr76 metallic glass

The effects of micro-additions (about 1 at.%) of Mo, Ti, Si and P on the thermal stability and crystallization behavior of Ni₂₄Zr₇₆ metallic glass have been investigated. Dynamic devitrification process of these melt-spun amorphous alloys have been followed by means of differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. The last two techniques have been employed for studying the microstructural evolution and for identification of the phases formed after crystallization of these alloys. Addition of the above elements results in an increase in thermal stability as indicated by the increase in crystallization temperature, and also by the increase in difference between the crystallization temperature and the glass transition temperature. The enhancement of the thermal stability has been analyzed in terms of the atomic size difference effect, cohesive energy effect, elastic property/physical parameter and thermodynamics of alloying effect. It is found that the enhancement of thermal stability can be well correlated with the thermodynamics of alloying behavior of the third elements in Ni₂₄Zr₇₆ alloy.     

Structural transformations in Co-P alloys produced by pulse-current electrodeposition

X-ray diffraction and differential thermal analysis are used to study the effect of pulse-current regimes on the structure and thermal stability of electrodeposited Co-P alloys. The temperature of the onset of crystallization of these alloys upon heating is found to increase as the phosphorus content increases. Phases, such as β-Co and Co₂P, are determined to be the end products of crystallization of the Co-P amorphous (in terms of X-ray diffraction) and microcrystalline alloys. Relaxation processes in these amorphous and microcrystalline structures are shown to be mainly affected by nonequilibrium crystallization conditions upon pulsecurrent electrolysis that are caused by high-rate changes in the cathode overvoltage.     

The Effect of Dy Substitution on the Glass-Forming Ability and Crystallization Behavior of Mg65Cu10Ni10Y10Zn5 Metallic Glass

The glass-forming ability, thermal stability, and crystallization behavior of Mg₆₅Cu₁₀Ni₁₀Y_10-xZn₅Dy_x (x?=?0, 2, and 4) alloys were investigated. The partial substitution of Dy for Y increases the activation energy of the first crystallization, but it decreases the glass-forming ability and thermal stability. Analyses on crystallization kinetics suggest that the substitution of Dy for Y decreases the nucleation rate. In addition, the examination of the crystallization phase after the isothermal annealing indicated that Dy addition suppresses the formations of Mg₂Cu and Mg and that it promotes the formation of MgZn crystalline phase. The decreasing glass-forming ability with the Dy substitution can be attributed to the narrower supercooled liquid region, higher Gibbs free energy, and the change of crystallization products.     

Structure of polycrystalline Al-Ni-Fe-La alloys after quenching and plastic deformation by shear under pressure

The structure and phase composition of aluminum-based polycrystalline alloys (85 at % Al) containing transition (Fe, Ni) and rare-earth (La) metals are studied by metallography, differential scanning calorimetry, X-ray diffraction, and electron-microscopic analysis after melt quenching and subsequent severe plastic deformation (SPD) by shear under pressure. The melt-quenched alloys are shown to have a four-phase structure consisting of an aluminum-based solid solution, intermetallics Al₃Ni and Al₁₁La₃, and iron intermetallics. SPD results in the fragmentation and spheroidization of all phase constituents of the alloys and in the dissolution of the iron intermetallics. A multiphase nanostructured state forms in the alloys. The nanocrystallite sizes after SPD at various deformation parameters are determined. The microhardness is maximal after deformation corresponding to six anvil revolutions at a pressure of 8 or 10 GPa. The structural parameters and the microhardnesses are compared after SPD by shear under pressure of the alloys having the same compositions and different structural states (namely, amorphous and polycrystalline) before deformation. An amorphous-nanocrystalline structure with the minimum nanograin sizes and the maximum microhardnesses forms in the alloys having an initial amorphous structure and subjected to SPD.     

Preparation,mechanical strengths,and thermal

Ni-based amorphous wires with good bending ductility have been prepared for Ni₇₅Si₈B₁₇ and Ni₇₈P₁₂B₁₀ alloys containing 1 to 2 at. pct Al or Zr by melt spinning in rotating water. The enhancement of the wire-formation tendency by the addition of Al has been clarified to be due to the increase in the stability of the melt jet through the formation of a thin A1₂O₃ film on the outer surface. The maximum wire diameter is about 190 to 200 μm for the Ni-Si (or P)-B-Al alloys and increases to about 250 μm for the Ni-Si-B-Al-Cr alloys containing 4 to 6 at. pct Cr. The tensile fracture strength and fracture elongation are 2730 MPa and 2.9 pct for (Ni_0.75Si_0.08B_{0.17 99}Al₁) wire and 2170 MPa and 2.4 pct for (Ni_0.78P_0.12B_0.1)₉₉Al₁ wire. These wires exhibit a fatigue limit under dynamic bending strain in air with a relative humidity of 65 pct; this limit is 0.50 pct for a Ni-Si-B-Al wire, which is higher by 0.15 pct than that of a Fe₇₅Si₁₀B₁₅ amorphous wire. Furthermore, the Ni-base wires do not fracture during a 180-deg bending even for a sample annealed at temperatures just below the crystallization temperature, in sharp contrast to high embrittlement tendency for Fe-base amorphous alloys. Thus, the Ni-based amorphous wires have been shown to be an attractive material similar to Fe- and Co-based amorphous wires because of its high static and dynamic strength, high ductility, high stability to thermal embrittlement, and good corrosion resistance.     

The effects of Cr additions to binary TiAl-base alloys

The effects of Cr additions to y-base alloys have been investigated, using bulk materials consolidated from rapid solidification-processed ribbons. The composition ranges studied were 0 to 4 at. pet Cr and 44 to 54 at. pet Al. It was found that Cr additions do not affect the deformation behavior of single-phase γ alloys. However, they significantly enhance the plasticity of Al-lean duplex alloys which contain grains of single-phase γ and grains of lamellar γ/α₂. Other Cr effects on microstructure, phase stability, site occupancy, and deformation sub-structures were characterized and correlated to the observed mechanical behavior. It was concluded that the ductilization effect of Cr in duplex alloys is partially due to the tendency of Cr to occupy Al lattice sites. Ductilization is also partially due to the ability of Cr to modify the Al partitioning and, therefore, the thermal stability of transformed α₂ laths.     

Oxidation and Crystallization Behavior of Quinary Zr-Based Bulk Metallic Glasses

Non-isothermal and isothermal oxidation behavior of four Zr-based bulk metallic glasses (Zr₅₈Cu₂₂Co₄Ag₄Al₁₂, Zr₅₈Cu₂₂Co₂Ag₆Al₁₂, Zr₅₈Cu₂₂Fe₄Ag₄Al₁₂, and Zr₅₈Cu₂₂Fe₂Ag₆Al₁₂ (compositions are in at.%)) has been studied in oxygen environment. Non-isothermal oxidation has been performed at different heating rates up to 1,173 K to understand the effect of progressive crystallization on the oxidation behavior. In addition, crystallization behavior of the glassy alloys has been studied, and activation energies have been calculated in an inert and oxygen environment. Partial replacement of iron with silver and cobalt has a distinct effect on the oxidation and crystallization behavior of the alloys. Oxidation of the glassy alloys starts with the dissolution of oxygen in the amorphous matrix followed by rapid oxidation after crystallization.     

Ball milling-induced nanocrystal formation in aluminum-based metallic glasses

Various experimental techniques have been used to investigate the effect of mechanical milling on the structural stability of rapidly solidified aluminum-based metallic glasses. Using transmission electron microscopy (TEM) and X-ray diffraction methods, the formation of nanocrystalline Al particles in some ball-milled Al-rich metallic glasses (such as Al₉₀Fe₅Gd₅ and Al₉₀Fe₅Ce₅) is clearly observed. For other compositions with lower Al concentration such as Al₈₅Ni₅Y₁₀, no such phase transformation can be detected by TEM or X-ray. However, differential scanning calorimetry (DSC) measurements show that the crystallization peaks of the ball-milled Al₈₅Ni₅Y₁₀ metallic glass shifted to higher temperatures, while the crystallization enthalpy associated with the first exothermic peak decreased to a lower value, revealing that certain structural changes have taken place as a result of mechanical deformation. The compositional dependence of the structural stability of Al-based metallic glasses against mechanical deformation suggests that the nanocrystal formation induced by a deformation process is different from that caused by a thermal process. The large plastic strain induced atomic displacements and the enhancement of atomic mobility during the deformation process, are the possible mechanisms of mechanical deformation-induced crystallization. Our results demonstrate a new way of obtaining nanophase glassy composite alloy powders which are suitable for engineering applications upon further consolidation processing.     

Effect of alloying addition on structure and thermal stability of Ti40Al60 prepared by mechanical alloying

Ternary (Ti₄₀Al₆₀)₁₀₀−XM_X (X = 5–15 at., M = Mo, Nb) alloys have been prepared by Mechanical Alloying, and the process was monitored by X-ray diffraction technique. The effects of a third additional element have been examined concerning the alloying process, structure and phase thermal stability. As already observed in Ti₄₀Al₆₀ matrix prepared with the same conditions, an amorphous alloy was obtained at the end of the process. A different solubility of Mo (very limited) or Nb (total dissolved) into the matrix was detected. Upon thermal treatment the third element addition caused, in both cases, an increased crystallization temperature with respect to the matrix. The more detailed investigation on niobium addition (5–10 at.%) evidenced the following path for powder crystallization: amorphous-disordered Al-ordered L1₀ phase. The evolution of the long-range order parameter revealed that the disorder → order transition is favoured due to the presence of Nb, but independent of its concentration.     

Phase Equilibria in the Be-Al-Fe System Using High-Energy Ion Beams: II

Ion beam methods have been used in a study of the beryllium rich region of the beryl-lium-aluminum-iron phase diagram. Tailored alloys formed by ion-implanting aluminum and iron into beryllium were annealed, and their evolution with time was followed by ion backscattering analysis. In this way, the maximum and minimum aluminum to iron atomic ratios in the ternary phase of nominal composition AlFeBe₄ were determined in the temperature range 773 to 1073 K; these ratios are 1.4 ±0.1 and 0.93 ±0.15, respec-tively, with any temperature dependence being less than the experimental uncertainty. In addition, the solubilities of aluminum and iron in beryllium were measured for the three-phase condition where α-Be, AlFeBe₄, and FeBe₁₁ coexist. When combined with previous ion beam results for the boundaries about the α-Be phase on the phase diagram, these data provide a detailed picture of the beryllium-rich region of the beryllium-aluminum-iron phase diagram.     

Influence of iron and silicon on the phase composition and structure of heat-resistant casting nikalines strengthened by nanoparticles

The phase composition of the Al-Ni-Mn-Fe-Si-Zr system is analyzed as applied to heat-resistant nikalines (aluminum alloys of a new generation based on Ni-containing eutectic), which are strengthened by the Al₃Zr (L1₂) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat-resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).     

Laves phase precipitation in Fe-Ta alloys

Development of an iron-base alloy hardened by particles of an intermetallic compound rather than a carbide is a desirable goal because of the greater thermal stability of such a dispersion. As a first step in the development of iron-base alloys hardened with the Laves phase, structural studies of binary Fe-Ta alloys have been undertaken. The structures of two phase Fe-Ta alloys have been studied by means of optical and transmission electron microscopy, X-ray diffraction, electron beam microprobe analysis, and scanning electron microscopy. The hardness change as a function of time at 600°, 700°, and 800°C has been determined for binary alloys with 1 at. pct Ta and 2 at. pct Ta in iron. Also, the uniaxial tensile strengths of solution treated, quenched, and aged samples have been determined. These studies suggest that the compound, Fe₂Ta, is isomorphous with the structure type, MgZn₂, (C14) and has a range of compositional homogeneity. The latter results correspond with the predictions of the Engel-Brewer correlation. Also, it has been found that precipitation occurs at grain boundaries, dislocations, and randomly throughout the matrix. Particles which form at dislocations have a (100)α habit plane; whereas a (110)α habit plane has been reported by others^1,3 for the hexagonal Laves phase in α iron. Hypereutectoid composition alloys quenched from the ö phase field have a completely retained § structure. Isothermal decomposition at 600°, 700°, and 800°C of alloys with the retained § structure results in a sizable hardness increase in 2 at. pct Ta alloys but only a modest increase in 1 at. pct Ta alloys. Brittle fracture of aged tensile specimens tested at room temperature reveals that the ductile-brittle transition temperature in tension is above room temperature.     

Crystallization kinetics of amorphous magnesium-rich magnesium-copper and magnesium-nickel alloys

Amorphous magnesium-rich alloys Mg _y X_1-y (X=Ni or Cu and 0.82<y<0.89) have been produced by melt spinning. The crystallization kinetics of these alloys have been determined by in situ X-ray diffraction (XRD) and isothermal and isochronal differential scanning calorimetry (DSC) combined with ex situ XRD. Microstructure analysis has been performed by means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Crystallization of the Mg-Cu alloys at high temperature takes place in two steps: primary crystallization of Mg, followed by simultaneous crystallization of the remaining amorphous phase to Mg and Mg₂Cu. Crystallization of the Mg-Cu alloys at low temperatures takes place in one step: eutectic crystallization of Mg and Mg₂Cu. Crystallization of the Mg-Ni alloys for a Mg content, y>0.85, takes place in two steps: primary crystallization of Mg and of a metastable phase (Mg_∼5.5Ni, with Mg content y=0.85), followed by the decomposition of Mg_∼5.5Ni. Crystallization of the Mg-Ni alloys for a Mg content y<0.85 predominantly takes place in one step: eutectic crystallization of Mg and Mg₂Ni. Within the experimental window applied (i.e., 356 K<T<520 K and 0.82<y<0.89), composition dependence of the crystallization sequence in the Mg-Cu alloys and temperature dependence of the crystallization sequence in the Mg-Ni alloys has not been observed.     

Effect of the partial substitution of samarium for lanthanum on the structure and electrochemical properties of La_(15)Fe_(77)B_8-type hydrogen storage alloys

La15Fe77B8 hydrogen storage alloys were prepared using a vacuum induction-quenching furnace. The results of X-ray diffraction(XRD) and scanning electron microscopy(SEM) suggested that La15–xSmxFe2Ni76Mn5B2(x=0, 2, 4, 6) alloys had multiphase structure including the main LaNi5 phase, La3Ni13B2 phase and(Fe, Ni) phase. With the increasing substitution of Sm for La, the main phase structure of alloys did not change, while the unit cell volumes decreased, the cycle stability was improved and the maximum discharge capacity decreased, but the low temperature maximum discharge capacity of the same substitution alloy was gradually approaching the maximum discharge capacity at room temperature, which showed that La15Fe77B8 hydrogen storage alloys of the partial substitution of Sm for La had better low-temperature dischargeability(LTD). For the same substitution alloys, self-discharge characteristics and cycle stability at low temperature were better than that at room temperature. Furthermore, the high-rate dischargeability(HRD) and the exchange current density I0 first increased and then decreased with the increasing of Sm content, whereas the hydrogen diffusion coefficient D in alloy bulk decreased gradually, which indicated that appropriate substitution of Sm for La improved the electrochemical kinetics properties of the alloys. The HRD was mainly dominated by the charge-transfer rate on the alloy surface.     

Quantitative analysis of the primary crystallization of iron-containing phases as applied to aluminum alloys of various doping systems

Aluminum-based multicomponent systems are analyzed using the Thermo-Calc program in order to determine the concentration boundaries in which the first primary crystals of Fe-containing phases appear. Projections of the liquidus surfaces are calculated as applied relative to the industrial cast alloys of three main groups, namely, Al-Si (silumins), Al-Cu (the AM5 type), and Al-Mg (magnaliums). It is shown that the primary crystallization of the following Fe-containing phases is most probable: in silumins these are the Al₅FeSi and Al₁₅(Fe, Mn)₃Si₂ phases and in magnaliums and the AM5-type alloys these are Al₃Fe and Al₆(Fe, Mn) phases. Based on the calculation of parameters of the primary crystallization of the Fe-containing phases, the possibility of evaluating the efficiency of iron removal from aluminum alloys is shown.     

Analysis of softening alloys of the Al-Ni system containing particles of variable dispersity

Regularities of the deformation strengthening and softening of aluminum alloys containing second-phase Al₃Ni particles 0.3 to 2.2 μm in size with a volume fraction from 0.03 to 0.1 are investigated during cold deformation and subsequent annealing at 0.6t _m. It is shown that the largest hardness increment is observed for alloys with a maximal fraction of fine particles (d = 0.3 μm) after rolling deformation larger than 0.4. Fine particles prevent the development of crystallization upon true deformation up to 2.3, thereby effectively inhibiting softening. An increase in the particle size to 1.2–2.2 μm stimulates nucleation during recrystallization, substantially accelerating this process. For example, in order to ensure recrystallization uniformly over the entire sheet volume at d = 2.2 μm, cold deformation with ? = 0.4 is sufficient.     

Structure and stability of the precipitates in melt spun ternary Al-transition-metal alloys

The decomposition of supersaturated solid solution of ternary, melt spun Al-transition-metal alloys has been examined using analytical transmission electron microscopy. It has been found that the presence of small amounts of iron in AlV, AlMo and AlCr alloys can give rise to a fine dispersion of P-phase precipitate in the grain centres. It has been shown that the P-phase is quasicrystalline phase and has an orientation relationship with Al matrix as: i2|〈001〉_Al, 〈τ²τ1〉_Al, i3|〈111〉_Al, 〈τ²10〉_Al; i5|〈τ10〉_Al, τ = (1 + √5)/2. The stability of quasicrystals is significantly improved by the presence of iron in A1-transition-metal alloys. The effect of iron on stabilising the quasicrystal precipitates is believed to be due to the fact that iron replaces the oversized transition metal (TM) atoms V, Cr and Mo in the smaller TM sites, resulting in a reduction of structural stress of quasicrystalline phase. The significance of these observations on the structure and stability of quasicrystal precipitates is discussed in terms of the development of high temperature dispersion strengthening Al-based alloys with transition metals.     

双辊铸轧热变形及热应力的数值模拟

结晶辊内部结构非常复杂,受热发生变形后,辊表面形状变得不规则,因此研究结晶辊温度场、热应力及热变形,掌握其分布规律,对于控制结晶辊的变形,得到均匀的铸带具有重要意义.以结晶辊为主要研究对象,采用热结构直接耦合方法计算结晶辊的温度场、热应力和热变形,为结晶辊的设计提供参考.结果表明,选用Be-Co-Cu作为结晶辊材质,辊转动30 s后,辊外表面温度和最大等效应力保持稳定,最高和最低温度分别为198和449℃,最大等效应力为1041 MPa;转动300 s后,辊内部温度及变形达到稳定状态,辊外表面径向位移都在0.4～0.5mm之间.通过对比Be-Co-Cu材质和钢材质的温度和最大等效应力,得出Be-Co-Cu材质更适合于制造双辊的结论.     

Thermodynamics of the massive,bainitic and martensitic transformations in FeC,FeNi,FeCr and FeCu alloys

The γ → α transformation in pure iron and iron alloys with dilute alloying elements is a five-staged process, each stage has its own transformation-start temperature and transformation product: the first and second stages are a massive-type and a bainitic-type transformation respectively, while the subsequent stages (3, 4 and 5) are martensitic transformations. Thermodynamic calculation reveals that the driving force varies linearly with the transformation-start temperature for each stage of the transformation in FeC, FeNi, FeCr and FeCu alloys. Based on the linear relations, the calculated M_a, B_s and M_s are in good agreement with experimental points.     

Development and characterization of high strength impact resistant Fe-Mn-(Al-, Si) TRIP/TWIP steels

Iron manganese steels with Mn mass contents of 15 to 30 % exhibit microstructural related superior ductility and extraordinary strengthening behaviour during plastic deformation, which strongly depends on the Mn content. This influences the austenite stability and stacking fault energy γ_fcc and shows a great impact on the microstructure to be developed under certain stress state or during severe plastic deformation. At medium Mn mass contents (15 to 20 %) the martensitic γ-ε-ά phase transformation plays an important role in the deformation mechanisms of the TRIP effect in addition to dislocation glide. With Increasing Mn mass content large elongation is favoured by intensive twinning formation. The mechanical properties of plain iron manganese alloys are strongly influenced by the alloying elements, Al and Si. Alloying with Al Increases the stacking fault energy and therefore strongly suppresses the martensitic γ-ε transformation, while Si sustains the γ-ε transformation by decreasing the stacking fault energy γ_fcc. The γ-ε phase transformation takes place in Fe-Mn-X alloys with γ_fcc ≤ 20 mJm⁻². The developed light weight high manganese TRIP and TWIP (twinning induced plasticity) steels exhibit high ultimate tensile strength (600 to 1100 MPa) and extremely large elongation of 60 to 95 % even at high strain rates of έ = 10³ s⁻¹. Particularly due to the advanced specific energy absorption of TRIP and TWIP steels compared to conventional deep drawing steels high dynamic tensile and compression tests were carried out in order to investigate the change in the microstructure under near crash conditions. Tensile and compression tests of iron manganese alloys with varying Mn content were performed at different temperatures and strain rates. The resulting formation of γ twins, ά- and ε martensite by plastic deformation was analysed by optical microscopy and X-ray diffraction. The deep drawing and stretch forming behaviour at varying deformation rates were determined by performing cupping tests and digitalised stress-strain-analysis.