温度诱导的液-液结构转变对Sn-10％Bi合金凝固的影响

以温度诱导的液-液结构转变为切入点,研究了Sn-10％Bi合金经不同过热处理后凝固行为和凝固组织的变化.首先利用自制的定向凝固装置进行了液-液结构转变对Sn-10％Bi合金的定向凝固影响的研究.然后测定经不同过热处理的合金熔体相应的凝固曲线,并观察凝固组织.结果表明,相对于在结构转变前保温处理的熔体,经历了结构转变的合金熔体,凝固时所需过冷度增大,并且凝固组织显著细化;揭示了温度诱导液-液结构转变对合金凝固行为及组织有着明显影响.     

2099 Aluminum-Lithium with Key-Locked Inserts for Aerospace Applications

The purpose of this study was to determine the acceptability of nonpenetrating, key-locked inserts in 2099 aluminum-lithium. The tests conducted to make this assessment were: (1) microscopic examination for thread damage and delaminations after key installation, (2) pull-out load at 21 °C (70 °F) and −179 °C (−290 °F), and (3) mechanical cycling tests at room temperature and −179 °C (−290 °F). The test results indicated that for the three sizes evaluated, key-locked inserts in 2099-T6 and 2099-T8 were acceptable and although delaminations did occur on some T6 temper specimens, it was only as a failure mode at ultimate load and such behavior was judged to be acceptable.     

熔体浇注温度和板倾斜度对倾斜板制备A356铝合金的凝固和显微组织的影响(英文)

采用倾斜板制备A356铝合金半固态浆料。通过倾斜板底部的逆流水冷却使A356合金熔体在流下倾斜板时发生局部凝固,从而导致在板壁上形成连续柱状枝晶。由于强制对流作用,这些树枝晶被折断成等轴和破碎的晶粒,然后被连续冲洗而在斜板出口形成半固态浆料。熔体浇注温度是影响凝固组织的重要条件,而倾斜度为优质半固态浆料提供必要的剪切作用。将得到的浆料在金属模具中凝固以制备理想显微组织的半固态铸造坯料。然后,通过热处理以提高半固态铸造坯料的表面质量。对半固态铸造和热处理后坯料的显微组织进行分析。研究熔体浇注温度(620,625,630和635°C)和板倾斜度(30°,45°,60°和75°)对斜板制备A356铝合金的凝固和显微组织的影响。结果表明:在625°C的熔体浇注温度和60°斜板倾角时,A356铝合金具有细小和球状的晶粒,是最佳的显微组织。     

Preparation of bulk β-FeSi2 by synthetical control of melt cyclical superheating,solidification and cooling process

A new method of melt cyclical superheating combined with the control of solidification and cooling process as well as appropriate heat treatment was proposed to prepare bulk β-FeSi₂. FeSi₂ precursor of φ18 × 17 mm in size was obtained under the conditions of melt superheating temperature 1550 °C, superheating time 10 min, recycling times 3, solidification rate 30 °C/s, cooling rate 12 °C/min from solidification temperature to 700 °C and cooling naturally from 700 °C to room temperature. The precursor had homogeneous and complete α + ε eutectic structure, with the rod-like ε phase of 1–2 μm in diameter. After the precursor with complete α + ε eutectic structure were annealed at 900 °C for 150 h, both the α and ε phases totally disappeared and were transformed into β-FeSi₂ except few residual Si-rich phase.     

Enhancing the thermoelectric performance of free solidified p-type Bi0.5Sb1.5Te3 alloy by manipulating its parent liquid state

In this work, an irreversible temperature induced liquid–liquid structural transition (TI-LLST) during the heating process was suggested by abnormal resistivity behaviors of Bi_0.5Sb_1.5Te₃ melt. Based on this information, by manipulating the parent liquid state in free solidification, series of explorations were carried out on the solidified structures and TE properties of Bi_0.5Sb_1.5Te₃ alloy. We found that, from the melt after TI-LLST, the solidified microstructures are evidently refined with more Te-rich eutectic strips precipitating on matrix boundaries. More significantly, hierarchical crystal defects are obviously increased, with tinier nanoprecipitates, more subgrains and boundaries, and much more densified lattice distortions. Consequently, the thermal conductivity, especially the lattice thermal conductivity, is decreased notably with the power factor increased moderately at high temperature. In addition, the ambipolar excitation temperature is shifted to higher value and the slope of thermal conductivity vs temperature is also declined. All these alterations contribute to a synergistic enhancement of the TE figure of merit (ZT) and the maximum figure shifts to higher temperature, with ZT_max = 0.78 at 442 K. The present work may provide a new hint for innovating preparation methods of bulk TE materials with simple free solidification.     

Liquation behavior in the weld HAZ of high Si nodular iron

In the present study, liquation behavior including the constitutional liquation phenomena in the weld heataffected zone (HAZ) of nodular cast iron with 4% Si was investigated. The thermal cycle of the weld HAZ was simulated using a Gleeble simulator at various peak temperatures and a fast heating rate of 1000 °C/sec was selected to observe the constitutional liquation phenomenon. Differential thermal analysis has shown that the eutectic constituents of γ + Laves and γ + Fe₃C begin to melt at 1120 °C and 1140 °C, respectively. Meanwhile, constitutional liquation by γ/graphite reaction occurred above 1140 °C, due to carbon enrichment around the graphite nodules.     

Lamellar boundary alignment of DS-processed TiAl−W alloys by a solidification procedure

In this study, a β solidification procedure was used to align the lamellae in a Ti-47Al-2W (at.%) alloy parallel to the growth direction. The Bridgman technique and the floating zone process were used for directional solidification. The mechanical properties of the directionally solidified alloy were evaluated in tension at room temperature and at 800°C. At a growth rate of 30 mm/h (with the floating zone approach), the lamellae were well aligned parallel to the growth direction. The aligned lamellae yielded excellent room temperature tensile ductility. The tensile yield strength at 800°C was similar to that at room temperature. The orientation of the γ lamellar laths in the directionally solidified ingots, which were manufactured by means of a floating zone process, was identified with the aid of electron backscattered diffraction analysis. On the basis of this analysis, the preferred growth direction of the bcc-β dendrites that formed at high temperatures close to the melting point was inferred to be [001]_β at a growth rate of 30 mm/h and [111]_β at a growth rate of 90 mm/h.     

Effects of ultrasonic irradiation and cooling rate on the solidification microstructure of Sn–3.0Ag–0.5Cu alloy

A comparative study on the microstructures of Sn–Ag–Cu alloy ingots grown by ultrasound-assisted solidification was carried out with a specific focus on the limits on the ultrasonic processing depth and time imposed by the cooling rate during the melt solidification. During air-cooling, increasing the ultrasonic power reduced the undercooling temperature and increased the solidification time, leading to β-Sn phase fragmentation from a dendritic shape into a circular equiaxed shape. The grain size was decreased from approximately 300 μm to 20 μm. When the cooling rate was increased from 4 °C/s in air to 20 °C/s in water, the macro-undercooling temperature was more greatly reduced by an increase in ultrasonic power, but the solidification time seemed to change only slightly because only a limited period for ultrasonic processing was permitted in the melt. Under both cooling rates, the microstructures were inhomogeneous along the processing depth. The functional depth and period for ultrasonic cavitation and acoustic steaming contributed to the differences in the solidification microstructures.     

Effect of heat-treatment on the nanostructural change of W-Cu powder prepared by mechanical alloying

W-30wt.%Cu powder prepared by mechanical alloying (MA) was annealed at various temperatures to investigate the structural change of MA W-Cu powder. From differential scanning calorimeter analysis and transmission electron microscope observation, it was revealed that the recovery of W in MA W-30wt.%Cu powder occurred at 700°C and the W grain started growing also at this temperature. The W grain had grown significantly after annealing at 900°C, and the Cu phase in the MA powder was found to act as liquid melt near 900°C. The microstructure of the sintered specimen was similar to that of the W-Cu alloy via liquid phase sintering. This microstructure, even at temperatures below Cu melting, was the new feature observed in the MA W-Cu powder. This suggests that such a microstructure is closely related to the inherent high diffusivity of the nanosized W crystallites as well as the liquid-like behavior of the Cu phase.     

The antimony-iron-niobium (Sb-Fe-Nb) system

Phase equilibria were established in the Nb-Fe-Sb ternary system for an isothermal section at 600 °C. Investigation of the phase relations was based on light optical microscopy, electron probe microanalysis, and X-ray diffraction experiments on arc-melted bulk alloys, which were annealed up to 1400 h. One ternary compound was observed: NbFeSb (MgAgAs type) without a significant homogeneity region at 600 °C. Except for NbFe_2−y , mutual solid solubilities at 600 °C were found to be very low, for example, <1 at.% Fe and <1 at.% Nb in the binary Nb antimonides and Fe antimonides, respectively. The binary Laves phase NbFe_2−y with the MgZn₂ type exhibits an extended homogeneity region dissolving at 600 °C up to 7 at.% Sb in the ternary without change of its structure type.     

Preparation of ultra-fine FeNiMnO<Subscript>4</Subscript> powders and ceramics by a solid-state coordination reaction

A mixed oxalate FeNiMn(C₂O₄)₃·nH₂O, a coordination compound, was synthesized by milling a mixture of ferrous iron chloride, nickel acetate, manganese acetate, and oxalic acid at room temperature. A spinel-structured FeNiMnO₄ powder with high sintering activity and chemical homogeneity was obtained by calcining the mixed oxalate in air at 800°C for 2 h. Dense FeNiMnO₄ ceramics with a relative density of ∼98% were achieved by sintering powder compacts at a lower temperature of 1100°C for 5 h. The specific resistivityρ _25°C and the thermal constant B_25/85°C were 4382 Ω·cm and 3373 K, respectively. The aging coefficient ΔR/R(%) of the ceramics after annealing at 150°C for 500 h was 0.6%.     

Effect of processing parameters on tensile properties of hot-drawn Al 2011-T8

Despite the wide-spread industrial use of drawn Al 2011 products, only an extremely limited number of studies are available on the effect of drawing parameters on the tensile behavior. In this study, the microstructural evolution and the tensile behavior of Al 2011-T8 specimens were studied with drawing ratios varying from 10 % to 40 % at different drawing temperatures of 350, 400 °C and 450 °C, respectively. Only a marginal change in the tensile properties of Al 2011-T8 was observed, despite the significant change in grain size ranging from 33 μm to 243 μm with different drawing parameters. Detailed fractographic examination suggested that low-melting, soft Pb-Bi globules greatly influenced the tensile behavior of Al 2011-T8, surpassing the effect of grain size. Based on the fractographic and micrographic observations, the tensile behavior of hotdrawn Al 2011-T8 specimens is discussed in conjunction with the effects of different drawing ratios and temperatures.     

Analysis of the solidification and deformation behaviors of twin roll cast Mg-6Al-X alloys

In this study, the solidification and deformation behaviors in twin roll cast (TRC) Mg-6Al-X alloys have been investigated. The TRC simulation results showed that the AX60 alloy tended to have lower segregation while the AZ60 had the highest segregation due to the different solidification behavior and thermal properties. Compared to the as-cast microstructure, the segregation area was well matched with the melt to roll nip distance predicted in simulation. Mg alloys with Ca or Sr elements showed weaker textures when compared to A6 alloys rolled at 350 °C. In addition, there was a significant change in (0002) pole figures from strong basal textures to random textures when the rolling temperature increased from 350 °C to 450 °C. This may be attributed to the non-basal slip system activity at high temperatures. The results of visco-plastic self-consistent simulation revealed that critical resolved shear stress of the tension twin increased with increasing rolling temperature. This led to tension twin suppression in compression, which were associated with enhancing the yield isotropy of Mg alloys. Furthermore, the relative activities of basal <a> slip in AX60 alloy were higher than the other Mg alloys. This means they were responsible for enhancing the formability and yield isotropy of Mg alloys.     

Coarsening of AA6013-T6 Precipitates During Sheet Warm Forming Applications

The use of warm forming for AA6xxx-T6 sheet is of interest to improve its formability; however, the effect warm forming may have on the coarsening of precipitates and the mechanical strength of these sheets has not been well studied. In this research, the coarsening behavior of AA6013-T6 precipitates has been explored, in the temperature range of 200-300 °C, and time of 30 s up to 50 h. Additionally, the effect of warm deformation on coarsening behavior was explored using: (1) simulated warm forming tests in a Gleeble thermo-mechanical simulator and (2) bi-axial warm deformation tests. Using a strong obstacle model to describe the yield strength (YS) evolution of the AA6013-T6 material, and a Lifshitz, Slyozov, and Wagner (LSW) particle coarsening law to describe the change in precipitate size with time, the coarsening kinetics were modeled for this alloy. The coarsening kinetics in the range of 220-300 °C followed a trend similar to that previously found for AA6111 for the 180-220 °C range. There was strong evidence that coarsening kinetics were not altered due to warm deformation above 220 °C. For warm forming between 200 and 220 °C, the YS of the AA6013-T6 material increased slightly, which could be attributed to strain hardening during warm deformation. Finally, a non-isothermal coarsening model was used to assess the potential reduction in the YS of AA6013-T6 for practical processing conditions related to auto-body manufacturing. The model calculations showed that 90% of the original AA6013-T6 YS could be maintained, for warm forming temperatures up to 280 °C, if the heating schedule used to get the part to the warm forming temperature was limited to 1 min.     

Al-18%Si合金凝固组织与熔体状态的相关性

本文以直流四电极法探索了Al-18%Si合金在升温过程中熔体的电阻率-温度（-ρT）关系,根据在800~950℃及950~1050℃区间-ρT的异常行为分析认为,后者对应液-液结构转变,其间原先的Si原子团簇被打破,原子重新排列形成新的细小团簇,液体结构更加均匀,而前者则为预转变。依据上述信息采取不同温度分别进行熔体过热处理来探索其凝固组织的差别,结果发现,相对于常规熔炼温度,在高于熔体结构转变温度（1150℃）进行熔体过热处理,初晶硅明显细化,而在预转变状态进行熔体过热处理并不能明显改变凝固行为和组织。     

Transition metal- chalcogen systems XI: the platinum- selenium phase diagram

The platinum-selenium phase diagram was investigated by differential thermal analysis, metallography, and X-ray powder diffraction methods. The two previously known intermediate phases, Pt₅Se₄ and PtSe₂, both melt congruently: Pt₅Se₄ at ∼1070 °C and PtSe₂ (under its own vapor pressure) at 1245 ± 10 °C. Pt₅Se₄ forms a eutectic with Pt at 1065 ± 2 °C and ∼42 at % Se and another one with PtSe₂ at 1067 ± 2 °C and somewhat below 45 at.% Se. On cooling, Pt and PtSe₂ form a metastable eutectic at 1037 ± 2 °C and ∼43 at % Se. Between PtSe₂ and Se, a degenerate eutectic was found at 221 °C, which also indicates negligible solubility of platinum in solid selenium.     

Study of the thermal stability of phases in the Mg-Al system

A part of the Al-Mg phase diagram was studied in the range of composition between 48 and 61 at.% Al by DSC and SEM/EDS methods. The temperature ranges of stability of the β, γ, and ɛ phases were considered. It was found that the congruent melting temperature of the β phase was 450±1 °C. The Al content in that phase was determined to be 61±1 at.% Al at 420 °C. The upper temperature limit of the stability of the ɛ phase was established to be 427±1 °C. The Al content changed from 54 at.% at 390 °C to 56 at.% at 420 °C. The lower temperature limit of the ɛ phase formation was not determined, as a result of a slow ɛ=β+γ reaction. The hypothetical λ or ζ phases were not found, but it was observed that decomposition of oxides might produce extra thermal effects.     

The effects of heat treatment condition and Si distribution on order-disorder transition in high Si steels

The decomposition and formation of ordered phases in steels with 5 to 6.5 %Si were investigated by a combined analysis of TEM and electrical resistivity measurements in order to determine the optimal heat treatment conditions for removal of ordered phases. TEM diffraction pattern study revealed that B2 ordered phase in 6.5 %Si steel was sufficiently dissolved by heat treatment at 850 °C for 1 h, and then rapidly re-formed during cooling. The critical cooling rate, above which the suppression of B2 phase formation was possible, increased rapidly with Si content higher than 5.6%. DO₃ phase appeared only in the case of as-cast samples containing Si content as high as 6.5%. The measurement of electrical resistivity change during the heat treatment showed that the atomic movement was substantially spurred above 800 °C, resulting in an active order-disorder transition. The removal of solidification segregation is necessary to reduce the amount of B2 ordered phase in the as-cast or hot-rolled state, to lower the heat treatment temperature for dissolution of B2 ordered phase, and to shorten the heat treatment time. This article is based on a presentation made in the 2003 Korea-Japan symposium on the “Current Issues on Phase Transformations”, held at Marriott Hotel, Busan, Korea, November 21, 2003, which was organized by the Phase Transformation Committee of the Korean Institute of Metals and Materials.     

The effect of thermal exposure on the mechanical properties of 2099-T6 die forgings, 2099-T83 extrusions, 7075-T7651 plate, 7085-T7452 die forgings, 7085-T7651 plate, and 2397-T87 plate aluminum alloys

Aluminum alloys 2099-T6 die forgings, 2099-T83 extrusions, 7075-T7651 plate, 7085-T7452 die forgings, 7085-T7651 plate, and 2397-T87 plate were thermally exposed at temperatures of 180 °C (350 °F), 230 °C (450 °F), and 290 °C (550 °F) for 0.1, 0.5, 2, 10, 100, and 1000 h. The purpose of this study was to determine the effect of thermal exposure on the mechanical properties and electrical conductivity of these alloys. The data shows that higher temperatures and longer exposure times generally resulted in decreased strength and hardness and increased percent elongation and electrical conductivity.     

Control of microwave dielectric properties in 0.42ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>−0.58TiO<Subscript>2</Subscript> ceramics by the quantitative analysis of phase transition

Phase constitutions of ZnNb₂O₆−TiO₂ mixture ceramics were significantly changed according to the sintering temperature. Phase transition procedures and their effect on the microwave dielectric properties of 0.42ZnNb₂O₆−0.58TiO₂ were investigated using X-ray powder diffraction and a network analyzer. The fractions of the phases composing the mixture were calculated by measuring integral intensities of each reflection. The structural transitions in 0.42ZnNb₂O₆−0.58TiO₂ were interpreted as the association of two distinct steps: the columbite and rutile to ixiolite transition present at lower temperatures (900–950°C) and the ixiolite to rutile transition at higher temperatures (1150–1300°C). These transitions caused considerable variation of microwave dielectric properties. Importantly, τ_f was modified to around 0 ppm/°C in two sintering conditions (at 925°C for 2 hr and at 1300°C for 2 hr), by the control of phase constitution.