Ni-12Fe-1Mn-0.3Al和Ni-2.7Mn-1.7Al-1.1Si-0.8Co合金的热电特性

研究了有特殊要求的火警信号系统用Ni-12Fe-1Mn-0.3Al和ni-2.7Mn-1.7Al-1.1Si-0.8Co合金的热电特性,分析了合金化元素对热电特性的影响.     

Cyclic hardening and softening of Al-2.9% Cu-2.2% Mg-0.6% Mn alloy

Electron microscopic research results are given for the Al-2.9% Cu-2.2% Mg-0.6% Mn alloy structure after different operating times corresponding to cyclic hardening or cyclic softening. It is shown that cyclic hardening results in precipitation of S particles and cyclic softening results in three processes: dissolution of S particles, precipitation of S particles instead of S ones and/or formation of regions free from precipitates. The main fatigue crack passes through cyclic-hardened material only and the hardening phase is merely the S particles. Relations between structure, cyclic hardening, cyclic softening and accumulated cyclic deformation are observed.     

High-temperature deformation characteristics of Ti-15at.% Al alloy

The deformation characteristics of Ti-15 at.% Al alloy have been investigated by compression tests in the temperature range 873 to 1273 K (0.44 to 0.64T _m) and by extensive transmission electron microscopy. Two types of deformation patterns were identified depending on the temperature: at lower temperatures below about 1073 K, the yield stress of the sample showed inverse temperature dependence, and serrations were found on the flow curves, whereas the normal dependences of the yield stress on temperature and strain rate were found at higher temperatures above about 1073 K. Corresponding dislocation substructures were composed of coarse bands of localized slip at 1023 K, and of rather uniformly distributed dislocations at 1123 K, and sub-boundaries as well as free dislocations at 1273 K. The main operating mechanisms in these temperature regimes were assumed to be the co-operative movement of numerous dislocations under the condition of the dynamic strain ageing, viscous glide of dislocations and dynamic recovery, respectively.     

Tensile deformation of a duplex Fe-20Mn-9Al-0.6C steel having the reduced specific weight

The room temperature deformation characteristics of a duplex Fe-20Mn-9Al-0.6C steel with the reduced specific weight of 6.84 g/cm³ in the fully solutionized state were described in conjunction with the deformation mechanisms of its constituent phases. The phase fraction was insensitive to annealing temperature in the range of 800-1100 °C. The ferrite grain size was also nearly unaltered but the austenite grain size slightly increased with increasing annealing temperature. This revealed that there is little window to control the microstructure of the steel by annealing. The steel exhibited a good combination of strength over 800 MPa and ductility over 45% in the present annealing conditions. Ferrite was harder than austenite in this steel. Strain hardening of both phases was monotonic during tensile deformation, but the strain hardening exponent of austenite was higher than that of ferrite, indicating the better strain hardenability of austenite. In addition, the strain hardening exponent of austenite increased but that of ferrite remained unchanged with increasing annealing temperature. The overall strain hardening of the steel followed that of austenite. Considering element partitioning by annealing, the stacking fault energy of austenite of the steel was estimated as ∼70 mJ/m². Even with the relatively high stacking fault energy, planar glide dominantly occurred in austenite. Neither strain induced martensite nor mechanical twins formed in austenite during tensile deformation. Ferrite exhibited the deformed microstructures typically observed in the wavy glide materials, i.e. dislocation cells. The mechanical properties of the present duplex steel were compared to those of advance high strength automotive steels recently developed.     

Microstructure studies in Al-6% Si-1.9% Cu-x% Mg alloys

The nature of precipitates formed in the aged Al-6% Si-1.9%Cu-x%Mg alloys (where x varies from 0.2 to 1.13) was investigated using scanning and transmission electron microscopy. Vickers hardness and grain size were measured. Results showed peak hardness around 4 and 10 h ageing time for 0.54% Mg and 1.13% Mg alloy, respectively. Hardness was found to increase with increasing magnesium content except for the 1.13% Mg alloy aged for 10 h. Q-phase particles have been observed and these are most probably responsible for the variation of hardness.     

Mg-9Al-3Si-0.375Sr-0.78Y合金的热变形行为及本构模型

利用Gleeble-3500热模拟试验机对Mg-9Al-3Si-0.375Sr-0.78Y合金试样进行等温恒应变速率压缩实验,研究其在温度250~400℃、应变速率0.001~10s~(-1)条件下的热变形行为。结果表明:在热变形过程中,峰值应力随着应变速率的降低和温度的升高而减小,且峰值应力对应变速率的敏感性随着变形温度的下降而增强。建立了考虑应变的热变形Arrhenius本构模型,模型精度良好,在300,350℃及0.001~10s~(-1)范围内,模型的平均绝对误差分别为1.57%和1.76%;合金的平均变形激活能为183.58k J/mol,平均应变速率敏感指数为0.1616。热变形过程中,α-Mg相呈现明显的动态再结晶特征,β-Mg₁₇Al₁₂相尺寸减小且分布均匀,初生Mg_2Si相较小。在低温(250~300℃)变形时,动态再结晶仅发生在晶界处。在高温(350~400℃)变形时,初生α-Mg晶粒发生了明显的动态再结晶。随着温度的增加和应变速率的降低,再结晶程度提高,再结晶晶粒逐渐长大。     

Investigation of the 12 orientations variants of nanoscale Al precipitates in eutectic Si of Al-7Si-0.6Mg alloy

Various orientations and diffraction patterns from nanoscale Al precipitates in eutectic Si were investigated by high-resolution transmission electron microscopy combined with transition matrix and stereographic projection.It was found that the Al precipitates had 12 variants,all orientation relationships can be expressed as:(001)Al//{111}Si,[110]Al//<110>Si.Further,a new diffraction pattern model from Al precipitates was established under[111]Si zone axis,which was in good agreement with the experiment data.The microstructure,adhesion strength and electronic structure of the interface between Al precipitate and Si matrix were studied by first-principles calculation and experimental observation.The results show that the covalent bonds are formed between interfacial Al and Si atoms,which play a key role in interfacial bind strength.Based on the Griffith fracture theory,the cracks tend to form and expand in the interior of Al precipitates firstly,and the interfaces can act as a protective layer to prevent crack propagation.Therefore,the nanoscale Al precipitates will improve the toughness of eutectic Si particles by releasing part of stress through lattice distortion.In addition,the stretched nanoscale Al precipitates can act as effective heterogeneous nucleation sites for high density deformation nanotwins in eutectic Si during deformation,which significantly improved the deformability of eutectic Si.     

Cavitation erosion resistance of Fe-26Mn-6Si-7Cr-1Cu shape memory alloy

Abstract

The cavitation erosion of low stacking fault energy Fe-26Mn-6Si-7Cr-1Cu shape memory alloy has been investigated in water using an ultrasonic vibratory apparatus, and compared with the behaviour of 0Cr13Ni5Mo stainless steel. It is shown that Fe-26Mn-6Si-7Cr-1Cu alloy has higher cavitation erosion resistance than 0Cr13Ni5Mo stainless steel. The cavitation erosion mechanism of Fe-26Mn-6Si-7Cr-1Cu was studied by examining the eroded surface using X-ray diffraction (XRD) and scanning electron microscopy (SEM). During early stages of cavitation erosion, Fe-26Mn-6Si-7Cr-1Cu alloy undergoes strain induced martensitic transformation. Exposure to further cavitation results in the deformation of ? martensite. The boundaries of ? martensite impede plastic deformation, leading to strain accumulation and subsequent material removal. On the basis of an XRD study and indentation tests, the better cavitaton erosion resistance of Fe-26Mn-6Si-7Cr-1Cu alloy is mainly ascribed to strain induced martensitic transformation, which can absorb impact energy without damage.     

Properties of electron-beam-welded and laser-welded austenitic Fe-28Mn-5Al-1C alloy

Austenitic Fe-28Mn-5Al-1C alloy was welded by electron-beam and CW CO₂ laser techniques. Tensile tests, impact tests, potentiodynamic and cyclic polarization measurements were used to evaluate the mechanical properties and corrosion behaviour of the weld materials, Metallographic examination showed that the microstructure of the electron-beam-welded and laser-welded metals consisted mainly of the columnar and equiaxed austenitic structures. Grain growth in the heat-affected zone (HAZ) was minimal for welding with these two techniques. The tensile and impact tests indicated that the weld materials exhibited lower tensile strength, percentage elongation, percentage reduction in area and impact energy than those of the base alloy. The polarization measurements revealed that the anodic polarization behaviour of the HAZs of the electron-beam-welded and laser-welded materials was identical to that of the base alloy when exposed in 1M Na₂SO₄ solution. However, the electron-beam-welded and laser-welded metals exhibited a higher current density in the passive region than that of the base alloy when exposed to 1N H₂SO₄ acid solution.     

Mechanism and kinetics of carbide dissolution in near alpha Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd titanium alloy

The present work evaluates the influence of bulk carbon content and aging temperature on the stability of carbide in near alpha Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd titanium alloy. The carbide particles were formed during heat treatment in the β phase field and preserved by water quenching. Subsequent aging treatments at 750–850 °C caused partial dissolution of these precipitates, as a result of the peritectoid reaction between the β phase and carbide. The models based on interface reaction controlled dissolution, via uniform atomic detachment, dislocation mechanism or vacancy flow, yielded experimental predictions comparable to the observed dissolution kinetics. Furnace cooling after heat treatment in the β phase field dissolved carbide particles completely, and the microstructure changed from acicular-like or block α to equiaxed α with increase of carbon content.     

Structural characteristics of a nickel-modified Al-20Si-3Cu-1Mg alloy powder

An attempt has been made to characterize a new, complicated Al-20Si-7.5Ni-3Cu-1Mg alloy powder produced by air atomization as a means of rapid solidification and its structural evolutions during continuous heating, in order to provide basic information for further investigations on its deformation behaviour and properties. The characterization consisted of size measurements, morphological observations, structural and thermal analyses of bulk powder, and microstructural examinations of individual powder particles. It was observed that the powder had a wide size distribution and irregular shapes, which were closely related to its varying internal structures. X-ray diffractometry (XRD) showed little shift of the diffraction line from the aluminium matrix of the powder, but a significant broadening, which has been attributed partly to the non-uniformity of supersaturation in the matrix of the powder and partly to the strains caused by the silicon crystals in the material. A differential scanning calorimetry (DSC) analysis revealed complex decomposition behaviour of the meta-stable aluminium matrix and transformations of nickel-bearing intermetallic compounds when heat was applied to the powder. XRD also showed that the meta-stable compounds formed in the powder did not match any known phases, and that they were transformed into Al₃Ni, Al₃(NiCu)₂ and Al₇Cu₄Ni intermetallic dispersoids upon heating. The analyses also indicated that, due to the addition of nickel, some copper-containing phases, initially desired to create precipitation strengthening effects, no longer existed. This would diminish the ageing response of the alloy and probably change its category to be non-heat treatable — an important modification that has not yet been recognized by the alloy designers and users. Examinations on the powder particle sections showed variations in microstructure with powder particle size. Transitions in solidification mode within powder particles in accordance with local conditions of undercooling and heat extraction were also observed. The significant inhomogeneities in the microstructure of the powder have raised a problem to which special attention should be paid in both powder production and subsequent processing.     

Crystallographic Analysis of Martensite in 0.2C-2.0Mn-1.5Si-0.6Cr Steel using EBSD

The crystallography of martensite formed in 0.2C-2.0Mn-1.5Si-0.6Cr steel was studied using the electron backscattered diffraction(EBSD) technique.The results showed that the observed orientation relationship(OR) was closer to that of Nishiyama-Wassermann(N-W) than Kurdjumov-Sachs.The martensite consisted of parallel laths forming morphological packets.Typically,there were three different lath orientations in a morphological packet consisting of three specific N-W OR variants sharing the same {111} austenite plane.A packet of martensite laths with a common {111} austenite plane was termed a crystallographic packet.Generally,the crystallographic packet size corresponded to the morphological packet size,but occasionally the morphological packet was found to consist of two or more crystallographic packets.Therefore,the crystallographic packet size appeared to be finer than the morphological packet size.The relative orientation between the variants in crystallographic packets was found to be near 60 /<110>,which explains the strong peak observed near 60 in the grain boundary misorientation distribution.Martensite also contained a high fraction of boundaries with a misorientation in the range 2.5-8.Typically these boundaries were found to be located inside the martensite laths forming sub-laths.     

Al-3%Cu-2%Li合金的热变形行为

在Gleeble-1500热模拟仪上进行热压缩实验,研究了变形温度为350~500℃,应变速率为0.001,0.01,0.1和1s-1时Al-3%Cu-2%Li合金的热变形行为。利用双曲正弦本构关系分析热变形中的流变应力,采用金相分析热变形中合金的显微组织变化。结果表明,该合金流变应力的大小受变形温度、应变速率的强烈影响,它随变形温度升高而降低,随应变速率提高而增大,该合金高温流变应力可采用Zener-Hollomon参数的函数来描述,其热变形激活能为325.48kJ/mol。     

Properties of austenitic Fe-25Mn-1Al-0.3C alloy for automotive structural applications

Austenitic Fe-25Mn-1Al-0.3C steel, cold-rolled and annealed at about 800 °C, exhibited 2.5 times higher tensile strength than current automotive ferritic sheet steel, while possessing comparable formability. The formation of strain-induced deformation twinning gave rise to an optimum combination of high strength and good formability.     

Chromate conversion coating on Al-0.2 wt.% Fe alloy

SEM and TEM investigations revealed that the chromate coating developed rapidly over the macroscopic alloy surface. The coating thickness increased over the immersion period employed in this study and was about 50 nm and 200 nm for coatings formed after 30 s and 120 s respectively. The coating is composed of chromium compounds with aluminium compounds probably concentrated at the alloy/coating interface.     

Elevated temperature deformation behaviour of multi-phase Ni-20 at % Al-30 at % Fe and its constituent phases

The mechanical behaviour of the multi-phase ( + /) alloy Ni-20 at % Al-30 at % Fe and alloys similar to its constituent and / phases, Ni-30 at % Al-20 at % Fe and Ni-12 at % Al-40 at % Fe, respectively, were investigated. When tested in tension at 300 K, the alloys exhibited 20%, 2% and 28% elongation, respectively. At elevated test temperatures (700, 900 and 1100 K), the multi-phase alloy exhibited increased ductility, reaching an elongation in excess of 70% at 1100 K without necking or fracture. Similarly, the alloy demonstrated increased ductility with increasing test temperatures. In contrast, the / alloy showed greatly reduced ductility with increasing temperature and was quite brittle both at 900 and 1100 K. Thus, whilst at room temperature the / phase improved the ductility of the + / aggregate, at elevated temperatures the phase alleviated the brittleness of the / phase, thereby preventing any embrittlement of the multi-phase alloy over the temperature range 300–1100 K. Also, whilst the phase improved the room-temperature strength of the multi-phase alloy, at elevated temperatures where the phase is known to be weak, the / phase improved the strength of the multi-phase alloy up to 900 K, beyond which the strength deteriorated due to disordering and lack of anomalous strengthening in the / component.