Effect of initial microstructure on hot workability of 7085 aluminum alloy

The hot workability of 7085 aluminum alloys with different initial microstructures （as-homogenized and as-solution treated） was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 ℃ and the strain rate ranging from 0.0001 to 1 s 1. The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 ℃, 0.01 s i and 450 ℃, 0.001 s-1, respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.

Simulation study on non-linear effects of initial melt temperatures on microstructures during solidification process of liquid Mg_7Zn_3 alloy

The non-linear effects of different initial melt temperatures on the microstructure evolution during the solidification process of liquid Mg7Zn3 alloys were investigated by molecular dynamics simulation, The microstructure transformation mechanisms were analyzed by several methods. The system was found to be solidified into amorphous structures from different initial melt temperatures at the same cooling rate of 1×10^12 K/s, and the 1551 bond-type and the icosahedron basic cluster （12 0 12 0 ） played a key role in the microstructure transition. Different initial melt temperatures had significant effects on the final microstructures. These effects only can be clearly observed below the glass transition temperature Tg; and these effects are non-linearly related to the initial melt temperatures, and fluctuated in a certain range. However, the changes of the average atomic energy of the systems are still linearly related with the initial melt temperatures, namely, the higher the initial melt temperature is, the more stable the amorphous structure is and the stronger the glass forming ability will be.

Effect of microstructure on short pulse duration shock initiation of TATB and initial response mechanism

Micro-TATB particles with different sizes and 3D nanoporous TATB architectures with different specific surface areas were prepared through recrystallization to study short pulse duration shock initiation properties by electric gun technology.For micro-TATB,the initiation threshold significantly decreases with TATB average size ranging from 79.7μm to 0.5μm.For 3D nanoporous TATB architecture,the initiation threshold decreases and then increases with specific surface areas increased from 9.6 m^2/g to36.2 m^2/g.The lowest initiation thresholds are obtained for the micro-TATB with average sizes of 1.3μm and 0.5μm,and 3D nanoporous TATB architecture with specific surface area of 22.4 m^2/g.The shock initiation thresholds of micro-TATB and 3D nanoporous TATB architectures show significantly decreases with the porosity increased.The decomposition reaction and thermal conductivity properties were further investigated to understand the initial response mechanism.High porosity provides more collapse sites to generate high temperature for formation of hot spots.The low thermal conductivity and decomposition temperature could enhance the formation and ignition of the hot spots,and initial decomposition reaction of TATB.The effect of the decomposition temperature is higher than that of the thermal conductivity on the shock initiation properties.The enhanced decomposition reaction could pro mote energy release and transfer process from the ignition to the combustio n.This work offe rs a new insight to understand the effects of microstructure on the shock initiation properties and the initial response mechanism of TATB.

Constitutive relation of weakly anisotropic polycrystal with microstructure and initial stress

Man （Nondestr Test Eval 15：191-214, 1999） derived the constitutive relation of a weakly-textured orthorhombic aggregate of cubic crystallites with effects of microstructure and initial stress. In this paper, a computational expression on the integration ∫SO（3） Q^× D^1m0dg is given. Then, by means of the computational expression, the general constitutive relation of a weakly-textured anisotropic polycrystal with the consideration of microstructure and initial stress is derived. As special cases of our general constitutive relation, two constitutive relations are given for an isotropic polycrystal and a weakly-textured anisotropic aggregate of cubic crystallites. The acoustoelastic tensor of the reference cubic crystal is derived to determine the material constants of the polycrystal. Two examples are given for understanding the physical meaning of the texture coefficients and the constitutive relations.

A discontinuous dynamic recrystallization model incorporating characteristics of initial microstructure

In order to describe and predict the kinetic process of discontinuous dynamic recrystallization （DDRX） during hot workingfor metals with low to medium stacking fault energies quantitatively, a new physically-based model was proposed by considering thecharacteristics of grain size distribution, capillary effect of initial grain boundaries （GBs） and continuous consumption of GBs. UsingIncoloy 028 alloy as a model system, experiments aiming to provide kinetic data （e.g., the size and volume fraction of recrystallizedgrain） and the associated microstructure were performed. Good agreement is obtained between model predictions and experimentalresults, regarding flow stress, recrystallized fraction and grain size evolution. On this basis, a thermo-kinetic relationship upon thegrowth of recrystallized grain was elucidated, i.e., with increasing thermodynamic driving force, the activation energy barrierdecreases.

Properties,Microstructures and Precipitate Morphology of Hot-rolled Interstital-Free(IF)Steel Sheets

In order to simplify production process and to decrease production cost of thicker cold-rolled iF steel sheets for deep drawing applications, a new hot-rolled IF steel sheet is developed through hot-rolling in or region. In this paper, properties, microstructures and precipitate morphology of hot-rolled iF steel sheets are described..

Microstructure and mechanical properties of the hot-rolled Fe16Mn0.6C steel plate

Results presented in this study contribute to investigation of the microstructure and mechanical properties of the hot-rolled Fe16Mn0.6C steel plates.The steel plates have been produced by being hot-rolled at temperatures ranging from 1100℃ to 850℃ in seven passes to 97.5% reduction in thickness and then cooled in a furnace of 650℃.Some plates have been annealed at temperatures ranging from 300℃ to 1100℃ for 5min to 60min,and then followed by water quenching.There are annealing twins in the hot-rolled Fe16Mn0.6C steel.Fe16Mn0.6C steel presents similar ductile behavior as X-IPTM steel,but much higher elongation than commercial martensitic steel (MP) 1000,dual phase (DP) 980,and transformation induced plasticity (TRIP) 980 steels.Fe16Mn0.6C steel experiences γε (-α) transformation in some local regions,but remains mostly austenite during the entire deformation process.Fe16Mn0.6C steel with special mechanical properties can be produced by using the appropriate anneal technology.Twinning induced plasticity(TWIP) effect only occurs in the Fe16Mn0.6C steel annealed at temperature higher than 900℃.

“Quartus scale” of hot-rolled strip steels and its formation mechanism

The types and growth of various oxide scales formed during the different phases of the production of hotrolled strip steel products are reviewed. Similarities and differences between the ＂tertiary scale＂ on the surface of carbon steels at high temperatures and the oxide scale on pure iron are compared. The micro-structural features of the ＂final oxide scale＂ on the surface of strip steels at room temperature as well as the relationship between these features and the position of the steel coil （plate） and the subsequent processes of recoiling, temper rolling and trimming, etc. are summarized. The actual oxide scales retained on the commercial hot-rolled strip steels at room temperature have been proposed to define as ＂ quartus scale＂ for the first time. The micro-structural development and phase transformation of the initial ＂tertiary scale＂ during and after cooling and coiling are described. The reasons for the ＂tertiary scale＂ on carbon steels differing from the oxide scale formed on pure iron, and the major influencing factors in the formation of various types of ＂quartus scales＂ are analyzed from both thermodynamic and dynamic viewpoints. The development mechanism of ＂ quartus scales＂ is discussed and the potential effects of the ＂ quartus scale＂ state （thickness, constitution, structure and defects）, on the rusting and pickling properties of commercial hot-rolled strip steel, as well as on the mechanical properties of oxide scales are analyzed.

Effect of sintering process on microstructure and magnetic properties of high frequency power ferrite

An oxide ceramic process was adopted to prepare high frequency manganese-zinc(MnZn)power ferrite.In combination with the microstructure analysis of material,the influences of sintering process on initial permeability(μ_(i))and high frequency loss in unit volume(P_(cv))of MnZn power ferrite were investigated.The results show that in order to obtain fine microstructure and high frequency properties,the preferable sintering temperature and atmosphere are 1230℃and oxygen partial pressure(P_(O_(2)))of 4%,respectively.

Numerical simulation on microstructural evolution during multipass hot-rolling of aluminum alloys

Numerical simulation on microstructural evolution during multipass hot rolling of aluminum alloys was performed by using DEFORM TM software and incorporating Zener Hollomon parameter Z . The distributions of equivalent stress, equivalent strain, equivalent strain rate and temperature, as well as the distribution of recrystallization fraction through the thickness of deformed specimen during multipass hot rolling of 5182 aluminum alloy, were all calculated. The results agree well with the metallographic examination of the deformed specimen on Gleeble 1500. [

Synthesis, Permeability and Microstructure of the Optimal Nickel-Zinc Ferrites by Sol-Gel Route

The optimum ferrite can be obtained through free-microstructural defects where such defects are always encountered in the conventional ferrites often caused by chemical inhomogeneity. In this study, Ni-Zn ferrite was synthesized and fabricated by means of a sol-gel route. Thermal gravimetric analysis (TGA) was used to study the thermal transforma-tion of the ferrite in air. Parts of the sol-gel powder heated at elevated temperatures were characterized by X-ray dif-fraction (XRD) method and Scanning Electron Microscopy (SEM) to reveal the crystallized single-phase and the struc-ture of the obtained ferrite. Fourier transform infrared spectroscopy (FT-IR) was assisted to investigate the structure. The microstructures of the toroidal cores were obtained at two different sintering temperatures and compared with those obtained via the classic method. In addition to that, the magnetic properties were measured. The initial magnetic permeability was found to increase with the increasing of the frequency as a result of the domain wall motions and the corresponding loss was small. Therefore, a well defined polycrystalline microstructure ferrite via an easier preparation methodology as compared to the classic method is obtained.

Influence of different microstructural features on impact toughness and crack initiation behavior of coarse grain heat-affected zone in X80 pipeline steel

Coarse grain heat-affected zone samples of X80 pipeline steel under different heat inputs were obtained through thermal welding simulation experiments with Gleeble 3500.Charpy impact tests and a combination of multiscale characterizations were conducted to investigate the influence of various microstructural features on impact toughness and crack initiation behavior.The results prove that, as the heat input increases, the number of M/A components increases, thereby degrading toughness and increasing hardness.Meanwhile, more M/A constituents tend to aggregate on prior austenite grain boundaries(PAGBs),and the overall dimensions of M/A and the width and volume fraction of the lath martensite substructure inside M/A islands would increase as well.These changes make intersections between boundary M/As and PAGBs become one of the preferred sites for crack initiation.In addition, only large-sized grotesque inclusions can act as a direct inducement of crack initiation.

Formation of surface-attached microstructured polyelectrolyte brushes

Surface-attached micropattemed polyelectrolyte brushes on planar solid surfaces are generated using free radical polymerization photo-initiated by self-assembled initiator monolayers. It is shown that the formed patterns can be either negative or positive with different patterning processes.

Influence of RE-rich phase distribution in initial alloy on anisotropy of HDDR powders

The influence of the RE-rich phase distribution in the precursor alloys on the anisotropy of the hydrogenation disproportionation desorption recombination（HDDR） processed powders is investigated. The homogenized ingot alloy and the as-cast strip casting（SC） alloy with a uniform RE-rich grain boundary phase lead to high anisotropy of the refined powders,acquiring degrees of alignment（DOA） of 0.62 and 0.54, respectively. The RE-rich phase aggregation results in a deteriorated DOA of the powders due to the drastic disproportionation rate, while a thin and uniform RE-rich phase distribution is beneficial for DOA. A reaction model of the initial particle microstructure is proposed for optimizing the HDDR powder anisotropy.

Microstructural evolution in Al-Zn eutectoid alloy by hot-rolling

The Al-Zn eutectoid alloy has been widely known as a typical superplastic metallic material, where fine-grained microstructure is usually obtained by heat treatment. Recently, thermo-mechanical controlled process has also been reported to provide a fine-grained microstructure. In the present study, Al-Zn alloy ingots of 20 mm in thickness were homogenized and hot-rolled to a thickness of 2 mm under three processes： 1） the specimen was air-cooled after homogenization and hot-rolled; 2） the specimen was water-quenched after homogenization and hot-rolled; 3） the specimen was immediately hot-rolled after homogenization. Microstructural observation showed that, in processes l and 3, lamellar microstructure was formed after homogenization, and became fragmented to fine-grained microstructure as the hot roiling process proceeded. In process 2, fine-grained microstructure without lamellar microstructure was attained throughout the hot-rolling process. A minimum grain size of 1.6 μm was obtained in process 3. Tensile tests at room temperature showed that the elongation to failure was the largest in process 3.

Thermomechanical controlled processing of hot-rolled multiphase steel containing Nb

Influence of thermo-mechanical controlled processing(TMCP),including two-stage rolling with laminar cooling,air cooling and ultra-fast cooling,on the microstructure and mechanical properties of three kinds of Nb-microalloeyed steels was investigated by hot-rolling experiment.Effect of chemistry compositions and microstructure on mechanical properties and the relationship between the multiphase microstructure' s formation with TMCP were analyzed.The results showed that the mixed microstructure containing ferrite,bainite,martensite and a small amount of retained austenite can be obtained by thermo-mechanical controlled processing.Size, quantity and distribution of the constituents(ferrite grain,bainite packet and M-A islands) significantly affect the mechanical properties of three kinds of Nb-microalloyed steels.Under the condition of similar TMCP parameters, there is a gradually decreasing tendency in tensile strength from high silicon Nb steel,high silicon Nb-Ti steel to low silicon Nb-Ti steel,and an opposite tendency in total elongation and product of tensile strength and ductility. Total elongation and product of tensile strength and ductility reach the maximum values(41%and 25256 MPa% respectively) for low silicon Nb-Ti steel.

Effects of laser shock processing,solid solution and aging,and cryogenic treatments on microstructure and thermal fatigue performance of ZCuAl_(10)Fe_(3)Mn_(2)alloy

The materials used in variable temperature conditions are required to have excellent thermal fatigue performance.The effects of laser shock processing(LSP),solid solution and aging treatment(T6),and cryogenic treatment(CT)on both microstructure and thermal fatigue performance of ZCuAl_(10)Fe_(3)Mn_(2) alloys were studied.Microstructure and crack morphology were then examined by scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS).The result showed that,after being subjected to the combination treatment of T6+CT+LSP,the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl_(10)Fe_(3)Mn_(2) alloy with the tensile strength,hardness,and elongation of 720 MPa,300.16 HB,and 16%,respectively,and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm.Moreover,the ZCuAl_(10)Fe_(3)Mn_(2) after combination treatment shows high resistance to oxidation,good adhesion between the matrix and grain boundaries,and dramatically reduced growth rate of crack.During thermal fatigue testing,under the combined action of thermal and alternating stresses,the microstructure around the sample notch oxidized and became loose and porous,which then converted to micro-cracks.Fatigue crack expanded along the grain boundary in the early stage.In the later stage,under the cyclic stress accumulation,the oxidized microstructure separated from the matrix,and the fatigue crack expanded in both intergranular and transgranular ways.The main crack was thick,and the path was meandering.

Interface analysis of 7B52 Al alloy laminated composite fabricated by hot-roll bonding

The bonding interface of 7B52 Al alloy laminated composite （ALC） fabricated by hot rolling was investigated using optical microscopy （OM）, transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, ultrasonic flaw detection （UFD）, and bonding strength tests. The results show that metallurgical bonding is achieved at the interface after composite rolling. The TEM analysis and tensile tests indicate that the 7B52 ALC plate combines high strength of the hard individual layer and good toughness of the soft individual layer. However, UFD technology and SEM analysis prove that the defects （thick oxide films, acid washed residues, air, oil and coarse particles） existing in the bonding interface are harmful to the bonding strength. To sum up, the composite roiling process is suitable for 7B52 ALC plate, and the content and size of the defects should be controlled strictly. Advanced surface treatment of each individual layer would be beneficial to further improve the bonding quality.

基于Al_(2)O_(3)/环氧树脂复合材料的盆式绝缘子在役态裂纹萌生及失效断裂机制研究

本文首先总结了近年盆式绝缘子失效破坏的一般规律和特征,然后截取典型失效区域试样,分析基体微观组织形貌和失效断口的形貌特征,最后采用纳米压痕力学技术对复合材料异质界面微观力学性能进行表征分析,阐释基于Al_(2)O_(3)/环氧树脂复合材料的裂纹萌生及失效断裂机制。结果表明:环氧树脂基体的断裂韧性值约为0.55 MPa·m^(1/2),在载荷作用下裂纹从环氧树脂基体中萌生,并不断扩展,当遇到高强度的Al_(2)O_(3)颗粒时因受阻而发生偏转,并沿着颗粒与基体的界面快速扩展。

蠕变-疲劳交互作用下P91钢变形行为研究进展

P91钢被广泛应用于热电机组的蒸汽管道中。近年来,峰值负荷调节导致了管道部件的蠕变-疲劳相互作用,构件常出现早于预期寿命的失效。针对这一问题,本文综述了P91钢在蠕变-疲劳交互作用下的力学响应、微观组织演化、裂纹萌生扩展规律三个方面的研究成果与进展。首先通过对比不同条件下蠕变-疲劳加载方式,论述了蠕变-疲劳变形过程中材料的微观组织演化规律。最后,根据载荷保持时间、加载频率、平均应力与应力幅的关系等外部服役条件的不同,阐述了P91钢微裂纹的萌生、扩展行为。