变形温度对SiCW/6061Al复合材料压缩变形期间基体金属流动和晶须重新取向的影响

借助观察和分析变形前后晶须取向和试样形状的变化，研究了晶须呈定向排列的SiCw/6061Al复合材料压缩变形期间金属流动和晶须重新取向的现象。研究结果表明，由于晶须的定向排列，SiCw/6061Al复合材料压缩变形期间基体金属的流动和晶须的重新取向强烈地依赖于变形温度。在较高温度压缩变形时，基体金属可以更均匀地流动，此时晶须是否发生重新取向与变形时环状和柱状试样的应变场有关；在较低温度变形时晶须不发生重新取向。     

Modeling Recrystallization of Austenite for C—Mn Steels during Hot Deformation by Cellular Automaton

By using a cellular automaton method,microstructure evolution of recrystallization in austenite during hot deformation was simulated for C-Mn steels.A model takes into account the influence of deformation temperature,strain,and strain rate on the dynamic recrystallization fraction,and the effect of the keeping time on the static recrystallization fraction based on a hot deformation test on a Gleeble-1500 simulator.In addition,the size changing of γgrains during continuous hot deformation was simulated by applying the model.     

近β钛合金高温压缩变形过程中流变软化行为研究进展

综述了近β钛合金高温压缩变形过程中流变软化行为的影响因素、流变软化机制及其分析方法以及基于流变软化机制的本构方程的发展,重点分析了变形工艺参数以及原始微观组织对流变软化行为的影响规律,此外,讨论了动态回复、动态再结晶、变形热等软化机制对软化现象的贡献,并提出了近β钛合金高温变形过程中关于流变软化现象亟待解决的问题,指出定量化及物理模型化是未来近β钛合金高温变形过程中流变软化现象的重要发展方向。     

金属热变形微观组织精密控制的研究进展

大多数承力关键金属构件在其生产过程中均需经历热变形工步。探讨了典型金属结构材料热变形中3种主要动态再结晶机制的流变行为、微观组织演变特征,并对热变形间隔及热变形后的亚动态再结晶行为进行分析,提出了相应的微观组织控制策略。讨论了第二相颗粒对热变形微观组织演变的影响以及通过第二相颗粒实现微观组织控制的方法。对在热变形中及热变形后冷却过程中会发生相变材料的热变形微观组织演变规律进行了分析。分析热变形过程中的微观组织演变规律,并建立相应的数值模型是实现微观组织精密控制的有效途径,因此简要讨论了不同微观组织演变数值模型的特点及适用性。综合考虑动态再结晶、亚动态再结晶的演变过程以及第二相颗粒和相变的影响规律,并结合基于物理冶金基础理论微观组织演变数值模型是实现热变形微观组织精密控制的必由之路。     

Relationship between microstructure and deformation behaviour during dynamic compression in Ti–3Al–5Mo–5V alloy

Abstract

The relationship between microstructure and deformation and damage behaviour during dynamic compression in Ti–3Al–5Mo–5V alloy has been studied using several experimental techniques, including optical microscopy, scanning electron microscopy and microhardness measurements. It was found that the deformation behaviour during dynamic compression was closely related to deformation parameters. After dynamic deformation, the deformation shear band that formed in the titanium alloy had microhardness similar to that of the matrix. However, the microhardness of the white shear band was much higher than the matrix microhardness. The effects of deformation parameters, including deformation rate and deformation degree, on deformation localisation were investigated. Based on the results from the present work, the microstructure and deformation processing parameters can be optimised. In addition, treatment methods after dynamic compression were explored to restore alloy properties. Using post-deformation heat treatment, the microstructure and property inhomogeneity caused by shear bands could be largely removed.     

The identification of dynamic recrystallization and constitutive modeling during hot deformation of Ti55511 titanium alloy

In the present paper, an internal-variable identification approach has been proposed to investigate the dynamic recrystallization (DRX) behavior during hot deformation and corresponding constitutive model has been constructed. Isothermal compression experiments of Ti55511 titanium alloy were conducted for verification. Plastic behavior is determined by dislocation evolution in many cases while deforming. The comparison between saturated and DRX critical dislocation density was made to distinguish the occurrence of dynamic recrystallization/recovery (DRV) during hot deformation. The influence of deformation parameters on DRX behavior was illustrated by dislocation evolution map, validated by the power dissipation efficiency distribution. DRX process during hot deformation of Ti55511 alloy tends to occur under moderate temperatures and low strain rates. In addition, a physical-based Arrhenius constitutive formula has been derived for DRX criticality. The strain-rate sensitivity coefficients during hot deformation were fixed as a constant equal to 1/6 and the deformation activation energy was related to the material's self-diffusion activation.     

Investigation of Subboundaries Evolution in Superplastically Deformed NiAl by Positron Lifetime

In order to study the subboundaries evolution in superplastically deformed NiAl,the positron lifetime change during superplastic deformation process was measured.It is shown that the superplastic deformation of NiAl has not influence on its τ2,the newly recrystallized grain boundaries formed during entire superplastic deformation process belong to the calegory of subboundaries and have not contribution to the superplastic strain.     

Ultrasonic fatigue of nickel-chromium alloys at low temperatures

The influence of low temperature ultrasonic deformation on the electrical resistivity and magnetic properties of nickel-chromium dilute solid solutions is examined. It is shown that changes in the electrical resistivity and magnetic properties of prequenched samples after ultrasonic fatigue can be explained by order-disorder processes during fatigue. It is concluded that ordering at low temperatures during the ultrasonic deformation is associated with high strain rate and high vacancy concentration produced by deformation.     

Formation of a random texture and ultrafine grains in AA 3003 aluminium alloy during the repeated shear deformation introduced by continuous confined strip shearing

Abstract

To investigate the microstructural development and corresponding texture evolution during repeated shear deformation, specimens of AA 3003 Aluminium alloy were deformed by continuous confined strip shearing based on equal channel angular pressing. Strip specimens were deformed by the shear forming process during up to eight passes, equivalent to effective strains of ~4.8. Texture evolution in the AA 3003 strips during the shear deforming process was studied by comparing the experimentally measured textures with simulated ones. Electron backscattered diffraction was employed to investigate detailed changes in microtextures and microstructures during repeated shear deformation. Softening associated with deformation is believed to be responsible for the formation of ultrafine grains and the random texture resulting from repeated shear deformation.     

Finite element modelling on microstructure evolution during multi-pass hot compression for AZ31 alloys using incremental method

Based on the principle of piecewise linearization, the incremental forms of microstructure evolution models were integrated into the thermo-mechanical coupled finite element(FE) model to simulate nonlinear microstructure evolution during multi-pass hot deformation. This is an unsteady-state deformation where dynamic recrystallization(DRX), meta-dynamic recrystallization(MDRX), static recrystallization(SRX) and grain growth(GG) take place during hot deformation or deformation interval. The distributions of deformation and microstructure for cylindrical AZ31 sample during single-pass and double-pass hot compressions were quantitatively calculated and compared with the metallographic observation. It is shown that both the deformation and microstructure are non-uniformly distributed due to the presence of friction between the die and the flat end of sample. The average grain size and its standard deviation under the double-pass hot compression are slightly smaller than those under single-pass compression.The simulated average grain sizes agree well with the experiments, which validates that the developed FE model on the basis of incremental forms of microstructure evolution models is reasonable.     

单向碳纤维/环氧树脂预浸料叠层的面内变形行为

为了充分了解热隔膜成型过程中预浸料的变形行为，通过偏轴拉伸测试探索了热固性单向碳纤维/环氧树脂预浸料在高温条件下的面内变形机制。研究参数包括试验温度、拉伸速率、预热时间和铺层顺序等。利用数字图像相关技术，在测试过程中监测单向碳纤维/环氧树脂预浸料的变形和纤维的旋转情况。结果表明，提高试验温度或降低拉伸速率均有利于促进单向碳纤维/环氧树脂预浸料的变形。铺层顺序对单向碳纤维/环氧树脂预浸料铺层的变形行为有很大影响，[45/–45/90]_S铺层方式比 [45/90/–45]_S铺层方式更有利于纤维旋转，且[45/–45/90]_S铺层方式变形阻力更小。采用铰链连接网(Pin-joined net, PJN) 理论对单向碳纤维/环氧树脂预浸料铺层变形过程中纤维角度变化进行预测并与实验结果进行对比，结果表明，用PJN理论预测的纤维旋转角度值与测试值存在较大偏差，说明其并不适用于预测热固性单向碳纤维/环氧树脂预浸料变形过程中纤维角的变化。同时，80℃预加热可以提高单向碳纤维/环氧树脂预浸料的变形阻力。      

Effective temperature rise during propagation of shock wave and high-speed deformation in metals

Two theoretical models are developed for the calculations of temperature rise during high-speed deformation and shock wave propagation. In the first model the calculations of the temperature distribution in metals during high-speed deformation are based on a model where the stationary high-speed deformation is considered as a propagation of shock wave with some fixed velocity in these metals. In this model the self-consistent system of equations describing the equation of state of metals and the conservation laws for momentum, energy and flow of energy is used for the determination of the temperature profile in the front of shock wave. The numerical calculations of the temperature distribution profile in shock wave front have been performed using the microscopic Thomas–Fermi–Dirac model for such metals as Al, Cu and Fe. In the second theoretical model the process of high-speed deformation is considered as an adiabatic process where a fraction of plastic deformation is converted into heat. The results of the numerical calculations of temperature rise during high-speed deformation in the dependence of strain to fracture are presented for metals: Al, Cu, Ni and Fe. It was shown that using these models the temperature during high-speed deformation can increase in different metals up to 1000 K.     

Modeling the crystallographic changes in processing of Al alloys

The evolution of deformation and recrystallization (RX) textures in 6016 Al alloy is analyzed in the current study by means of experimental measurements and numerical simulations. The deformation texture is modeled with various Taylor-type homogenization models whereas the development of RX texture is analyzed by evaluation of energy stored during the plastic deformation in grains of various orientations employing crystal plasticity (CP) calculations. It is shown that the main features of texture which evolve during discontinuous RX could be reproduced by taking into consideration both a microgrowth selection criterion and orientation selection based on crystallographically resolved stored energy of deformation. The influence of the strain heterogeneities on the development of RX texture is analyzed on the basis of CP and results derived from finite element calculations.     

粉末高温合金中夹杂物特性及其质量控制

研究了粉末高温合金中夹杂物特性及对材料断裂行为的影响 ,研究内容包括 :夹杂物的性质及来源、夹杂物在材料变形过程中的形变特征、夹杂物对材料疲劳断裂行为的影响等 ,同时研究了盘件在生产过程中夹杂物质量控制方法 .     

行星轧制变形程度对TP2铜管材组织及性能的影响

目的研究行星轧制变形程度对TP2铜管材在轧制和联拉时的组织和性能的影响。方法采用金相显微分析和拉伸实验,研究行星轧制变形程度对TP2铜管铸坯轧拉态以及拉拔态组织及性能的影响规律。结果经连续铸造的TP2铸坯为柱状晶,且由外向内成长。经行星轧制、联拉后的管材晶粒纤维流线,其晶粒显著拉长,随着轧制变形程度的增加,流线减弱,晶粒更加细化。轧制变形程度为93%与90%的轧管屈服强度、抗拉强度分别降低了22.83%和7.59%,伸长率提升了4.44%,塑性变形能力增加。结论随着轧制变形程度的增加,联拉管抗拉强度略有提高,而伸长率得到了保持。     

Effect of deformation ratio on fibril deformation in fatigue of polystyrene

Small-angle X-ray scattering has been used to measure the deformation of craze fibrils during mechanical fatigue of polystyrene. The maximum deformation of the sample in the fatigue cycle was kept constant while the minimum deformation was varied. When the minimum deformation was 50% or more of the maximum, the load on the craze fibrils remained tensile. When the minimum deformation was reduced below this, the load on the fibrils became compressive and they buckled. The main effect of minimum sample deformation on fatigue life occurred in the regime where the fibrils remained straight. In this regime a decrease in minimum sample deformation caused a considerable decrease in fatigue life. At low minimum sample deformations the effects of minimum deformation on fatigue life were not large. These effects probably stem from the fibril strains involved in the deformation processes.     

低温变形Nb微合金钢铁素体相变的数学模型

以热力学和动力学理论为基础，研究了Nb微合金钢热变形过程中铁素体相的形核及长大过程，在形核速率计算中引入变形储能、晶界凸阶及微合金元素的作用，建立了低温变形诱导铁素体相变的动力学模型，分析了热变形参数和化学成分对相变分数和晶粒尺寸的影响．变形温度的降低和变形程度的增加，促进了α相变过程，相变体积分数增加，晶粒得到细化．C与Mn含量增加的效果则相反．模型应用于热轧带钢生产过程的模拟，计算结果和实测结果吻合良好．     

铁基低镍电热合金的热变形行为

利用热模拟技术对铁基低镍电热合金的热变形行为进行了试验研究。绘制出了该合金的高温变形真应力－真应变曲线，并结合热变形后的显微组织分析了影响合金热变形行为的因素，给出了该合金热变形的回复激活能。     

Respiration measurement using fibre-optic deformation sensor

Untreated fibre is not sensitive to bending deformation. In this paper, a fibre-optic deformation sensor has been developed by introducing a light leakage zone on one side of fibre, which measures bending deformation directly. A respiration measurement system based on fibre-optic deformation sensors is developed. Two fibre-optic sensors are bonded to an elastic belt that is fixed around the chest, which ensures the deformation curvature of the sensors changes during respiration. The light leakage zones of two sensors are arranged at the same cross-section of the belt and the directions of two light leakage zones are opposite. In this case, the throughput of one sensor increases and the other decreases during respiration. A differential system is established by these two fibre-optic sensors, which improves the sensitivity of the measurement system. The proposed fibre-optic respiration measurement system enables a quantitative assessment of the respiratory depth and respiratory rate.     

Microstructural evolution of a Ni-Co based superalloy during hot compression at γ'sub-/super-solvus temperatures

The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated by isothermal compression tests performed at γ'sub-solvus(1090℃)andγ'super-solvus temperatures(1150℃)with a wide strain rate range from 0.001 to 10 s-1 under a true strain of 0.693.Electron backscatter diffraction(EBSD),electron channeling contrast imaging(ECCI)and transmission electron microscope(TEM)techniques were used to characterize the microstructures.The results revealed that the dynamic recrystallization(DRX)volume fraction increased and stored energy of the γ matrix grains decreased with increasing the strain rate during γ'sub-solvus temperature defor-mation,while the opposite phenomena were observed during γ'super-solvus temperature deformation.The comprehensive effect of initial grain size,primary y'phase,twins and adiabatic temperature rise led to these results.The primary γ'particles undergone the deformation behavior within itself and obviously accelerated the DRX of the matrix.The microstructural evolution proved that discontinuous dynamic recrystallization(DDRX)was the dominant mechanism during the hot deformation carried out at both γ'sub-solvus and γ'super-solvus temperatures.Primary γ'particles obviously accelerated the nucleation step and retarded the growth step of DDRX during γ'sub-solvus temperature deformation.Besides,the acceleration effect of primary γ'particles on DDRX increased with the increase of strain rate.Continuous dynamic recrystallization(CDRX)was confirmed to be an assistant mechanism during γ'super-solvus temperature deformation and was promoted with the increase of strain rate.