共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of Materials Processing Technology》2014,214(2):175-182
The annealed 1100 aluminum foils were welded at room temperature with an ultrasonic metal welding (UMW) method. Effects of two key parameters (the oscillation amplitude and the deformation reduction of the welded foils) on the microstructural evolution were investigated. With the increase of oscillation amplitude, the deformation and the grain refinement of the foils in the welded specimen were homogeneous, but the grain size was not less than 25 μm. With the increase of deformation reduction, the microstructures were inhomogenously changed from the initial coarse grains (45 μm) into the dynamically recrystallized fine grains (2 μm) in the upper foil, but they changed little in the lower foil. For both cases, the microstructural evolutions attributed to the grains and/or sub-grains rotation. The dynamic recovery and the followed continuous dynamic recrystallization were the active deformation mechanism during UMW according to the observation of the thermal and the deformation textures. The effects of both ultrasonic amplitude and deformation reduction on the hardness of the builds were measured. 相似文献
2.
研究了应变诱发熔化激活法 (SIMA)制备半固态LY11合金过程中的变形温度、变形速度、等温温度和保温时间等工艺参数对LY11合金组织演变的影响。研究结果表明 ,要获得均匀、细小的非枝晶组织 ,必须合理地匹配SIMA工艺参数 相似文献
3.
A. I. Grigor’ev N. A. Petrushov S. O. Shiryaeva 《Surface Engineering and Applied Electrochemistry》2017,53(4):345-351
In fourth-order nonlinear asymptotic calculations for eccentricity (which measures the stationary deformation of a charged drop in an external electrostatic field) and first-order calculations for the dimensionless amplitude of its oscillations, the frequency of a strongly charged drop in a weaker external uniform electrostatic field is calculated. The deformation corrections to the frequency related to the change in the equilibrium shape of a drop in comparison with its spherical shape are found. As the surface area of a drop in an external field increases, the oscillation frequency of the drop decreases and the deformation correction has one sign (negative). When the drop charge tends to critical (to the limit, om the sense of stability with respect to the superposition of its own and induced charges), the value of the correction is comparable to the frequency in order of magnitude. 相似文献
4.
A new history of internal pressure in the hydroforming processes of tubes is developed to attain high formability. The effect of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes is examined using both finite element simulation and experiment. The deformation behaviour during the hydroforming is greatly affected by the oscillation of internal pressure. For a monotonic history of small internal pressure, the wrinkling was caused by insufficient bulging, whereas the necking and bursting occurred for a monotonic history of large internal pressure. The occurrence of these defects can be avoided by oscillating the internal pressure in the pulsating hydroforming. The improvement of formability in the pulsating hydroforming is due to both low pressure and oscillation of pressure. The effects of the amplitude and cycle number of pressure in the pulsating hydroforming on the deformation behaviour are investigated. It is found the oscillation of internal pressure is effective in preventing the occurrence of defects. 相似文献
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针对现有的等离子弧-MIG复合焊接过程中的双弧排斥问题,基于MIG焊丝位移规律性改变提出了一种新型的MIG焊丝振荡与等离子弧共熔池的复合焊接工艺.通过调节MIG焊丝电机转速(振荡频率)和振荡振幅进行了焊接工艺试验.结果表明,随着电机转速(振荡频率0~41 Hz)的增加,等离子弧与MIG电弧排斥减弱,耦合趋势增大.尤其是电机转速为2 000 r/min(振荡频率33 Hz)时,共熔池复合焊接效果较好;MIG焊炬振荡振幅为1 mm时,电弧形状最为稳定,但振荡频率和振荡振幅过大均不利于焊接过程稳定性;MIG焊炬振荡提高了熔滴过渡频率,使焊丝尖部呈现小熔滴过渡,减小了焊接飞溅.对接试验力学性能测试表明,抗拉强度、抗弯强度均随振荡频率的提高呈现先增大后减小趋势,分析认为MIG焊炬振荡具有一定搅拌熔池的作用,有效提高了焊接接头的力学性能. 相似文献
7.
Lei Che Masahide Gotoh Yoshiaki Horimoto Yukio Hirose Lin Yang 《Journal of Materials Engineering and Performance》2008,17(3):445-453
This article deals with the characterization of the mechanical behaviors of spheroidized carbon steels, which contain ferrite
and spheroidal cementite. The aim of the study is to identify the deformation behaviors of cementite particles by x-ray diffraction
and to correlate them to the residual stress state evolution. The stress state evolutions for both phases during an in situ 4-point bending test and after a uniaxial tensile test that have been well followed by x-ray diffraction. After each tensile
loading, optical observation is made to correlate the determined residual stress state with the microstructure. The coupling
of techniques helps us to characterize the deformation evolution of spheroidal cementite in the carbon steel: at the initial
state, the cementite shows the same elastic behavior as the ferrite; at the next state, the ferrite begins to deform plastically
but the cementite deforms elastically; then, plastic relaxation occurs in the ferrite while the cementite still deforms elastically
until finally breaking. 相似文献
8.
《International Journal of Cast Metals Research》2013,26(4):249-256
AbstractThe deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons. 相似文献
9.
Cryogenic torsion pendulums being developed for research in gravitational physics serve well for exceptionally accurate measurements of nonlinear and anelastic properties of torsion fibers at low temperature (77 K and 4.2 K) at low frequency (0.01 Hz) in a pre-plastic regime of high shear strain (0.0001–0.003). The measurements use a torsion pendulum suspended by a thin fiber (typically 20 μm×24 cm), oscillating with an amplitude of many revolutions. In a few oscillation cycles, oscillation amplitude and frequency may be determined to better than one part in 108, and harmonic deviations from simple harmonic motion (at 77 K) with fractional accuracy better than 10−9, enabling very accurate determination of the decrement, modulus defect, and hysteresis loop of the system as a function of oscillation amplitude. 相似文献
10.
S. O. Shiryaeva A. I. Grigor’ev N. Yu. Kolbneva 《Surface Engineering and Applied Electrochemistry》2018,54(1):20-31
An analysis is carried out on the electromagnetic radiation of an uncharged drop oscillating in an electrostatic field using nonlinear asymptotic calculations for two small parameters (the value of a dimensionless stationary deformation of an initially spherical drop and the amplitude of its capillary oscillations). In the external electrostatic field, on the top of the drop, electric charges with the opposite signs are formed, to which the “effective” charges located on the drop’s symmetry axis are added relatively. Since the distance between those “effective” charges is about the length of the drop’s radius, they form a dipole, which at the distances much longer than the sizes of the drop creates a similar electric field as the drop itself. During the oscillation of the drop surface, the dipole will also oscillate, which will generate the electromagnetic waves of the dipole type. 相似文献
11.
A. I. Grigoriev N. V. Voronina S. O. Shiryaeva 《Surface Engineering and Applied Electrochemistry》2011,47(3):235-241
Using the asymptotic analytical procedure of the second order of smallness with respect to the ratio between the amplitude
of a wave and the radius of a jet for the calculation of the wave motion of a finite amplitude on the surface of a cylindrical
jet of an ideal incompressible dielectric liquid, it was found that the nonlinear corrections for the jet’s profile and the
potential of the fields of the rates and electrostatic potentials inside and outside of the jet have a resonance character.
In a degenerate resonance interaction between the wave, which determines the initial deformation and the waves that become
excited owning to the nonlinearity of the hydrodynamic equations, the waves with different symmetry (with different azimuthal
numbers) can participate. 相似文献
12.
通过金相显微镜、扫描电镜对车轮钢(CL50)铸态/热轧态和热处理态组织中夹杂物的形态分布进行研究,并利用能谱对夹杂进行成分分析。结果表明,在S含量极低的情况下,CL50车轮钢中氧化物夹杂主要呈球形或多边形,随机分布,在轧制过程中不发生变形;增大S含量,铸态组织中开始出现球状、串珠状以及条状MnS-氧化物复合夹杂物,且有在晶界聚集的趋势,主要分布于网状铁素体或者孤岛铁素体中;热处理后夹杂物则分布于网状铁素体中,说明夹杂物在一定程度上促进铁素体的形核。在890℃热处理过程中夹杂物形态和分布没有明显变化。 相似文献
13.
The effects of the superimposed oscillating load while using the continuous stiffness measurement (CSM) technique on the extracted indentation stress–strain (ISS) curves were systematically investigated using spherical nanoindentation tests performed on a variety of samples, using probes of 1 and 100 μm radii. Particular care was afforded to the corrections that were needed on the load, displacement and stiffness signals to account for the effect of the superimposed oscillations. A decrease in the oscillation frequency from the commonly used 45 Hz caused the measured stiffness values to decrease. This resulted in questionable high strain hardening values in the ISS curves. The noise levels in the recorded stiffness signal were significantly higher while using an oscillation amplitude of 1 nm. It was concluded that these observations are artifacts of the machine dynamic control systems and do not represent the material’s true behavior. The CMS signal with a 45 Hz oscillation frequency and 2 nm amplitude appears to produce most reasonable values of stiffness values and is therefore the best choice for reliably extracting ISS curves for the materials studied. 相似文献
14.
Haitao Jiang Xiaoli Li Aiming Xiong Miaoquan Li 《Journal of Materials Engineering and Performance》2003,12(3):249-253
For semi-solid metal forming, it is essential to fabricate the semi-solid materials with spheroidal microstructure. Among
several fabrication techniques of the semi-solid materials, (strain-induced melt activation (SIMA) is an ideal candidate with
the advantages of simplicity and low equipment costs. In this paper, the microstructure evolution of LY11 alloy (approximately
corresponding to ASTM 2017) was investigated in the SIMA process, which had two essential stages: deformation and isothermal
heat treatment. The deformation stage was conducted using a CSS-1100C material testing machine and the isothermal heat treatment
stage was performed in a resistance furnace. Different levels of deformation temperatures, ram velocities, isothermal temperatures,
and holding times were used in this investigation. The microstructure of LY11 alloy was observed by a NEOPHOT-1 optical microscope.
The results indicated that the processing parameters must be selected properly to obtain the fine, uniform and spheroidal
microstructure by SIMA. The deformation-recrystallization mechanism for microstructure evolution in SIMA process was supported
by experimental evidence. 相似文献
15.
连铸结晶器振动下弯月面处温度波动的模拟实验 总被引:4,自引:0,他引:4
设计了连铸结晶器弯月面处传热模拟实验,测量了在结晶器振动情况下弯月面处的温度,发现该处的温度随着结晶器的振动而产生周期性的变化,实验结果表明,结晶器振动频率越大,振动幅值,结晶器冷却强度以及结晶器与铸坏间的接触压力越小,因结晶器振动而产生的弯月面温度波动亦越小,据此认为,连铸弯月面温度波动是导致铸坯表面缺陷产生的一个重要原因,基于此“温度波动”现象,分析了包括高频小振幅振动,软接触结晶器电磁连铸,热顶结晶器等诸多技术改善坯表面质量的机理。 相似文献
16.
纳米Ni薄膜在摩擦过程中塑性行为的分子动力学模拟 总被引:1,自引:0,他引:1
用分子动力学模拟研究了金刚石压头在Ni晶体薄膜上的摩擦过程和薄膜塑性变形行为的纳观机制.结果表明:在摩擦过程中,穿晶层错和棱形位错环是纳米薄膜结构传递塑性变形的两种载体,纳米薄膜晶界捕获位错阻滞了塑性变形向薄膜晶界下方材料中传播.摩擦过程中易在较薄的薄膜表面和薄膜晶界之间产生穿晶层错,穿晶层错的产生增加了薄膜蓄积塑性变形的能力,从而抑制材料表面摩擦力在黏滑过程中的振荡幅度;在比较厚的薄膜中不易生成穿晶层错,在摩擦过程中位错环依次向体材料发射,并与晶界反应,湮灭于晶界,黏滑动摩擦响应与单晶相似.由于不同厚度薄膜塑性变形产生的位错结构不同,使得在摩擦过程中亚表面微结构的演化亦不同. 相似文献
17.
M. N. Georgiev E. G. Volkova V. V. Sagaragze K. G. Valkov 《The Physics of Metals and Metallography》2012,113(11):1096-1106
The paper presents the results of studying the structure and cracking resistance of so-called carbide-free nonalloyed and alloyed bainitic spheroidal graphite irons. The effect of retained austenite on the static cracking resistance of the irons is shown. Transmission electron microscopy (TEM) is used to elucidate the structural affinity of bainitic ferrite (??B) and dislocation or lath martensite. A high dislocation density (1.1 × 1011 cm?2) and a small amount of extremely dispersed carbides in bainitic ferrite are the main cause of the increased strength of the irons. The presence of hardened ferrite, along with the possibility of the plastic deformation of retained austenite, yield a high cracking resistance of the bainitic spheroidal graphite irons. The parameters of isothermal hardening are determined at which the maximum resistance to crack propagation is reached. 相似文献
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《International Journal of Cast Metals Research》2013,26(1):30-40
AbstractThe thermal transport properties of five predominately pearlitic grades of grey, compacted graphite and spheroidal graphite iron have been investigated by the laser flash technique. Samples have been taken from cylinders cast in controlled thermal environments designed to produce three dissimilar cooling rates. Digital image analysis has been utilised in order to characterise the different graphite morphologies. The results indicated linear relationships between the thermal transport properties and the roundness of the graphite and the nodularity for compacted graphite and spheroidal graphite iron. A pronounced decrease in the thermal conductivity occurred when the lamellar graphite structure was transformed into compacted graphite. The thermal conductivity of compacted and spheroidal graphite iron has been recalculated with good accuracy over a temperature range of 25–500°C by means of regression analysis. 相似文献