Cyclic Deformation Behaviors of $$ [\bar{5}79] $$-Oriented Al Single Crystals

During the cyclic deformation of [[`5]79] [\bar{5}79] , Al single crystals with a high stacking fault energy produced slip bands that were characterized by wavy slip. Its cyclic stress response curve demonstrated that the specimen experienced hardening–softening–secondary hardening in sequence with repeated fluctuation stresses usually less than 10 MPa, which is far lower than those of Cu, Ni, and Ag single crystals. Finally, the whole surface of the Al single crystals was covered with intense intrusion and extrusion, and the cell structure is the most typical dislocation arrangement. These cells mainly comprise loose clusters of dislocations, which move more freely. In the center of the cell, the dislocation density is relatively low, and most dislocations concentrate in the cell wall. At room temperature, compared with cyclically deformed Cu, Ni, and Ag single crystals, the cyclic deformation behaviors of Al single crystals show significant differences, which are highlighted in this study.     

A Stacking Fault Energy Perspective into the Uniaxial Tensile Deformation Behavior and Microstructure of a Cr-Mn Austenitic Steel

A Cr-Mn austenitic steel was tensile strained in the temperature range 273 K (0 °C) ≤ T ≤ 473 K (200 °C), to improve the understanding on the role of stacking fault energy (SFE) on the deformation behavior, associated microstructure, and mechanical properties of low-SFE alloys. The failed specimens were studied using X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The SFE of the steel was estimated to vary between ~ 10 to 40 mJ/m² at the lowest and highest deformation temperatures, respectively. At the ambient temperatures, the deformation involved martensite transformation (i.e., the TRIP effect), moderate deformation-induced twinning, and extended dislocations with wide stacking faults (SFs). The corresponding SF probability of austenite was very high (~10^?2). Deformation twinning was most prevalent at 323 K (50 °C), also resulting in the highest uniform elongation at this temperature. Above 323 K (50 °C), the TRIP effect was suppressed and the incidence of twinning decreased due to increasing SFE. At elevated temperatures, fine nano-sized SF ribbons were observed and the SF probability decreased by an order (~10^?3). High dislocation densities (~10¹⁵ m^?2) in austenite were estimated in the entire deformation temperature range. Dislocations had an increasingly screw character up to 323 K (50 °C), thereafter becoming mainly edge. The estimated dislocation and twin densities were found to explain approximately the measured flow stress on the basis of the Taylor equation.     

应变速率对Q&P钢拉伸变形行为的影响

以汽车用先进高强度Q&P钢为研究对象,分析了应变速率对Q&P钢拉伸性能及变形行为的影响。结果表明,随应变速率增加,Q&P钢的强度增加,断裂延伸率则呈先下降(10-4s-1～10s-1),后上升至峰值(8×10s-1),之后再下降(102s-1～103s-1)的趋势。变形过程中强度的增加可能同形变回复受限,位错运动受阻有关。而断裂延伸率的变化主要与不同应变速率下Q&P钢中残余奥氏体向马氏体转变(即TRIP效应)有关。     

Effect of Postweld Heat Treatment on the Microstructure and Cyclic Deformation Behavior of Laser-Welded NiTi-Shape Memory Wires

NiTi wires of 0.5 mm diameter were laser welded using a CW 100-W fiber laser in an argon shielding environment with or without postweld heat-treatment (PWHT). The microstructure and the phases present were studied by scanning-electron microscopy (SEM), transmission-electron microscopy (TEM), and X-ray diffractometry (XRD). The phase transformation behavior and the cyclic stress–strain behavior of the NiTi weldments were studied using differential scanning calorimetry (DSC) and cyclic tensile testing. TEM and XRD analyses reveal the presence of Ni₄Ti₃ particles after PWHT at or above 623 K (350 °C). In the cyclic tensile test, PWHT at 623 K (350 °C) improves the cyclic deformation behavior of the weldment by reducing the accumulated residual strain, whereas PWHT at 723 K (450 °C) provides no benefit to the cyclic deformation behavior. Welding also reduces the tensile strength and fracture elongation of NiTi wires, but the deterioration could be alleviated by PWHT.     

Effect of Tempering Time on Microstructure, Tensile Properties, and Deformation Behavior of a Ferritic Light-Weight Steel

In the present study, a ferritic light-weight steel was tempered at 973 K (700 °C) for various tempering times, and tensile properties and deformation mechanisms were investigated and correlated to microstructure. ??-carbides precipitated in the tempered band-shaped martensite and ferrite matrix, and the tempered martensite became more decomposed with increasing tempering time. Tempering times for 3 days or longer led to the formation of austenite as irregular thick-film shapes mostly along boundaries between the tempered martensite and the ferrite matrix. Tensile tests of the 1-day-tempered specimen showed that deformation bands were homogeneously spread throughout the specimen, and that the fine carbides were sufficiently deformed inside these deformation bands resulting in high strength and ductility. The 3-day-tempered specimen showed a small amount of boundary austenite, which readily developed voids or cracks and became sites for fracture. This cracking at boundary austenites became more prominent in the 7- and 15-day-tempered specimens, as the volume fraction of boundary austenites increased with increasing tempering time. These findings suggested that, when the steel was tempered at 973 K (700 °C) for an appropriate time, i.e., 1 day, to sufficiently precipitate ??-carbides and to prevent the formation of boundary austenites, that the deformation occurred homogeneously, leading to overall higher mechanical properties.     

温度冲击对花岗岩动态拉伸力学性能的影响

在特定情况下,岩体工程中的岩石会经历温度快速变化（温度冲击）,因此研究温度冲击对岩石的影响对实际工程中岩体的稳定性分析有重要意义。通过将花岗岩试件加热至3种高温（200,400,600 ℃）,并采用3种方法冷却,研究了温度冲击对花岗岩物理性质的影响;使用分离式霍普金森压杆研究了温度冲击对花岗岩动态拉伸特性的影响,发现其动态拉伸强度随加热温度和冷却速率的增大而减小;使用高速摄影仪记录试件拉伸破坏时的裂纹形态,结合碎块形态,分析温度冲击对花岗岩的损伤程度,得出200 ℃加热条件下花岗岩不产生温度冲击,而在400 ℃和600 ℃加热条件下,花岗岩损伤程度随加热温度和冷却速率的增大而增大。     

The Effect of Solute Content on the Slip Behavior in 7XXX Series Aluminum Alloys

The microstructures of three high strength, high purity Al-Zn-Mg-Cu alloys, in the T6 temper, were characterized extensively using quantitative optical metallography and quantitative transmission electron microscopy. Only the solute content (Mg + Zn) of these alloys was varied for this study. These alloys were shown to be identical in grain size and shape, dispersoid (E-phase) and grain boundary precipitate (ν) populations, and precipitate free zone widths. The matrix microstructures consisted of ordered GP zones and ν′ and differed only in the volume fraction of these strengthening precipitates. The higher solute alloys had the higher yield strengths and volume fractions of matrix precipitates. Subsequent slip behavior analysis of prestrained tensile specimens demonstrated that slip band spacings and slip step heights increased with increasing solute content for the same macroscopic strain (ε_p = 0.02). A work softening model by Hornbogen and Gahr was shown to predict this tendency toward increased strain localization with higher solute levels. Formerly a Research Assistant at Carnegie-Mellon University     

Effect of the Deformation Twin Density on the Corrosion Behavior in TWIP Steel

Based on its excellent tensile strength-ductility property combination,twinning-induced plasticity (TWIP) steel shows great potential in applications for structural components in automobile industry.The aim of this research is to investigate the corrosion resistance properties and corrosion mechanism under room temperature in TWIP steel.The influence of the deformation twin density on corrosion property was primarily considered by salt spray test.The specimens used in the investigation are as-annealed and as-deformed respectively.The microstructure and corrosion resistance property were characterized by scanning electron microscope (SEM),optical microscope (OM) and so on.There are some annealing twins distributed randomly in austenitic grains in the as-annealed specimen.After the specimen was subjected to tensile experiment,the density of the deformation twins increased sharply,which are different from the annealing twins in size and morphology.It was found that the corrosion potential of the as-annealed is lower than that of the as-deformed and the corrosion current density behaves contrarily.After immersed in 5% NaCl solution salt spray for 48h,the as-deformed showed a bit better than the as-annealed in corrosion resistance.With the time prolonged,the gap between the two specimens in corrosion resistance increased rapidly.The corrosion morphologies varied in color and shape.Further investigation,carried out by SEM and EDS,indicated that as-annealed and the as-deformed followed pitting corrosion and uniform corrosion mechanism respectively.The reason for the difference in corrosion mechanism is possibly the presence of the deformation twins.The deformation twins formed during the tensile test refine grains by way of segmentation.The twin boundaries largely belong to the coincidence site lattice (CSL),which is on lower energy state.It suggests that the twins not only play a role in strengthening,but also improve effectively the corrosion resistance in TWIP steel.     

大塑性变形对纯铜力学性能的影响

室温下采用锻压对纯铜进行了大变形加工，对变形后的纯铜样品进行了拉伸和硬度测试，并采用扫描电镜对拉伸试样的断口进行了分析。研究结果表明：经过大变形后，由于纯铜的晶粒得以细化，抗拉强度、屈服强度、硬度和断裂延伸率都显著增加。     

Effect of Interparticle Friction on the Cyclic Behavior of Granular Materials Using 2D DEM

This study presents the influence of the interparticle friction angle on the cyclic behavior of granular materials using the two-dimensional (2D) discrete-element method (DEM). The numerical sample was modeled with oval-shaped particles, whereas the isotropically compressed dense sample was prepared from the initial sparse sample using periodic boundaries. Biaxial cyclic shear tests were simulated with different interparticle friction angles. It was noted that the width of the stress-strain cyclic loops becomes thin when the interparticle friction angle increases. It was also noted that the induced fabric anisotropy is more pronounced during unloading than loading. Moreover, a strong correlation between macro- and microquantities was observed for strong contacts during cyclic loading.     

The Effect of Graphite Fraction and Morphology on the Plastic Deformation Behavior of Cast Irons

The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron.     

Effect of Cu and Li Contents on the Serrated Flow Behavior of Al-Cu-Li Based Alloys

Metallurgical and Materials Transactions A - The serrated flow behavior of Al-Li, Al-Cu and Al-Cu-Li alloys was studied in solution-treated condition under a range of strain rates at ambient...     

Effect of Oxygen Partial Pressure on the Cyclic Oxidation Behavior of Mo76Si14B10

Hot-pressed and arc-melted Mo₇₆Si₁₄B₁₀ (at. pct) exhibits α-Mo solid solution, Mo₃Si, and Mo₅SiB₂ in microstructures with varying morphologies. Cyclic oxidation tests performed at oxygen partial pressures of 0.21 and 1 atm show the mass loss of the hot-pressed alloy to be ≈1.5 and ≈4 times less, respectively, than that of the arc-melted alloy. The thickness of the protective silicate layer increases with an increase of both Mo_ss grain size and oxygen partial pressure in the environment.     

The Effect of Thermomechanical Processing on the Tensile, Fatigue, and Creep Behavior of Magnesium Alloy AM60

Tensile, fatigue, fracture toughness, and creep experiments were performed on a commercially available magnesium-aluminum alloy (AM60) after three processing treatments: (1) as-THIXOMOLDED (as-molded), (2) THIXOMOLDED then thermomechanically processed (TTMP), and (3) THIXOMOLDED then TTMP then annealed (annealed). The TTMP procedure resulted in a significantly reduced grain size and a tensile yield strength greater than twice that of the as-molded material without a debit in elongation to failure (ε _f ). The as-molded material exhibited the lowest strength, while the annealed material exhibited an intermediate strength but the highest ε _f (>1 pct). The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material. The as-molded material exhibited the lowest fatigue threshold values and the lowest fatigue resistance. The annealed material exhibited the greatest fatigue resistance, and this was suggested to be related to its balance of tensile strength and ductility. The fatigue lives of each material were similar at both room temperature (RT) and 423 K (150 °C). The tensile-creep behavior was evaluated for applied stresses ranging between 20 and 75 MPa and temperatures between 373 and 473 K (100 and 200 °C). During both the fatigue and creep experiments, cracking preferentially occurred at grain boundaries. Overall, the results indicate that thermomechanical processing of AM60 dramatically improves the tensile, fracture toughness, and fatigue behavior, making this alloy attractive for structural applications. The reduced creep resistance after thermomechanical processing offers an opportunity for further research and development.     

Effect of Nitrogen Content on the Tensile and Stress Corrosion Cracking Behavior of AISI Type 316LN Stainless Steels

This paper deals with the effect of nitrogen on the tensile and stress corrosion cracking (SCC) behavior of type 316LN stainless steel. Yield stress (YS) and ultimate tensile stress (UTS) increased while the ductility [% total elongation (% TE)] decreased with increasing nitrogen content. Evaluation by conventional assessment parameters, such as ratios of UTS, % TE and SCC susceptibility index, derived by SCC testing using the slow strain rate testing (SSRT) technique indicated an improvement in SCC resistance on increasing the nitrogen content. However, crack growth rates, calculated from ratios of fracture stress from the SSRT tests in liquid paraffin and boiling 45 % magnesium chloride in SSRT tests, and the constant load tests at loads corresponding to 20 % YS in boiling 45 % magnesium chloride conclusively established that the SCC resistance of type 316LN stainless steel decreased with increasing nitrogen content.     

不锈钢带拉矫过程变形行为的数值模拟研究

建立了不锈钢拉伸弯曲矫直过程的有限元仿真模型,该模型针对不锈钢拉矫机辊组配置和旋转压下的特点,采用了窄条三维壳单元对带钢进行特征建模。为提高计算效率,带钢网格进行了局部细化。对304不锈钢典型规格带钢拉矫过程进行模拟,伸长率计算值与实测值吻合较好。对带钢拉矫过程特征位置点经过各辊组的应力应变分析表明:带钢伸长率主要由1号弯曲辊组提供,而2号、3号矫直辊组对带钢伸长率的贡献不明显。该研究得到的不锈钢带拉矫过程变形行为可为拉矫工艺参数确定和优化提供理论基础。