Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature

In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel （AISI 316L） and one nickel-base alloy （Alloy 617） have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromech- anisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650℃.

Indirect Tensile Characterization of Graphite Platelet Reinforced Vinyl Ester Nanocomposites at High-Strain Rate

An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrical compression) test method for brittle materials is utilized along with conventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanoplatelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.

Effects of Strain Rate on Stress Corrosion of S355 Steel in 3.5% NaCl Solutions

The stress corrosion of S355 steel in 3.5% NaCl solution under the different strain rates was analyzed with the slow strain rate test（SSRT）, the stress corrosion cracking（SCC） behaviors of S355 steel under the different strain rates in the solution were investigated, and the fracture morphologies and compositions of corrosion products under the different strain rates were analyzed with scanning electron microscopy（SEM） and energy dispersive spectrometerry（EDS）, respectively. The experimental results show that the SCC sensitivity index is the highest when the strain rate is 2×10-6, and the medium corrosion is the main reason resulting in the highest SCC sensitivity index. The SCC sensitivity index is the least when the strain rate is 5×10-6, and the stress is the main reason resulting in the stress corrosion. The SCC sensitivity index is the middle when the strain rate is 9×10-6, the interaction of stress and medium is the stress corrosion fracture mechanism.

Effect of Temperature and Strain Rate on Dynamic Properties of Low Silicon TRIP Steel

The dynamic tensile test of 0.11C-0.62Si-1.65Mn TRIP steel was carried out at different strain rates and test temperatures. The results show that both temperature and strain rate affect the retained austenite transformation. At high strain rates, the uniform elongation decreases, whereas the total elongation and energy absorption increase. The tensile strength is less strain rate sensitive. With raising test temperature, the tensile strength is reduced and the mechanical properties generally deteriorate, especially at 110℃,However, excellent mechanical properties were obtained at 50℃ and 75℃.

Energy Absorption of Pultruded Glass-Graphite/Epoxy Hybrid Composites under High Strain-Rate Induced Transverse Tension

This paper focuses on the dynamic tensile response of glass-graphite/epoxy composites illustrating improvement in energy absorption through hybridization. The dynamic response and energy absorption characteristics of pultruded hybrid combinations of glass and graphite fibers in an epoxy matrix subjected to induced transverse tension at high strain-rate in a modified Split Hopkinson Pressure Bar (SHPB) apparatus, are presented. Transverse tensile strength was determined by diametral compression of disc samples (Brazilian indirect tensile test method). Diametral crack initiation and strain to failure were monitored with a Shimadzu HPV-2 high-speed video camera at a recording speed of 500,000 fps and Digital Image Correlation (DIC). Adequate measures were taken to ensure that initiation of specimen failure occurred at the exact center of the disc specimen, and propagated through the diameter along the compressive loading axis, for the induced transverse tension tests to be valid. A study of the strength and specific energy absorption demonstrates the benefits of hybridization. Under induced transverse tensile loading condition, the pure glass/epoxy (GL60) exhibited higher strength than pure graphite/epoxy (GR60). Pure graphite/epoxy (GR60) has higher specific energy absorption capacity than pure glass/epoxy (GL60) in transverse tension. Among all hybrids, GR30 has the highest specific energy absorption under transverse tension. Overall, hybrid GL48, with 48% low-cost glass fibers in the inner core and 12% high-cost graphite fibers in outer shell, was found to exhibit better performance under induced transverse tension at high strain-rates, showing the benefits of hybridization.

氯离子质量浓度对Inconel 740H合金应力腐蚀开裂性能的影响

采用慢应变速率拉伸试验和应力腐蚀裂纹扩展试验方法,研究了630~700℃高参数先进超超临界机组候选镍基合金Inconel 740H在0、1、20 mg/L氯离子水环境中的应力腐蚀开裂性能及规律,并探讨了高质量浓度氯离子促进应力腐蚀裂纹的萌生和扩展的相关机理。结果表明:高质量浓度氯离子促进740H合金的应力腐蚀开裂,合金应力腐蚀敏感性指数断后伸长损失I_(scc(δ))随氯离子质量浓度升高而增大;当氯离子质量浓度升高至20 mg/L时,断口中部和断口边缘均呈沿晶脆性断裂特征,断口附近有大量沿晶二次裂纹,此时合金发生了应力腐蚀开裂。在20 mg/L氯离子水环境中裂纹平均扩展速率达1.15×10^(–6) mm/s,是高纯水中裂纹平均扩展速率的111.7倍。

条形缺陷对L360管线钢环焊缝硫化物应力腐蚀开裂敏感性的影响

通过抗硫化物应力腐蚀试验、慢应变速率拉伸试验、氢含量测试等方法研究条形缺陷对H_(2)S环境下L360管线钢环焊缝硫化物应力腐蚀开裂敏感性的影响。结果表明,环焊缝在72%、85%和110%SMYS(最小屈服强度)应力水平下,热影响区出现裂纹且裂纹长度随加载应力增大而增大;条形缺陷环焊缝试样在屈服点后快速发生断裂,其断裂应变(0.024)仅为非缺陷环焊缝试样的21.05%;条形缺陷存在促进氢离子在裂纹尖端聚集从而加剧发生开裂倾向,消氢处理技术可以有效降低氢含量,降低环焊缝抗硫化物应力腐蚀开裂敏感性降低。

应变率对高固含量HTPB推进剂力学特性与破坏机制的影响

通过不同拉伸速率下的单轴拉伸力学性能试验,研究了应变率与90%固含量(固体颗粒的质量分数)HTPB推进剂力学性能之间的相关性,并采用扫描电镜对拉伸断面进行了观察,分析了应变率对推进剂力学性能和破坏机制的影响。结果表明,在低应变率条件下,推进剂的应力—应变曲线出现了弧段现象;随着应变率增加,推进剂应力—应变曲线逐渐由5段式变为4段式;推进剂的初始模量、最大抗拉强度随应变率的增大呈现出上升趋势;推进剂的最大延伸率随应变率增大呈现出降低趋势,在应变率为1190.48×10^(-4)s^(-1)时最大延伸率仅为33.9%;随着应变率增大,高固含量HTPB推进剂的破坏机制逐渐由颗粒“脱湿”转变为基体撕裂,无颗粒破碎产生。

高温水蒸气环境中TP439不锈钢的应力腐蚀开裂敏感性

目的 研究TP439不锈钢在高温水蒸气环境中的应力腐蚀开裂行为,并探讨水蒸气和温度对其应力腐蚀开裂敏感性的影响规律。方法 采用慢应变速率拉伸试验方法研究了TP439不锈钢在400~600℃水蒸气环境中的应力腐蚀开裂行为,利用SEM和EDS分析试样断口区域的形貌及元素分布。结果 同一应变速率(2×10^(-5) s^(-1))下,随着温度在400~600℃范围内升高,TP439不锈钢在空气和水蒸气环境中的屈服强度、抗拉强度和断裂能均逐渐降低,延伸率逐渐增大。400℃和500℃时,试样在水蒸气环境中的抗拉强度较空气环境中有所降低,而延伸率较空气环境中增大。600℃时试样在水蒸气环境中的力学性能较空气环境中无明显差别。试样在400、500、600℃水蒸气环境中的应力腐蚀开裂敏感性指数分别为0.7%、1.2%和-2.8%,应力腐蚀开裂敏感性较低。试样在400~600℃水蒸气环境中的断口均呈现韧性断裂特征,断口形貌整体由韧窝和微孔组成,颈缩现象显著,断口附近未发现二次裂纹。温度在400~600℃范围内升高时,断口的韧窝特征更加明显,颈缩程度逐渐增大,600℃时断口侧面的氧化膜表面Cr含量明显降低,主要由Fe的氧化物形成。结论 水蒸气对TP439不锈钢的应力腐蚀开裂行为起促进作用。基于应力腐蚀开裂敏感性指数和断口的分析,在应变速率为2×10^(-5) s^(-1)的400~600℃水蒸气环境中,TP439不锈钢的应力腐蚀开裂敏感性较低。

硅酸锌车间底漆对船体钢在海水中氢脆行为的影响研究

目的 研究硅酸锌车间底漆对船体钢在海水中氢脆行为的影响,为船舶建造涂装工艺提供数据支撑。方法 采用电化学测试、慢应变速率试验(SSRT)、断口微观形貌观察,考察带有硅酸锌车间底漆的船体钢在海水中的氢脆行为。结果 自腐蚀状态下,船体钢及其涂层试样的SSRT断口均以韧性断裂为主,氢脆系数均小于10%,没有明显的氢脆敏感性。–0.94 V阴极保护状态下,船体钢及其涂层试样的SSRT宏观断口均出现了不同程度的撕裂痕,微观断口出现小解理面特征。以硅酸锌涂层做底漆的试样,撕裂痕以及解理面特征最显著,氢脆系数增大最为明显。当船体钢/硅酸锌/环氧耐磨涂层表面出现破损时,氢脆敏感性系数进一步增大。结论 阴极保护状态下,硅酸锌底漆会增加船体钢在海水中的氢脆敏感性。

高强度马氏体不锈钢的小能量冲击疲劳行为研究

随着钻具失效的不断发生,越来越多的研究者进行服役工况下钻具失效-断裂行为的机理研究。在服役过程中钻具受到复杂载荷的作用,既有静载荷也有大能量单次冲击载荷和小能量多次冲击载荷,小能量多次冲击载荷会造成材料冲击疲劳。研究了新型高强度马氏体不锈钢在不同冲击能量下的材料的冲击疲劳失效行为。结果表明,材料的冲击疲劳寿命的影响因素主要是加载的冲击能量,即冲击能量越高材料的冲击疲劳寿命越低,但冲击能量的变化不会改变材料的断裂形式。在疲劳裂纹萌生阶段,冲击能量的提高可使裂纹快速萌生。在疲劳裂纹扩展阶段,冲击载荷作用于裂纹尖端并使裂纹逐渐扩展。最后,建立了裂纹长度a与循环周次N的函数关系,计算了裂纹的扩展速率。

不同温度下6082铝合金的抗应力腐蚀性能

采用慢应变速率拉伸试验方法研究了6082铝合金板材在不同温度下的抗应力腐蚀性能,采用光学显微镜和透射电镜观察其显微组织,采用扫描电镜对其进行断口分析。结果表明:6082铝合金板材在70℃,3.5%(体积分数)NaCl溶液中的应力腐蚀敏感性指数为6.6%,在50℃,3.5%(体积分数)NaCl溶液中的应力腐蚀敏感性指数为2.3%;试样断口均无应力腐蚀特征,合金晶内析出了弥散分布的细小Mg2Si相,晶界析出了不连续分布的Mg2Si相,不能形成连续的沿晶腐蚀通道,试样表现为较好的抗应力腐蚀性能;温度升高使试样在腐蚀溶液中的抗拉强度下降幅度较大,试样在70℃下的应力腐蚀敏感性指数偏高。

金属材料高温拉伸试验控制模式及试验速率的选择

对GB/T 228.2—2015金属材料高温拉伸试验标准中的方法A和方法B从控制模式、试验速率要求两方面进行了分析解读,选用不同方法和速率从应力-应变曲线、应变速率-时间曲线、屈服强度三方面分析,并对分析设定不同试验速率进行验证。结果表明,采用引伸计反馈控制实施方法A1,实际应变速率波动超差,应力-应变曲线易发生畸变,对Rp0.2的测试结果造成误判;采用横梁位移反馈控制实施方法A2和方法B,选择合适的试验速率,测定参数的应变速率能够满足标准要求,可以获得稳定可靠的应力-应变曲线和较为一致的试验结果。

Effect of hydrogen on the stress corrosion cracking behavior of X80 pipeline steel in Ku'erle soil simulated solution

Hydrogen was a key factor resulting in stress corrosion cracking （SCC） of X80 pipeline steel in Ku＇erle soil simulated solution. In this article, the effect of hydrogen on the SCC susceptibility of X80 steel was investigated further by slow strain rate tensile test, the surface fractures were observed using scanning electron microscopy （SEM）, and the fracture mechanism of SCC was discussed. The results indicate that hydrogen increases the SCC susceptibility. The SEM micrographs of hydrogen precharged samples presents a brittle quasi-cleavage feature, and pits facilitate the transgranular crack initiation. In the electrochemical impedance spectroscopy （EIS） measurement, the decreased polarization resistance and the pitting resistance of samples with hydrogen indicate that hydrogen increases the dissolution rate and deteriorates the pitting corrosion resistance. The potentiodynamic polarization curves present that hydrogen also accelerates the dissolution rate of the crack tip.

Effect of pre-deformation on the stress corrosion cracking susceptibility of aluminum alloy 2519

The effects of pre-deformation and strain rate on the stress corrosion cracking （SCC） behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension （SSRT）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones （PFZ） become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.

Stress Corrosion Cracking of Nitrogen-containing Stainless Steel 316LN in High Temperature Water Environments

Stress corrosion cracking （SCC） of stainless steels and Ni-based alloys in high temperature water coolant is one of the key problems affecting the safe operation of nuclear power plants （NPPs）. The nitrogen-added stainless steel is a kind of possible candidate materials for mitigating SCC since reducing the carbon content and adding nitrogen to offset the loss in strength caused by the decrease in carbon content can mitigate the problem of sensitization. However, the reports of SCC of nitrogen-added stainless steels in high temperature water are few available. The effects of applied potential and sensitization treatment on the SCC of a newly developed nitrogen-containing stainless steel （SS） 316LN in high temperature water doped with chloride at 250 ℃ were studied by using slow strain rate tests （SSRTs）. The SSRT results are compared with our data previously published for 316 SS without nitrogen and 304NG SS with nitrogen, and the possible mechanism affecting the SCC behaviors of the studied steels is also discussed based on SSRT and microstucture analysis results. The susceptibility to cracking of 316LN SS normally increases with increasing potential. The susceptibility to SCC of 316LN SS was less than that of 316 SS and 304NG SS. Sensitization treatment at 700℃ for 30 h showed little effect on the S CC of 316LN S S and significant effect on the S CC of 316 S S. The predominant cracking mode for the 316LN S S in both annealed state and the state after the sensitization treatment was transgranular. The presented conditions of mitigating stress corrosion cracking are some useful information for the safe use of 316LN SS in NPPs.

Mechanical properties and stress corrosion cracking behaviour of AZ31 magnesium alloy laser weldments

An AZ31 HP magnesium alloy was laser beam welded in autogenous mode with AZ61 filler using Nd-YAG laser system.Microstructural examination revealed that the laser beam weld metals obtained with or without filler material had an average grain size of about 12 μm.The microhardness and the tensile strength of the weldments were similar to those of the parent alloy.However,the stress corrosion cracking （SCC） behaviour of both the weldments assessed by slow strain rate tensile （SSRT） tests in ASTM D1384 solution was found to be slightly inferior to that of the parent alloy.It was observed that the stress corrosion cracks originated in the weld metal and propagated through the weld metal-HAZ regions in the autogenous weldment.On the other hand,in the weldment obtained with AZ61 filler material,the crack initiation and propagation was in the HAZ region.The localized damage of the magnesium hydroxide/oxide film formed on the surface of the specimens due to the exposure to the corrosive environment during the SSRT tests was found to be responsible for the SCC.

Behavior of Stress Corrosion Cracking in a Magnesium Alloy

Slow strain rate testing （SSRT） was employed to study the stress corrosion cracking （SCC） behavior of ZE41 magnesium alloy in 0.01 M NaCl solution. Smooth tensile specimens with different thicknesses were strained dynamically in both longitudinal and transverse direction under permanent immersions at a strain rate of 10-6 s-1. It is found that ZE41 magnesium alloy is susceptible to SCC in 0.01 M NaCl solution. The SCC susceptibility of the thinner specimen is lower than that of the thicker specimen. Also, the longitudinal specimens are slightly more susceptible to SCC than the transverse specimens. The SCC mechanism of magnesium alloy is attributed to the combination of anodic dissolution with hydrogen embrittlement.

Improvement of hydrogen embrittlement and stress corrosion cracking by annealing for Al-4.4Mg-0.6Mn alloy

With no annealing treatment, cathodic polarization trends in 5083F A1 alloy revealed concentration polarization and activation polarization. However, the annealed specimens have lower current densities at corrosion protection potential compared to the non-annealed specimen. The results of SSRTs conducted in seawater at the applied potential range of-l.8 V to -0.5 V indicated that the maximum tensile strength, elongation, and time-to-fracture had high values at applied potentials of -0.7 to -1.4 V. The maximum tensile strength, elongation, and time-to-f？acture decreased when the potential values were beyond this range in either anodic or cathodic direction. In general, the increased shear lip caused by annealing treatment indicates elongation. Time-to-fracture would likely increase with elongation. Potentials between -0.5 V to -0.6 V were found to be in the region of stress corrosion cracking. The corrosion protection zone was determined to be -0.7 V to -J,4 V because these potential ranges produced good mechanical properties. Potential less than -1.4 V produced a fractured surface with a mixture of dimples （ductile fractures） and a quasi-cleavage pattern resulting from the effects of hydrogen gas.

Stress-corrosion behavior and characteristics of the friction stir welding of an AA2198-T34 alloy

To better understand the stress-corrosion behavior of friction stir welding(FSW),the effects of the microstructure on the stress-corrosion behavior of the FSW in a 2198-T34 aluminum alloy were investigated.The experimental results show that the low-angle grain boundary(LABs)of the stir zone(SZ)of FSW is significantly less than that of heated affected zone(HAZ),thermo-mechanically affected zone(TMAZ),and parent materials(PM),but the grain boundary precipitates(GBPs)T1(Al2CuLi)were less,which has a slight effect on the stress corrosion.The dislocation density in SZ was greater than that in other regions.The residual stress in SZ was+67 MPa,which is greater than that in the TMAZ.The residual stress in the HAZ and PM is-8 MPa and-32 MPa,respectively,and both compressive stresses.The corrosion potential in SZ is obviously less than that in other regions.However,micro-cracks were formed in the SZ at low strain rate,which indicates that the grain boundary characters and GBPs have no significant effect on the crack initiation in the stress-corrosion process of the AA2198-T34.Nevertheless,the residual tensile stress has significant effect on the crack initiation during the stress-corrosion process.