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61.
《International Journal of Hydrogen Energy》2019,44(45):25054-25063
The tensile properties and crack propagation rate in a type 316 austenitic stainless steel prepared by vacuum induction melting method with different residual hydrogen contents (1.1–11.5 × 10−6) were systematically investigated in this research work. The room temperature tensile properties were measured under both regular tensile (12 mm/min) and slow tensile (0.01 mm/min) conditions, and the fracture properties of the tensile fractures with both rates were analyzed. It shows that the hydrogen induced plasticity loss of stainless steel strongly depends on the tensile rate. Under regular tensile condition, there is no plastic loss even when the hydrogen content is up to 11.5 × 10−6 while in the slow tensile condition, the plastic loss can be clearly identified rising with the increasing H contents. The fatigue crack propagation rate was tested at room temperature, and the crack growth rate formula (Paris) of the 316 stainless steels with varied H contents were obtained. The fatigue crack propagation rate test shows that the crack growth rate of the 316 stainless steel with 8.0–11.5 × 10−6 hydrogen is significantly higher than that of benchmark steel. 相似文献
62.
《International Journal of Hydrogen Energy》2022,47(4):2723-2734
To investigate the evaluation method of hydrogen compatibility of A286 superalloy in high pressure hydrogen gas, SSRT tests of hydrogen-charged specimens were conducted at ambient temperature at various strain rates. The relative reduction in area (RRA), one of the ductility parameters, was determined. The hydrogen content in the hydrogen-charged specimen was the same as the equilibrium hydrogen content on the specimen surface at 150 °C in 70 MPa hydrogen gas. The strain rate dependence of RRA was smaller than that of RRA obtained in 70 MPa hydrogen gas at 150 °C. All the hydrogen-charged specimens showed slip-plane fractures in the grains in their cores. However, the specimens in 70 MPa hydrogen gas at 150 °C showed fracture surfaces morphology ranging from dimples to quasi-cleavages and intergranular fractures with decreasing strain rate. These dissimilarities are expected to arise from differences in the hydrogen concentration behaviors of the specimens during the deformation process. 相似文献
63.
《International Journal of Hydrogen Energy》2019,44(60):32292-32306
Hydrogen embrittlement (HE) behavior was investigated in a low carbon medium Mn steel with three different volume fraction of retained austenite (RA), which was obtained after different heat treatments. The hydrogen permeation test showed a higher permeability for directly water quenched specimen compared to quench-tempered specimens. Melt extraction test showed hydrogen concentration increased with hydrogen charging current density in the order of directly quenched specimen, QLA, quenched with low-temperature annealed specimens and QHA quenched with high-temperature annealed specimens. Slow strain-rate tensile test was employed to examine the HE behavior, the HE indices decreased with the increase of RA irrespective of increased hydrogen concentration. HE susceptibility can be suppressed by raising intercritical annealing temperature because Mn enrichment increases the stability of RA. 相似文献
64.
Polyethylene, as non-polar material, shows a high affinity especially to liquid non-polar aromatic and aliphatic hydrocarbons, and liquid hydrocarbons (LHC) to a certain extent migrate into the bulk material by sorption, leading to material plasticization (i.e., drop in modulus and yield stress). This paper aims to study the crack growth mechanism and failure behavior of commercial pipe grade materials when exposed to deionized water or LHC (90/10 wt% i-octane/toluene) under the simultaneous application of cyclic loads. The results of the cyclic crack growth experiments with three PE 100 pipe grades, using cracked round bar (CRB) specimens and performed at two different temperatures (35 °C and 60 °C), are compared in terms of the specimen lifetimes, and the micro-modes and kinetics of failure by referring to concepts of fracture mechanics. Most importantly, while crack advance is preceded by crack-tip crazing in water, shear yielding takes place at crack-tips in the LHC environment. 相似文献
65.
《材料科学技术学报》2019,35(11):2647-2651
Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-entropy materials,a novel high-entropy(HE) rare-earth zirconate solid solution(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))2 Zr_2 O_7 was designed and successfully synthesized in this work.The as-synthesized(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2 Zr_2 O_7 is phase-pure with homogeneous rare-earth element distribution.The thermal conductivity of as-synthesized(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2 Zr_2 O_7 at room temperature is as low as 0.76 W m-1 K-1.Moreover,after being heated at 1500 ℃ for 1-18 h,the average grain size of(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2 Zr_2 O_7 only increases from 1.69 μm to 3.92 μm,while the average grain size of La_2Zr_2O_7 increases from 1.96 μm to 8.89 μm.Low thermal conductivity and sluggish grain growth rate indicate that high-entropy(La_(0.2)Ce_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2))_2Zr_2O_7 is suitable for application as a thermal barrier coating material and it may possess good thermal stress-induced cracking resistance. 相似文献
66.
《Journal of the European Ceramic Society》2017,37(4):1865-1871
A very tough zirconia matrix is interesting to fabricate alumina-toughened zirconia (ATZ) and composites generally processed from 3Y-TZP do not exhibit very high toughness. The strategy of lowering the yttria content to increase toughness however is normally associated with an increased hydrothermal aging susceptibility. In this work, a 0.4 mol% La2O3 doped 2Y-TZP matrix was investigated to realize a 20 wt.% alumina toughened zirconia composite with a substantially high aging resistance. The higher transformation toughening in the composite shifted the V-KI towards higher KI values, while preserving the slope of the curve, resulting in a threshold KI0 of 4.0 MPa m1/2 and fracture toughness (KIC) of 7.1 MPa m1/2. These composites can offer a better compromise between aging and crack resistance than traditional 3Y-TZPs and plain ATZ composites without La2O3 doping. 相似文献
67.
Biogeochemical processes mediated by microorganisms in river sediments (hyporheic sediments) play a key role in river metabolism. Because biogeochemical reactions in the hyporheic zone are often limited to the top few decimetres of sediments below the water-sediment interface, slow filtration columns were used in the present study to quantify biogeochemical processes (uptakes of O2, DOC, and nitrate) and the associated microbial compartment (biomass, respiratory activity, and hydrolytic activity) at a centimetre scale in heterogeneous (gravel and sand) sediments. The results indicated that slow filtration columns recreated properly the aerobic-anaerobic gradient classically observed in the hyporheic zone. O2 and NO3- consumptions (256 +/- 13 microg of O2 per hour and 14.6 +/- 6.1 microg of N-NO3- per hour) measured in columns were in the range of values measured in different river sediments. Slow filtration columns also reproduced the high heterogeneity of the hyporheic zone with the presence of anaerobic pockets in sediments where denitrification and fermentation processes occurred. The respiratory and hydrolytic activities of bacteria were strongly linked with the O2 consumption in the experimental system, highlighting the dominance of aerobic processes in our river sediments. In comparison with these activities, the bacterial biomass (protein content) integrated both aerobic and anaerobic processes and could be used as a global microbial indicator in our system. Finally, slow filtration columns are an appropriate tool to quantify in situ rates of biogeochemical processes and to determine the relationship between the microbial compartment and the physico-chemical environment in coarse river sediments. 相似文献
68.
The electrochemical corrosion and mechanical behaviors of the charged magnesium were investigated using Mott–Schottky (M–S) test and slow strain rate test (SSRT), respectively. The results showed that the hole carrier and vacancy concentrations in the corrosion film increased after cathodic charging due to the formation of magnesium hydroxide. The increasing vacancy concentration caused the increase of the permeation rate of hydrogen to the interior of matrix. When the inner stress caused by synergistic effect of hydrogen pressure and expansion stress of the formation of magnesium hydride was above the fracture strength, crack initiated and propagated. It indicated that hydrogen embrittlement (HE) mechanism for the stress cracking corrosion (SCC) of magnesium and its alloys. After cathodic charging, the corrosion resistance and mechanical properties of matrix deteriorated. 相似文献
69.
70.
In this paper, dynamic mechanical analysis (DMA), dielectric spectroscopy (DS) and positron annihilation lifetime spectroscopy (PALS) were used to study chlorinated butyl rubber (CIIR), in order to shed light on its unique relaxation behaviors. The dynamic mechanical loss tangent of CIIR reveals an asymmetrical broad structure with a maximum peak on the high-temperature side and a shoulder peak on the low-temperature side. DS clarifies that the shoulder peak, which exactly corresponds to the ″ peak, is the α process originating from the local segmental motion. While the maximum peak is assigned to the slow process arising from the motion of longer chain segments. The slow process exhibits stronger frequency dependence than the α process. The PALS analysis also shows the two processes; moreover, it suggests that CIIR exhibits very effective chain packing. It is due to the effective chain packing that the motion of longer chain segments is retarded and separates from the local segmental motion in time scale. This effect is another reason for the two-peak structure of CIIR, besides the low intermolecular co-operativity. 相似文献