共查询到20条相似文献,搜索用时 15 毫秒
1.
The difference in the hydrogen charging methods, immersion in a NH4SCN aqueous solution, and cathodic electrolysis in a NaOH aqueous solution, did not affect the hydrogen state present in the steel, but it did affect the surface state of the specimens through corrosion, causing fracture strength to fluctuate in tensile testes. As for stress application method, the fracture strength at lower crosshead speeds in tensile tests was consistent with that found for hydrogen precharging prior to stress application in CLTs as long as hydrogen charging was conducted by cathodic electrolysis. However, the fracture strength obtained with concurrent hydrogen charging without precharging prior to stress application in CLTs was higher than that with hydrogen precharging prior to stress application in CLTs regardless of the same hydrogen content. In other words, delayed fracture susceptibility was affected by the order of hydrogen charging and stress application for quasi-cleavage fracture associated with local plastic deformation, i.e., dislocation motion. Therefore, by taking into account the cathodic electrolysis in the NaOH solution, the low crosshead speed and the order of hydrogen charging and stress application, the fracture strength in CLTs, and tensile tests coincided with respect to quasi-cleavage fracture even though the stress application methods were different. 相似文献
2.
A stress application method in delayed fracture susceptibility tests was investigated using 1450 MPa class tempered martensitic steel. Its fracture mode under hydrogen charging was mainly intergranular because of its relatively small Si content of 0.21 mass pct. The conditions for consistency in fracture strength between tensile tests and constant load tests (CLTs) were clarified: first, to conduct hydrogen precharging before stress application; and second, to choose a sufficiently low crosshead speed in tensile tests. When hydrogen precharging was not conducted before CLTs, the fracture strength was higher than the values in CLTs with hydrogen charging and in tensile tests. If the crosshead speed was too high, the fracture strength obtained was higher than the values in CLTs. The dependence of the fracture strength on crosshead speed was seen for both notched and smooth bar specimens. These results suggested that plastic deformation, i.e., dislocation motion, was related to intergranular fracture with a tear pattern as well as to quasi-cleavage fracture. In addition, cathodic electrolysis in an alkaline solution containing NaOH should be used as the hydrogen charging method to avoid the effects of corrosion. 相似文献
3.
C. L. Baker J. Chene I. M. Bernstein J. C. Williams 《Metallurgical and Materials Transactions A》1988,19(1):73-82
The entry and subsequent interaction of hydrogen on the mechanical properties of the single crystal nickel-base super alloy
CMSX-2 has been studied. Significant amounts of hydrogen were introduced by high temperature hydrogen charging in molten salts
which led to an increased lattice parameter and microhardness and to a degradation in tensile elongation to failure whose
extent scales with the depth of the hydrogenated zone. In this region a fracture mode change from a {111} to a {100} type
also occurred. The values of the binding energy of hydrogen to solidification voids and the effective hydrogen pressure in
the voids were estimate. 相似文献
4.
In this study, the stress corrosion cracking (SCC) resistance of AA5083 is intentionally degraded by a series of progressively longer annealing treatments at 448 K (175 °C) that create a two-phase microstructure. Precipitation of strongly anodic Mg2Al3, known as β-phase, occurs heterogeneously with substantial precipitation along the grain boundaries, as observed by differential interference microscopy. Ultimate tensile strength, yield strength, and strain to failure of AA5083 alloy were found to be independent of the amount of β-phase precipitates, making AA5083 an ideal system to study the relative contributions of anodic dissolution and hydrogen embrittlement. Open circuit dropwise exposure SCC tests with precracked double cantilever beam (DCB) specimens made from the AA5083 alloy with different heat treatment conditions were conducted using 3.5 pct NaCl solution at an initial stress intensity factor (K I ) of \( 1 5\,{\text{ksi}}\sqrt {\text{in}} .\;\left( { 1 6. 5\,{\text{MPa}}\sqrt {\text{m}} } \right). \) Two SCC characteristics, initial crack growth rate and incubation time, were found to be strongly dependent on the amount of β-phase precipitates. Initial crack growth rate increased sigmoidally as a function of heat treatment time with an inflection point between 120 and 240 hours of sensitization time, while the incubation time decreases monotonically with sensitization time. Additionally, fracture surfaces investigated by scanning electron microscopy demonstrated characteristics of intergranular cracking with multiple crack tips. Discussion centers on the evidence supporting anodic dissolution of β-phase grain boundary precipitates as a primary mechanism of SCC in severely sensitized AA5083 alloy and the potential contribution of hydrogen embrittlement in the failure of grain boundary ligaments between β-phase grain boundary precipitates in less severely sensitized conditions. 相似文献
5.
Douglas M. Symons Anthony W. Thompson 《Metallurgical and Materials Transactions A》1996,27(1):101-110
The effect of hydrogen on the fracture of a nickel-base superalloy, alloy X-750, was investigated in the HTH condition. The
effect of hydrogen was examined through tensile testing incorporating observations from scanning electron microscopy and light
microscopy. The ductility at 25 °C, as measured by elongation to failure for tensile specimens, was reduced from 21 pct for
noncharged specimens to 7.3 pct for 5.7 ppm hydrogen and to 3.5 pct for 65 ppm hydrogen. The elongation to failure was a function
of the strain rate and test temperature. For hydrogen-charged specimens, the elongation decreased as the strain rate decreased
at a constant temperature, while for a constant strain rate and varying temperature, there was a maximum in embrittlement
near 25 °C and no embrittlement at -196 °C. For the noncharged specimens, the elongation monotonically increased as temperature
increased, while there was no noticeable effect of strain rate. Prestraining prior to charging dramatically decreased elongation
after hydrogen charging. When the strain rate was increased on the prestrained specimens, more plastic deformation was observed
prior to failure. Failure did not occur until the flow stress was reached, supporting the proposition that plasticity is required
for failure. The intergranular failure mechanism in alloy X-750 was a microvoid initiation process at grain boundary carbides
followed by void growth and coalescence. The void initiation strain, as determined from tensile data and from sectioning unfractured
specimens, was observed to be much lower in the hydrogen-charged specimens as compared to noncharged specimens. The reduced
ductility may be explained by either a reduction of the interfacial strength of the carbide-matrix interface or a local hydrogen
pressure at the carbide-matrix interface. 相似文献
6.
Various heat treatments applied to a fine-grained high strength low alloy (HSLA) steel resulted in producing different grain sizes. Optical and scanning electron microstructures of the different alloy states exhibited varying ferrite grains which have increased with the increase of annealing time and decrease of cooling rates. TEM structures of the as-received HSLA steel displayed characteristics microstructural features, distribution, and morphology of microalloy precipitates. Hardness and tensile strength values have decreased with the increase of grain sizes. Potentiodynamic electrochemical polarization of the different alloy states in 3.5 wt pct NaCl solution showed typical active metal/alloy behavior. Tensile specimens of the as-received and heat-treated alloy cathodically charged with hydrogen, followed by tensile testing, did not indicate any noticeable loss of ductility. FESEM fractographs of hydrogen-charged samples showed a few chain of voids in the presence of cup and cone ductile fracture features in tensile-tested samples without hydrogen charging as well. 相似文献
7.
《Acta Metallurgica Materialia》1993,41(7):1979-1987
Hydrogen embrittlement has been studied in continuous cast sheet of an Ni3Al alloy (Ni77.83Al21.73Zr0.34B0.1). When tensile tests were performed at the initial strain rate of 5.8 × 10−5 s−, the elongation decreased from 32.7% for no charging to 1.9% for 330 min of cathodic charging with 50 mA/cm2 current, but the yield stress did not change. The fracture mode changed partially from dimple to intergranular and cleavage modes. At a faster strain rate of 5.8 × 10−3 s−1, hydrogen embrittlement was less pronounced, but the yield stress increased with hydrogen content and multiple cracks were generated. Plastically pre-deformed (2–26% elongations) and subsequently charged specimens failed after yielding, which occurred at the final pre-deformation stress. Our results suggest that the grain boundary or the interior of the grain was not weakened by hydrogen, rather hydrogen-enhanced localized plasticity caused the loss of ductility in B-doped Ni3Al alloy. 相似文献
8.
9.
The effects of hydrogen on the tensile properties and fracture processes at room temperature were investigated. Specimens
were tested at various strain rates in air or under different cathodic charging-current densities. The slopes of the stress-strain
curves were essentially identical for all the specimens, except that the fracture points varied under different test conditions.
Macroscopically, hydrogen only affected the elastic deformation behavior, but microscopically, the embrittlement was caused
by the heterogeneous nucleation of localized plastic deformation. The degree of hydrogen embrittlement increased as the charging
current increased or as the strain rate decreased. With the same charging current and time, longer dynamic charging resulted
in more severe embrittlement. Before fracture took place, the strength of the alloy could be completely restored if hydrogen
had been removed. Hydrogen diffusivity and solubility were used to draw the time-dependent hydrogen concentration profiles
for the specimens under different charging conditions. The difference in the mechanical properties was correlated with the
hydrogen concentration within the specimen.
Formerly Graduate Student, Department of Materials Science and Engineering, National Tsing Hua University. 相似文献
10.
摘要:对热轧0.1C-5Mn中锰钢进行了3种不同的处理制度:在两相区分别进行5min(TG7样)和30min退火(TG8样),随后将一部分TG8样再500℃回火60min(TG8-500样),其余TG8样则拉伸预变形5%(TG8-5%样),然后利用电化学充氢和慢应变速率拉伸实验研究了3种试样的氢脆敏感性。结果表明,3种试样的奥氏体体积分数均约为12%,然而其氢含量和氢脆敏感性却不同,其中TG8-500样几乎不呈现氢脆敏感性,而TG7和TG8-5%样的氢脆敏感性指数分别为56%和67%。扫描电镜断口分析表明,充氢的TG7和TG8-5%样的拉伸断口呈现穿晶+沿晶的混合断裂机制,而充氢的TG8-500样则呈现韧窝韧性断裂,且存在较多的二次裂纹。3种实验钢氢脆敏感性的这种差异主要与其微观组织特征特别是原奥氏体晶界的逆转变奥氏体有关。 相似文献
11.
Hydrogen-induced fracture of ductile Fe3Al-based intermetallics was studied through mechanical testing, fracture surface observation, andin situ transmission electron microscopy (TEM) tests of tensile specimens. Mechanical properties of ordinary ductile X-80 pipeline
steel (low-alloy steel) were tested and compared with Fe3Al intermetallics. Elongations of the Fe3Al alloy decreased from 14 to 10 pct, with increases in the strain rate from 10−6 to 10−3/s. The elongation reduction of Fe3Al was caused by the hydrogen-induced fracture. There was no elongation reduction when the testing was done in mineral oil.
Non-necking occurred near the fracture section, and the fracture surfaces mainly consist of cleavage and partial intergranular
morphologies. Elongation near the fracture surface of the Fe3Al intermetallics was about 14 pct, which is the same as the total elongation. For the pipeline steel, however, an elongation
near the fracture cross section was greater than 130 pct, which was much higher than its total elongation of 17 pct.In situ TEM observation on a tensile test sample showed crack propagation accompanied by dislocation plasticity. When the Fe3Al was precharged cathodically, the crack tip was sharp. Its radius was much less than that obtained without hydrogen charging.
The crack propagated along the grain boundary for the charged specimens, but penetrated the grain boundary for the specimen
without hydrogen charging. Effects of hydrogen on plastic deformation and grain-boundary cracking are discussed in this article. 相似文献
12.
Yunsung Kim Dongjun Shin Youngsuk Kim Dae Whan Kim Sungsoo Kim Wonjong Nam Yong‐Suk Kim Kristián Máthis Heeman Choe 《国际钢铁研究》2013,84(8):812-817
The thin‐plate specimen of 316L austenite stainless steel was charged with hydrogen using a cathodic charging technique. Despite the short diffusion distance of hydrogen predicted by the diffusion‐controlled model for a semi‐infinite sheet, the Vickers hardness measurements revealed the full effect of hydrogen in the center of the cross‐sections of thin‐plate specimens as well as in the vicinity of the outer surfaces, which appears to be due to the short‐circuit diffusion mechanism along the grain boundaries. The room‐temperature tensile properties of both undeformed and deformed (20, 40%) samples were examined and compared. Hydrogen softening was apparent in both types of samples. For example, the 40% deformed sample showed an approximately 17 and 7% lower yield and tensile strength, respectively, after H charging at a strain rate of 2 × 10?4 s?1 with a concomitant decrease in ductility compared to that without H. 相似文献
13.
14.
采用室温拉伸、光学显微镜和扫描电镜研究了不同恒载荷条件下7055铝合金型材的应力腐蚀性能。结果表明,在腐蚀周期内,随着应力腐蚀载荷的提高,试样的强度并未出现明显的下降,而塑性下降40%。应力腐蚀载荷越接近材料的屈服强度,塑性下降就越明显,抗拉应变和延伸率均有降低。应力腐蚀试样表层部分区域有明显的点蚀、沿晶腐蚀空洞和裂纹;拉伸时,腐蚀缺口处会产生明显的应力集中而成为起裂源,拉伸断口边缘被腐蚀区域为明显的沿晶断裂。 相似文献
15.
H. Couque R. J. Asaro J. Duffy S. H. Lee 《Metallurgical and Materials Transactions A》1988,19(9):2179-2206
An investigation was conducted into the effects of temperature, loading rate, and various micro-structural parameters on the
initiation of plane strain fracture of a plain carbon AISI 1020 steel. Ferrite and prior austenite grain sizes were chosen
as the principal microstructural features to be in-vestigated. The microstructural variations were accomplished by changing
the austenitizing tempera-ture and by altering the cooling rate during normalization. Fracture toughness tests were conducted
using precracked notched round bars loaded in tension to produce two stress intensity rates,viz.,K
1 = 1 MPa √m s-1 andK
1
= 2 × 106 MPa √m s-1. In addition, Charpy impact tests along with quasistatic and high rate plasticity tests were conducted. The plasticity tests
were done in torsion at shear strain rates of
. Testing temperatures covered the range from -150 °C to 150 °C which encompassed fracture initiation modes involving transgranular
cleavage to fully ductile fracture. Micromechanical processes involved in void and cleavage micro-crack formation were identified
and quantified. For these purposes notched round tensile tests and subsequent metallographic observations along with TEM and
SEM observations of the plane strain fracture toughness specimens were performed. The experimental results and quantitative
micro-modeling using simple fracture models provide a means of correlating both quasistatic and dynamic fracture toughness
with microstructures. 相似文献
16.
尽管中锰钢的强塑性等力学性能得到了较大幅度提升,但要大规模地应用于汽车部件制造,仍需解决材料在制造和服役过程中面临的氢脆等系列难题,在此背景下,利用电化学充氢、氢热分析仪、慢应变速率拉伸试验机及扫描电镜等研究了两种不同状态(热轧和温轧)0.1C 5Mn中锰钢在650 ℃保温30 min(两相区退火处理)后的氢脆敏感性。结果表明,热轧和温轧退火样的微观组织分别为板条状及等轴+板条状的铁素体与奥氏体的复相组织。尽管温轧退火样的强度比热轧退火样提高了约150 MPa,伸长率降低了约5%,但两者的强塑积均可达到约33 GPa·%。两种试验材料充氢时吸附的氢绝大部分为对应低温逸出峰的可扩散性氢,温轧退火试验材料的氢脆敏感性低于热轧退火钢。充氢热轧退火样断口起裂处的断裂机制为穿晶断裂+沿原奥氏体晶界的脆性沿晶断裂;温轧退火样的起裂处则为空心韧窝+包括奥氏体(变形后转变为马氏体)晶粒的实心韧窝,后者实际上为沿着奥氏体和铁素体界面起裂的一种脆性沿晶断裂。造成两种试验材料氢脆敏感性不同的原因主要是其微观组织及其所引起的氢致断裂方式的差异。 相似文献
17.
Effect of hydrogen charging on dislocation behavior in Ni-Cr and Ni<Subscript>2</Subscript>Cr alloys
Kaori Miyata 《Metallurgical and Materials Transactions A》2003,34(6):1249-1257
The effects of hydrogen charging on the dislocation behaviour in Ni-Cr binary alloys have been investigated by means of transmission
electron microscope (TEM) observations using single-crystalline specimens. The deformation mode of Ni-Cr alloys in the absence
of hydrogen is characterized by planar dislocations. However, hydrogen charging changed the dislocation configurations to
promote curved dislocations, such as dislocation loops and dipoles. The hydrogen-affected dislocation configurations are enhanced
with increasing Ni content and reducing Cr content. Weak-beam images show that the Shockley partials of the hydrogen-affected
dislocations frequently constrict to make kinks and cross-slip, as if the dislocations were generated by a thermally activated
process. The effect of hydrogen charging on superdislocations of a Ni2Cr superstructure has been also investigated using an aged 70Ni-30Cr alloy. While the deformation mode in the Ni2Cr superlattice is classified as five variants of superdislocation triplets and one variant of ordinary dislocations, the
hydrogen charging has preferred the ordinary dislocations to the superdislocation triplets. The results suggest that the charged
hydrogen changes the local plasticity to affect the deformation dynamics in Ni-Cr alloys, where the influence of hydrogen
on the plasticity is sensitive to the Ni/Cr concentration and the symmetry of atomic arrangement. 相似文献
18.
19.
C. S. Carter 《Metallurgical and Materials Transactions B》1971,2(6):1621-1626
The effect of heat treatment on the tensile, fracture toughness, and stress corrosion properties of a high strength maraging steel (nominal composition 16.3 Ni?12.87 Co?4.98 Mo?0.78 Ti) is described. A maximum ultimate tensile strength of 323 ksi, combined with a fracture toughnessK Ic of 62 ksi \(\sqrt {in} \) , was achieved. This strength level appears to be the maximum which can be achieved in maraging type steels without decreasing the crack tolerance below that of currently used high strength low alloy steels. Reversion to austenite did not improve either the fracture toughness or stress corrosion resistance relative to completely martensitic microstructures with equivalent strength. 相似文献
20.
Fatemeh Yousefi Reza Taghiabadi Saeid Baghshahi 《Metallurgical and Materials Transactions B》2018,49(6):3007-3018
In this study, the mechanical properties of as-cast and FSPed Al-2Ni-xMn alloys (x?=?1, 2, and 4 wt pct) were investigated and compared with those of the as-cast and FSPed Al-4Ni alloy. According to the results, the substitution of 2 wt pct Mn for 2 wt pct Ni leads to the formation of fine Mn-rich intermetallics in the microstructure increasing the tensile strength, microhardness, fracture toughness, and specific strength of alloy by 22, 56, 45, and 35 pct, respectively. At higher Mn concentrations, the formation of large Mn-rich platelets in the microstructure reduces the tensile properties. Friction stir processing at 12 mm/min and 1600 rpm significantly enhances both the strength and ductility of the alloy. The tensile strength, yield strength, fracture strain, fracture toughness, microhardness, and specific strength of FSPed Al-2Ni-4Mn alloy improved by 97, 83, 30, 380, 152, and 110 pct, respectively, as compared to those of the as-cast Al-4Ni alloy. This can be attributed to dispersion strengthening of Ni- and Mn-rich dispersoids, formation of ultrafine grains, and elimination of casting defects. The fractography results also show that the brittle fracture mode of the as-cast Mn-rich alloys turns to a more ductile mode, comprising fine and equiaxed dimples in FSPed samples. 相似文献