Hydrogen embrittlement of pseudobinary l12-type Ni3(Alo.4Mno.6) intermetallic compound

The mechanical properties of the Ll₂-type intermetallic compound Ni₂(Al_0.4,Mn_0.6), which exhibited enough deformability accompanied with the positive temperature dependence of yield stress, were examined from the point of view of its susceptibility to hydrogen embrittlement. Remarkable and moderate increases of elongation and ultimate tensile strength were observed by evacuating and with increasing strain rate, respectively, although the yield stress was almost constant independent of not only testing environment but also strain rate. On the other hand, the cathodically precharged hydrogen showed deteriorated elongations while the baking treatment resulted in restoration of elongation. Fractographic observation revealed the expected correlation between elongation and fracture mode; with increasing elongation the transgranularly fractured region increased. From this result, it is suggested that hydrogen can be removed from the specimen interior by evacuating or baking, and also that hydrogen can be injected from the sample surface by hydrogen charging; that is to say, hydrogen permeation is almost reversible for both processes. It is thus concluded that the present alloy has severe hydrogen embrittlement susceptibility, both from the residual hydrogen in the specimens as well as from that penetrated from the environment. formerly Graduate Student with Tohoku University, Sendai, Japan,     

Deformation and fracture behavior of an 8090 Al-Li alloy at cryogenic temperature

The deformation and fracture behavior of 8090 Al-Li alloy at low temperature has been studied by the in situ SEM observation of L-T and S-T oriented specimens. It shows that the overall deformation mode of both L-T and S-L oriented specimens changes from the planar slip to the homogeneous deformation with decreasing temperature. Such change in the deformation mode with the test temperature results in the increase in elongation of L-T oriented specimen with decreasing temperature, but not that of S-L oriented specimen. It has been suggested that the different mechanism is operating in controlling the low temperature mechanical behavior of Al-Li alloys depending on the specimen orientation. It shows that the overall deformation mode, e.g., homogeneous deformation vs. planar slip, is critical when the fracture occurs mostly transgranularly such as in L-T orientation. On the other hand, when the fracture occurs intergranularly such as in S-L orientation, other factors such as grain boundary strength play a more critical role than the overall deformation mode.     

Microstructural effects on moisture-induced embrittlement of isothermally forged TiAl-based intermetallic alloys

By using isothermally forged TiAl-based intermetallic alloys, various microstructures (of γ-grain, duplex, dual-phase, and fully lamellar microstructures) were prepared. These TiAl-based intermetallic alloys were tensile tested in vacuum and air as functions of strain rate and temperature to investigate microstructural effects on the moisture-induced embrittlement. All the intermetallic alloys with different microstructures showed different levels of reduced tensile stress (or elongation) in air at room temperature. The reduction in tensile stress (or elongation) due to testing in air diminishes as the testing temperature (or strain-rate) increases. From the fracture stress-temperature curves, it was found that the γ-grain microstructure was the most resistant to the moisture-induced embrittlement, and the dual-phase microstructure was the most susceptible to the moisture-induced embrittlement. Also, the moisture-induced embrittlement of the TiAl-based intermetallic alloys with a fully lamellar microstructure depends on the lamellar spacing and is reduced with decreasing lamellar spacing. The possible reasons for the observed microstructural effect on the moisture-induced embrittlement were discussed, in association with hydrogen behavior and properties in the constituent phases and at some interfaces.     

Influence of Chemical Composition of Mg Alloys on Surface Alloying by Diffusion Coating

A recently developed technique of surface alloying by diffusion-coating has been used to produce coatings on Mg alloys with various Al and Zn contents. The experimental results show that both Al and Zn solutes in the alloy promote the diffusion of alloying elements through grain refinement of the substrate alloys and through reduction of diffusion active energy because of the reduction of melting temperature of the alloys. Therefore, the efficiency of surface alloying increases by diffusion coating. Thick, dense, uniform, and continuous layers of intermetallic compounds, which consist of a τ-phase layer and a β-phase layer, can be produced on the surface of various Mg alloys. The intermetallic compound layers not only have microhardness values that are 4 to 6 times higher than the substrate but also provide effective protection of the Mg alloys from corrosion in 5 pct NaCl solution at room temperature.     

Intermetallic growth and mechanical behavior of low and high melting temperature solder alloys

The presence of an intermetallic is often an indication of good wetting in a solder joint. However, excessive intermetallic growth and the brittleness of the intermetallic layer may be detrimental to joint reliability. This study examined the growth and mechanical behavior of interfacial intermetallics between copper and six solder alloys commonly used in electronics assembly. The solder alloys tested were 60Sn-40Pb, 63Sn-37Pb, 95Sn-5Sb, 96.5Sn-3.5Ag, 50Pb-50In, 50Sn-50In, and 40In-40Sn-20Pb. The 50Sn-50In and 40In-40Sn-20Pb exhibited faster solid state growth of the intermetallic layer at 100 °C as compared to the near-eutectic Sn-Pb control solder. The 50In-50Pb had a slower growth rate, relative to 63Sn-37Pb, at the aging temperature of 170 °C due to slower reaction rate kinetics of indium with copper. The 96.5Sn-3.5Ag and 95Sn-5Sb had similar intermetallic growth rates at 170 °C and 205 °C, and the aging was comparable to that of the 63Sn-37Pb alloy. The 95Sn-5Sb solder/copper intermetallic had a faster growth rate of the Cu₃Sn layer than was observed in the Sn-Ag or Sn-Pb alloys. Modified fracture toughness and low load indentation tests were used to characterize the mechanical behavior of the intermetallics. The intermetallics were harder than both the base metal and the solder alloy. The fracture behavior of the joints in tension was dependent upon the strength of the solder alloy. Solders with low strengths failed in the solder by plastic deformation. The failure of solders with higher strengths was dependent upon intermetallic thickness. When the intermetallic was thin, fracture occurred in the solder or at the solder/ intermetallic interface. As the interfacial intermetallic thickened, the fracture path moved into the intermetallic layer.     

Effect of Al and Gd Solutes on the Strain Rate Sensitivity of Magnesium Alloys

Pure magnesium and two binary alloys, Mg-1 wt pct Al and Mg-1.4 wt pct Gd, have been prepared with comparable grain sizes and textures. The alloys have been tensile tested at various strain rates and temperatures to examine the strain rate sensitivity (SRS). It has been found that Mg and Mg-Al show increasing SRS with increasing deformation temperatures. The Mg-Gd alloy showed decreasing SRS with increasing deformation temperatures and exhibited a negative SRS at 200 °C and 250 °C. Above these temperatures, the SRS returned to a positive value. The elongation to fracture was not effected by the SRS, and it has been concluded that for the alloys and conditions examined, the influences of mechanical twinning and dynamic recrystallization dominate the elongation behavior, rather than the SRS.     

A fractal model for cavity damage and fracture of materials during superplastic deformation

A fractal model for cavity damage and fracture of materials during superplastic deformation is proposed in this paper. The formula which shows the effect of gauge dimensions and grain size on total superplastic elongation was inferred. The formula shows that the finer the grain size, the larger the elongation of specimen and a larger elongation can be obtained by increasing the gauge width and thickness or by decreasing the gauge length of specimen under the same deformation condition. The prediction of the new formula is consistent with most experimental results observed up to now.     

Hydrogen-induced cleavage fracture of Fe3Al-based intermetallics

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.     

Hydrogen-assisted ductile fracture in porous iron

The present paper has studied the effect of porosity and hydrogen on the deformation and fracture properties in porous iron using double notched specimen tests and quantitative metallography analyses to characterize void growth. The presence of hydrogen produced the greatest hardening effect in the sample with a porosity of 0.037. It was found that while the effect of hydrogen on the reduction in area was greatest in the specimen with a porosity of 0.037, its effect on the fracture energy did not depend on the porosity. The ductile fracture surface morphology remained the same in all the specimens without and with hydrogen except for the sample with porosity of 0.003 where hydrogen induced some quasi-cleavage fracture. The quantitative metallography analysis of voids in the region near the fracture surface and below the unfractured notch has demonstrated that hydrogen causes the void growth to increase prior to plastic instability. The effect of hydrogen on the void growth was found to be slightly enhanced as the porosity was increased. The microscopic process of hardening induced by hydrogen is presented. The mechanism for hydrogen-assisted void growth is discussed in light of a recently developed model using a dislocation theory.     

电场时效对铝锂合金性能和断裂特征的影响

研究了电场时效处理对 14 2 0合金板材性能的影响 ,探讨了其作用机理。研究发现 ,电场时效可在一定程度上提高合金的延伸率 ,且试样作负极时效果更明显 ;但电场对合金的强度几乎没有影响 ;电场时效还改变了合金的断裂方式 ,减小了沿晶分层断裂比例 ,增加了穿晶断裂比例和微区塑性变形。电场是通过对空位的作用来影响合金的析出相变、PFZ的形成和合金元素的晶界偏析 ,从而改善合金的性能     

High temperature strength and ductility of recrystallized Ni3Al-Ni3Mn alloys

The tensile properties of pseudobinary Ll₃-type intermetallic compounds based on Ni₃Al and Ni₃Mn were examined on recrystallized specimens. The alloys with manganese composition lower than 15 at. pct were tested from room temperature to 1073 K (1273 K for some alloys). The yield stress appears to be controlled by solid solution hardening (athermal component) at room temperature and by the so-called Kear-Wilsdorf mechanism (thermal component) at elevated temperatures. The activation constant for the latter mechanism,i.e., for the anomalous positive temperature depen-dence of the yield stress, increases with increasing the manganese composition. The tensile elongation shows a maximum at 9 at. pct Mn and at intermediate temperatures (≈700 K). Also, at sufficient higher temperatures (1273 K), an increase of elongation due to dynamic recrystallization was ob-served. The temperature and compositional dependence of the ultimate tensile strength are similar to that of the elongation. The fracture mode was closely correlated with the elongation behavior: the more the transgranular fracture, the higher the ductility. formerly Graduate Student, Tohoku University, Sendai, Japan,     

Characteristics of Mechanical Properties and Microstructure for 316L Austenitic Stainless Steel

 A comparative study on mechanical properties and microstructure of 316L austenitic stainless steel between solution treated specimen and hot rolled specimen was conducted. After a specimen was subjected to solution treatment at 1050 ℃ for 6 min, its mechanical properties were determined through tensile and hardness tests. Based on the true stress vs true strain and engineering stress vs engineering strain flow curves, the work hardening rate has been explored. The results show that the solution treated specimen has an excellent combination of strength and elongation, and that this steel is easy to work-hardening during deformation. Optical microscope, scanning electron microscope, transmission electron microscope and X-ray diffraction examinations were conducted, these reveal that twins in 316L austenitic stainless steel can be divided into suspended twin and transgranular twin which have different formation mechanisms in growth, and that the deformation induced martensite nucleated and grown in the shear band intersections can be observed, and that the fracture surfaces are mainly composed of dimples and exhibit a tough fracture character.     

Effect of ordering on susceptibility to hydrogen embrittlement of a Ni-base superalloy

The effect of ordering on susceptibility to hydrogen embrittlement of a Ni-base superalloy (alloy C-276) has been investigated by means of tensile tests in air and with hydrogen-charging in 1N-H₂SO₄ solution. The annealed specimen has exhibited intergranular fracture by hydrogen-charging, resulting in a marked reduction in tensile elongation and ultimate tensile strength. The mode of fracture was changed by aging at 773 K, and the transgranular fracture has been found to be dominant in the aged specimens. The susceptibility to hydrogen embrittlement, as identified by the test method used in this study, seems to be reduced by short-term aging, though it turns out to be increased again by further aging. The fractured boundaries have been characterized using electron channeling pattern (ECP) analysis of adjacent grains. It is found that the misorientation of grain boundaries plays an important role in fracture, and ∑3 boundaries, twin boundaries in a face-centered cubic (fcc) lattice, are most likely to fracture in the aged specimens. Transmission electron microscopy (TEM) observation has shown that a short-range ordering reaction from a disordered fcc lattice into an ordered Ni₂(Cr, Mo) (Pt₂Mo type) super-lattice takes place by aging, and hence, superdislocation triplets with APB (antiphase boundary) become predominant when deformed. It is also seen that in the aged specimens, deformation twinning is another mode of deformation, and this leads to the transgranular fracture at twin boundaries by hydrogen-charging. These results suggest that a change in the mode of deformation after aging plays a major role in fracture due to hydrogen embrittlement as a consequence of the heterogeneous interaction between slip dislocations and twin boundaries.     

Effect of Graphite Nodule Diameter on Water Embrittlement of Austempered Ductile Iron

DuctileironwasdevelopedbyMorrogh[1]in 1940s.Theappearanceofaustemperedductileiron (ADI)in1970sessentiallyaffectedthemetallurgical researchofductileiron[2,3].ADIhasverygood properties[4-15].Itisproducedbyaustemperingcon ventionalductileiron,andthemicrostr…     

High-temperature environmental embrittlement of thermomechanically processed TiAl-based intermetallic alloys

Thermomechanically processed TiAl-based intermetallic alloys with various alloy compositions and microstructures were tensile tested in various environmental media, including air, water vapor, and a gas mixture of 5 vol pct, H₂ + Ar, as functions of temperature and strain rate. All the TiAl-based intermetallic alloys showed reduced tensile fracture stress (or elongation) in air, in water vapor, and in a gas mixture of 5 vol pct H₂ + Ar, not only at ambient temperature (RT ∼ 600 K), but also at high temperature, from 600 to 1000 K (and sometimes at temperatures higher than 1000 K). The high-temperature environmental embrittlement of TiAl-based intermetallic alloys depended upon the microstructure. The factors causing the high-temperature environmental embrittlement may include hydrogen atoms decomposed from water vapor (H₂O) or hydrogen gas (H₂), similar to those causing the low-temperature environmental embrittlement. Also, it is demonstrated that the oxidized scale is effective in reducing high-temperature environmental embrittlement.     

α污染层对Ti-6Al-4V铸造钛合金组织与性能的影响

对真空冶炼铸造Ti-6Al-4V钛合金(简称ZTC4)表面α污染层的组织、氧氢含量及纳米硬度趋势进行了研究,分析了α污染层对铸造钛合金拉伸性能的影响。结果表明,α污染层为粗大的片状结构,最大深度为0.28 mm;与心部区域相比,氧元素含量增加了1.64倍,氢元素减少了1倍,0硬度值增加了0.94倍,α污染层对ZTC4的拉伸性能影响显著,与不含α污染层试样相比,屈服强度、抗拉强度、延伸率和断面收缩分别降低了14.2%、12.5%、20%和35%,这是由于氧等原子固溶在试样表面形成脆而硬的α污染层,在拉伸载荷作用下α层不易变形形成多源断裂,在材料最薄弱区域形成宏观断裂源并向基体快速扩展,最后形成脆性解理断裂。     

Effect of Yttrium on Microstructures and Properties at Elevated Temperature of Mg-0.8Zr-0.35Zn Alloys

Asthelighteststructuralmetalmaterial ,themostobviousadvantagesofmagnesiumalloyaretheirhighspecificstrengthandspecificstiffness ,superdampingcapacityandmachinability ,excellentelectromagneticshieldingandnon toxicity .Theincreasingattentionhasbeenpaidonthepracticalapplicationofmagne siumalloysastheenergysavingandenvironmentpro tectionarebecomingtheworldfocus .However ,somedisadvantagessuchasignitableandcombustibledur ingmeltingandcastingandtheirrelativelypoorprop ertiesatelevatedtemperaturelimit…     

Study on Co-Permeation of Solid Rare Earth, Boron and Vanadium

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Effect of surface carburization on dynamic deformation and fracture of tungsten heavy alloys

Effects of surface carburization on dynamic deformation and fracture behavior of tungsten heavy alloys were investigated in order to improve the penetration performance. Dynamic torsional tests using a torsional Kolsky bar were conducted on four specimens, three of which were carburized by the case carburization process. The test data were then compared with hardness, Charpy impact energy, adiabatic shear banding, deformation and fracture mode, and penetration performance. With increasing carburization temperature and time, surface hardness increased, but impact energy decreased. The dynamic torsional test results indicated that for the carburized tungsten specimens, cleavage fracture occurred in the center of the gage section with little shear deformation, whereas shear deformation was concentrated at the center of the gage section for the conventionally processed specimen without carburization. The deformation and fracture behavior of the carburized specimens correlated well with the observation of the impacted penetrator specimens, i.e., microcrack initiation at tungsten particles and cleavage crack propagation. Since the cleavage fracture mode is thought to be beneficial for self-sharpening, these findings suggest the beneficial effect of the surface carburization on the penetration performance.     

Effect of Co content on the stress-corrosion cracking behavior of 7091-type aluminum powder alloys

An investigation of the stress-corrosion cracking (SCC) behavior of three aluminum powder alloys, containing 0.0, 0.4, and 0.8 wt pct Co, using double cantilever beam specimens has shown a significant increase in SCC resistance with increasing Co content. This resistance to cracking takes the form of both a decrease in plateau crack velocity and an increase in the threshold stress intensity factor for cracking (K _ISCC ) as the Co content increases. The SCC fracture is intergranular and the crack path is tortuous because of the oxides and Co₂Al₉ intermetallic particles contained within the powder metallurgy alloys. We propose that the improvements in SCC resistance result from the Co₂Al₉ particles, which catalyze the recombination and evolution of hydrogen, thereby reducing hydrogen absorption and embrittlement. Formerly with Martin Marietta Laboratories