Subgrain strengthening of aluminum conductor wires

The influence of wire processing variables on the formation of subgrain structures and strengthening in three aluminum conductor materials is described. Electrical conductor grade aluminum, an Al-Fe-Mg alloy and an Al-Fe-Co alloy each develop subgrain structures with mean linear intercepts (•L) in the range of 0.4 to 1.5 μm with several sequences of wiredrawing and partial annealing. The yield strengths of these wires were found to obey a a = σ₀ +k(•L) ^m relationship, with an exponentm = -1 independent of the processing sequence used to arrive at the structure. The role of precipitate particles in the alloys is to raisek above that for EC-A1 while Mg in solid solution increases σ₀. The precipitates also affect the development of the substructure during the wiredrawing and annealing.     

Subgrain strengthening of aluminum conductor wires

The influence of wire processing variables on the formation of subgrain structures and strengthening in three aluminum conductor materials is described. Electrical conductor grade aluminum, an Al-Fe-Mg alloy and an Al-Fe-Co alloy each develop subgrain structures with mean linear intercepts (?L) in the range of 0.4 to 1.5 μm with several sequences of wiredrawing and partial annealing. The yield strengths of these wires were found to obey a a = σ₀ +k(?L)^m relationship, with an exponentm = -1 independent of the processing sequence used to arrive at the structure. The role of precipitate particles in the alloys is to raisek above that for EC-A1 while Mg in solid solution increases σ₀. The precipitates also affect the development of the substructure during the wiredrawing and annealing.

     

Microstructural effects on hydrogen embrittlement in a high purity 7075 aluminum alloy

A high-purity 7075 alloy was heat treated to produce a variety of precipitate sizes and populations in grain interiors and at grain boundaries. Specimens were then evaluated for slip character and hydrogen embrittlement susceptibility following cathodic precharging or by simultaneous cathodic charging and straining. Embrittlement susceptibility was found to correlate very well with the size and type of matrix precipitates, consistent with the rationale that slip character controls the extent of dislocation transport of hydrogen and thereby may control and dominate the distribution of hydrogen in the material and the degree of hydrogen embrittlement. The results also indicate that a smaller role is played by grain boundary precipitates in controlling hydrogen embrittlement susceptibility.     

Precipitation strengthening of the aluminum alloy AA6111

There is an increasing use of aluminum alloy sheet in automotive applications due to the desire to decrease vehicle weight. The current study provides a detailed quantitative study on precipitation strengthening in AA6111, which is the alloy of choice in North America for exposed body panels. Transmission electron microscopy was used to characterize the average size, the size distribution, the volume fraction, and the crystal structure of the hardening precipitates for aging at 180 °C (a) directly after solution treatment and (b) following 2 weeks of natural aging. The results indicate that both β″ and Q′ phases co-exist throughout the aging cycle with the relative amount of Q′ being increased both with increased aging time at 180 °C and when natural aging precedes aging at 180 °C. A strengthening model was developed which uses the size distribution and the volume fraction of precipitates as the primary inputs to predict the yield stress. An important feature of this model was that only one fitting parameter was necessary to give very good agreement with the experimental results.     

Influence of temperature and strain-rate on liquid metal embrittlement of an aluminum alloy containing bismuth inclusions

Elevated temperature, slow strain-rate tensile tests were carried out on a large-grained A1-0.23 wt% Ti alloy containing 1.5 wt% Bi in the form of inclusions present at grain boundaries. It was found that a marked reduction in ductility occurred over a very narrow temperature range (~ 10°C) centred about the Bi melting point for notched specimens tested at a strain-rate of 10^-3 s^-1. Tension tests carried out on smooth samples at three strain-rates 10^-2, 10^-3 and 10^-4 s^-1) indicate that an increase occurs in the severity of embrittlement at higher rates of strain. This observed degradation in mechanical properties is clearly a manifestation of classical liquid metal embrittlement (LME). Fractographic evidence indicates a transition occurs from transgranular fracture by void coalescence to intergranular fracture by grain boundary wedge crack nucleation and growth once the Bi inclusions become molten. At higher temperatures there is a brittle-to-ductile transition after which the strains associated with grain boundary sliding are readily accommodated by grain boundary migration. It was found that a wedge crack nucleation and growth model accounts for the abrupt transition to intergranular fracture due to a reduction in fracture surface energy associated with the melting of Bi.     

Role of heat treatment and cathodic charging conditions on the hydrogen embrittlement of HP 7075 aluminum alloy

The response of an equiaxed-grained, high-purity 7075 aluminum alloy to hydrogen as a function of heat treatment and temperature of cathodic charging has been studied. Room-temperature (RT) tensile tests following RT or 120 °C cathodic charging revealed that hydrogen embrittlement susceptibility was dependent on both heat treatment and charging conditions. However, intergranular behavior was only observed following RT charging, limited to a zone a few grains deep from the surface. This fracture appearance has been considered in terms of the possible formation of an aluminum- or magnesium-base hydride at room temperature, compounds which are thermodynamically unstable at the 150 °C charging temperature. Reasons for the observed embrittlement following high-temperature charging are also considered. Formerly with Carnegie Mellon University.     

物流机器人铝合金机械臂的表面强化与力学性能研究

为提高物流机器人机械臂用铝合金的硬度和拉伸性能,单道熔覆WC-Ni涂层对比分析熔覆层的形貌和硬度,并在拉伸棒表面进行多道熔覆制备拉伸试样。结果显示,随着激光功率的增大,单道熔覆层高度先增大后减小,熔池深度增大,熔覆层宽度增大,稀释率先减小后增大,当激光功率为1.0 kW时单道熔覆层稀释率达到最小,与基体结合强度达到最大,冶金结合效果较优。熔覆层有新相W₂C、NiAl、Ni₃Al、M₇C₃、M₂₃C₆生成,熔覆层顶部由胞状晶组成,中部存在大量WC颗粒和M₇C₃、M₂₃C₆析出相,结合区主要由具有方向性的树枝晶组成。单道熔覆层HV硬度先增大后减小,最大值为960.6,多道抗拉强度为313 MPa,延伸率为1.3%,相比于基体分别提高了21.8%和降低了27.8%,多道熔覆层与基体之间的拉伸断口较平坦。     

强化固溶对2014铝合金组织与性能的影响

铸锭中粗大的第二相和非平衡结晶析出的粗大晶界共晶相具有组织“遗传”效应,常规的铸锭均匀化、铸锭变形加工以及变形态的固溶处理工艺可以提高合金元素的均匀化程度和在铝基体中的固溶度,达到减少粗大第二相和共晶相造成不利影响的目的,但传统的热处理工艺不能彻底消除粗大的第二相,制约了合金性能,通过铸锭强化均匀化和变形组织的强化固溶处理,可以基本消除粗大的第二相,大幅度提高合金的性能,对2014铝合金的研究结果表明,与常规热处理相比,强度提高10％以上,σ_b,σ_(0.2)分别达到531 MPa和471 MPa,此时延伸率仍达到10％。     

A fractographic study of gaseous hydrogen embrittlement and liquid-metal embrittlement in a tempered-martensitic steel

Crack growth in D6ac steel in liquid mercury, gaseous hydrogen, and air environments was studied. Specimens were tested in the as-quenched condition and after tempering at various temperatures up to 700°C. In air, a dimpled transcrystalline fracture mode was observed for all heat-treatments. In mercury and hydrogen environments, the fracture mode and appearance depended on the heat-treatment but was remarkably similar in mercury and hydrogen environments for each condition. Quasi-cleavage, “brittle” intercrystalline fracture, dimpled intercrystalline fracture, and dimpled transcrystalline fracture modes were observed; the dimples observed after fracture in embrittling environments were generally shallower than those observed after fracture in air. The mechanisms of liquid-metal embrittlement and gaseous hydrogen embrittlement are discussed in the light of these observations and other work relevant to understanding the mechanisms of embrittlement. It is concluded that adsorbed atoms at crack tips facilitate dislocation nucleation or possibly decohesion, depending on the fracture mode.     

The cooperative relation between temper embrittlement and hydrogen embrittlement in a high strength steel

A sample plate of HY 130 steel (5 pet Ni-0.5 pet Cr-0.5 pet Mo-0.1 pet V-0.1 pet C) was found to be quite susceptible to temper embrittlement. Step-cooling produced a shift in transition temperature of 583 K (310°C). In the step-cooled condition the plane strain stress intensity threshold for crack growth in 0.1 N H₂SO₂ was about 22 MNm^-3/2 (20 ksi √in. ) and the fracture mode was inter granular, whereas in the unembrittled condition the threshold for a 1.27 cm (1/2 in.) plate (not fully plane strain) was around 104.5 MNm^-3/2 (95 ksi Vin. ) and the fracture mode was mixed cleavage and microvoid coalescence. The interaction between the impurity-induced and the hydrogen embrittlement is discussed in terms of Oriani’s theory of hydrogen embrittlement. Formerly Research Fellow, Department of Metallurgy and Materials Science, University of Pennsylvania     

Grain boundary strengthening at elevated temperatures: Creep of aluminum doped zinc bicrystals and polycrystals

Creep of zinc bicrystals and polycrystals was investigated in the power law creep regime. Very small amounts (less than 0.1 mass%) of aluminum reduced creep rate by one order of magnitude. Grain boundary sliding and migration were impeded by the aluminum addition. Grain boundary strengthening due to mutual constraint of deformation between neighboring grains was proved to be effective in the power law creep regime. This strengthening mechanism was found to be as important as other major strengthening mechanisms available in the power law creep regime. Grain boundary strengthening disappears in pure zinc because of prominent grain boundary sliding, but it appears once grain boundary sliding is prevented by the small aluminum addition. This is the primary cause of the significant strengthening obtained by the small aluminum addition.     

Correlation of gamma-gamma prime mismatch and strengthening in Ni/Fe-Ni base alloys containing aluminum and titanium as hardeners

Various authors have invoked coherency strains and disregistry between the crystal lattices of the matrix and γ′ phase to account for considerable hardening in γ′-strengthened superalloys. Hagel and Beattie correlated the mode of precipitation with the degree of its lattice mismatch. Heydt and Whitney used this approach during the development of an Fe-Ni base high temperature alloy. To understand the role of such a relationship, an investigation of a few experimental Ni-base/Fe-Ni base alloys was carried out. These alloys were strengthened by variable titanium, aluminum, and molybdenum additions and contained chromium. Lattice parameters of the solution treated and aged samples were measured. The γ′ phase was electrolytically extracted for lattice parameter determinations, and γ?γ′ mismatch calculated. The γ?γ′ mismatch calculated. The γ?γ′ mismatch was correlated with room temperature hardness and stress rupture properties at 1200°F. The influence of alloying additions, matrix and γ′ lattice parameters were interrelated.     

Aging embrittlement and grain boundary

“Clean” 3.5NiCrMoV steels with limited contents in trace elements (P, Sn, As, Sb) are commonly provided for manufacturing big rotor shafts. The possible increase in temperature in future steam turbines has promoted the development of “superclean” steels characterized by an extra drastic decrease of manganese and silicon contents. Their higher cost in comparison to “clean” steels leads to concern above which temperature they must be considered as mandatory for resisting aging embrittlement in operation. 3.5NiCrMoV “clean” steel samples (Mn = 0.30 pct; Si = 0.10 pct) were aged at 300 °C, 350 °C, and 400 °C for 10,000 hours up to 30,000 hours. No embrittlement results from aging at 300 °C and 350 °C, but holding at 400 °C is highly detrimental. Auger spectroscopy confirms that, when aging at 400 °C, phosphorus is the main embrittling trace element. It is suggested that grain boundary embrittlement is associated with the building of a layer that contains, on the one hand, Ni and P and, on the other hand, Mo and Cr. Head of the Testing and Head of the Testing and Head of the Testing and     

Dislocation transport and hydrogen embrittlement

Tensile tests of several austenitic stainless steels show that when smooth bar samples are exposed to very high pressure hydrogen significant degradation in mechanical properties is observed. This degradation is accompanied by fracture along interfaces such as grain and twin boundaries although microvoid coalescence remains a prominent fracture feature. The interface cracking and loss in ductility increases as the exposure pressure increases to 172.5 MPa and at the higher pressures the adverse effects of hydrogen are enhanced by warm working operations. Rationalization of these data show that dislocation transport of hydrogen is not required in the embrittlement process; constraint, local lattice dilation, hydrogen content of interfaces are the dominant variables influencing the hydrogen affected fracture processes.     

Radiation-induced changes in bone

Radiation therapy has important applications in curative, adjuvant, and palliative therapy for a wide range of malignant conditions. Evidence of radiation therapy may be seen on radiologic images obtained subsequent to therapy. Bone growth disturbances may be observed in the immature axial or appendicular skeleton. Complications in the mature skeleton include osteoradionecrosis, pathologic fracture, and radiation-induced neoplasms. Radiologic features of mandibular osteoradionecrosis include ill-defined cortical destruction without sequestration. In osteoradionecrosis of the ribs, clavicle, scapula, and humerus, radiography may demonstrate osteopenia, disorganization and coarsening of trabecular architecture, and cortical irregularity; computed tomography more clearly depicts subtle fractures, alterations in bone architecture, and dystrophic soft-tissue calcification. In osteoradionecrosis of the spine, hematopoietic cellular elements of the spinal marrow are replaced with fat, which has high signal intensity on T1-weighted magnetic resonance images and intermediate signal intensity on T2-weighted images. Radiation-induced changes in the pelvis include osteopenia, increased bone density, and widening and irregularity of the sacroiliac joints. Radiation-induced osteochondromas are radiographically identical to those that arise spontaneously. Radiographic findings in radiation-induced sarcoma demonstrate an aggressive pattern of bone destruction. Awareness of the varied radiographic manifestations of radiation-induced changes in bone and correlation with clinical features and the radiation field will usually allow distinction of these changes from those associated with other pathologic conditions.