Slip-band damage and extrusion

1957 ◽  
Vol 242 (1229) ◽  
pp. 198-202 ◽  
Keyword(s):  
Slip Band ◽  
Aluminium Alloys ◽  
Copper Alloy ◽  
Silver Chloride ◽  
Pure Aluminium ◽  
Crystal Material ◽  
Slip Bands ◽  
Local Softening ◽  
Softening Process

Slip-band extrusion was first observed in a fatigued aluminium +4% copper alloy, but has now been found to occur in many other materials. It takes the form of a thin ribbon or scroll of the crystal material projecting as much as 20 μ from the slip band. The thickness of the ribbon varies with different materials and fatigue conditions, that observed on the above alloy being less than 0⋅1 μ . The process of reverse slip which causes slip-band ridges and grooves on the surface of fatigued materials is thought to be the mechanism by which the extrusion occurs. However, the confinement of the slip to a few active planes as occurs in most aluminium alloys is due to some localized softening process. The local softening processes can be identified in some materials as recrystallization, ageing and a combination of both effects. In pure aluminium and some aluminium alloys holes may also be observed along the slip bands. By using silver chloride it has been revealed that both extrusion and crevices may form by what seems to be the same process of reverse slip. In this material, cracks may propagate by the formation of voids ahead of the root of the slip crevice.

Effect of Equal-Channel Angular Pressing (ECAP) on Creep in Aluminium Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 2904-2909 ◽  
Author(s):  
Vàclav Sklenička ◽  
Jiří Dvořák ◽  
Marie Kvapilová ◽  
Milan Svoboda ◽  
Petr Král ◽  
...  
Keyword(s):  
Equal Channel Angular Pressing ◽  
Aluminium Alloys ◽  
Creep Resistance ◽  
Room Temperature ◽  
Creep Behaviour ◽  
Coarse Grained ◽  
Pure Aluminium ◽  
Creep Tests ◽  
Angular Pressing ◽  
Compression Creep

This paper examines the effect of equal-channel angular pressing (ECAP) on creep behaviour of pure aluminium, binary Al-0.2wt.%Sc alloy and ternary Al-3wt.%Mg-0.2wt.%Sc alloy. The ECAP was conducted at room temperature with a die that had a 90° angle between the channels and 8 repetitive ECAP passes followed route BC. Constant stress compression creep tests were performed at 473 K and stresses ranging between 16 to 80 MPa on ECAP materials and, for comparison purposes, on the initial coarse-grained materials. The results showed that the creep resistance of the ECAP processed Al-Sc and Al-Mg-Sc alloys was markedly deteriorated with respect to unpressed coarse-grained materials.

The mechanism of work-hardening and slip-band formation

1957 ◽  
Vol 242 (1229) ◽  
pp. 147-159 ◽  
Keyword(s):  
Single Crystals ◽  
Slip Band ◽  
Work Hardening ◽  
Stage I ◽  
Polycrystalline Materials ◽  
Temperature Dependent ◽  
Band Formation ◽  
Slip Bands ◽  
Three Stages ◽  
The Difference

A summary is given of some present ideas on the mechanism of work-hardening of single crystals and polycrystalline materials. In particular, the difference is stressed between the three stages of hardening: stage I, or easy glide; stage II, the region of rapid hardening accompanied by short slip lines; and stage III, the region of slow or parabolic hardening which is temperature-dependent and in which long slip bands are formed.

Creep Rupture of Ductile Materials under Variable Load

1965 ◽  
Vol 7 (2) ◽  
pp. 193-197
Author(s):  
J. Singer
Keyword(s):  
Aluminium Alloys ◽  
Constant Load ◽  
Creep Rupture ◽  
Rupture Time ◽  
Variable Load ◽  
Pure Aluminium ◽  
Ductile Materials ◽  
Creep Deformations

Hoff derived expressions for the creep rupture time when the creep deformations are governed by the Norton-Bailey law, which yielded results in agreement with experiments for pure aluminium and some aluminium alloys. He later extended the analysis for other creep laws. The author has extended Hoff's analysis for a constant load to a load which varies with time, the material being considered incompressible. Several suitable examples have been considered.

Comparison between Pile-Up Singularities and Stress Fields Induced by Thin Slip Bands. Application to the Prediction of Grain Boundary Microcrack Nucleation

2013 ◽  
Vol 592-593 ◽  
pp. 61-66
Author(s):  
Maxime Sauzay ◽  
Mohamed Ould Moussa
Keyword(s):  
Slip Band ◽  
Tensile Deformation ◽  
Finite Thickness ◽  
Local Stress ◽  
Stress Fields ◽  
Stress Concentrations ◽  
Griffith Criterion ◽  
Slip Bands ◽  
Pile Up ◽  
Microcrack Initiation

Slip localization is widely observed in metallic polycrystals after tensile deformation, cyclic deformation or pre-irradiation followed by tensile deformation. Such strong deformation localized in thin slip bands induces local stress concentrations in the quasi-elastic matrix around, at the intersections between slip bands (SBs) and grain boundaries (GBs) where microcrack initiation is often observed. Since the work of Stroh, such stress fields have been mostly modeled using the dislocation pile-up theory which leads to stress singularities similar to the LEFM ones. The Griffith criterion has then been widely applied, leading usually to strong underestimations of the macroscopic stress to GB crack initiation. In fact, slip band thickness is finite: 20nm-1000nm depending on material, temperature and loading conditions. Then, many slip planes are plastically activated through the thickness, and not only one single atomic plane. To evaluate more realistic stress fields, numerous crystalline finite element (FE) computations have been carried out using microstructure inputs (slip band aspect ratio, crystal and GB orientation...). A strong influence of slip band thickness close to the slip band corner has been highlighted, which is not accounted for by the pile-up theory. But far away, the thickness has a negligible effect and the predicted stress fields are close to the one predicted by the pile-up theory. Closed-form expressions are deduced from the numerous FE computation results allowing a straightforward prediction of GB stress fields. Slip band plasticity parameters, such as length and thickness, as well as crystal orientation, GB plane and remote stress are taken into account. The dependence with respect to the various parameters can be understood in the framework of matching expansions usually applied to cracks with V notches of finite thickness. As the exponent of the GB stress close-field is only about one-half of the pile-up or LEFM crack one, the Griffith criterion may not be used for GB microcrack prediction in case of finite thickness. That is why finite crack fracture mechanics is used together with both energy and stress criteria. Taking into account SB finite thickness, t>0, leads to predicted remote stresses to GB microcrack initiation three to six times lower than the ones predicted using the to pile-up theory, in agreement with experimental data.

Modeling of Fatigue Slip Bands and Application to Notch Fatigue Problems

2008 ◽  
Author(s):  
Hiroshi Matsuno
Keyword(s):  
Fatigue Strength ◽  
Slip Band ◽  
Equivalent Stress ◽  
Cyclic Stress ◽  
Empirical Equations ◽  
Fundamental Idea ◽  
Slip Bands ◽  
Heat Treated ◽  
Fatigue Data ◽  
Stress Ratios

In the present paper, equivalent stress ratios (REQ-ratios), which have been proposed as parameters for correspondence between cyclic stress conditions of notched and unnotched specimens, are reviewed. The REQ-ratios are formulated based on a concept of plastic adaptation hypothesized for a fatigue slip band from a viewpoint of macro-mechanics. A method for diagramming fatigue strength of metals based on the parameter of the REQ-ratios is newly proposed. The method diagramming together the fatigue strength of notched and unnotched specimens is applied not only to fatigue problems of usually annealed, normalized and heat-treated materials but also to those of severely heat-treated and surface-treated ones. Fatigue strength diagrams are characterized with two types of fatigue strength: σw1 and σw2. The character of σw2 appears not only in specimens with sharp notches but also in unnotched specimens fatigue-tested at lower RN-ratios. Criteria on fatigue strength σw1 and σw2 are derived from the fatigue strength diagrams and formulated as empirical equations. Characteristics of fatigue slip bands are reviewed and two types of fatigue mechanisms are proposed related with fatigue strength σw1 and σw2 from a viewpoint of micro-mechanics. Consequently, it is found that the hypothesis of plastic adaptation is a very useful and fundamental idea for modeling a fatigue slip band and also for analyzing fatigue data of practical metals and alloys.

scholarly journals Anodisation of Aluminium Alloys by Micro-Capillary Technique as a Tool for Reliable, Cost-Efficient, and Quick Process Parameter Determination

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Daniela Nickel ◽  
Dagmar Dietrich ◽  
Roy Morgenstern ◽  
Ingolf Scharf ◽  
Harry Podlesak ◽  
...  
Keyword(s):  
Process Parameters ◽  
Cross Sections ◽  
Aluminium Alloys ◽  
Focused Ion Beam ◽  
Corrosion Behaviour ◽  
Film Formation ◽  
Ion Beam ◽  
Parameter Determination ◽  
Pure Aluminium ◽  
Glass Capillary

Anodisation is essential for improving surface properties of aluminium alloys and composites regarding wear and corrosion behaviour. Optimisation of the anodising process depends on microstructural constituents contained in aluminium alloys and represents a key task, consisting of the control of process parameters and electrolyte formulation. We applied the micro-capillary technique known from corrosion studies and modified it to form anodic aluminium oxide films on high-strength aluminium alloys in comparison to pure aluminium in sulphuric acid. A glass capillary with an opening of 800 μm in diameter was utilized. Corresponding electrochemical measurements during potentiodynamic and potentiostatic anodisation revealed anodic current responses similar to conventional anodisation. The measurement of film thickness was adapted to the thin anodised spots using ellipsometry and energy dispersive X-ray analysis. Cross sections prepared by focused ion beam milling confirm the thickness results and show the behaviour of intermetallic phases depending on the anodising potential. Consequently, micro-capillary anodising proved to be an effective tool for developing appropriate anodisation conditions for aluminium alloys and composites because it allows quick variation of electrolyte composition by applying low electrolyte volumes and rapid film formation due to short process durations at small areas and more flexible variation of process parameters due to the used set-up.

A Study of a New Generation of Multi-Functional Aluminium Alloys for the Power Industry

2011 ◽  
Vol 690 ◽  
pp. 439-442 ◽  
Author(s):  
Beata Smyrak ◽  
Tadeusz Knych ◽  
Andrzej Mamala ◽  
Piotr Uliasz ◽  
Michał Jabłoński
Keyword(s):  
Aluminium Alloys ◽  
Power Transmission ◽  
Electrical Power ◽  
Cost Effective ◽  
Present Condition ◽  
Pure Aluminium ◽  
The One ◽  
Manufacturing Technologies ◽  
New Generation ◽  
The Impact

This paper discusses the most current issues of overhead power transmission relative to the development of new conductive materials with unconventional technological and operational qualities. The present condition is based on the one hand on the traditional aluminium-steel conductors with their numerous weaknesses, and on the other hand on state of the art design solutions employing self-supporting, highly-conductive, and thermally and rheologically resistant aluminium alloys. A gap exists between pure aluminium-based conductors which are no longer sufficient and conductors made of precipitation hardened aluminium alloys, which even though they allow to achieve perfect properties, they are not sufficiently cost-effective as for their complex manufacturing technologies. For these reasons, light and sufficiently strong materials based on aluminium are needed, which enable simplified technologies for processing into conductors. Non-precipitation hardened aluminium alloys with such alloy additives as Fe, Si, Cu, Mg, Ti, B, and rare earth metals are preferred in this area. An appropriate composition of these elements, as well as manufacturing and alloy production technology (casting, rolling and drawing) create potential opportunities to obtain wires and conductors with application properties required by electrical power engineering. This paper thoroughly analyses the impact of various elements on the formation of mechanical and electrical properties of aluminium alloys.

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