Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite

Influence de l'hydrogène sur les mécanismes de déformation et d'endommagement des alliages de titane et de zirconium

L'hydrogène, élément rarement dissociable des alliages de titane et de zirconium, confèrent à ceux-ci des propriétés physico-chimiques particulières dont les conséquences sur les processus de déformation et d'endommagement sont incontestables. A travers cet écrit nous faisons une synthèse des résultats acquis dans ce domaine en nous attachant à préciser les relations connues entre les différents états microstructuraux des alliages et les propriétés mécaniques. Le point le plus marquant, dans ce contexte, est le rôle du couple oxygène-hydrogène sur les mécanismes de déformation et d'endommagement

Microstructural size effects on mechanical properties of high purity nickel

International audienceThe aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 mm to 12.5 μm. The influence of the thickness, grain size and ratio thickness to grain size on the mechanical properties and strain hardening were investigated by mechanical tests and TEM observations. The results show the presence of three different domains of mechanical behaviour: polycrystalline, multicrystalline and quasi-single crystalline depending on the thickness and on the number of grains across the thickness. The transition between the three domains is due to the occurrence of surface effects involving a decrease in the long-range internal backstress revealed by the TEM observations

Study of the cyclic softening of an under-aged gamma'-precipitated nickel-base superalloy (Waspaloy)

This study deals with the cyclic behaviour at room temperature of a nickel-base superalloy, strengthened by shearable γ precipitates. A special attention is paid to the influence of the controlled plastic strain εa. Whatever εa, a softening of the stress amplitude follows the first cycles hardening stage. This phenomenon is discussed in terms of back and effective stress evolutions. The decreasing of the total stress amplitude is mainly carried by the kinematic stress lowering, except for the lowest plastic strain level (0.05%), where the isotropic stress decreasing predominates. With the help of dislocations features, the interna1 stress is analyzed as a consequence of simultaneous activation of several slip systems

Microstructural size effects on mechanical properties of high purity nickel

The aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 mm to 12.5 lm. The influence of the thickness, grain size and ratio thickness to grain size on the mechanical properties and strain hardening were investigated by mechanical tests and TEM observations. The results show the presence of three different domains of mechanical behaviour: polycrystalline, multicrystalline and quasi-single crystalline depending on the thickness and on the number of grains across the thickness. The transition between the three domains is due to the occurrence of surface effects involving a decrease in the long-range internal backstress revealed by the TEM observations

Stacking fault energy (s.f.e.) and grain size effects (d) on the tensile behaviour of f.c.c. polycrystalline alloys at 300 K: Back stress and effective stress evolutions

The aim of this work is to provide experimental results to understand grain size and stacking fault energy effects (γ/µb) on tensile hardening f.c.c. alloys. The hardening rate is discussed in terms of back stress (X) and effective stress evolutions. Irrespective of the material studied, tensile hardening behaviour before necking is divided into three stages (I, II, and III). These stages were previously discussed using qualitative and semiquantitative TEM observations [1] . In particular, we have shown that intergranular back stress evolution relates the hardening rate in stage I, where single and planar slip are observed in most of the grains. In the other stages, latent hardening and intragranular back stress are the main parts of the hardening rate in relation with the formation of heterogeneous dislocation structures. An increase of grain size and/or a decrease of stacking fault energy favour planar slip and then stage I, in terms of plastic strain. The transition between stage II and stage III seems to be less dependent on grain sizes irrespectively of s.f.e.. The classical Hall-Petch relation is discussed in terms of back and effective stresses for different plastic strain levels. If these two components verify the Hall-Petch relation, however, effective stress is less dependent on grain size than back stress. This last dependence increases in stage I, where intergranular back stress is the main part of hardening and decreases in the other stages where this component decreases and intragranular back stress increases. The grain size effect on effective stress is well explained in terms of mean length path using dislocation modelling

The Influence of the Back Stress (X) and the Hardening Rate (dX/Xεpqe) on Void Nucleation in α/β Titanium Alloys

The study of void nucleation in four α/β titanium alloys has provided nucleation criteria corresponding to voids at the α/β interface. This macroscopic nucleation criterion, written as ∑m=f(εpqe), was explained with the help of microscopic observations. Microscopic parameters such as plastic strain in the α-phase or local hydrostatic stress σm at the α/β interface have been linked to the damage initiation. Besides, the influence of the different heterogeneity levels on the macroscopic nucleation criterion was demonstrated using the macroscopic mechanical parameters : back stress (X) and hardening rate (dX/Xεpqe) which express the plastic strain incompatibilities and their evolution in such alloys

Influence of deposition parameters on microstructure and contamination of electrodeposited nickel coatings from additive-free sulphamate bath

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