Determination of dislocation boundary spacings from length per area measurements in EBSD data sets

In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor is derived for isotropic microstructures.Two measures based on length per unit area for the determination of the cross-link boundary spacing in high strain deformation microstructures are then compared.A geometric method based on subtraction of the contribution to the length per area of the lamellar boundaries gives the best results,though in some cases a method based on boundary misorientation angles may be preferred.

Observation on Emitting Dislocation from Grain Boundary by TEM

The observation on emitting dislocations from grain boundaries by TEM during Cu elongation has been performed. It is shown that there exists the 'ledge' at the grain boundaries in fee pure Cu, which is able to emit dislocations into grain under action of stress.

Temperature dependence of microstructure and texture in cold drawn aluminum wire

The effect of strain and drawing temperature on the evolution of microstructure and fiber textures of aluminum wiresdrawn at room temperature and cryogenic temperature was investigated by TEM and EBSD observations.The results show that lowangle boundaries frequency increases and high angle boundaries frequency decreases with strain increasing when the strain is low.Athigh strain,most of grain and dislocation boundaries are parallel to the drawn direction and low angle boundaries frequencydecreases and high angle boundaries frequency increases with strain increasing.The decrease of deformation temperature leads tomicrostructure finer and low angle boundaries frequency increasing.Texture analysis indicates that volume fraction of complextexture component decreases with strain increasing and a mixture of?111?and?100?fiber texture forms at high strain.?111?is stableat low strains but?100?becomes stable at high strain.The decrease of temperature can enhance the stability of?111?orientation athigh strain.

A STUDY OF RATE-DEPENDENCE AT ELEVATED TEMPERATURE FOR AN Al-Cu-Mg ALLOY

The hot deformation of an Al-Cu-Mg alloy was studied in the two temperature ranges (room temperature-300℃ and 400℃-480℃). The rate-independent flow curves are typical of elasto-plastic response with significant work hardening followed by strain softening below 300℃. Similar dislocation structures with high density tangled into grain interiors were observed by TEM, which suggests that the process of obstacles arresting mobile dislocations results in this macroscopically rate-independence. At 400-480℃, all rate dependent flow behaviors characterized by a continuous softening after an initial work hardening at a small plastic strain show large tensile elongations. Long dislocation segments around the second phases infer their good mobility to climb across obstacles. Grain boundary morphology observed by TEM suggests that the capacity of the grain boundaries to absorb the dislocations sensitively accounts for the rate-dependent mechanical properties.

Strong size effect on deformation twin-me diate d plasticity in body-centered-cubic iron

Deformation twinning serves as an important mode of plastic dissipation processes in nanoscale body-centered cubic(BCC)metals,but its origin and spatio-temporal features are mysterious.Here,applying in situ tensile experiments,we report a strong size effect on mediating the twinning behaviors and twin boundary(TB)-dislocation interaction mechanisms in BCC iron(Fe)nanowires(NWs).There exists a critical diameter(d)of∼2.5 nm,above which the deformation twinning rather than dislocation slip dominates the plasticity.Unlike the traditional reflection TBs,the intermediate isosceles TBs are consis-tently observed as mediated by the 1/12<111>partial dislocations.Moreover,we uncover two distinct TB-related deformation mechanisms,including twin variant re-orientation and TB cracking for NWs with d<17 nm and d>17 nm,respectively.Further molecular dynamics and statics simulations provide the basic underlying mechanisms for size-dependent plasticity,which have been largely overlooked in previous experimental investigations.Our findings highlight the importance of grain size in mediating the deformation behaviors in Fe,serving as possible guidance for exploring single-crystalline and poly-crystalline Fe-based materials(e.g.steel)with optimized mechanical performance.

Effect of Strain Path Reversal on Austenite Grain Subdivision and Deformation Induced Ferrite Transformation Studied by Hot Torsion

The effects of large strain and strain path reversal on the deformation microstructure evolution in austenite below the recrystallisation temperature were studied by hot torsion using a non-transforming Fe-30wt%Ni model austenitic alloy.Results show that the high angle boundaries (HABs) can be generated by both microstructure mechanism through dislocation accumulation and texture mechanism via subgrain rotation.However,multiple strain path reversals lead to less well-developed HABs in the original grains compared to single reversal deformed to the same amount of total accumulative strain.This effect is attributed to the subgrain rotation mechanism being less effective at small strains.In comparison,the same hot torsion tests were conducted using a microalloyed steel at a temperature between Ae 3 and Ar 3.After single strain path reversal,substantial deformation-induced austenite-to-ferrite phase transformation was observed.Meanwhile,a test with multiple strain path reversals but with the same total strain produces much lower levels of strain-induced ferrite formation.This difference is correlated to the observations made in the Fe-30wt%Ni model alloy.It is believed that the different amount of strain-induced ferrite originated from the different levels of strain-induced HABs within the austenite which act as ferrite nucleation sites.

Revealing substructure in clock-rolled Ta aided with triple focused ion beam

Clock rolling was developed to make defor- mation microstructure homogenize in high-purity Ta. The substructure of deformed Ta was revealed by electron back-scatter diffraction （EBSD） technique aided with triple focused ion beam （FIB）. The results indicate that the triple FIB method can produce a mirror surface required by EBSD analysis. The clock rolling works well for the homogenization of deformed microstructure. Particularly, the local stored energy in { 111 } orientated grains is largely reduced by clock rolling, whereas it is enhanced in {100} orientated grains because of the occurrence of grain subdivision.