Difference In Plastic Deformation Research Articles

Nanoscratching-induced plastic deformation mechanism and tribology behavior of Cu/Ta bilayer and multilayer by a molecular dynamics study

Molecular dynamics simulations are adopted to study the deformation mechanism and friction and wear properties of Cu/Ta bilayer and multilayer during a nanoscratching process. The results indicate that in bilayer the Cu/Ta interface adsorbs and blocks dislocation propagation, while the Ta/Cu interface acts as an emission source of dislocations. In multilayers (particularly for thickness δ = 25 Å), the dislocation could overleap the hard Ta layer and then nucleate in the next Cu layer although the friction shear is still in the first Cu layer, indicating the deformation transition of plasticity-elasticity-plasticity across Cu/Ta/Cu layers due to stress transfer. The increase in monolayer thickness facilitates dislocation propagation and deformation recovery, as well as surface removal quantified by wear volume. Severer plastic deformation and surface removal occur in Cu layer while higher friction appears in Ta layer. The preferred accumulation of worn Ta atoms in the left front, up to 80% in δ = 45 Å multilayer and 60% in others, is observed and attributed to the nonsymmetrical slip directions. The differences in plastic deformation and tribological property indicate a critical thickness of about 25 Å used to guide the ultraprecise manufacture of Cu interconnections in microdevices or semiconductor industry.

A CDM-like constitutive law for predicting degradation of strength and ductility of steel subjected to cyclic loading

This paper presents a continuum-damage-model-like constitutive law embedding cohesive cracks with plasticity-induced damage to represent the degradation of strength and ductility of steel under cyclic loading. The proposed constitutive law accommodates an arbitrary hyperelasticity-based plastic model with the use of the deformation gradient multiplicatively decomposed into separation-induced, elastic and plastic parts, and incorporated with an additional isotropic hardening rule endowed with a memory surface. While the elastic–plastic deformation along with isotropic and kinematic hardening is represented by a Hencky-type model, the separation-induced deformation gradient due to material separation is employed to embed an arbitrary cohesive traction separation law (CTSL) into the hyperelasticity-based plastic model. Also, a plasticity-induced damage variable is added to the selected CTSL to degrade the critical energy release rate. In addition, a new material constant is introduced to adjust the ratio between the critical values of cohesive traction and material separation width in the CTSL. On the other hand, the additional hardening rule depending on memory surface is appended in conjunction with the conventional isotropic and kinematic hardening rules to reflect the difference in plastic deformation with various ranges of cyclic loading. Several experiments are conducted to identify the material parameters and verify the validity of the proposed model. By reference to the experimental results, the capability of our proposed constitutive law is demonstrated in predicting the degradation of tensile strength and breaking elongation of a steel after cyclic loading.

Effect of bainite morphology on deformation compatibility of mesostructure in ferrite/bainite dual-phase steel: Mesostructure-based finite element analysis

Ferrite/bainite (F/B) dual-phase pipeline steels with excellent balance of strength, ductility, and toughness have been broadly applied in oil and gas pipeline transmission. While, the deformation capacity of the steels is related to the grain size, volume fraction and morphology of the two phases. In this work, Representative volume elements (RVE) models based on real mesostructure and abstract model were built, and then the effect of the bainite morphology on the deformation compatibility of the mesostructure for F/B dual-phase steels were studied. Results show that the bainite morphology influence the strain localization within the mesostructure during the deformation process, as a result, the mesostructure with banded bainite possesses better deformation compatibility than the mesostructure with equiaxed bainite. Based on the abstract model, the aspect ratio of bainite significantly affects the deformation compatibility between the ferrite and bainite. The difference of plastic deformation (DPD) and the strain localization factor (SLF) rapidly decrease when the aspect ratio of bainite increases from 1 to 3.06. With the further increase of the aspect ratio of bainite, the DPD and SLF have a little change. The results will help to comprehend the deformation mechanism of the F/B dual-phase steels.

Comparative analysis of plastic deformation of NiTi and CuNiTi wires submitted to mechanical cycling

Objective: The aim of this study was to evaluate the plastic deformation of NiTi and CuNiTi archwires submitted to mechanical cycling. Material and Methods: Orthodontic archwires made of CuNiTi of five commercial brands (n=10) were used: RMO, Orthometric, Ormco, Aditek and Eurodonto; and a Control Group of NiTi archwire: Aditek thermoactivated. All the archwires, with caliber 0.016”, were fitted into the slots of four conventional brackets, aligned and fixed to an acrylic plate. The test was performed by applying a load of 3 N and frequency of 2 Hz between the most central brackets, limited to 10,000 cycles. After cycling, the presence or absence of archwire fracture was observed. When there was no fracture, the archwires were analyzed relative to plastic deformation with the use of a transferer, measuring the angulation of the deformed archwire. Results: The results showed that there was no fracture in any of the wires analyzed. The Kruskal-Wallis test showed differences among the angulations of the orthodontic archwires (p=0.0009). With exception of the Ormco wires, the other types presented plastic deformation. The highest median of the angulation value was observed for the Aditek Copper NiTi archwire. The lowest median values were observed for the RMO, Eurodonto and Ormco archwires. The Aditek thermoactivated and Orthometric archwires presented intermediate angulation. Conclusion: None of the archwires analyzed presented fracture. These archwires presented differences in plastic deformation, irrespective of the presence of copper in their chemical composition. The Ormco archwire was the only type that presented no deformation whatever. KeywordsMechanical cycling; Copper; Deformation; Orthodontic wires; Fracture.

410 中性子回折によるフェライト鋼の圧縮引張変形その場測定(OS4-(3),OS4 オーガナイズドセッション≪材料・組織と加工≫)

Plastic deformation is known to be affected by texture, distribution of crystal orientation in grain, because of the difference of mechanical property in each grains. The difference of plastic deformation in crystal orientation is considered to be a cause of an internal stress between namely, "hard" and "soft" grain. However, the detail mechanism of producing the internal stress is unclear. In the present study, change of lattice plane distance during compressive and tensile deformation in Ferritic steel was measured by in-situ neutron diffraction. As a result, residual lattice strain of each grain shows anisotropic behavior by its crystal orientation.

Comparative study of symmetric and asymmetric deformation of Al single crystal under microscale laser shock peening

Laser shock peening by a micron sized laser beam is a process in which compressive residual stresses are induced in order to improve material fatigue life of micro scale components. The size of the laser target interaction zone is of the same order of magnitude as the target material grains and thus the effects of anisotropic material response must be taken into account. Single crystals are therefore chosen to study such anisotropy. It is also of interest to investigate the response of symmetric and asymmetric slip systems with respect to the yield surface. In presented work, analytic, numerical and experimental investigations of two different orientations, (110) and (1 1 4) of aluminum single crystals are studied. Anisotropic slip line theory is employed for the construction of slip line fields for both orientations and compared with numerical results. Theory is further used to explain the difference in plastic deformation for two different orientations. Lattice rotations on the top surface and cross section are also measured using Electron Backscatter Diffraction (EBSD), while residual stress is measured using X-ray microdiffraction. Both the analytical and numerical models are then validated via experimental results.

Effect of surface chemistry on the mechanical response of metals in sliding tribocorrosion systems

The effect of the applied potential on the deformation behaviour of a 316L stainless steel subject to tribocorrosion was investigated using a tribometer equipped with an electrochemical cell. Two potentials were compared: a cathodic potential where no oxide forms on the metal surface and a passive potential where a few nanometer thick oxide film forms. The wear, frictional and electrochemical response was recorded as a function of the number of sliding cycles. In parallel, wear morphology and near surface micro-structure of the steel were analysed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Significantly higher wear was observed at the passive potential; neither dissolution reactions nor differences in friction could account for this difference in deterioration. TEM analysis revealed that differences in plastic deformation of the steel appear between passive and cathodic conditions already from the first sliding cycle. The near surface microstructure of the wear track formed at passive potential exhibited smaller grain size and the presence of deformation α′ martensite. This effect was attributed to the passive film that, despite its thinness, interferes with the activity of dislocations and promotes strain accumulation and wear.

Plastic Deformation and Mechanical Softening of Pd40Cu30Ni10P20 Bulk Metallic Glass During Nanoindentation

Nanoindentation tests of Pd40Cu30Ni10P20 bulk metallic glass were performed over a wide range of indentation rates (from 0.04 up to 6.4 mN s−1) under the standard load control mode. New results using the feedback displacement control mode are also presented. The dependence of the pop-in formation on the loading rate is investigated. Variations in hardness and reduced elastic modulus as a function of the indentation rate are observed. A softening effect occurs when increasing the loading rate. This is explained by the differences in plastic deformation achieved at different indentation rates. The displacement control mode was used to avoid the shear localization of the free volume, leading to the almost complete absence of pop-ins along the loading curve. The obtained results suggest that plastic flow in bulk metallic glasses is governed by the rate of creation of free volume, which depends on the strain rate and its localization into shear bands.

Influence of Cu Deposition Conditions on The Microstructure and Adhesion of Cu/Cr Thin Film To Polyimide Film

AbstractsThe microstructure of Cu thin films in various deposition conditions and the influence of their microstructure on the adhesion strength between Cu/Cr films and polyimides were studied. Cr films (50 nm thick) and Cu films (500 or 1000 nm thick) were deposited on polyimide films by DC magnetron sputtering. The Ar pressure during Cu deposition was controlled to 5, 50, and 100 mtorr. The microstructure was characterized using SEM and TEM. The adhesion strength between Cu/Cr and polyimide was measured using a modified Tpeel test. Plastic deformation of the peeled metal was qualitatively measured using the XRD technique. The Cu film sputtered at 5 mtorr has a dense and uniform structure, while lowdensity regions or open boundaries between columns exist in the film deposited at higher pressure. As sputtering pressure increases, open boundaries are observed more frequently. The peel adhesion strength of Cr film to polyimide increases with Cu sputtering pressure. The adhesion change of Cu/Cr film can be interpreted as the difference in plastic deformation. Open boundaries in the Cu film seem to play an important role in increasing the amount of plastic deformation in the metal film during peeling.