Boundary Dislocations Research Articles

1 0 0] Dislocation core extension and decomposition in BCC bicrystal under biaxial loading

The evolution of grain boundary dislocation structure under biaxial tension–compression loading is simulated by the phase field crystal (PFC) method for small angle symmetric tilt grain boundary (STGB) of body center cubic (BCC) bi-crystal. Extension of the STGB dislocation core under the strain and the extended width of the core with the strain increasing are studied. In the elastic deformation process under the loading, the extension of the grain boundary dislocation core is accompanied by increasing the strain energy of the system. When the extension of the dislocation core reaches maximum critical width, the extended dislocation core occurs to decompose into three dislocation cores, in which two cores is in no-extended state, the Burgers vector direction of which is in the same direction of the original extended dislocation. The other dislocation core is of the extended type which Burgers vector direction is opposite to the Burgers vector direction of the original extended dislocation core. By establishing the macroscopic energy equation of the extended dislocation core system, it can be well revealed that the elastic strain energy is mainly stored in the extended dislocation defects and the complete lattice of the matrix. At the same time, it also reveals the function relationship between the energy of the extended dislocation core and the width of the extended dislocation during the biaxial loading process of the bi-crystal, as well as the critical condition of energy instability and the change of the energy barrier of the system for the dislocation extension core decomposition.

Shear-coupling of graphene grain boundaries: Elementary mechanisms, effects of topology, and role of buckling

Engineering grain boundary structure is a promising method for rational control of the microstructure and mechanical properties of two-dimensional materials. In bulk materials, shear stresses can drive grain boundary migration through the dislocations in grain boundaries. However, while shear coupling of grain boundaries has been studied in bulk materials like nanocrystalline copper, its translation to two-dimensional materials where out-of-plane deformation can relieve in-plane shear is not yet established. We investigate how the low flexural rigidity of graphene effects shear coupled grain boundary motion using atomic scale simulations of flat and buckled grain boundaries. We define the coupling shear strain as the strain at which a grain boundary has advanced by one Burgers vector and is at equilibrium and the critical shear strain as the strain at which migration of the first dislocation in the grain boundary becomes thermodynamically favorable. We show that the out-of-plane deformation does not influence the coupling shear strain and is governed only by the grain boundary topology. While the critical shear strain is altered somewhat by the low flexural rigidity due to buckling induced softening, it is also still dominated by the grain boundary topology. Our atomic scale results are synthesized into two models that predict the coupling and critical shears.

Enhanced fatigue endurance limit of Cu through low-angle dislocation boundary

How to remarkably elevate the high-cycle fatigue resistance of metallic materials under cyclic loading is a crucial, yet technically challenging issue for major structural applications. Either traditional strengthening approaches or newly-developed hierarchical nanostructural modifications has been demonstrated to usually display a limited ability of enhancing the 107-cycle fatigue endurance limit. Here, we introduce massive nano-scaled low-angle dislocation boundaries in coarse grained pure Cu by means of simple drawing process, not only enhancing the tensile strength obviously, but also imparting a fatigue limit as high as 130 MPa and a fatigue ratio of 0.35, which is a record for pure Cu. Upon cyclic loading, the extensive activation of strongly confined dislocation slip within homogeneous dislocation cells (with cell size of about 300 nm) effectively mediates cyclic plastic strain with slightly cyclic softening. The elevated stress resistance of DC Cu to cyclic loading is primarily attributed to the high density of built-in low-angle dislocation cells, which are strong and also suppress local surface roughening and crack initiation, thereby contributing to an enhanced fatigue life.

Periodic microstructure of Al–Mg alloy fabricated by inter-layer hammering hybrid wire arc additive manufacturing: Formation mechanism, microstructural and mechanical characterization

Inter-layer plastic deformation is an effective method to improve the mechanical properties of wire arc additive manufacturing (WAAM) components. In this study, the inter-layer hammering hybrid WAAM process was applied, and a periodic microstructure composed of alternate coarse and fine grain regions was obtained. These regions were defined as the work hardening region (W region) and recrystallization region (R region) according to the respective formation mechanism. The grain size, texture intensity, grain boundary misorientation angle, phase structure, and dislocation density in these two regions were systematically investigated, and their contributions to the mechanical properties were analyzed. The results show that hammering, especially with increase of hammering times, maintains the depth of recrystallization of each layer at 1.0 mm and increases the ratio of the R region. The grain size in the R region was significantly refined, and the dislocation density in the R region was lower than that in the W region due to the dislocation release by recrystallization caused by subsequent deposition heat, and sub-grains were formed in the W region. The best tensile properties were achieved in the horizontal direction when the inter-layer region was hammered 3 times. The ultimate tensile stress (UTS) exceeded 400 MPa and the elongation exceeded 13%. However, the change in pore morphology caused anisotropy in hammered samples.

Deformation characteristics and performance evolution of superalloy capillary drawn by electrically assisted microforming

Thin-walled superalloy capillaries are considered the core components of the heat exchanger in the hypersonic vehicle. To achieve the precise and efficient fabrication of capillaries, this study proposes an electrically assisted (EA) microforming process and investigates the deformation characteristics and performance evolution of capillaries under electric current. Experimental results show the EA drawing at 600 °C enhances the grain coordinated deformation capacity and dislocation recovery, while the ultrafast complete recrystallization and gradient grain microstructure are achieved by the EA annealing above 800 °C for 15 s. The microstructural evolution improves ductility and avoids macro defects, which is related to the reduction of activation energy of dislocation and grain boundary motion under the electroplastic mechanisms. In addition, the inhibition of the electric current on the increase in wall thickness is attributed to the increase in friction coefficient and the shedding of the oxide layer, while the electric current improves surface quality by forming ultrafine grains, oxidizing peaks, and healing troughs. Compared with the conventional manufactured capillaries, the surface quality, tensile strength, and elongation of the EA manufactured capillaries with the size of φ0.9 mm × 58 μm are increased by 129.0%, 31.1%, and 9.4%, respectively. A heat exchanger module integrated by the EA manufactured capillaries can cool the 25 m/s airflow from 1000 to 672 °C within 1 ms.

Effect of the Severe Plastic Deformation on the Corrosion Resistance of a Tantalum-Tungsten Alloy.

Tantalum and its alloys are regarded as equipment construction materials for processing aggressive acidic media due to their excellent properties. In this study, the influence of severe rolling (90%) on the dissolution rate of a cold-rolled Ta-4%W sheet in different directions was investigated during immersion testing and the corresponding mechanism was discussed. The results show that the dissolution rate of the cold-rolled sample is significantly lower than that of the undeformed sample. The corrosion resistance followed the sequence of "initial" < "90%-ND" < "90%-RD" < "90%-TD", while the strength is in positive correlation with the corrosion resistance. Severe rolling promotes grain subdivision accompanied by long geometrically necessary boundaries and short incidental dislocation boundaries on two scales in the cold-rolled sample. The volume elements enclosed by geometrically necessary boundaries form preferential crystallographic orientations. Such preferential crystallographic orientations can greatly weaken the electrochemical process caused by adjacent volume elements, resulting in greatly reduced corrosion rates in the severely deformed sample. The unexpected finding provides a new idea for tailoring the structures of tantalum alloys to improve both their strength and corrosion resistance.

Boost thermoelectric properties of n-type PbSe:Ag2Se:Ag in the vicinity of the percolation threshold

We study the microstructure and thermoelectric performance of n-type (PbSe)100-x-y:(Ag2Se)x:(Ag)y (x = 0 − 6, y = 0–28) films. For the (PbSe)71:(Ag2Se)5:(Ag)24, the carrier concentration enhanced in the vicinity of the percolation threshold. The high carrier concentration leads to a large average PFavg at the low temperature range of 300−523 K, the maximum PFavg for (PbSe)100-x-y:(Ag2Se)x:(Ag)y samples is ∼37.83 μW cm−1 K−2, which is about 200% higher than that of pure PbSe films (∼19.16 μW cm−1 K−2). In addition, PbSe:Ag2Se:Ag grain boundary and edge dislocation can engender intrinsically low thermal conductivity. The low thermal conductivity leads to a high zT and the maximum zT values for (PbSe)71:(Ag2Se)5:(Ag)24 samples is ∼0.63 at room temperature, which is more than 250% higher than that of pure PbSe films (zT = 0.25).

Finite strain crystal plasticity-phase field modeling of twin, dislocation, and grain boundary interaction in hexagonal materials

Twin, dislocation, and grain boundary interaction in hexagonal materials, such as Mg, Ti, and Zr, has critical influence on the materials’ mechanical properties. The development of a microstructure-sensitive constitutive model for these deformation mechanisms is the key to the design of high-strength and ductile alloys. In this work, we have developed a mechanical formulation within the finite strain framework for modeling dislocation slip- and deformation twinning-induced plasticity. A dislocation density-based crystal plasticity model was employed to describe the dislocation activities, and the stress and strain distributions. The model was coupled with a multi-phase-field model to predict twin formation and twin-twin interactions. The coupled model was then employed to study twin, dislocation, and grain boundary interactions in Mg single- and polycrystals during monotonic and cyclic deformation. The results show that twin-twin interactions can enhance the strength by impeding twin propagation and growth. The role of dislocation accommodation on twin-twin interactions was twofold. Dislocation slip diminished twin-twin hardening by relieving the development of back-stresses, while it effectively relaxed the stress concentration near twin-twin intersections and thus may alleviate crack nucleation. The plastic anisotropy in each grain and the constraints imposed by the local boundary conditions resulted in stress variations among grains. This stress heterogeneity was responsible for the observed anomalous twinning behaviour. That is, low Schmid factor twins were activated to relax local stresses and accommodate the strain incompatibility, whereas the absence of high Schmid factor twins was associated with slip band-induced stress relaxation.

Investigation on the strengthening behaviour of micro-scale copper fiber

Due to the size effect, the material exhibits the characteristics of "the smaller, the stronger", but there are limits to the improvement of material strength. In this paper, the 200 μm pure copper fiber is reduced to 23 μm by the cold drawing method. The stress-strain curve and microscopic analysis, it is concluded that grain boundary strengthening, texture strengthening and dislocation strengthening are the main strengthening methods of copper fiber. Cold drawing improves the fiber strength by reducing the grain size and changing the texture orientations. With the grain refinement, the texture orientation of copper fiber, gradually changed from the random distribution orientations to <001> and <111> preferred orientations. However, the evolution of the texture orientation does not always follow the same path. The increase of <101> oriented grains provide more plastic deformation space for the further refinement of copper fiber. When the fiber diameter reaches 23 μm, the grain orientation deflects to the preferred orientations of <111> and <001> again. For the copper fiber, the conditions for further refinement by orientation transformation gradually disappear, so that the strength of copper fiber approaches the critical value, which can be confirmed by the distribution of grain size at the fracture.

Study on the Effects of the Composite Addition of Al-5Ti-0.8C and La on the Microstructure and High-Temperature Mechanical Properties of ZL205A Alloy.

The effects of Al–5Ti–0.8C and the rare-earth element La on the microstructure and high-temperature mechanical properties of ZL205A alloy were investigated. We found that the grains of 0.1%La + 0.3%Al–5Ti–0.8C alloy were fine, the morphology of the as-cast Al2Cu phase was fragmented, and the precipitated phase was fine after T5 treatment. In particular, the high-temperature mechanical properties of 0.1%La + 0.3%Al–5Ti–0.8C alloy were significantly improved above 250 °C. The reason for the increase in high-temperature plasticity was attributed to the Al–La phase and the TiC particles, which refined the grains and reduced the tendency for intergranular fracture at high temperatures. More importantly, the high-temperature strengthening mechanism of the Al–5Ti–0.8C master alloy compounded with La was a result of the TiC introduced by the Al–5Ti–0.8C alloy, and the Al11La3 formed by the addition of La refined the grains in the matrix, promoted the precipitation of the needle-like θ’(Al2Cu) phase, reduced the size of the θ’(Al2Cu) phase, decreased the PFZ (Precipitation Free Zone), and increased the θ’(Al2Cu) phase number, hindering dislocation and grain boundary motion.

Experimental and Modeling Study of Phase-Specific Flow Stress Distribution in Intercritically Annealed Quenching and Partitioning Steels

To meet the increasing demand and stringent requirements of automotive structural steels, intercritically annealed quenching and partitioning (QP) steels are attracting significant attention owing to their excellent strength–plasticity balance. However, to date, limited reports have focused on the correlation between the microstructure and strength of intercritically annealed QP. In this study, the mechanical behaviors of QP steels with different Si contents were investigated by developing a physical-based mechanical model based on microstructural characterizations. In situ neutron diffraction was used to analyze the evolution of the phase constitution. Si content influenced the phase transformation behavior of the test steel. In the early stages of deformation, Si-strengthened steel exhibited lower retained austenite (RA) stability and faster transformation kinetics. The variation in the RA volume fraction with the deformation was fitted using a segmented exponential function. Based on the microstructure and strengthening mechanisms, a mechanical model considering grain refinement during phase transformation was proposed. The model was validated using intercritically annealed QP steels with different Si contents. The transformation-induced plasticity effect, that is, the contribution of RA to the strength, was discussed from two perspectives. Deformation-induced martensite (DIM) exhibited a significant work-hardening rate owing to the high solid solution strengthening by carbon and the high dislocation density. The residual RA after the DIM transformation exhibited a non-negligible stress distribution. Particularly, the grain boundary density and dislocations increased with strain, strengthening the remaining RA.

Dynamic recrystallization behavior and strengthening mechanism of Mg–Gd–Y–Zn–Zr alloy during isothermal MDF process

As one of severe plastic deformation (SPD) methods, multi-directional forging (MDF) technology is an effective way to refine grains. The microstructure, texture evolution and mechanical properties of homogenized Mg–13Gd–4Y–2Zn–0.5Zr (wt. %) alloy during isothermal MDF process were synthetically investigated in the paper. The results showed that the mean grain size of the alloy decreased gradually with the MDF passes increased. After 4 passes, the average grain size of the alloy was refined to 2.7 μm, and the microstructure distribution was uniform. On the one hand, with the increasing of the MDF passes, the massive intergranular LPSO phases are gradually broken up and formed a deformation zone. The plate-like Mg5(Gd,Y) precipitates were located interior the grains. On the other hand, the spherical Mg5(Gd,Y) phases were randomly distributed with the increasing of MDF passes. In addition, the maximum texture intensity of the MDFed alloy on (0001) basal plane gradually was weaken from 15.993 of the 1MDFed alloy to 4.245 of the 4MDFed alloy, which was attributed to the increasing of volume fraction of dynamic recrystallized (DRXed) grains via MDF method. And the dynamic recrystallization (DRX) mechanisms were continuous DRX (CDRX), discontinuous DRX (DDRX), particle stimulated nucleation (PSN) and kink induced DRX. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) after 4 passes were 385 MPa and 360 MPa respectively. The excellent mechanical properties of the alloy were owing to the grain boundary strengthening, dislocation strengthening, texture strengthening and precipitation strengthening. In addition, the second phase particles such as lamellar LPSO phases, broken block-shaped LPSO phases, spherical Mg5(Gd,Y) phases and plate-like Mg5(Gd,Y) phases were demonstrated to be the strengthening phases.

Solid-state alloying of Al-Mg alloys by accumulative roll-bonding: Microstructure and properties

In this study, a novel solid-state alloying approach was adopted to fabricate Al-Mg alloys with high Mg contents (CMg) by accumulative roll-bonding (ARB) of Al and Mg elemental materials to ultrahigh cycles. Experimental results showed that the degree of alloying increased with the increase of ARB cycles and a supersaturated α-Al solid solution accompanied with nanoprecipitates was formed in the Al-Mg alloys by ARB to 70 cycles. The as-prepared Al-Mg alloys exhibited enhanced mechanical properties, with a maximum tensile strength of ∼ 615 MPa and a tensile elongation of ∼ 10% at CMg = 13 wt.%. The high strength can be attributed to different mechanisms, namely solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening. The Al-Mg alloys showed increased work hardening with increasing CMg, due to the enhanced formation of nanoprecipitates. Meanwhile, no obvious drop in the intergranular corrosion (IGC) resistance was found in the Al-Mg alloys with CMg up to 13 wt.%. Moreover, sensitization treatment was found to induce little decrease in the IGC resistance of the Al-Mg alloys with CMg ≤13 wt.%. We found that the excellent IGC resistance was due to the suppression of grain boundary precipitation by the preferred formation of precipitates within the grains that were induced by ARB. Our study indicated the novelty of the present solid-state alloying approach to achieving a superior combination of high mechanical properties and IGC resistance in Al-Mg alloys.

Achieving superior strength and ductility in 7075 aluminum alloy through the design of multi-gradient nanostructure by ultrasonic surface rolling and aging

Aluminum alloys were used in various fields due to their high specific strength and low density. However, the disadvantage of low strength limits its wider application. In this work, the effect of ultrasonic surface rolling process (USRP) and artificial aging on microstructure and mechanical properties of 7075 aluminum alloy were investigated in detail. The results indicated that a multi-gradient nanostructure (MGNS) layer, i.e., grain gradient and precipitation gradient, was generated on the surface of the alloy. The tensile strength of the aged-USRP sample (692 MPa) was about 63 % higher than that of the coarse-grained sample (425 MPa), and the plasticity was comparable to that of the coarse-grained specimen. The underlying mechanisms of grain refinements, precipitation behavior and their effects on tensile properties were quantitatively analyzed. The high strength of the aged-USRP sample originated from grain boundary strengthening, precipitation strengthening, dislocation strengthening and synergistic strengthening. The activation of geometrically necessary dislocations (GNDs) during tensile deformation improved the plastic coordination ability of different microstructures. Thus, excellent strength-ductility synergy of 7075 aluminum alloy was obtained. • Multi-gradient nanostructure was formed on the surface of 7075 Aluminum Alloy. • Gradient nanostructure of type and number density of precipitates formed. • The multi-gradient nanostructure enhanced strength-ductility synergy of the alloy.

Effect of deformation amount distribution in the austenite recrystallization temperature region on the microstructure and mechanical properties of the X70 pipeline steel

ABSTRACT In this study, the effect of deformation amount distribution of X70 pipeline steel on the microstructure and mechanical properties in the austenite recrystallization temperature region are investigated. The results reveal that the austenite grain size is smaller and more uniform by increasing the last-pass rough rolling deformation amount in the austenite recrystallization region. An increase in the last-pass rough-rolling deformation amount can also improve the strength and low-temperature toughness. The deformation mechanism and microstructural evolution based on the last-pass in the austenite recrystallization temperature region are clarified. The final microstructure refinement effect of granular bainite and acicular ferrite attribute to the finer and more uniform original austenite grain size. The main strengthening mechanisms are grain boundary strengthening and dislocation strengthening. The high proportion of the high-angle grain boundary is significantly greater for improving the strength and toughness, which impedes dislocations to slip across grain boundaries.

A combined thermal desorption spectroscopy and internal friction study on the interaction of hydrogen with microstructural defects and the influence of carbon distribution

Hydrogen interactions with different microstructural defects were analysed in ultra-low carbon steel, with specific focus on the influence of carbon distribution. For this purpose, the steel was cold rolled and subjected to various annealing treatments, obtaining microstructures ranging from as cold rolled, over recovered up to fully recrystallized. Optical microscopy, transmission electron microscopy and hardness measurements were used to obtain information on the grain boundary structure and dislocation density. Positron annihilation spectroscopy measurements revealed metastable open volume defects related to both dislocations and vacancy clusters. The carbon distribution was characterized by internal friction experiments. Hydrogen interactions were studied by thermal desorption spectroscopy and internal friction measurements of samples electrochemically pre-charged with hydrogen.The most dominant contribution in hydrogen trapping in the cold rolled material is provided by dislocations. However, their contribution is strongly reduced after annealing at temperatures in the range between 300 K and 600 K due to dissolution of metastable kink-pairs and small carbon-vacancy clusters. Dissolution of such clusters provides fresh supply of carbon to dislocations, which reduces the dislocation trapping capacity for hydrogen due to carbon-hydrogen repulsion. The presence of carbon also reduces the vacancy mobility, allowing clustering and growth during cold rolling resulting in strong hydrogen trapping sites. Binding energies at dislocations were obtained from thermal desorption spectroscopy and internal friction measurements and compared to various models. The small discrepancy in the activation energy is argued to originate from the quantum effect. Hydrogen release from vacancy clusters is determined by the energy required for complete cluster dissolution.

Interface dislocations and grain boundary disconnections using Smith normal bicrystallography

The CSL/DSCL model for interfaces in crystalline materials offers a unified framework to study interface dislocations in phase boundaries and disconnections in grain boundaries. The model relies on the existence of a coincidence relation between the two lattices that meet at an interface. The model’s ability to quantitatively predict the thermodynamics and kinetics of interfaces has been demonstrated for a limited set of symmetric tilt grain boundaries (STGBs) in cubic materials and twin boundaries. However, the lack of a general framework of interface defects prevents its applicability to arbitrary rational boundaries. In this paper, we present a mathematical framework based on the Smith normal form (SNF) for integer matrices to study the bicrystallography of rational phase and grain boundaries. One of the main results of the paper is a constructive proof of the invariance of the coincident site lattice (CSL) under discrete relative displacements of the parent lattices (of possibly different kind) by a displacement shift complete lattice (DSCL) vector. In addition, we obtain necessary and sufficient conditions on two lattices, related by not only rotations but also lattice distortions, for the existence of a coincidence relation. We first apply these results to explore coincidence relations in arbitrary phase boundaries, and study interface dislocations. In particular, we demonstrate the framework for a phase boundary formed by a strained hexagonal lattice and a square lattice. As a second application, we show how to enumerate all possible (geometric) disconnection modes in arbitrary rational grain boundaries, including glide and non-glide modes in both STGBs and asymmetric-tilt grain boundaries (ATGBs). The constructive nature of the framework lends itself to an algorithmic implementation based exclusively on integer matrix algebra to construct all interfaces that admit CSLs up to a prescribed size, and determine disconnection modes in grain boundaries. We demonstrate the use of SNF bicrystallography on selected bicrystal misorientation axes/angles in face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal (hex) lattices.

Impact of the plastic deformation microstructure in metals on the kinetics of recrystallization: A phase-field study

The sensitivity of recrystallization kinetics in metals to the heterogeneity of microstructure and deformation history is a widely accepted experimental fact. However, most of the available recrystallization models employ either a mean field approach or use grain-averaged parameters, and thus neglecting the mesoscopic heterogeneity induced by prior deformation. In the present study, we investigate the impact of deformation-induced dislocation (subgrain) structure on the kinetics of recrystallization in metals using the phase-field approach. The primary focus here is upon the role of dislocation cell boundaries. The free energy formulation of the phase-field model accounts for the heterogeneity of the microstructure by assigning localized energy to the resulting dislocation microstructure realizations generated from experimental data. These microstructure realizations are created using the universal scaling laws for the spacing and the misorientation angles of both the geometrically necessary and incidental dislocation boundaries. The resulting free energy is used into an Allen-Cahn based model of recrystallization kinetics, which are solved using the finite element method. The solutions thus obtained shed light on the critical role of the spatial heterogeneity of deformation in the non-smooth growth of recrystallization nuclei and on the final grain structure. The results showed that, in agreement with experiment, the morphology of recrystallization front exhibits protrusions and retrusions. By resolving the subgrain structure, the presented algorithm paves the way for developing predictive kinetic models that fully account for the deformed state of recrystallizing metals.

Controlling the columnar-to-equiaxed transition during Directed Energy Deposition of Inconel 625

In this work, the grain orientation and mechanical properties of Inconel 625 are tailored by varying the process parameters during directed energy deposition. Under the same deposition speed, increasing the current is effective in promoting the columnar-to-equiaxed transition due to modifications on the thermal cycle. The solidification conditions (temperature gradient and cooling rate) were characterized during the process. A comparison with an existing solidification map for Inconel 625 indicates that the temperature gradients in the melt pool of the sample fabricated with larger current decrease sufficiently to permit the nucleation and growth of equiaxed grains. Uniaxial tensile testing showed that the sample with equiaxed grain microstructure exhibits a higher yield strength (increase by 36 %) when compared to the sample with columnar grains. Contributions of various strengthening mechanisms to the yield strength are quantified in terms of grain boundary strengthening, dislocation strengthening, and solid-solution strengthening. It is found that the higher yield strength of samples that possess equiaxed grains can be attributed to the enhanced dislocation strengthening arising from the large average Taylor factor. • The temperature gradient can be tailored by adjusting the process parameters. • A transition from coarse columnar grains to fine equiaxed grains was achieved. • The sample with equiaxed grains exhibits greater yield strength. • The high Taylor factor resulted in an increase in the strength of the test sample.

Inconsistent evolvement of micro-structures and corrosion behaviors in cold/warm deformed austenitic stainless steel

The effects of cold/warm deformation on the micro-structures and corrosion properties of type 304 stainless steel (SS) were studied by micro-structural analysis and electro-chemical tests. Strain-induced α′ martensite was produced by cold deformation but not by warm deformation at 100 °C, and it significantly influenced the surface nanohardness of SS. The corrosion resistance of the cold deformed 304 SS continued to decrease as the deformation reduction increased, while the corrosion resistance of the warm deformed 304 SS first decreased and then increased. The increases in strain-induced α′ martensite and dislocation tend to promote corrosion, but the increases in low-∑ coincidence site lattice boundaries, low angle grain boundaries and the severely disrupted random grain boundaries tend to resist corrosion. Warm deformation may provide a possibility of obtaining type 304 SS with high-strength and corrosion resistance, which is attributed to the coupling effect of dislocation and grain boundary.