Effect Of Thermomechanical Processing Research Articles

Effect of thermomechanical processing on mechanical properties and microstructural evolution of Al-Mg-Zn alloy

This study investigates the impact of thermomechanical processing route on the microstructural evolution, and mechanical properties (tensile strength, hardness and elastic plastic (J1c) fracture toughness) of the 7075-aluminum alloy. As received 7075 Al Alloy underwent for the solution heat treatment (SHT) followed by artificial aging and cold rolling (CR) process, respectively. Generally, it was observed that cold rolling of 7075 Al alloy is very challenging, but in this work 90% cold rolling successfully achieved by optimizing the thermo-mechanical process. The novel heat treatment process for achieving the 90% cold rolling reduction as follow: firstly, SHT was performed at 470°C for 8hours(h), there after aging at 140°C for 21h was performed. Characterization techniques like X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) was employed to assess the microstructure and phase constituents. Elastic plastic (J1c) fracture toughness was studied well on SHT, peak aged and rolled sample. Additionally, Vickers hardness and tensile test were performed. Aging and Cold rolling treatment effectively enhanced tensile strength and hardness ascribed to formation of fine rod shape precipitates of η"(Mg2Zn3) and formation of sub grains with localized strain accumulation, respectively. Split diffraction spots with satellite pattern in long range ordering has also observed in selected area electron diffraction (SAED) pattern of η" attributable to stacking faults and periodic arrangement of precipitates, respectively, as a consequence of this 90% cold rolling of 7075 Al alloy was accomplished. The maximum Vickers hardness, Tensile strength and Elastic plastic (J1c) fracture toughness values were achieved after SHT (470°C for 2h), peak aged (PA) (140°C for 21h) and 90% cold rolling are 226 HV, 526MPa and 344.54kJ/m2, respectively.

Effect of Thermomechanical Processing on the Transformation Kinetics, Microstructure and Mechanical Properties of a Continuously Cooled Cementite-free Bainitic Steel

Abstract The combination of forming with continuous cooling bainitic steels offers a new path for reaching energy-efficient manufacturing chains. Improved energy efficiency is achievable thanks to the suppression of conventional, energy-intensive heat treatments. In the present paper, different thermomechanical processing strategies, including laboratory and industrial scale forgings, were assessed alongside their impact on the resulting microstructure. Firstly, phase transformation kinetics were assessed in precisely controlled environments via dilatometry coupled to in situ techniques. Secondly, the microstructure, mechanical properties, and forgeability of large-scale forged components were investigated in laboratory and industrial conditions. These investigations were also assisted by finite element method simulation. The comparison between controlled and industrial-scale conditions illustrates pitfalls in the transfer of knowledge to conditions approaching a real manufacturing chain. Nevertheless, alloy and process design is shown to be a key aspect to overcome the discussed challenges, allowing homogeneous bainite microstructures and mechanical properties to be achievable over a flexible range of processing conditions.

Effects of Thermo-Mechanical Processing on the Microstructure and Mechanical Properties of β -Type Titanium Alloys

This study investigates the microstructural evolution and mechanical behavior of severe cold-rolled β-type Ti-29Nb-13Ta-4.6Zr (TNTZ) alloys under systematic solution heat treatments (ST) at 1063 K for durations ranging from 5 to 60 minutes. This comprehensive analysis provides valuable insights into the microstructural and mechanical characteristics of TNTZ alloys under varying solution heat treatment durations, offering a foundational understanding for optimizing their application in engineering contexts. Microstructural analysis reveals that both solution-treated (ST) and cold-rolled (CR) samples exhibit a predominant single body-centered cubic (BCC) β phase, while cold-rolled and solution-treated (CST-Q) samples display a combination of β and martensite orthorhombic α'' phases. ST samples demonstrate equiaxed grains with an average diameter of ~72 μm, albeit with limited clarity. In contrast, CST-Q samples treated for over 10 minutes exhibit finer equiaxed grains within the 7-14 μm range. Hardness values increase with prolonged solution heat treatment, reaching approximately ~183 HV for ST and ~234 HV for CR. Moreover, hardness continues to rise with increasing treatment duration, reaching ~204 HV for CST10Q, ~229 HV for CST30Q, and ~242 HV for CST60Q. Mechanical properties, including tensile strength, yield strength, and elongation, vary across samples. ST shows values of ~710 MPa, ~610 MPa, and ~25%, CR with ~1305 MPa, ~395 MPa, and ~17.5%, CST5Q with ~1042 MPa, ~440 MPa, and 17.5%, CST10Q with ~1010 MPa, ~650 MPa, and 21%, and CST60Q with ~930 MPa, ~660 MPa, and ~21%. Fracture surfaces of all samples exhibit dimple structures and microvoid nucleation, indicative of ductile failure.

Effects of hydrocolloids on mechanical properties, viscoelastic and microstructural properties of starch-based modeling clay

The effects of various hydrocolloids (guar gum, xanthan gum, and carboxymethyl cellulose) on the texture, rheology, and microstructural properties of modeling clay prepared with cassava starch were investigated. Notably, incorporation of 3 % guar gum and 4 % xanthan gum into starch-based modeling clay resulted in enhancements of 94.12 % and 77.47 % in cohesiveness, and 64.70 % and 66.20 % in extensibility, respectively. For starch-based modeling clay with added guar gum and xanthan gum, compared to formulations without hydrocolloids, the linear viscoelastic range exceeded 0.04 %, and the frequency dependence of both maximum creep compliance (Jmax) and storage modulus (G′) was significantly reduced. This indicates a more stable network structure and enhanced resistance to deformation. Results from Fourier Transform Infrared (FTIR) spectroscopy and X-ray diffraction (XRD) confirmed that the physical interactions between starch and various hydrocolloids, along with the addition of these hydrocolloids, inhibited the degradation effect of thermomechanical processing on the crystalline structure of starch. With the addition of guar gum, it is observed that a continuous and dense network structure forms within the starch-based modeling clay, and starch particles are distributed uniformly. In conclusion, hydrocolloids enhances the properties of starch-based modeling clay, introducing an innovative solution to the modeling clay sector.

Effect of thermomechanical processing on microstructure evolution and mechanical properties of metastable β Ti–5Al–5V–5Mo–3Cr alloy

Two distinct thermomechanical processing (TMP) schedules are applied to as-cast Ti-5553 alloy pancakes, to optimize its microstructure and mechanical performance. While TMP-I involves 40 % thickness reduction via forging, TMP-II employs rolling with 20 % thickness reduction. Typical bimodal microstructures with nearly similar sizes, distributions, and morphologies for the primary αp grains and colonies of secondary αs and β are noted to generate for both TMP-I and TMP-II. Certainly, rolling for only half the extent of that used for forging, appears ideal and economical for obtaining the targeted microstructure. Interestingly, similar and improved localized hardness values with respect to as-cast alloy, are obtained for bimodal microstructure, generated through both the TMP schedules. However, indentation size effect is noted to be nominally lower for the rolled alloy, thereby proving its suitability for large-scale application. Global behavior assessed through tensile tests also shows that bimodal microstructures obtained through forging or rolling leads to higher strengths, toughness and ductility, as compared to as-cast counterparts. This is primarily owing to non-uniform strain distribution in the as-cast alloy, resulting to crack initiation and failure, as revealed through digital image correlation-based study. Overall, TMP employing rolling with reduced deformation in particular appears beneficial for the mechanical property improvement of the alloy.

Effect of thermomechanical processing on compressive mechanical properties of Ti–15Mo additively manufactured by laser metal deposition

A bidirectional powder deposition strategy was employed to additively manufacture Ti–15Mo wt% using laser metal deposition. The as-built alloy was subsequently subjected to post-fabrication uniaxial thermomechanical processing at strain rates of 0.00055s−1, 0.0011s−1, 1s−1, and 4s−1, with strains of 20 % and 40 %. Experiments were conducted at room and elevated temperatures. Phase identification, elemental and microstructural characterisation were conducted using x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The three distinct zones, namely the fusion, remelted and heat affected zones, identified in each deposited layer of the as-built microstructure were retained after thermomechanical processing. After processing, electron backscatter diffraction was used to analyse deformation mechanisms. Deformation accommodation in β matrix was predominantly by a combination of slip and α′′ martensite which formed as a primary product at columnar and sub-columnar grain boundaries. However, the operation of {332}⟨113⟩ and {112}⟨111⟩ β-twinning was also determined, howbeit with a very small surface fraction. This implies a small surface fraction of secondary α′′ martensite forming within β-twins in the deformed microstructure. Compressive mechanical properties showed a strong dependence on strain rate as higher flow stress and compressive strength were obtained at higher strain rates. Grain structure homogenisation was not achieved after thermomechanical processing as there were α dominated regions as well as martensite/twin dominated regions which implies that an-isotropic tensile properties would emerge after tensile deformation on multiple pre-TMCPed samples. However, columnar β-grains were refined by a combination of precipitated α and deformation induced β-twins and martensite.

A machine learning approach for accelerated design of magnesium alloys. Part A: Alloy data and property space

Typically, magnesium alloys have been designed using a so-called hill-climbing approach, with rather incremental advances over the past century. Iterative and incremental alloy design is slow and expensive, but more importantly it does not harness all the data that exists in the field. In this work, a new approach is proposed that utilises data science and provides a detailed understanding of the data that exists in the field of Mg-alloy design to date. In this approach, first a consolidated alloy database that incorporates 916 datapoints was developed from the literature and experimental work. To analyse the characteristics of the database, alloying and thermomechanical processing effects on mechanical properties were explored via composition-process-property matrices. An unsupervised machine learning (ML) method of clustering was also implemented, using unlabelled data, with the aim of revealing potentially useful information for an alloy representation space of low dimensionality. In addition, the alloy database was correlated to thermodynamically stable secondary phases to further understand the relationships between microstructure and mechanical properties. This work not only introduces an invaluable open-source database, but it also provides, for the first-time data, insights that enable future accelerated digital Mg-alloy design.

The effect of thermomechanical processing on the piezoelectric and electrical conductivity of PLA/2.5%MWCNT composite

The electrical properties of polymer materials, such as electrical conductivity and piezoelectricity, are significantly influenced by the ratio of amorphous to crystalline regions. Additionally, the alignment of added particles and formed crystallites is another factor that affects these properties. Conversely, a well-designed thermomechanical process can significantly impact the rate of change. This study investigates nanocomposite production with an optimal percentage of modified nanoparticles using a revamped electrospinning process and fully effective post-processing. Piezoelectric constant d33 of PLLA-2.5%CNT discussion was pioneered in this article. It was proved that the crystallinity percentage of nanocomposites can be improved by up to 70% by applying a suitable thermomechanical process and adding a suitable percentage of particles. The formation of the ordered phase, the creation of a special pattern for the movement of electrons, and the change in the conformation of the carbonyl group are the reasons for increasing the piezoelectric constant from 0.2 to 3 and increasing the electrical conductivity by 1000 orders of magnitude. Among other reasons, we can mention the alignment increment of polymer particles and crystallites and their way of texturizing in order to apply thermomechanical processing.

Effect of Thermo-Mechanical Processing on Initiation and Propagation of Stress Corrosion Cracking in 304L Austenitic Stainless Steel

Despite the high corrosion resistance of austenitic stainless steels (SSs), a significant reduction of stress corrosion cracking (SCC) resistance has been reported in cases of high residual stress and metastable microstructural features. In this study, the effect of thermo-mechanical processing (TMP) on the initiation and propagation of SCC in 304L SS was studied. To better understand the SCC mechanisms, three TMPs conditions—welded, solution annealed at 1050 °C for tens of seconds, and straightened—were used. The research focused on analyzing the initial microstructure, residual stress, and hardness along the depth direction to assess SCC resistance and establish correlations with the observed SCC modes. Experimental results demonstrated that transgranular SCC was observed in regions exhibiting elevated residual stress induced by welding and straightening processes. Furthermore, the presence of strain-induced martensite transformation and slip bands formed during plastic deformation were identified as additional factors contributing to the susceptibility of SCC. The study findings highlighted that the magnitude and distribution of residual stresses, in conjunction with microstructural evolution, could be varied depending on the specific TMP condition, leading to different SCC susceptibilities, cracking modes, and directions.

Effect of thermomechanical processing of building stainless wire to increase its durability

A traditional use of high cumulative reduction ratios is not effective for manufacturing wire with high performance and mechanical properties, since cold plastic deformation reduces the wire diameter, while hot deformation has its own limitations. Thus, thermomechanical treatment of rolled steel has a huge potential to reduce costs and improve product quality when used in the construction industry. Such processing allows metalworking industries to increase the economic effect due to a more complete satisfaction of the requirements for the mechanical properties of finished rolled products. The article developed a new technology for thermomechanical processing of stainless steel wire, consisting of preliminary heat treatment to obtain an austenitic structure and traditional drawing followed by cryogenic cooling. As a result of such treatment, an ultrafine-grained structure was obtained, consisting of a mixture of austenite and α-martensite, with high strength and plastic properties. To analyze the features of the obtained microstructures, modern methods of metallographic analysis were used, such as scanning electron microscopy, transmission electron microscopy, and analysis of backscattered electron diffraction patterns. The microstructure is obtained after deformation at both temperatures and consists of a mixture of α-martensite and austenite. A structure with an average grain size of 0.5 µm was obtained by drawing using cryogenic cooling, and a microstructure of 1 µm was obtained at room temperature. The results obtained allow us to expect an increase in the performance and durability of stainless steel wire, which can be used for various purposes.

On the normal and inverse Portevin–Le Chatelier behavior in hot rolled Inconel 617 superalloy

In the present study the effect of hot rolling process on the normal and inverse Portevin-Le Chatelier behavior was investigated. The hot rolling process was carried out at 950 °C, 1050 °C, and 1150 °C to capture the effect of thermomechanical process on elimination or postponing of dynamic strain aging phenomenon in Inconel 617 during subsequent deformation process. The tensile test was performed within the temperature range between 350 °C and 750 °C at a constant strain rate. The microstructure evaluations were carried out by optical microscope and scanning electron microscope. The serrated flow was observed in the stress-strain curves at specific temperatures. The type of serrations changed from type B to type C at the strain rate of 5 × 10−4 s−1 as the tensile test temperature was enhanced. The change of normal PLC effect to the inverse PLC effect was intensified when the hot rolling temperature was increased; Hence, the inverse PLC effect was observed at 750 °C in the sample which had rolled at 1150 °C. Whilst the serrated flow was not seen at 750 °C in the samples which had rolled at 950 °C and 1050 °C. The critical strain, for the initiation of the serrated flow was found to reduce with the increasing temperature of hot rolling from 950 °C to 1150 °C. After tensile test, the microstructural evaluations revealed the proven substantial role of precipitation of γ′ and the Cr-rich M23C6 carbides in pinning of the mobile dislocations, which led to the inverse PLC effect.

Effect of rolling temperature on the occurrence of dynamic strain aging of Inconel 617 superalloy

Inconel 617 specimens were hot rolled at 950 °C, 1050 °C, and 1150 °C to examine the effect of thermomechanical processing on the occurrence of dynamic strain aging (DSA), followed by performing the tensile tests at temperature range of 350 °C–750 °C with the strain rates of 5 × 10−4 s−1, 5 × 10−3 s−1, and 1 × 10−2 s−1. The microstructural evolution was studied by an optical microscope, a scanning electron microscope (SEM), and differential scanning calorimetry (DSC). The stress-strain curves were analyzed in terms of serration intensity and types. The serrated flow at temperature range of 450 °C–750 °C underwent changes by the strain rate and the temperature, and the serration type changed from types A + B and B to type C. The transformation of Portevin-Le Chatelier (PLC) effect from normal to the inverse PLC effect was observed at a temperature higher than 550 °C. The activation energy was calculated and it was found that the diffusion of Cr and Mo substitutional atoms are mainly responsible for the DSA effect in hot rolled Inconel 617 superalloy. The hot rolling temperature was also found to have a significant impact on the occurrence of DSA. Moreover, it was indicated that as the hot rolling temperature increases from 950 °C to 1150 °C, the occurrence of dynamic strain aging is intensified.

Effects of thermomechanical processing on microstructures, mechanical properties, and biodegradation behaviour of dilute Zn–Mg alloys

Currently, zinc has been considered as one new attractive biodegradable metal for medical implant applications due to its favoured properties such as biocompatibility and recyclability. However, the cast pure zinc usually possesses coarsening microstructures, which hinders it to obtain a suitable combination of mechanical strength and degradation rate. Here, the microstructural controlling of zinc was firstly realized via alloying dilute Mg contents and thermomechanical processing. Then, the in vitro biodegradation behaviour of dilute Zn–Mg alloys was investigated accordingly using the Hank's solution. Finally, the mechanisms of mechanical strengthening and in vitro biodegradation were explored. Specifically, the Mg-50wt%Zn master alloy was added into cast Zn melt to form the binary Zn–Mg alloys with different Mg addition contents (i.e. 0, 0.05wt%, 0.1wt%, and 0.4wt%). The initial reduction of grain sizes was achieved by over 90% owing to the grain refinement generated by master alloy. In the as-cast alloys, the average grain size was decreased from over 2 mm for pure Zn to 23.7 μm for Zn-0.4wt%Mg. Subsequently, the thermomechanical processing (i.e. hot rolling at room temperature, 100°C, 150°C, and 250°C) was applied onto the cast Zn–Mg alloys to achieve further microstructural manipulation. Further grain refinement occurred in the different as-rolled Zn–Mg alloys. The in vitro corrosion resistance of all samples was assessed through the potentiodynamic polarization (PDP) test in the Hanks' solution for 14 days at 37°C. The corrosion rates depended on alloying contents, grain sizes, twins and texture. The synergetic regulation of mechanical strength and degradation rate could be adjusted by appropriately using master alloys and thermomechanical processing. For practical medical applications, the present work provides some insights on solving the dilemma between mechanical properties and biodegradation process.

A review on β-Ti alloys for biomedical applications: The influence of alloy composition and thermomechanical processing on mechanical properties, phase composition, and microstructure

Titanium and its alloys are potential materials for orthopedic implant applications due to their appropriate biological and mechanical behavior. As biocompatibility and biomechanical compatibilities are essential parameters for determining a biomedical implant's performance and service life, this research review article discussed the novel Ti alloys with nontoxic and biocompatible alloying elements with an elastic modulus similar to the bone. Among Ti alloys, β-Ti alloys are appropriate for load-bearing implant applications due to lower elastic modulus and nontoxic elements, including Ti, Ta, Nb, Zr, Sn, and Mo. Even though the β-Ti alloys possess a lesser elastic modulus compared to other metallic biomaterials, two issues associated with β-Ti alloys that result in implant failure are that they still possess a higher elastic modulus than human bone and they have insufficient strength. Alloy composition and thermomechanical processing characteristics play a vital role in altering the mechanical properties and microstructure of β-Ti alloys. Hence, this review article emphasizes the alloying and thermomechanical processing effects on the mechanical properties and microstructure of β-Ti alloys.

Investigation of some thermomechanical processing effects on the structure and properties of a TiNiCu shape memory alloy

A Ti50Ni45Cu5 shape memory alloy (SMA) was cast, homogenized and hot rolled into 0.5 mm-thick lamellas. After homogenization, the intercrystalline Ti2(Ni, Cu) based solid solution, gradually decomposed with the increase of hold temperature and time, as pointed out by optical, scanning electron and atomic force microscopy. After hot rolling, by wire spark erosion, rectangular specimens with the dimensions 0.5 mm × 2 mm × 6 mm were cut each one with a mass of 0.44 g. Since the specimens experienced a thermoelastic martensitic transformation, while being martensitic at room temperature (RT) they were soft and could be easily bent against cylindrical calibers, in order to induce their “cold” (martensitic) shape. When heated, up to 100 °C with a hot air gun, they readily recovered, by shape memory effect (SME) their initial straight form, also known as “hot shape”. Thermomechanical training cycles were subsequently applied, consisting in: (i) RT bending; (ii) hot air gun heating and (iii) air cooling. These cycles were repeated up to 50 times. The effects of the thermomechanical training cycles were subsequently analyzed, by differential scanning calorimetry, on fragments cut from the active sections of the specimens. It was noticed that training basically increased thermal hysteresis. Finally, experiments were performed which demonstrated the capacity of Ti50Ni45Cu5 SMA elements to develop.

On the Effect of Hot Rolling on Inclusion Size and Distribution in a Cast AISI 1070 Steel Railroad Wheel

The goal of this work is to examine the effect of hot deformation on shrinkage porosity and nonmetallic inclusions in an AISI 1070 grade steel industrially produced wheel casting. Steel cleanliness is an important consideration as it influences the mechanical properties of the final product. A high density of porosity and inclusions have been shown to be detrimental for mechanical properties, especially during hot rolling. Using a laboratory-scale rolling mill, cast preforms were subjected to a 66% cumulative reduction to determine the effect of thermomechanical processing on void closure and inclusions that may produce anisotropy in mechanical properties. Quantitative automated feature analysis, AFA, of inclusion type, size, morphology, and distribution was conducted utilizing an Aspex PICA 1020 scanning electron microscope to determine differences in inclusions and shrinkage porosity in the as-cast and as-rolled conditions. The results were compared with previously reported impact toughness values which indicated a trend with MnS projected length and average impact toughness in the T-L orientation. Reduction in shrinkage porosity was also verified utilizing 3D micro-X-ray CT scans. The AFA results showed a decrease in shrinkage porosity from 177 ppm in the as-cast condition to less than 35 ppm after rolling. Pores were in general much smaller and widely distributed after hot rolling and this would suggest improved impact properties. Analysis of nonmetallic inclusions revealed three primary categories of inclusions that included MnS, Al2O3, and complex inclusions that mainly consisted of MnS with an Al2O3 core, with small quantities of mixed silicates of Mn and Al and calcium aluminates (CaAl2O4).

Tribological behavior of as-cast and wrought Al–Mg2Si hybrid composites reinforced by Ti-based intermetallics

In this study, the tribological properties of Al–15Mg2Si (AC), Al–15Mg2Si–3TiB2–TiAl3 (C31), and Al–15Mg2Si–5TiB2–4TiAl3 (C54) in-situ composites were evaluated. In the as-cast state, the optimal results were obtained for the C31 sample, where the wear rate and the average coefficient of friction (ACOF) under the load of 60 N decreased by ∼54% and ∼27% compared to those obtained for the AC sample, respectively. Morphological modification of primary and eutectic Mg2Si particles and increasing the volume fractions of TiB2 particles were characterized as key factors for improving wear resistance of C31 sample. On the other hand, the presence of needle-like TiAl3 particles resulted in severe delamination and separation of tribolayer and increased mass loss of C54 sample. Alternatively, the fragmentation and redistribution of eutectic/primary Mg2Si and TiB2/TiAl3 particles during elevated-temperature deofrmation, the reduction of casting defect by thermomechanical processing effects, as well as intense grain refinement by dynamic recrystallization (DRX) improved the mechanical properties of hot-extruded samples and led to a notable enhancement in the load bearing behavior and stability of the formed tribolayer even under high loads. Therefore, the wear mechanism changed from the combination of severe delamination, adhesive, and three-body abrasive wear in the as-cast composites to mild abrasive wear in the hybrid composites subjected to hot deformation by the extrusion process. Consequently, in the optimal condition and under load of 60 N, the wear rate decreased from 29.6 to less than 10 mg/km and ACOF decreased by about 24% in hot-extruded C54 sample compared to the AC sample.

Effect of thermomechanical processing on the mechanical properties of CuZn10 alloy

Abstract The effects of thermomechanical processing on the grain size, tensile strength, and strain rate of a CuZn10 alloy were investigated. Microstructures of thermomechanically treated samples were introduced using a scanning electron microscope. The relationships between the flow stress, reduction ratio, annealing temperatures, and strain rates were detected for determination of activation energies and optimized thermomechanical parameters. The effect of grain size on the mechanical properties was examined by tensile and microhardness tests. The typical fractographs of samples after tensile tests were examined using a scanning electron microscope. It was observed that the annealing temperature and aging time have significant effects on the optimum grain size. Mechanical properties of the thermomechanically treated samples were improved by strain rate, deformation ratio, annealing temperature, and aging time.

Grain boundary modification and plasticization of pure nickel wires via torsion and annealing

Pure nickel wires are conducted to “torsion and annealing” grain boundary modification to study the effect of thermomechanical process (TMP) on grain boundary characteristics and plasticity. Compared with the initial sample, the elongation of the sample subjected to the optimal TMP increases by 103% while its tensile strength only reduces by 1.8%. A new micro index is presented to comprehensively indicate the coupling effect of grain size and grain boundary characteristic distribution on material plasticity. Numerous special boundaries generate during the initial recrystallization stage in TMP. The interfaces between recrystallization nuclei and the adjacent matrixes are basically incoherent Σ3ic boundaries. EBSD and TEM observations manifest that Σ3 boundaries, especially Σ3ic boundaries, have much weaker resistance on dislocation slip compared with random boundaries. The essence of plasticizing by GB modification is to make the material keep in the state that just completes recrystallization and contains as much as Σ3ic boundaries through coordinated TMP.

Effect of thermomechanical processing via rotary swaging on grain boundary character distribution and intergranular corrosion in 304 austenitic stainless steel

In the present work, the thermomechanical processing consisting of rotary swaging deformation and annealing treatment was performed to optimize the grain boundary character distribution (GBCD) of 304 austenitic stainless steel. To systematically investigate the effect of GBCD evolution on intergranular corrosion (IGC), double loop electrochemical potentiokinetic reactivation and electrolytic oxalic acid etch tests were employed. The experimental results show that the fraction of low-Σ coincident site lattice (CSL) boundaries increased from 58.1% to 74.0% for the specimen swaged to 0.06 true strain and then annealed at 1050 °C for 5 min duration. By characterizing the evolution of GBCD as a function of strain level in terms of low-Σ CSL boundaries fraction, average twin-related domain (TRD) size, average number of grain per TRD and fractal dimension of the maximum random boundary connectivity, the grain boundary engineering (GBE) microstructure was realized by the occurrence of prolific multiple twinning events during strain-induced boundary migration while static recrystallization has a detrimental effect on optimizing GBCD for the prolific of new strain-free grains with random boundaries. The IGC resistance of the GBE-treated 304 austenitic stainless steel is enhanced by inhibiting the nucleation and propagation of IGC cracks, resulting from the increase in the fraction of low-Σ CSL boundaries, especially Σ3 boundaries and the disruption of random boundary network connectivity.