Localized corrosion degradation of metallic materials is a key factor that significantly impacts their lifetime and safety. Existing localized corrosion assessment methods for metallic materials are mainly based on corrosion simulation experiments in laboratory and corrosion exposure experiments in real environmental. However, these experiments are often complex, lengthy, and costly. Localized corrosion simulation can be achieved with the continuous improvement in the theory and measurement of localized corrosion, and the rapid development of numerical calculation, simulation software, and programing. Numerical models based on the classical continuum mechanics (CCM) apply a spatial differential equation to describe the interaction between material points, and singularity appears when solving discontinuous problems such as corrosion degradation. The peridynamics (PD) theory based on nonlocal applies time differential-spatial integration to describe the interaction between the material points and breaks through the bottleneck of the CCM theory on discontinuous problems. This paper reviews the state of the art of PD applied in localized corrosion modeling, including pitting corrosion, crevice corrosion, intergranular corrosion, galvanic corrosion, and stress corrosion cracking by combing with the relevant theories and numerical implementations of the localized corrosion degradation model based on the PD theory. Finally, the challenges and outlook of PD applied in corrosion modeling are discussed.

The AlSi10Mg alloy fabricated using selective laser melting (SLM) has attracted attention because of its excellent quality and properties. However, the mechanical properties of SLM AlSi10Mg alloy cannot meet the requirements of the high strength of aluminum alloys in the aerospace industry. To improve the mechanical properties of SLM AlSi10Mg alloy, AlSi10Mg-Er-Zr powders were prepared using in situ alloying mechanism and gas atomization. The relative density, microstructure, and mechanical properties of SLM AlSi10Mg-Er-Zr alloys have been investigated. The results show that the relative density of AlSi10Mg-Er-Zr alloys fabricated using SLM reaches 99.20%. The SLM AlSi10Mg-Er-Zr alloy has a microhardness value of 156.5 HV. The ultimate tensile strength (UTS) and yield strength (YS) of the SLM AlSi10Mg-Er-Zr alloy can reach 461 and 304 MPa, respectively. Compared with the conventional AlSi10Mg alloy, the microhardness has been increased by 25.8%; the UTS and YS are increased by 22.6% and 26.7%, respectively. The fine-grain and solid solution strengthening associated with SLM processing with the addition of Er and Zr elements, as a result of increased grain size refinement and solid solubility of Si element in the α-Al matrix, are responsible for the improvement in the mechanical properties.

7xxx series aluminum alloys are well-known structural materials, and they have been used in various fields, such as aerospace and vehicle, owing to their low density, high strength, and good formability. However, they are susceptible to stress corrosion cracking (SCC). SCC reduces the service life of these alloys and limits their application. With the development of the aerospace and vehicle industries, high-strength 7xxx series aluminum alloys are manufactured as semiproducts with large sections, such as thick plates, to avoid welding and jointing defaults. Quenching is a critical step for producing thick plates because their properties, such as SCC susceptibility, are sensitive to the quenching rate, and the quenching rate is generally lower at the center layer than at the surface layer during quenching. In this study, the effect of quenching rate on the SCC susceptibility of 7136 aluminum alloy was investigated using immersion end-quenching technique and slow strain rate tensile (SSRT) test. The strength, elongation, and fracture time of the samples after SSRT in oil and NaCl solution were obtained, and the crack features on and near the fracture surface were examined using SEM. SCC susceptibility was evaluated using the reduction rates of strength, elongation, fracture time, and stress corrosion sensitivity index (I_SSRT). The mechanism is discussed herein based on microstructural examination using SEM, EBSD, STEM in a HAADF mode, and EDS. Results show that the SCC susceptibility of the alloy first increases and then decreases with the decrease in the quenching rate. The SCC susceptibility is the highest at the quenching rate of approximately 5.3°C/s with the Ithe number and size of quench-induced precipitates increase gradually, and the precipitate free zones (PFZs) near grain boundary (GB) and subgrain boundary (SGB) widen; and the contents of Zn and Mg in precipitates at grain boundaries increase rapidly when the quenching rate is greater than 5.3^oC/s, and Cu content increases rapidly when the quenching rate is lower than 5.3^oC/s. The quench-induced changes in the morphology and chemical composition of precipitates at GB/SGB are the main reasons for the SCC susceptibility to increase first and then decrease with the decrease in the quenching rate.

Al-Si multicomponent alloys are commonly used in automotive and aerospace fields owing to their excellent castability, good wear resistance, and low coefficient of thermal expansion. After adding Cu and Mg followed by appropriate heating, Al₂Cu, AlCuSiMg, or Mg₂Si phases precipitate in an α-Al matrix. Hypereutectic AlSiCuMg alloys have been used in wear-resistant products, such as engine cylinders, pistons, and air-conditioning rotors, owing to the hardening effect of Si particles and the solid solution strengthening and precipitation strengthening effects of Cu and Mg. The evolution behaviors of secondary phases and the grains of the spray-formed Al25Si4Cu1Mg (mass fraction, %) alloy were examined via OM, XRD, SEM + EBSD, TEM, hardness tests, and phase diagram calculations. The results showed that the hot extrusion microstructure of spray-formed hypereutectic AlSi alloys comprises equiaxed α-Al, proeutectic Si, eutectic Si, eutectic AlCuSiMg, a eutectic Al₂Cu phase, and a low volume fraction Fe-bearing phase at the micron level but without a lamellar morphology. α-Al contained both micro-nano and nano-sized Al₂Cu phases precipitates. Over the temperature range of 475-495^oC, the precipitated Al₂Cu phase and some of the eutectic Al₂Cu phase redissolved, and the residual Al₂Cu phase concentrated to a Fe-bearing phase and coarsened. The volume fraction and size of the AlCuSiMg phase increased. However, when solution-treated at less than 515^oC, the volume fraction of the AlCuSiMg phase began to decrease, and no overburning structure was observed. When the solution temperature exceeded 515^oC, the incipient melting of the nonequilibrium eutectic phase increased with increasing solution temperature. The main characteristics of the overburning structure were the network eutectic and grain boundary broadening. The hardness of the spray-formed Al25Si4Cu1Mg alloy was dependent on five factors: the solid solubility of solute atoms, the volume fraction of the residual second phase, the grain size of α-Al, the scale of the Si phase, and the incipient melting of the nonequilibrium eutectic phase.

Pure Ti can form twins during deformation due to the hcp crystal structure, and some kinds of twins can easily form under certain conditions, thus affecting the properties of materials. It has considerable influence on the properties of materials through the regulation of twin types and variants. This work investigates the effect of the dislocation slip of adjacent grains on the selection of twin variants during the deformation of pure Ti. The dynamic plastic deformation (DPD) of commercially pure Ti (99.9%) was performed at liquid nitrogen temperature (-196^oC). The microstructure before and after the deformation was observed using EBSD. The influence of twinning on Schmid factor (m) before and after deformation was investigated, and a mechanism for selecting twin variants of polycrystalline pure Ti was proposed. The results show that after DPD at liquid nitrogen temperature, high-density primary twins appeared in pure Ti, followed by secondary and double twins. After twinning, the Schmid factor of basal slip changed noticeably, and the m of a large number of grains was close to 0.5. Based on the geometric compatibility factor (m') of the original slip and twin matching relationship and the Schmid factor of an adjacent grain (m₁), a new orientation compatibility factor ω (ω = m₁·m') was established, and the selection of twin variants in the plastic deformation of polycrystalline pure titanium was quantitatively analyzed. It was discovered that the ω determines the selection of twin variants in pure Ti, and the pyramidal slip <a> of the adjacent grain plays a significant role in promoting the initiation of twin variants.

SiC-fiber-reinforced γ-TiAl composite materials are promising for high-temperature structural applications owing to their excellent mechanical properties. However, the interfacial reaction of the composites during subsequent high-temperature processing and service is unstable as elements continue to diffuse around the interfacial reaction layer at high temperatures, and more interfacial reaction products are generated. When excessive brittle reaction products are generated, they have detrimental effects on the mechanical properties of the composites. Therefore, to better design and control the interfacial reaction, it is particularly important to study the formation and growth of the complex interfacial products of the composites. In this study, the formation mechanism of interfacial reaction products and thermal stability of SiC_f/TiAl composites were investigated by thermal exposure for different time. First, the SiC_f/TiAl composites were prepared by suction casting. Next, the specimens were examined by SEM and TEM to investigate the element diffusion and composition of the interfacial reaction products of the as-prepared composites. The interfacial reaction products in the as-prepared composites were mainly composed of a fine equiaxed TiC layer near a carbon layer and a coarse equiaxed TiC layer near a titanium alloy coating. Then, the thermal exposure was conducted at 800^oC to investigate the growth of the interfacial reaction products and thermal stability of the interfacial reaction layer. The results show that the thickness of the interfacial reaction layer increased with heat exposure time. Meanwhile, interfacial stratification was observed during the growth of the interface reaction layer. Further, the growth kinetics curve of the reaction layer was drew according to the thickness of the reaction layer with time, and the interfacial reaction growth rate was determined. According to the morphology and TEM analysis results, the interfacial reaction layer was divided into four layers after 200 h thermal exposure, unlike in the as-prepared state. From the fiber side to matrix side, fine-grained TiC, coarse-grained TiC, (Ti, Zr)₅Si₄, and Ti₃Sn + Ti₂AlC layers, respectively, were observed. Finally, the formation mechanism of the interfacial reaction products and element diffusion of SiC_f/TiAl composites under different conditions were studied, the interfacial stratification occurred during thermal exposure because some TiC participated during the formation of Ti₂AlC.

Refractory high-entropy alloys (RHEAs) have great application potential in extreme conditions due to their outstanding high-temperature properties. However, several issues, such as high density, poor room temperature plasticity, and high cost limit their practical application. A new Ti_0.5Zr_1.5NbTa_0.5Sn_0.2 (molar ratio) RHEA with a medium density of approximately 8.0 g/cm³ was prepared to address the aforementioned issues; the effects of heat treatment temperature on the alloy's microstructure and mechanical properties were systematically examined. The findings indicate that as-cast Ti_0.5Zr_1.5NbTa_0.5Sn_0.2 RHEA contains Zr-rich and Ta-rich bcc phases and lath-like Zr₅Sn₃ intermetallics in the crystal. The volume fraction of the Ta-rich bcc phase gradually decreases with the increase in heat treatment temperature, and Zr₅Sn₃ intermetallic first increases and then decreases. The sample presents a near single-phase bcc structure when the heat treatment temperature is 1400^oC. A series of samples have good compressive plastic deformation ability under quasi-static conditions, and the alloy's yield strength increased gradually with an increasing heat treatment temperature. The sample's yield strength quenched at 1400^oC is as high as 1749 MPa. The alloy showed strain rate strengthening effect under dynamic loading, and the yield strength significantly increased. The sample's yield strength quenched at 1400^oC reaches 2750 MPa; however, the plastic deformation ability is reduced. The reason why the strength increases with the heat treatment temperature is that the 9.8% average atomic size difference results in a significant solid solution strengthening effect.

Ti-Al-Nb alloys are widely used in the aerospace industry and are promising candidate materials for turbine engines owing to their relatively low density, high specific strength, and good oxidation resistance. Here, the effects of the cooling rate and undercooling on phase constitution, microstructure evolution, B2 phase formation, and micromechanical properties of the rapidly solidified Ti_{75 - x} Al _x Nb₂₅ (x = 22, 45, atomic fraction, %) alloy were investigated. With a decrease in the droplet diameter, the primary B2 phase of Ti₅₃Al₂₂Nb₂₅ alloy transforms from coarse dendrite to equiaxed grain under free fall. For the rapidly solidified Ti₃₀Al₄₅Nb₂₅ alloy droplet, the nucleation and growth of the B2 phase transforms from the center of the γ dendrite to γ-grain boundaries, and the volume fraction of the B2 phase decreases with the droplet diameter. Under the condition of arc melting and vacuum suction casting (VSC), with an increase in the cooling rate, the average diameter of the B2 dendrite of the Ti₅₃Al₂₂Nb₂₅ alloy decreases from 515 to 370 μm. For the Ti₃₀Al₄₅Nb₂₅ alloy, the solidified microstructure changes from irregular (γ + B2) lamellae to regular (γ + B2) lamellar, to acicular (γ + B2) microstructure, and Al segregation is inhibited. The microhardness of Ti_{75 - x} Al _x Nb₂₅ alloy increases with a decrease in the droplet diameter, and the maximum microhardness of each alloy is 11.57 GPa and 7.7 GPa, respectively, which are 64% and 22% higher than that of VSC, respectively, thereby indicating that the coupled effect of a large cooling rate and high undercooling can effectively enhance the microhardness of the Ti-Al-Nb alloy.

GH2909 alloy is a low expansion superalloy developed on the base of GH2907 alloy. The mass fraction of Si is increased to accelerate the precipitation of ε phase, which improves resistance to stress-induced oxidative brittleness at grain boundaries. Increasing the mass fraction of Si also complicates the types of precipitates, and there is a long-time argument for determining precipitates in GH2909 alloy. The mechanical property is closely related to microstructure and precipitate. This work investigated the microstructure evolution of GH2909 low expansion superalloy during standard heat treatment by SEM, TEM, EPMA, and micro-chemical phase analysis. The Laves phase is the predominant phase in the wrought GH2909 alloy, according to the study. In the GH2909 alloy, the Si-rich Laves phase has a blocky form and a short rod shape. In solution treatment, the Laves phase dissolves gradually. After two-stage solution treatment, the short rod-shaped Laves phase almost completely dissolves. Slow cooling is needed to avoid re-precipitation of short rod shape Laves phase during solution treatment because Laves phase is sensitive to the cooling rate. Discontinuous G phase particles decorate grain boundaries after normal heat treatment, and a sizable discal phase precipitates in the matrix. There is also a fine phase rich in Ni and Ti in the matrix with the chemical formula Ni_2.26Fe_0.16Co_0.50Nb_0.62Ti_0.43Al_0.02. In the GH2909 alloy, the Laves phase, G phase, and ε phase are high in Si and Nb. During precipitation, these phases compete for Si and Nb elements. Furthermore, the micro-chemical phase analysis results demonstrate that 30% of the Si in the GH2909 alloy is finally precipitated. As a result, Si should be given special consideration in the microstructure control of the GH2909 alloy.

Lightweight and safety of automobiles is the development trend of high-strength automobile fasteners, which is conducive to saving resources and protecting the environment. High-strength fasteners connect parts of engine, and their strength affects the overall life of the engine, thereby affecting the safety performance of the vehicle. Presently, high-strength fastener steels for cars are mainly 35CrMo, and the fastener strength reaches 10.9/12.9 level, which must fulfill sufficient delayed fracture and fatigue properties. Therefore, it is important to develop cold heading steel with high fatigue and strong plasticity matching. In this study, the microstructure, mechanical properties, and strengthening mechanism of Cr-Mo microalloyed cold heading steel, under different thermomechanical control processes (TMCPs), were investigated using OM, SEM, and TEM. The results show that the TMCP parameters affect the structure and mechanical properties of the experimental steel. With an increase in the finish rolling temperature and acceleration of the cooling rate, the ferrite-pearlite composite structure in the steel gradually changes to bainitic, dislocation density gradually increases, tensile strength monotonously increases, and elongation fluctuates. When the finish rolling temperature is 935^oC, the microstructure is mainly uniformly distributed bainite phase, which is in the form of short rod and granular, and there is dislocation entanglement. The experimental results show that this process has the best strength and toughness matching. Its tensile strength and elongation reach 925 MPa and 20%, respectively, and the hardness at 7 mm from the quenched end (J7) is 53.1 HRC. When the finish rolling temperature is 900^oC, grain refinement strengthening is the main strengthening mechanism, accounting for 31%-36% of the yield strength; when the finish rolling temperature is more than 935^oC, dislocation strengthening is the main strengthening mechanism, accounting for the total strength of 35%-38%. The hardenability results show that the hardenability of the experimental steel is unaffected by the microstructure and mechanical properties, and it maintains high-quality hardenability. In addition, a model of the end quenching curve of the Cr-Mo microalloyed steel is established to predict hardenability.

There has been a push in the past few decades to increase the operating temperature of steam generators to the ultra-supercritical (USC) regime. This requires that creep-resistant alloys can operate at 650-700°C for 30 years. P91 and P92 steels are commercially applied in USC steam generator applications. However, these steels fail due to the coarsening of M₂₃C₆ and Laves phases during long-term service. Therefore, it is significant to restrict the formation of easily coarsened precipitates. In this study, a martensitic heat-resistant steel strengthened by single MX precipitates is designed using the Thermo-Calc software, as Fe-0.03C-10Cr-0.2Zr-0.3V. The yield strength, tensile strength, and elongation at room temperature are 266 MPa, 413 MPa, and 38%, respectively. The high-temperature hardnesses of specimens aged at 700^oC for 1, 10, 100, and 1000 h were tested at 700^oC after normalizing treatment, which illustrates that the high-temperature hardness of the specimens remains stable with increased aging time. In addition, TEM was used to characterize the precipitates in the heat-resistant steel aged for different times. It is found that with the increase of aging time (1-1000 h), the average size of the precipitates increases from 10.8 to 17.8 nm. The composition of MX precipitates in the specimens aged for 1000 h is Zr_0.46Nb_0.14C_0.4 and the volume fraction is 0.29%. According to the creep test results, the threshold stresses at 650 and 700^oC are 54.5 and 28.4 MPa, respectively.

The cyclic-deformation mechanism of face-centered cubic (fcc) pure metals or single-phase alloys, i.e., decreasing the stacking fault energy (SFE) of materials through alloying could lead to the transition of dislocation slip mode from wavy slip to planar slip, thereby, improving fatigue properties has been achieved after extensive research. However, except for diminishing SFE, alloying treatment can increase the degree of short-range ordering (SRO) in the alloy, which could equally promote the activation of planar slip just as the lower SFE does in alloys. However, most studies only emphasized the unilateral effect of SFE but ignored the action of SRO. For some single-phase fcc alloys, such as Cu-Mn, Cu-Ni, and some high-entropy alloys, the effect of SRO cannot be ignored. Therefore, in this study, the high SFE Cu-Mn alloys with different SRO degrees were selected as the target materials and general rules and micromechanisms for the effect of SRO on their tension-tension fatigue deformation and damage behavior were investigated under different stress amplitudes. The results show that with the increase of SRO degree, the dislocation slip mode changes from wavy to planar slip. Fatigue-cracking mode changes from dominating intergranular cracking to slip-band cracking, and the tension-tension fatigue life of Cu-Mn alloys is improved. The abovementioned effects are manifested as a synchronous improvement of fatigue strength coefficient ($σ^{'}_{f}$) and fatigue strength exponent (b) in the Basquin relation. The analysis shows that the enlargement of $σ^{'}_{f}$ is mainly owing to the solid solution strengthening of Mn element, and the planar-slip enhanced work-hardening capacity, whereas the increase in b stems from the higher deformation uniformity and slip reversibility governed by planar slip. In summary, this study provides guide for improving the fatigue properties of fcc metals.