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The effect of Ce on the corrosion behavior of Fe–36Ni Invar alloy was investigated in a 3.5 wt% NaCl solution. The proper addition of Ce enhanced the corrosion resistance. The second-phase particles were gradually transformed in type, size, and number following the addition of Ce, which alleviated the localized corrosion behavior. The appropriate Ce content increased the fraction of low coincident site lattice boundaries. Furthermore, the enhancement of protectiveness and compactness of the passive film was achieved. However, overadded Ce led to the degradation of corrosion resistance. 0.0170 wt% Ce was advised for the sake of the enhancement of corrosion resistance.

With the implementation of the global two-carbon policy, energy saving and CO2 emission reduction have become important developmental goals of the automobile manufacturing industry. At present, the combination of high temperature for the automobile gear steel and short carburizing time is the most direct carbon reduction countermeasure for gear production enterprises. However, the problem of abnormally coarsened austenite grains often occurs in the high-temperature carburization of gear steel. With the increase in carburizing temperature, the degree of mixing crystals becomes serious. As a requirement of gear manufacturing enterprises, microalloying is carried out on the carburized gear steel. Upon the addition of microalloying elements, the second-phase particles are precipitated during heating, and the pinning effect is generated to prevent the movement of austenite grain boundaries, thus preventing the abnormal growth of austenite grains. Although the second-phase particles precipitate at the usual carburizing temperature, the partial solid solution of particles appears. In this work, the effects of the heating temperature and holding time on the austenite grain size of gear steel are studied to clarify the mechanisms of complex austenite grain growth and second-phase particle precipitation for the realization of fine austenite grain size after high-temperature carburization. The influence of the contents of microalloying elements (Nb, Al) on the pinning effect, precipitation position, and solution temperature of the second-phase particles (Nb (C, N)/AlN) are also discussed. Austenite grain growth models, critical sizes of austenite grain abnormal growth, and pinning force models of second-phase particles are summarized. The austenite grain growth model is based on the Beck equation, and the most common models are the modified Sellars and Arrhenius models. For the study of the inhibition effect on austenite grains, the pinning force model is used to study the critical size of austenite by modifying the dimensionless constant (A) of the Zener equation mainly through the pinning effect (Pz) produced by all particles on the grain boundary. After the experimental data are obtained, the trend of austenite growth can be predicted accurately by fitting the curve using the mathematical method. The precipitated second-phase particles are generally distributed along the grain boundary. Nb (C, N) particles have a higher solution temperature than AlN particles, so they are more stable at high temperatures. When the temperature exceeds the grain coarsening temperature, the precipitated particles become dissolved or coarsened. The mixed crystal structure generally starts to appear at about 1000 ℃, and adding the appropriate amount of microalloying elements can increase the coarsening temperature.

A cellular automata model was established to simulate grain coarsening processes pinned by second-phase particles. The influences of particle coarsening, precipitation, growth and dissolution, which contain complex changes of size and number density of the particles, on the grain coarsening kinetics were investigated by considering the following two factors: average pinning force per particle and particle number density. The simulation results showed that the average pinning force per particle was related to the particle size, but little influenced by the particle number density. The investigations about the grain boundary/particles interactions showed that the increase of number fraction of particles, which located at the grain boundary junctions, should be the reason for the increase of average pinning force per particle. Then the limiting grain size was researched and compared to the results of some other models. The results showed that the average number of particles to stagnate a grain was related to both the number density and size of particles. At last, the comparisons between the present simulation results and the other simulation and experimental results showed that the present models were efficient in simulating the grain coarsening processes pinned by second-phase particles. [ABSTRACT FROM AUTHOR]

Reasonable control of the content of niobium (Nb) in a steel slab is of great significance to improve the strength of the slab and the regularity of precipitation of precipitates. In this study, the high-temperature strength and precipitates of the same steel with four different Nb contents (A: 0.006%, B: 0.031%, C: 0.050%, D: 0.065%) were tested and analyzed. The results show that when the Nb content is 0.031%, the tensile strength and yield strength of the steel reach the ideal state; the two-phase particles that precipitated in the Q355GJ steel after heat treatment are mainly square- and star-shaped (Ti, Nb) (C, N) composite precipitates, and their amount increases with the increase in Nb content. Most of the two-phase particles (84%) precipitated in the steel with the Nb content of 0.031% are smaller than 80 nm, and the continuous increase in the Nb content cannot increase the precipitation amount of the two-phase particles in the steel, but can increase the size of the two-phase particles. [ABSTRACT FROM AUTHOR]

A phase-field model was revised to study the abnormal growth of Goss grains during the annealing process in Fe-3%Si steels, in which the interaction between the second-phase particles and Goss grain boundaries (GBs) was considered. The results indicate that the abnormal growth of Goss grains occurs due to the different dissolvability of the particles at Goss GBs compared with the other GBs. Moreover, the degree of abnormal growth increases first and then decreases with an increasing particle content. Meanwhile, the size advantage of Goss grain can further promote the degree of abnormal growth. Two types of island grains were found according to the simulated results, which is consistent with the experimental observations. A proper GB dissolvability of particles is the key factor for the formation of isolated island grains, and a higher local particle density at GBs is the main reason for the appearance of serial island grains. These findings can provide guidance for the desired texture control in silicon steels. [ABSTRACT FROM AUTHOR]

The trade-off between strength and ductility is a longstanding puzzle in metallic materials. Here we present a novel strategy to acquire simultaneously high strength and ductility in a low-alloyed Mg-3.16Zn-0.97Ca-0.55Al-0.44Ag (wt.%) alloy by forming special core-shell structured reinforcements in grain interior through a modified thixoforming technique. The core-shell structured reinforcements consist of inner core of MgZn 2 second-phase particles (SP p) and outer shell of a transition zone rich in nano- β 1 ′ (Mg 4 Zn 7) precipitates. A superior combination of strength and ductility is achieved in the magnesium alloy with an excellent strengthening and toughening efficiency, which is better than the existing counterparts where precious rare earth elements or more elements are contained. At initial deformation stage, the transition zone (1.41 GPa in hardness) mitigates the sharp strain gradient between the hard SP p (1.85 GPa) and soft matrix (822 MPa) by intensifying dislocation accumulation. Subsequently, excessive < 1 ¯ 011>{10 1 ¯ 2} twins are emitted from SP p , leading to the successive formation of quilted-looking twins, apparent crossing twins, double twins and real crossing twins that prevailed with type dislocations where secondary {10 1 ¯ 1}-{10 1 ¯ 2} and {10 1 ¯ 2}-{10 1 ¯ 2} twins occur. The formation of twin networks in three-dimension facilitates quadruple interaction between dislocation, twin, precipitate and SP p , promoting the overall deformation coordination and leading to an enhanced work hardening. This work provides a promising strategy to produce high-performance magnesium alloys at a considerably low cost. [Display omitted] [ABSTRACT FROM AUTHOR]

A cellular automata model was established to simulate grain coarsening processes pinned by second-phase particles. The influences of particle coarsening, precipitation, growth and dissolution, which contain complex changes of size and number density of the particles, on the grain coarsening kinetics were investigated by considering the following two factors: average pinning force per particle and particle number density. The simulation results showed that the average pinning force per particle was related to the particle size, but little influenced by the particle number density. The investigations about the grain boundary/particles interactions showed that the increase of number fraction of particles, which located at the grain boundary junctions, should be the reason for the increase of average pinning force per particle. Then the limiting grain size was researched and compared to the results of some other models. The results showed that the average number of particles to stagnate a grain was related to both the number density and size of particles. At last, the comparisons between the present simulation results and the other simulation and experimental results showed that the present models were efficient in simulating the grain coarsening processes pinned by second-phase particles.

A phase-field model was revised to study the abnormal growth of Goss grains during the annealing process in Fe-3%Si steels, in which the interaction between the second-phase particles and Goss grain boundaries (GBs) was considered. The results indicate that the abnormal growth of Goss grains occurs due to the different dissolvability of the particles at Goss GBs compared with the other GBs. Moreover, the degree of abnormal growth increases first and then decreases with an increasing particle content. Meanwhile, the size advantage of Goss grain can further promote the degree of abnormal growth. Two types of island grains were found according to the simulated results, which is consistent with the experimental observations. A proper GB dissolvability of particles is the key factor for the formation of isolated island grains, and a higher local particle density at GBs is the main reason for the appearance of serial island grains. These findings can provide guidance for the desired texture control in silicon steels.

• A general approach is provided to unveil the micromechanism of strength-damage trade-off. • The microstructure-based constitutive model is developed to predict strain hardening behavior of particle-reinforced alloys. • The strain gradient effect emerges as the pivotal source of the micromechanism of strength and damage trade-off. • The comprehensive effects of particle size and volume fraction on strength-damage trade-off are explored. The strength and damage are mutually exclusive in most alloys. It is still a challenge to understand the role of microstructural features in affecting strength and damage tolerance simultaneously. In this study, we provide a general approach to unveil the micromechanism of strength and damage trade-off in second-phase reinforced alloy. Concretely, a microstructure-based constitutive model incorporating the strain gradient plasticity theory is developed to evaluate the overall mechanical behavior and local deformation behavior of particle-reinforced alloys by finite element simulations. The strain gradient effect exacerbates the non-uniform stress distribution, particularly enhancing the local stress level around the particle-matrix interface, thereby improving the total strain hardening of the alloys. Importantly, the strain gradient effect can significantly expand regions with local stress levels surpassing the critical stress for microcrack nucleation, ultimately leading to damage initiation and failure. This elucidates the micromechanism underpinning the trade-off between strength and damage. By revealing the competitive relationship between local stress concentration and microcrack nucleation stress, the comprehensive effects of particle size and volume fraction on the strength, strain hardening and damage tolerance are quantitatively predicted. It is recommended to adjust the particle volume fraction based on reducing the particle size to obtain the desired properties. The present work discerns the inherent origin of the strength-damage trade-off in particle-reinforced alloy and sheds light on the role of the particle size and volume fraction on the strength and damage tolerance, which can offer valuable guidance for developing high-performance particle-reinforced materials. [ABSTRACT FROM AUTHOR]

The effect of the solid solution of second-phase particles on the austenite grain growth behavior at different heating temperatures and holding times of Nb-Ti high-strength IF steel is examined. The experimental results showed that the solid solubility of Nb in austenite increased significantly with temperature, dispersion and fine second-phase particles continued to dissolve in austenite. The pinning effect weakened and the austenite grains increased slowly. When temperature reached 1050 °C, a large number of second-phase particles (NbC, TiC, etc.) gradually dissolved in austenite. The solid solubility of microalloyed elements in austenite used for testing steel was different. To make these elements dissolved completely and, at the same time, obtain fine-grained austenite, heating temperature needs to be kept between 1050–1100°C and the holding time limited to 30–40 min. The austenite grain growth model is constructed based on the experimental data. The calculated values are in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

A theoretical model is established to address the effect of nanoscale twinning near a second-phase particle on crack growth in fine-grained magnesium alloys. The numerical solutions of singular integral equations are obtained by the considering complex variable method of Muskhelishvili, the superposition principle of elasticity, and the distributed dislocation technique. The expressions of stress intensity factors near the left crack tip are derived, and the energy release rate (ERR) characterizing the condition for crack propagation is also calculated. The influences of relevant parameters such as the location of nanoscale twin, the size of particle, and the relative distance between the inhomogeneity and the left crack tip on the ERR are examined in detail. The results indicate that the ERR is strongly influenced by the nanoscale twinning and the second-phase particle. The hard inhomogeneity decreases the ERR while the soft inhomogeneity increases the ERR when nanoscale twinning is not taken into account. At the same time, there is competition between the effects of the hard particle and nanoscale twinning on the ERR, and the nanoscale twin band with an optimum size displays the best toughening effect. [ABSTRACT FROM AUTHOR]

Amorphization of the second phase particles in irradiated zirconium alloys tends to lead to defect formation, radiation growth and corrosion resistance reduction, while conventional annealing requires higher temperature to promote amorphous crystallization transformation, which may reduce the performance of materials. Based on the difference of electrical properties between the second phase particles and the matrix, the pulsed electric current can induce the crystallization of amorphous second phase particles at a lower temperature by introducing additional electrical free energy, so as to achieve the microregion regulation of materials. The pulsed electric current effectively reduces the recrystallization activation energy of the second phase particles from 96 kJ/mol to 63.68 kJ/mol, thus lowering the recrystallization barrier to accelerate its process. The proposed pulsed electric current can rapidly reverse the crystal structure of amorphous second phase particles at lower temperatures, which provides a novel idea for adjusting the microstructure of metal materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The subsurface damage and surface integrity of a spherical diamond indenter sliding against a face-centred cubic copper (100) surface considering the pore and second-phase particle effects is investigated by means of molecular dynamic simulations of nanoindentation followed by nanomachining. In this investigation, we establish an analytical model for pore healing, and provide a criteria to determine whether or not pore can be healed. The results show that with increase of machining distance pore becomes smaller and then closes due to machining-induced compressive stress, resulting in low material damage and strong structure stability. Compared to free pore workpiece, machining force slightly relies upon the existence of pore and second-phase particle while friction coefficient strongly depends on the existence of that. In addition, particle induces work hardening due to Lomere-Cottrel lock and dislocation slip during machining metal matrix composites. It is helpful to understand the relation of machining performance and material parameter for obtaining higher surface integrity and lower subsurface damage during machining porous metals and particle reinforced metal matrix composites. [ABSTRACT FROM AUTHOR]

In this work, a new method for detecting cathodic second-phase particles on the Mg alloy surface has been developed based on in situ observation of the blade-abraded surfaces of AZ31, AZ61, and 99.9 % pure Mg during the immersion in concentrated alkaline solutions. Continuous local gas evolutions were observed at certain points on the blade-abraded surface, and second-phase particles were found at the same positions, revealing the presence of cathodic particles at the gas evolution sites. The continuous local gas evolution reaction was found to be coupled with not only oxide formation reaction on the Mg matrix around the cathodic particles but also dissolution of Mg at the area within 2-3 μm distance from the cathodic particle. The gas evolution rate appeared to be proportional to the size of cathodic particles, and various cathodic particles containing Fe, Mn, Al, and/or Si were found to be present in the Mg alloys. Based upon the experimental results, it is concluded that the new method is simple, fast, and non-destructive, and it can be used to detect all the cathodic second-phase particles present on the entire surface of Mg alloys, irrespective of the sample shape and size. [ABSTRACT FROM AUTHOR]

The interaction between recrystallization and concurrent precipitation is strongly dependent on the heating rate during annealing. In this study, the effects of heating rate on the grain structure, recrystallization texture and resulting mechanical properties upon annealing of a cold-rolled Al–Mn alloy under strong and weak concurrent precipitation conditions, resulting from different homogenization procedures, were investigated. It is clearly shown that increasing the heating rate leads to finer grain size, less elongated grain structure and reduced flow stress for both cases. In the case of strong concurrent precipitation, a sharp P-texture component is obtained after recrystallization, with its intensity decreasing with increasing heating rate. On the other hand, Cube is the major texture component when concurrent precipitation is weak, and its strength increases with increasing heating rate. The different effects brought about by the heating rate on the recrystallization texture of the two cases, which has not been addressed in the literature so far, are further discussed in view of the differences in precipitation behaviour. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural evolution of polymineralic contact metamorphic calcite marbles (Adamello contact aureole) with variable volume fractions of second-phase minerals were quantitatively analyzed in terms of changes in grain size and nearest neighbor relations, as well as the volume fractions, dispersion and occurrences of the second phases as a function of changing metamorphic conditions. In all samples, the calcite grain size is controlled by pinning of grain boundaries by second phases, which can be expressed by the Zener parameter (Z), i.e., the ratio between size and volume fraction of the second phases. With increasing peak metamorphic temperature, both the sizes of matrix grains and second phases increase in dependence on the second-phase volume fraction. Two distinct coarsening trends are revealed: trend I with coupled grain coarsening limited by the growth of the second phases is either characterized by large-sized or a large number of closely spaced-second phase particles, and results finally in a dramatic increase in the calcite grain size with Z. Trend II is manifest by matrix controlled grain growth, which is retarded by the presence of single second-phase particles that are located on calcite grain boundaries. It is supported by grain boundary pinning induced by triple junctions, and the calcite grain size increases moderately with Z. The two different grain coarsening trends manifest the transition between relatively pure polymineralic aggregates (trend II) and microstructures with considerable second-phase volume fractions of up to 0.5. The variations might be of general validity for any polymineralic rock, which undergoes grain coarsening during metamorphism. The new findings are important for a better understanding of the initiation of strain localization based on the activation of grain size dependent deformation mechanisms. [Copyright &y& Elsevier]

Several alloying elements involving Zr, Cu, Zn and Sc were added to Al-Mg sheet alloys in order to obtain an excellent combination of high strength and good high-temperature formability. Microstructural examination showed that coarse intermetallic particles were formed in the microstructure and their amounts changed with variations of the alloying elements. During warm rolling of thermomechanical treatments prior to warm deformation, the coarse particles initiated cracks, decreasing the warm formability. For healing the crack damage and further improving the warm formability, a process of hot isothermal press was developed and optimized to the sheet alloys. With this process, the biaxial stretch formability at 350°C was improved by 22% for an aluminum alloy containing a large amount of coarse particles. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate chip breakability, turning tests for various wrought aluminum (Al) alloys were carried out with a cemented carbide tool (K10) in dry and wet cutting conditions. In the alloys, Al2Cu, Al6Mn, Mg2Si, Al–Fe–Si system compounds and eutectic Si were observed as second-phase particles. Chip breakability of the alloys containing Al2Cu or Si were superior to those of those containing Mg2Si or Al–Fe–Si. This tendency was more prominent in wet cutting than in dry cutting. The second-phase particles of Al2Cu and Si in these alloys fractured during the machining process. It was estimated that the fractured second-phase particles acted as the cause of chip breaking. Moreover, the increase of the chip breakability in wet cutting was attributed to the Rehbinder effect due to the penetration of cutting oil into the micro-cracks. [Copyright &y& Elsevier]

Abstract: The effect of Mn content on fracture toughness and strength is investigated in Mg–6wt.%Al–1wt.%Zn alloy. As a result, the addition of 0.1–0.15wt.% of manganese, which is close to the solubility limit of manganese is the most effective to avoid a significant reduction of fracture toughness and takes advantage of solution strengthening at the same time. The addition of Mn above the solubility resulted in the reduction of fracture toughness due to the formation of Mn-bearing particles. We defined the minimum size of void-nucleating particles and found that this minimum size increased with decreasing fracture toughness due to the formation of Mn–Al particles by the excessive manganese addition. In such a case, the reduction of the size of the second-phase particles is effective in improving the fracture toughness. [Copyright &y& Elsevier]

In this study, the evolution of second-phase particles in a twin-roll-casted (TRC) Al-Mg-Si alloy is analyzed, and the influence of this evolution on recrystallization texture and mechanical anisotropy is investigated. Based on the obtained results, homogenization significantly affects second-phase particles by promoting dissolution of Mg 2 Si phases, transformation of the Fe-rich intermetallic phase, and precipitation of AlMgSi dispersoids. During TRC and homogenization, different distributions of second-phase particles (coarse intermetallic phases and fine dispersoids) are achieved. These distributions control the recrystallization texture intensity and components and have a great impact on mechanical anisotropy. For example, the TRC sheet that has a large number of coarse intermetallic particles is characterized by very weak Cube-ND {001} 〈310〉 texture. This sheet has the highest average normal anisotropy r (0.71) and lowest planar anisotropy ∆ r (0.077) among the investigated samples. Compared to the non-homogenized sheet, the homogenized counterparts exhibit enhanced texture intensity due to the dissolution or transformation of the intermetallic phase and increase in the number of fine dispersoids. Moreover, the main texture component in these sheets gradually changes to Cube {001} 〈100〉 orientation. To improve the application prospects of the TRC Al-Mg-Si alloy, further studies must be conducted regarding the effects of alloy designing and short process optimization on the material. • Interaction between second phases evolution, texture and mechanical anisotropy. • Evolution of second phase occurs with homogenization time increasing. • Intermetallic particles induce weak Cube-ND while fine dispersoids strongly suppress it. • TRC alloy (no homogenization) in T4P possessed r ¯ (0.71) and ∆ r (0.077) values. [ABSTRACT FROM AUTHOR]

[Display omitted] • The SMC exhibits superior oxidation and spallation resistance. • The scale formed on SMC is compact and consist of complex inter-overlapped oxides. • The accelerated outward diffusion of Mn enhanced the oxidation resistance of SMC. • The preferentially oxidised particles key the scale to improve the spallation resistance. In this work, the presence of second-phase particles was found can significantly improve the oxidation and spallation resistances of a high-manganese austenitic heat-resistant steel. We show this unexpected improvement is originated from three correlated phenomena caused by the second-phase particles. First, the stratified growth of scale is avoided due to the chemical inhomogeneity of the novel steel. Further, the selective oxidation of second-phase particles provides a pinning effect for the scale. Last but not least, the accelerated outward diffusion of Mn reduces the critical Cr concentration for the formation of a stable protective Cr 2 O 3 layer. [ABSTRACT FROM AUTHOR]

In the present study, the morphology and growth kinetics of discontinuous precipitation (DP) in Cu-15Ni-8Sn-xV alloys were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the DP colony presents a lamellar structure consisting of alternating lamellae of α-Cu matrix and γ-DO 3 phase ((Cu x Ni 1-x) 3 Sn). In addition, the growth kinetics of DP in Cu-15Ni-8Sn alloy was evaluated using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation and the time exponent can be ascertained between n = 2 and n = 1. It also demonstrates that the initiation of DP in Cu-15Ni-8Sn alloy occurs at grain edges and boundaries. Moreover, the activation energy (Q) of DP is determined to be about 75 kJ/mol by using the Arrhenius equation, thus DP reaction is believed to be controlled by grain boundary diffusion. Interestingly, the addition of V has an obvious effect on the suppression of DP in Cu-15Ni-8Sn alloy. It can be determined that the activation energy (Q) of DP in Cu-15Ni-8Sn-0.2V alloy is about 350 kJ/mol, which is much larger than that of in Cu-15Ni-8Sn alloy. The increasing activation energy of DP after adding V can certainly suppress the formation of DP greatly. Additionally, it is found that a larger number of Ni 3 V particles generate accompanied by addition of V in Cu-15Ni-8Sn-0.4V alloy. Therefore, the considerable precipitated Ni 3 V particles impose a strong pinning effect on grain boundary, which also should be responsible for the resultant suppressing effect. Besides, the interlamellar spacing of DP increases and the growth rate of lamellae decreases with increasing V content when aging at 673 K. • The DP in Cu-15Ni-8Sn-xV alloys were investigated. • The DP in Cu-15Ni-8Sn alloy can be suppressed by addition of V. • The growth kinetics of DP was evaluated by using the JMAK equation. • The interlamellar spacing of DP increases with increasing V content. [ABSTRACT FROM AUTHOR]