Alloying is conventionally used for advancing properties of engineering materials. But with increasing degree of alloying, materials become more resource dependent and more costly, and recycling and reuse of materials become more difficult. As nowadays sustainability is becoming a more and more important index for materials development, novel strategies for sustainable materials development is highly desired. In this paper, a sustainable “plain” approach to advancing materials without changing chemical compositions is proposed, i.e., architecturing imperfections across different length-scales. Novel properties and performance can be achieved in the “plain” materials with less alloying or even non-alloying. Basic concept, principle, as well as potential applications of the “plain materials” approach will be introduced.

The volume fraction and stabilization of retained austenite at room temperature were determined by the degree of stable element partitioning of austenite. The element diffusion behaviors usually had a close relationship with crystal defects, and dislocation multiplication caused by high temperature deformation might also increase the vacancy concentration, which contributed to the diffusion of substitutional atoms and interstitial atoms. By adopting a new treatment process of intercritical deformation-hold-quenching (DIQ), the effect of Mn partitioning and the structure evolution of bainite under the deformation in intercritical area were studied. The microstructure, dislocation density and distribution of alloy elements, especially the volume fraction of retained austenite, were characterized by means of OM, SEM, TEM, EPMA and XRD. The results indicated that the grains of ferrite and the lathes of martensite were refined, the number of the block martensite was decreased, and dislocation density was increased from 0.36×10¹⁴ m^-2 to 1.20×10¹⁴ m^-2 after deformation. The mutual movement of dislocation slip increased vacancy concentration and the number of interstitial solute atoms, accelerated the diffusive rate of C atoms and Mn atoms from α phase to γ phase, and promoted the partitioning effect of Mn element in the critical region. Eventually, the contents and areas of C and Mn enrichment were increased. By adopting the process of intercritical deformation-hold-austenitizing-quenching-partitioning in bainitic region-quenching (DI&Q&PB), the volume fraction of retained austenite was increased from 11.5% to 13.9%, and the carbon content in retained austenite was increased from 1.14% to 1.28%.

Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress σ_f for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8%Ni steel welding metals is presented to analyze the experimental results.

The environment of the tidal zone is very complex. The interactions of dry-wet alternation and sea erosion lead to serious corrosion of steel structures, which makes it difficult to adopt protective methods. Therefore, it is of great significance to study the corrosion and protection methods of steel in tidal zone. For long-scale steel through the tidal zone and immersion zone, there is a big difference in corrosion behavior with complete immersion condition, the potential of the steel surface changes due to the influence of oxygen concentration difference and tidal fluctuations or other factors. In this study, the galvanic current and open circuit potential of the long-scale AH32 steel were monitored in simulated tidal zone. The results shows that the potential at different tide levels and different immersion depths for a long-scale AH32 specimen is not unified, with the macro cell was formed by the difference of oxygen supply, which caused internal galvanic current. The essence of the galvanic current is the net current that was generated by the sum of anode and cathode current. Galvanic current at different positions on the long-scale AH32 specimen varies with the tidal movement periodically in tidal zone. When tide is at the highest level, the galvanic current of all parts accesses a maximum value, and among these maximum values, the largest one is at the middle part of specimen, which causes the biggest anodic dissolution current density. According to the variation of the galvanic current, the time distributions of the drying, wetting and immersion states were calculated, and the results showed that the corrosion scale of the long-scale AH32 specimen at different positions depends on the time all location of wetting and immersion in tidal zone. The macro cell caused the galvanic current when all parts of the specimen were immersed. At wetting state, the solution resistance of the thin liquid film is very large, which leads to the change of the driving potential of the macro cell into the potential drop. Thus, macro cell is ineffective in the wetting state and cannot produce the galvanic current. According to the relation between wetting time and quantity of electricity at wetting state, the maximum wetting time of the long-scale AH32 specimen is shown above average mean tide level in tidal zone, which indicates that the corrosion loss of this part is maximum due to wetting state. In addition to weight loss measurements, maximum of it for long-scale AH32 specimen was obtained at the average mean tide level caused by immersion state. It can be indicated the maximum weight loss of the long-scale AH32 specimen should appear upper the average mean tide level part in tidal zone. These results were consistent with measurements of corrosion rates.

The low cycle fatigue (LCF) experiments of nickel-based turbine disc alloy GH4738 have been carried out at different temperatures in air to investigate the influence of temperature on fatigue crack growth (FCG) behavior of GH4738 alloy. The FCG curves (da/dN-ΔK and a-N) and their regularity have been obtained. The results show that there is a sensitive range of temperature in which the fatigue life for GH4738 decreases sharply. The microstructures and fracture surface morphologies of the GH4738 samples tested at different temperatures were observed by FE-SEM, and changes of the mechanical properties of GH4738 at high temperature were also taken into account through modifying the stress intensity factor amplitude, ΔK. The interruption experiments were carried out at 700 ℃ and room temperature, respectively, to investigate the crack growth mode and oxidation degree at the crack tip and grain boundary of the samples. And the essential reason of temperature influence on FCG behavior of GH4738 was discussed. The result showed that as the temperature increases, the fatigue crack growth rate (FCGR) of GH4738 accelerates, the fracture surface tends to coarse, and the failure mode converts from a mixed transgranular and intergranular fracture to totally intergranular fracture. The fatigue crack growth lifetime decreases remarkably at 650~700 ℃, existing a temperature-sensitive region under ΔK=40 MPam^1/2 and 30~40 μm grain size conditions, which is mainly caused by the oxidation at elevated temperature, independent of the microstructure and mechanical property. Oxygen diffuses into the grain boundary through crack tip and slip band, or penetrates directly into the grain boundary, reacts with active elements (Co, Ti, Al) and generates brittle oxides. These brittle oxides result in weakening of grain boundary and significant decrease of fatigue property of GH4738.

Due to their excellent high-temperature strength, and good oxidation resistance, Ni₃Al-based alloys have long attracted considerable interest as a class of high-temperature structural material. These properties, combined with their unique high thermal conductivity, make them ideal for special applications, such as blades in gas turbines and jet engines. However, polycrystalline Ni₃Al alloys show almost no ductility and extremely low fracture resistance at ambient temperatures. Ni₃Al alloys with the high ductility at room-temperature can be adjusted by the microstructure through directional solidification (DS) and matching. It has been shown that the electric field can refine the solidification structure, reduce the dendrite spacing, promote the diffusion and change the solute redistribution in the solidification process. In order to improve the room temperature ductility of Ni₃Al alloy, the effect of current intensity on microstructure of DS Ni-25Al alloy is investigated. In this work, the effects of constant current intensity and NiAl phase on the microstructure are researched. The results show that in the DC electric field, as the result of the aggregation of current along dendrite tip and the Joule heat at the tip of dendrite, the primary dendritic spacing (λ) decreases with the increasing of current intensity. And the solid-liquid interface tends to be straight resulting from the Joule heat and Peltier effect caused by the segregation of current and the difference in conductivity between solid and liquid interface. When no direct current is applied the DS samples contain the L1₂ structure of Ni₃Al matrix and B2 structure of NiAl precipitate phase. The microstructure is a duplex structure which consist of gray Ni₃Al matrix and black NiAl precipitates. NiAl precipitates with regular shape and has obvious orientation along with the growth direction. When the DC current is applied, NiAl precipitates is irregular and dispersion and has no obvious directionality, due to Joule heat effect generated by the current effect, the undercooling increased and the precipitated NiAl phase transformed into thin martensite NiAl phase with twin crystal symmetry from the NiAl-B2 type structure.

High alloying Ni-based powder metallurgy (PM) superalloys show excellent fatigue performance and damage tolerance properties, and good creep resistance at 750 ℃, and are used for advanced gas turbine disks and other hot components. The hot-working window of high alloying PM superalloy is narrow because of its poor workability. The formation of the γ+γ′ microduplex structure during the thermomechanical processing always results in a decrease in flow stress and a promotion of hot plasticity. However, the stability of the γ+γ′ microduplex structure has not been evaluated. The high temperature flow behavior of a Ni-based superalloy FGH98 prepared by hot isostatic pressing has been examined by means of uniaxial compression testing isothermally at 1060, 1105, 1138 and 1165 ℃ and at constant true strain rates between 0.01 and 10 s^-1. The microstructural evolution and instabilities during plastic flow have been studied. Under all testing conditions, the as-hipped material exhibits flow hardening, flow softening and steady-state flow sequentially with the true strain increased. The dynamic recrystallization occurs and the γ+γ′ microduplex structures are generated when steady state flow or highest strains achieved at temperatures below the γ′ solvus. The formation of the γ+γ′ microduplex structures results in a remarkable decrease in grain size and a promotion of hot plasticity. The relationships between steady-state grain sizes and steady-state stresses during deformation and the formation mechanism of the γ+γ′ microduplex structure were analyzed. The possibility of the microstructure controlling during hot working was discussed.

The (R, Ce)-Fe-B magnets have been successfully industrialized in recent years. The mechanical property of sintered permanent magnets is one important aspect of their comprehensive performances, which directly influences the service reliability and the production cost. In this work, the bending strength, fracture toughness, Vickers hardness and brittleness index of commercial (R_1-xCe_x)_30.5’31.5Fe_bal.-B₁M₁ (mass fraction, %) magnets with different Ce contents have been investigated. The microfractures of the magnets were observed by SEM equipped with EDS. It shows that the bending strength and the fracture toughness of (R, Ce)-Fe-B magnets have a downward tendency with increasing Ce content x, while the Vickers hardness of the magnets varies irregularly with Ce content. The optimum mechanical properties have been obtained in the (R_1-xCe_x)_30.5~31.5Fe_bal.-B₁M₁ magnet with x=0.15; the bending strength, fracture toughness and brittleness index of the magnet with x=0.15 are obviously superior to those of the ordinary sintered Nd-Fe-B magnets. Some flocculent oxide phases have been discovered in the (R, Ce)-Fe-B magnet with x=0.15. The flocculent phases may absorb part of energy during crack propagating, and reduce the stress concentration at a crack tip, which is beneficial to strengthening and toughening of (R, Ce)-Fe-B magnets. However, the mechanical properties are obviously worse for the magnet with x=0.45 (Ce/ΣRE=45%). That is probably because the microstructures of the magnet with x=0.45 become deteriorated, in which abnormally large grains have been observed. The results confirm that the fracture mechanism of sintered (R, Ce)-Fe-B magnets with different Ce contents mainly appears intergranular fracture.

The process of production and working environment of heat exchangers call for materials with good elevated temperature properties. However, the previous investigations were mainly focused on their room temperature properties. The relationship between microalloying and high temperature properties, especially creep properties of Al-Mn-based alloys are barely discussed. In order to improve the industrial applications of Al-Mn-based alloys, the effect of Mg, Ni and Zr additions and annealing process on the microstructure and high temperature properties of Al-Mn-based alloys were studied in this work. The investigated alloys were treated in two ways, first one is cold-rolling and heat treatment at 873 K for 10 min, and the second one is cold-rolling, heat treatment at 623 K for 1 h and 873 K for 10 min. The results indicate that annealing process has remarkable effect on the grain shape, fine equiaxed crystal grains are obtained in the former, while stable elongated grains are obtained for precipitation precedes recrystallization at 623 K in the latter. With Mg addition, more AlMnSi phase precipitated during annealing. The addition of Zr and Ni increases the type and amount of heat resistant compounds, precipitate Al₃Zr and AlMnSiNi, which are beneficial to improving high temperature properties of Al-Mn alloy. Al-Mn-0.3Mg-0.2Ni alloy has the best elevated temperature properties, and the tensile strength of it is 102 MPa (50 MPa higher than Al-Mn alloy) at 523 K. And the steady-creep rate is strongly decreased to 3.93×10^-8 s^-1, two orders of magnitude smaller than Al-Mn alloy at the temperature of 523 K under the stress of 40 MPa. With dispersoids compli cated or increased, the movement of dislocations are pinned strongly, which are contribute to improving the creep properties of Al-Mn alloy for the creep is mainly controlled by dislocation climb.

Hot stamping is an alternative technology to produce ultra-high strength steel (UHSS) with a tensile strength above 1 GPa for automotive bodies. At present, the hot-dip Al-10%Si (mass fraction) coating is used as a shield coating for the hot stamping steels, which protects the steels from surface oxidation and decarburization, and enhances their corrosion resistance. However, the microstructure evolution and compounds of hot-dip Al-10%Si coating during austenitization of 22MnB5 hot stamping steel are not clear yet. In this work, the thermo-mechanically induced microstructure evolution of hot-dip Al-10%Si coating is observed using SEM after austenitization of 22MnB5 hot stamping steel at 900 ℃ for different times, and the elemental depth profiles are analyzed in hot-dip Al-10%Si coating by EDS and GD-OES. The results show that before austenitization, the hot-dip Al-10%Si coating consisted of an aluminum matrix, pure silicon, and the intermetallic compound Fe₂SiAl₇, which was formed by eutectic reaction, there was a thin layer, which was composed of Fe₂Al₅ and FeAl₃ between the intermetallic compound Fe₂SiAl₇ and the steel substrate. When 22MnB5 hot stamping steel was austenitized at 900 ℃, the ternary eutectic phase Al+Si+τ₆ was transformed into an Al-Fe-Si ternary intermetallic compound or Fe-Al binary intermetallic compound gradually in the hot-dip Al-10%Si coating. When the austenitizing time was 2 min, the Al-10%Si coating was composed of the intermetallic compound Fe₂SiAl₇, Fe₂Al₅ and FeAl₂ phases; when the austenitizing time was 5 min, the Al-10%Si coating was composed of FeAl₂, Fe₂SiAl₂ and Fe₅SiAl₄ phases; when the austenitizing time was 8 min, the Al-10%Si coating was composed of FeAl₂ and Fe₅SiAl₄ phases. Because the diffusion rate of Al atoms was much larger than that of Fe atoms in the diffusion layer of intermetallic compound Fe₂SiAl₂ and coating/steel substrate, the amount of Al atoms which diffused and reacted from the coating to the grain boundaries or grain of steel substrate was much larger than that of the Fe atoms which diffused from the steel substrate to the Al-10%Si coating, also the number of vacancies which diffused from the steel substrate to the Al-10%Si coating was much larger than the other way round. Due to this imbalance, the Kirkendall void was formed in the interface between the diffusion reaction layer and the Al-10%Si the coating. The hot-dip Al-10%Si coating can be used as the protective layer, since it has a stable Al₂O₃ film formed on its surface, and its thermal oxidation was very limited, during the 22MnB5 hot stamping steel austenitizing. But the protective performances of Al-10%Si coating could be poor, because the high temperature ductility of brittle intermetallic compound was low, which induced a lot of micro cracks that were perpendicular to the interface of coating/steel substrate, and penetrated the whole coating during the diffusion process of hot-dip Al-10%Si coating.

NiPtAl coatings are widely used as overlaying coatings besides bondcoats for thermal barrier coating (TBC) systems within high temperature environment. Oxidaiton behavior of NiPtAl coatings is mainly contribution for the failure of TBC systems or overlaying coatings. An initial oxide layer growth characteristics play a key role in extending lifetime of TBC system or overlaying coatings. In this work, the oxidation experiments of the Pt modified aluminide coating on CMSX-4 Ni-based alloy were carried out at 1150 ℃ for 1 h in 80%Ar+20%O₂. The microstructures of oxide on the NiPtAl coatings are studied by OM, SEM, TEM and Raman spectroscopy. The results indicated that the oxide layer on the NiPtAl coatings included stable and met-stable Al₂O₃ after 1 h oxidation, and part of spalled oxide layer as well as pores within the oxide layer. The 0.5 μm thickness whisker-like θ-Al₂O₃ could form on NiPtAl coating during the initially oxidation stage. At the initial oxidation stage θ-Al₂O₃ fastly grew which resulted β-NiAl to γ'-Ni₃Al transformation. The Pt particles formed on the inter-surface between α-Al₂O₃ and θ-Al₂O₃ layer due to a less Pt solid solubility in γ'-Ni₃Al compared to β-NiAl in the coating. Fast growth of initial Al₂O₃ could induce pores formation within the alumina layer. The pores and stress due to oxidation and phase transformation could decrease the alumina adherence, and at last result in the oxide spallation.

Metallic thin films have many properties that bulk metals do not possess, such as high impedance. Recently, increasing attention has been paid to high impedance surface in the design of antennas and absorbers. Metallic thin films used in composite materials can realize the perfect matching of electromagnetic wave in different materials. The use of metallic thin films in electromagnetic functional materials results in significant increase of the absorbing intensity and operating bandwidth. But it usually needs to pay a huge amount of manpower, material resources and a longer period of time to design excellent electromagnetic functional materials with metallic films. So it is greatly significant to understand clearly the electromagnetic influence of metallic film for designing excellent performance materials and saving costs by simulation software. Al film is a typical non-magnetic metal film. In this work, the electromagnetic reflectivity of Al films and glass fiber reinforced resin matrix composite had been studied. High frequency electromagnetic field calculation software FEKO was employed to calculate the reflection coefficient of the composites. The effect of composites' real part of permittivity ε_r, dielectric loss tangent tanδ_ε, permeability μ_r and magnetic loss tangent tanδ_μ on microwave reflectivity had been discussed. The equivalent electromagnetic parameters of glass fiber reinforced resin matrix composite had been obtained through a comparison between simulation and experimental results. Due to resonance phenomena of the embedded Al film in the glass fiber reinforced resin matrix composite with certain thickness, there is an optimum resistance value of Al film that makes the composite structure have minimum reflection. Through the calculation of Al film and glass fiber reinforced resin matrix composite with different structure, the thickness relationship between Al films in calculation and Al films prepared by magnetron sputtering had been obtained. According to the theory of transmission line, the resistance of resonance is analyzed by MATLAB. This method is also applicable to the resistance solution of the homogeneous metal films at any position in the composite or frequency selective surfaces. The equivalent electromagnetic parameters of Al film and glass fiber reinforced resin matrix composite in simulation had been ascertained, and the simulation results agree well with the experimental results.

Misrun and cold shut are common defects in casting productions, which could make surface accuracy of castings poorer, even leading to cracking and casting scraps in them. The formation process of misrun and cold shut is hard to be observed directly only by experiment measures, since casting filling process is in a state of high temperature flow inside mold. The key to predict the defects accurately is the way to handle the effect of liquid-solid conversion on flow behavior. On the basis of existing methods for treating liquid-solid conversion, a calculation model of mushy region flow behavior through measurement of solid-fraction is developed, which can effectively investigate the flow behavior of mushy region in different stages. Generally, the critical solid-fraction method is adopted for mushy region with high solid-fraction, in consideration of that only the speed of high solid-fraction region is supposed to be zero during casting filling process. The variable viscosity method is applied for mushy region with low solid-fraction, due to casting filling process being unlikely to form toothpaste-like flow. However, the porous medium drag-based model is used for mushy region with middle solid-fraction, because only the middle solid-fraction region can be equivalent to porous medium. Combining the above three methods, a flow-field calculation program considering the effect of liquid-solid conversion on flow behavior during casting filling process is developed, in which finite volume method (FVM) is included for discretization equations; the pressure implicit with splitting of operator (PISO) algorithm is added for coupling pressure and velocity; the volume of fluid (VOF) algorithm is also combined for interface tracking. An numerical simulation of water-filled S-shaped channel is performed in the case of taking no account of liquid-solid conversion, and the simulated results coincide better with the experimental results, which certifies for its accuracy as an adopted model. Since the bottom filling casting craft is commonly used in single-shape casting, a comparison between the calculated results obtained using other single models and those using this model at different control parameters, is needed. The better agreement between them indicates that this new model is appropriate for calculating the flow behavior in mushy region.

P92 steel is a typical 9%~12%Cr ferrite heat-resistant steel with good high temperature creep resistance, relatively low linear expansion coefficient and excellent corrosion resistance, so it is one of important structural materials used in supercritical thermal power plants. Fusion welding technology has been widely used to assemble the parts in thermal power plant. When the supercritical unit is in service, its parts are constantly subjected to combination of tensile, bending, twisting and impact loads under high temperature and high pressure, and many problems such as creep, fatigue and brittle fracture often occur. It has been recognized that welding residual stress has a significant impact on creep, fatigue and brittle fracture, so it is necessary to study the residual stress of P92 steel welded joints. The evolution and formation mechanism of welding residual stress in P92 steel joints under multiple thermal cycles were investigated in this work. Based on SYSWELD software, a computational approach considering the couplings among thermal, microstructure and mechanics was developed to simulate welding residual stress in P92 steel joints. Using the developed computational tool, the evolution of residual stress in Satoh test specimens was studied, and welding residual stress distribution in double-pass welded joints was calculated. In the numerical models, the influences of volume change, yield strength variation and plasticity induced by phase transformation on welding residual stress were taken into account in details. Meanwhile, the hole-drilling method and XRD method were employed to measure the residual stress distribution in the double-pass welded joints. The simulated results match the experimental measurements well, and the comparison between measurements and predictions suggests that the computational approach developed by the current study can more accurately predict welding residual stress in multi-pass P92 steel joints. The simulated results show that the longitudinal residual stress distribution around the fusion zone has a clear tension-compression pattern. Compressive longitudinal residual stresses generated in the fusion zone and heat affected-zone (HAZ) in each pass, while tensile stresses produced near the HAZs. In addition, the numerical simulation also suggests that the transverse constraint has a large influence on the transverse residual stress, while it has an insignificant effect on the longitudinal residual stress.