Nuclear reactor pressure vessel is the irreplaceable component of the nuclear power plant and its integrity is one of the key issues of any nuclear power plant for long term operations. Various nanofeatures, including solute clusters, matrix damage and grain boundary segregation formed in reactor pressure vessel steels in the face of neutron irradiation. These ultrafine microstructural features lead to an increase in the ductile brittle transition temperature as is the measure used to describe the irradiation embrittlement. The balance of features depends on the composition of the reactor pressure vessel steels and the irradiation conditions. This paper reviews the current phenomenological knowledge and understanding of the basic mechanisms and relevant influence factors for irradiation embrittlement of nuclear reactor pressure vessel steels. To be specific, the formation and evolution processes of the embrittling features are presented. Also, the influences of material variables, such as copper, nickel and manganese contents on irradiation embrittlement and those of irradiation variables, such as neutron flux and post irradiation annealing are summarized. In addition, fundamental research issues that remain to be addressed are briefly pointed out.

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. At present, the widely used protection method in tidal zone is coating which is effective in short term. However, it is easy to cause blister failure during the long-term service process, and it will increase the maintenance cost. Sacrificing anode protection is the most common method used in the seawater environment due to its advantages such as low cost, simple operation, no external current, no interference with adjacent metal facilities, good current dispersion ability, easy management and maintenance and high efficiency, etc.. However, in the tidal zone, sacrificial anode protective is effective only when the protected metal is in seawater immersion state. After the tide receded, the protected metal exposes in air. At this time, the current loop is destroyed, and the sacrificial anode protection effect is weakened. Therefore, it is commonly known that the sacrificial anode protection method can not protect the whole tidal zone against corrosion. At present, the corrosion process and mechanism of steel structures under sacrificial anode protection in the tidal zone are not clear. In order to study the corrosion mechanism of sacrificial anode protection, a corrosion experimental trough was designed to simulate the tidal zone and immersion zone. The electrode potential of Q235B mild steel under different protecting area of sacrificial anode in it was monitored in situ by the electrochemical workstation. The results show that under the sacrificial anode protection, the long scale specimen of Q235B steel is protected well, the corrosion degree in the tidal zone gradually reduces with the decrease of tide level, and the protected height increases with the increase of sacrificial anode area. Protective effect of sacrificial anode is mainly decided by the IR drop of specimen surface when the steel structures are exposed in the air, the smaller value of IR drop, the better protection effect. However, although the protection effect of steel structures can be improved by increasing the metal area of sacrificial anode, sometimes a part of steel structure may be in the state of excessive protection. The effective way to solve the corrosion problem of tidal zone needs to cooperate the sacrificial anode with other protective methods.

Precipitation strengthening plays an important role on improving the mechanical properties of steels, NiAl and Cu-rich phases are two kinds of common precipitates. This work aims to reveal the precipitation characteristics of these two phases in martensite and retained austenite in precipitation strengthening steel by atom probe tomography (APT). The hot rolled samples were aged at 500 ℃ for 1 h after solution treatment at 900 ℃ for 2 h, followed by microstructure analysis. The results show that NiAl and Cu-rich phases form in martensite phase as well as at martensite/austenite phase boundaries, while no precipitate develops in retained austenite. Precipitation was not observed near the phase boundaries in martensite. Equivalent radius, spacing and concentration of the strengthening phases at phase boundary are larger than that inside martensite. In addition, NiAl phase tend to separate from Cu-rich phase, and the separated tendency becomes stronger at phase boundaries than in martensite. Besides, the growth of NiAl and Cu-rich phases at phase boundary differs from that within martensite, which should be induced by the defect density difference between them.

Conventional pack boriding (CPB) has shortcomings of high processing temperature and long process duration for producing boride coating with an effective thickness. Alternating current field enhanced pack boriding (ACFEPB) is a new approach for overcoming those shortcomings in CPB. In the present work, ACFEPB was carried out on a 45 medium carbon steel at low and medium temperatures (450~800 ℃) by applying a 50 Hz alternating current field (ACF) during the pack boriding for revealing effects of ACF on the treatment. Understanding characterization of the ACFEPB better will lay a good foundation for investigating the mechanism of the ACF on the boriding and optimizing the new process. Experimental results showed that nearly same thick boride coatings were obtained in target surface of samples located in different positions right between the parallel ACF electrodes, while less thick boride coatings were found in samples not within the region. All ACFEPB samples' boride coatings were thicker than that of corresponding CPB, which demonstrated that applying an appropriate ACF could notably enhance the boriding. A linear relation was shown in the profile of ACFEPB coating thickness vs the boriding temperature. The coating thickness of the ACFEPB at 800 ℃ increased with the increase of the ACF current. And the coating thickness vs the boriding time exhibited a parabolic character. Morphology similar to the CPB coating was presented in the ACFEPB coating. The saw-tooth shaped boride penetrated perpendicularly to the substrate. However, fewer or no FeB phase was found in ACFEPB coating when comparing with CPB coating treated at same temperature with same duration. More micro-porosities were found in the near surface zone of single Fe₂B phase coating by ACFEPB, which was an indication that more vacancies moved from the substrate to the near surface region. Although a temperature rise caused by the ACF was detected in the sample during the boriding, the heating effect of the ACF to the sample and the boriding media was not the main reason for ACF's enhancing effect to boriding. The ACF’s electro-magnetic effect should be the main factor for the enhancement. The ACF induced current would lead more vacancies in the treated sample, which promoted the diffusion in the substrate. The ACF should also intensify chemical reactions and diffusions in the boriding media with the energy from the ACF and the ACF's electro-magnetic stirring effect. More active boron-containing species formed and moved to the sample's surface to accelerate the formation of borides.

As a candidate package material for high level radiation waste disposal, the crevice corrosion behavior of Q235 low carbon steel weld joint was investigated in a solution simulated to the groundwater in the northwest part of China. The influences of temperature and oxygen content were evaluated. The microstructure of the weld joint was observed by OM, and SEM and surface profile were employed to analyze the crevice corrosion behavior of the weld joint. Open circuit potential of different regions of the weld joint was measured by electrochemical method. Experimental results indicated that the increases of temperature and oxygen content could promote the occurrence of crevice corrosion, and facilitate the corrosion processes both inside and outside the crevice. Fusion zone with a microstructure of clustered ferrite was the most severe corroded area in the weld joint, followed by weld metal, which was characterized by a coarse widmanstaetten structure. The microstructures of base metal and heat affected zone were fine and homogeneous, so these two regions underwent slighter corrosion.

The corrosion-abrasive wear behavior of lower bainite ductile iron was investigated by corrosion-abrasive wear tests. The main factors of mass loss rate were analyzed. SEM and TEM were used to observe the worn surfaces. The strain-hardening effects beneath the contact surfaces were analyzed by microhardness profiles. The influence of load to corrosion resistance was researched by polarization curves. The results show that the main corrosion wear mechanism was corrosion mass loss and furrow wear. The roughness of worn surface, friction between sample and abrasive, depth of furrow all increased with the test load, which increased the corrosion-abrasive wear rate sharply. Meanwhile, the corrosion micro-cell formed along with the appearance of graphite ribbon and delamination at a higher load, which enhanced the corrosion rate rapidly, and the fracture of delamination resulting from plastic deformation fatigue was another critical factor of the increased mass loss. With the increase of test load, dislocation multiplication and pile-up took place in the retained austenite, which improved the wear resistance of material to some extent. However, the improvement was limited. The average mass loss rate was still increased from 0.16 g/(cm²·h) to 0.42 g/(cm²·h) with the increase of test load; the corrosion current density (i_corr) was enhanced from 0.56 mA/cm² to 5.62 mA/cm² along with the increase of roughness. In addition, the mass loss curves of lower bainite ductile iron were divided into three stages: point contact wear (initial stage), surface contact wear (transition stage) and fatigue wear (stability stage).

With the fast development of industry, a serious global problem, pollution, becomes more apparent. A large number of wastewater is discharged, causing the environment pollution. Supercritical water oxidation (SCWO) becomes the most effective method to treat the wastewater within recent years, but the material used in the equipment plays a key role in restricting the application of the SCWO process. Currently, during the SCWO wastewater treatment process, 304 austenitic stainless steel, alloy 625, P91 and P92 steels are the mainly preheater and reactor materials. In order to reduce the serious corrosion and improve economic efficiency of the materials for this process, a new corrosion resistant Ni-based alloy (called X-2# alloy) has been developed with an aim of replacing the previous ones. In particular, it is highly important to the related behavior of this new alloy welding with the original SCWO. Therefore, the microstructure and mechanical properties of the welding joint of the new alloy and 304 austenitic stainless steel with manual argon arc welding were investigated. The microstructure and fracture morphologies of the welding joint were analyzed through OM, SEM and EDS, and the detailed analysis of the micro-hardness, tensile strength and other mechanical properties were performed. The results demonstrated that the parent material with the typical 40~65 mm grains size is helpful for dissimilar steel welding, and the microstructure in fusion zone of X-2# side does not show welding defects. However, some ferrites are further formed near the fusion zone of 304 stainless steel sides. There are Cr-rich and Ni-poor distributions in the ferrites. The grain grows seriously in both the areas near the remelt zone and 304 stainless steel side of heat affected zones (HAZs), which affect heavily the performance of welding joint. In addition, the results also uncover that the Vickers-hardness is the minimum in the HAZ. At room temperature, the fracture location of the tensile tests of X-2#/304 is in the welding seam, whereas at 500 ℃ the corresponding position is in the 304 matrix. Due to the strengthening effects of Al, W and Mo elements, the high temperature mechanical properties of X-2# alloy have been found to be even better than those of the 304 austenitic stainless steel.

Rupture life is a main property for a material using at high-temperature condition. Usually, the rupture life is gained from creep rupture test. As creep and stress relaxation are two main behaviors for a material served in high-temperature environment, it is important to work out the interrelationship through which one of the two behaviors can be deduced from the other one. Recently, a number of researchs have taken stress relaxation test to replace creep rupture test on studying the creep behavior, and furthermore predicting the rupture life and the stress relaxation test is proved to be superior to the traditional creep rupture test for its short time, small at damage, abundant of information and so on. In this work, the stress relaxation test was used to analyze the creep behavior of two HR3C heat resistant steels with different grain sizes. Additionally, considering the change of microstructure during serve period, the aged HR3C steel was used to compare with as-received HR3C steel for studying the aging effects on the creep behavior. Furthermore, the creep behavior was correlated to their microstructure characteristics. The result was shown that the creep behaviors of two HR3C heat resistant steels varied significantly in spite of their similarity in chemical composition. The coarse grained HR3C steel had lower creep rate, larger stress exponent, greater activation energy and higher creep resistance than that of fine grained HR3C steel for both as-received one and aged one. The long-term aging process damaged the microstructures of two HR3C steels, increased aged HR3C steel's creep rate, lowered stress exponent and activation energy and reduced creep resistance. And the damaging effects on the coarse grained HR3C steel were larger than that on fine grained HR3C steel, which meant the coarse grained HR3C steel had much more stable creep resistance than that of fine grained HR3C steel.

Over the past decades, traditional hard transition metal nitride films, such as TiN, have been widely used as machining and metal-forming tools coating materials due to their high hardness and chemical stability. With the rapid development of modern industrial technology, TiN has been unable to meet the requirements of modern industry, nanocomposite films because of its excellent comprehensive performance have attracted more and more scholars' attention. TiWN film as one of the TiN-based films has become a better substitute material. However the room temperature tribological property of TiWN film is not ideal, which limits its use of performance. According to the published experimental studies, C can well improve the room temperature tribological property because of its self-lubricating performance. However the effects of C content on the hardness of TiWN film is still not clear. The effects of C on mechanical property and the friction and wear property of TiWN film remain to be investigated. A series of TiWCN composite films with various C contents have been synthesized by magnetron sputtering technique. The microstructures, mechanical properties and the friction and wear property were investigated by XRD, SEM, nano-indentation, high temperature ball-on-disc tribo-meter, respectively. The results show that TiWCN composite films consist of fcc structure TiWCN phase and hcp structure Ti₂N phase. With the increase of C content, the hardness of TiWCN films increases first and then decreases, the wear rate decreases first and then increases, while the friction coefficient gradually decreases. The maximum hardness of 35.97 GPa and the minimum wear rate value of 1.26×10^-5 mm³·N^-1·m^-1 are obtained when C content is 11.25%. The minimum friction coefficient of 0.32 is obtained when C content is 13.68%. The friction coefficient and wear rate of TiWCN composite films are lower than that of TiWN films when the temperature is below 370 ℃; while the values are higher than that of TiWN films when the temperature exceeds 370 ℃. C added to the TiWN films improves mechanical properties and the room temperature friction and wear properties of the films though does not enhance the high temperature friction and wear properties of the films.

It is well known that in peak-aged conditions age-hardenable aluminum alloys usually have high strength but low corrosion resistance. Low corrosion resistance of peak-aged Al alloys limits their applications in some corrosive conditions. In order to enhance the corrosion resistance, over-ageing treatments are often carried out but at the expense of strength. Therefore, it is of great industrial value to improve both strength and corrosion resistance of Al alloys simultaneously. In the present work, a novel two-step ageing treatment consisted of high-temperature pre-ageing and low-temperature re-ageing was proposed to improve both the tensile properties and intergranular corrosion (IGC) resistance of Al-Mg-Si-Cu alloys simultaneously. Furthermore, the effects of pre-ageing time at 180 ℃ and re-ageing time at 160 ℃ on the mechanical property and IGC susceptibility of the 6061 Al alloy were investigated by tensile testing and immersion corrosion testing. It was shown that after the optimized two-step ageing treatment of 180 ℃, 2 h+160 ℃, 120 h, the 6061 Al alloy had slightly higher strength than that of the conventional peak-aged samples and no susceptibility to intergranular corrosion. TEM observation revealed that the microstructures of the two-step treated 6061 Al alloy were consisted of high density of b″ phase along with small amount of Q' phase in the matrix and discontinuously distributed, spherical grain boundary precipitates, which led to high strength and IGC resistance of the 6061 Al alloy, respectively. The formation of the characteristic microstructures were attributed to the different decreased level of atomic diffusion rate between the matrix and grain boundary when decreasing from relatively high pre-ageing temperature to low re-ageing temperature, which resulted in the relatively slow growth of the matrix pre-precipitates and rapid coarsening of the grain boundary pre-precipitates, simultaneously.

The mechanical properties and work hardening behavior of columnar-grained HAl77-2 brass were investigated by means of room temperature tensile test, EBSD and TEM. The effects of grain size on the work hardening rate and tensile ductility of the alloy were discussed. Some references reported that deformation twinning developed in the equiaxed-grained brass led to a reduction in slip length of dislocation and an increase in the work hardening rate at the second stage in the curve of work-hardening vs strain. In this work, however, the results showed that the low-angle subgrain boundaries distributed parallelly were formed in the columnar grain and reduced the slip length of dislocation at the second stage, which was responsible for the rise of the work hardening rate. With increasing grain size, both the yield strength and ultimate tensile strength of the columnar-grained HAl77-2 brass decreased, but its elongation to failure increased significantly from 70.4% for the grain size of 2.0 mm to 84.4% for the grain size of 6.0 mm. Higher performance to resist the plastic instability and better deformation uniformity mainly contributed to the ductility improvement of the larger-grain-sized columnar-grained HAl77-2 brass.

Industrial wastewater shows the characteristics of high concentration, complex composition and difficulty to degrade. Supercritical water oxidation (SCWO) gains extensive attention and application in wastewater treatment. This method of wastewater treatment is carried out in the high temperature, high pressure, strong corrosion and oxidation conditions. Thus, the corrosion resistance of the materials used in the treatment equipment should possess excellent performance. Especially for the preheater or reactor piping material, the problem is more outstanding. In this work, a new corrosion resistant Ni-based alloy used in supercritical water oxidation environment was investigated. The microstructure and fracture morphologies of the welding joint were observed and analyzed by OM, SEM and EDS, and the microhardness, tensile strength and other mechanical properties were tested as well. The results indicate that the welding seam of the alloy welding joint can be categorized into cast structure. The microstructure of fusion zone has no welding defect, and the heat affected zone (HAZ) has no grain coarsening phenomenon. The grain size of the alloy is 65 mm. The Vickers hardness of the alloy welding seam are less than the matrix. However, as the number of isometric crystals increases, the Vickers hardness of welding remelting zone becomes large. Because of including W, Mo, Al ,Ti in the alloy, X-2# alloy welding joint has good high-temperature strength and thermal stability. Due to the tensile strength of welding joints in the new alloys is lower than the parent materials, the welding seam is the weakest link. The tensile tests at room temperature and high temperature show tenacity fractures, and the fracture mechanism is mixed with normal fault and shear fault.

Grain size is one of the most important parameters which affect the mechanical properties of cast polycrystalline superalloys. To study the effect of grain refinement on the creep behaviors of K417G superalloy, the creep behaviors of K417G superalloy with four grain sizes were investigated at 760 ℃/645 MPa, 900 ℃/315 MPa and 950 ℃/235 MPa. The longitudinal section of the fracture surface, crack propagation path, dislocation structure and plastic deformation distribution in the vicinity of the cracks were investigated by using SEM, TEM and EBSD techniques, thus the deformation mechanism and effect of grain refinement on the creep properties of K417G superalloy were determined under different creep conditions. The results showed that the effects of grain refinement on the creep property of the alloy varied with the temperatures and stress. At 760 ℃/645 MPa, grain refinement improved the creep life and reduced the steady-state deformation rate of the alloy. The creep deformation was dominated by intragranular deformation. At 900 ℃/315 MPa, as grain size decreased, the creep life increased firstly and then decreased, while the steady-state deformation rate decreased firstly and then increased. The creep deformation showed a competitive effect of intragranular deformation and grain boundary sliding. At 950 ℃/235 MPa, the creep life decreased and the steady-state deformation rate increased with the decrease of the grain size. Grain boundary sliding was the main deformation mode. At the same time, grain refinement could cause a refinement of the dendrite and carbide of the alloy, which would also affect the creep behavior of the alloy to a small extent. The TEM observation showed that at 760 ℃/645 MPa, the dislocations interacted with g' particles through shearing mechanism and no dislocation network was found in the matrix. While at 900 ℃/315 MPa and 950 ℃/235 MPa, the dislocations crossed the g' particles through Orowan bypass mechanism, dislocation network formed in the matrix, and M₂₃C₆ precipitated in the interior of the grains, which had a orientation relationship between the M₂₃C₆ precipitates and matrix .

The solidification process of alloys are not just liquid to solid phase transformation, in fact in some alloys liquid to gas and gas to liquid phase transformation processes happen. A method incorporating the full diffusion-governed phase transformation kinetics into a multiphase volume average solidification model is presented. The motivation to develop such a model is to predict the multiple effect of inclusions precipitation behavior in castings. A key feature of this model, different from most previous ones which usually assume an infinite solute mixing in liquid lead to erroneous estimation of the multiphase diffusion path, is that diffusions in solid, liquid and gas phases are considered. Here solidification of Fe-Bi-Mn ternary alloy is examined. As MnS and Bi have large differences in the solute partition coefficient, diffusion coefficient and liquidus slope, the multiphase diffusion path shows differently from those predicted by infinite liquid mixing models. In this work, a three-dimensional mathematical model for a three-phase flow during its horizontai solidification was studied based on diffusion-governed phase transformation kinetics. Effects of Fe-Bi-Mn ternary alloy solidification on solid-liquid-gas phase transformation were considered. The free-cutting phase precipitation behavior was studied and multiphase transformation and multiphase diffusion path of free-cutting phase precipitation behavior were analyzed. Results show that the multiphase transformation-diffusion is strongly influenced by free-cutting phases precipitation behavior: MnS has a relatively large partition coefficient and small diffusion coefficient with larger M_ls,MnS (solid-liquid mass transfer rate of MnS). During solidification, C^*_s,MnS (solid interface concentration of MnS) may become even larger than C_l,MnS (liquid concentration of MnS), MnS in liquid is assumed to be fully ‘trapped’ in solid and there is no longer any enrichment of MnS; however Bi has a relatively small partition coefficient and large diffusion coefficient with smaller M_ls,Bi (solid-liquid mass transfer rate of Bi) and negative M_gl,Bi (liquid-gas mass transfer rate of Bi), during solidification, C_l,Bi (liquid concentration of Bi) always greater than C^*_s,Bi (solid interface concentration of Bi). In addition, due to the existence of Bi-gas phase, Bi continuous to flow, enriched in the solidified around MnS. Calculated results show good agreement with experimental data.

The solid/gas eutectic unidirectional solidification process is a new kind of technology fabricating the lotus-type porous structure. Besides having the properties of large specific surface area, excellent sound absorption, penetrating performance etc. of traditional porous materials, the particularity of the lotus-type porous structure makes it has extraordinary mechanical and thermal properties. There is a great potential for lotus-type porous aluminum in the field of lightweight engineering and heat dissipation of chip owing to its low density, outstanding corrosion resistance and high thermal conductivity. However, the fabrication of lotus-type porous aluminum has always been more difficulty than other metals. Until porous aluminum with excellent pore structure was fabricated under very small solidification rates (0.008~0.015 mm/s) and high superheat degrees of melt (240~340 K), the proper processing parameters were recognized to be essential for the coupled growth of solid/gas phases for Al-H₂ system, especially the solidification rate. In this work, a three-dimensional time-dependent model describing the evolution of single pore was established based on the theoretical analysis of mass transfer, gas bubble nucleation, pore growth, interruption and detachment. The morphology of single pore under different solidification rates were simulated during the Gasar process by using the finite difference method for Al-H₂ system. The research reveals: coupled growth of solid/gas phases can be achieved under the solidification rates from 0.15 mm/s to 0.005 mm/s. The average pore diameter which ranges from 100 mm to 1100 mm increases with decreasing the solidification rate. The pore length also increases while the pore aspect ratio is nearly a constant about 40 with decreasing the solidification rate. The simulated average pore diameter is in good agreement with the experimental values when solidification rate equals to 0.015 mm/s, and then being slightly lower than the experimental ones with decreasing the solidification rate. The diffusion of hydrogen into the melt during the solidification process is regarded as the main reason of the discrepancy between simulated and experimental average pore diameters. The maximum value of the simulated solidification rates for coupled growth of solid/gas phases in Al-H₂ system first increases from less than 0.01 mm/s to 0.15 mm/s and then being a constant, while the minimum ones increase from about 0.0001 mm/s to 0.01 mm/s with improving the overheat degree of melt and hydrogen partial pressure. By comparing the relative parameters of Al-H₂ and Cu-H₂ systems, the solubility of hydrogen is regarded to be the main parameter which determines solidification rates of coupled growth of solid/gas phases for Al-H₂ system.