With the continuous development of intelligent society, piezoelectric sensors are increasingly used. The types, structures, measurement principles and application scenarios of piezoelectric sensors are described. The research progress on sensitive element materials is reviewed, and the application of high-temperature piezoelectric materials and lead-free piezoelectric materials is summarized. Finally, the future development direction of piezoelectric sensors is prospected.

Research progress on four piezoelectric application materials in the field of energy harvesting, including piezoelectric ceramics, multi-stacked piezoelectric ceramics, piezoelectric polymers and piezoelectric composites, is reviewed. The structural characteristics, preparation methods, and application occasions are highlighted, and the research trends of the piezoelectric materials in future is proposed.

Rubber is an important material in mechanical engineering industries. Rubber sealing materials play a key role in many mechanical instruments, and aging of rubber seals may cause unpredictable failures or even huge losses. Hence, aging research of rubber sealing materials are attracting great attentions. The aging research progress of rubber sealing materials is reviewed, including aging behavior and mechanism, effects of stress and chemical media on aging, lifetime evaluation indexes and prediction, and aging analysis techniques. The existing problems in aging research of rubber sealing materials are discussed. Future research perspectives are proposed, including studies on accelerated aging methods, aging mechanism, correlation between accelerated aging and natural aging of rubber seals, and so on.

The wire and arc additive manufacturing (WAAM) has gained more and more attention because of its unique advantages in forming large-scale components, and has become one of the most widely used metal additive manufacturing technology. The development history of WAAM is described. The influence of process parameters on the morphology of deposited layer and the evolution mechanism of microstructure is analyzed from the perspective of “shape and property control”. The numerical simulation methods for residual stress and their advantages and disadvantages are discussed, and it is pointed out that the combination of computational fluid dynamics and finite element method is one future research trend. The common methods for controling the residual stress and deformation, as well as the problems and challenges in wire and arc additive manufacturing, are summarized.

Additive manufacturing is an important development direction of advanced manufacturing technique for metal parts, but the metal powder for additive manufacturing has some problems such as insufficient research and development, weak stability and incomplete standards, which seriously restrict its development. The basic principles of common spherical metal powder preparation techniques including centrifugal atomization method, two-stream atomization method and spheroidization method are summarized, and their advantages, disadvantages and development status are introduced. It is proposed that the development of domestic additive manufacturing powder preparation technique can start from two aspects. One is to carry out process and equipment improvement and standardization research on traditional methods, and build automated factories; the other is to strengthen the research on basic theories of powdering and explore new processes.

On the basis of active and passive vibration control principles, four piezoelectric smart materials used in vibration control field, including single layer piezoelectric ceramics, multi-stacked piezoelectric ceramics, piezoelectric fiber composite and 0-3 type piezoelectric composite, are reviewed. The research progress of the structural characteristics, preparation process of the materails and their application for vibration attenuation in the fields of machinery manufacturing, aerospace and marine shipping are highlighted. The research direction in future of the piezoelectric materials is proposed.

As a main raw material for metal additive manufacturing, spherical metal powder characteristics play an important role in the performance of additive manufacturing parts. The efficient preparation of high-quality spherical metal powder has become an important development direction to promote the upgrading of additive manufacturing technologies and industrial applications. The main preparation methods of spherical metal powder including gas atomization, plasma rotating electrode atomization and plasma atomization are introduced. The technical principle and the influence of important process parameters on powder characteristics are discussed, and the future development direction of these three types of technologies is prospected.

Fatigue failure analysis processes and fatigue life assessment methods for metal materials are reviewed. The evaluation theories and models which were used widely in engineering, such as the Miner linear cumulative damage theory, the energy method, the elastic-plastic finite element method, the overload retardation model, are mainly introduced. The application conditions, advantages and disadvantages of these methods and models are also analyzed. With the development of the experimental technique and computer simulation technology, the assumptions will be more accuracy. Therefore the combined method of experiment and computer simulation for the fatigue life prediction and assessment of metal materials will be one of the most important development directions in the future.

When the thermal stress caused by sudden temperature change of ceramic materials exceeds its strength, materials will happen to crack, peel and even fracture, and then failure. Therefore, the study of thermal shock resistance of ceramic materials becomes a hot spot. The evaluation theory of thermal shock resistance of ceramic materials and the methods for testing and characterizing are described. The methods of improving thermal shock resistance, including strengthening and toughening, improving thermal conductivity, reducing thermal expansion coefficient, and reducing elastic modulus, are reviewed. The external influencing factors of thermal shock resistance are summarized. The development direction of improving thermal shock resistance of ceramic materials in future is proposed.

The rapid development of high technology puts forward higher requirements for the development of high-performance copper materials. Copper matrix composites have been widely used because of their high strength and good electrical and thermal conductivity, wear resistance, corrosion resistance and high-temperature stability; their preparation processes are constantly developing, and great progress has been made in recent years. The characteristics and research progress of the main preparation processes of copper matrix composites, including powder metallurgy technique, casting process, mechanical alloying, internal oxidation, in-situ synthesis, melt infiltration, and friction stir processing, are reviewed. The development direction of copper matrix composite preparation technology in the future is prospected.

When pulse currents are applied to metal materials, thermal and non-thermal effects will occur.The coupling of the two effects can promote dislocation movement and atom diffusion and increase the mobility of vacancy diffusion, leading to the evolution of microstructure of metal materials and forming an electroplastic effect.On the basis of the basic theory of electroplastic effects, the research progress on the pulse current treatment regulating the microstructure of metal materials and the application of pulse currents in auxiliary plastic processing and cutting processing are reviewed.It is pointed out that future researches are focused on the coupling mechanism of thermal effects and non-thermal effects in pulse current treatment and pulse current assisted processing, and current density distribution in application to complex structure parts, etc.

3D braided composites have a spatial network structure formed by continuous fiber bundles inside; therefore 3D braided composites have higher interlayer strength than traditional laminated composites, and have higher impact resistance and crack propagation resistance than metal materials. The meso-scale geometrical modeling methods of 3D braided composites are described in detail. The research progress on dynamic tensile and compression properties, dynamic failure criteria and high-speed impact properties of 3D braided composites is reviewed. The future research direction in meso-scale geometrical modeling and dynamic tensile testing of 3D braided composites is pointed out.

In recent years, the rapid development of integrated circuit, heat exchanger, semiconductor industry has put forward higher requirements for the thermal conductivity of SiC ceramics. The thermal conductivity at room temperature of SiC ceramics is much lower than the theoretical value of single crystal SiC because of the defects such as lattice oxygen, grain boundary and porosity. The effects of additives and sintering process on the thermal conductivity at room temperature of SiC ceramics are reviewed. The future development direction of high thermal conductivity SiC ceramics is prospected.

Sputtering targets are the key raw materials for the preparation of thin films by magnetron sputtering, and their quality determines the performance of the sputtered thin films. Precious metal sputtering targets are widely used in the preparation of high-performance thin films because of their excellent physical and chemical properties. The research progress on the preparation methods, technical requirements and application of precious metal sputtering targets is reviewed. The development direction of high purity, large size, high utilization rate, and integrated development of target production and sputtering film is put forward.

Development of high speed and high performance of mechanical equipments requires higher strength and better wear resistance of wear-resistant copper alloys. Although performance of traditional aluminum bronze series, manganese brass series and lead brass series alloys has been improved, their application scope is limited by various factors, such as material characteristics, processing technology and environmental protection, respectively. The application status and research progress of five typical wear-resistant copper alloys with high application values including Cu-Ni-Sn series, Cu-Al₂O₃ series, Cu-Nb series, Cu-C series (including copper/graphite, copper/graphene and copper/carbon nanotubes) and complex brass are described from preparation process, properties and application field. The problems in their development and application are analyzed, and their development prospect is also discussed.

Silicon carbide ceramic has high strength and thermal conductivity, and good chemical stability, and is widely used in aerospace, petrochemical, integrated circuits and other fields; however, defects are easy to form in the silicon carbide ceramic during processing because of its high hardness and brittleness, which restricts the application of silicon carbide ceramic with complex structures. The preparation processes of silicon carbide ceramic with complex structures are described, and the advantages and disadvantages of the commonly used preparation technologies, such as cold isostatic pressing combined with pressure-free sintering, gel injection molding combined with reactive sintering, slip casting combined with reactive sintering, 3D printing combined with reactive sintering, are analyzed in order to provide a certain theoretical reference for the preparation of silicon carbide ceramic with complex structures.

As a commonly used metal material, copper is limited in its application due to its low strength. Because of its excellent comprehensive properties, graphene has attracted wide attention as a potential reinforcement. Graphene reinforced copper matrix composites combine the great properties of both copper and graphene, and have become an research hotspot. The preparation processes and comprehensive properties of graphene reinforced copper matrix composites are introduced. The characteristics of various preparation processes, strengthening mechanism and configuration design are emphatically discussed, and the improvement approaches to solve the two main technical difficulties of weak bonding of composite interface and difficult dispersion of graphene are summarized. Finally, the preparation process of graphene reinforced copper matrix composites is prospected.

Plasma sprayed coatings have been widely used in surface protection engineering due to the excellent properties such as wear resistance, high temperature resistance and corrosion resistance. Pores are an important structural defect of plasma sprayed coatings. Excessive pores can lead to premature detachment failure of the coatings and shorten the service life, and therefore porosity is an important indicator to evaluate the coating quality. The pore formation mechanism, influencing factors, and the effect of the pores on the coating performance are briefly discribed. The research status of the porosity reduction of plasma sprayed coatings is reviewed from the aspects such as spraying process parameter optimization, laser remelting treatment, and modification of spraying materials. Moreover, the problems and development directions in the development of plasma sprayed coatings are summarized.

Under the background of increasing demand for lightweight, liquid die forging technique with excellent formability has been widely concerned. The lightweight design criteria and key points of lightweight design of equipments are summarized, and the application of liquid die forging aluminum alloy in equipments is introduced. The research progress on liquid die forging technique of aluminum alloy from the aspects of process principle and characteristics, forming materials, forming die and forming equipment is reviewed. Finally, the research and development direction of this technique in the future is put forward.

Development in recent years of hot stamping steels, including ordinary hot stamping steel, hot stamping steel with high hardenability and oxidation resistance, high strength ductile hot stamping steel, ultra high strength hot stamping steel, high hydrogen embrittlement sensitivity hot stamping steel and ultra high strength hot stamping steel reinforced by nanoparticles, is summarized. The relation between lightweight and functionality of hot stamping steel parts, the relation between strength and hydrogen embrittlement and the influence mechanism of microstructure refinement on strength and toughness are analyzed. The suggestions for the further development direction of hot stamping steels are put forward.

G20Mn5 cast steel plates with thickness of 8 mm were connected by metal active gas (MAG) arc butt welding with one-side two-pass welding method. The microstructure, hardness, tensile property and fatigue property of the joint were studied. The results show that the joint had the good surface and no obvious welding defects were found. The joint consisted of base metal, heat affected zone and weld zone, and the heat affected zone was subdivided into incomplete normalized zone, normalized zone and overheated zone. From the base metal to the weld center, the hardness of the joint increased first and then decreased. The fusion zone had the highest hardness of about 70 HRB, and the hardness of the weld was 55-60 HRB, which was a little higher than that of the base metal. The tensile strength of the joint was obviously higher than that of the base metal, while the percentage elongation after fracture was lower than that of the base metal. The high cycle fatigue strength of the joint was equivalent to that of the base metal, and both fractured at heat affected zone. The properties of the joint met the design requirements.

Domain structure is deemed as the remarkable microstructural feature of ferroelectric materials, and its spontaneous polarization vector can be switched by the external applied electric/mechanical field (namely domain switching), leading to multiply electromechanical properties of ferroelectric materials. Starting from the theory of domain switching, research progress on the domain switching criterion is reviewed, and research results of the domain-wall dynamics and the domain switching-dependent fracture mechanics are described. It is aimed at providing some references for the micromechanics research of ferroelectric materials.

The characteristics and advantages of powder injection molding of titanium and titanium alloys are described in brief. The research progress on powder injection molding of titanium and titanium alloys is reviewed in terms of raw material powder, binder system, injection molding process, performance and microstructure after formation, etc. The research direction in future for powder injection molding of titanium and titanium alloys is also proposed.

Surface texture technique is a new type surface modification technique, which can effectively improve the tribological properties of materials through machining patterns with a certain shape and size, and with regular arrangement on the surface of materials by micro-fabrication technique. Surface texture plays an important role in mechanical friction pairs because of its outstanding advantages in improving the tribological characteristics of materials. The common texture preparation methods are introduced; the wear reducation mechanism of surface texture under different working conditions is described; the influence of surface texture topography and its geometric parameters on the wear resistance is summarized. The development direction of surface texture technology is prospected.

Synchrotron radiation source with high spatial and temporal resolution is a large-scale scientific instrument representing kernel creativity of modern fundamental sciences. Research progress on in-situ loading machines based on high-energy X-ray 3D tomography is described. A set of in-situ loading rigs independently developed by the author team on the basis of Shanghai synchrotron radiation source and Beijing synchrotron radiation facility since 2011, including in-situ tensile, compression, low-cycle fatigue, high-cycle fatigue and super high-cycle fatigue testing machine as well as the sample environment, and researches on high-strength lightweight materials (such as laser welded aluminum alloy and additively manufactured aluminum and titanium alloys) are concisely discussed. The results show that in-situ loading machines play a key role in characterizing microstructural damage evolution of advanced materials, and also are the major supporting of large-scale scientific instruments related to national competitiveness.

Electrodeposition is the most widely used method for preparing nickel-based composite coatings at present. The characteristics of different electrodeposition methods are introduced. The effects of current density, bath pH, surfactant, content and size of second phase particles on the quality of nickel-based composite coatings are reviewed. The types and application status of nickel-based composite coatings are summarized. In the end, the future development of electrodeposited nickel-based composite coatings is prospected.

The dynamic tensile properties of 6061 aluminum alloy was studied by the uniaxial tensile experiment at strain rates of 0.08,35,110,210,550 s^-1. The trure stress-ture strain curves were obtained at different strain rates. A plastic deformation constitutive model of the aluminum alloy was established based on the Johnson-Cook model, and the model was verified. The results show that, with the increase of strain rate, yield strength of 6061 aluminum alloy increased and elongation after fracuture decreased, but its fracture strength had not obvious changes. The constitutive model can describe well the change of flow stress of 6061 aluminum alloy during plastic deformation.

The shape memory effect, shape memory mechanism, types and preparation methods of thermal-induced shape memory polymer are reviewed. The influencing factors of shape memory performance are discussed. The application status of thermal-induced shape memory polymer is introduced. The application prospect of thermal induced shape memory polymer is expected.

Laminated structures designed by bionics principle can better solve intrinsic brittleness problems of carbide ceramics. It is now one of the most effective ways to strengthen and toughen carbide ceramics, and has good application prospects. The structural design features of laminar ceramics are described. The preparation, performance and main toughening mechanisms of SiC and B₄C laminar ceramics are reviewed. The development of carbide laminar ceramic materials is summarized and prospected.

Cermet is widely used in manufacturing cutting tools because of its excellent strength, high temperature thermal conductivity and thermal stability of metal materials, and high temperature resistance and corrosion resistance of ceramic materials. The lack of wear resistance and hardness of cermet limits its application range, which can be solved by preparing hard coating on its surface, but the bonding strength of the coating is weak, resulting in peeling off of the coating. The preparation method of the hard coating, the influencing factors on the bonding strength between the coating and the substrate are introduced, and the methods to improve the bonding strength of the hard coating are expounded. Finally, the preparation technique and the improvement of bonding strength of hard coating on cermet surface are prospected.

Ferroelectric materials have unique photovoltaic properties due to their polarized electric field, and are widely used in many fields, especially in photovoltaic power generation. The generation mechanism of internal electric field (photovoltaic mechanism) in ferroelectric materials, and the effects of electric field regulation mechanism on photovoltaic properties of ferroelectric materials are reviewed from aspects of the preparation of narrow band gap ferroelectric materials, enhancing visible light absorption by self-doping of oxygen deficiency constructing composite heterojunction, preparing multipole axial molecular ferroelectrics, and regulating the domain orientation and distribution in ferroelectric materials by external polarization field. The research direction of improving photovoltaic performance by regulating internal electric field is pointed out.

Magnetic field-controlled directional solidification provides a new route to prepare high-quality alloys and castings, and is of great significance for improving the metallurgical quality of products and developing new preparation techniques. The main research progress on the directional solidification of nickel-based superalloys under magnetic field in recent years is summarized. Several typical effects between magnetic field and metal conductive melt are described. The revolution of the directional solidification structures of nickel-based superalloys under static magnetic field, alternating magnetic field, pulsed magnetic field and traveling magnetic field, and the influence of magnetic field on typical solidification defects such as stray grains and on the creep properties of superalloys are systematically summarized. The formation mechanisms of solidification structures and defects under different types of magnetic fields are discussed. Finally, the development trend and breakthrough points of directional solidification of superalloys under magnetic field are prospected.

Ceramics have numerous excellent properties such as low density, high hardness and wear resistance, but their practical applications in the structural materials field are still extremely cautious. The fundamental reasons are the flaw sensitivity of ceramics and the imperfect theory of ceramic failure prediction. The common flaws in the process of ceramic preparation are introduced, and the physical nature of the random distribution of ceramic strength is analyzed, and then the research status of strength prediction in ceramics under the action of flaws is summarized. It is pointed out that non-destructive testing, in-situ testing and computer simulation technology could be comprehensively used in the future to explore the mechanism of flaw inducing cracking and the quantitative law of ceramic-strength response, and meanwhile attention should be paid to the influence of flaws on ceramic-strength in the actual service environment(fatigue, thermal shock, etc.).

Bi_1.5-xBa_xZnNb_1.5O₇(x=0.05, 0.10, 0.15, 0.20, molar ratio) ceramics were prepared by solid sintering method. The effects of barium doping on sintering property, structure and dielectric property of the ceramics were studied. The results show that the sintering temperature of the ceramics decreased from 1 050℃ to 960℃ after barium doping. The phase of the ceramics was composed of single pyrochlorite, and its diffraction peak shifted to a small angular direction as the doping amount of barium increased. The dielectric constant and dielectric loss of the ceramics increased with increasing barium doping amount. Under different frequencies, the ceramics with different barium doping amount showed dielectric relaxation at low temperatures. The dielectric relaxation peak became widening and flattening with increasing barium doping amount, and shifted to high temperature directions. With increasing barium doping amount, the dielectric relaxation degree of the ceramics decreased first and then increased, and the relaxation activation energy and temperature coefficient increased first and then decreased.

Macro fiber composite (MFC for short) is a new type of piezoelectric fiber composite material. Devices made of MFC are both sensors and actuators. With a d₃₃ mode MFC actuator as an example, the piezoelectric constitutive equation of MFC is given. Advantages and disadvantages of three methods for preparing piezoelectric fiber sheets are summarized and compared. Finally, the current status of MFC application is illustrated by listing the actual application cases of MFC actuator in different fields. The application and development prospect of MFC is presented.

The progressive failure model of fiber reinforced plastics and the continuous damage model of composite laminate of the Ls-Dyna software were applied to simulate the mechanical response and damage modes of carbon fiber reinforced plastic laminates under in-plane shear loads, with the mechanical parameters obtained by quasi-static uniaxial tensile and in-plane shear tests. The applicability of the two models was compared. The results show that in the initial linear elastic stage during in-plane shearing, the two models could simulate the mechanical characteristics of the carbon fiber reinforced plastic laminates. As the load continued to increase, the load-displacement simulation curve obtained by the progressive failure model still rose linearly, and dropped rapidly after reaching the load peak; the simulation curve had a large deviation from the test curve. When the material was damaged, because of the introduction of damage parameters, the load-displacement simulation curve obtained by the continuous damage model was nonlinear, which was in good agreement with the test curve.

The 304 stainless steel substrate was grinded to 1200^# (1^# process), 2000^# (2^# process) by sandpaper in sequence and grinded to 2000^# and polished by diamond polishing paste with size of 0.5 μm (3^# process), respectively, and then the CrMoN coating was deposited on the surface. The phase composition, surface and cross-section morphology, hardness, surface hydrophobicity, corrosion resistance and conductivity of the coating were studied. The results show that the roughness of the coating surface deposited on the substrate surface pretreated with 1^# process was the largest, followed by that pretreated with 2^# process, and the roughness that pretreated with 3^# process was smallest. The phase of the coating consisted of CrN, Cr₂N and Mo₂N. With decreasing substrate surface roughness, the microhardness, free corrosion potential and water contact angle of the coating increased, and the corrosion current density and interface contact resistance after polarization decreased. The comprehensive properties of the CrMoN coating deposited on the substrate surface pretreated with 2^# process were excellent, which were close to those pretreated with 3^# process.

Ultra-high strength steels are important materials for the lightweight and safety of motor vehicles. The development and application of 1.5 GPa and above grade high-performance press-hardening steel are the key. In recent 10 a, the manufacturing technology of microalloying press-hardening steels and their parts have developed rapidly, achieving the performance such as high bending angles, hydrogen embrittlement resistance, high toughness and high hardenability; therefore the passive safety performance and lightweight of vehicles are improved. The development and application status of microalloying press-hardening steels are summarized, including the development and application of 1.5-2.0 GPa grade Nb microalloying, V microalloying, Nb-V composite microalloying and Nb-V(Mo) composite microalloying press-hardening steels, and the effects of microalloying on the nanoscale second phase precipitation and grain refinement; the hydrogen embrittlement resistance and its mechanism of microalloying press-hardening steels; the sharp corner cold bending property of microalloying press-hardening steels and its influence on the collision safety performance; the fracture failure performance of microalloying press-hardening steels. The manufacture and application of microalloying press-hardening steels in the future are also prospected.

With Ti-6Al-4V titanium alloy powder and LaB₆ powder as raw materials, the in-situ synthesized TiB+La₂O₃/TC4 titanium matrix composite and TC4 titanium alloy were prepared by selective laser melting. The phase compostion, microstructure, hardness and compressive strength of the composite and the titanium alloy were studied and compared. The results show that the microstructures of the composite and the titanium alloy were both composed of columnar β grains and acicular α' martensite distributed in grains. The size of the β grains and α' martensite clusters of the composite were smaller, and the proportion of large angle grain boundary was higher. TiB and La₂O₃ reinforcements were formed by in-situ reaction of LaB₆ and titanium. TiB was elongated and distributed along a certain direction. La₂O₃ was in shape of small spheres, and dispersed on grain boundaries and in grains. The microhardness and room temperature/high temperature compressive strength of the composite were higher than those of the titanium alloy.

Accelerated water bath moisture absorption tests at 25 ℃ and 50 ℃ were carried out on carbon fiber reinforced polymers (CFRP) laminates, and the uniaxial tension and three-point bending tests were performed. The rule of the moisture absorption, tensile strength and bending strength varying with the moisture absorption time and the bath temperature was studied. The failure mechanism of the CFRP laminates was discussed. A residual strength model of CFRP laminates was established by fitting the experimental data. On the basis of the environmental equivalent coefficient, the hygrothermal aging life of the laminates was predicted. The results show that the average saturation moisture absorption rate of CFRP laminates at 50 ℃ was 0.77%, and was larger than 0.33% at 25 ℃. At the same moisture absorption time, the moisture absorption rate at 50 ℃ was higher than that at 25 ℃. The tensile strength and bending strength decreased by 7.4% and 17.2% after moisture absorption saturation at 50 ℃ compared with that before moisture absorption, respectively, and the decrease degree was higher than those after moisture absorption saturation at 25 ℃. The higher the bath temperature, the more serious the interface damage between CFRP laminate carbon fiber and resin, and the more obvious the cracks. The real aging life prediction method on the basis of residual strength and environmental equivalent coefficient could provide evidence for the service reliability evaluation of CFRP laminates in hygrothermal environment.