Heat treatments in the temperature range of 800~950℃for 10~60 min was applied to water-quenched Ti65 alloy, in order to investigate the martensite decomposition and its effect on tensile properties at room temperature. The results show that detectable martensite decomposition is already found at 800℃ with a holding time of only 10 min. The martensite decomposition occurs through the diffusion of β-stabilizing elements from the interior of α' plate to the interface to form β phase. The morphology of the β phase changes from irregular to regular rods of varied aspect ratio with prolonged holding time. Increasing temperature leads to apparent coarsening of the decomposition products. Both room-temperature tensile and yield strengths decrease after the heat treatments. Nearly constant strength was found for the heat treatments in the range from 800℃/40 min across 850℃ 20 min/40 min/60 min to 900℃/20 min. The decrease of strength is attributed mainly to the weakened solution strengthening induced by the decomposition of martensite phase. After the completion of the decomposition of the martensite phase, the strength remains almost constant due to the balance between the weakening induced by the coarsening of α plate and the strengthening by the dispersed α₂ particles.

A nickel base single crystal superalloy DD413 was coated with platinum modified aluminide (Pt-Al) coating via successively Pt electrodepositing and vapor phase aluminizing, then the degradation behavior of the Pt-Al coating/ DD413 alloy after long-term thermal exposure in air at 850℃ and 1000℃is studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that with the extension of thermal exposure time, MC carbide and σ-TCP phase dissolve to varying degrees in the interdiffusion of zone (IDZ), accompanied by M₂₃C₆ carbide precipitation on the interface. At the same time, the size of the secondary reaction of zone (SRZ) and σ-TCP phase increases continuously. In the substrate beneath the coating, cubic γ' precipitates are spheroidized and connected with each other in a raft shape. The higher thermal exposure temperature, the more obvious the above microstructure degradation process. It can be seen from the comparative analysis that the microstructure degradation after long-term thermal exposure is closely related to the diffusion of elements at high temperatures.

The interfacial properties of modified carbon fiber reinforced polyimide resin matrix composites at 300℃ were studied by using argon inductively coupled radio-frequency plasma (ICP). Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray electron spectroscopy (XPS) and other analytical test methods were used to systematically study the effects of argon plasma treatment time on the morphology, roughness and chemical composition of fiber surface before and after continuous carbon fiber modification, and the change law of the interface strength of Carbon fiber reinforced polyimide resin matrix (CF/PI) composites at 300℃. The results show that after the optimal time of argon plasma treatment for 7 min, the morphology of the carbon fiber surface becomes rough, the structural characteristics of unevenness appear, the surface oxygen element content increases from 11.43% to 16.28%, the polar functional group -C-O- content increases to 14.37%, and the wettability of the fiber surface increases. The interlayer shear strength (ILSS) value of carbon fiber and polyimide resin matrix increased from 76 MPa to 86.2 MPa at 300℃, indicating that argon plasma treatment can improve the interfacial properties of CF/PI composites at 300℃.

The metal materials manufactured by laser selective melting technology have better mechanical properties than traditional casting materials and are suitable for the manufacture of various complex parts. However, the defects introduced in the process implementation are the main factors restricting the fatigue properties. Therefore, the mechanical performance of the SLM prepared 316L stainless steels was assessed. The results show that the tensile strength, yield strength, and elongation of 316L stainless steel formed by laser selective melting process are 816.8, 720.4 MPa, and 33.83%, respectively, which are much higher than that of the forged parts. However, it is found that the measured data of fatigue life are much dispersed due to the initiation of cracks on defects in the surface and/or near-surface during fatigue testing. The reference S-N curve of the material was obtained by the maximum likelihood method, and the fatigue limit was predicted to be 259 MPa. At the same time, combined with the √area parameter and the extreme statistical method, the maximum defect and fatigue limit of the material was predicted. The error between the fatigue limit prediction results and the test results is less than 10%, which provides a partial safety estimation method for the safety evaluation of the material.

The large coarsened primary carbides precipitated from melt during solidification is a main factor that impacts the property of M50 bearing steel. In this paper, the effect of adding a relatively large amount of high purity rare earth on the precipitation of primary carbides is studied, including the La-Ce mischmetal and pure Ce. The characterized casting microstructure demonstrated that adding rare earth can effectively reduce and refine the primary carbides, especially for the ingot with addition of only high purity Ce. The mechanism of the effect of rare earth addition on the precipitation of primary carbides is then revealed. On the one hand, the added rare earth modified the traditional inclusions into the compound with rare earth, which can be the effective nucleation agent for δ-ferrite and austenite during solidification. And consequently, the dendritic grains and its secondary arm spacing can be refined, which is favor of impeding the diffusion of carbide formation elements in the liquid and then retards the carbide growth. On the other hand, the ab initio molecular dynamics simulations demonstrated that Ce can interact with other elements in the melt and lower the diffusion coefficients of Fe and C, and thus in turn lowers the growth rate of carbide and makes the primary carbides precipitated finer and more dispersive.

The effect of biocide and D-amino acid on the corrosion behavior of 20# carbon steel, N80 steel and P110 steel in the media of SRB+IOB mixed bacteria, was comparatively assessed by using weight loss method, electrochemical measurements and SEM. In the tests without biocide, P110 suffered from severe corrosion with weight loss of 0.278 mm/a, while weight loss of 20# and N80 were 0.149 and 0.148 mm/a respectively, while uniform and dense biofilms with deposited corrosion products formed on the surface of all the steels; in the tests with biocide, the corrosion of the three steels slowed down, it is found that the formed rust scales on the surface of steels with significantly lower content of Ca Mg, P, and S, but with cracks and spallation steels. The electrochemical measurement results also revealed that the corrosion rate of three steels was significantly reduced when they were immersed for 14 d in the corrosive media with addition of biocides. The corrosion mechanism of SRB and IOB mixed bacteria is probably due to that SRB oxidizes Fe to Fe²⁺ through its own metabolism, and Fe²⁺ is further oxidized by IOB to Fe³⁺, and IOB provides environmental conditions for SRB so as to form a synergistic effect. It is proposed that D-amino acids and biocide effectively inhibit MIC behavior by regulating the bacterial gene expression and destroys the cell structure, as well as the oxygen concentration difference environment. Due to the different content of C, Cu and others, the corrosion rate of the three steels may be different under the sterile conditions.

The effect of laser shock peening (LSP) on the residual stress and fatigue properties of 8Cr4Mo4V steel was studied by numerical simulation and experimental verification in terms of the residual stress evolution, microstructure observation, hardness and rotating bending fatigue performance tests. The results show that LSP causes a large compressive residual stress on the surface of 8Cr4Mo4V steel, which was acquired to be -607 MPa and -584 MPa by finite element method and the experimental measurement. During the process of LSP, the plasma shock wave may shatter carbides on the surface of the steel into smaller pieces, while induce the secondary precipitation of subsurface carbides and the severe plastic deformation of the substrate near the surface, thus increasing the surface hardness of the 8Cr4Mo4V steel. The increase of residual stress and surface hardness and the precipitation of secondary carbides on the subsurface may effectively inhibit the initiation of fatigue cracks and slow down the crack propagation rate. Therefore, the crack source is transferred from the surface layer to the subsurface layer. The fatigue strength of 8Cr4Mo4V steel after LSP is increased by about 45.95% and the rotating bending fatigue performance is significantly improved.

It is helpful to understand the microstructure evolution characteristics and mechanical properties of monocrystalline SiC semiconductor devices during contact from the perspective of atomic scale to understand the microscopic mechanism of subsurface damage behavior and phase transformation. Based on the Vashishta potential function of molecular dynamics, the microscopic evolution characteristics of the nano-indentation induced dislocation rings, the amount of phase transformation and the contact mechanical properties of the corresponding monocrystalline SiC surface were studied, and the effect of extreme service temperature on the subsurface damage behavior and the contact mechanical properties were analyzed. The results show that the plastic deformation of SiC subsurface damage is mainly caused by dislocation nucleation, dislocation accumulation and dislocation slip, whilst the dislocation ring goes through four evolution stages during contact, i.e., dislocation nucleation, dislocation ring growth, dislocation ring reproduction and dislocation ring brittle break. Besides, with the increasing temperature, the maximum bearing capacity, hardness, Young's modulus and contact stiffness curves of silicon carbide materials show a parabolic trend of decline. The main reason is that the higher the temperature is, the SiC lattice is easy to get rid of the bondage of atomic bond energy, resulting in lattice defects, and easy to breed dislocation, which result in the enrichment of stress concentration on subsurface of materials at lastly. As a result, the mechanical properties of SiC materials are greatly reduced while being contacted. In addition, the subsurface stress concentration is also the fundamental reason for the phase transformation from cubic to sphalerite for SiC materials. With the increase of temperature, the amount of phase transformation increases. The dynamic contact plastic deformation and micro-structure evolution of SiC in semiconductor devices under loading, and the phase transformation are significantly dependent on the operating temperature. The rising temperature related change of crystal lattice and the generation of random rough spots on the surface are the main causes of contact adhesion. This study may provide a deeper understand on contact mechanical properties and sub-surface damage behavior at extreme service temperatures, and will also enrich the understanding of the contact failure mechanism of nano silicon carbide.

Electromagnetic absorbing material is one of the key materials for the realization of equipment stealth protection. Moreover, electromagnetic absorbing materials with high electromagnetic absorption and corrosion resistance will play a key role in special marine environments. Herein, the CS@rGO/EP composite functional coating with excellent microwave absorbing performance and anti-corrosion properties is successfully fabricated through physical mixing method with CS@rGO as wave absorbing filler, and the epoxy resin (EP) as matrix. The structure and properties of the CS@rGO/EP composite functional coating were characterized. The results display that the CS@rGO/EP composite functional coating possess excellent microwave absorbing properties. When the CS@rGO absorber content is 20% and the coating thickness is 1.1mm, the minimum reflection loss value of the coating can reach -25.03 dB. Meanwhile, the coating can maintain well adhesion to the steel substrate after the coating/Q235 carbon steel plate has been immersed in 5%NaCl or NaOH solutions for 30 days, and electrochemical tests manifest that the corrosion rate of the coating/Q235 steel is as low as (6.53×10^-6 mm·a^-1), i.e. a high protection efficiency (92.86%). All in all, the good comprehensive performance of CS@rGO/EP composite functional coating shows its great application potential in special service environments.