In this research，the effects of heat treatment on corrosion fatigue performance of ZBAl7-7-4-2 copper alloy for ships were studied，and the mechanism of the effect of heat treatment on the microstructure of ZBAl7-7-4-2 copper alloy were discussed，which provided an important basis for improving the applications of ZBAl7-7-4-2 copper alloy in marine components such as seawater valves，filters，pumps，impellers and propellers. ZBAl7-7-4-2 copper alloy was heat treated at 900 ℃ in a vacuum heat treatment furnace and then cooled with argon atmosphere after heat treatment. The chemical composition，microstructure and corrosion fatigue fracture morphology of ZBAl7-7-4-2 copper alloy including casting state and heat treatment were analyzed by scanning electron microscope （SEM） and transmission electron microscope （TEM）. The corrosion fatigue strength of ZBAl7-7-4-2 copper alloy including casting state and heat treatment were tested by rotating and bending fatigue testing machine，the rotating speed of which was 3000 r·min⁻¹. In the process of fatigue testing，the ambient temperature and relative humidity were 20 ℃ and 48%，respectively，the medium was artificial seawater，and the stress ratio was -1. According to the national standard of “GB/T24176-2009/ISO 12107：2003 Statistical scheme and analysis method of fatigue test data of metal materials”，the corrosion fatigue strength of ZBAl7-7-4-2 copper alloy including casting state and heat treatment were calculated. The corrosion fatigue crack propagation rate was measured on the electro-hydraulic servo material testing machine with the transverse loading method. The sample thickness was 12 mm，the width was 24 mm，and the notch length was 3.55 mm. The results showed that the microstructure of casting ZBAl7-7-4-2 copper alloy was mainly dendritic crystal，which was composed of α phase and κ phase. κ phase was an intermetallic compound，which had a great influence on the properties of the alloy，and could be classified into κ_Ⅰ phase，κ_Ⅱ phase，κ_Ⅲ phase and κ_Ⅳ phase according to its shape，size and distribution position. Due to the low Fe content of the alloy，no κ_Ⅰ phase was formed，and α phase was the matrix of Cu-based replacement solid solution. κ_Ⅱ phase was NiAl phase with the shape of a ball or flower，distributed in the grain. κ_Ⅲ phase was distributed at the grain boundary in the form of layer or intermittent ball drop，and was also NiAl phase. κ_Ⅳ phase was Fe-rich phase，distributed in the grins with small particles. In the casting ZBAl7-7-4-2 copper alloy，the dislocation density was high and there were a lot of twins. Compared with the casting state，the density of κ_Ⅳ phase distribution increased，while the dislocation density decreased and the twin crystal disappeared in the microstructure of ZBAl7-7-4-2 copper alloy after heat treatment. Under the condition of 90% confidence and 10% failure probability，the corrosion fatigue strength of ZBAl7-7-4-2 copper alloy after heat treatment was 132.52 MPa，which increased by 54% compared with the corrosion fatigue strength of the casting state （85.98 MPa）. The relationship between fatigue crack growth rate and stress intensity factor range expression （da/dN-ΔK） at the stable crack expansion stage of the casting state was da/dN=1.653×10⁻¹¹×ΔK^5.220 （fitted by Paris formula）. da/dN-ΔK expression at the stable crack expansion stage of ZBAl7-7-4-2 copper alloy after heat treatment was da/dN=8.6064×10⁻¹²×ΔK^5.4405 （fitted by Paris formula）. After heat treatment，the corrosion fatigue crack expansion rate of ZBAl7-7-4-2 copper alloys reduced compared to the casting state，which was in relation to the increasing of corrosion fatigue strength after heat treatment. Corrosion fatigue fracture morphology including source of fatigue，expansion area and instantaneous break area were observed. Fatigue cracks occurred at the surface defects of the specimen because the maximum alternating stress was distributed on the surface of the specimen. After initiation，the fatigue cracks continued to expand in a river-like pattern，showing cleavage fracture characteristics and accompanied by cleavage steps. There were parallel fatigue bands with intersecting light and shade in the expansion zone，and obvious dimples could be seen in the instantaneous break area. The distance between fatigue bands of ZBAl7-7-4-2 copper alloy after heat treatment was greater than that of the casting state.

Wire electric explosion method involves introducing a large pulse current into metal wire to create an electric explosion process，resulting in the production of metal powders. This method is commonly used to produce nano-scale spherical powders and offers advantages such as small size，low energy consumption，and high performance of the resulting spherical metal powders. This study utilized W-25%Re （mass fraction，the same below） alloy wire with a diameter of 0.3 mm as the raw material and employed the wire electric explosion method to produce micron-sized spherical W-25%Re alloy powders. The findings offered valuable insights for the efficient production of high-quality micron-sized spherical refractory alloy powder for selective laser melting （SLM） applications. The spherical W-25%Re alloy powder prepared in the experiment was categorized into five kinds particle size ranges：<5，5~35，35~60，60~165 and >165 μm. These particle sizes were chosen for analysis to investigate the microstructures and properties of spherical W-25%Re alloy powders. The powders morphology，laser particle size，flowability，apparent density，tap density，oxygen content and phase were measured using scanning electron microscope，laser particle size analyzer，flowability and apparent density tester，multi-functional powder physical property tester，oxygen and nitrogen analyzer，and X-ray diffraction （XRD）. The particle size 5~35，35~60，60~165 and >165 μm exhibited excellent sphericity，a high spheroidization rate. The particle size <5 μm featured small particle size and large specific surface area，leading to strong van der Waals forces among particles and potential agglomeration. Additionally，the particle size 5~35，35~60，60~165 and >165 μm demonstrated nearly 100% spheroidization rate. Except for the powder with particle size <5 μm，which had a wide distribution range due to severe agglomeration，the particle size distribution of the other four powders were narrow and relatively concentrated. The powders with a particle size of <5 μm were smaller and more active. The oxygen content of the powder raw materials was significantly increased，while powders with a particle size of >165 μm might introduce impurities due to waste residues，leading to a relatively high oxygen content. Furthermore，powders in other particle size ranges of oxygen content similar to that of W-25%Re alloy wire，aligning with the principle that finer powders had higher activity and oxygen content. Re content in the powder varied depending on the particle size. For particles with particle size <5 μm，Re content was 28.03%，slightly higher than that of the raw material wire. In contrast，Re content in powders of other particle size segments closely matched that of the raw material. This discrepancy might be due to impurity oxygen combining with rhenium at high temperatures during wire explosion，forming volatile oxides that adhere to powder particles upon cooling. The larger specific surface area of particles with particle size <5 μm led to more oxide deposition，resulting in a slightly higher Re content compare to the raw wire material. Except for powders with particle size <5 μm，which tended to agglomerate and had poor fluidity，and powders with particle size >165 μm，which were often discarded as waste，the flowability of powders with particle size of 5~35，35~60 and 60~165 μm were 6.95，5.09 and 5.34 s·（50 g）⁻¹，respectively，indicating good flowability，and their apparent densities were 12.00，11.42 and 11.57 g·cm⁻³，respectively，while tap densities were 13.2，12.3 and 12.6 g·cm⁻³. The minimal variation in bulk and tapped densities within this particle size range suggested that the prepared powder exhibited good sphericity and density. For particles with particle size <5 μm，the phases were the tetragonal crystal system W_0.4Re_0.6 phase，cubic crystal system W_0.8Re_0.2 and W₃Re phase. For particles with particle size of 5~35，35~60，60~165 and > 165 μm exhibited cubic crystal system W₁₃Re₇ phase. When particle size increased from 8.945 to 217.98 μm，the solidification structure on the surface of the powder particles gradually changed from a lack of obvious crystalline state and cellular crystals to dendrites. The relationship between the particle size （d） and the secondary dendrite arm spacing （λ） was expressed as：λ=0.727+5.59×10⁻³d. As the particle size increased，the secondary dendrite arm spacing also increased，demonstrating a linear correlation between the two. The interior of spherical W-25%Re alloy powders exhibited high density and had no obvious defects. As the particle size increased，the internal grain structure changed from cellular crystals to dendrites. The micron-sized spherical W-25%Re alloy powders，producing through wire electric explosion，demonstrated excellent overall properties. The particles with particle size of 5~35 μm possessed high sphericity，uniform particle size distribution，low oxygen content，good fluidity，high bulk density and tap density. These characteristics made it well-suited for meeting the powder performance requirements of SLM technology.

The traditional methods of detecting volatile organic compounds （VOCs） are not able to provide real-time monitoring，and are complex to operate. Therefore，there is a need to develop a portable and cost-effective alternative to satisfy market requirements. The gas sensor technology is a potential means of dealing with this issue. Cadmium stannate （Cd₂SnO₄） is a n-type semiconductor metal oxide that is simple to synthesize and exhibited good thermal stability and high electron mobility. The actual application of gas sensing materials is hampered by the limitations of single metal oxide，including high operating temperatures，low gas response values，slow response times，and so on. The gas sensors based on metal oxide semiconductor materials could enhance their gas-sensing performance through morphology control，noble metal ion modification，and construction heterostructure. Tungsten disulfide （WS₂），an n-type semiconductor material with high specific surface area and high electron mobility，when combined with metal oxides could be used to modify or enhance the gas sensing properties of the material. In this research，cadmium nitrate tetrahydrate （Cd（NO₃）₃·4H₂O） and tin tetrachloride pentahydrate （SnCl₄·5H₂O） were utilized as raw materials. After thorough mixing and adjustment of pH to 9.5，the resulting suspension was held at 170 ℃ for 16 h. Then，it was cooled，filtered，washed，and dried to obtain a white solid. The solid was subsequently ground and placed in a muffle furnace，heated at a rate of 5 ℃·min⁻¹ until it reached 550 ℃，and held for 2 h to obtain yellow Cd₂SnO₄ powder. Five different volumes of WS₂ dispersion were taken and placed into beakers，and the same amount of Cd₂SnO₄ powder was added. The combination was stirred with anhydrous ethanol for 2 h and then treated with ultrasound for 2 h. Next，the resulting solution was centrifugally washed，dried，and ground thoroughly. X-ray diffraction （XRD），X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM） were used to characterize the phase composition and microstructure of the composite materials. XRD patterns of the composite materials showed separate diffraction peaks，which could be attributed to the overlapping of the peak positions of WS₂ and Cd₂SnO₄ crystal planes but with large differences in diffraction peak intensities. XPS spectra showed no impurity elements and a consistent distribution of elemental valence states with the target product，confirming the successful synthesis of Cd₂SnO₄. From SEM images of Cd₂SnO₄ and WS₂/Cd₂SnO₄ composites，it could be observed that the addition of WS₂ reduced the agglomeration of Cd₂SnO₄ particles and increased the material’s specific surface area，thereby exposing more active sites and enhancing the gas sensing properties. The gas sensing properties of Cd₂SnO₄ and WS₂/Cd₂SnO₄ composites were tested，and it was found that the addition of WS₂ enhanced the gas sensing properties of Cd₂SnO₄. Testing eight different gases at various temperatures，it could be found that the composite material exhibited the highest response to trimethylamine. With the addition of 2.5% of WS₂ （WCS-2.5 composite），the composite showed response of 37.1 to 100×10⁻⁶ trimethylamine and 6.5 to ethanol at 170 ℃，which were respectively 24.7 and 6.5 times higher than pure Cd₂SnO₄ under the same conditions. The incorporation of WS₂ not only heightened the response of Cd₂SnO₄，but also enhanced its gas selectivity. The response and recovery curves illustrated that the response and recovery times of composite material to 100×10⁻⁶ trimethylamine were 83 and 12 s at 170 ℃，respectively. The composite material still showed response of 1.5 when the trimethylamine concentration was 0.1×10⁻⁶. The gas sensing properties of materials were significantly influenced by relative humidity. The results showed that the response of the composite material to 100×10⁻⁶ trimethylamine was considerably impacted by relative humidity. This phenomenon could be ascribed to the promotion of oxygen adsorption by water at low relative humidity，whereas high relative humidity led to water molecules occupying the active sites on the material surface，consequently diminishing its sensitivity. The gas sensing mechanism of the composite material was elucidated using the surface charge control theory. In ambient air，oxygen molecules received electrons from the conduction band of the gas sensing material，resulting in the formation of oxygen ions and an increase in material resistance. In the presence of trimethylamine gas，the oxygen ions reacted with trimethylamine，thereby releasing the acquired electrons and reducing the resistance of the gas sensing material. In word，WCS-2.5 composite represented a promising candidate for trimethylamine detection.

Nickel is an important raw material for fabrication of high-temperature alloys and corrosion-resistant alloys due to its high melting point，corrosion resistance，oxidation resistance，ductility and other excellent properties. As one kind of key strategic resources，nickel has been widely used in aerospace，defense，nuclear energy and other important fields. However，China is a typical nickel-deficit country，and the dependence on foreign nickel ore reaches as high as 95%. Recycling of nickel-contained scrap can effectively alleviate the shortage of nickel resources，and is of great significance to ensure the safe and sustainable supply of nickel resources in China. Compared with other types of nickel-contained scraps，nickel-based high-temperature alloy scrap exhibits higher recovery value because of its advanced preparation process and containing various kinds of strategic metal elements. Currently，different methods including pyrometallurgical，hydrometallurgical，and pyro-hydrometallurgical processing are applied for recycling scrap nickel-based high-temperature alloys. However，these methods have disadvantages such as multi-step processing and relatively low utilization rates. What's more，the achieved products by the above methods usually are metal elements or corresponded salts. To achieve same-level utilization of scrap nickel-based alloys，a direct re-melting method through vacuum induction melting is used to recycle scrap 690 alloy. However，re-melted 690 alloy shows poor performance，especially deterioration of ductility，which is resulted from a large number of Cr₂O₃ inclusions distrusted in re-melted 690 alloy. Consequently，Cr₂O₃ inclusions cannot be removed effectively through the direct re-melting method. Therefore，carbon thermal reduction was proposed to solve this problem in this study. Scrap 690 alloy was obtained through aging treatment at 850 ℃ for 360 h by considering that oxidation as well as microstructure coarsening were the main factors for serving failure of 690 alloys. The above scrap 690 alloy were re-melted using carbon thermal reduction at 1550 ℃，and the carbon reduced 690 alloy was obtained. Fe content of the alloy was analyzed using inductively coupled plasma optical emission spectrometer（ICP-OES），while titration was used to determine Cr content. Oxygen-nitrogen-hydrogen analyzer was utilized to analyze O and N content，and carbon-sulfur analyzer was used to determine C and S content. The microstructure and fracture morphology of three types of 690 alloys were observed using optical microscopy （OM），scanning electron microscopy （SEM） equipped with energy dispersive spectroscopy （EDS），and X-ray diffraction（XRD）. Microhardness was performed using Vickers microhardness tester under conditions of Load retention for 10 s at test force of 1960 N. The tensile properties of three types of 690 alloys were tested by electronic universal testing machine at room temperature and 650 ℃. SEM images indicated that a large amount of Cr₂₃C₆ precipitates were uniformly distributed in carbon reduced 690 alloy，while there were almost no inclusions of Cr₂O₃. Moreover，the oxygen content of carbon reduced 690 alloy decreased to 88×10^-6. Therefore，it could be reasonably included that the inclusions of Cr₂O₃ were successfully transformed into precipitates of Cr₂₃C₆ through the carbon thermal reduction method. As a result，the mechanical properties of carbon reduced 690 alloy significantly improved. The hardness of carbon reduced 690 alloy was HV 278. The tensile strength of carbon reduced 690 alloy at room temperature and 650 ℃ was 672 and 395 MPa，respectively，which was 10.5% and 44.2% higher than those of standard 690 alloy. More importantly，the elongation at room temperature and 650 ℃ of carbon reduced 690 alloy was increased 18.8% and 96.0%，respectively，compared with direct re-melted 690 alloy. The difference in mechanical properties between the two types of remelted 690 alloys was mainly related to the type and distribution of second-phase particles. The inclusions of Cr₂O₃ were brittle particles，which were prone to stress concentration at the interface between inclusions and matrix. Their distribution would not get changed accordingly during plastic deformation，where voids and cracks were easily formed，leading to an obvious decrease in the tensile ductility of direct re-melted 690 alloy. For carbon reduced 690 alloy，the unfavorable inclusions of Cr₂O₃ were transformed into beneficial precipitates of Cr₂₃C₆ benefited from the carbon thermal reduction method. During the tensile test，Cr₂₃C₆ precipitates could slow down the aggregation and growth of micropores，hinder crack generation，and improve the ductility of alloy. Furthermore，a large amount of uniformly distributed Cr₂₃C₆ precipitates contributed to the higher strength of carbon reduced 690 alloy due to dispersion strengthening effect. Also，these precipitates of Cr₂₃C₆ contributed to the fine grain microstructure，where grain boundary strengthening was achieved. These results indicated that recycling of scrap 690 alloy using carbon thermal reduction could effectively remove the oxide inclusions，and improve both the strength and ductility of re-melted 690 alloy.

Among the biosorbents for precious metal recovery，polyphenols have always been a research hotspot. Among them，tannins containing phenolic substances on the surface of persimmon skin have always been a research hotspot，but tannins soluble in water are not conducive to solid-liquid separation，so loading persimmon tannins on the surface of resin has always been the focus of research. However，the high cost of loading modification is not conducive to its popularization and application in industrial production. Grape skin waste generated during wine preparation accounts for 25%~35% of the total consumption of grapes and contains a large number of phenolic substances. Currently，there are few studies on the absorption and recovery of gold using grape skins. This paper proposed the selective adsorption of gold using grape skins containing polyphenols. The grape peel was prepared by a hydrothermally treatment of the mixture of raw grape peel particle and water at 120 ℃ for 12 h with the solution with modifier. Then the above-mentioned suspension was filtrated and the peel was washed 3 times with distilled water and then dried at 80 ℃ for 12 h. A series of adsorption experiments were carried out and showed that only 30 min could reach a high adsorption efficiency and adsorption capacity of gold. With the prolonging of adsorption time，the adsorption efficiency of gold would gradually approach to a platform. With the increasing of the temperature，the adsorption efficiency and the adsorption capacity of gold would slightly be increasing. Above experimental data were used for fitting by pseudo-first-order and pseudo-second-order kinetic equations，and it could be found that they fit the latter model well. By comparing the adsorption capacity of the theoretical calculation and the experimental result，it could be found that the results obtained based on the pseudo-second-order model were more identical，meaning that this model was more appropriate to describe the adsorption process. The kinetic parameters of adsorption of grape peel from the pseudo-second-order model were used for fitting by Arrhenius equation，and it could be found that they fit the model well. The adsorption reaction activation energy on grape peel for gold was 2.1925 kJ·mol⁻¹. With HCl concentration from 0.5 to 6 mol·L⁻¹，the adsorption efficiency of gold was kept at 98.01% to 97.13%，and the adsorption of Fe，Zn and Cu was kept at 0 to 2.31%，0 to 16.05%，1.05% to 12.57%，showing a gradual increasing trend when HCl concentration increased. The concentration of HCl had a litter impact on the adsorption of Fe，Zn and Cu. By comparison，grape peel adsorbent had great selective adsorption for gold，even in the condition of high HCl concentration. The maximum adsorption capacity for gold in 0.1 mol·L⁻¹ HCl media was assessed to be 34 g_Au·kg⁻¹ at room temperature. Langmuir and Freundlich models were used to fit the isotherm adsorption data，and it was found that the Langmuir model could better describe the adsorption process. Oxidation and reduction potential （ORP） value of the solution during the adsorption process would decrease drastically，which provided another proof of the reduction occurring in the adsorption of gold ions towards the grape peel adsorbent. The higher temperature，the faster decrease of ORP value. Scanning electron microscopy （SEM） images demonstrated that grape peel surface was slightly plush，after adsorption of gold，it turned to the surface of the adsorbent with a number of tiny gold particles. According to X-ray diffraction （XRD） and polarizing microscope，the polyphenols in frape peel successfully reduced the gold ions in the solution to obtain solid gold particles. According to Fourier transform infrared spectroscopy （FTIR），it was easy to see that the intensity of C=C bond assigned for the stretching decreased，thus demonstrating the oxidation of phenolic groups to carbonyls. On the other hand，it was evident to observe that C=O bond also decreased after adsorption of gold. The above results indicated that the polyphenols on the surface of grape peel reduced the gold ions into the adsorption solution. According to X-ray photoelectron spectroscopy （XPS），it could be confirmed that after protonation in the acidic solutions，OH bond of polyphenol in grape peel was positively charged and adsorbed the negatively charged ${\text{AuCl}}_{\text{4}}^{\text{-}}$ from the solution. Afterwards，C=C bond from polyphenol contained the large π bonds would donate rich electrons to reduce the adsorbed ${\text{AuCl}}_{\text{4}}^{\text{-}}$ into the gold element. More than 99.9% gold ions would be reduced to be the gold element after adsorption，and the large π bonds in the aromatic structure of polyphenol were believed to be the dominant electron donator responsible for the reduction of gold，and it showed that the adsorption mechanism of gold adsorption on grape peel was the electrostatic attraction coupled with reduction reaction. Therefore，the adsorbent could selectively adsorb gold and had a large adsorption capacity for gold，and this research put bio sorbents into industrial production to provide guidance research.

β transus temperature （T_β） is a very important process parameter. Due to the fluctuation of composition and different content of interstitial elements，the phase transformation temperature of titanium alloy products of the same brand and different batches can have a deviation of tens of degrees. In order to ensure the quality stability of materials，β phase transformation temperature of each batch of titanium materials is measured in industrial production. At present，Thermal analysis method and metallographic method are commonly used for measuring the transformation point of titanium alloy. In this paper，it was measured by differential scanning calorimetry for β transformation temperature of α-type，α+β-type and metastable β-type titanium alloys to analyze the applicability of transition temperature in differential scanning calorimetry （DSC）. The microstructure of the sample was observed and analyzed by metallographic microscope during DSC measurement process，the influence mechanism of phase transformation，room temperature and high temperature microstructure of titanium alloy on DSC measurement data was studied. The effect of heating rate on DSC results of TC4 sample was studied to observe the optimal DSC parameter. At the same time，in order to determine the accuracy of DSC method in measuring the transformation point temperature of titanium and titanium alloy，the metallographic method was used for data comparison and analysis. The results showed that DSC could be used to measure β phase transformation point of various types of titanium alloys. According to metastable β-type titanium，especially in hot working state or solid solution state，there was no obvious endothermic/exothermic peak in DSC curve，it was suggested that β titanium alloys could be heat treated in 650 ℃/1 h +550 ℃/1 h air cooling （AC） before DSC measurement to ensure sufficient α phase precipitation. For forging α+β-type titanium alloy，due to the difference and transformation of titanium alloy microstructure during DSC heating and cooling，there was a large deviation between the first measurement and the subsequent measurement results. The original state of TC4 was hot working state，the original α phase was broken or disintegrated，the initial crystallographic relationship between α and β phase was destroyed，the microstructure was equiaxed α phase + intergranular β. When it was heated to β phase，the phase transformation needed to overcome large resistance. Due to no holding time in the heating process of DSC method，T_β moved to high temperature. After cooling from 1120 ℃，α and β phases followed the burgers orientation relationship：（110）_β∥（0001）_α，［111］_β∥［1120］_α，the microstructure was primitive β grain boundary + fine lamellar β transformation structure. On the second repeated temperature rise，α→β transition proceeded inversely along the habitual surface during cooling，the phase transition resistance was greatly reduced and T_β was close to the real phase transition temperature. After the third DSC test，the microstructure was no longer changed and remained original β grain boundary + fine lamellar β. It could be seen that the results of phase transformation point of titanium after the first time were the actual phase transformation temperature for forging α+β，usually the second result could be used as the final T_β. The phase transition point temperatures were 989 ℃ （10 ℃·min⁻¹），989 ℃ （20 ℃·min⁻¹） and 996 ℃ （30 ℃·min⁻¹） respectively. When the heating rate was 10 ℃·min⁻¹，the phase transition endothermic peak was very flat，the peak shape was small，and the thermal effect was not obvious. When the heating rate increased to 20 and 30 ℃·min⁻¹，the phase transition reaction peak was obvious，the peak shape was sharp，and the sensitivity was improved. The measured value of 20 ℃·min⁻¹ was roughly consistent with that of 10 ℃·min⁻¹，and the phase transition point temperature of 30 ℃·min⁻¹ was relatively high. During DSC test，the heating rate was directly proportional to the thermal hysteresis effect of the sample. The larger the heating rate，the more serious the thermal hysteresis phenomenon was. The slower the heating rate was，the smaller the thermal hysteresis effect was，the higher the resolution was，but the sensitivity was reduced. So，based on the above data and reasons，it was suggested that the heating rate should be measured at 20 ℃·min⁻¹ for TC4 by DSC. The metallographic method was used to verify the accuracy of DSC measurement，it showed that the phase transition point data of differential scanning calorimetry and metallography β were very close，the difference was only 7 ℃. Due to the characteristics of low thermal conductivity of titanium alloy and fast heating rate，there was not enough time for the complete phase transition reaction，resulting the thermal lag effect during DSC measurement and the results difference between the differential scanning calorimetry and metallographic. Therefore，DSC measurement results were relatively reliable. After temperature correction，DSC method could be used as a fast and reliable means for phase transition point temperature measurement.

Cemented carbide is a composite material prepared by powder metallurgy with refractory metal compounds（WC，TiC，TaC，NbC，etc.）as matrix and transition metal elements （Co，Fe，Ni，etc.） as binder phase. It is widely used in the fields of machine tool cutting tools，mining and rock drilling tools，tensile die and wear-resistant parts. Coated gradient cemented carbide is the most commonly used cutting tool and plays an important role in precision machining. When used in combination with TiC，TiN，Ti （C，N） and Al₂O₃ coatings，cracks often occur between coating and matrix due to the different thermal expansion coefficients，which affects the cutting performance and service life of the tool. The binder-rich and γ-free layer of the gradient cemented carbide can improve the toughness of the alloy surface，reduce the crack generation and prevent its propagation. In this paper，the formation mechanism and preparation method of γ-free layer gradient cemented carbide are sketched，the application and development of phase diagram calculation method on the simulation of gradient layer formation are summarized，and the effects of powder size，sintering process and alloy compositions （including nitrogen source，binder phase and secondary carbide） on gradient layer formation and alloy properties are described in detail. The future research direction of gradient cemented carbide with high-performance coating has also been prospected. The formation of the gradient layer is based on the strong thermodynamic coupling between Ti and N atoms. During the sintering process，denitrification occurs at the surface of the cemented carbide. Ti （C，N） phase in the surface layer dissolves continuously into the liquid binder phase along with the outward diffusion of N and the inward diffusion of Ti through the liquid binder phase，resulting in the formation of the γ-free surface gradient layer. The formation of the gradient layer is affected by many factors. CALPHAD method can accurately describe the phase diagram thermodynamics and diffusion dynamics information of the multi-component material system under different alloy compositions and process conditions based on the Gibbs free energy and atomic mobility parameters of each phase. The evolution law of the microstructure and its control mechanism can be studied effectively. Combined with the hardness and fracture toughness model，the hardness and fracture toughness of the gradient layer can be also predicted. The accuracy and reliability of the simulation on the gradient layer formation are mainly affected by three aspects，that is，the thermodynamic database，the diffusion kinetic database and the labyrinth factor characterizing effective diffusion coefficient. Many efforts have been made on their improvement to make the simulation more accurate. However，there still exist some limitations in material design only using CALPHAD approach. The labyrinth factor，as a key factor affecting the simulation results，is mainly obtained by experience at present. The diffusion couple test or tracer diffusion test can be designed to obtain the reliable labyrinth factor. In the development and research of high-performance gradient cemented carbide，the finer powder size of the raw materials has been utilized to prepare ultrafine gradient cemented carbide. A thicker gradient layer and higher hardness are obtained，but the fracture toughness is reduced. The traditional two-step sintering process system has been maturely applied to the preparation of graded cemented carbide，but some new preparation processes are still in the preliminary stage of exploration. The use of new nitrogen sources，binder phases and secondary carbides has proved to be an effective means to change the gradient layer structure or improve the properties of the alloy. Besides TiN and Ti （C，N），more new nitrogen sources are being applied，and external nitrogen sources and nitrogen-free graded cemented carbides are also being studied gradually. New binder phases such as intermetallic compounds and high entropy alloys have been successfully applied to homogeneous cemented carbide and cermet，but there is little research on graded cemented carbide，and more attempts should be made in the future. The strengthening mechanism of new secondary carbides needs to be further explored. the evaluation of the service performance of the coating tool is limited for the gradient cemented carbides as the matrix with the new nitrogen sources，binder phases and secondary carbides. In the development of the new gradient cemented carbide，the combination with the coating and the cutting performance of the new gradient cemented carbide should be paid attention to in addition to the gradient layer and mechanical properties. Multi-scale material computational simulation and material genetic engineering methods have been successfully applied in steel materials，aluminum alloys and other alloy systems，greatly accelerating the material research and development cycle. In the future，methods such as multi-scale material computational simulation and material genetic engineering can be focused on to greatly accelerate the material development cycle. The multi-scale simulation of graded cemented carbide can be carried out to reveal the formation and control mechanism of the gradient layer structure from different layers. Based on material genome engineering，high-throughput experiments and high-throughput calculations can be carried out，and the big-data platform for graded cemented carbides can be established to realize the rapid screening and development of newly graded cemented carbides in terms of composition，process and properties.

7055 aluminum alloy treated by traditional peak ageing （T6） had the highest tensile strength and a poor corrosion resistance. The high alloying element content and extremely complicate precipitation behavior during heat treatments of 7055 aluminum alloy led to the diversity of micro-area composition，which showed a great difference of corrosion resistance. High Cu content at grain boundaries could improve the corrosion resistance 7055 aluminum. In order to improve the corrosion resistance of 7055 aluminum alloys treated by traditional peak ageing （T6），7055 aluminum alloy plates prepared by snake rolling were used as experiment materials for different heat treatment processes. The equilibrium phase diagram of 7055 aluminum alloy was calculated by JMatPro software and the precipitate temperature of the main precipitates of MgZn₂ （η phase），Al₂CuMg （S phase） and Al₃Fe were 430，454 and 570 ℃，respectively. According to the precipitate temperature of S phase，three cooling pretreatment temperatures （465，455 and 445 ℃） were selected to heat-treat 7055 aluminum alloy plates，respectively. The solid solution （480 ℃×1 h） and cooling pretreatment of 7055 aluminum alloy plate were carried out on Gleeble-3500 thermal simulation test machine，and ageing process were performed in the air circulating furnace. EIectrochemical Impedance Spectroscopy （EIS） of different heat-treated samples was measured by Zennium electrochemical workstation. According to GB/T 7998-2005 test standard，the accelerated corrosion test of the aged samples for 12 h was carried out. The corrosion environment was neutral corrosion solution （35 g NaCl+10 ml H₂O₂+100 ml H₂O） at （35±3） ℃ in aqueous solution. The corrosion depths of the samples were observed and measured by Axio imager microscope. The effects of cooling pre-treatment on the precipitate behavior，micro-zone composition of 7055 aluminum alloy plates were studied by means of scanning electron microscopy （SEM），scanning transmission electron microscopy （STEM）. The cooling pre-treatment could cause the local enrichment of alloying elements，and the precipitation of S phase was closely related to the content of Cu elements at the grain boundary. After water quenching，the content of solute atoms at grain boundaries firstly increased and then decreased with the decrease of pre-treatment temperature. When the pretreatment temperature was 455 ℃，the solute content of grain boundary was the highest，and the contents of Zn，Mg and Cu elements were 3.97%，3.63% and 3.15%，respectively. When the pre-treatment temperature was 445 ℃，S phase precipitated，the solute content of Mg and Cu at grain boundary decreased and the contents of Zn，Mg and Cu elements were 4.13%，2.83% and 2.47%，respectively. The sample pretreated by 455 ℃was aged by peak ageing process （Sample CPt455+T6），and then was compared with sample treated by traditional T6 （Sample SS+T6）. Compared with Sample SS+T6，the size of intragranular precipitates of Sample CPt455+T6 slightly increased，while the precipitates at grain boundary was obviously different. In the cooling pretreatment stage at 455 ℃，alloying elements quickly segregated to grain boundaries，which shortened the diffusion time of alloying elements gathering to grain boundaries during aging. Therefore，the discontinuous η phase formed at the grain boundaries of Sample CPt455+T6，whileSample SS+T6 had a continuous η phase at grain boundaries. Micro-area composition analysis presentedη-MgZn₂ phases at grain boundary in Sample CPt455+T6 had higher Cu content than that of Sample SS+T6. After intragranular corrosion test，the corrosion depth of Sample SS+T6 was （68±5） μm，while the corrosion depth of Sample CPt455+T6 was （154±5） μm. The larger the diameter of circular arc in electrochemical impedance spectroscopy （EIS）curves，the greater the impedance and the better the corrosion resistance. The circular arc diameter of Sample CPt455+T6 was larger than that of Sample SS+T6. Therefore，the corrosion resistance of Sample CPt455+T6 was better than that of Sample SS+T6. η-MgZn₂ phases at the grain boundaries were regarded as an anodic during corrosion. For continuous η-MgZn₂ phases in Sample SS+T6，the formed corrosion channel could continuously expand along the grain boundaries. The discontinuous η phase in Sample CPt455+T6 could cut off corrosion channels，which made the corrosion only occur in the local area of grain boundaries and the integrity of grain boundaries were retained. Thus，Sample CPt455+T6 had better intergranular corrosion resistance thanSample SS+T6. the probability of Cu atoms replacing Zn atoms in grain boundaries η of Sample CPt455+T6 was larger than that of Sample SS+T6，it led to the positive shift of the corrosion potential of η phase，which reduced the potential difference between the grain boundaries η phase and the precipitate free zone. Based on the test and characterization results，the conclusion we could get were the content of grain boundaries solute atoms increased with the cooling pretreatment temperature decreased. When the cooling pretreatment temperature was 445 ℃，S phase precipitated and the solute content at grain boundary decreased. Compared with SS+T6 process，CPt455+T6 process caused discontinuous η phase with high Cu content to precipitate at grain boundaries of 7055 aluminum alloy. Furthermore，compared with SS+T6 process，CPt455+T6 process could enhance AC impedance spectroscopy and intergranular corrosion resistance of 7055 aluminum alloy.

The glass-ceramic dielectric material is a composite material of glass and ceramic phase coexist. The glass-ceramic can achieve complete densification and possess high breakdown field strength. It can precipitate high dielectric constant ceramic phase through controlled crystallization process，so that the glass-ceramic has moderate dielectric constant. Therefore，as a new type of dielectric energy storage material，dielectric glass-ceramic has a good prospect in the application field of high-voltage capacitors. However，the low dielectric constant and high dielectric loss of glass-ceramic hinder the further development of this material. In this paper，titanate ceramic phase was introduced into niobate glass-ceramic system to increase the dielectric constant and alkali metal ions with small radius were removed to reduce the dielectric loss. BaO-SrO-PbO-TiO₂-SiO₂-Nb₂O₅ nanocomposite dielectric materials with different TiO₂ and Nb₂O₅ contents were prepared via melting-quenching-controlled crystallization technology. And the effect of TiO₂ and Nb₂O₅ contents on properties of BaO-SrO-PbO-TiO₂-SiO₂-Nb₂O₅ glass-ceramic system were characterized by X-ray diffraction （XRD），differential thermal analysis （DTA），scanning electron microscopy （SEM） and dielectric properties test. The results showed that the crystallization activation energy decreased gradually with the value of TiO₂/Nb₂O₅ increased，which meant that the increased of TiO₂ / Nb₂O₅ ratio in BaO-SrO-PbO-TiO₂-SiO₂-Nb₂O₅ glass-ceramic system was conducive to crystallize. XRD results showed the glass samples all had obvious amorphous characteristics，indicating there was no crystal phase precipitation in the glass matrix. The samples after crystallization treatment at 800 ℃ precipitated pyrochlore structure Pb₂Nb₂O₇ phase，tungsten bronze structure （Ba，Sr，Pb） Nb₂O₆ phase and perovskite structure （Sr，Pb） TiO₃ phase，and the intensity of the diffraction peak of Pb₂Nb₂O₇ phase increased as the value of TiO₂/Nb₂O₅ increased. It meant that the increased of TiO₂/Nb₂O₅ ratio promoted the precipitation of Pb₂Nb₂O₇ phase. With the increased of crystallization temperature，the diffraction peak intensity of Pb₂Nb₂O₇ phase gradually decreased，but the diffraction peak intensity of （Sr，Pb） TiO₃ and （Ba，Sr，Pb）Nb₂O₆ phase gradually increased. The results indicated that the increase of crystallization temperature inhibited the formation of Pb₂Nb₂O₇ phase but promoted the growth of （Sr，Pb） TiO₃ and （Ba，Sr，Pb） Nb₂O₆ phase. After the crystallization treatment at 900 ℃ and 1000 ℃，Pb₂Nb₂O₇ phase still existed in the samples with more TiO₂ content，but the diffraction peak intensity decreased with the increase of the crystallization treatment temperature. The microstructure analysis results showed that after crystallization treatment at 1000 ℃，the crystal particles of all samples were approximately spherical. The dielectric properties test showed that the dielectric constant and dielectric loss of the glass-ceramic sample increased with the increase of the crystallization temperature. This was attributed to the growth of ceramic phase with the increased of crystallization temperature. After crystallization at 800 ℃ and 900 ℃，the dielectric constant gradually decreased with the increase of the TiO₂/Nb₂O₅ ratio，which caused by the precipitation of the low dielectric constant pyrochlore structure Pb₂Nb₂O₇ phase. After crystallization at 1000 ℃，it was found that the dielectric constant increased firstly and then decreased with the increase of the ratio of TiO₂/Nb₂O₅. The increase in dielectric constant was due to the change in the composition that promoted the precipitation of the perovskite structure titanate ceramic phase. The decrease in dielectric constant related to the precipitation of low dielectric constant phases. The glass-ceramic samples with excellent dielectric properties were obtained by adjusting TiO₂ and Nb₂O₅ contents. The maximum dielectric constant （~1310） of the glass-ceramic with 12% TiO₂ and 24% Nb₂O₅ contents was obtained，and the dielectric loss kept at a low level of 0.0093. The dielectric constant of glass-ceramic with TiO₂ content of 10% and Nb₂O₅ content of 26% decreased slightly，but still higher than 1000，and dielectric loss decreased to 0.0079. Since no alkali mental ions with small radius were introduced into system，the dielectric loss kept below 0.01. At the same time，it had good temperature stability of dielectric constant，and the fluctuation range of dielectric constant was less than 10% at -40~80 ℃. It was also found that the polarization curves of glass-ceramic were slender，the residual polarization intensity was small，and the energy loss was small in the charging and discharging process，indicating that the material had high energy release efficiency. Therefore，BaO-SrO-PbO-TiO₂-Nb₂O₅-SiO₂ glass-ceramic as high voltage ceramic capacitor medium showed a good application prospect.