The weld toe area of a three-time repair welding joint of 30CrMnSiNi2A steel was treated by ultrasonic impact. The effects of the ultrasonic impact on the microstructure, mechanical properties and residual stress of the repair welding joint were studied by microstructure observation, tensile test, hardness test and residual stress test. The results show that the ultrasonic impact caused grain refinement and plastic deformation in the area about 100 μm from the surface of the repair welding joint. The influence of ultrasonic impact on the tensile properties of the welding joints was small because the thickness of ultrasonic impact affected layer was smaller than that of the welding parts. The microhardness of the repair welding joint surface increased significantly by ultrasonic impact, which was related to grain refinement and the increase of dislocation movement resistance on the surface of the repair welding joint. Ultrasonic impact could transform the harmful residual tensile stresses accumulated in multiple repair welding into beneficial compressive stresses.
Fe50-xMn30Cr10Co10(VC)x (x=0, 1, 3, atomic fraction/%) high-entropy alloy coatings were prepared on Q235 steel plate surface by laser cladding technique. The effect of VC addition on the micromorphology, phase composition, hardness, wear resistance and corrosion resistance of the coating was studied. The results show that the high-entropy alloy coatings with three VC additions were well bonded with the substrate, and there were only a few defects such as holes in the coatings. The three coatings were all composed of solid solution phases with a face-centered cubic structure. With increasing VC addition, the structure of the high-entropy alloy coating was refined, and the microhardness increased. The addition of VC could improve both wear resistance and corrosion resistance of Fe50Mn30Cr10Co10 high-entropy alloy coating, and the more the VC was added, the better the wear resistance and corrosion resistance were.
As-cast Ti28Co14Ni37.12Zr20.88 high entropy alloy was tempered at different temperatures ( 673,723 K). The effects of tempering temperature on the microstructure and mechanical properties of the high entropy alloy were studied. The results show that the microstructures of the as-cast, 673 K tempered and 723 K tempered alloy were composed of a TiNi matrix phase of a body-centered cubic structure and a small amount of a face centered cubic structure Ti2Ni second phase. With the increase of tempering temperature, the grains of TiNi phase and Ti2Ni phase were refined. After tempering heat treatment, the elastic limit and yield strength of the as-cast alloy increased. The compressive strength of the 673 K tempered alloy was lower than that of the as-cast alloy, but when the tempering temperature increased to 723 K, the compressive strength increased and was higher than that of the as-cast alloy. The fracture mechanism of the as-cast high entropy alloy was mainly cleavage fracture, supplemented by intergranular fracture and ductile fracture. The fracture mechanism of the 673 K tempered and 723 K tempered high entropy alloy was mainly cleavage fracture, supplemented by intergranular fracture.
Fe-2%Cu-0.4%C iron-based powder metallurgy material was boronized at 950 ℃ for 5 h by solid powder boronizing method with a boronizing agent containing CeO2. The effects of CeO2 addition (0,2%, 4%, mass fraction) on the microstructure and friction and wear properties of the boronizing layer were studied. The results show that the boronizing layer with different addition amounts of CeO2 had a single Fe2B phase. With the increase of CeO2 addition, the surface roughness of the boronizing layer increased, and the thickness, hardness and wear resistance increased first and then decreased. When the mass fraction of CeO2 was 2%, the thickness and hardness of the boronizing layer were the largest, about 144 μm and 58.0 HRC, respectively. At this time, the surface integrity of the boronizing layer was relatively good, the amount of wear was the smallest, about 0.008 g, and the wear resistance was the best.
Friction stir welding of 7N01 aluminum alloy was carried out under different press amounts (0.3, 0.7, 1.0 mm). The effects of press amounts on the cross-sectional morphology, tensile properties, anti-tear properties, and fatigue properties of the joint were studied. The results show that the press amount had little effect on the tensile properties of the 7N01 aluminum alloy friction stir welding joint. When the press amount was 0.7, 1.0 mm, respectively, the crack initiation energy, crack propagation energy, and tear strength of the joint were similar. When the press amount was 0.3 mm, the crack initiation energy, crack propagation energy, and tear strength of the weld area of the joint were significantly reduced. The fatigue strength of the welding joint increased with the increase of the press amount. The fatigue properties and crack propagation resistance of the welding joint were the best when the press amount was 1.0 mm.
α-FeOOH nanorods were prepared by hydrothermal method with FeSO4·7H2O and CH3COONa·3H2O as raw materials, and then α-Fe2O3 nanorods were obtained by sintering the synthesized α-FeOOH nanorods at 250 ℃ for 2 h. The catalytic performance of α-FeOOH and α-Fe2O3 nanorods on the thermal decomposition of ammonium perchlorate was investigated by differential thermal and thermogravimetric analysis. The results show that pure phase α-FeOOH nanorods with an average diameter of 18 nm were prepared by hydrothermal reaction at 100 ℃ for 6 h. After sintering the synthesized α-FeOOH nanorods at 250 ℃ for 2 h, the pure hexagonal phase α-Fe2O3 nanorods with an average diameter of 16 nm were obtained. The catalytic effect of α-Fe2O3 and α-FeOOH nanorods on the thermal decomposition of ammonium perchlorate was significant; after adding 2 mass% α-Fe2O3 nanorods and 2 mass% α-FeOOH nanorods, the end decomposition temperature of ammonium perchlorate decreased by 40 ℃ and 54 ℃, and the high temperature decomposition peak temperature decreased by 51.1 ℃ and 61.6 ℃, respectively. When the mass fraction of α-Fe2O3 nanorods reached 10%, the high temperature decomposition peak temperature was reduced by about 90.9 ℃.
Nanobeam precursor was prepared by solvothermal reaction at 200 ℃ with zinc acetate, manganese acetate and ammonium bicarbonate as raw materials and seignette salt as structure guide agent. The optimal addition amount of seignette salt and solvothermal reaction time were determined according to the shape of the precursor. The ZnMn2O4 nanobeams for cathode of lithium ion batteries were prepared by calcining the precursors at 250, 350 ℃ for 2 h. The microstructure and electrochemical performance of the ZnMn2O4 nanobeams were stdied. The results show that one-dimensional nanobeams with intact structure could be obtained when the solvothermal time was 12 h and the seignette salt addition amount was 1 mmol. The ZnMn2O4 nanobeams could be obtained at the two calcining temperatures, but the ZnMn2O4 nanobeams obtained at 350 ℃ showed better electrochemical performance; the specific capacity of ZnMn2O4 nanobeams could still be maintained at 892 mA·h·g-1 after 60 cycles at current density of 100 mA·g-1. Under the high current density of 2 A·g-1, the specific capacity could still reach 416.2 mA·h·g-1.
The steel with a ferrite + pearlite microstructure was quenched at 910 ℃+tempered at different temperatures (500, 550, 600 ℃) to obtain the ultra-high strength grade casing drilling steel. The obtainal casing drilling steel was subjected to impact tests at different temperatures (-60-20 ℃). The effects of tempering and impact test temperatures on the impact toughness and fracture mechanism of the casing drilling steel were studied. The results show that as the tempering temperature increased, and the martensite in the casing drilling steel gradually disappeared, and the tempered sorbite structure was formed. Meanwhile, the impact energy consumed in room temperature impact increased, and the maximum impact load decreased. The impact fracture macromorphology of the steel tempered at different temperatures was both fiber zone and shear lip, and the fracture mechanism was ductile fracture. The ductile-brittle transition temperature of the casing drilling steel tempered at 550 ℃ was -33.64 ℃. As the impact test temperature decreased, the impact energy gradually decreased, the fracture macromorphology changed from a complete fiber region to a nearly complete radiation region, and the fracture micromorphology changed from complete dimple to a quasi-cleavage structure containing local dimple structures.
Niobium containing dual phase steel hot-rolled under the same process parameters was cooled to 610 ℃ by primary water cooling at a cooling rate of 60 ℃·s-1 or to 461, 434, 410 ℃ by two-stage water cooling at different cooling rates and coiled. The effects of the coiling temperature and cooling rate on the microstructure and tensile properties of the hot-rolled dual phase steel were analyzed. The results show that the microstructures of the hot-rolled dual phase steel under the four processes were all mainly composed of ferrite and martensite, and bainite appeared at the coiling temperature of 461 ℃ and below. With the decrease of coiling temperature, the content of martensite decreased, and the bainite presented dispersed granular, aggregated granular and lath shape successively. The yield strength of the hot-rolled dual phase steel increased, the tensile strength first decreased and then increased, the yield ratio increased, and the precentage elongation after fracture first increased and then decreased. When two-stage water cooling at primary and secondary cooling rates of 53,79 ℃·s-1 to 461 ℃ and coiling, the tensile properties of the hot-rolled dual phase steel were the best, with the average yield strength, average tensile strength, and average precentage elongation after fracture of 459 MPa, 591 MPa, and 35.63%, respectively.
Composite coating of Fe45Cr16Mo16C18B5 iron-based amorphous alloy containing 15wt% Al2O3-13% TiO2 ceramic phase was prepared by plasma spraying technology, and was subjected to a pin-disk friction and wear test. By comparing with those of iron-based amorphous alloy coating, the friction and wear behavior of the composite coating under different loads (20, 30, 50 N) and pin rotational speeds (300, 500, 800 r·min-1) was studied, and its wear mechanism was analyzed. The results show that when the pin rotational speed was 300 r·min-1, the wear rate of the composite coating decreased by nearly 50% compared with that of the iron-based amorphous alloy coating under different loads, and the wear mechanism of the composite coating changed from abrasive wear to fatigue wear as the load increased. When the load was 30 N, the wear scar depth and wear rate of the composite coating first increasd and then decreasd with the increase of the pin rotational speed, both reached the maximum at 500 r·min-1. When the pin rotational speed was 500 r·min-1 and 800 r·min-1, the wear mechanism of the composite coating was adhesive wear.
Sn-(20-x)Bi-xIn (x=0,1,2,3,4,5, mass fraction/%) solder was prepared, and its melting and wetting properties were analyzed. Brazing experiments were conducted on copper substrate with Sn-(2-x)Bi-xIn solder, and the effect of indium content on the microstructure at the brazing interface was studied. The results show that with the increase of indium content, the melting point of the solder decreased. When the mass fraction of indium was 5%, almost no eutectic structure was formed in the solder. The wetting angle of the solder first decreased and then increased, and the wetting area first increased and then decreased with increasing indium content. When the mass fraction of indium was 4%, the wettability of the solder was the best. The thickness of intermetallic compound layer at the brazing interface increased, and the composition of the intermetallic compound changed from Cu6Sn5 to Cu6Sn5 and Cu6(InSn)5.
NiCuZn soft magnetic ferrite was prepared by solid state sintering with raw powder of different particle size prepared by changing the secondary ball milling time (1-6 h). The effect of the particle size on the microstructure and magnetic properties of the soft magnetic ferrite was studied. The results show that the powder particle size decreased with the extension of secondary ball milling time, and the size distribution gradually concentrated. The uniformity of grain size of soft magnetic ferrite prepared became better and then worse, and the grain boundary became clear and then blurred. With the decrease of the powder particle size, the initial permeability, saturation magnetic induction intensity, relative density and resistivity of the soft magnetic ferrite increased first and then decreased, and the power loss decreased first and then increased. When the secondary ball milling time was 3 h, the powder partide size was mainly between 2.5-3.5 μm, with average particle size of 3.237 μm. At this time, the grain boundary of the prepared soft magnetic ferrite was relatively clear, and the grain size was relatively uniform. The initial permeability and saturation magnetic induction intensity reached the maximum value of 1385 H·m-1 and 360 mT, respectively, and the power loss reached the minimum value of 284 kW · m-3.
The 4Cr5Mo2V steel was quenched at 1 000-1 090 ℃. The tempering hardness of the test steel quenched at the same temperature was adjusted to 55,52 HRC by tempering twice at different temperatures, and the effects of the quenching temperature and tempering process on the microstructure, impact toughness and high temperature (350 ℃) wear resistance were studied. The results show that when the tempering hardness was the same, too high or too low quenching temperatures would reduce the toughness of the test steel and aggravate the peeling of the wear surface material, thereby reduced the wear resistance. Under the same tempering hardness, the toughness and high temperature wear resistance of the test steel quenched at 1 030 ℃ were the best, and at 1 090 ℃ were the worst. When the quenching temperature was the same, the test steel tempered at relatively low temperatures had higher tempering hardness, which could support the surface oxide layer, so its wear resistance was better than that tempered at relatively high temperatures. The recommended heat treatment process for 4Cr5Mo2V steel was 1 030 ℃×30 min oil quenching +560 ℃×2 h tempering for twice.
N80 steel sheet was polished and then modified by fluorination with 1H,1H,2H, 2H-perfluorodecyltriethoxysilane, and the effect of fluorination modification on the corrosion resistance of the test steel in 3.5wt% NaCl solution and anti-scaling performance in simulated seawater was studied. The results show that after immersion in NaCl solution for 7 d, the surface corrosion of the fluorination modified specimen was the lightest, and the low frequency (0.01 Hz) impedance modulus was 450 Ω·cm2, which was much larger than that of the unpolished and polished specimens. After seven-time rapid evaporation scaling tests, the scaling amount of the fluorination modified specimen was reduced by about 42.55% and 37.00% those of the unpolished and polished specimens, respectively. After 35-day of multi-field coupling scaling test, there was no obvious scaling phenomenon in the fluorination modified specimen, and the scaling amount was close to 0. Fluorination modification could improve the corrosion resistance and anti-scaling performance of N80 steel.
A modified combined high and low cycle fatigue life prediction model was established based on Manson-Halford model by studying the damage equivalence relationship between high cycle fatigue and low cycle fatigue, and introducing an influence factor to reflect the influence of the interaction between high cycle fatigue and low cycle fatigue loads. The modified model was verified by the test data of TC11 titanium alloy, LY12-CZ aluminum alloy, 45 steel and GH4033 nickel-base alloy. The results show that the fatigue life prediction results of TC11 titanium alloy, LY12-CZ aluminum alloy and GH4033 nickel-base alloy by using the modified model were within the range of two times of error. About 78% of the predicted fatigue life of 45 steel was in the range of two times of error. The modified model had high prediction accuracy and was suitable for the prediction of high and low cycle composite fatigue life.
Isothermal compression tests were conducted on electron beam cladding solidified Inconel 718 alloy (EBLS 718 alloy) and electron beam refining Inconel 718 alloy (EBS 718 alloy). The deformation temperatures were 1 010, 1 050, 1 100, 1 140 ℃, and the strain rates were 0.001,0.01,0.1,1 s-1. The thermal deformation rheological behaviors of the two alloys were compared and studied. Based on the Arrhenius constitutive equation, the constitutive equations of the two alloys were established. The results show that the rheological behavior of the two alloys under different deformation temperatures and strain rates was similar; the flow stress increased with increasing strain rate, and decreased with increasing deformation temperature. Due to the layered interface, the EBLS 718 alloy exibited yield decrease phenomenon at a lower temperature during hot compression deformation, lower deformation activation energy, and more obvious dynamic softening effect. The main deformation mechanism of the two alloys was mainly high temperature climbing mechanism caused by lattice self diffusion.
Tungsten inert gas wire arc additive manufacturing was carried out with the GH4169 superalloy welding wire. The prediction model of the relationship between welding current, welding speed, wire feeding speed and the size of single pass multi-layer welding bead layer width and layer height was established by the quadratic regression general rotation combination scheme, and the calculation was verified by test. The results show that the maximum relative errors of the prediction model of the layer width and the layer height of single pass multi-layer welding bead were 5.22% and 5.82%, respectively, indicating that the established prediction model had high reliability. The effect of welding speed, welding current and wire feeding speed on the forming size of single pass multi-layer welding bead was coupled with each other. The biggest factor affecting the layer width of single pass multi-layer welding bead was the welding current, and the biggest factor affecting the layer height was the wire feeding speed.