The NiAl alloys modified by reactive element(RE),dysprosium(Dy),were produced by arc melting.The microstructures of the modified alloys were investigated by field emission-scanning electron microscope(FE-SEM)equipped ...The NiAl alloys modified by reactive element(RE),dysprosium(Dy),were produced by arc melting.The microstructures of the modified alloys were investigated by field emission-scanning electron microscope(FE-SEM)equipped with energy dispersive spectroscope(EDS)and back scatter detector.Cyclic oxidation tests at 1 200℃were conducted to assess the cyclic oxidation performance of the alloys.The Dy dopant prevents the surface rumpling of the oxide scale and the formation of cavities beneath the oxide scale.The pegs consisting of Dy-rich oxide inclusion core and an outer alumina sheath develop deeply in the alloy and improve the oxide scale adhesion.0.05%-0.1%(molar fraction)Dy dramatically improves the cyclic oxidation resistance of the NiAl alloy. Too high concentration of Dy is deleterious because of the fast oxidation rate caused by severe internal oxidation.展开更多
Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerica...Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.展开更多
By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the inter...By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the internal friction stress and creep lifetimes of the superalloy are investigated by means of the measurement of the creep curves and microstructure observation. Results show that, compared to the P-type structure alloy, the full heat treated state alloy displays a bigger internal friction stress value of dislocation motion during steady state creep and a longer creep lifetimes. The creep activation energies of the full heat treated and P-type structures alloys are measured to be 462 kJ/mol and 412 kJ/mol, respectively. Thereinto, the P-type rafted γ′ phase in the alloy is transformed into the N-type structure during tensile creep. And the N-type γ′ phase transformed from the P-type structure displays a shorter size in length, this is a main reason of the P-type structure alloy possessing a shorter creep lifetimes due to creep dislocation moving easily over the rafted γ′ phase.展开更多
Laser cladding of preplaced Al + Ir powders on a ZM5 magnesium alloy was performed to enhance the corrosion resistance of the ZM5 magnesium alloy. A metallurgical bond was obtained at the coating/substrate interface....Laser cladding of preplaced Al + Ir powders on a ZM5 magnesium alloy was performed to enhance the corrosion resistance of the ZM5 magnesium alloy. A metallurgical bond was obtained at the coating/substrate interface. The corrosion potential (Ecorr) of the laser cladded sample was 169 mV positive to that of the untreated ZM5 substrate,while the corrosion current (Icorr) was some one order of magnitude lower. The laser cladded sample,unlike the untreated ZM5 substrate,showed a passive region in the polarization plot. Immersion tests confirmed that the corrosion resistance of the laser cladded ZM5 sample was significantly enhanced in 3.5 wt.% NaCl solution. The Al-rich phases of AlIr,Mg17Al12,and Al formed in the cladding layer and the rapid solid characteristics were contributed to the improved corrosion behavior of the coating.展开更多
The surface oxygen-diffusion-permeation behaviors of Ti based alloys were investigated. MEF4A optical microscopy and HMV-2000 micro-hardness tester were employed to characterize the microstructure and micro-hardness o...The surface oxygen-diffusion-permeation behaviors of Ti based alloys were investigated. MEF4A optical microscopy and HMV-2000 micro-hardness tester were employed to characterize the microstructure and micro-hardness of the oxygen-permeated alloys. The results show that the micro-hardness of Ti based alloys are sharply enhanced by the permeation of oxygen. The microstructure and micro-hardness of oxygen-permeated layer are strongly related to the oxygen-diffusion-permeation techniques. The solid solution of oxygen in α phase can improve the transformation temperature from α phase to β phase and enlarge the region of α phase so as to improve the micro-hardness of surface layer. Therefore, surface oxygen-diffusion-permeation would be a feasible method to reinforce Ti based alloys based on the solid solution of oxygen in α-Ti. At last, a diffusion-solution model was put forward.展开更多
This paper describes effects of 40 kHz ultrasound on the oxide films of stainless steel in sulphate electrolytes so as to determine the transmitted power and to characterize mass transfer and peak current density on t...This paper describes effects of 40 kHz ultrasound on the oxide films of stainless steel in sulphate electrolytes so as to determine the transmitted power and to characterize mass transfer and peak current density on the electrode surface. Emphasis was mainly laid on electrochemical oxidations and peeling mechanism of oxide films in sonicated sulphate solutions (0.5 and 1.0 mol/L). Polarization voltammetry, current response traces and SEM analysis were carded out in order to provide full information as to oxide films surface. Results shows that the rate of electrochemical oxidation, the shape of polarization curves and the surface micrographs in sonicated sulphate electrolytes are different from those obtained without introduction of ultrasound. It is concluded that ultrasound can change the electro-chemical behavior of oxide films by its cavitaion effects, which would produce transient mechanical impulsive force and enhance electrochemical reactions.展开更多
The influence of surface pre-treatments, shot-peening (SP) and laser remelting (LR), on oxygen permeation behaviors of titanium alloy TC11 was investigated. Optical microscope, SEM with EDAX, XRD, and microhardness te...The influence of surface pre-treatments, shot-peening (SP) and laser remelting (LR), on oxygen permeation behaviors of titanium alloy TC11 was investigated. Optical microscope, SEM with EDAX, XRD, and microhardness tester were employed to characterize the microstructure, composition and hardness of this alloy. The results show that the surface roughness is increased by shot-peening, and the microstructure with fine-grain can be obtained by LR pre-treatment. The pre-treated samples were oxygen-permeated at (810± 10) ℃ for 10 h in atmospheric air. The outer layer consists essentially of TiO2, trace Ti2 N, Ti3Al and Ti3AlN for the SP pre-treatment and thin oxygen solution layer is found in the subsurface layer. As for LR pre-treatment, the outer layer consists mainly of TiO2 and small amounts of TiO, and the inner layer consists of alpha crystals, rich in interstitial atoms. Samples by LR pre-treatment has thicker hardened layer with higher hardness values in comparison with SP pre-treated ones.The boost diffusion of oxygen and hardening mechanisms were discussed based on the experimental results.展开更多
In order to improve aero engine performance, it is necessary to reduce the welding residual stress of aero engine blisk. In this paper, finite element method was employed to simulate electron beam welding process of b...In order to improve aero engine performance, it is necessary to reduce the welding residual stress of aero engine blisk. In this paper, finite element method was employed to simulate electron beam welding process of blisk, in accordance with the deducing formula( p = kh ) , the heat input is changed with the weld depth to control welding residual stress of blisk. The calculation results show that welding residual stress of blisk can be controlled effectively by reducing the heat input on the conditions of meeting the demand of weld penetration and guaranteeing the welding quality, a new theoretical method and some numerical data are provided for controlling welding residual stress of blisk.展开更多
A β--NiAI alloy with normal purity, a S-doped and a Dy and S co-doped (Y-NiAI alloys were prepared by arc-melting and their corresponding S contents were less than 20 ×10-6, 33 ×10-6 and 22 × 10-6, re...A β--NiAI alloy with normal purity, a S-doped and a Dy and S co-doped (Y-NiAI alloys were prepared by arc-melting and their corresponding S contents were less than 20 ×10-6, 33 ×10-6 and 22 × 10-6, respectively. The isothermal oxidation behavior of the alloys at 1200 ℃ was investigated and the extent of S segregation at the scale-alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from e- to β-Al2O3, while the addition of Dy retarded this process. For the S- doped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scale-alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.展开更多
基金Projects(50731001,50771009)supported by the National Natural Science Foundation of ChinaProject(PCSIRT/IRT 0512)supported bythe Program for Changjiang Scholars and Innovative Research Team in Chinese University
文摘The NiAl alloys modified by reactive element(RE),dysprosium(Dy),were produced by arc melting.The microstructures of the modified alloys were investigated by field emission-scanning electron microscope(FE-SEM)equipped with energy dispersive spectroscope(EDS)and back scatter detector.Cyclic oxidation tests at 1 200℃were conducted to assess the cyclic oxidation performance of the alloys.The Dy dopant prevents the surface rumpling of the oxide scale and the formation of cavities beneath the oxide scale.The pegs consisting of Dy-rich oxide inclusion core and an outer alumina sheath develop deeply in the alloy and improve the oxide scale adhesion.0.05%-0.1%(molar fraction)Dy dramatically improves the cyclic oxidation resistance of the NiAl alloy. Too high concentration of Dy is deleterious because of the fast oxidation rate caused by severe internal oxidation.
文摘Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.
基金Supported by the National Natural Science Foundation of China (No 50571070)
文摘By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the internal friction stress and creep lifetimes of the superalloy are investigated by means of the measurement of the creep curves and microstructure observation. Results show that, compared to the P-type structure alloy, the full heat treated state alloy displays a bigger internal friction stress value of dislocation motion during steady state creep and a longer creep lifetimes. The creep activation energies of the full heat treated and P-type structures alloys are measured to be 462 kJ/mol and 412 kJ/mol, respectively. Thereinto, the P-type rafted γ′ phase in the alloy is transformed into the N-type structure during tensile creep. And the N-type γ′ phase transformed from the P-type structure displays a shorter size in length, this is a main reason of the P-type structure alloy possessing a shorter creep lifetimes due to creep dislocation moving easily over the rafted γ′ phase.
基金Projects(51475073,51605076,51875079) supported by the National Natural Science Foundation of ChinaProject(2017YFB1301701) supported by the National Key Research and Development Program of China
基金the National Natural Science Foundation of China (No. 50371093).
文摘Laser cladding of preplaced Al + Ir powders on a ZM5 magnesium alloy was performed to enhance the corrosion resistance of the ZM5 magnesium alloy. A metallurgical bond was obtained at the coating/substrate interface. The corrosion potential (Ecorr) of the laser cladded sample was 169 mV positive to that of the untreated ZM5 substrate,while the corrosion current (Icorr) was some one order of magnitude lower. The laser cladded sample,unlike the untreated ZM5 substrate,showed a passive region in the polarization plot. Immersion tests confirmed that the corrosion resistance of the laser cladded ZM5 sample was significantly enhanced in 3.5 wt.% NaCl solution. The Al-rich phases of AlIr,Mg17Al12,and Al formed in the cladding layer and the rapid solid characteristics were contributed to the improved corrosion behavior of the coating.
文摘The surface oxygen-diffusion-permeation behaviors of Ti based alloys were investigated. MEF4A optical microscopy and HMV-2000 micro-hardness tester were employed to characterize the microstructure and micro-hardness of the oxygen-permeated alloys. The results show that the micro-hardness of Ti based alloys are sharply enhanced by the permeation of oxygen. The microstructure and micro-hardness of oxygen-permeated layer are strongly related to the oxygen-diffusion-permeation techniques. The solid solution of oxygen in α phase can improve the transformation temperature from α phase to β phase and enlarge the region of α phase so as to improve the micro-hardness of surface layer. Therefore, surface oxygen-diffusion-permeation would be a feasible method to reinforce Ti based alloys based on the solid solution of oxygen in α-Ti. At last, a diffusion-solution model was put forward.
文摘This paper describes effects of 40 kHz ultrasound on the oxide films of stainless steel in sulphate electrolytes so as to determine the transmitted power and to characterize mass transfer and peak current density on the electrode surface. Emphasis was mainly laid on electrochemical oxidations and peeling mechanism of oxide films in sonicated sulphate solutions (0.5 and 1.0 mol/L). Polarization voltammetry, current response traces and SEM analysis were carded out in order to provide full information as to oxide films surface. Results shows that the rate of electrochemical oxidation, the shape of polarization curves and the surface micrographs in sonicated sulphate electrolytes are different from those obtained without introduction of ultrasound. It is concluded that ultrasound can change the electro-chemical behavior of oxide films by its cavitaion effects, which would produce transient mechanical impulsive force and enhance electrochemical reactions.
基金Project (50171073) supported by the National Natural Science Foundation of China
文摘The influence of surface pre-treatments, shot-peening (SP) and laser remelting (LR), on oxygen permeation behaviors of titanium alloy TC11 was investigated. Optical microscope, SEM with EDAX, XRD, and microhardness tester were employed to characterize the microstructure, composition and hardness of this alloy. The results show that the surface roughness is increased by shot-peening, and the microstructure with fine-grain can be obtained by LR pre-treatment. The pre-treated samples were oxygen-permeated at (810± 10) ℃ for 10 h in atmospheric air. The outer layer consists essentially of TiO2, trace Ti2 N, Ti3Al and Ti3AlN for the SP pre-treatment and thin oxygen solution layer is found in the subsurface layer. As for LR pre-treatment, the outer layer consists mainly of TiO2 and small amounts of TiO, and the inner layer consists of alpha crystals, rich in interstitial atoms. Samples by LR pre-treatment has thicker hardened layer with higher hardness values in comparison with SP pre-treated ones.The boost diffusion of oxygen and hardening mechanisms were discussed based on the experimental results.
基金The research was supported by Postdoctoral Science Foundation of China (No. 20070410900) and Heilongjiang Postdoctoral Fund (No. LBH-Z07129 ).
文摘In order to improve aero engine performance, it is necessary to reduce the welding residual stress of aero engine blisk. In this paper, finite element method was employed to simulate electron beam welding process of blisk, in accordance with the deducing formula( p = kh ) , the heat input is changed with the weld depth to control welding residual stress of blisk. The calculation results show that welding residual stress of blisk can be controlled effectively by reducing the heat input on the conditions of meeting the demand of weld penetration and guaranteeing the welding quality, a new theoretical method and some numerical data are provided for controlling welding residual stress of blisk.
基金supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 51071013 and 51231001the National Basic Research Program (973 Program) of China under Grant Nos. 2010CB631200 and 2012CB625100
文摘A β--NiAI alloy with normal purity, a S-doped and a Dy and S co-doped (Y-NiAI alloys were prepared by arc-melting and their corresponding S contents were less than 20 ×10-6, 33 ×10-6 and 22 × 10-6, respectively. The isothermal oxidation behavior of the alloys at 1200 ℃ was investigated and the extent of S segregation at the scale-alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from e- to β-Al2O3, while the addition of Dy retarded this process. For the S- doped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scale-alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.