The crack tip stress-strain fields of the elastic-plastic cracked specimens have been analyzed using finite element calculations.The crack initiation and steady propagation behaviours have also been investigated by me...The crack tip stress-strain fields of the elastic-plastic cracked specimens have been analyzed using finite element calculations.The crack initiation and steady propagation behaviours have also been investigated by means of slip line pattern etching technique and mechanical tests. The results show that there are HRR near field and distant field in the crack tip region,and the later depends on the specimen configuration.The crack initiation behaviour is controlled by a single parameter J.In contrast,the steady crack propagation is affected by the distant strain field and can not be described by single parameter only.展开更多
By method of TIG,two kinds of welding materials were filled in and under certain welding craft conditions,1Cr18Ni9Ti and 2Cr13 were welded.The microstructure of two kinds of welded joints were observed and analyzed by...By method of TIG,two kinds of welding materials were filled in and under certain welding craft conditions,1Cr18Ni9Ti and 2Cr13 were welded.The microstructure of two kinds of welded joints were observed and analyzed by OM,SEM.Through seawater immersion test,polarization curves and AC impedance spectroscopy of two kinds of welding joints were obtained.The results show that 2Cr13 and 1Cr18Ni9Ti welded joints are typical columnar crystal,the microstructure is lath martensite+austenite+carbide.The welded joints that filled in 308 and H1Cr21Ni10Mn7Mo welding wires,corrosion resistance has same change rule:Austenite base metal>HAZ near Austenite>welded joint>HAZ near Martensite>Martensite base metal.The every zone contrast of two kinds of welded joint corrosion resistance obtains:the welded joints filled in 308>the welded joints filled in H1Cr21Ni10Mn7Mo.展开更多
The effects of Fe content on the microstructure,phase constituents and microhardness of the as-cast,800℃or 1000℃-annealed Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=13−66)alloys were investigated.Not all these alloys are compos...The effects of Fe content on the microstructure,phase constituents and microhardness of the as-cast,800℃or 1000℃-annealed Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=13−66)alloys were investigated.Not all these alloys are composed of the single FCC phase.The BCC and B2 phases are found.It is confirmed that the BCC phase in the Al7Cr20Fe66Ni7 alloy is transformed from the FCC phase at about 900℃ during cooling.While in the 800℃-annealed Al7Cr20Fe60Ni13 alloy,the FCC phase is stable and the hardness decreases.After annealing at 1000℃,for the precipitation of the B2 particles,the Al content in the FCC phase decreases,which results in decreasing of the alloy hardness.Moreover,after annealing at 800℃,a small amount of Al-rich B2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix,which increases the hardness of the Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=41−49)alloys.These results will help to the composition design and processing design of the Al−Cr−Fe−Ni based high-entropy alloys.展开更多
Precursor of nanocrystalline Zno.sNio.sFe2O4 was obtained by grinding mixture of ZnSO4.7H2O, NiSO4.6H2O, FeSO4.7H2O, and Na2CO3.10H2O under the condition of suffactant polyethylene glycol （PEG）-400 being present at ...Precursor of nanocrystalline Zno.sNio.sFe2O4 was obtained by grinding mixture of ZnSO4.7H2O, NiSO4.6H2O, FeSO4.7H2O, and Na2CO3.10H2O under the condition of suffactant polyethylene glycol （PEG）-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts and drying it at 373 K. The spinel Zn0.5Ni0.5Fe2O4 was obtained via calcining precursor above 773 K. The precursor and its calcined products were characterized by differential scanning calorimetry （DSC）, Fourier transform infrared （FF-IR）, X-ray diffraction （XRD）, and vibrating sample magnetometer （VSM）. The result showed that Zn0.sNio.sFe204 obtained at 1073 K had a saturation magnetization of 74 A.mLkg-1. Kinetics of the crystallization process of Zn0.5Ni0.5Fe2O4 was studied using DSC technique, and kinetic parameters were determined by Kissinger equation and Moynihan et al. equation. The value of the activation energy associated with the crystallization process of Zr0.5Ni0.5Fe2O4 is 220.89 kJ-mol-1. The average value of the Avrami exponent, n, is equal to 1.59±0.13, which suggests that crystallization process of Zn0.5Ni0.5Fe2O4 is the random nucleation and growth of nuclei reaction.展开更多
A Ni-Cr/BN composite was produced by a active sintering process. The powder of nickel carbonyl,Cr2O3 and C were used as the original materials,and a hexagonal BN(h-BN) powder was added as a solid lubricant. The influe...A Ni-Cr/BN composite was produced by a active sintering process. The powder of nickel carbonyl,Cr2O3 and C were used as the original materials,and a hexagonal BN(h-BN) powder was added as a solid lubricant. The influence of sintering temperature,heating rate and holding time on the properties of Ni-Cr/BN were studied. The composition and microstructure of Ni-Cr/BN were analysed by X-ray diffraction(XRD) and the optical microscopy(OM). The frictional behavior and hardness were measured with ring-block friction testing machine and Brinell hardness tester respectively. The results show that Ni-Cr is the matrix and a low-melting eutectic compound is the bonding phase in the composite. The porosity reaches 48% and the value of hardness reaches HB18 when the composite is fabricated at 1 100 ℃ for 1 h. Its wear rate is 7.44×10-5 g/min,and the average friction coefficient is 0.266. These properties make such composite suitable for use as self-lubricating material.展开更多
文摘The crack tip stress-strain fields of the elastic-plastic cracked specimens have been analyzed using finite element calculations.The crack initiation and steady propagation behaviours have also been investigated by means of slip line pattern etching technique and mechanical tests. The results show that there are HRR near field and distant field in the crack tip region,and the later depends on the specimen configuration.The crack initiation behaviour is controlled by a single parameter J.In contrast,the steady crack propagation is affected by the distant strain field and can not be described by single parameter only.
基金supported by the Anhui Provincial Natural Science Foundation(Grant No.2008085 QE 231).
文摘By method of TIG,two kinds of welding materials were filled in and under certain welding craft conditions,1Cr18Ni9Ti and 2Cr13 were welded.The microstructure of two kinds of welded joints were observed and analyzed by OM,SEM.Through seawater immersion test,polarization curves and AC impedance spectroscopy of two kinds of welding joints were obtained.The results show that 2Cr13 and 1Cr18Ni9Ti welded joints are typical columnar crystal,the microstructure is lath martensite+austenite+carbide.The welded joints that filled in 308 and H1Cr21Ni10Mn7Mo welding wires,corrosion resistance has same change rule:Austenite base metal>HAZ near Austenite>welded joint>HAZ near Martensite>Martensite base metal.The every zone contrast of two kinds of welded joint corrosion resistance obtains:the welded joints filled in 308>the welded joints filled in H1Cr21Ni10Mn7Mo.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51771035,51671037)Natural Science Foundation of Jiangsu Province,China(BK20161190)the Priority Academic Program of Jiangsu Higher Education Institutions,China.
文摘The effects of Fe content on the microstructure,phase constituents and microhardness of the as-cast,800℃or 1000℃-annealed Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=13−66)alloys were investigated.Not all these alloys are composed of the single FCC phase.The BCC and B2 phases are found.It is confirmed that the BCC phase in the Al7Cr20Fe66Ni7 alloy is transformed from the FCC phase at about 900℃ during cooling.While in the 800℃-annealed Al7Cr20Fe60Ni13 alloy,the FCC phase is stable and the hardness decreases.After annealing at 1000℃,for the precipitation of the B2 particles,the Al content in the FCC phase decreases,which results in decreasing of the alloy hardness.Moreover,after annealing at 800℃,a small amount of Al-rich B2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix,which increases the hardness of the Al_(7)Cr_(20)Fe_(x)Ni_(73)−x(x=41−49)alloys.These results will help to the composition design and processing design of the Al−Cr−Fe−Ni based high-entropy alloys.
基金financially supported by the National Natural Science Foundation of China (No.21161002)the Guangxi Science and Technology Agency Research Item,China (No.0992001-5)
文摘Precursor of nanocrystalline Zno.sNio.sFe2O4 was obtained by grinding mixture of ZnSO4.7H2O, NiSO4.6H2O, FeSO4.7H2O, and Na2CO3.10H2O under the condition of suffactant polyethylene glycol （PEG）-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts and drying it at 373 K. The spinel Zn0.5Ni0.5Fe2O4 was obtained via calcining precursor above 773 K. The precursor and its calcined products were characterized by differential scanning calorimetry （DSC）, Fourier transform infrared （FF-IR）, X-ray diffraction （XRD）, and vibrating sample magnetometer （VSM）. The result showed that Zn0.sNio.sFe204 obtained at 1073 K had a saturation magnetization of 74 A.mLkg-1. Kinetics of the crystallization process of Zn0.5Ni0.5Fe2O4 was studied using DSC technique, and kinetic parameters were determined by Kissinger equation and Moynihan et al. equation. The value of the activation energy associated with the crystallization process of Zr0.5Ni0.5Fe2O4 is 220.89 kJ-mol-1. The average value of the Avrami exponent, n, is equal to 1.59±0.13, which suggests that crystallization process of Zn0.5Ni0.5Fe2O4 is the random nucleation and growth of nuclei reaction.
文摘A Ni-Cr/BN composite was produced by a active sintering process. The powder of nickel carbonyl,Cr2O3 and C were used as the original materials,and a hexagonal BN(h-BN) powder was added as a solid lubricant. The influence of sintering temperature,heating rate and holding time on the properties of Ni-Cr/BN were studied. The composition and microstructure of Ni-Cr/BN were analysed by X-ray diffraction(XRD) and the optical microscopy(OM). The frictional behavior and hardness were measured with ring-block friction testing machine and Brinell hardness tester respectively. The results show that Ni-Cr is the matrix and a low-melting eutectic compound is the bonding phase in the composite. The porosity reaches 48% and the value of hardness reaches HB18 when the composite is fabricated at 1 100 ℃ for 1 h. Its wear rate is 7.44×10-5 g/min,and the average friction coefficient is 0.266. These properties make such composite suitable for use as self-lubricating material.
