The effect of tensile stress and trace amounts of impurities on the creep activation energyof platinum was studied and the creep mechanism was disscussed.
The steady-state creep behavior of unidirectional C/C(1-D-C/C) composite with pyrolytic carbon matrix was investigated at high temperatures up to 2160℃ and under tensile stress from 133.83 to 213.46MPa. Based on the ...The steady-state creep behavior of unidirectional C/C(1-D-C/C) composite with pyrolytic carbon matrix was investigated at high temperatures up to 2160℃ and under tensile stress from 133.83 to 213.46MPa. Based on the creep experiment of single specimen method, the apparent activation energy and the stress exponent for steadystate creep were determined by the use of a self-made apparatus and an auto-testing system. Value of apparent activation volume is provided and the creep mechanism has also been discussed.展开更多
Atomic simulations are executed to investigate the creep responses of nano-polycrystalline(NC) niobium established by using the Voronoi algorithm. The effects of varying temperature, applied stress, and grain size(GS)...Atomic simulations are executed to investigate the creep responses of nano-polycrystalline(NC) niobium established by using the Voronoi algorithm. The effects of varying temperature, applied stress, and grain size(GS) on creep properties and mechanisms are investigated. Notably, the occurrence of tertiary creep is exclusively observed under conditions where the applied stress exceeds 4.5 GPa and the temperature is higher than 1100 K. This phenomenon can be attributed to the significant acceleration of grain boundary and lattice diffusion, driven by the elevated temperature and stress levels. It is found that the strain rate increases with both temperature and stress increasing. However, an interesting trend is observed in which the strain rate decreases as the grain size increases. The stress and temperature are crucial parameters governing the creep behavior. As these factors intensify, the creep mechanism undergoes a sequential transformation: initially from lattice diffusion under low stress and temperature conditions to a mixed mode combining grain boundaries(GBs) and lattice diffusion at moderate stress and mid temperature levels, and ultimately leading to the failure of power-law controlled creep behavior, inclusive of grain boundary recrystallization under high stress and temperature conditions. This comprehensive analysis provides in more detail an understanding of the intricate creep behavior of nano-polycrystalline niobium and its dependence on various physical parameters.展开更多
The creep properties of as-cast Mg-9Al-1Si alloy and Mg-9Al-1Si-1SiC composite were compared.The results show that Mg-9A1-lSi-lSiC composite performs a better creep resistance than that of Mg-9Al-1Si alloy at constant...The creep properties of as-cast Mg-9Al-1Si alloy and Mg-9Al-1Si-1SiC composite were compared.The results show that Mg-9A1-lSi-lSiC composite performs a better creep resistance than that of Mg-9Al-1Si alloy at constant temperature and stress(473 K,70MPa).Besides,the creep behavior of Mg-9Al-1 Si-1SiC composite at various temperature from 448 K to 498 K and under stresses of 70-90 MPa were systematically investigated.The Mg-9Al-1 Si-1SiC composite exhibited a stress exponent from 5.5 to 6.9 and the creep activation energy fell within the range of 86-111 kJ/mol.The results showed that the creep mechanism of Mg-9Al-1Si-1SiC composite was mainly attributed to the effects of secondary phase strengthening mechanism and dislocation climb mechanism.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
The effect of Zr on the behavior of compressive creep in as cast ZA27 alloy was investigated in the temperature range of 20160 ℃ and under different compressive stresses in the range of 50137.5 MPa with special appar...The effect of Zr on the behavior of compressive creep in as cast ZA27 alloy was investigated in the temperature range of 20160 ℃ and under different compressive stresses in the range of 50137.5 MPa with special apparatus. The results show that the primary compressive creep strains and steady creep rates of ZA27 Zr alloy and ZA27 alloy increase with increasing temperature and stress. However, the primary compressive creep strain and steady creep rate of the ZA27 Zr alloy are lower than that of the ZA27 alloy below 100 ℃, but higher at 160 ℃. The compressive creep behaviors in both ZA27 Zr alloy and ZA27 alloy obey an empirical equation ln t=C-n ln σ+ Q/RT , and the exponent stress n is 3.63 for ZA27 Zr alloy and 3.46 for ZA27 alloy, respectively, the activation energy Q is 87.32 kJ/mol for ZA27 Zr alloy and 81.09 kJ/mol for ZA27 alloy. Different material structural constants are associated with different compressive creep behaviors in the alloy. The compressive creep rate in the alloy is controlled by the lattice diffusion of zinc and dislocation limb.展开更多
By adding small amount of Mg to the wrought superalloys,the steady stage of creep,and es- pecially the tertiary stage of creep are prolonged.Also,the steady creep rate is decreased within the range of low strain rates...By adding small amount of Mg to the wrought superalloys,the steady stage of creep,and es- pecially the tertiary stage of creep are prolonged.Also,the steady creep rate is decreased within the range of low strain rates.At higher strain rates,however,the effect of Mg on creep rate vanishes.This may be attributed to the Mg dissolution in the matrix.A mechanism of the effects of Mg addition on creep behaviors is proposed.展开更多
This paper is about the use of power law model to fit experimental creep data of PP reinforced with calcium carbonate nanofiller at 10% optimum volume fraction with a view to characterizing the new material (PPC2) par...This paper is about the use of power law model to fit experimental creep data of PP reinforced with calcium carbonate nanofiller at 10% optimum volume fraction with a view to characterizing the new material (PPC2) parametrically. The creep parameters were evaluated for neat (PPC0) and reinforced PP (PPC2) to establish the influence of reinforcement on the creep variables like creep rate and creep activation energy. The coefficient parameter A estimated within the stress level range 13.08MPa-22.88MPa has the range 0.0165-0.0651 while the exponent parameter n has 0.299-0.370. The creep stress coefficient K and exponent m has the respective values 161.495 and 0.3288 for PPC0 and 1881.4965 and 0.5448 for PPC2. The value of the parameter p similar to Larson-Miller has the value 4014.1871. Two creep function models used found that PPC0 has higher activation energy with value 9.3642E-20 J/mol for the stress 13.08MPa and PPC2 has values for the stresses 13.08MPa, 19.61MPa and 22.88MPa as 5.55998E- 20J/mol,5.4573E-20J/mol and 4.845E-20J/mol respectively. Of the two master curves produced, that following Larson-Miller parameter is recommended as the relationship between lnσ and parameter f(σ) is relatively linear and will give better results than the curve assumed to follow Sherby-Dorn that will give average result.展开更多
基金Supported by the National Natural Science Foundation of China
文摘The effect of tensile stress and trace amounts of impurities on the creep activation energyof platinum was studied and the creep mechanism was disscussed.
文摘The steady-state creep behavior of unidirectional C/C(1-D-C/C) composite with pyrolytic carbon matrix was investigated at high temperatures up to 2160℃ and under tensile stress from 133.83 to 213.46MPa. Based on the creep experiment of single specimen method, the apparent activation energy and the stress exponent for steadystate creep were determined by the use of a self-made apparatus and an auto-testing system. Value of apparent activation volume is provided and the creep mechanism has also been discussed.
基金Project supported by the Doctoral Scientific Research Starting Foundation of Nanchang Hang Kong University,China(Grant No.EA201903209)。
文摘Atomic simulations are executed to investigate the creep responses of nano-polycrystalline(NC) niobium established by using the Voronoi algorithm. The effects of varying temperature, applied stress, and grain size(GS) on creep properties and mechanisms are investigated. Notably, the occurrence of tertiary creep is exclusively observed under conditions where the applied stress exceeds 4.5 GPa and the temperature is higher than 1100 K. This phenomenon can be attributed to the significant acceleration of grain boundary and lattice diffusion, driven by the elevated temperature and stress levels. It is found that the strain rate increases with both temperature and stress increasing. However, an interesting trend is observed in which the strain rate decreases as the grain size increases. The stress and temperature are crucial parameters governing the creep behavior. As these factors intensify, the creep mechanism undergoes a sequential transformation: initially from lattice diffusion under low stress and temperature conditions to a mixed mode combining grain boundaries(GBs) and lattice diffusion at moderate stress and mid temperature levels, and ultimately leading to the failure of power-law controlled creep behavior, inclusive of grain boundary recrystallization under high stress and temperature conditions. This comprehensive analysis provides in more detail an understanding of the intricate creep behavior of nano-polycrystalline niobium and its dependence on various physical parameters.
基金Shanxi provice scientific facilities and instruments shared service platform of magnesium-based matierals electric impulse aided forming(201805D141005)National Natural Science Foundation of China(51404166,51704209,U1810208)+3 种基金Science and Technology Major Project of Shanxi province(20191102008,20191102007,20181101008)Natural Science Foundation of Shanxi Province(201701D121045)Shanxi Province Science Foundation for Youths(2016021063)The Projects of International Cooperation in Shanxi(201803D421086).
文摘The creep properties of as-cast Mg-9Al-1Si alloy and Mg-9Al-1Si-1SiC composite were compared.The results show that Mg-9A1-lSi-lSiC composite performs a better creep resistance than that of Mg-9Al-1Si alloy at constant temperature and stress(473 K,70MPa).Besides,the creep behavior of Mg-9Al-1 Si-1SiC composite at various temperature from 448 K to 498 K and under stresses of 70-90 MPa were systematically investigated.The Mg-9Al-1 Si-1SiC composite exhibited a stress exponent from 5.5 to 6.9 and the creep activation energy fell within the range of 86-111 kJ/mol.The results showed that the creep mechanism of Mg-9Al-1Si-1SiC composite was mainly attributed to the effects of secondary phase strengthening mechanism and dislocation climb mechanism.
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.
文摘The effect of Zr on the behavior of compressive creep in as cast ZA27 alloy was investigated in the temperature range of 20160 ℃ and under different compressive stresses in the range of 50137.5 MPa with special apparatus. The results show that the primary compressive creep strains and steady creep rates of ZA27 Zr alloy and ZA27 alloy increase with increasing temperature and stress. However, the primary compressive creep strain and steady creep rate of the ZA27 Zr alloy are lower than that of the ZA27 alloy below 100 ℃, but higher at 160 ℃. The compressive creep behaviors in both ZA27 Zr alloy and ZA27 alloy obey an empirical equation ln t=C-n ln σ+ Q/RT , and the exponent stress n is 3.63 for ZA27 Zr alloy and 3.46 for ZA27 alloy, respectively, the activation energy Q is 87.32 kJ/mol for ZA27 Zr alloy and 81.09 kJ/mol for ZA27 alloy. Different material structural constants are associated with different compressive creep behaviors in the alloy. The compressive creep rate in the alloy is controlled by the lattice diffusion of zinc and dislocation limb.
文摘By adding small amount of Mg to the wrought superalloys,the steady stage of creep,and es- pecially the tertiary stage of creep are prolonged.Also,the steady creep rate is decreased within the range of low strain rates.At higher strain rates,however,the effect of Mg on creep rate vanishes.This may be attributed to the Mg dissolution in the matrix.A mechanism of the effects of Mg addition on creep behaviors is proposed.
文摘This paper is about the use of power law model to fit experimental creep data of PP reinforced with calcium carbonate nanofiller at 10% optimum volume fraction with a view to characterizing the new material (PPC2) parametrically. The creep parameters were evaluated for neat (PPC0) and reinforced PP (PPC2) to establish the influence of reinforcement on the creep variables like creep rate and creep activation energy. The coefficient parameter A estimated within the stress level range 13.08MPa-22.88MPa has the range 0.0165-0.0651 while the exponent parameter n has 0.299-0.370. The creep stress coefficient K and exponent m has the respective values 161.495 and 0.3288 for PPC0 and 1881.4965 and 0.5448 for PPC2. The value of the parameter p similar to Larson-Miller has the value 4014.1871. Two creep function models used found that PPC0 has higher activation energy with value 9.3642E-20 J/mol for the stress 13.08MPa and PPC2 has values for the stresses 13.08MPa, 19.61MPa and 22.88MPa as 5.55998E- 20J/mol,5.4573E-20J/mol and 4.845E-20J/mol respectively. Of the two master curves produced, that following Larson-Miller parameter is recommended as the relationship between lnσ and parameter f(σ) is relatively linear and will give better results than the curve assumed to follow Sherby-Dorn that will give average result.
