The present study deals with the effect of cold deformation and subsequent aging on the microstructure and mechanical properties of AI-Cu-Si-Mg alloy. Differential scanning calorimetry indicates that precipitation occ...The present study deals with the effect of cold deformation and subsequent aging on the microstructure and mechanical properties of AI-Cu-Si-Mg alloy. Differential scanning calorimetry indicates that precipitation occurs in the temperature range of 258-272℃ for the as quenched wrought alloy. The activation energy value estimated by Kissinger method for the aforesaid precipitation reaction is obtained as 106 kJ/mol. 45% cold deformation prior to aging indicates the first dissolution reaction at about 50℃ and the precipitation reaction at a temperature of about 82℃. Microstructural investigations have revealed the formation of fine precipitates within the matrix after aging of the cold deformed sample. As-quenched alloy reveals prominently the aging response, The increase in hardness, yield and tensile strength with simultaneous decrease in elongation in the deformed alloy is found to be primarily due to the deformation strengthening and not due to the precipitation hardening.展开更多
The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimat...The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimated by introducing the equationproposed by Thompson, Spaepen and Turnbull. It can be seen that the Gibbs free energy differences decrease firstas the increases of Sn addition smaller than 3, then followed by a decrease due to the successive addition of Snlarger than 3, indicating that the thermal stabilities of these glass forming alloys increase first and then followed by adecrease owing to the excessive addition of Sn. Furthermore, the activation energy of Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9) and(Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9))_(0.97)Sn_3 was evaluated by Kissinger equation. It is noted that the Sn addition increases theactivation energies for glass transition and crystallization, implying that the higher thermal stability can be obtainedby appropriate addition of Sn.展开更多
The law and activation energy of annealing embrittlement for three kinds of popular Fe B Si amorphous alloys have been studied. For comparison, the crystallization activation energy (CAE) of these alloys was measure...The law and activation energy of annealing embrittlement for three kinds of popular Fe B Si amorphous alloys have been studied. For comparison, the crystallization activation energy (CAE) of these alloys was measured by XRD equal first peak height method and conventional Kissinger method. The structural relaxation activation energy (SRAE) of these alloys was measured by Curie temperature method or internal friction method. Through the comparison and analysis of the activation energies of annealing embrittlement, crystallization and structural relaxation, the related influencing factors on annealing embrittlement of Fe based amorphous alloys are elucidated.展开更多
The thermal decomposition of ammonium perchlorate (AP) with Al and Zn metallic particles was studied at different heating rates in dry air atmosphere and the combustion behavior of AP/Al/Zn propellant was evaluated. T...The thermal decomposition of ammonium perchlorate (AP) with Al and Zn metallic particles was studied at different heating rates in dry air atmosphere and the combustion behavior of AP/Al/Zn propellant was evaluated. The exothermic reaction kinetics was studied by differential thermal analysis (DTA) in non-isothermal conditions and compare with the thermal decomposition of pure AP and AP/aluminum particles analyzed in the same experimental conditions. The Arrhenius parameters were estimated according to the Ozawa and Kissinger methods. The calculated activation energies for the low and high temperature exothermic reactions were 91 and 229 kJ/mol for pure AP, 90 and 112 kJ/mol for 80 wt% AP/20 wt% Al particles. When zinc was incorporated, activation energy of 56 kJ/mol was determined for the only exothermic peak observed for 90 wt% AP/10 wt% Zn and 44 kJ/mol for 78.4 wt% AP/19.6 wt% Al/2 wt% Zn propellant composition.展开更多
A new Ni–Cr–Si–B–Fe fi ller material is prepared for transient liquid-phase(TLP)bonding of Inconel 718 superalloy by mechanical alloying technique.The melting temperature range of the fi ller material and its acti...A new Ni–Cr–Si–B–Fe fi ller material is prepared for transient liquid-phase(TLP)bonding of Inconel 718 superalloy by mechanical alloying technique.The melting temperature range of the fi ller material and its activation energy of melting are determined by diff erential scanning calorimetry technique.The activation energy and melting temperature of the alloy powder decrease with increasing milling time.Inconel 718 alloy was joined via TLP by using the newly developed fi ller material.The eff ect of TLP bonding temperature and time on microstructural evolution and mechanical properties of the joint was investigated.Three distinct microstructural regions were observed in the bonding area:isothermal solidifi cation zone consisting of a single-phase solid solution,diff usion aff ected zone consisting of extensive diff usion-induced precipitates of metallic boride,and unaff ected base material.The ultimate shear strength and microhardness of the TLP-bonded joint increase with bonding time and temperature.展开更多
By measuring and analyzing the crystallization activation energy (CAE) of Fe-based amorphous alloy Fe79B16Si5 and Fe78B13Si9, it is reconfirmed and further analyzed that the conventional Kissinger method does not conf...By measuring and analyzing the crystallization activation energy (CAE) of Fe-based amorphous alloy Fe79B16Si5 and Fe78B13Si9, it is reconfirmed and further analyzed that the conventional Kissinger method does not conform with the premise of Kissinger equation, namely, samples with different heating rates should keep a constant fraction of transformation at the exothermal peak temperature Tp of DSC thermogram. The XRD equal first peak height (EFPH) method is applied to CAE measurement of Fe-based amorphous alloy for the first time. It is shown again that the EFPH method coincides with the premise of Kissinger equation. The procedure of EFPH method is introduced in detail in this paper. The accuracy in determining CAE of amorphous alloy may be improved by applying the EFPH method. As a result, the mechanism of embrittlement of amorphous alloy may be better elucidated.展开更多
In order to understand the strength developing law of the epoxy asphalt mixture,a curing reaction model of the epoxy asphalt binder was proposed based upon the thermokinetic analysis.Given some assumptions,the model w...In order to understand the strength developing law of the epoxy asphalt mixture,a curing reaction model of the epoxy asphalt binder was proposed based upon the thermokinetic analysis.Given some assumptions,the model was developed by applying the Kissinger law as well as Arrhenius equation,and the differential scanning calorimetry was performed for estimating the model parameters.To monitor the strength development of the epoxy asphalt mixture,a strength test program was employed and then results were compared to those produced from the proposed model.The comparative evaluation shows that a good consistency exists between the outputs from test program and the proposed model,indicating that the proposed model can be used effectively for simulating the curing reaction process for the epoxy asphalt binder and predicting the strength development for the epoxy asphalt mixture.展开更多
Devitrification study of Ge15Te82Sb3 is compared to Ge14Te84.5Sb1.5 amorphous alloys using differential scanning calo-rimetry (DSC) and X-ray diffraction;we show tellurium effect in isothermal crystallization phenomen...Devitrification study of Ge15Te82Sb3 is compared to Ge14Te84.5Sb1.5 amorphous alloys using differential scanning calo-rimetry (DSC) and X-ray diffraction;we show tellurium effect in isothermal crystallization phenomena. The DSC traces of Ge15Te82Sb3 fixed at 413?C show the phase separation in the sample with increasing transition temperatures Tg followed by two crystallization temperatures Tc1 and Tc2. This sample is compared to Ge14Te84.5Sb1.5 which crystallized by two transition temperatures and two crystallization temperatures Tc1 and Tc2. By X. Rays diffraction, we show that this behaviour is due to the presence of two phases in the amorphous sample with composition vitreous change during heating sample, the most important first one corresponds to the tellurium crystallization in the hexagonal form with 1.8 eV activation energy. The second correspond essentially to the crystallization of Te+ GeTe phase with 2.1 eV activation energy.展开更多
The differential thermal analysis （DTA） curves were measured at different heating rates in flowing air for studying the synthesis of the spinel LiMn2O3 with Li2CO3 and MnO2, The reaction began at about 503K, and fin...The differential thermal analysis （DTA） curves were measured at different heating rates in flowing air for studying the synthesis of the spinel LiMn2O3 with Li2CO3 and MnO2, The reaction began at about 503K, and finished at about 873K. The apparent activation energy of Kissinger method was about 122.77kJ.mol^-1, the reaction orderwas 1.67, the frequency factor was 7.81×10^9, and therefore the dinetic epuation was dδ/dt=A·exp（- E/RT）·（1-δ）^n=7.81×10^9, exp（-122770/RT）·（l-δ）^1.67 . Coats-Redfem integral method was used to analyze the DTA curves of the samples at different heating rates, and the calculated apparent activation energy and frequency factor were 112. 13kJ· mol^-1 and 1.18 × 10^9, respectively, rather close to that of Kissinger method. X-ray diffraction （XRD） and scanning electron microscope （SEM） results shown that the synthesized LiMn2O3 possesses pure phase, regular shape and normal particle distribution.展开更多
文摘The present study deals with the effect of cold deformation and subsequent aging on the microstructure and mechanical properties of AI-Cu-Si-Mg alloy. Differential scanning calorimetry indicates that precipitation occurs in the temperature range of 258-272℃ for the as quenched wrought alloy. The activation energy value estimated by Kissinger method for the aforesaid precipitation reaction is obtained as 106 kJ/mol. 45% cold deformation prior to aging indicates the first dissolution reaction at about 50℃ and the precipitation reaction at a temperature of about 82℃. Microstructural investigations have revealed the formation of fine precipitates within the matrix after aging of the cold deformed sample. As-quenched alloy reveals prominently the aging response, The increase in hardness, yield and tensile strength with simultaneous decrease in elongation in the deformed alloy is found to be primarily due to the deformation strengthening and not due to the precipitation hardening.
文摘The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimated by introducing the equationproposed by Thompson, Spaepen and Turnbull. It can be seen that the Gibbs free energy differences decrease firstas the increases of Sn addition smaller than 3, then followed by a decrease due to the successive addition of Snlarger than 3, indicating that the thermal stabilities of these glass forming alloys increase first and then followed by adecrease owing to the excessive addition of Sn. Furthermore, the activation energy of Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9) and(Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9))_(0.97)Sn_3 was evaluated by Kissinger equation. It is noted that the Sn addition increases theactivation energies for glass transition and crystallization, implying that the higher thermal stability can be obtainedby appropriate addition of Sn.
文摘The law and activation energy of annealing embrittlement for three kinds of popular Fe B Si amorphous alloys have been studied. For comparison, the crystallization activation energy (CAE) of these alloys was measured by XRD equal first peak height method and conventional Kissinger method. The structural relaxation activation energy (SRAE) of these alloys was measured by Curie temperature method or internal friction method. Through the comparison and analysis of the activation energies of annealing embrittlement, crystallization and structural relaxation, the related influencing factors on annealing embrittlement of Fe based amorphous alloys are elucidated.
文摘The thermal decomposition of ammonium perchlorate (AP) with Al and Zn metallic particles was studied at different heating rates in dry air atmosphere and the combustion behavior of AP/Al/Zn propellant was evaluated. The exothermic reaction kinetics was studied by differential thermal analysis (DTA) in non-isothermal conditions and compare with the thermal decomposition of pure AP and AP/aluminum particles analyzed in the same experimental conditions. The Arrhenius parameters were estimated according to the Ozawa and Kissinger methods. The calculated activation energies for the low and high temperature exothermic reactions were 91 and 229 kJ/mol for pure AP, 90 and 112 kJ/mol for 80 wt% AP/20 wt% Al particles. When zinc was incorporated, activation energy of 56 kJ/mol was determined for the only exothermic peak observed for 90 wt% AP/10 wt% Zn and 44 kJ/mol for 78.4 wt% AP/19.6 wt% Al/2 wt% Zn propellant composition.
基金financially supported by the Department of Mechanical engineering and Central Instruments Facility of Indian Institute of Technology Guwahati,India-781039。
文摘A new Ni–Cr–Si–B–Fe fi ller material is prepared for transient liquid-phase(TLP)bonding of Inconel 718 superalloy by mechanical alloying technique.The melting temperature range of the fi ller material and its activation energy of melting are determined by diff erential scanning calorimetry technique.The activation energy and melting temperature of the alloy powder decrease with increasing milling time.Inconel 718 alloy was joined via TLP by using the newly developed fi ller material.The eff ect of TLP bonding temperature and time on microstructural evolution and mechanical properties of the joint was investigated.Three distinct microstructural regions were observed in the bonding area:isothermal solidifi cation zone consisting of a single-phase solid solution,diff usion aff ected zone consisting of extensive diff usion-induced precipitates of metallic boride,and unaff ected base material.The ultimate shear strength and microhardness of the TLP-bonded joint increase with bonding time and temperature.
文摘By measuring and analyzing the crystallization activation energy (CAE) of Fe-based amorphous alloy Fe79B16Si5 and Fe78B13Si9, it is reconfirmed and further analyzed that the conventional Kissinger method does not conform with the premise of Kissinger equation, namely, samples with different heating rates should keep a constant fraction of transformation at the exothermal peak temperature Tp of DSC thermogram. The XRD equal first peak height (EFPH) method is applied to CAE measurement of Fe-based amorphous alloy for the first time. It is shown again that the EFPH method coincides with the premise of Kissinger equation. The procedure of EFPH method is introduced in detail in this paper. The accuracy in determining CAE of amorphous alloy may be improved by applying the EFPH method. As a result, the mechanism of embrittlement of amorphous alloy may be better elucidated.
基金Funded by the Project of National Science and Technology Ministry of China(No.2009BAG15B03)
文摘In order to understand the strength developing law of the epoxy asphalt mixture,a curing reaction model of the epoxy asphalt binder was proposed based upon the thermokinetic analysis.Given some assumptions,the model was developed by applying the Kissinger law as well as Arrhenius equation,and the differential scanning calorimetry was performed for estimating the model parameters.To monitor the strength development of the epoxy asphalt mixture,a strength test program was employed and then results were compared to those produced from the proposed model.The comparative evaluation shows that a good consistency exists between the outputs from test program and the proposed model,indicating that the proposed model can be used effectively for simulating the curing reaction process for the epoxy asphalt binder and predicting the strength development for the epoxy asphalt mixture.
文摘Devitrification study of Ge15Te82Sb3 is compared to Ge14Te84.5Sb1.5 amorphous alloys using differential scanning calo-rimetry (DSC) and X-ray diffraction;we show tellurium effect in isothermal crystallization phenomena. The DSC traces of Ge15Te82Sb3 fixed at 413?C show the phase separation in the sample with increasing transition temperatures Tg followed by two crystallization temperatures Tc1 and Tc2. This sample is compared to Ge14Te84.5Sb1.5 which crystallized by two transition temperatures and two crystallization temperatures Tc1 and Tc2. By X. Rays diffraction, we show that this behaviour is due to the presence of two phases in the amorphous sample with composition vitreous change during heating sample, the most important first one corresponds to the tellurium crystallization in the hexagonal form with 1.8 eV activation energy. The second correspond essentially to the crystallization of Te+ GeTe phase with 2.1 eV activation energy.
文摘The differential thermal analysis （DTA） curves were measured at different heating rates in flowing air for studying the synthesis of the spinel LiMn2O3 with Li2CO3 and MnO2, The reaction began at about 503K, and finished at about 873K. The apparent activation energy of Kissinger method was about 122.77kJ.mol^-1, the reaction orderwas 1.67, the frequency factor was 7.81×10^9, and therefore the dinetic epuation was dδ/dt=A·exp（- E/RT）·（1-δ）^n=7.81×10^9, exp（-122770/RT）·（l-δ）^1.67 . Coats-Redfem integral method was used to analyze the DTA curves of the samples at different heating rates, and the calculated apparent activation energy and frequency factor were 112. 13kJ· mol^-1 and 1.18 × 10^9, respectively, rather close to that of Kissinger method. X-ray diffraction （XRD） and scanning electron microscope （SEM） results shown that the synthesized LiMn2O3 possesses pure phase, regular shape and normal particle distribution.
