The non-isothermal crystallization kinetics of Ni55Nb35Si10 amorphous alloy,prepared by mechanical alloying,was studied using differential scanning calorimetry.The amorphous alloy showed one-stage crystallization on h...The non-isothermal crystallization kinetics of Ni55Nb35Si10 amorphous alloy,prepared by mechanical alloying,was studied using differential scanning calorimetry.The amorphous alloy showed one-stage crystallization on heating,which led to the formation of nano-intermetallic crystals in amorphous matrix.The apparent activation energy for the crystallization of the alloy,determined by the Kissinger equation,was relatively high(468 kJ/mol),indicating that this amorphous alloy has high thermal stability.Changes in the activation energy during the crystallization process,were also evaluated by iso-conversional methods.The results showed that it decreases slowly from the beginning to crystallized fractionα=0.35 and it remains almost constant to the end of the process.The nano-crystallization mechanism for the non-isothermal crystallization of the amorphous alloy was explained by determining Avrami exponents.Transmission electron microscopy studies revealed the microstructural modification of amorphous alloy via nanocrystallization during annealing.The results suggest that the nucleation rate decreases with increasing time and the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth.A predictive equation was obtained based on the Sestak-Berggren autocatalytic model to describe quantitatively the non-isothermal crystallization kinetics.展开更多
Ti3 AL-Nb-Mo composites were prepared by SHS using initial powder mixtures of Ti-Al-Nb-Mo and their corrosion and mechanical properties were studied to develop bioand environmental materials. The composites reached 99...Ti3 AL-Nb-Mo composites were prepared by SHS using initial powder mixtures of Ti-Al-Nb-Mo and their corrosion and mechanical properties were studied to develop bioand environmental materials. The composites reached 99.8% of theoretical density after the direct consolidation. The composites shows equiaxed primary a2 in a matrix of fine secondary a2 plates and ordered 82 (Bo) forming a basket weave structure. The strain rate sensitivity (m = dlnσ/dlne) at 2% strain is 0.008. Corrosion potential and corrosion rate of the composites formed by SHS were -151. 5m VSHE and 5. 72× 10^(-8)A/cm2 for Ti3 Al-10Nb-1. 5Mo and - 138.4m VSHE and 4. 12×10^(-8)cm2 for Ti3 Al-12Nb-1.5Mo in a 50% NaOH-10%FeCI3 solution, respectively. Corrosion resistance decreased with niobium content in the composites and chloride content in the aqueous solution. Selective corrosion of a2 phase in a matrix occurred in the corrosion environment which suggests that the corrosion potential and rate changes are related to the niobium content and Q2 phase in a matrix.展开更多
基金supported by the Future Material Discovery Program of the National Research Foundation of Korea(NRF) funded by the Ministry of Science,ICT and Future Planning(MSIP)of Korea(2016M3D1A1023532)
文摘The non-isothermal crystallization kinetics of Ni55Nb35Si10 amorphous alloy,prepared by mechanical alloying,was studied using differential scanning calorimetry.The amorphous alloy showed one-stage crystallization on heating,which led to the formation of nano-intermetallic crystals in amorphous matrix.The apparent activation energy for the crystallization of the alloy,determined by the Kissinger equation,was relatively high(468 kJ/mol),indicating that this amorphous alloy has high thermal stability.Changes in the activation energy during the crystallization process,were also evaluated by iso-conversional methods.The results showed that it decreases slowly from the beginning to crystallized fractionα=0.35 and it remains almost constant to the end of the process.The nano-crystallization mechanism for the non-isothermal crystallization of the amorphous alloy was explained by determining Avrami exponents.Transmission electron microscopy studies revealed the microstructural modification of amorphous alloy via nanocrystallization during annealing.The results suggest that the nucleation rate decreases with increasing time and the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth.A predictive equation was obtained based on the Sestak-Berggren autocatalytic model to describe quantitatively the non-isothermal crystallization kinetics.
文摘Ti3 AL-Nb-Mo composites were prepared by SHS using initial powder mixtures of Ti-Al-Nb-Mo and their corrosion and mechanical properties were studied to develop bioand environmental materials. The composites reached 99.8% of theoretical density after the direct consolidation. The composites shows equiaxed primary a2 in a matrix of fine secondary a2 plates and ordered 82 (Bo) forming a basket weave structure. The strain rate sensitivity (m = dlnσ/dlne) at 2% strain is 0.008. Corrosion potential and corrosion rate of the composites formed by SHS were -151. 5m VSHE and 5. 72× 10^(-8)A/cm2 for Ti3 Al-10Nb-1. 5Mo and - 138.4m VSHE and 4. 12×10^(-8)cm2 for Ti3 Al-12Nb-1.5Mo in a 50% NaOH-10%FeCI3 solution, respectively. Corrosion resistance decreased with niobium content in the composites and chloride content in the aqueous solution. Selective corrosion of a2 phase in a matrix occurred in the corrosion environment which suggests that the corrosion potential and rate changes are related to the niobium content and Q2 phase in a matrix.
