采用涂Na Cl/Na2SO4盐方法研究了DZ466合金在850℃和950℃条件下热腐蚀行为.结果表明:合金的腐蚀层包括三个区域,最外层为(Ni,Co)O氧化物层,次外层为尖晶石结构氧化层(Ni,Co)Cr2O4,内层为内腐蚀层,850℃时该层为Ni3S2,而950℃时除Ni3S2...采用涂Na Cl/Na2SO4盐方法研究了DZ466合金在850℃和950℃条件下热腐蚀行为.结果表明:合金的腐蚀层包括三个区域,最外层为(Ni,Co)O氧化物层,次外层为尖晶石结构氧化层(Ni,Co)Cr2O4,内层为内腐蚀层,850℃时该层为Ni3S2,而950℃时除Ni3S2外,在靠近次外层还形成内氧化Al2O3;在850℃和950℃时合金的热腐蚀机制相同,氧化膜连续性的破坏,是合金遭受热腐蚀的主要原因;热腐蚀增重曲线均符合抛物线规律,其速率常数分别为3.1×10-11g2·cm-4·s-1和1.5×10-9g2·cm-4·s-1,热腐蚀激活能分别为179.2 k J·mol-1和138.3 k J·mol-1.展开更多
The effects of heat treatments on typical microstructures of directionally solidified（DS） Ti-45Al-8Nb-（W,B,Y）（molar fraction,%） alloys prepared by the Bridgeman method were studied.Two typical DS microstructures...The effects of heat treatments on typical microstructures of directionally solidified（DS） Ti-45Al-8Nb-（W,B,Y）（molar fraction,%） alloys prepared by the Bridgeman method were studied.Two typical DS microstructures including full lamellae with cellular growth morphology and massive structure with dendritic growth morphology were examined.The results show that the heat treatment of 1250 ℃ for 24 h ＋ 900 ℃ for 30 min＋air cooling can efficiently eliminate the B2 phase in the DS alloys and change the massive structure of the rapid DS alloy into lamellar microstructure.Columnar lamellar colonies with widths of 150-200 μm and 50-100 μm respectively were observed in intercellular and dendritic arm regions.The heat treatment of 1 400 ℃ for 12 h＋900 ℃ for 30 min＋air cooling could simultaneously remove the B2 phase,massive structure and solidification segregations from the DS alloys,however,it caused severe growth of grains.展开更多
Microstructure instabilities of the fully lamellar Ti-45Al-8.5Nb-（W,B,Y） alloy were investigated by SEM and TEM after long-term thermal cycling（500 and 1000 thermal cycles） at 900 °C. Two major categories of ...Microstructure instabilities of the fully lamellar Ti-45Al-8.5Nb-（W,B,Y） alloy were investigated by SEM and TEM after long-term thermal cycling（500 and 1000 thermal cycles） at 900 °C. Two major categories of microstructure instability were produced in the alloy after the thermal cycling： 1） The discontinuous coarsening implies that grain boundary migrations are inclined to occur in the Al-segregation region after the long-term thermal cycling, especially after 1000 thermal cycles. Al-segregation can be reduced during the process of long-term thermal cycling as a result of element diffusion; 2） The α2 lamellae become thinner and are broken after 1000 thermal cycles caused by the dissolution of α2 lamellae through phase transformation of α2→γ. The γ grains nucleate within the α2 lamellae or（α2＋γ） lamellae in a random direction.展开更多
文摘采用涂Na Cl/Na2SO4盐方法研究了DZ466合金在850℃和950℃条件下热腐蚀行为.结果表明:合金的腐蚀层包括三个区域,最外层为(Ni,Co)O氧化物层,次外层为尖晶石结构氧化层(Ni,Co)Cr2O4,内层为内腐蚀层,850℃时该层为Ni3S2,而950℃时除Ni3S2外,在靠近次外层还形成内氧化Al2O3;在850℃和950℃时合金的热腐蚀机制相同,氧化膜连续性的破坏,是合金遭受热腐蚀的主要原因;热腐蚀增重曲线均符合抛物线规律,其速率常数分别为3.1×10-11g2·cm-4·s-1和1.5×10-9g2·cm-4·s-1,热腐蚀激活能分别为179.2 k J·mol-1和138.3 k J·mol-1.
基金Projects(50771013,50871127)supported by the National Natural Science Foundation of China
文摘The effects of heat treatments on typical microstructures of directionally solidified（DS） Ti-45Al-8Nb-（W,B,Y）（molar fraction,%） alloys prepared by the Bridgeman method were studied.Two typical DS microstructures including full lamellae with cellular growth morphology and massive structure with dendritic growth morphology were examined.The results show that the heat treatment of 1250 ℃ for 24 h ＋ 900 ℃ for 30 min＋air cooling can efficiently eliminate the B2 phase in the DS alloys and change the massive structure of the rapid DS alloy into lamellar microstructure.Columnar lamellar colonies with widths of 150-200 μm and 50-100 μm respectively were observed in intercellular and dendritic arm regions.The heat treatment of 1 400 ℃ for 12 h＋900 ℃ for 30 min＋air cooling could simultaneously remove the B2 phase,massive structure and solidification segregations from the DS alloys,however,it caused severe growth of grains.
基金Project(2011CB605500)supported by National Basic Research Program of ChinaProject(51171015)supported by National Natural Science Foundation of China+2 种基金Project(2012M520166)supported by China Postdoctoral Science FoundationProject(2012Z-06)supported by State Key Laboratory for Advanced Metals and Materials,University of Science and Technology Beijing,ChinaProject(FRF-TP-12-164A)supported by Fundamental Research Funds for the Central Universities of China
文摘Microstructure instabilities of the fully lamellar Ti-45Al-8.5Nb-（W,B,Y） alloy were investigated by SEM and TEM after long-term thermal cycling（500 and 1000 thermal cycles） at 900 °C. Two major categories of microstructure instability were produced in the alloy after the thermal cycling： 1） The discontinuous coarsening implies that grain boundary migrations are inclined to occur in the Al-segregation region after the long-term thermal cycling, especially after 1000 thermal cycles. Al-segregation can be reduced during the process of long-term thermal cycling as a result of element diffusion; 2） The α2 lamellae become thinner and are broken after 1000 thermal cycles caused by the dissolution of α2 lamellae through phase transformation of α2→γ. The γ grains nucleate within the α2 lamellae or（α2＋γ） lamellae in a random direction.
