Recrystallization of cold-rolled discontinuous, precipitation microstructurewhich has fine laminar structure in an Al-40 percent Zn (atom fraction) binary alloy is investigatedby optical microscopy, SEM and TEM. It is...Recrystallization of cold-rolled discontinuous, precipitation microstructurewhich has fine laminar structure in an Al-40 percent Zn (atom fraction) binary alloy is investigatedby optical microscopy, SEM and TEM. It is found that there are two kinds of recrystallizationmechanisms: continuous coarsening (CC) and discontinuous coarsening (DC). The latter can be dividedinto coarsening mainly driven by stored deformation energy at colony boundaries and slip bands andthe one mainly driven by boundary energy in the area with little deformation. It is shown that theaddition of Cu can retard the nucleation of coarsening cells and their growth. X-Ray diffractionanalysis indicated the metastable phase CuZn_4 transformed into equilibrium phase A;_4Cu_3Zn duringthe heating process.展开更多
The coarsening mechanism and kinetics of discontinuous precipitation (DP) in Al-Zn-(Cu) alloys were studied by means of optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. The results sho...The coarsening mechanism and kinetics of discontinuous precipitation (DP) in Al-Zn-(Cu) alloys were studied by means of optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. The results show that the coarsening mechanism is different as the aging temperature varies. At a low temperature (150℃), the coarsening occurs through the dissolution and spheroidization of fine laminar structure of DP; at high temperatures (above 200℃), the discontinuous coarsening (DC) of DP microstructure mainly occurs, forming coarsening cells with a larger laminar distance. The growth velocity of coarsening cells rapidly reaches the maximum, and then decreases with the increase of time. The coarsening velocity of DP microstructure decreases due to the addition of Cu element.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Recrystallization of cold-rolled discontinuous, precipitation microstructurewhich has fine laminar structure in an Al-40 percent Zn (atom fraction) binary alloy is investigatedby optical microscopy, SEM and TEM. It is found that there are two kinds of recrystallizationmechanisms: continuous coarsening (CC) and discontinuous coarsening (DC). The latter can be dividedinto coarsening mainly driven by stored deformation energy at colony boundaries and slip bands andthe one mainly driven by boundary energy in the area with little deformation. It is shown that theaddition of Cu can retard the nucleation of coarsening cells and their growth. X-Ray diffractionanalysis indicated the metastable phase CuZn_4 transformed into equilibrium phase A;_4Cu_3Zn duringthe heating process.
文摘The coarsening mechanism and kinetics of discontinuous precipitation (DP) in Al-Zn-(Cu) alloys were studied by means of optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. The results show that the coarsening mechanism is different as the aging temperature varies. At a low temperature (150℃), the coarsening occurs through the dissolution and spheroidization of fine laminar structure of DP; at high temperatures (above 200℃), the discontinuous coarsening (DC) of DP microstructure mainly occurs, forming coarsening cells with a larger laminar distance. The growth velocity of coarsening cells rapidly reaches the maximum, and then decreases with the increase of time. The coarsening velocity of DP microstructure decreases due to the addition of Cu element.
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.
