Micro-alloying effects of yttrium on the recrystallization behavior of an alumina-forming austenitic（AFA）stainless steel were investigated.It was found that the grain growth kinetics of the steels doped with different amounts of yttrium（i.e.,0,0.05 and 0.10mass% Y）could be described by an Arrhenius type empirical equation.Added Y could interact with carbon and influence the morphology of carbides both inside grains and on the grain boundaries,thus altering the grain boundary mobility and grain growth.The steel doped with 0.05mass% yttrium showed the highest activation energy of grain growth and the most retarded recrystallization behavior,which mainly resulted from the high density of fine carbides both inside grains and on the grain boundaries.However,excess addition of0.10mass% Y induced coarsening and then lowered density of carbides,which alleviated the yttrium effects.The results also manifest that micro-alloying of rare-earth elements such as yttrium is an effective way for controlling grain growth behavior during recrystallization of AFA steels,which may have great implications on engineering applications.
Wu-xin ZHAOYuan WUSui-he JIANGHui WANGXiong-jun LIUZhao-ping LU
In this study, mechanical tests were conducted oil a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates （10^-4-10^4 s^-1） to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical prop-erties. Microstructures of various samples both before and after deformation were examined using elec-tron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy （HEA）, in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the mas-sive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of-63% are obtained at 2.3×10^3 s^-1, indicating that the alloy has great potential for energy absorption upon impact loading.
In this paper, effects of cryogenic thermal cycling on deformation behavior and thermal stability of the Zr46Cu46AI8 bulk metallic glass （BMG） were studied. The results show that with the increase of the number of cryogenic thermal cycles （CTC）, thermal stability remains almost unchanged, while the plasticity is increased, indicating that the cryogenic thermal cyclic treatment is an effective way to improve plasticity of metallic glasses without distinctly deteriorating thermal stability. Our analysis suggests that the increase in the defect density resulted from the cryogenic thermal treatments are responsible for the plasticity increment. Variation of yield strength can be well interpreted from microstructural percolation which affected by both density and characteristic volume of the defect sites.
Wenli SongXiaohe MengYuan WuDi CaoHui WangXiongjun LiuXianzhen WangZhaoping Lu
To address the main stumbling-block of bulk metallic glasses （BMGs）, i.e., room temperature brittleness, designing BMG matrix composites has been attracted extensive attention. Up to date, BMG composites in various alloy systems have been successfully developed by forming crystalline phases embedded in the amorphous matrix through either ex-situ or in-situ methods. In this paper, a brief review of our recent work in this topic will be presented and the novel approaches to improving composite formability and mechanical properties will also be highlighted. The main purpose of this manuscript is not to offer a comprehensive review of all the BMG composites, but instead focuses will be placed on illustrating recently developed advanced BMG composites including Fe-based BMG composite with no metalloids, AI-based BMG composite and BMG composites reinforced by the TRIP （transformation-induced plasticity） effects. The basic ideas and related mechanisms underlying the development of these novel BMG composites will be discussed.
