The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercool...The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.展开更多
The aim of this paper is to report the results of experiments carried out on Al-Cu alloys with different Cu contents,studying the microstructure evolution during holding in the semi-solid state.The 3-D microstructure ...The aim of this paper is to report the results of experiments carried out on Al-Cu alloys with different Cu contents,studying the microstructure evolution during holding in the semi-solid state.The 3-D microstructure was observed by in situ X-ray microtomography carried out at ESRF Grenoble,France.The variation of the solid-liquid interface area per unit volume during holding was determined.In addition,local observations show that two coarsening mechanisms of the solid particles occur simultaneously:dissolution of small particles to the benefit of larger ones by an Ostwald-type mechanism and the growth of necks between solid particles due to coalescence.These observations confirm that in situ X-ray tomography is a very powerful tool to study the microstructure evolution in the semi-solid state and the influencing mechanisms in real-time.展开更多
文摘The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.
基金project ANR-05-BLAN-0286-01 TOMOSOLIDAL supported by the French Agence Nationale de la Recherche,which is gratefully acknowledged
文摘The aim of this paper is to report the results of experiments carried out on Al-Cu alloys with different Cu contents,studying the microstructure evolution during holding in the semi-solid state.The 3-D microstructure was observed by in situ X-ray microtomography carried out at ESRF Grenoble,France.The variation of the solid-liquid interface area per unit volume during holding was determined.In addition,local observations show that two coarsening mechanisms of the solid particles occur simultaneously:dissolution of small particles to the benefit of larger ones by an Ostwald-type mechanism and the growth of necks between solid particles due to coalescence.These observations confirm that in situ X-ray tomography is a very powerful tool to study the microstructure evolution in the semi-solid state and the influencing mechanisms in real-time.
