Morphological evolution and growth kinetics of Kirkendall voids in binary alloy system during deformation process-Phase field crystal simulation study

The formation and growth of Kirkendall voids in a binary alloy system during deformation process were investigated byphase field crystal model.The simulation results show that Kirkendall voids nucleate preferentially at the interface,and the averagesize of the voids increases with both the time and strain rate.There is an obvious coalescence of the voids at a large strain rate whenthe deformation is applied along the interface under both constant and cyclic strain rate conditions.For the cyclic strain rate appliedalong the interface,the growth exponent of Kirkendall voids increases with increasing the strain rate when the strain rate is largerthan1.0×10-6,while it increases initially and then decreases when the strain rate is smaller than9.0×10?7.The growth exponent ofKirkendall voids increases initially and then decreases gradually with increasing the length of cyclic period under a square-waveform constant strain rate.

富含氧空位的NiFe氢氧化物衍生的具有超疏气纳米阵列形貌的磷化物及其全解水性能

对高效催化剂进行多尺度调控可优化中间体的吸附能量(原子层面),并实现快速传质(三维宏观层面),这对于提升整体水分解性能至关重要.在本工作中,我们首先在镍铁氢氧化物中引入氧空位,然后通过磷化反应将其转化为具有纳米阵列形态的NiFe-Vo-P催化剂.在析氧反应催化过程中,NiFe-Vo-P表面会原位形成磷酸盐阴离子及具有催化活性的Ni(Fe)OOH,能显著优化反应中间体的吸附强度.结果表明,NiFeVo-P在过电位为289 mV时电流密度可达1.5 A cm^(-2).同时,其超亲水/超疏气纳米阵列形貌可有效促进传质,在25和70℃的条件下,可在~2.0V的电池电压下分别获得580 mA cm^(-2)和1.0 A cm^(-2)的电流密度,是未进行超疏气形貌工程催化剂的电流密度的2倍以上.

Influence of heating parameters on properties of the Al-Si coating applied to hot stamping

The Al-Si coating of ultra-high strength steel has been applied to hot stamping more and more widely, owing to solving the problem of oxidation and decarburization. However, the evolution of Al-Si coating during the heating process was rarely studied in the previous study. The tests about the influence of heating parameters, such as heating temperature, heating rates and dwell time, on properties of the Al-Si coating were carried out on the Gleeble-3500 thermal simulator. The properties of the Al-Si coating, for instance, volume fraction of FeAl intermetallics, α-Fe layer as well as porosity and 3D surface topography, were explored in the study. Results showed that more and more Kirkendall voids and cracks appeared in the Al-Si coating when the heating temperature exceeded 600°C. The heating rates almost had no influence on properties of the Al-Si coating when the temperature was equal to or lower than 500°C. The volume fraction of FeAl intermetallics in the coating with dwell time from 3 s to 8 min at 930°C was0, 6.19%, 17.03% and 20.65%, separately. The volume fraction of the α-Fe layer in the coating changed from zero to 31.52%with the prolonged dwell time. The porosity of the coating ranged from 0.51% to 4.98% with the extension of dwell time. The unsmooth degree of the surface of the coating rose gradually with the increasing of heating rates and the extension of dwell time.The 3D surface topography of the coating was determined by the comprehensive effect of atoms diffusion, new formed phases,surface tension and the degree of oxidation of the coating surface. Experiments indicated that rapid heating was not suitable for the coating when the temperature exceeded 500°C. Experiments also demonstrated that enough dwell time was essential to obtain the superior properties of the coating.