GROWTH MODE AND MODIFICATION OF GRAPHITE IN CAST IRON MELT

Using liquid quenching technique,the change of growth mode of graphite in cast iron melt was analysed.Based on the interface structure theory of crystal growth,the concept of multiplication of spiral growth steps was advanced and two basic multiplication models were given.It was proposed that multiplication of spiral steps is responsible for the change of growth mode of graphite in cast iron melt.The modifying elements such as Ce promote multiplication of spiral steps,which is regarded as the core of modification.Origination of screw dislocation and branch of the sector blocks in radius direction,both of which are essential to spheroidization of graphite in the melt,are caused by multiplication of spiral steps:and so is thickening of graphite plates.

A multistep attachment process:Transformation of titanate nanotubes into nanoribbons

The mechanism of the conversion of titanate nanotubes into nanoribbons is of considerable interest.The details of the transformation processes involved when nanoribbons are produced from a P25 TiO 2 powder precursor by alkaline hydrothermal treatment have been investigated systematically by transmission electron microscopy.A multistep attachment model is proposed for the growth at the early stage of coarsening.The treatment duration has a strong effect on the change in product morphology from hollow nanotubes into nanoribbons,since the nanotubes cannot retain their morphology in the strong alkaline solution for extended periods of time.Most of the nanotubes were etched and dissolved,providing the nutrients for subsequent nanoribbon growth.Some stable nanotubes grew spirally internally to form nanowires or became connected together to form rafts which acted as the grains for nanoribbon growth.With increasing hydrothermal time,a large number of nanotubes and other fragments became attached to the grains which began to grow larger and eventually formed the nanoribbons,in a process in which the stepped faces and kinked faces became fused and were eliminated while the flat faces were retained in the nanoribbon morphology.

Modes of Grain Selection in Spiral Selector during Directional Solidification of Nickel-base Superalloys

The modes of grain selection in spiral selector were investigated by both a ProCAST simulation and experimental confirmation.The results show that the efficiency of grain selection in starter block is associated with the geometry shape.At the early stage of grain selection,the optimization of grain orientation is dominated by competitive grain growth,but the optimization of grain orientation in starter block is gradually dominated by geometry shape at the later stage of grain selection.Besides,the spiral part could also optimize the orientation of the selected single crystal when the initial angle is large enough,and the single crystal selection in spiral parts with different pitch lengths and initial angles is dominated by different modes.The simulation results agree well with experimental ones.

How Temperatures Affect the Number of Dislocations in Polymer Single Crystals

The influence of crystallization temperature （Tc） on the number of spiral growths on poly（butylene succinate） （PBS） single crystals, obtained by self-seeding method, was systematically studied. The studies show that the statistical average number of spiral growths formed on the PBS single crystals decays exponentially with respect to the To. Inspired by BCF （Bruton, Cabrera and Frank） theory and L-H （Lauritzen and Hoffman） theory, a thermodynamic model has been proposed, in which the origin of spiral growth was treated as a nucleation process. The model suggests that the nucleation rate of spiral growth depends on the inverse square of super-cooling degree, which predicted the density of spiral growth formed on lamellae, and was consistent with the experiments very well.