To compare the difference of morphological evolution of HDPE micropart and macropart, micropart with 200 lm thickness and macropart with 2000 lm thickness were prepared. The PLM images of micropart and macropart exhibited a similar ''skin-core'' structure, but the micropart showed a much larger fraction of orientation layer. The SEM observation of core layer of micropart featured an unoriented lamellae structure and shear layer of micropart showed a highly oriented shish-kebab structure. The 2D-WAXD patterns of shear layer of macropart indicated twisted oriented shish-kebab (KM-I) structures, how-ever that of micropart indicated untwisted oriented shishkebab (KM-II) structures which was firstly found in microinjection molding. The diffraction pattern of the micropart exhibited stronger azimuthal dependence than the shear layer of macropart, indicating the most pronounced orientation of HDPE chains within lamellae. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: [452][453][454][455][456][457][458][459][460][461][462] 2012

In order to study the growth process and morphology of dendrite directly, a phase field model of binary alloy was established. In this model the order parameter equation was coupled with the temperature field and the solute field. The growing processes and morphology of dendrite were simulated by using this phase field model. Through analyzing the results, we discussed the effects of anisotropic strength and temperature gradient on dendrite morphology. The results shows that with the increasing of anisotropic strength, the dendrite growth rate of the dendrite will increase and the secondary branches appear more clearly. Besides, the temperature gradient has influence on the appearance of secondary arms during the dendrite growing. With the increase of temperature gradient, the size of secondary dendrite arms increase.