Showing 2 results for H. Ghasemi
H. Ghasemi, M. A. Faghihi Sani, Z. Riazi,
Volume 4, Issue 3 (Summer &Autumn 2007 2007)
Abstract
Abstract: The effect of phase development on peel strength of alumina-copper metalized joint has
been investigated. The alumina-copper joint was prepared in three stages. The alumina substrate
was, first, metalized at 1500°C in H2-furnace by a new formulation. In the second step, a nickel
layer was electroplated on the metalized layer with approximately 10µm thickness. Finally, copper
strips were bonded to metalized alumina with Ag-Cu (72-28) filler metal. The peel strength of the
joint was 9.5±0.5 Kg/cm which shows approximately 30% increase in comparison to previous
works. By study of fracture surface and crack propagation path, it has been concluded that this
increase is due to the formation of more spinel phase.
M. Divandari,, H. Arabi, H. Ghasemi Mianaei,
Volume 5, Issue 3 (Summer 2008 2008)
Abstract
Abstract: Thermal fatigue is a stochastic process often showing considerable scatter even in
controlled environments. Due to complexity of thermal fatigue, there is no a complete analytical
solution for predicting the effect of this property on the life of various components, subjected to
severe thermal fluctuations. Among these components, one can mention car cylinder, cylinder head
and piston which bear damages due to thermal fatigue. All these components are usually produced
by casting techniques. In order to comprehend and compare the thermal fatigue resistance of cast
Al alloys 356 and 413, this research was designed and performed. For this purpose, several
samples in the form of disc were cast from the two alloys in sand mould. The microstructures of the
cast samples were studied by light microscopy in order to choose the samples with the least
amounts of defects for thermal fatigue tests. The results of thermal fatigue tests showed that the
nucleation of microcracks in Al-356 alloy occurred at shorter time relative to those occurred in Al-
413 alloy under the same test conditions. In addition, the density of micro-cracks in Al-356 alloy
was more than that of Al-413 alloy. The results of fractography on 356 alloy indicated that the
cracks were generally nucleated from inter-dendritic shrinkage porosities and occasionally from
the interface of silicon particles with the matrix. The growth of these micro cracks was along the
dendrite arms. Fractography of 413 alloy fracture surfaces showed that nucleation of microcracks
was often associated with silicon particles.
