Intermetallics are commonly described by comparatively complex crystal structures which results in bigger unit cells, low probability of dislocation movement and brittle phases. This effect may have positive but also negative impact.

Intermetallic compounds are necessary for good metallurgical bonding, however excess IMCs would degrade the mechanical reliability. IMCs are generally hard and brittle in nature. So, when you have the higher amount of IMCs in the joint, the stiffness and tensile strength would increase but you will loose the ductility of the joint (which is an important characteristic of joints). Even, it has seen that if you have a higher volume fraction of IMCs than the bulk material, your joint strength would decrease. Hope it will help you. If you need any further info, let me know.

thank you professor Gert Nolze, yes low probability of dislocation movement, this is a reason why the tensile increased.

thank you mister Soud Choudhury, yes you help me lot for understanding, Intermetallic compounds are necessary for good metallurgical bonding. and in same time they low the ductility very interesting. OK I will contact you when I need help, thanks .

depending in witch properties you want to be enhance   

IMCs are brittle and their formation is inevitable for some welding processes, especially fusion welding processes. IMCs can weaken welded joints and their thickness need to be controlled to be as thin as possible.

dear Dezhi Li, how about immecible systemme?, for exmple (Fe-Cu) or (Fe-Mg). can we find IMCs in friction welding processes.