For the development of thick metal/metal graded-boundary materials, the fabrication of Ni/Steel graded-boundary material was carried out by high energy density beam. In order to produce compositionally graded boundary layer between substrate steel and added Ni metal, multiple surface alloying treatments were performed with both CO_2 laser beam and electron beam. Ni sheet metal was placed on low carbon steel, and a laser beam was irradiated on that surface to produce a homogeneous alloyed layer. On this first surface alloyed layer another Ni sheet was placed and a laser beam was irradiated again to produce the second surface alloyed layer. Sequential repetition of laser surface-alloying treatment for 5 tunes resulted in a compositionally graded region with the thickness of about 4mm from 65% Ni on surface to 0% in substrate. In this case root porosities were formed in lower part of graded layer due to characteristic property of laser processing and also solidification shrinkage cracks were formed in center of keyholes due to rapid cooling. Similar procedures were carried out by electron beam surface alloying treatment to produce graded-boundary layer. Sequential surface-alloying treatment for 4 times resulted in a compositionally graded region with the thickness of about 6mm from 80% Ni on surface to 0% in substrate. In this case root porosities were not formed in graded layer, but solidification shrinkage cracks were also formed due to rapid cooling.
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