Abstract
With the purpose of developing thick metal/metal graded-boundary materials, the fabrication experiment of Cr/Steel graded-boundary materials was carried out using a laser beam and an electron beam. In order to produce a compositionally graded boundary region between the substrate steel and the added Cr metal, a series of surface alloying treatments were performed with both a CO2 laser beam and an electron beam. A Cr sheet was placed on a commercial low carbon steel, and then a CO2 laser beam was irradiated on the surface to produce a homogeneous alloyed layer. On this first surface-alloyed layer, another Cr sheet was placed and then the CO2 laser beam was used again to produce a second surface-alloyed layer. Four sequential repetitions of the laser surface alloying treatment resulted in a compositionally graded region with about a 2 mm thickness from 60%Cr and 40%Fe in the surface region to 0%Cr and 99%Fe in the substrate. Similar procedures were carried out by an electron beam surface alloying treatment to produce Cr/Steel graded-boundary material. Four sequential surface-alloying treatments resulted in a compositionally graded region with a thickness of about 1 mm from 60%Cr and 40%Fe in the surface region to 0%Cr and 99%Fe in the substrate. In both cases, no visible root porosities were found in the graded-boundary region. Since the structures of both the high Cr graded-boundary region and the substrate were both BCC, there was almost no volume change and thus no appreciable cracks were formed in the boundary region between the alloyed layers and the substrate even after rapid cooling.
