Papers by Keyword: ARB Process

Abstract: A 36mass% Ni austenitic steel was deformed to equivalent strains of 0.8 to 4.8 by the accumulative roll-bonding (ARB) process at 500°C, with slight lubrication. We analyzed the microstructure and crystallographic analysis by employing the electron back-scatter pattern (EBSP) technique in a field emission gun (FEG) SEM. After several ARB cycles, ultrafine lamellar boundary structures elongated in the rolling direction (RD) formed uniformly in the material. Observations indicated that the mean spacing of high-angle lamellar boundaries determined from the EBSP results decreased exponentially as a function of equivalent strain. The fraction of high-angle boundaries (HABs) increased, thus the average misorientation of the boundaries increased with increasing strain. In the six-cycle ARB-processed specimen, the mean spacing of the uniform lamellar boundaries was 150 nm, the fraction of HABs was 75%, and the average misorientation was 32°. The ultrafine lamellar boundary structure in the 36%Ni austenitic steel was finer and straighter than in ferritic steel (IF steel) deformed under similar conditions, probably because recovery occurs more easily in ferritic steel than austenitic steel.

Abstract: An oxygen free high conductivity (OFHC) copper (99.99%) was intensely deformed by the accumulative roll-bonding (ARB) process up to equivalent strain of 4.8 at ambient temperature. The microstructure evolution during the ARB process was explained by grain subdivision. The deformed specimens revealed dislocation cell structures at low strain and elongated ultra fine grains separated by high angle boundaries at high strain. The spacing of the high angle lamellar boundary exponentially decreased as a function of strain. The fractions of high angle boundaries (HAB) and the low angle boundaries (LAB) were nearly equal even at strain of 3.2, which was significantly different from the ARB processed Al alloys and ferritic steel where the HAB fraction was above 70% at the same strain. TEM observations indicated a mixed microstructure of dislocation boundaries and cell walls with dislocation tangle at low strain of 1.6, and small recrystallized grains partly appeared above strain of 3.2. As a result, the LAB fraction due to partial recrystallization was high even at strain of 4.8. The occurrence of recrystallization is attributed to high purity of the OFHC copper, the accumulated dislocation density, and the adiabatic heating during the ARB process of one-pass large reduction without lubrication.