Microstructures and properties of high-strength alloys severely deformed by machining

Microstructures and properties were examined on the chip specimens severely deformed to a given shear strain (gamma) by machining in the high-strength Ni-base Inconel X-750 alloy and 6061-T6 aluminum alloy. Chip specimens has a deformation structure principally composed of elongated grains (for example, a few mu m to about 100 mu m in length and about 1 mu m to a few tens pm in width for the chip specimen of gamma approximate to 3 of the Inconel X-750 alloy). Many subgrains separated by small or medium angle grain boundaries (misorientation, theta<15 degrees) were also observed within relatively large grains. In the case where detailed analysis by FESEM/EBSP was possible, the fraction of large angle grain boundaries (theta<15 degrees) and that of medium angle grain boundaries (5 degrees <=theta < 15 degrees) were relatively small, and most of grain boundaries were small grain boundaries (1 degrees <=theta < 5 degrees) in the chip specimens of both alloys. Internal friction of the chip specimen was much larger than that of the original material. Large internal friction of the chip specimens was principally attributed to many cracks formed during machining. The hardness of chip specimens largely increased with increasing shear strain imposed by machining in the Inconel X-750 alloy, although the increase of hardness with shear strain was not so large in the 6061-T6 alloy.