Extrusion behavior of gas atomized nanostructured Al88.7Ni7.9Mm3.4 alloy powders

The effects of powder size on the extrusion behavior of Al88.7Ni7.9Mm3.4 alloy, prepared by gas atomization followed by degassing and hot extrusion, were studied by a combination of microscopy (optical, scanning and transmission electron) and hardness testing. The alloy powders exhibited different microstructures depending on the powder size. The powders −26 μm in diameter consisted of nanocrystalline particles of embedded in an amorphous matrix. The aspect ratio of the elongated band was in the range of 5–10 for the −26 μm powder extrudate, and 10–30 for the 45–53 μm powder extrudate, which is much smaller than the theoretically expected value of 125 at the extrusion ratio of 25:1. The lower aspect ratio of the 5–30 at smaller particles size indicates that the resistance to plastic flow increases with decreasing powder size. The elongated bands in the extrudate microstructure were found to be harder than the surrounding areas.