Preparation And Properties Of A Al-based Bulk Amorphous Alloy By Powder Metallurgy

In this dissertation, bulk sized Al-Ni-Ce alloys with low glass forming ability have been successfully synthesized by using powder metallurgy technology.The microstructure and thermal properties of the gas atomized alloy powders were studied. The influence of the particle size on the microstructure was also investigated. The larger the particle size of the gas atomized powders, the larger the volume fraction and size of crystalline phase. The powders with size less than 10μm have fully amorphous structure.Gas atomized alloy powders were transferred into amorphous state by using ball-milling technique. The surface morphology, the microstructure and thermal properties of the as-milled powders were systematically analyzed. The influence of proccessing parameters on the surface morphology, the microstructure and the thermal properties of as-milled powder during ball milling process was also stated. Fully amorphous Al-Ni-Ce alloy powders can be prepared under argon atmosphere via batch-type ball milling method with a rotate speed of 400 r/min, and a ball-to-powder weight ratio of 10: 1. With the identical technological parameters, higher rotate speed can deteriorate the formation of amorphous phase. During the ball-milling process, alloy powders deformed and generated defects under the external mechanical force. The amorphous phase transformation firstly happened on the surface and then these amorphous pieces broken, dropped and welded together, and thus new particle surface appeared. Such phase transformation took place repeatedly until the powder particles completely amorphized.The Al-Ni-Ce amorphous alloy powders have been sintered by using spark plasma sintering (SPS) at different temperatures. The relative density, microstructure, and mechanical properties of sintered Al-Ni-Ce alloy were studied. With increasing the sintering temperature, the mechanical properties of the sintered samples enhanced. The compressive strength and the hardness for the bulk samples sintered within supercooled liquid region can reach up to 950 MPa and 374 HV, respectively. The viscous flow and crystallization are considered as the two competing factors for the densification process. The optimum sintering temperature range from 563 K to 583 K for the alloy studied. The effect of powder shape on the sintering behaviors was studied. The results indicate that, the densification degree of the sintered samples from the gas atomized spherical powders is significantly greater than that from the as-milled irregular powders...