Preparation Of W-Ni And W-Ni-Cu Nano-composite Powders And Laser Sintering Of Powder Mixture

Nano-W/Ni and Nano-W/Ni/Cu composite powders were successfully obtained via high energy ball milling (HEBM), using the micrometric W/Ni and W/Ni/Cu powders as the raw materials. Meanwhile, the structural evolution and performance of laser sintering of W/Ni and W/Ni/Cu powders compacts were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) were used to investigate the phases, crystal size, morphological changes and microstructure of nanocomposite powders and laser sintering samples. The mechanism regarding the formation of nanocomposite powders is elucidated.W-10%Ni mixed powders were milled using the rotation speed of 400 rpm. With increasing the milling time, the X-ray diffraction peaks are broadening and lattice distortions are serious. After milling for 10h, the intermetallic compound Ni4W was found. After milling for 20h, the particulates were homogeneously distributed and the size changed to ~3μm. W-10%Ni mixed powders were milled using the rotation speed of 400 rpm. With increasing milling time, the X-ray diffraction intensity and grain size of the composite powders were reduced. After milling for 1h, the particulate size changed to ~5μm. After milling for 5h, the intermetallic compound Ni4W was found.W-Ni-Cu mixed powders were milled using the rotation speed of 400 rpm. With increasing milling time, the X-ray diffraction peaks of Ni disappeared and the starting irregular powders became flattened, eventually became equiaxed. After milling for 50h, the particulate size changed to ~5μm. After milling for 100h, the intermetallic compound Ni4W was found. W/Ni composite powder compacts were laser sintered using the same laser processing parameters. It shows that using W-10%Ni composite powders results in poor densification, due to a limited liquid phase and poor wettability. Poor densification with severe balling phenomena and a superheating of the melt is obtained at a high Ni content of 30wt.%, because of a excessive liquid formation. Using an optimal Ni content of 20 wt.% leads to a compatible interfacial microstructure, so as to obtain a favorable sintered density.W/Ni/Cu composite powders compacts were laser sintered using the same laser processing parameters.The scanning electron microscope(SEM) analyses show that mass fraction of W-Ni-Cu effects microstructure. It can be seen that columnar crystals were formed for 20W-40Ni-40Cu system and dendritic crystals for 40W-20Ni-40Cu system. Theories of metal solidification for laser sintering were discussed.