Improving the glass forming ability of Ni-W-B-X (X=Co, Mo, Mn)alloy system

The main objective of this study is to increase the critical casting thickness of Ni51W31.6B17.4 metallic glass alloy, which has very high potential to be used as a precursor to produce metal matrix composite reinforced with borides. A two stage approach was used in oder to achieve the objective. At the first stage, in order to reduce the liquidus temperature of the alloy, cobalt, molybdenum and manganese substitutions for tungsten were made in amounts ranging between 10-20 at%. At the second stage, the compositions which are promising for obtaining amorphous structure were determined and Er, Sm, Y, Zr (2-6 at%), La and Nd (6 at%) substitutions were made for the nickel in these compositions in order to make Ni phase precipitation more difficult. Microstructural and thermal properties of the samples were investigated by material characterization methods. It is found that Co and Mo substitutions significantly reduce the liquidus temperature of the alloys and facilitate producing finer microstructures. Since finer microstructures suggest that the alloys can be cooled faster due to Co and Mo additions, this is important for glass formation. Also, it was determined that Er, Sm, Y, Zr, La and Nd substitutions for Ni promote crystallization and has a negative effect on glass forming ability of the alloys.