Effect of cobalt and tungsten on mechanical properties of Ni-CoWB composites

CoWB reinforced composites were produced by using metallic glass alloys Ni37.6W22.5Co22.5B17.4 and Ni27.6W27.5Co27.5B17.4 as precursors. For this purpose, the alloys were heat treated isothermally for different periods at temperatures above their crystallization temperatures. The effects of the microstructural properties of the obtained composites on the mechanical properties and corrosion resistance of the composites were investigated. It was determined that the microhardness values of the composites produced by the crystallization of the Ni27.6W27.5Co27.5B17.4 metallic glass alloy were higher than the composites produced by the crystallization of the Ni37.6W22.5Co22.5B17.4 metallic glass alloy. While the highest hardness value of the composites produced by crystallization of Ni37.6W22.5Co22.5B17.4 metallic glass alloy was 1474 HV, the highest hardness value of the composites produced by crystallization of Ni27.6W27.5Co27.5B17.4 metallic glass alloy was found to be 1580 HV. The reason for this increase in hardness value is that Ni27.6W27.5Co27.5B17.4 metallic glass alloy has higher Co and W content than Ni37.6W22.5Co22.5B17.4 metallic glass alloy and as a result Ni27.6W27.5Co27.5B17.4 composites obtained by heat treatment of metallic glass alloy contain a higher volume fraction of CoWB phase than composites obtained by heat treatment of Ni37.6W22.5Co22.5B17.4 metallic glass alloy. It was determined that the fracture toughness values of the composites produced by the crystallization of both metallic glass alloys were low (<10 MPa.m1/2). Because the average grain size of the CoWB phase precipitated in the structure of the composites produced by the crystallization of the Ni27.6W27.5Co27.5B17.4 metallic glass alloy is higher than the average grain size of the CoWB phase precipitated in the structure of the composites produced by the crystallization of the Ni37.6W22.5Co22.5B17.4 metallic glass alloy fracture toughness value was found to be higher. The corrosion behavior of the composites produced by the crystallization of both alloys in 3.5% NaCl and 1M HCl solutions was measured. The composite produced by crystallization of Ni37.6W22.5Co22.5B17.4 metallic glass alloy showed higher corrosion resistance for both solutions because it has higher Ni content.