Sintering Characteristics of Iron and Cobalt Doped Silver-tungsten Metal-matrix Composites

Abstract

Silver-Tungsten composites are known as electrical contact materials used in circuit breakers and industrial relays. The performance of the contact during their service life depends upon high strength and anti-weld properties of these materials. Despite their promising industrial applications, the literature dealing with their production route is still limited. Therefore, a comprehensive study exploring the structure related properties with great emphasis on the sintering process of these materials is carried out. Therefore, in this study, the successful production of a homogeneous composite powder with controlled tungsten particle size using co-precipitation and two stage reduction techniques is followed by the compaction and sintering processes. Thus, high density compacts are produced from Fe and Co doped silver-tungsten powder using powder metallurgy technique. Various environments and sintering conditions, including N 2 atmosphere and temperatures up to 1000°C, to obtain successful compacts from both doped and un-doped powders, are investigated. The morphologies and the microstructures of the sintered compacts obtained under the different sintering conditions are characterized and assessed using Scanning Electron Microscopy (SEM). Results display excellent agreement with the published studies and no evidence was found for the activated sintering of silver-tungsten by Fe additions. Also, the homogeneity of silver-tungsten in compacts is completely lost in the Fe-doped powders. However, Co additions help to facilitate the sintering between silver and tungsten whilst retaining a high homogeneity between the silver and tungsten in the sintered product.

Effect of Co Additions on the Densification Behavior of the Ag-W Composite Powder Compacts at Various Sintering Temperatures

“…The precipitated silver tungstate analysis is made by atomic absorption spectroscopy and the molecular formula for precipitated silver tungstate (Ag 2 WO 4 ) is obtained (Calculated Formula= Ag1.96 WO4.01), see Es-Saheb and Azhar [8]. From the formula it is clear that the silver/tungsten ratio is very close to the theoretical value 2:1 and the oxygen content calculated from the total mass of specimen also agrees with the theoretical value for silver tungstate.…”

“…A summary of the most important related issues, results, procedures, and findings are reported below. For more details and information on the analyses, materials, measurements and experimental techniques involved refs [6]- [8] can be consulted. However, in this section typical examples of the main findings related to the pressing and sintering processes are presented.…”

“…Then, in order to preserve the homogeneity and distribution of silver and tungsten, the reduced material was pressed and sintered below the melting point of silver. This suggested two stage reduction process is used later, by Qureshi et.al [5] and recently by Es-Saheb and Azhar [6]- [8]. They added some iron and cobalt as sinter aids to improve the sintered product density and produce silver tungstate composite with controlled homogeneous structure.…”

Effects of chemical substitution on the structural and optical properties of α-Ag2−2xNixWO4(0 ≤ x ≤ 0.08) solid solutions

“…2,21,23 However, less attention has been devoted to a-Ag 2 WO 4 crystals doped with different types of impurities. 24 Generally, successful doping requires substituent and host ions with comparable ionic radii and charges, allowing only a small disturbance in the crystal framework. This has been achieved in a-Ag 2 WO 4 , whose crystal structure is extremely flexible.…”