The silver –tungsten and silver-molibdenum infiltrated composites
Marcin Madej, Jan Leżański
Quarterly No. 1, 2009 pages 40-44
DOI:
keywords: composites of W-Ag and Mo-Ag, sintering, infiltration
abstract The W-Ag and Mo-Ag electrical contact materials are produced exclusively by means of powder metallurgy (PM). Tungsten and molybdenum are used for contacts utilised in heavy-duty applications. Composites containing 30-80 wt. % silver resist arc erosion and possess good anti-welding characteristics and acceptable interface resistance. The properties of PM electrical contacts depend on both their composition and manufacturing process. This means that the particle size, and distribution of the refractory phase, the homogeneity of the microstructure, and amount of porosity affect the electrical, mechanical, and thermo-physical properties of the composite material. In principle, the W-Ag and Mo-Ag composite materials can be produced by two techniques. Attempts have been made to describe the influence of production process parameters on the microstructure and properties of Mo-Ag composites. The compositions of powder mixtures are W + 30% Ag, W + 40% Ag, Mo + 30% Ag and Mo + 40% Ag. W + 5 wt. % Ag and Mo-5 wt. % Ag mixtures were prepared by tumbling the powders for 30 minutes. They were subsequently cold pressed in a rigid die on a single action press. The pressure was adjusted individually to assure around 25% green porosity. Prior to infiltration the compacts were sintered in hydrogen at 1100°C for one hour. The porous skeletons were finally contact infiltrated with Ag-1wt. % Ni alloy at 1100 and 1200°C for one hour in hydrogen. Considerable differences in hardness, bending strength and electrical conductivity between the materials obtained from infiltration at 1100 and 1200°C have been observed, with higher hardness, bending strength and electrical conductivity numbers are achieved with direct infiltration at 1100°C. The as-infiltrated microstructures are characterised by even distri-bution of tungsten/molybdenum, silver and small residual porosity. From the analysis of the obtained results and microstructural observations it may be concluded that infiltration of composites W-Ag and Mo-Ag has proved to be a suitable technique whereby nearly fully dense material is produced at low cost and with better properties are achieved in lower temperatures of infiltration, such as 1100°C.