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L. Wierzbicki, W. Malec, J. Stobrawa, B. Cwolek and B. Juszczyk

Studies Into New, Environmentally Friendly Ag-Cu-Zn-Sn Brazing Alloys of Low Silver Content

The paper present selected results of the research conducted for elimination of toxic cadmium from silver based brazing alloys of Ag-Cu-Zn-Cd type. The investigations were conducted with nine new alloys of constant, low silver content (25%) and diversified copper (38.8-46%), zinc (19-32%) and tin (3-10%) contents. Tin was selected as potentially the best cadmium substitute basing on literature review and analysis of equilibrium systems.

For examinations and tests a series of ingots in laboratory scale was manufactured, as well as some ingots in pilot scale for the selected, most promising alloys. Complex metallographic examinations of the brazing alloys samples produced in various conditions were made as well as analyses of their phase composition. Also mechanical properties of the samples both in ambient and in elevated temperatures were examined, and physical and technological properties and usability of the alloys were determined. The last stage of the study covered laboratory trials of brazing using the selected alloys.

Basing on the results it can be said that there is a possibility to substitute selected cadmium containing silver-based alloys with environmentally friendly alloys of Ag-Cu-Zn-Sn type of relatively low silver content. Low range of melting point was reached, as preliminary assumed. Mechanical properties of the studied alloys strongly depend on temperature, and present limited plasticity in room temperature, while at high temperature (over 500°C) present superplasticity. The examined alloys show good spreadability and the brazing tests confirmed their good reactions both with copper and brass base in a wide temperature range.

Open access

B. Juszczyk, J. Kulasa, S. Malara, M. Czepelak, W. Malec, B. Cwolek and Ł. Wierzbicki

Abstract

The results of research into influence of chemical composition on structure and tribological properties of copper-based composites intended for slide bearings are presented in this paper. The study was focused on copper alloys with lubricating phase particles in form of graphite, tungsten disulphide (WS2), molybdenum disulphide (MoS2) and glassy carbon. The metallic matrix of composite materials was composed of alloys from Cu-Sn-Zn system. The mass content of lubricating phase particles was from 5 to 20%. The process of production of subject materials included the processes conducted with full or partial contribution of liquid phase and it was conducted by two methods. Both the method of classic powder metallurgy and stir casting method were used for the production of composites. Lubricating phase particles heated to the temperature of 200°C were introduced to liquid metal bath and then the process of stirring and casting to moulds was performed. In case of production of composites by powder metallurgy, the process included mixing of bronze powders and lubricating phase particles, and then their consolidation. Sintering process was conducted in temperature between 750-800°C. The produced materials were tested in terms of microstructure and tribological properties with the CSM Instruments tribometer.

Open access

B. Juszczyk, J. Kulasa, W. Malec, Sz. Malara, M. Czepelak and L. Ciura

Abstract

The paper presents results of the studies into influence of individual particles of lubricating phase on microstructure and tribological properties of copper based composite materials for slide bearings. The studied material was composed of copper alloys with lubricating phase particles, e.g. in a form of graphite and glassy carbon. The metallic matrix of composite materials consisted of Cu-Sn type alloys. Production of the examined materials included processes with complete or partial participation of liquid phase and was conducted in two ways. In production of composites both classical powder metallurgy technology was applied and a method of melting with simultaneous mechanical stirring in liquid state (stir casting). Particles of lubricating phases were heated up to the temperature of 200°C and introduced into a liquid metal and then stirring process at constant rate of 1500 rpm rotational speed was applied. To improve wettability of graphite and glassy carbon particles titanium was introduced into the metallic matrix.

In production of the composites by powder metallurgy methods the process consisted of mixing of bronze powders and particles of non-metallic phases and then their consolidation. Both quantitative and qualitative structure analysis of the produced composites was performed. Also through evaluation of tribological properties (friction coefficient, wear) with CSM Instruments high temperature tribometer THT was conducted.

Open access

B. Juszczyk, J. Kulasa, A. Gubernat, W. Malec, L. Ciura, M. Malara, Ł. Wierzbicki and J. Gołębiewska-Kurzawska

The paper shows results of the study into influence of chemical composition and consolidation process conditions on changes of physical and electrical properties of silver-based composites used in production of electric contacts. The investigations addressed influence of content of zinc oxide (ZnO) and modifying additions in a form of silver tungstate (Ag2WO4) and silver molybdate (Ag2MoO4) on changes in density, porosity and electrical conductivity. Density of the produced compacts was established by geometric method. The results of density measurements were used in determination of total porosity of sinters. Also arc erosion was examined to determine applicability of the produced composites for production of electric contacts. The erosion was measured as mass loss of individual materials after specific number of connections. The studies were conducted at current intensity of 10 A and voltage of 500V. The scope of the studies covered also evaluation of kinetics of sintering of the examined composites and determination of the mechanisms of mass transport in the process. Studies into kinetics of sintering were conducted in the air atmosphere at constant temperature of 900°C.

Production of the examined composite materials consisted of mechanical synthesis of powders of silver, zinc oxide and silver tungstate and molybdate, and then their consolidation by two-sided pressing and subsequent sintering. In cold pressing various pressures were applied 200, 300 and 400 MPa. Sintering was performed with a partial participation of liquid phase in temperature of 900°C. Also additional two-sided pressing was applied under pressure of 500 MPa and stress-relieving recrystallization annealing was performed as the final operation.