Tomasz Piwowarczyk

Wettability of hardmetal surfaces prepared for brazing with various methods

Hardmetals belong to the materials hardly wettable by liquid brazing alloys, so they should not be brazed without removing the surface layer after sintering. In the paper, mechanical and chemical methods of preparing a hardmetal surface for brazing are discussed. Special attention is paid to the electrolytic etching method that gives very good energetic properties to surfaces of hardly wettable materials. Electrolytic etching of hardmetals consists in anodic dissolution of tungsten carbide grains in water solution of alkaline metal hydroxides. The α phase (WC) is removed from surfaces of carbide preforms, leaving the much better wettable β phase (Co-W-C). Cobalt does not show amphoteric properties, so it does not dissolve in bases. With regard to brazing, besides significant development of the surface, an especially profitable feature of this method is isolating the metallic cobalt phase, which allows easier wetting by brazing alloys. On the grounds of surface roughness measurements, parameters of electrolytic etching were determined to remove WC grains from surfaces of carbide performs and to obtain much higher Co fraction on the brazed surface. The presented results are based on measurements of wetting angles on B40 hardmetal surfaces, isolated α and β phases and C45 steel, as well as on EDX cobalt analysis on hardmetal surfaces.

Analysis of adhesive properties of B2 hardmetal surface

Hardmetals belong to hardly wettable materials, so they should not be bonded without previous removing the surface layer left after sintering. The paper describes mechanical and chemical methods of preparing hardmetal surface for such processes as gluing and brazing. Particular attention is paid to the method of electrolytic etching that offers very good energetic properties of hardly wettable materials. In order to analyse the surface adhesive properties of hardmetals, measurements of roughness and wetting angle were performed, as well as electron microscopic examination and EDX analysis.

Composite adhesive joints of hardmetals with steel

Newest developments in the field of gluing and processing of plastics permit obtaining adhesive materials with profitable properties: high mechanical parameters, increased thermal conductivity, low electrical resistivity, increased rigidity, limited residual stresses or reduced creep [1] , [2] . This is possible by composite structure of adhesives, i.e. binders enriched with filling materials – additional phases of different kind, grain size and fraction. In the paper, effect of reinforcing adhesive materials with continuous and powdery fillers on shear strength of adhesive joints is discussed. Presented are also results of electron microscopy examinations and EDX analysis.

Soldering of aluminium with copper

Soldering of aluminium with copper becomes more significant, because of relatively low process temperature of about 400–450°C. It is applied not only in electrotechnical industry, in joining Al–Cu conductors, but also in cooling and air-conditioning equipment and in solar construction of collectors (Winiowski A. Lutowanie twarde aluminium i jegostopów – nowe trendy technologiczne, Biuletyn Instytutu Spawalnictwa, nr 6/2000, Fontargen GmbH. Löten in der Kälte- und Klimatechnik, Eisenberg. 2001 and Fontargen GmbH. Aluminium-Löten. Eisenberg 2003). In this paper, problems concerning Al–Cu soldering are presented. For soldering, zinc solders with the addition of 2, 4, and 15 wt% Al have been used. Results of wettability and spread factor measurements of zinc solders on aluminium and copper surface, as well as metallography, microhardness, and shearing tests of Al–Cu joints are presented. Effects of copper pipes with aluminium plate soldering with application of flux coating solders are also described.

Assessment of Macro and Microstructure of Welded Joints Made of Steel P265GH Using Various Combinations of Welding Consumables

The article presents the assessment of the macro and microstructure of welded joints made in steel P265GH using various combinations of filler metal wires and shielding gases. In addition to microstructural analysis, tests involved hardness measurements of all of the joint zones, i.e. the weld, HAZ and the base material. In addition, each specimen (i.e. the weld and the base material) was subjected to the analysis of chemical composition. The performed analysis made it possible to determine the degree of morphological conformity of welding consumables with steel P265GH.