BRAZING & SOLDERING TODAY Manufacturing Flux Cored Welding Wire Cobalt Nickel Hardface Stainless Alloy Steel Tool Steel Maintenance Forge Alloys Custom Alloys WELDING JOURNAL 59 TECHNOLOGY NEWS Eight biocompatible Ti-Co-based active brazing alloys were developed, including Ti-22.6Co-2.5Si, Ti-20Co-7Cr, and Ti-13.7Co-2.5Ni (at.-%). The brazing temperature was 1200°C, holding for 40 min. These alloys were analyzed with regard to the melting behavior and their wettability on an alumina surface. Contact angles on alumina varied from 41.5 deg for Ti-22.6Co-2.5Si to 49 deg for Ti-13.7Co-2.5Ni alloy. In addition, all three alloys exhibited moderate hardness that can prevent cracking of the coating during cooling. Moreover, cell viability (life-death staining) was performed using mouse L929 fibroblast cells to make a first statement about the cytocompatible behavior of these new materials. Successful results were achieved, and three brazing alloys were chosen as prospective materials for the deposition of biocompatible coating in manufacturing hip prostheses. Friction Surfacing of Steel by Soldering and Production of Press Fit/Pressure-Soldered Joints Friction surfacing by soldering (FSbS), as a method to deposit thin layers of copper, zinc, or aluminum on rotation symmetric steel components, was developed and studied at the Dresden University of Technology, Germany. This method can be applied to manufacture a press fit/pressure-soldered joint (PF/PSJ) or surface finishing of steel shafts (Ref. 7). A machine for depositing soft coatings by FSbS was developed as part of a cooperative project. The range of coating thickness was 54–135 microns in the case of copper, 22–145 microns for aluminum, and 11–50 microns for zinc. Analysis of highresolution scanning electron microscope images revealed there was no mixed crystal area for the combination of copper/ steel and aluminum/steel. Meanwhile, intermetallic phases exist between the zinc coating and steel substrate. In addition, results for the PF/PSJ with joint areas coated by FSbS showed a comparable result as far as the optimal rated electroplated PF/PSJ. The soldered joints of friction-coated steel parts reached 50 MPa in shear strength. Pressureless Joining with Silver Nanoparticles at Low Temperatures Metallic silver has a melting point of 961°C, and it can therefore be classified as a brazing material. Joining methods using silver at lower temperatures are based on silver sintering. Significantly lower sintering temperatures can be achieved when small silver particles — and especially silver nanoparticles — are involved. A new method was studied at Technische Universität Berlin, Germany, to sinter silver at temperatures below 250°C without applying pressure. In contrast to other approaches where nanoparticles are used, a silver-organic complex was used as a bulk material (Ref. 8). It generated silver nanoparticles only upon heating and shows different phase stages. Appearance of a liquid metal-like phase is advantageous for pressureless processing. Added silver COR-MET, INC. 12500 Grand River Rd. Brighton, MI 48116 PH: 800-848-2719 FAX: 810-227-9266 www.cor-met.com sales@cor-met.com For info, go to www.aws.org/ad-index For info, go to www.aws.org/ad-index
Welding Journal | February 2014
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