Silver ternary alloy

Abstract

A firestain and tarnish-resistant ternary alloy of silver, copper and germanium contains from more than 93.5 wt % to 95.5 wt % Ag, from 0.5 to 3 wt % Ge, optionally 0.5 wt % Zn and the remainder, apart from incidental ingredients (if any), impurities and grain refiner, copper. In order to further protect an article made from the alloy, it may be surface treated with an alkanethiol, alkyl thioglycollate, dialkyl sulphide or dialkyl disulphide. Embodiments of the above alloy exhibit relatively low elution of copper when subjected to a simulated sweat test.

1 . An alloy, comprising:
 from 93.5 wt % to 95.5 wt % of silver;   from 0.5 to 3 wt % of germanium;   1-40 parts per million of boron;   and the remainder, apart from impurities, being copper;   the weight ratio of copper to germanium being from 4:1 to 3:1; and   the alloy being resistant to the development of porosity and brittleness, the development of hot short cracking defects when investment cast, the development of cracks or shattering on annealing and quenching and the development of cracks and sagging when heated for joining or torch annealing.   
     
     
         2 . The alloy of  claim 1 , wherein the weight ratio of copper to germanium is about 3.5:1. 
     
     
         3 . The alloy of  claim 1 , which comprises from 1.0 wt % to 1.5 wt % of germanium. 
     
     
         4 . The alloy of  claim 1 , which comprises about 94.5 wt % of silver, about 4.3 wt % of copper and about 1.2 wt % of germanium. 
     
     
         5 . The alloy of  claim 1 , which comprises 5-20 ppm of boron. 
     
     
         6 . The alloy of  claim 1 , wherein said alloy is a finished or semi-finished shaped article. 
     
     
         7 . The alloy of  claim 6 , wherein said finished or semi-finished shaped article is casting. 
     
     
         8 . The alloy of  claim 6 , wherein said finished or semi-finished shaped article is produced or partially produced from a sheet or a strip. 
     
     
         9 . The alloy of  claim 1 , which comprises more than 93.5 wt % of silver. 
     
     
         10 . The alloy of  claim 1 , which further comprises 0.5 wt % of zinc. 
     
     
         11 . An alloy, comprising:
 from 93.7 wt % to 95.5 wt % silver;   from 1.0 to 1.5 wt % germanium; 1-40 parts per million of boron;   and the remainder, apart from impurities, being copper;   the weight ratio of copper to germanium being from 4.5:1 to 3:1; and   the alloy being resistant to the development of porosity and brittleness, the development of hot short cracking defects when investment cast, the development of cracks or shattering on annealing and quenching and the development of cracks and sagging when heated for joining or torch annealing.   
     
     
         12 . The alloy of  claim 11 , which further comprises 0.5 wt % of zinc. 
     
     
         13 . The alloy of  claim 11 , comprising about 93.7 wt % of silver Ag, about 5.1 wt % Gu of copper and 1.2 wt % of germanium. 
     
     
         14 . A ternary alloy of silver, copper and germanium, comprising:
 from more than 93.5 wt % to 95.5 wt % of silver;   from 0.5 wt % to 3 wt % of germanium; and   a remainder comprising, apart from incidental ingredients in amounts that are not detrimental to mechanical strength and tarnish resistance of said ternary alloy, impurities and grain refiner and copper,   said ternary alloy being resistant to developing of hot short cracking defects when investment cast and resistant to developing of cracks and sagging when heated for joining or torch annealing.