| During the application of jewelries, the safety problems such as nickel allergy and bacterialinfection are becoming more and more prevalent, it damages the consumer’s physical and mentalhealth. As the decorations of long time contacting with skin or being implanted in the tissue,metal jewelries have close relationship with metallurgical engineering, materials science andbiomedical engineering discipline. Based on our earlier research of common jewelry materialsand production processes in jewelry market, stainless steel for jewelry was chosen as the mainline in this paper, and three aspects of experimental investigation were carried out from theviewpoint of biomaterial and metallurgical engineering, including the nickel release rates ofmetallic jewelry materials, the antibacterial modification of S316L stainless steel and highnitrogen nickel-free antibacterial stainless steel, so that guidance can be provided for solvingnickel allergy and bacterial infection problem, and the selection, development and application ofmetallic jewelry materials.The most widely used nickel containing materials, including stainless steels, cupronickel,nickel bleached karat white gold and nickel plating layer, were chosen as the nickel release testobjects, the samples were treated by the common processing technology, and then their nickelrelease rates under various conditions were tested according to the nickel release standard testmethods. The effects of various physiological environment, shaping method, surface treatmentmethod and heat treatment process on nickel release rate of stainless steel and other nickelcontaining material for jewelry were determined experimentally and the mechanism wasanalyzed, and it is pointed out that the evaluation of a material’s nickel release rate and allergyrisk can not be separated from its specific conditions. It is found that there is no correspondenceof nickel release rates to nickel content, inclusions and cold deformation will promote nickelrelease, and it presents anisotropy for cold deformation, while appropriate heat treatment canreduce nickel release rate. The rougher the material surface is, the more nickel ions are released,while nickel plating layer can obviously improve nickel release rate. In different physiologicalenvironment, S316L’s nickel release rate shows the sequence as “artificial body fluid> artificialsweat> urine> artificial salivaâ€.It is determined that the actual nickel release rates of BZn10-25, S201and S303stainlesssteels,10K and18K nickel bleached gold alloys under all various conditions significantly exceed the threshold specified in Nickel Directives, the allergy risks for these materials are high,especially for BZn10-25and S303. The practical nickel release rate of mirror polished S316Lstainless steel under solid solution state is very low, it should be safe and can’t go so far as toarouse nickel allergy for most people, however, when the material is under an adverse conditionssuch as cold work, as-cast, annealing, sand blasting, sand pushing, etc, its nickel release rateswill increase by different degrees, especially when two or more of these promoting factors addtogether, the actual nickel release rate will reach or exceed the specified threshold, it can notcompletely exclude the risk of nickel allergy for long term wearing. Therefore, it is pointed outthat the development of nickel-free materials and technologies is the only way to avoid nickelallergy risk thoroughly.Since the ordinary stainless steels have no antibacterial performance, S316L was selectedfor antibacterial modification and the thin-film adhering quantitative bacteriostasis method wasused to test the antibacterial property. Aim at the question of copper bearing stainless steel agingtreated at the sensitized interval to acquire antibacterial efficacy, suitable amount of Ce/La or Agwith tiny solubility in the matrix of stainless steel were used as antibacterial agents, by means ofcomprehensive grain refining measures, the modified stainless steel acquired antibacterialperformance with no need of aging treatment. According to the experimental results, theantibacterial mechanism of Ce/La or Ag modified stainless steel is put forward, when the steelcontacts with bacteria for some time, the Ce/La or Ag ions released from the enrichment phaseare absorbed to the bacterial surface because of the electrostatic adsorption, their action on thecell wall and protein will produce antibacterial efficacy.It is found that Ce or La modified S316L stainless steel shows Hormesis effect against S.aureus and E. coli, only when Ce or La content reaches a certain amount can the modifiedstainless steel realize antibacterial effect, The more amount of Ce or La is added, the betterantibacterial performance is achieved, however, too much amount of Ce or La will damage theprocessability and corrosion resistance, and increase nickel release rate. It is shown that theaddition of Ce or La alone in S316L is difficult to obtain the optimal combination of corrosionresistance, antibacterial capability and processability, and0.15~0.2wt%Ce or La is suggested tobe the trade-off for the best overall performance.Through the comprehensive grain refining measures, including vaccum arc melting, water-cooled copper crucible to accelerate solidification and~0.1wt%niobium,0.04~0.06wt%silver can be dispersed in the stainless steel matrix in the form of tiny Ag-rich phase, themodified stainless steel shows excellent antibacterial efficacy against S. aureus and E. coli, and itwill not abate after repetitive use and wear. It is found that silver modified stainless steel hasbetter corrosion resistance in microbial environment, however, too much silver will degrade thecorrosion resistance in non-microbial environment, and nickel release rate will slightly increasealso.In view of the possible risk of nickel allergy for S316L stainless steel after beingantibacterial modified, the material selection principle of high nitrogen nickel-free stainless steelfor jewelry was put forward and the experimental material00Cr18Mn18Mo2N0.55wasdetermined based on it. The material has excellent pitting corrosion resistance in non-microbialenvironment, however, well-developed biofilm will form on its surface when it contacts withbacterial suspension, and the bacterial growth is obviously promoted, inducing microbiologicalcorrosion. The root cause of bacterial serious adhesion is inferred to be that high nitrogenstainless steel provides a rich nutritional basement for bacteria growth. It is suggested that highnitrogen stainless steel is not suitable for microbial environment unless after antibacterialmodification. Copper and silver were selected as the antibacterial agents. It is found that thebacterial adhesion on00Cr18Mn18Mo2N0.55stainless steel containing about3.5wt%Cu can beimproved after aging treatment at800℃for one hour, but the sterilization efficacy is weak, andthe precipitated Cr2N will degrade its corrosion resistance, the longer the aging time, the moreserious the damage to corrosion resistance. It is determined that copper is unsuitable asantibacterial agent in high nitrogen stainless steel. Higher silver content is needed in00Cr18Mn18Mo2N0.55to realize sterilization efficacy than in S316L and it is presumed to bethe comprehensive effect of competition result of silver’s sterilizing bacteria and nitrogen’spromoting bacterial growth, slow-release function of silver ammino ions and manganeseimproving the solubility of silver in the matrix.00Cr18Mn18Mo2N0.55containing0.13~0.15wt%silver is designed and developed, this modified material has relatively goodantibacterial property, it can hinder bacterial adhesion and biofilm development, and improvemicrobiological corrosion resistance, it still keeps excellent pitting corrosion resistance andcorrosion wear resistance in non-microbiological environment, and it has no risk of nickel allergy and metal toxicity and can meet the processing requirement of jewelry, therefore it is apromising jewelry material with superior overall properties to S316L. |
