Institute of Technology, Pedagogical University of Cracow, Podchorążych 2, 30-084 Kraków, Poland; AIT Austrian Institute of Technology GmbH, Center for Health & Bioresources, Biomedical Systems, Viktor Kaplan Straße 2, 2700 Wr. Neustadt, Austria.
AIT Austrian Institute of Technology GmbH, Center for Health & Bioresources, Biomedical Systems, Viktor Kaplan Straße 2, 2700 Wr. Neustadt, Austria.
Mater Sci Eng C Mater Biol Appl. 2020 Apr;109:110543. doi: 10.1016/j.msec.2019.110543. Epub 2019 Dec 13.
Enhancing the strength of Mg-based biodegradable alloys without decreasing their corrosion resistance is a major engineering challenge. In addition, the growing demand for effective reduction of infections and inflammation after implant placement motivates the design of alloys with appropriate compositions or coatings. One promising alloying element is silver, whose antibacterial effect has long been known. Therefore, a Mg-4% Ag alloy was selected for this study. The alloy was investigated under three conditions: as-cast, after T4 treatment, and after T4 treatment with subsequent equal-channel angular pressing (ECAP) using a newly developed double-ECAP die, which offers an equivalent strain per pass of 1.6. The first pass through the double-ECAP die was conducted at 370 °C and the second at 330 °C using route B. The microstructure of the as-cast Mg-4% Ag consisted of large grains (several hundred microns) and a dendritic structure with micron-sized MgAg precipitates. T4 heat treatment caused dissolution of the dendrites and formation of a solid solution without changing the grain size. Consequently, the ultimate compressive strength (UCS) was increased by approximately 30%, and the compressive strain at fracture reached approximately 23%. The compressive yield strength (CYS) remained nearly constant at approximately 30 MPa. Subsequent ECAP led to strong grain refinement (from 350 μm to 38 μm after one pass and 15 μm after two passes) and further increases in the CYS and UCS, to 45 and 300 MPa after the first pass and 62 and 325 MPa after the second pass, respectively. The as-cast alloy exhibited a very high degradation rate in a simulated body fluid at approximately 36 °C. The degradation rate of the alloy after T4 treatment was much lower. Subsequent ECAP had no significant effect on the degradation properties. Thus, it can be concluded that grain refinement has little effect on the degradation rate.
提高镁基生物可降解合金的强度而不降低其耐腐蚀性是一个重大的工程挑战。此外，植入物放置后有效减少感染和炎症的需求促使设计具有适当成分或涂层的合金。一种有前途的合金元素是银，其抗菌作用早已为人所知。因此，选择 Mg-4%Ag 合金进行本研究。该合金在三种条件下进行了研究：铸态、T4 处理后和 T4 处理后随后使用新开发的双通道角挤压（ECAP）进行 ECAP，每通过一次的等效应变为 1.6。双通道 ECAP 模具的第一次通过在 370°C 进行，第二次在 330°C 进行，路线 B。铸态 Mg-4%Ag 的微观结构由大晶粒（几百微米）和具有微米级 MgAg 析出物的枝晶结构组成。T4 热处理导致树枝晶溶解并形成固溶体，而晶粒尺寸不变。因此，极限抗压强度（UCS）增加了约 30%，断裂时的压缩应变达到了约 23%。压缩屈服强度（CYS）几乎保持不变，约为 30MPa。随后的 ECAP 导致强烈的晶粒细化（一次通过后从 350μm 细化到 38μm，两次通过后细化到 15μm），CYS 和 UCS 进一步增加，第一次通过后分别达到 45MPa 和 300MPa，第二次通过后分别达到 62MPa 和 325MPa。铸态合金在模拟体液中约 36°C 时表现出非常高的降解速率。T4 处理后的合金降解速率要低得多。随后的 ECAP 对降解性能没有显著影响。因此，可以得出结论，晶粒细化对降解速率影响不大。
