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Comparative analysis of domestic and foreign standards for metallographic examination of α+β titanium alloy for surgical implants
Li Fan, Gao Na, Zhang Luwen, Guo Linlin, Lou Gui, Zhang Bo
Microstructure requirements of titanium alloy in surgical implant standards in domestic and foreign were compared and analyzed. The microstructure of plates in GB/T 13810-2017 requires that the original β grain should be fully broken, and continuous grain boundary α phase is not allowed, the microstructure of bars and wires should conform to figure A.1 (a-i) of the standard. The latest versions of ISO 5832-3, ASTM F136, and ASTM F1472 all specify that the microstructure shall be equiaxial and/or elongated primary α phase distributed on the transformed β matrix, with no continuous α network on the prior β grain boundaries. Among them, the transverse microstructure of the bars in ISO 5832-3 shall correspond to A1-A9 in ISO 20160. Combined with the thermal mechanical processing technology of titanium alloy, when the temperature of hot processing and recrystallization is lower than the β transition temperature, or slowly cooling, high volume fraction of primary α phase and intergranular β will be obtained, recrystallization treatment at close to the β transition temperature will obtain equiaxial primary α phase uniformly distributed on the β matrix, which is represented by A1-A9 in the standard spectrum. After recrystallization above the β phase transition temperature, continuous grain boundary α, network α and lamellar α phases are obtained between the coarse β grains, which are manifested as A10-A24 in the standard diagram.
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