バイオメディカル応用のための形状記憶NiTi材料の腐食挙動の検討

Examination of the Corrosion Behavior of Shape Memory NiTi Material for Biomedical Applications.

抄録

本研究では、形状記憶合金として知られるNiTi合金（Ni55％-Ti45％）試料の腐食および摩耗試験を行った。標準的な金属組織学的に調製された試料の微細構造画像は、光学顕微鏡装置とEDS分析装置付きSEMを用いて得られた。腐食試験は、標準空気との接触を遮断した人工体液のビーカーに試料を網で浸漬した。電気化学的腐食分析は、合成体液中および室温で電位差試験を行った後に実施した。調査したNiTi超合金の摩耗試験は、乾燥環境と体液中で20Nと40Nの荷重をかけて往復摩耗試験を実施した。摩耗中、対材質の100CR6品質の鋼球を、単位線長13mm、摺動速度0.04m/sで、合計300mにわたって試料表面に擦り付けた。体液中での電位差分極腐食試験および浸漬腐食試験の結果、腐食電流値の変化に比例して試料の平均50%の厚み減少が観察された。さらに、腐食摩耗での試料の重量減少は、乾式摩耗の場合よりも20%少なかった。これは、高荷重における表面の酸化皮膜の保護効果と、体液の摩擦係数の低減効果によるものと考えられる。

In this study, corrosion and wear tests of NiTi alloy (Ni 55%-Ti 45%) samples, known as shape memory alloy, which offer a shape recovery memory effect between memory temperatures ranging from 25 to 35 °C, have been carried out. The standard metallographically prepared samples' microstructure images were obtained using an optical microscope device and SEM with an EDS analyzer. For the corrosion test, the samples are immersed with a net into the beaker of synthetic body fluid, whose contact with the standard air is cut off. Electrochemical corrosion analyses were performed after potentiodynamic testing in synthetic body fluid and at room temperature. The wear tests of the investigated NiTi superalloy were carried out by performing reciprocal wear tests under 20 N and 40 N loads in a dry environment and body fluid. During wear, a 100CR6-quality steel ball of the counter material was rubbed on the sample surface for a total of 300 m with a unit line length of 13 mm and a sliding speed of 0.04 m/s. As a result of both the potentiodynamic polarization and immersion corrosion tests in the body fluid, an average of 50% thickness reduction in the samples was observed in proportion to the change in the corrosion current values. In addition, the weight loss of the samples in corrosive wear is 20% less than that in dry wear. This can be attributed to the protective effect of the oxide film on the surface at high loads and the effect of reducing the friction coefficient of the body fluid.