Wang Jianqiu, Li Nianxing, Rao Guangbin, Han En-Hou, Ke Wei
Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China.
Dent Mater. 2007 Feb;23(2):133-7. doi: 10.1016/j.dental.2006.01.001. Epub 2006 Feb 8.
This paper aimed to study the mechanism of the cracking of orthodontic NiTi wire.
Two orthodontic NiTi wires were subjected: (1) optical and scanning electron microscopy (SEM) to observe the fracture surface; (2) energy dispersive X-ray spectroscopy to determine the composition of the surface product; (3) anodic polarization to remove the surface product. Samples of NiTi alloy were subjected to the constant loading test to study the stress corrosion cracking (SCC) behavior of NiTi shape memory alloy in artificial saliva.
The results showed that there were three typical areas at the fracture surface of NiTi orthodontic wire. Area '1' was a tool-made notch. Crack initiated from the root of this notch and propagated to form Area '2', which was perpendicular to the wire axis and covered by surface film. This film consisted of Na, K, Cl, P, S and O except Ni and Ti. The cracking process of NiTi alloy under the constant loading test depended on the pH of saliva and applied stress. The crack length was about 262microm, the longest at 300MPa and pH 3.0.
A tool-made notch in orthodontic NiTi wires can cause SCC. At high stress and low pH, this NiTi alloy was most sensitive to cracking.
本文旨在研究正畸镍钛丝的断裂机制。
对两根正畸镍钛丝进行了以下操作：（1）光学显微镜和扫描电子显微镜（SEM）观察断裂表面；（2）能量色散X射线光谱法测定表面产物的成分；（3）阳极极化去除表面产物。对镍钛合金样品进行恒载试验，研究镍钛形状记忆合金在人工唾液中的应力腐蚀开裂（SCC）行为。
结果表明，镍钛正畸丝的断裂表面有三个典型区域。区域“1”是一个加工制造的缺口。裂纹从该缺口根部萌生并扩展形成区域“2”，该区域垂直于丝轴并被表面膜覆盖。除镍和钛外，该膜由钠、钾、氯、磷、硫和氧组成。镍钛合金在恒载试验下的开裂过程取决于唾液的pH值和施加的应力。裂纹长度约为262微米，在300MPa和pH 3.0时最长。
正畸镍钛丝中加工制造的缺口可导致应力腐蚀开裂。在高应力和低pH值下，这种镍钛合金对开裂最敏感。
