Original Title Failure Analysis titanium tubing price Site Direct Attack — — Analysis of Fracture Causes of Nickel-Titanium Wire With the development of modern medicine nickel-titanium alloy has been widely used in human body minimally invasive implant medical devices in the medical field because of its excellent biocompatibility radiopacity non-impact of nuclear magnetic resonance mechanical properties corrosion resistance shape memory effect and superelasticity Background of the Titanium welding pipe event A batch of nickel-titanium alloy implantable medical devices were broken during X-ray examination after production and assembly The production process of the nickel-titanium wire comprises the steps of braiding heat treatment setting cleaning coating heat setting self-inspection and X-ray inspection Therefore a series of inspection methods are used to analyze the fracture causes of nickel-titanium wire and the corresponding improvement measures are put forward Physical and chemical test The chemical composition analysis mechanical property test and cleanliness test were carried out on the nickel-titanium wire in the nickel-titanium alloy product The results are shown in Table 1-3 It can be seen that the three indexes meet the technical requirements of GB 24627 2009 Table 1 Chemical composition (mass fraction) of nickel-titanium wire Table 2 Mechanical Property
There are obvious gray mud pattern corrosion products in the corrosion pits far away from the fracture as shown in Fig 5 with typical stress corrosion characteristics Fig 2 Micro-morphology of NiTi wire fracture Fig 3 SEM morphology of Ni-Ti wire fracture 3 Analysis of chemical composition in microarea Energy spectrum (EDS) analysis was carried out on the crack source area of the fractured nickel-titanium wire ti6al4v eli the gray corrosion products in the surface corrosion pits near the small wave peak or trough the contaminated yellow substances on the envelope the rusty substances on the braided die rod and the heat-shrinkable tube used for heat setting The results are shown in Fig 6 ~ 8 Fig 4 Microscopic morphology of corrosion pits near the fracture of nickel-titanium wire Fig 5 Microscopic morphology of corrosion pits of NiTi wire far away from fracture Fig 6 EDS spectrum of crack source area of nickel-titanium wire Fig 7 EDS spectrum of NiTi wire corrosion pit and coated yellow substance Fig 8 EDS spectra of rust and heat-shrinkable tube on braided die rod The main chemical components of the yellow substance in the visible crack source area corrosion pits and coating are bromine nickel titanium and a small amount of iron manganese chromium vanadium 3d titanium wire calcium sodium chlorine sulfur and other elements Bromine comes from heat-shrinkable tubes while iron manganese chromium vanadium calcium sodium chlorine and sulfur mostly come from rusty substances in moulds Analysis and discussion 1 Fracture characteristics
As is known to all HF has a strong corrosive effect on nickel-titanium wires In order to explore the influence of HBr on nickel-titanium wires titanium round bar the following tests were carried out in a simulated stress corrosion environment the tensile stress existing in the nickel-titanium wire was artificially created and then the nickel-titanium wire was placed in HBr solution for 1 H taken out and placed for 4 H and then broken The fracture was microscopically observed and the results are shown in Figure 9 Fig 9 Fracture morphology of nickel-titanium wire after HBr stress corrosion test It was found that HBr also had stress corrosion effect on NiTi wire and the fracture morphology of NiTi wire was similar to that of the broken wire which proved that the batch of products had stress corrosion cracking ti6al4v in the area where there were small wave peaks or troughs in the medium environment containing bromine compounds Conclusions and recommendations During the braiding process the stress of the nickel-titanium wire was not well eliminated and the corrosion medium was introduced into the braiding die rod and the heat-shrinkable tube which led to the stress corrosion cracking of the nickel-titanium wire in the nickel-titanium implant device It is suggested that the small wave crest of the braided die rod should be designed into a large wave crest to better relieve the stress in the production process; the braided die rod should be dried in time and the rusty substances on the surface of the braided pattern rod should be cleaned regularly to prevent the introduction of corrosive media Author Shi Xiaoli Senior Engineer Shenzhen Leading Medical Service Co Ltd Return to Sohu to see more Responsible Editor yunchtitanium.com
