davis

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 Test Results of Ni-Ti Wire Expand the full text Table 3 Test Results of Nickel Titanium Wire Cleanliness 1 Macro analysis The fracture of nickel-titanium wires in this batch of nickel-titanium alloy products mostly occurred near the small wave peak or trough, and there were many corrosion pits distributed in the crack source area and the surface near the non-fracture small wave peak or trough; yellow substances were found in the product envelope area; the fracture was a transverse flat fracture without obvious plastic deformation,Titanium 6Al4V wire, belonging to macroscopic brittle fracture, as shown in Figure 1. Fig. 1 Macroscopic morphology of fractured Ni-Ti wire 2 Microscopic analysis of fracture The fractured NiTi wire was immersed in ethanol solution and cleaned by ultrasonic vibration, and then the fracture and crack source area were observed by JSM-6510 scanning electron microscope. The crack source of the fractured nickel-titanium wire starts from the corrosion pit on the surface of the wire, as shown in Fig. 2; the crack propagation zone is a cleavage fracture, and the instantaneous fracture zone is a flat dimple, as shown in Fig. 3; there are many corrosion pits on the side of the crack source and on the surface of the wire near the small wave peak or trough, as seen in Fig. 4; There are obvious gray mud pattern corrosion products in the corrosion pits far away from the fracture,titanium exhaust tubing, 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, 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, calcium, sodium, 3d titanium wire ,titanium plate gr7, 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 The fracture of the nickel-titanium wire in the failed product started from the corrosion pits on the surface of the nickel-titanium wire, the crack source area of the fracture was corrosion pits, the crack propagation area was cleavage, the instantaneous fracture area was flat dimples, and the fracture was brittle fracture.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,ti6al4v, Senior Engineer, Shenzhen Leading Medical Service Co., Ltd. Return to Sohu to see more Responsible Editor:. yunchtitanium.com