Analysis OAnalysis On Crack Fault Of Titanium Alloy Self-locking Nutn Crack Fault Of Titanium Alloy Self-locking Nut

      At the end of the 20th century, the national development strategy went smoothly and presented an upward trend. In particular, the proposal and development of the “921” project greatly improved China’s comprehensive national strength and international status. The boom in high-tech  fields means that there is a pressing demand for new technologies, materials and energy. The advantages of titanium alloy make it meet the material requirements of the cutting-edge technology industry, and it is more and more widely used in the construction of satellites and aircraft and other important fields. Therefore, in the face of the phenomenon of self-locking nut crack in titanium alloy, this kind of fault must be thoroughly studied and analyzed to avoid accidents in future applications.

      The introduction

      Titanium alloy itself as a new type of alloy material, has the advantages that traditional alloy material cannot be compared with, made of titanium alloy into a self-locking nut, the parts themselves are very strong and tight connection, in preventing vibration and caused by the parts loose performance is superior, with high strength and low density characteristics. Therefore, the titanium alloy self-locking nut is favored by the aircraft manufacturing industry and other high-end machine manufacturing industry, and is used in the connection of many machines. The connection for the machine equipment, is a very important position, once the problem occurs failure, it is likely to cause the entire machine cannot be used serious consequences.

　　In the face of this situation, the crack fault of titanium alloy self-locking nut is analyzed and studied, and the corresponding rectification measures are proposed, which is of great significance in both protecting the safety of personnel and equipment and in promoting the improvement of technology. In this paper, the crack fault of some titanium alloy self-locking nuts is described and analyzed.

　　 (I) Cracking of self-locking nuts in titanium alloy

　　In order to better find out the possibility of causing faults and find corresponding solutions, we found some titanium alloy self-locking nuts with cracks, and marked and checked the nuts with problems, conducted simulation experiments and recorded experimental data. During the experiment, we not only carefully observed and recorded the titanium alloy self-locking nut with cracks, but also found the titanium alloy self-locking nut with no problems for comparison and analysis. The crack distribution location is shown in the figure:　　

      Through inspection, it was found that the cracks in the titanium alloy self-locking nut were not random but regular. There were not many cracks in location, which were concentrated on the internal surface of the short axis and the external surface of the long axis, and the crack direction showed a longitudinal development. Thus it can be seen that the crack caused by sudden and unexpected conditions can be basically eliminated, and further analysis of the cause of the fault is needed.

　　Self-locking nut titanium alloy in our country, as the main application direction, is mainly used as aerospace components, so the quality of titanium alloy self-locking nut processing and manufacturing requirements also more and more high, due to the alloy material itself is a kind of composite material, use new materials as spare parts, in the process of manufacturing and processing the necessary quality control is crucial.

　　With the development of titanium alloy manufacturing technology and application field expands unceasingly, the technology of casting titanium alloy parts and components on various aspects of performance requirements also increased, at the same time for some special industries and advanced in the field of application of titanium alloy self-locking nuts such key components, increase its structural complexity have become increasingly obvious, like the traditional view that “all the deformation of titanium alloys suitable for casting alloy” thought has also been gradually has been fixed. As alloy using temperature and to increase the intensity of work, the spare parts such as titanium alloy casting into self-locking nut, according to the using area and function will also add a different element, the element also increase the dosage, but at the same time, must consider the alloy casting performance, liquid solidification interval crystalline structure, mechanical properties, etc., so as long as there is on one aspect in the operation of the inaccuracies or omissions appeared, will lead to casting titanium alloy self-locking nut quality problem occurs, as shown in the above crack phenomenon. After considering many factors, the cause of crack is further analyzed.

　　 (I) Factors causing crack of titanium alloy self-locking nut

　　 (1) Influencing factors in casting process

　　The casting of titanium alloy self-locking nut still relies on the new material of titanium alloy as the main body. From the perspective of the properties of the material itself, different from many traditional alloys known, titanium alloy material has very high chemical activity, so it is easy to have violent chemical reaction with N, O and N in the air. Not only that, the refractory used in casting is also very easy to react with titanium alloy. In the casting process of titanium alloy material, the use of mold is an indispensable aspect. Moreover, the investment casting of titanium alloy self-locking nut is much more difficult than the investment casting of aluminum and steel alloy parts, which needs special means to achieve. Mainly with the help of mold by compression, it will be make it shrink, and then on the basis of flattening for a certain treatment and then forming. The choice of die in this process has great influence on the final setting of titanium alloy self-locking nut.

　　By choosing several different shape size mold to test, basic can draw the following conclusions: (1) titanium alloy material as a kind of plastic material, also have their own critical point, the flattening process of titanium alloy self-locking nut, if flattened more than the limit of material itself, destroyed the plasticity of the materials, in this case, because of the long axis and short axis surface curvature is different, so, cracks appeared on the surface and outside surface is not affected.

         (2) Different radius curvature of selected dies will also have an impact. The inner surface of titanium alloy self-locking nut cast with less radius curvature will be seriously deformed, and the inner surface of the short axis will be cracked or deformed to varying degrees. On the contrary, when the radius curvature of the mold is too large, although the outer surface of the long axis is intact, the inner surface of the short axis will crack to different degrees.

　　 (Ⅱ) Influencing factors in the processing process

　The self-locking titanium alloy nuts already formed need further processing, and the most common processing method is heat treatment system. Method for further processing is normally to squish forming material, so at the same time the extrusion die on the chosen option of new type heat resistant mold to ensure furnace to container transportation speed is faster. In order to avoid in the process of heating and extruding just casting titanium alloy is fresh from the lock nut itself as the metal material is easily contaminated by gas pollution especially by oxidation,  it is also necessary to adopt the appropriate protective measures. But usually in the heat treatment, it is easy to make the surface of the metal contaminated because of improper control, although will parts after heat treatment in vacuum under the environment of the processing of solid solution aging, but the surface of the existing pollution still prone to oxidation, the hardness and plasticity of titanium alloy self-locking nut itself.

　　 (3) Influencing factors in the use process　　

      The titanium alloy self-locking nut also has the possibility of cracking in the process of using. As this part is usually used in the joint or reinforcement, it is easy to install due to improper operation caused by wear and damage, or repeated disassembly parts, etc. The titanium alloy self-locking nut was damaged to different degrees, and the wear resistance of the parts was reduced, which is easy to lead to cracking phenomenon.

　Conclusion: From the above analysis, it can be seen that there are many factors affecting the crack of titanium alloy self-locking nut. Each factor cannot be ignored, so it is important to select the mold with appropriate size and shape and strictly measure the radius of curvature of the mold in the casting of self-locking titanium alloy nuts in the future.　　

      Moreover, in the processing process, the solution step can be advanced, so as to avoid oxidation corrosion and pollution of the nut surface in the solution aging stage; During the use of titanium alloy self-locking nuts, technicians should install them correctly to avoid damage and wear on the parts, strengthen the inspection of the parts with titanium alloy self-locking nuts, maintain them regularly, and replace the defective parts in time.

      It can be seen that by improving the technical level and strengthening the awareness of prevention, the crack of titanium alloy self-locking nut can be effectively prevented, so as to avoid the occurrence of faults.