Supervisor(s): China Association for Science and Technology Sponsor(s): Chinese Society of Aeronautics and Astronautics (CSAA); AVIC Beijing Institute of Aeronautical Materials (BIAM) CN：11-3159/V
Journal of Aeronautical Materials is supervised by China Association for Science and Technology, and sponsored by Chinese Society of Aeronautics and Astronautics (CSAA) and AVIC Beijing Institute of Aeronautical Materials (BIAM). The journal provides the latest academic researches regarding Chinese aeronautic and astronautic materials, in order to promote aeronautic and astronautic technologies, make a platform for scientific researchers, and push forward the progress of aeronautic and astronautic materials. Its scope covers aeronautic and astronautic materials, preparation processing, calculation, simulation, properties and characterization of materials. It also reviews on aeronautic and astronautic materials with promising applications.
The journal is included in CA, SA, Pж(AJ), CSCD.
Editor-in-Chief Dai Shenglong
Associate Editor Cao Chunxiao, Tao Chunhu, Lian Jianmin, Jin Haipeng
The surface integrity of carburized M50NiL steel was studied by optical microscope, scanning electron microscope (SEM), atomic force microscope (AFM), microhardness tester and residual stress tester. The fatigue properties of the two specimens were measured by the rotating bending fatigue test, and the fatigue test results were simulated and analyzed. The results show that the rotating bending fatigue of carburized M50NiL steel is originated in the sub-surface in the ideal case without considering the surface processing defects. The surface stress concentration factor produced by general grinding causes the fatigue source to be moved from the surface to the sub-surface. Precision grinding improves the surface quality by optimizing the grinding process, effectively restrains the stress concentration of the working surface, and returns the fatigue source from the surface to the sub-surface. The maximum rotating bending fatigue life can be increased by 30 times and the average is 15 times.
A modified Tanaka-Mura model was carried out to derive the equivalent stress amplitude at stress ratio R = −1 of complex fatigue stress and the effect of compressive residual stress on fatigue life. Then, the fatigue of notched specimens with gradient surface strengthening layer was investigated by means of numerical simulation. The results indicate that the fatigue initiation life and the initiation site of notched specimen are related with the thickness of the strengthening layer, the surface-to-internal hardness ratio and the residual stress. There is a critical thickness. If the strengthening layer thickness is less than the critical value, fatigue crack is initiated at the interface of the matrix and the strengthening layer, otherwise, at the surface of the notch root. The critical thickness value is increased with the increase of surface-to-internal hardness ratio. Residual compressive stress has little effect on the fatigue initiation life, but the residual tensile stress decreases the fatigue initiation life obviously.
To improve the fatigue resistance of bolt connecting hole, the effect of double cold expansion (DCE) of hole on the fatigue life of TB6 titanium alloy was investigated. The fatigue fracture, surface roughness, residual stress, hardness and microstructure of the hole wall were characterized by scanning electron microscope (SEM), roughmeter, X-ray diffractometer (XRD), microhardness tester and optical microscope. The mechanism of DCE on the fatigue life of hole was also investigated. The results show that the mean value of the fatigue life of DCE specimen is much higher than that of the interference fit specimen. The surface integrity of the hole wall is improved after DCE. The roughness decreases remarkably. The deep surface strengthening layer with high hardness and deep residual compressive stress field is formed around the hole through severe plastic deformation of the microstructure of the hole wall. It is considered that the improvement of surface integrity plays an important role on the enhancement of fretting fatigue life.
The paper presents the domestic and overseas current status of the steel applied to aircraft landing gear in combination of the design concept and requirements for aircraft landing gear. The application features and concept of the steel used for landing gear are summarized and the domestic and overseas status is compared. For the moment, the low-alloy ultra-high strength steel and high-alloy ultra-high strength steel are all being used in the material system for aircraft landing gear steel, and the complete technical system for its anti-fatigue manufacturing is built. At present, China’s development and application of high strength steel applied to aircraft landing gear is at the world advanced level. At last, the prospect for future development is analyzed.
Ultra-high strength steel with high tensile strength, good toughness, high specific strength, modulus and other characteristics are widely used in aviation, aerospace, national defense and other fields. Ultra-high strength steel is preferred material for aircrafts, aero-engines and other aviation equipment. The application of ultra-high strength steel represents a country’s highest level of steel research and production, and it is also an important symbol of the development of national science and technology and national defense industry. The development and application of high purity smelting technology for manufacture of ultra-high strength steels in China and overseas are briefly reviewed in the paper, and then the control ability about the impurity elements such as S, P, O and N in typical ultra-high strength steels, and the research status and development trend of non-metallic inclusions control are discussed. The progress in research work of high purity smelting technology for ultra-high strength steels carried out by the authors in recent years is introduced. It shows that the control level of impurity elements and non-metallic inclusion has been greatly improved, and it also creates a new route for China to manufacture the ultra-high strength steel with high alloy, especially with high purity for ultra-high strength stainless steel, bearing steel and gear steel. Finally, the development direction of high purity smelting technology of ultra-high strength steel in China is pointed out.
The fatigue curves of C250 steel, TA29 titanium alloy and FGH96 powder metallurgy (PM) superalloy with stress concentration coefficients
Kt = 1 and
Kt = 1.7 were investigated, and the effect of shot peening on the fatigue curve under the stress concentration condition was also studied. The results show that the 10
7 conditional fatigue limits of C250 steel, TA29 titanium alloy and FGH96 PM superalloy decrease from 757 MPa, 366 MPa and 566 MPa to 526 MPa, 240 MPa and 465 MPa respectively while the stress concentration coefficients increase from
Kt = 1 to
Kt = 1.7, indicating that the three kinds of high-strength materials have the stress concentration sensitivity of fatigue limit obviously. Moreover, after shot peening, the fatigue limits rise to 597 MPa, 297 MPa and 530 MPa respectively when the
Kt is 1.7, which indicates that shot peening can mitigate fatigue limit stress concentration sensitivity of high-strength alloys from a technological point of view. On the other hand, the 10
5-cycle and 10
7-cycle strength differences of titanium alloy and PM superalloy are reduced with the increase of stress concentration coefficient, showing that shot peening can reduce the dispersion of fatigue test data.
The microstructural and crystallographic features of the surface deformation layer in Al-Zn-Mg-Cu alloy induced by milling were investigated by means of transmission electron microscope (TEM) and precession electron diffraction (PED) assisted nanoscale orientation mapping. The result shows that the surface deformation layer is composed of the top surface of equiaxed nanograins/ultrafine grains and the subsurface of lamellar nanograins/ultrafine grains surrounded by coarse grain boundary precipitates (GBPs). The recrystallized nanograins/ultrafine grains in the deformation layer show direct evidence that dynamic recrystallization plays an important role in grain refining process. The GBPs and grain interior precipitates (GIPs) show a great difference in size and density with the matrix due to the thermally and mechanically induced precipitate redistribution. The crystallographic texture of the surface deformation layer is proved to be a mixture of approximate copper {112} <111>, rotated cube {001} <110> and F{111} <112>. The severe shear deformation of the surface induced by milling is responsible for the texture evolution.
A new concept of intrinsic
S-N curve was proposed. Then the influencing factors caused by manufacture were introduced based on the fatigue life double-parameter model and the effects of influencing factors caused by manufacture on
S-N curve were discussed. GH4149 was employed to obtain the
S-N curves with different stress concentrations. The specimens had three surface states resulting from different manufacturing processes which were traditional machining process, machining process with surface integrity and advanced surface strengthening technology. The sensitivity of fatigue resistance coefficient (
Mf) and theoretical fatigue limit (
Sc) to
Kt was analyzed. The results show that the fatigue properties of the smooth specimens and notched specimens both are improved after surface strengthening. When the stress concentration is relatively low, the increase of fatigue resistance coefficient (
Mf) plays a more important role for the improvement of fatigue life after surface strengthening. Nevertheless, the improvement of theoretical fatigue limit (
Sc) becomes more and more important with the increase of
Kt. Moreover, it is helpful to analyze the changes of
S-N curve using the influencing factors caused by manufacture for deepening the understanding of anti-fatigue manufacture.
In order to provide the relatively accurate experimental basis for optimizing parameters and controlling surface metamorphic layer, ball end high-speed milling experiments of TC17 titanium alloy were carried out utilizing one of experimental design techniques based on the response surface methodology. The surface roughness model was built, variance analyses were applied to check the significances of surface roughness model and input parameters, and the effect of parameters on surface roughness was analyzed. Meanwhile, the residual stress, microhardness and microstructure under the conditions of high, medium and low levels of parameters were investigated. The results indicate that the model can predict the surface roughness effectively and the feed per tooth and radial depth of cut have an obvious effect on the surface roughness. Residual compressive stresses are detected on all milled surfaces and the surface residual stresses are increased with the increase of the level of the milling parameters. The compressive residual stress layer is approximately 20 μm regardless of the level of milling parameters. The process of thermal softening, then work hardening, and finally tending stabilization is observed in the microhardness profiles. The grains of the surface layer are broken and bent, and the thickness of plastic deformation layer is approximately 10 μm.
Turning experiments and Deform-3D finite element methods were used to study the formation mechanism of surface metamorphic layer on turning GH4169 processed. The investigations were carried out by analyzing the changes of cutting force, temperature, strain field, residual stress, micro-hardness, microstructure, as well as the distribution of the above all along the direction of the depth under various processing parameters. The results show that the surface metamorphic layer is formed due to the thermal-mechanical coupled effects on the microstructure of the material in the machining process. The cutting force, heat and strain of surface material are increased with the increase of machining intensity. Besides the higher strength of machining, the greater changes of plastic deformation, metallographic and grain deformation are acquired. In the range of processing parameters, the depth of temperature layer is 130–200 μm; the depth of strain layer is 100–220 μm; the depth of residual stress layer is 80–110 μm; the depth of hardened layer is 50–80 μm; and the depth of surface metamorphic layer is 2.5–5 μm.
