航空材料学报

2020, 40(2): 1-2.

[Abstract](2165) [FullText HTML] (1406) [PDF 291KB](36)

Abstract:

Deformation mechanism and microstructure evolution of hot extruded GH738 alloy fabricated by spray forming

Yue WANG, Wenyong XU, Na LIU, Liang ZHENG, Hua YUAN, Zhou LI, Guoqing ZHANG

2020, 40(2): 1-7.

[Abstract](4167) [FullText HTML] (2482) [PDF 35976KB](32)

Abstract:
The research on hot deformation including flow behavior, microstructure evolution via EBSD method and the constitutive characteristic model of hot extruded GH738 alloy fabricated by spray forming was conducted by using Gleeble-3500^TM simulator at the temperature range of 950~1150 ℃, strain rate range of 0.001~1 s^–1 and engineering strain of 50%. The results show that the flow stress decreases with increasing of the deformation temperature and decreasing of the strain rate. The peak flow stress of coarse grain GH738 is higher than that of fine grain within the extruded GH738 alloy. The activation energy Q of extruded GH738 alloy is 651.08 kJ·mol^–1. The hot deformation activation energy Q of GH738 alloy is tending to increasing with the decreasing of the original average grain size. The microstructure evolutes from original stretched grain to equiaxed grain with the increasing deformation temperature through the onset of recrystallization. The full dynamic recrystallization microstructure is obtained at the temperature above 1000 ℃ and the microstructure tend to coarsen with the higher deformation temperature.

CAFE simulation of directional solidification structure of low nickel austenitic stainless steel

Chen QIN, Zhao LI, Liping ZHAO, Yajun JIANG, Lichao CHEN, Huimin ZHANG, Zhihua TIAN

2020, 40(2): 8-15.

[Abstract](2413) [FullText HTML] (1419) [PDF 1006KB](34)

Abstract:
In this paper, through the secondary development of ProCAST&CAFE software, the dynamic boundary conditions of solidification process were established, the temperature field and solid fraction in the directional solidification process of low nickel austenitic stainless steel were simulated, and the effect of the pull rate on solidification microstructure was discussed. The results shows that the withdrawal rate is in the range of 15~200 μm/s, as the solidification speed increases, the isotherm becomes dense, gummy zone narrowing. And as the solidification rate increases, the primary dendrite arm gradually refines and the secondary dendrite arm becomes dense and coarse. In addition, as the withdrawal rate increases in the range of 15 to 200 μm/s, the lateral heat dissipation of the edge of the casting is gradually smaller than that of the central longitudinal heat dissipation, and the axial deviation of the dendrites is reduced from 27.66 ° to 25.964 °. At the same time, the comparative analysis simulation results are in good agreement with the experimental results, and the simulation calculation process is more reasonable.

Doping effect of Ce on structure and mechanical properties of NiAl intermetallics

Xuelan HU, Ruizhi LU, Zhilong WANG, Yi LIU, Yaru WANG

2020, 40(2): 16-21.

[Abstract](2687) [FullText HTML] (1548) [PDF 796KB](37)

Abstract:
Based on the first-principles method of the density functional theory, the study analyzed the influence of rare earth element Ce on the structure and mechanical properties of NiAl intermetallics. The study was needed to use Vienne Ab-inito Simulation Package (VASP). The results show that Ce preferentially occupies the Al site in NiAl by comparing formation energy of Ce occupying the Ni site and Ce occupying the Al site. After Ce occupied the Al site, the NiAl supercell is changed, lattice constant is augmented, and as the concentration of Ce increases, the degree of augment in the lattice constant of NiAl gets larger. By analyzing the figures of charge density and state density, it is found that Ce interacts with adjacent atoms and it exists the orbital hybridization and bonding among them. Furthermore, some physical parameters, such as elastic constants, elastic modulus , etc. , were calculated. The results show that Ce reduces the hardness and weakens the stiffness of NiAl. However, through Pugh’s empirical criterion, it’s found that Ce improves the toughness of NiAl. With increasing the concentration of Ce, the toughness of NiAl is better, but the degree of reduction in the hardness and stiffness is larger.

AIP multi-layer coating on DZ125 superalloy substrate

Pengfei ZHANG, Jianping LI, Yan CAI, Xiaoming DING

2020, 40(2): 22-27.

[Abstract](2375) [FullText HTML] (1434) [PDF 1093KB](17)

Abstract:
The deposited-diffusion multi-layer coating (NiCrAlYSi + AlYSi) on top of DZ125 superalloy substrate with the thickness of 60 μm was fabricated by arc ion plating (AIP). The morphology and phase structure of the coating were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. It was found that a lot of β-NiAl phases were formed on the outer layer of the coating. The content of Al element contained in the coating was gradually decreased from the outer layer to the inner layer, and a multi-layer coating with a concentration gradient was formed. This phenomenon was good for forming a dense Al₂O₃ scale on the surface of the coating at high temperature and further improving the self-healing ability of the scale. The oxidation behavior and hot corrosion performance of the coating samples were tested at the temperature of 1150 ℃ and 900 ℃, respectively. The experimental results show that the oxidation-resistant performance of the superalloy substrate is obviously improved in combination of multi-layer coating. Meanwhile, the service temperature and lifetime of the substrate have been effectively improved.

Structure and corrosion resistance of cold spray coating prepared on friction stir welded high strength aluminum alloys

Changyu ZHAO, Ruisheng YANG, Hua ZHANG, Qilong GUO, Tongge SHAO, Guanri LIU

2020, 40(2): 28-34.

[Abstract](2624) [FullText HTML] (1496) [PDF 1881KB](23)

Abstract:
In order to improve the corrosion resistance of the friction stir welding (FSW), the Al coating was prepared on the 2219 aluminum alloy friction stir welding joint via cold spraying technology. The structure and corrosion resistance of the Al coating were characterized by digital microscope, scanning electron microscope and electrochemical workstation. The results indicate that Al coating deposited by cold spraying technology on the FSW joint is a compact structure, and the porosity is 0.77%. There are equiaxed crystals, refined grains and elongated grains in the coating. The interface of the coating is mainly mechanical occlusion. The interface quality of the coating/joint area is obviously better than that of the coating/BM. Coating corrosion sensitivity is lower than that of FSW joints, and the corrosion potential and corrosion current density of the coating are far below the heat affected zone. Cold spray coating reduces the corrosion sensitivity of FSW joints. The intergranular corrosion test shows that the corrosion resistance of the coating is better than that of the FSW joint. In terms of corrosion depth, the coating is only 50% of HAZ after 6 h’s corrosion. The cold spray technology prominently improves the corrosion resistance of the FSW joint.

Numerical simulation of temperature field of wear-resistant anti-corrosion laser cladding self-lubricating coating on 300 M super-strength steel

Ming PANG, Quanxiu LIU

2020, 40(2): 35-42.

[Abstract](2761) [FullText HTML] (1454) [PDF 922KB](34)

Abstract:
In order to improve the anti-wear properties of 300M super-strength steel for aircraft landing gear shock absorbing strut, and to break through the technical bottleneck such as cracks induced by the excessive temperature gradient in laser cladding wear-resistant anti-corrosion self-lubricating coating, the "birth and death" method and the APDL procedure of ANSYS were used to simulate the molten pool's thermal cycle for the 300M super-strength steel's laser cladding wear-resistant anti-corrosion self-lubricating coating. The change of thermophysical parameters with different temperatures for self-lubricant and wear-resistant materials , latent heat in phase change, external heat exchange during laser cladding, laser cladding power, laser cladding scanning velocity and other factors, which affect the temperature field, molten pool, temperature gradient during the laser cladding process were considered. The results indicate that the melting of the substrate requires a combination of laser and molten powder, etc. to bring the effective energy conducted to the region reach the critical value of melting, the increase rate of the melting height of the substrate decreases first and then increases with the increase of the laser power, the decrease rate of the melting height of the substrate decreases first and then becomes larger with the increase of the laser scanning speed. Due to the comprehensive factors of different temperatures and cooling rates in different laser cladding areas, the vertical section of the laser cladding wear-resistant anti-corrosion self-lubricating coating bath is a spoon-shaped molten pool. With the increase of the laser power, due to the difference in the temperature response of the energy input to different regions of the cladding layer, the temperature gradient in the Z-direction and the maximum cooling rate increases. With the increase of laser scanning velocity, the laser input energy decreases, which decreases the combined effects of high-temperature region temperature and rapid local heating of the laser. Meanwhile, the temperature gradient in the Z-direction decreases. Under the condition of maintaining the bonding strength of the cladding layer, the substrate melting zone can be controlled to minimize and lower the temperature gradient by controlling laser parameters reasonably.

Experimental study on fatigue cracking in pre-corroded aluminum alloy 2024-T4 via digital image correlation

Haipeng SONG, Changchun LIU

2020, 40(2): 43-52.

[Abstract](2766) [FullText HTML] (1491) [PDF 1756KB](32)

Abstract:
The fatigue cracking behavior in pre-corroded AA2024-T4 associated with three different levels of maximum stresses and stress ratios via three-dimensional digital image correlation (3D-DIC) was investigated. The spatial-temporal characteristic of crack initiation and propagation was visually displayed through strain field evolution, while the fracture morphology of determined key damage regions was further examined. Experimental results show that localized corrosion penetrated in the edges of specimens promotes fatigue crack initiation and affects crack nucleation location, accompanied with hydrogen embrittlement. Identified crack orientations (range 60°-68° from the loading direction) reveal that the early growth of fatigue crack can be described by K_Ⅰ/K_Ⅱ-mixed mode. Four typical failure modes (single crack fracture, multi-crack coalescence, multi-crack competition and multi-crack parallel growth) are observed and discussed.

Effect of surface integrity evolution on high-temperature fatigue property of FGH95 alloy

Xuekun LUO, Xiaoyan WU, Kechang WANG, Xin WANG, Zhihui TANG

2020, 40(2): 53-60.

[Abstract](2381) [FullText HTML] (1450) [PDF 811KB](46)

Abstract:
Surface integrity state after machining has an important effect on the service life of metal parts and components. The effects of four kinds of surface integration processing methods on the high-temperature fatigue properties of FGH95 alloy were investigated. These four surface processing methods were AR (grinding), GCSSP (grinding and cast steel shot peening), GCSP (grinding and ceramic shot peening) and GDSP (grinding and double shot peening). The surface roughness, residual stress distribution and micro-hardness were characterized by roughness tester, X-ray diffraction (XRD) stress tester and micro-hardness tester. The rotating-bending fatigue life with notched specimens (stress concentration factor, K_t = 1.7) was investigated. The results indicate that the fatigue life of specimens increased largely by GCSSP, GCSP and GDSP compared with AR specimens respectively. Furthermore, GDSP process can obtain the best surface residual stress field distribution, gradient distribution of micro-hardness, surface roughness and improvement of the high-temperature fatigue property.

Experimental and simulation study on Ⅰ-Ⅱ mixed-mode fatigue crack growth of TC4-DT welded joint

Xiaogang LIU, Xiaolin ZHU, Haiding GUO

2020, 40(2): 61-69.

[Abstract](2378) [FullText HTML] (1624) [PDF 1097KB](27)

Abstract:
The crack growth in the structure shows the complex Ⅰ-Ⅱ mixed-mode under the combined tensile and shear fatigue loading. It is of great significance to understand its growth law for evaluating the fatigue life of structures accurately. In order to study the fatigue crack growth law of Ⅰ-Ⅱ mixed-mode welded joint of TC4-DT alloy, compact tension-shear (CTS) specimens were designed and machined, fatigue crack growth tests of welded joints under different loading angles were carried out, curves and fatigue crack growth paths of welded joints under Ⅰ-Ⅱ mixed-mode crack propagation were obtained. Based on the above situation, the equivalent stress intensity factor of Ⅰ-Ⅱ mixed-mode was introduced and the Paris law was employed to deduce the Ⅰ-Ⅱ mixed-mode crack growth rate equation of TC4-DT welded joint. In addition, the extended finite element method (XFEM) was adopted to simulate the fatigue crack growth progress of Ⅰ-Ⅱ mixed-mode crack, and the growth law under different loading modes were obtained and compared with test results. The research shows that the error values of the cracking angle under different loading modes are less than 10% compared simulation with experiment. What's more, the simulated growth paths are agree with the experimental results well. XFEM shows its advantages in simulating crack problems. XFEM can predict mixed-mode fatigue crack growth paths effectively.

Effect of Cu/Ni foil interlayer on microstructure and mechanical properties of laser welded aluminum/steel joints

Xuelong CAO, Gang WANG, Chang XING, Caiwang TAN, Junjun JIANG

2020, 40(2): 70-78.

[Abstract](2515) [FullText HTML] (1304) [PDF 4164KB](27)

Abstract:
Laser welding of aluminum/steel dissimilar metals with Ni and Ni/Cu foils as intermediate layers was studied in this paper. The effect of Cu/Ni foil on microstructure and properties of dissimilar laser welded aluminum/steel joints was systematically investigated. Scanning electron microscope (SEM) and its own energy dispersive spectrometer (EDS) were used to observe and analyze the microstructure of the weld cross section and the element distribution in each area. X-ray diffractometer (XRD) was used to analyze the main phase of the welded joint, and tensile testing of welded joints using an electronic universal testing machine to characterize its mechanical properties. The results show that the tensile strength of the welded joint is greatly improved when Cu/Ni foil is added, compared with Ni foil as the interlayer only. The most obvious effect is that Cu foil with a thickness of 0.02 mm is added. The addition of Cu foil changes the phase composition, element distribution and microstructure of the aluminum/steel interface, and increases the fluidity of the molten pool. In the brittle phase of Fe-Al near the stainless steel side, some Fe atoms are replaced by Cu and Ni to form a new ternary ductile phase, which inhibits the generation of Fe-Al binary brittle intermetallic compounds and effectively improves the weldability of aluminum/steel. Therefore, the addition of Cu/Ni foil can effectively improve the metallurgical reaction in the process of aluminum/steel dissimilar laser welding, so as to improve the mechanical properties of welded joints.

Simulation of lightning protection performance of composite materials with different aluminum spraying parameters

Xiang LU, Miao ZHAO, Zezhong SHAN

2020, 40(2): 79-88.

[Abstract](2341) [FullText HTML] (1309) [PDF 1173KB](43)

Abstract:
In order to study the damage law of composite material full and partial aluminum spraying protection system lightning strike protection caused by lightning current, the lightning damage process and ablation mechanism were analyzed, the energy balance mathematical model of composite laminated plate lightning protection was established. On this basis, a thermal-electrical coupling analysis finite element model of carbon fiber reinforcement plastic (CFRP) with the composite material reference specimen, full-scale spraying aluminum and partial spraying aluminum protection system subjected to lightning current had been established based on ABAQUS, and lightning strike ablation damage was analyzed. The experimental results verified the validity of the simulation, and the lightning ablation damage index DI was introduced.The ablation damage law of three different models under different aluminum coating thickness and different peak lightning current was obtained, and the damage characteristics of composites under two different local aluminum spray protection systems were compared and analyzed. The results show that the relation between the ablative damage area of composite material and the thickness of aluminum coating in the lighting protection system is functionally fitted, both of which satisfy the functional relation of power function.

Ultrasonic pulse-echo reflection and through-transmission methods for porosity measurement in carbon fiber-reinforced polymer composites

Junwei SHI, Songping LIU, Guoli XUN

2020, 40(2): 89-99.

[Abstract](2724) [FullText HTML] (1515) [PDF 2467KB](44)

Abstract:
To detect void defects and determine porosity levels, carbon fiber-reinforced polymer composites were characterized through two kinds of ultrasonic methods, namely pulse-echo reflection and through-transmission. In order to evaluate the ability and the advantages of these two series of experiments, the tests were carried out on a set of specimens, which were manufactured to vary the porosity by altering the pressures used during the cure cycle in an autoclave. The ultrasonic experimental measurements were shown to be in good agreement with metallographic tests in the porosity range of 0.0% to 3.0%. Despite the consistency of both techniques, ultrasonic pulse-echo reflection method has shown itself to be more sensitive to sub-millimeter voids and more capable of evaluating porosity of lower levels, whereas ultrasonic through-transmission method provides better penetration with regard to higher levels of porosity or thicker plates.

2020 Vol. 40, No. 2