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Du D.,Northwestern Polytechnical University | Liu D.,Northwestern Polytechnical University | Meng B.,Xian Aircraft International Corporation | Zhang X.,Northwestern Polytechnical University
Science China Technological Sciences

The effects of grit blasting (GB), shot peening (SP) pretreatment and high velocity oxygen fuel(HVOF) sprayed WC-17Co cermet coating on the fatigue properties of the novel ultra-high strength TC21 titanium alloy were investigated with a rotating bending fatigue test machine. The basic properties and surface integrity of the coating were investigated by using X-ray diffraction (XRD), surface roughness meter, microscopic hardness tester, scanning electron microscopy (SEM) and X-ray stress test instruments. The results showed that the residual compressive stress could be introduced into the surface of TC21 alloy by GB and SP pretreatment, and that HVOF sprayed WC-17Co coating was compactly bonded with TC21 alloy substrate and it significantly improved the surface hardness of the substrate. However, there was a certain residual tensile stress in the sublayer of the coating. SP could significantly increase fatigue resistance of TC21 alloy due to the surface residual compressive stress. There was no significant effect on fatigue resistance by GB treatment due to the offset between the influence of surface residual compressive stress and the surface notch effect. The fatigue resistance of TC21 alloy was significantly reduced by HVOF WC-17Co coating prepared with GB pretreatment. This could be attributed to the relaxation of surface residual compressive stress during the HVOF heating process, pore defects and residual tensile stress distribution in the WC-17Co coating with low toughness, and the surface notch induced by GB. The fatigue resistance of TC21 alloy was slightly reduced by HVOF WC-17Co coating prepared with SP pretreatment. This was attributed to the offset between the advantage effect by SP and disadvantageous effect of WC-17Co coating and high temperature factor during the HVOF process. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg. Source

Wang W.,Xian University of Architecture and Technology | Li Y.,Xian Aircraft International Corporation | Wang Q.,Xian University of Architecture and Technology | Wang K.,Xian University of Architecture and Technology | Hai M.,Xian University of Architecture and Technology
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering

TC4 titanium alloy plate was jointed by friction stir welding in air and forced cooling condition separately, and microstructure transformation characteristics in different zones of the joint were investigated by OM and TEM. The result shows that the joint consists of stir zone, thermo-mechanically affected zone and base material, and they have different microstructure characteristics as a result of different thermal cycle and plastic deformation in different zones. Base material annealed after heat rolling is characterized by primary α and β phase. Stir zone is fully lamellar α+β structure, which is mainly controlled by phase transformation from β monophase to lamellar α+β phase in air. Thermo-mechanically affected zone exhibits bimodal microstructure of equiaxed α grain and α+β lamellar microstructure. Its transformation characteristic is dynamic recrystallization and phase transformation. Stir zone is characterized by acicular martensite in forced cooling condition, which is mainly controlled by martensite transformation. Source

Xiao X.D.,Northwestern Polytechnical University | Wang Y.J.,Northwestern Polytechnical University | Zhang W.,Xian Aircraft International Corporation | Wang J.B.,Northwestern Polytechnical University | Wei S.M.,Northwestern Polytechnical University
Journal of Materials Processing Technology

Stress peen forming is widely used in aerospace industry to form the thin components with complex geometry. In the stress peen forming, the prestressing condition is a critical factor that need to be precisely controlled. In this study, the effects of the prestress on the peening deformations are investigated by using static and dynamic simulations. A regularly parked four-shot model is used to study the interactions of adjacent shot treatments. To verify the finite element model with precisely controlled parameters, regularly indenting tests are adopted. The analytical results reveal that the tensile prestress enhances the shot dimple and the plastic region sizes. The contributions of the prestress to the induced bending moments and stretching forces are indicated with two scale factors. Comparison of the single-shot model and regular parked four-shot model shows the peening effects can be equivalent within certain averaging regions. The static and dynamic simulations are compared on dimple sizes and forming effects. Finally, the indenting and peening tests are carried out to verify the analytical results. © 2015 Elsevier B.V. All rights reserved. Source

Quan Y.,Xidian University | Jiang Z.,Xidian University | Huang X.,Chinese Naval Aeronautical Engineering Academy | Li W.,Xian Aircraft International Corporation
Xi'an Dianzi Keji Daxue Xuebao/Journal of Xidian University

Because of being highly dependent on the threshold and lacking the consideration of global solutions, the Nearest Neighbors Algorithm(NNA) will make some mistakes when the density of targets is high. To solve this problem, global search strategy, gating and dynamic programming are used to build a new correlation algorithm-the Global Best Track Correlation Algorithm(GBTCA). In two experiments, both of the two algorithms are run and compared to NNA, GBTCA, which shows that the new algorithm has a higher correct correlation rate and is less dependent on threshold values. Source

Du D.,Northwestern Polytechnical University | Liu D.,Northwestern Polytechnical University | Sun Y.,Xian Aircraft International Corporation | Tang J.,Northwestern Polytechnical University | Zhang X.,Northwestern Polytechnical University
Advanced Materials Research

In this paper, the influence of different machining methods (including rough turning, finish turning, and longitudinal polishing after finish turning) on rotating bending fatigue properties of TC21 which belonged to a new ultra high strength titanium alloy was studied. The influence of machining methods on surface integrity of TC21 titanium alloy was measured by using surface profile measurement, scanning electron microscopy, metallography microscope, micro-hardness instrument and X-ray diffraction residual stress analyzer. And fatigue fractography of specimens was further investigated. Then the mechanism of fatigue resistance which was affected by machining surface integrity was discussed. The results indicated that the fatigue life of finish turning and longitudinal polishing after finish turning was increased 3.96 times and 17.34 times compared with rough turning, respectively. The machining surface integrity had important influence on fatigue property of TC21 titanium alloy, which caused by the differences of surface roughness and texture as the dominant factors, and then the variation in surface micro-hardness, metallographic microstructure and the surface residual stress were not the main factors on three above-mentioned machining methods. By using longitudinal polishing after finish turning processing method for preparation of TC21 titanium alloy parts could ensure good surface integrity and excellent fatigue performance. © (2012) Trans Tech Publications. Source

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