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Acta Metallurgica Sinica(English Letters) 2009年第2期22卷 131-137页

作者： Xiaohua ZHANG daoxin liu Corrosion and Protection Research Laboratory Northwestern Polytechnical University Xi＇an 710072 China

Effects of the temperature, slip amplitude, and contact pressure on fretting fatigue （FF） behavior of the Ti811 titanium alloy were investigated using a high frequency fatigue machine and a home-made high temperature apparatus. The fretting fatigue failure mechanism was studied by observing the fretting surface morphology features. The results show that the sensitivity to fretting fatigue is high at both 350 and 500 ℃. The higher the temperature, the more sensitive to the fretting fatigue failure is. Creep is an important factor that influences the fretting fatigue failure process at elevated temperatures. The fretting fatigue life of the Ti811 alloy does not change in a monotonic way as the slip amplitude and contact pressure increase. This is owing to the fact that the slip amplitude affects the action of fatigue and wear in the fretting process, and the nominal contact pressure affects the distribution and concentration of the stress and the amplitude of fretting slip at the contact surface, and thus further influences the crack initiation probability and the driving force for propagation.

关键词： Fretting fatigue (FF) Elevated temperature Titanium alloy Slip amplitude Creep

Influence of surface coating on Ti811 alloy resistance to fretting fatigue at elevated temperature

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Rare Metals 2009年第3期28卷 266-271页

作者： ZHANG Xiaohua liu daoxin Corrosion and Protection Research Lab Northwestern Polytechnical University Xi＇an 710072 China

An extensive study of the composition distribution, bonding strength, hardness, and wear resistance of a 0Cr18Ni9 film deposited on a Ti811 titanium alloy surface by ion beam enhanced deposition （IBED） is presented. Shot peening was introduced to post-treat the modified surface to synergistically improve the fretting fatigue resistance of the Ti811 alloy at 350°C. The results indicate that the 0Cr18Ni9 film with high density, small grain size, low void radio, and high bonding strength can be prepared using IBED. As a result, the hardness, wear resistance, and fretting fatigue resistance of the Ti811 alloy are increased to a remarkable extent. Compared with shot peening treatment or IBED 0Cr18Ni9 film alone, the Ti811 titanium alloy with an IBED 0Cr18Ni9 film combined with shot peening shows a higher fretting fatigue resistance at 350°C. This is due to the synergistic effect of the high wear resistance of the film surface and the residual compressive stress induced by shot peening.

关键词： titanium alloys fretting fatigue elevated temperature shot peening ion beam enhanced deposition

Finite Element Method Analysis of the Stress for Line Pipe with Corrode Groove During Outdoor Storage

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Acta Metallurgica Sinica(English Letters) 2013年第2期26卷 188-198页

作者： Zhuanzhao YANG daoxin liu Xiaohua ZHANG Northwestern Polytechnical University

The basic principle of corrode groove on outside of steel pipe during storage was analyzed in this paper, namely the water film on the contacted surface of steel pipe, which gathered from humidity in the air, rain or gel, and the suspended particles in air, and the corrosive composition, such as SO2, CO2, O2 and NaCI, in addition to the inhomogeneity of the organization and composition, which lead to the corrosion cell reaction, so that cause the corrosion initial from the contact surface of the between steel pipes, so as to form the corrosion groove. At the same time, the corrosion groove with depth of 0.125t （t pipe wall thickness） on the pipe of φ 1016 mm×21 mm ×70 API SPEC 5L was simulated using the FEM （finite element method）, and the stress and strain distribution of the defect area near corrosion groove were solved at the inner pressure of 12 MPa, 10 MPa, 8 MPa, 6 MPa, 4 MPa and 2 MPa, respectively, which showed that no matter the pressure values were, the maximum stress and strain were lied at the bottom of corrosion defects groove and were in good linear relationship with the internal pressure increasing from 2 MPa to 6 MPa. When the internal pres- sures were greater than 6 MPa, they felled into the nonlinear model and to be yielded or even to be destroyed. In addition, the residual strength and the limit operation pressure of the corrode pipe with the defects groove of 0.125t were calculated or simulated according to the theoretical calculation, the finite element method based on the stress, the finite element method based on strain, DNV-RP-F101, ASME B31G and experimental methods respectively. The results showed that the residual strength and the limit operation pressure of the defective parts solved by the finite element method based on stress were 424 MPa, and 15.34 MPa, respectively, which was very close to that of experimental method, the residual strength was 410 MPa and the limit operation pressure 14.78 MPa. Besides, the results also showed that it

关键词： Finite element methods (FEM) Storage Corrode Groove Stress analysis von Mises equivalent stress

Mechanical and corrosion fatigue behaviors of gradient structured 7B50-T7751 aluminum alloy processed via ultrasonic surface rolling

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Journal of Materials Science & Technology 2020年第5期40卷 88-98页

作者： Xingchen Xu daoxin liu Xiaohua Zhang Chengsong liu Dan liu Corrosion and Protection Research Laboratory Northwestern Polytechnical UniversityXi’an 710072China

In this work,ultrasonic surface rolling process(USRP)was utilized to produce a gradient structured layer on 7 B50-T7751 aluminum alloy,and the mechanical properties and corrosion fatigue behavior of treated samples were *** results reveal that underwent USRP,a 425~m thick gradient structure and a 700~m deep compressive residual stress field are created,aluminum grain size become fine(~67 nm),and the corrosion rate of treated surface reduces by 60.08%owing to the combined effect of compressive residual stress and surface *** corrosion fatigue strength is enhanced to 117%of that of 7 B50 Al alloys by means of USRP due to the introduced compressive residual stress,which is considered as the major favorable factor in suppressing the initiation and early propagation of corrosion fatigue ***,the gradient structure is an important factor in providing a significant synergistic contribution to the improvement of corrosion fatigue performance.

关键词： Aluminum alloy Mechanical properties Corrosion fatigue behavior Gradient structure Compressive residual stress Ultrasonic surface rolling process

Contribution of ultrasonic surface rolling process to the fatigue properties of TB8 alloy with body-centered cubic structure

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Journal of Materials Science & Technology 2021年第2期61卷 63-74页

作者： Dan liu daoxin liu Mario Guagliano Xingchen Xu Kaifa Fan Sara Bagherifard College of Civil Aviation Northwestern Polytechnical UniversityXi'an 710072China Department of Mechanical Engineering Politecnico di MilanoMilan 20156Italy

The effect of ultrasonic surface rolling process(USRP) as a severe plastic deformation technology was investigated on the evolution of microstructure, residual stress and surface morphology of TB8 alloys with body-centered cubic structure. Stress-controlled rotating-bending fatigue tests indicated increased fatigue strength in USRP samples prepared using different number of passes compared to the base material, which was attributed to the presence of gradient structure surface layers. Five subsequent USRP passes resulted in the highest fatigue strength, due to the optimal surface properties including higher extent of grain refinement, larger compressive residual stresses, "smoother" surface morphology and increased micro-hardness. However, the effect of USRP technology on improving fatigue strength of TB8 alloy was not significant in comparison with that of other titanium alloys(for example, Ti6 Al4 V), which was attributed to the notable surface residual stresses relaxation revealed from measurements on postfatigued USRP samples. Electron backscatter diffraction analysis confirmed that fatigue crack initiation occurred in the larger grains on the surface with high Schmid factor. Small cracks were found to propagate into the core material in a mixed transgranular and intergranular mode. Further analysis indicated that grain growth existed in post-fatigued USRP-treated TB8 samples and that the average geometrically necessary dislocations value reduced after fatigue loading.

关键词： Ultrasonic surface rolling process Gradient structure layers Fatigue crack Rotating-bending fatigue TB8 alloys

Improving fatigue performance of Ti-6Al-4V alloy via ultrasonic surface rolling process

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Journal of Materials Science & Technology 2019年第8期35卷 1555-1562页

作者： Chengsong liu daoxin liu Xiaohua Zhang Dan liu Amin Ma Ni Ao Xingchen Xu Corrosion and Protection Research Laboratory Northwestern Polytechnical University

The effect of a gradient nanostructured(GNS) surface layer obtained by ultrasonic surface rolling process(USRP) on the fatigue behavior of Ti-6Al-4V alloy has been studied in this paper. Microstructure, surface topography, surface roughness and residual stress measurements were performed to characterize the surface under different conditions. Rotating bending fatigue tests were carried out to evaluate the fatigue behavior of different treatments. The results present a remarkable fatigue performance enhancement for the Ti-6Al-4V alloy with a GNS surface layer obtained by application of USRP with respect to the untreated condition, notwithstanding its considerable surface roughness due to severe ultrasonic impacts and extrusions. Mechanical surface polishing treatment further enhances the beneficial effects of USRP on the fatigue performance. The significantly improved fatigue performance can mainly be ascribed to the compressive residual stress. Simultaneously, the GNS surface layer and surface work hardening have a synergistic effect that accompanies the effect of compressive residual stress.

关键词： Ultrasonic surface rolling process Fatigue Compressive residual stress Gradient nanostructured surface layer Ti-6Al-4V alloy

Effect of Shot Peening and Plasma Electrolytic Oxidation on the Intergranular Corrosion Behavior of 7A85 Aluminum Alloy

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Acta Metallurgica Sinica(English Letters) 2014年第4期27卷 705-713页

作者： Zuoyan Ye daoxin liu Chongyang Li Xiaoming Zhang Zhi Yang Mingxia Lei Corrosion and Protection Research Laboratory Northwestern Polytechnical University AVIC the First Aircraft Institute

The effects of shot peening（SP） and plasma electrolytic oxidation（PEO） on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85（AA 7A85） were investigated by electrochemical polarization and electrochemical impedance *** intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron *** results show that AA 7A85-T7452 is very sensitive to intergranular *** would significantly improve its intergranular corrosion *** is attributed to the combination action of residual compressive stress and grain *** would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide ***,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.

关键词： 7A85 aluminum alloy Plasma electrolytic oxidation Shot peening Intergranular corrosion Residual stress

Coordinately Improving the Wear and Fatigue Properties of Ti6Al4V Alloy by Designed CrZr-alloyed Layer

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Journal of Wuhan University of Technology(Materials Science) 2018年第5期33卷 1216-1222页

作者： YU Shouming liu daoxin ZHANG Xiaohua liu Chengsong Institute of Corrosion and Protection School of AeronauticsNorthwestern Polytechnical UniversityXi＇an 710072China School of Materials Science ＆ Engineering Xi＇an University of TechnologyXi＇an 710048China

A CrZr-alloyed layer was prepared through a pre-zirconizing and subsequent chromizing treatment on a Ti6Al4V *** the removal of the top Cr deposit and Ti4Cr layers,a（Cr,Zr）-Ti solidsolution layer was *** microstructure,composition,microhardness and toughness of the（Cr,Zr）-Ti solid-solution layer were *** results showed that the pre-addition of Zr played an important role in inhibiting the precipitation of the soft Ti4Cr phase,which in turn allowed us to obtain a material characterized by a remarkable *** and fatigue tests showed that the（Cr,Zr）-Ti solid-solution layer could coordinately improve the properties of the Ti6Al4V *** was mainly due to the good match of hardness and toughness of the（Cr,Zr）-Ti solid-solution *** addition,the gradual change in composition and mechanical properties was conducive to the coordinated deformation between the（Cr,Zr）-Ti solid-solution layer and the Ti6Al4V substrate during fatigue *** reduced the stress concentration in correspondence of the interface between the two materials.

关键词： Ti6Al4V alloy surface alloying wear fatigue hardness and toughness

Microstructure and Tribological Behavior of a TiO_2/hBN Composite Ceramic Coating Formed via Micro-arc Oxidation of Ti–6Al–4V Alloy

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Journal of Materials Science & Technology 2016年第10期32卷 1071-1076页

作者： Ni Ao daoxin liu Shuaixing Wang Qing Zhao Xiaohua Zhang Mengmeng Zhang College of Aeronautics Institute of Corrosion and Protection Northwestern Polytechnical University National Defense Key Discipline Laboratory of Light Alloy Processing Science and Technology Nanchang Hangkong University

A composite coating containing hexagonal boron nitride（hBN） particles and titanium oxide（TiO_2） was formed on the surface of Ti-6Al-4V alloy via micro-arc oxidation（MAO）. The effect of quantity of the hBN-particles added into electrolyte on microstructure, composition, and wear behavior of the resulting composite coatings was investigated. Microstructure, phase composition, and tribological behavior of the resulting MAO coatings were evaluated via scanning electron microscopy, X-ray diffraction, and ball-on-disc abrasive tests. The results reveal that the TiO_2/hBN composite coating consisting of rutile TiO_2, anatase TiO_2, and an hBN phase was less porous than particle-free coating. Furthermore, the presence of hBN particles in the MAO coating produced an improved anti-friction property. The composite coating produced in the electrolyte containing 2 g/L of hBN particles exhibited the best wear *** outer loose layer of the MAO coatings was removed by a mechanical polishing process, which led to a significant improvement in the wear resistance and anti-friction properties of the MAO coatings and highlighted an essential lubricating role of hBN particles in the composite coatings. However, wear mechanism of the MAO coatings was not relevant to the presence of hBN particles, where fatigue wear dominated the anti-fraction properties of the MAO coatings with and without hBN particles.

关键词： Ti-6Al-4V alloy Micro arc oxidation hBN particle Wear

Application of the Same-Stuff and Equal-Strength Laser Cladding Technology on the Repaired Semishrouded Impeller

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稀有金属材料与工程 2012年第S1期41卷 78-80页

作者： Zhang Haicun liu Mingxia liu daoxin Guo Wenyong Zhi Jinhua Zhou Yafeng Xian Shaangu Power CO LTD Xian 710075 Peoples R China NW Polytech Univ Sch Aeronaut Xian 710072 Peoples R China

0Cr17Ni4Cu4Nb powder was used to investigate the same-stuff laser repair(LR)technology on the semishrounded *** improve the repaired effect,heat treatment was used after LR forming *** means of optical microscopy,scan electron microscopy(SEM),micro-hardness tester and tensile tests,the microstructure of the coating was investigated and mechanical properties were *** experimental results show that cladding layer is well bonded to the substrate,the microstructure of the laser repaired zone(LRZ)is coarse martensite which will be refined after *** mechanical property experiments indicate that the micro-hardness and toughness would be increased after heat-treatment,the strength of LRZ after heat-treatment is 1050～1200 MPa,while the strength of normal laser repaired sample is 1000～1050 *** refinement effect due to the heat treatment plays an important role in the improvement of the mechanical properties of *** examination and the real operation of the impeller after repairing also confirmed the reliability of this same-stuff and equal-strength laser cladding technology.

关键词： laser cladding microstructure strength impeller