Effect of Different Laser Energy Nitriding on the Fretting Wear Performance of Zr Alloy

The zirconium(Zr)alloy fuel cladding is one of the key structural components of a nuclear reactor and the first and most important line of defense for accommodating fission products.During the operation of nuclear reactors,Zr alloy fuel cladding is subjected to extreme harsh environments,such as high temperature,high pressure and high flow rate for a long period of time.The wear and corrosion resistance of Zr alloys is important for the safe operation of nuclear reactors.Surface modification can effectively improve the corrosion and wear resistance of fuel cladding.Compared with coating technology,nitriding technology does not have problems for bonding between the coating and the substrate.Current research on surface nitriding of Zr alloys mainly focuses on plasma nitriding and ion implantation techniques.Research on laser nitriding of Zr alloy surfaces and their fretting wear characteristics is scarce.In this study,the surface of Zr alloy was treated with laser nitriding at different laser energies.The microstructure of Zr alloy treated with different laser energies and its fretting wear performance were studied.The results showed that after nitriding with different laser energies,the surface of the Zr alloy showed a typical molten state after melting,vaporizing and cooling under the thermal effect of the laser,and this state was more obvious with the increase of the laser energy.At the same time,doping of N atoms and formation of the ZrN phase led to different cooling rates in the molten zone that produced large tensile stresses after cooling.This led to cracks on the surface of Zr alloys after laser nitriding at different energies,and the crack density increased with increasing laser energy.This also led to an increase in the surface roughness of the Zr alloy with increasing laser energy after laser nitriding treatment.Due to the presence of water in the industrial nitrogen,nitrides were generated on the surface of the sample along with some oxides.When the laser energy was 100 mJ,there was no ZrN generation,and N existed mainly as a diffusion layer within the Zr alloy substrate.ZrN generated when the laser energy reached 200 mJ and above,which increased with the increase of laser energy.Due to the generation of ZrN phase and the presence of some oxides,the surface Vickers hardness of Zr alloys after laser nitriding treatment at different energies increased by 37.5%compared to Zr alloys.After laser nitriding treatment,the wear mechanism of Zr alloys changed.For the untreated Zr alloys,the wear mechanism was dominated by delamination and spalling wear,accompanied by oxidative and abrasive wear.The phenomenon of delamination and peeling decreased with the increase of laser energy.Wear mechanisms changed to predominantly abrasive wear with oxidative wear and delamination spalling.The wear volume of sample nitriding with laser energy 400 mJ was reduced by 46.5%compared with that of untreated Zr alloy.

基于FRET构建A型肉毒毒素活性检测的高通量方法

目的利用荧光共振能量转移(FRET)构建针对A型肉毒毒素酶活性检测的高通量体外方法。方法构建只识别A型肉毒毒素的基于双荧光标记底物的重组表达质粒,将其构建的质粒转入大肠杆菌表达系统进行表达,对表达后的荧光标记底物重组蛋白进行纯化和透析并保存备用;利用A型肉毒毒素轻链(ALc)对重组蛋白进行酶切检测活性;对本检测方法的条件进行优化;ALc切割荧光标记底物测定其酶动力学参数K_(m)与K_(cat)值。结果重组表达质粒构建成功,通过大肠杆菌表达系统表达后检测明显出现目的条带,对其纯化后获得的重组蛋白纯度在90%左右,命名重组蛋白为CYA。对CYA通过酶ALc、B型肉毒毒素轻链(BLc)进行酶切鉴定,结果显示CYA只能被ALc酶切产生与预期相符的两个蛋白片段,不能被BLc酶切。对基于FRET底物的条件优化得到:设定滤光片灵敏度在65~110之间;实时动态检测间隔为2 min/次,动态检测时间为30~120 min,底物CYA合适的浓度范围0.5~32μmol/L。CYA在ALc酶作用下随时时间的变化与荧光值528与485的比值作图最小在0.5左右,最大时约为0.9。酶动力学参数测定ALc切割CYA的值K_(cat)值为(5±0.4)s^(-1)和K_(m)为(2.33±0.21)μmol/L。结论成功构建了基于FRET技术的A型肉毒毒素活性检测的高通量体外分析方法。

Dual motion fretting wear behaviors of titanium and its alloy in artificial saliva

A dual motion combined by radial and tangential fretting was achieved on a modified hydraulic fretting wear test rig. The dual motion fretting tests of medical pure titanium （TA2） and Ti6Al7Nb alloy in artificial saliva were carried out under varied contact inclined angles （45° and 60°）, and the maximum imposed load varied from 200 to 400 N at a constant loading speed of 6 mm/min. The effects of the cyclic vertical force and the inclined angle were investigated in detail. Dynamic analysis in combination with microscopic examinations shows that the wear scar and plastic deformation accumulation present a strong asymmetry. The Ti6Al7Nb has better wear resistance than TA2 in artificial saliva at the same test parameters, and with the increase of inclined angle and decrease of imposed load, the wear reduces accordingly. The wear mechanisms of pure titanium TA2 and Ti6Al7Nb alloy under the condition of dual motion fretting in artificial saliva are abrasive wear, oxidative wear and delamination.

Fretting Wear Characteristics of Nuclear Fuel Cladding in High-Temperature Pressurized Water

In pressurized water reactor(PWR),fretting wear is one of the main causes of fuel assembly failure.Moreover,the operation condition of cladding is complex and harsh.A unique fretting damage test equipment was developed and tested to simulate the fretting damage evolution process of cladding in the PWR environment.It can simulate the fretting wear experiment of PWR under different temperatures(maximum temperature is 350℃),displacement amplitude,vibration frequency,and normal force.The fretting wear behavior of Zr-4 alloy under different temperature environments was tested.In addition,the evolution of wear scar morphology,profile,and wear volume was studied using an optical microscope(OM),scanning electron microscopy(SEM),and a 3D white light interferometer.Results show that higher water temperature evidently decreased the cladding wear volume,the wear mechanism of Zr-4 cladding changed from abrasive wear to adhesive wear and the formation of an oxide layer on the wear scar reduced the wear volume and maximum wear depth.

基于FRET成像探究棕榈酰化修饰调节Fyn激酶活性

目的探讨棕榈酰化修饰调节非受体酪氨酸激酶Fyn活性的分子机制。方法利用荧光共振能量转移(fluorescence resonance energy transfer,FRET)技术实时检测细胞中的Fyn活性,并结合棕榈酰化位点缺失和共转染蛋白质酪氨酸激酶(C-terminal Src kinase,CSK)表达质粒研究其分子机制。结果实验发现,(C3,C6)任一位点的棕榈酰化缺失能引起Fyn的高活性表达,且C6位点影响更显著。已知CSK激活后发生膜转移,FRET检测证实其对细胞中的Fyn活性有下调作用,但不能有效调控(C3,C6)棕榈酰化位点缺失的Fyn(GSS)活性。结论本文结果初步支持了Fyn活性受细胞内的物理空间定位分布的一种调控机制假设,即棕榈酰化缺失的Fyn(GSS)受细胞膜上CSK抑制性的调节作用被减弱,从而促进了组成性的高活性表达。

用于血清胰岛素测定的荧光共振能量传递(FRET)免疫检测法的建立

目的研究探讨新型荧光染料Dylight(DL)和金纳米颗粒(AuNP)间荧光共振能量转移(FRET)效应,并将其与免疫竞争法结合构建一种新型胰岛素荧光免疫检测方法。方法分别将胰岛素抗原(Ag)和胰岛素抗体(Ab)与DL和AuNP进行偶联,形成DL-Ag偶联物和AuNP-Ab偶联物。利用它们间产生的FRET效应以及免疫竞争反应,建立针对胰岛素的新型荧光免疫检测方法。然后对该检测方法的检测性能进行评估和实际样品的应用研究。结果该荧光免疫检测方法不仅表现出较高的检测灵敏度(0.015 ng/mL),较快的检测时间(4 min)以及较好的检测特异性,而且成功地用于血清胰岛素的检测,回收率在96.9%~121.1%之间。结论新型荧光染料DL和AuNP间FRET效应可应用于血清胰岛素的荧光免疫检测。

Numerical Simulation of Fretting Fatigue Damage Evolution of Cable Wires Considering Corrosion and Wear Effects

In this paper,a numerical model of fretting fatigue analysis of cablewire and the fretting fatigue damage constitutive model considering the multi-axis effect were established,and the user material subroutine UMAT was written.Then,the constitutive model of wear morphology evolution of cable wire and the constitutive model of pitting evolution considering the mechanical-electrochemical effect were established,respectively.The corresponding subroutines UMESHMOTION_Wear and UMESHMOTION_Wear_Corrosion were written,and the fretting fatigue lifewas further predicted.The results showthat the numerical simulation life obtained by the programin this paper has the same trend as the tested one;the error is only about 0.7%in the medium life area;When the normal contact force increases from 120 to 240 N,the fretting life of cable wire decreases by 25%;When the evolution of wear morphology and corrosion effect are considered simultaneously,the depth of the wear zone exceeds 0.08mm after 600,000 loads,which ismuch larger than 0.04 mmwhen only the evolution of wear morphology is considered.When the evolution of wear morphology and corrosion morphology is considered simultaneously,the damage covers the whole contact surface after 300,000 loads,and the penetrating damage zone forms after 450,000 loads,which is obviously faster than that when only the wearmorphology evolution is considered.Themethod proposed in this paper can provide a feasible numerical simulation scheme for the visualization of the damage process and accurate life prediction of cable-supported bridges.

Friction and wear of 7075 aluminum alloy induced by torsional fretting

The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.

Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires in-creases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.

利用FRET技术检测不同力学条件下T细胞中ERK活性的脉冲现象

目的探索Jurkat T细胞中胞外调节蛋白激酶(extracellular regulated protein kinases,ERK)活性动力学以及基质刚度对ERK活性的影响。方法利用荧光共振能量转移(fluorescence resonance energy transfer,FRET)技术实时观测Jurkat细胞中ERK活性的变化,或细胞处于I型胶原基质胶中检测其影响。结果部分Jurkat细胞中存在ERK活性脉冲现象,频率约为3次/h,FRET振幅变化约为20%。在抗体激活T细胞抗原受体(T-cell receptor,TCR)的条件下,ERK脉冲依然存在,频率和振幅无显著变化。当细胞处于I型胶原水凝胶中,随着胶基质刚度增加,脉冲频率有所下调。结论Jurkat T细胞中存在自发的ERK活性脉冲现象,初步实验显示其频率受基质刚度影响。而该信号波动的生理意义和分子机制仍有待探索。

荧光共振能量转移(FRET)的定量检测及其应用

荧光共振能量转移(Fluorescence Resonance Energy Transfer,FRET)技术被广泛应用于活细胞中生物大分子构象变化和分子间动态相互作用的实时研究.针对光谱串扰和供体受体间的浓度比等困扰FRET效率定量检测的两大难题,已经发展了多种定量检测FRET效率的方法.作者结合自己的研究结果介绍了多种FRET效率定量检测技术在细胞信号转导机制研究中的应用.

FRET技术及其在蛋白质-蛋白质分子相互作用研究中的应用

简要综述了FRET方法在活细胞生理条件下研究蛋白质 蛋白质间相互作用方面的最新进展 .蛋白质 蛋白质间相互作用在整个细胞生命过程中占有重要地位 ,由于细胞内各种组分极其复杂 ,因此一些传统研究蛋白质 蛋白质间相互作用的方法 ,例如酵母双杂交、免疫沉淀等可能会丢失某些重要的信息 ,无法正确地反映在当时活细胞生理条件下蛋白质 蛋白质间相互作用的动态变化过程 .荧光共振能量转移 (fluorescenceresonanceenergytransfer ,FRET)是近来发展的一项新技术 ,此项技术的应用 ,为在活细胞生理条件下对蛋白质 蛋白质间相互作用进行实时的动态研究 。

Fretting wear and friction oxidation behavior of 0Cr20Ni32AlTi alloy at high temperature

The fretting wear behavior of 0Cr20Ni32AlTi alloy was investigated with crossed cylinder contact under 80 N at 300 and 400 °C.Wear scar and debris were analyzed systematically by scanning electron microscopy and X-ray photoelectron spectroscopy.The results show that the friction logs are mixed fretting regime and gross slip regime with the magnitudes of displacement of 10 and 20 μm,respectively.Severe wear and friction oxidation occur on the material surface.A large number of granular debris produced in the fretting process can be easily congregated and adhered at the contact zone after repeated crushes.The resultant of friction oxidation is mainly composed of Fe3O4,Fe2O3,Cr2O3 and NiO.Temperature and friction are the major factors affecting the oxidation reaction rate.The fretting friction effect can enhance the oxidation reaction activity of surface atoms of 0Cr20Ni32AlTi alloy and reduce the oxidation activation energy.As result,the oxidation reaction rate is accelerated.

Effect of nitrogen ion implantation dose on torsional fretting wear behavior of titanium and its alloy

Various doses of nitrogen ions were implanted into the surface of pure titanium, Ti6Al7Nb and Ti6Al4V, by plasma immersion ion implantation. Torsional fretting wear tests involving flat specimens of no-treated and treated titanium, as well as its alloys, against a ZrO2 ball contact were performed on a torsional fretting wear test rig using a simulated physiological medium of serum solution. The treated surfaces were characterized, and the effect of implantation dose on torsional fretting behavior was discussed in detail. The results showed that the torsional fretting running and damage behavior of titanium and its alloys were strongly dependent on the dose of the implanted nitrogen ions and the angular displacement amplitude. The torsional fretting running boundary moved to smaller angular displacement amplitude, and the central light damage zone decreased, as the ion dose increased. The wear mechanisms of titanium and its alloys were oxidative wear, abrasive wear and delamination, with abrasive wear as the most common mechanism of the ion implantation layers.

基于SPHD及FRET技术的蛋白质传感器

蛋白质传感器作为一种分析蛋白质与其他分子之间作用力的有效手段已经越来越显示出其优点,但是蛋白质在基底表面的变性问题对于研究者来说仍然是一个挑战.作者介绍了一种具有高灵敏度的蛋白质传感器,即利用DNA引导固定(DDI)方法,将DNA-蛋白质复合物通过DNA双链特异性杂交固定在硅基底表面,从而有效保持了蛋白质的活性,并且引入荧光共振能量传递(FRET)技术以及电势扫描发卡去杂交(SPHD)技术降低非特异性吸附带来的荧光信号.这种蛋白质传感器在蛋白质识别以及DNA杂交方面具有显著区分不同体系荧光信号的能力.

利用FRET技术在活细胞内观察EGF对PKA作用的时空成像

cAMP依赖的蛋白激酶(protein kinase A, PKA)在细胞生长与分化过程中扮演重要角色,特别是在调节Ras信号通路引起的细胞增殖效应中起着重要作用。为了在活细胞内动态观察表皮生长因子(epidermal growth factor, EGF)对PKA的作用,采用一种可以检测PKA酶活性的报告蛋白(A-kinase activity reporter, AKAR)——这种报告蛋白是利用荧光共振能量转移(fluorescence resonance energy transfer,FRET)原理设计的,使其在人类肺癌细胞(ASTC-a-1)中稳定表达。加入EGF刺激因子后,随时间变化的成像分析显示出在活细胞生理条件下被EGF作用的PKA酶活性变化的时空信息。这些资料为EGF作用PKA提供了直接的实时证据。

基于FRET技术构建破伤风毒素和B型肉毒毒素酶类抑制剂高通量体外筛选方法

目的利用FRET技术构建破伤风毒素和B型肉毒毒素酶类抑制剂高通量体外筛选方法。方法构建针对破伤风毒素和B型肉毒毒素的双荧光标记底物的重组表达质粒,表达并纯化荧光标记底物重组蛋白;利用A型肉毒毒素轻链(ALc),B型肉毒毒素轻链(BLc)和破伤风毒素轻链(TLc)分别对目的蛋白进行酶切反应。对基于双荧光标记底物高通量体外筛选方法的条件进行优化。酶动力学参数分别测定TLc和BLc切割底物荧光标记底物的Km和Kcat值。结果设计并成功构建荧光标记底物的重组表达质粒。表达并纯化后获得纯度为90%左右的重组蛋白,命名为CYVAMP。利用ALc、BLc和TLc分别对CYVAMP进行酶切,CYVAMP能被BLc和TLc识别切割而不能被ALc切割。对基于双荧光标记底物高通量体外筛选方法的条件优化得到:CYVAMP较适宜的范围为0.2~32μmol/L,酶标仪滤光片灵敏度设定的较合适的设置范围在65~110;(对于96孔板)动态实时检测间隔时间2 min较为合适,检测持续时间从30 min到120 min较合适。CYVAMP在内肽酶BLc作用下随反应时间变化与荧光值528与485比值作图最大时在1.5左右,最小在0.5左右。酶动力学参数测定得到BLc酶切CYVAMP的Km和Kcat值分别为(17.6±2.6)μmol/L和(4.16±0.28)s-1。TLc酶切CYVAMP的Km和Kcat值分别为(40.8±3.5)μmol/L和(2.65±0.32)s-1。结论成功构建基于FRET技术的分析法能满足对破伤风毒素和B型肉毒毒素的检测及抑制剂的高通量体外筛选所需。

Fretting wear behavior of Inconel 690 in hydrazine environments

The friction and wear behaviors of Inconel 690 flat against Si3Ni4 ball were investigated using a hydraulic fretting test rig equipped with a liquid container device. The loads of 20-80 N, reciprocating amplitudes of 80-200 μm and two different environments （distilled water and hydrazine solution at temperatures from 25 to 90 ℃） were selected. The results show that the ratio of Ft/Fn is lower in distilled water than that in hydrazine solution at the same temperature in the slip regime. Both the ratio of Ft/Fn and wear volume gradually increase with increasing medium temperature under the given normal load and displacement amplitude. Besides the displacement amplitude and load, temperature also plays an important role for wear behavior of Inconel 690 material. The increase of temperature could reduce the concentration of dissolved oxygen, and promote the absorption reaction of hydrazine and dissolved oxygen. As a result, the oxidative corrosion rate is obviously lowered. Abrasive wear and delamination wear are the main mechanisms of Inconel 690 in distilled water. However, in hydrazine solution the cracks accompanied by abrasive wear and delamination wear are the main mechanisms.

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

Experimental and numerical study on fretting wear and fatigue of full-scale railway axles

This study investigated the fretting wear and fatigue of full-scale railway axles.Fatigue tests were conducted on full-scale railway axles,and the fretting wear and fretting fatigue in the fretted zone of the railway axles were analysed.Three-dimensional finite element models were established based on the experimental results.Then,multi-axial fatigue parameters and a linear elastic fracture mechanics-based approach were used to investigate the fretting fatigue crack initiation and propagation,respectively,in which the role of the fretting wear was taken into account.The experimental and simulated results showed that the fretted zone could be divided into zones I-III according to the surface damage morphologies.Fretting wear alleviated the stress concentration near the wheel seat edge and resulted in a new stress concentration near the worn/unworn boundary in zone II,which greatly promoted the fretting crack initiation at the inner side of the fretted zone.Meanwhile,the stress concentration also increased the equivalent stress intensity factor range DKeq below the mating surface,and thus promoted the propagation of fretting fatigue crack.Based on these findings,the effect of the stress redistribution resulting from fretting wear is suggested to be taken into account when evaluating the fretting fatigue in railway axles.