Fretting damage of TiN coated zircaloy-4 tube

Fretting has been reported and investigated for over 50 years. However, it is still one of the modern plagues for several industrial machineries. Especially, fretting of fuel rod cladding material, zircaloy-4 tube, in pressurized water reactor (PWR) must be reduced and avoided. Thin hard coatings are employed to improve the tribological properties such as friction and wear of conventional engineering materials. Among these coatings, physical vapor deposition (PVD) TiN coating is probably one of the most frequently and successfully used PVD coatings for the mitigation of fretting wear. Therefore, in this study a fretting wear experiment was performed using TiN coated zircaloy-4 tube as the fuel rod cladding material and uncoated zircaloy-4 tube as one of the grids. The fretting tester was designed and manufactured for this experiment. The number of cycles, slip amplitude and normal load were selected as main factors of fretting. The type of contact was cylinder-to-cylinder contact. The worn surface was observed by optical microscope, 3-D surface measuring instrument and scanning electron microscope (SEM). The results of this research showed that the wear volume of TiN coated zircaloy-4 tube decreased about 1.2–3 times more than uncoated tube and wear mechanisms were brittle fracture, fatigue fracture, adhesion, abrasion and oxidation.     

Mechanical and experimental investigation on nuclear fuel fretting

A mechanical approach to the nuclear fuel fretting problem is studied in this paper to find a possible and efficient way of a wear restraint. Two different contours of the spacer grid spring and dimple were developed to increase the contact area. Fretting wear experiments were carried out for the developed springs and tube specimens. Contact forces of 10 and 30 N, and slip displacements of 50–100 μm were applied under the environment of air as well as water at room temperature. Wear scars on the rods were examined to observe the effect of the mechanical approach on the wear. Especially, the influence of a contour deviation which occurred during fabrication and the wear particle accumulation in the clearance region were investigated in detail. It was found that the contact shape influenced the feature and the behavior of the length, width and volumetric shape of the wear. For the model of fuel fretting wear, equivalent depth (D_e) is suggested as a new parameter that can represent the wear severity.     

Fretting wear mechanisms of Zircaloy-4 and Inconel 600 contact in air

The fretting wear behavior of the contact between Zircaloy-4 tube and Inconel 600, which are used as the fuel rod cladding and grid, respectively, in PWR nuclear power plants was investigated in air. In this study, number of cycles, slip amplitude and normal load were selected as the main factors of fretting wear. The results indicated that wear increased with load, slip amplitude and number of cycles but was affected mainly by the slip amplitude. SEM micrographs revealed the characteristics of fretting wear features on the surface of the specimens such as stick, partial slip and gross slip which depended on the slip amplitude. It was found that fretting wear was caused by the crack generation along the stick-slip boundaries due to the accumulation of plastic flow at small slip amplitudes and by abrasive wear in the entire contact area at high slip amplitudes.     

Experimental Study of the Fretting Wear Behavior of Incoloy 800 Alloy at High Temperature

The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.     

Research on torsional fretting wear behaviors and damage mechanisms of stranded-wire helical spring

Wear on the local area of steel wires’ surface is attributed to torsional fretting on the working process of stranded-wire helical spring. A mathematical model to calculate normal contact force and angular displacement amplitude among the wires is established first when the spring is impacted. With the experimental parameters obtained from the model, the torsional fretting test, which stimulates torsional fretting among the wires in the working process of the spring, is realized successfully on a newly developed fretting tester. Torsional fretting behaviors are strongly dependent upon normal contact force, angular displacement amplitude, and number of cycles. There are three basic types of T-θ curves (short for torque), angular displacement curves during the process of torsional fretting, namely, parallelogram, elliptic, and linear T-θ curves. To analyze the damage mechanisms, distribution maps of oxygen in the wear scar of spring wires under different working conditions are revealed. The damage gets slight in the partial slip region, mainly with the abrasive wear and the slight oxidative wear, whereas the wear mechanisms are mainly the abrasive wear, the oxidative wear, and the delamination, accompanied with obvious plastic deformation in the mixed fretting and slip regions.

     

恒定动能作用下薄壁管的冲击微动磨损行为研究

在新型冲击微动磨损试验机上对四种常见材料的薄壁管(不锈钢、铜合金、纯钛和铝合金)进行了冲击磨损试验,考察了材料属性、冲击能量对薄壁管损伤行为的影响。对其冲击动力学行为、磨损行为进行了分析。研究结果表明,不同材料金属管的能量吸收率、冲击接触力和冲击管变形有显著差异;同一种材料,随着初始冲击动能的增大,冲击过程中接触力、冲击管变形和冲击吸收能也在增大。通过分析磨痕微观形貌和磨痕轮廓,发现薄壁管的冲击磨损抵抗性能与材料属性密切相关;随着初始冲击动能的增加,材料损伤加剧,其损伤机制为疲劳磨损。     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

AZ91D镁合金微动磨损特性研究

采用液压高精度材料试验机考察了平面一球面接触的AZ91D镁合金摩擦副的微动磨损行为，分析了位移幅值、法向载荷和频率等参数对摩擦因数和磨损体积的影响，考察了不同实验条件下的磨斑形貌，并探讨了其磨损机理。结果表明：AZ91D镁合金的微动区域可分为部分滑移区、混合区和滑移区3个区域，粘着磨损、疲劳磨损和磨粒磨损分别是3个区域的主要磨损机制；磨损体积随着位移幅值和法向载荷的增加而增大，但却随着频率的增大而减小。在微动部分滑移区和混合区，摩擦因数随着位移增大迅速增加；在微动滑移区，摩擦因数随法向载荷的增大而减小，而位移幅值和频率对摩擦因数的影响较小。     

中性腐蚀环境下钢丝的微动疲劳行为

在自制的微动疲劳试验机上开展中性腐蚀环境下单根钢丝的微动疲劳实验,考察在相同接触载荷下,不同振幅对钢丝的微动疲劳行为的影响,并用扫描电子显微镜观察疲劳钢丝的磨痕和断口形貌,研究钢丝微动疲劳断裂机制.结果表明:在较大的振幅下,钢丝的微动区均处于滑移状态,而在较小振幅下,钢丝的微动区从滑移状态逐渐转变为黏着状态;磨损机制主要为磨粒磨损、疲劳磨损、腐蚀磨损和塑性变形;钢丝疲劳寿命随着微动振幅的增大而减小;钢丝的疲劳断口可分为3个区域,即疲劳源区、裂纹扩展区及瞬间断裂区.     

Application of influence function method on the fretting wear of tube-to-plate contact

The structural integrity of steam generators in nuclear power plants is much dependent on the fretting wear characteristics of Inconel 690 U-tubes. The influence function method for the tube-to-plate contact model is demonstrated in this study to investigate the fretting wear problems on the secondary side of the steam generator, which are caused by flow induced vibrations between the U-tubes and supports. Two-dimensional numerical contact model is developed and formulated in terms of the Cauchy singular integral equation. The distributions of normal pressures, shear stresses and displacement fields are derived between two contact bodies which have similar elastic properties. Based on the algorithms for normal pressures and relative slip, a numerical approach is developed to simulate the fretting wear of tube-to-plate contacts. The work rate model is adopted in this study to find the wear amounts between two materials. The results are compared with the solutions by finite element analyses to validate the application of the present method to fretting wear problems.     

Fretting wear of carburized titanium alloy against ZrO2 under serum lubrication

Fretting wear of carburized titanium alloys was investigated on the universal multifunctional tester (UMT) with the ball-on-flat fretting style under bovine serum lubrication. The tangential load and friction coefficient during the fretting process were analyzed, and the evolution of fretting log during the fretting process was investigated to understand the wear mechanism of the titanium alloy and carburized titanium alloy. Furthermore, the wear scar was examined using a SEM and three-dimension surface profiler. It was found that the friction coefficient of the titanium alloy increased faster than that of carburized titanium alloy in the first stage under serum lubrication, and then remained steady with a similar value in the second stage. The Ft-D curve indicated that there was wear mechanism transition from gross slip to mixed stick and slip. Finally, it was observed that there was a slight damage of the titanium alloy and carburized titanium alloy showed excellent performance during the fretting wear process under serum lubrication. All of the results suggested that carburized titanium alloy was a potential candidate for the stem material in artificial joints.     

Effect of contact load on fretting fatigue behaviour of steel wires

Abstract

The tension–tension fretting fatigue tests of steel wires were performed on a self-made fretting fatigue test equipment under contact loads ranging from 40 to 70 N and a strain ratio of 0·8. The results showed that when the contact load increased, the fretting regime of steel wires transformed from gross slip regime to mixed fretting regime. The fretting fatigue life in the mixed fretting regime was significantly lower than that in the gross slip regime. The main fretting wear mechanisms in the gross slip regime, where there were serious fretting damage and a lot of wear debris, were abrasive wear and fatigue wear. Microcracks were observed in the fretting scar of the mixed fretting regime, and the main fretting wear mechanisms were adhesive and fatigue wears. The fretting wear scar was the fatigue source region, and the fatigue fracture surface could be divided into three regions.     

四种核电用包壳材料的微动磨损性能研究

在切向微动磨损试验机上对4种核电用包壳材料(Zr合金、Zr/Cr涂层、FeCrAl和ODS-FeCrAl)进行切向微动磨损试验,考察不同包壳材料的微动磨损特性.研究结果表明:不同包壳材料的摩擦因数、耗散能曲线和形变有显著差异;4种包壳材料在切向微动过程中均处于部分滑移区.通过分析磨痕微观形貌和磨痕轮廓,发现ODS-Fe...     

Comparative study on rod fretting behavior of different spacer spring geometries

The resistance to fretting wear is one of the most important parameters of fuel assembly behavior in the reactor. To choose and optimize the designs with regards to this aspect, it is necessary to carry out lots of model tests. This paper describes the results of some of them carried out to determine the fuel rod fretting behavior for different support conditions. The tests were carried out in a special autoclave in water and at room temperature, with the test excitation being applied by an electromagnetic force excitation system. The test objects consisted of a test rod made of zirconium alloy, supported in three spacer grid cells with convex spring profiles of different geometries (i.e. different radii of curvature). The grid-to-rod diametral gap measured 0.1 mm at all locations. Due to these conditions of support, both impact and sliding motions can simultaneously occur at the interface between the contact surfaces. The dimensions of the fretting marks found after testing for 100 h were measured using mechanical instruments and an interferometer. The results showed that fretting increases the more, the smaller the radius of curvature of the convex support elements. This is due, on the one hand, to the smaller contact surface and, on the other, to certain features of the spring design. Given that the shapes of the fretting marks can vary widely, evaluation of fretting on the basis of fretting depth alone is insufficient. Instead, it is important to determine the entire geometry or shape of the fretting mark and thus the wear volume. The conclusions of this study are limited to the explored parameters and must not be extrapolated to any operational product without further investigations.     

690合金材料的微动磨损特性研究

利用微动磨损试验机,在载荷50N以及位移幅值为60μm、100μm、150μm的工况下,研究了690合金材料在常温下的微动磨损行为及其动力学特性,采用激光共焦扫描显微镜(LCSM)和扫描电子显微镜(SEM)观察磨痕微观形貌。结果表明,载荷和位移幅值对微动特征有很大的影响,微动运行完全处于滑移状态。在滑移区,滑移磨损严重、磨痕面积大。690合金材料的磨损机制主要表现为磨粒磨损与剥层的共同作用。     

2.25Cr1Mo传热管切向微动磨损性能研究

钠冷快堆换热器中的冷却剂与构件之间的流致振动会导致传热管发生微动磨损。以钠冷快堆换热器传热管候选材料2.25Cr1Mo钢为研究对象，研究其在不同法向载荷(10、20、30 N)下的切向微动磨损行为和损伤演变规律；采用光学显微镜(OM)、扫描电镜(SEM)及EDS对磨痕的形貌及摩擦化学反应进行分析；通过白光干涉仪获得传热管的磨损量。结果表明：随着法向载荷的增加，2.25Cr1Mo钢的微动模式由完全滑移转变为部分滑移，摩擦因数、磨损体积随着法向载荷的增加先增加后减小；当载荷为10～20 N时，2.25Cr1Mo钢的主要磨损机制为磨粒磨损、分层剥落以及氧化磨损，当载荷为30 N时，主要磨损机制为黏着磨损、塑性变形和氧化磨损。     

The effect of slip amplitude on fretting

The effect of slip amplitude on the mechanism of fretting was investigated. Measurements of wear volume, frictional coefficient and of electrical contact resistance were carried out to clarify the wear mechanism. X-ray microdiffraction was used to observe the difference of wear behaviour, and scanning electron microscopic observations were made.At small slip amplitudes wear damage was small compared with that at larger amplitudes the transition being in the region of 70 μ.At smaller slip amplitudes fretting oxidation, a mild type of wear occurs. At larger slip amplitudes, adhesion and abrasion together with oxidation cause fretting wear. At much larger slip amplitudes, wear similar to reciprocating sliding wear occurs.     

Fretting fatigue of zinc coated low carbon steel EN H320 M

The object of the present study was to investigate the influence of zinc coatings on steel sheets during fretting fatigue and fatigue tests. The influence of the fatigue stress range, normal pressure and amplitude of slip, on the fracture life was studied for both coated and uncoated EN H320 M steel. The wear produced by fretting was measured and compared with the fracture life evolution for different values of slip amplitude. The wear scars and the fracture surfaces were examined by scanning electron microscopy to identify the degradation mechanism. Although zinc films do not influence the fatigue life of the tested steel, when fretting is superposed on to a fatigue stress the coating markedly improves the fracture life.     

Fretting Wear Study of PEEK-Based Composites for Bio-implant Application

The failure caused by fretting wear is a key issue in orthopedic applications as well as other engineering applications. In this study, fretting wear tests were conducted on poly (ether ether ketone) (PEEK), glass fiber reinforced PEEK (GFRPEEK) and carbon fiber reinforced PEEK (CFRPEEK), respectively. Surface characterizations of tested specimens were performed using XRD, microhardness tester, 3D white-light interfering profilometry, SEM and optical microscopy to analyze their wear features. The obtained results showed that the fibers increased the microhardness values and reduced the friction coefficients and wear rates of PEEK-based composites. The fretting regimes of PEEK, GFRPEEK and CFRPEEK were gross slip. The fretting wear mechanisms of those PEEK composites were dominated by abrasive wear, adhesive wear and delamination. CFRPEEK has demonstrated superior fretting wear characteristics, and hence, is a potential bio-implant material for applications such as artificial joints.     

Development of a test device for the evaluation of fretting in point contact

Fretting wear and fatigue may occur between any two contacting surfaces, wherever short‐amplitude reciprocating sliding is present for a large number of cycles. A test device has been developed for the evaluation of fretting fatigue and wear in partial and gross slip conditions. Three similar sphere‐on‐plane contacts run at the same time. Normal force, tangential force or displacement amplitude and constant bulk stress can be controlled and measured separately. Reciprocating tangential displacement is produced with rotational motion, the amplitude and frequency of which can be adjusted and controlled accurately by an electric shaker. The number of load cycles for crack initiation and growth is determined with strain‐gauge measurements near the fretting point of contact. The contact surfaces are measured with 3D optical profilometer before fretting measurements to determine actual contact geometry. The measurements were done with quenched and tempered steel. The initial results indicate that cracks are mostly formed in partial slip conditions, whereas fretting wear is more heavily involved in gross slip conditions. The initiation of a crack occurs near the edge of the contact in the slip direction, where the calculated cracking risk has its maximum value in partial slip conditions. The number of cracks increases as the displacement amplitude, i.e. friction force, increases in partial slip conditions. Copyright © 2008 John Wiley & Sons, Ltd.