Ti(CN)涂层的宏观应力与破坏方式SCIEI

用Nb-752薄长条做衬底材料,按C_2H_2/N_2分别为3/2和2/3两种气体流量比获得Ti(CN)_(3/2)和Ti(CN)_(2/3)两种涂层,由单面镀膜样品弯曲的曲率半径计算出涂层的宏观残余应力约为2—3GPa,其中热应力占10—20％,涂层与基材界面处应力状态分析表明,界面存在一剪切残留应力并计算大小为0.1—0.2GPa。此外,采用应力圆法分析涂层受力状态,讨论了涂层受外载作用下的破坏方式。     

Direct measurement of strain behavior of compression loaded plasma-sprayed yttria-stabilized zirconia

Direct measurement of the stress-strain behavior of stand-alone plasma-sprayed 7 wt.% Y₂O₃-ZrO₂ (YSZ) coatings was made at room temperature. YSZ coatings were evaluated in the as-sprayed condition, and after heat-treatments for 10, 50, and 100 h at 1200 °C using both monotonic and two different cyclic uniaxial compression loading profiles. Heat-treatments were used to change the primarily mechanically interlocked system of lamella to a chemical interlocked system. Monotonic loading of the coatings indicated three different moduli. The first modulus was lower (~ 10 GPa) than observed typically in a plasma sprayed coating. The relatively easy deformation associated with the low modulus was attributed to minor sample crushing near its ends. The second modulus observed was ~ 24 GPa and is due to closure of cracks oriented perpendicular to the stress and lamella sliding and compaction. The third modulus measured ranged from 40 to 48 GPa and represents the elasticity of the material after the easy crack closure and lamella sliding events have occurred. In repeated cyclic loading to a compressive stress of 60 MPa, the coatings were observed to demonstrate large amounts of non-recoverable strain during the first several load/unload cycles, presumably due to permanent sliding and compaction of lamella. Permanent strain tended to a minimum amount after ~ 20 load/unload cycles. Increased cyclic loading from 20 to 320 MPa in 20 MPa increments revealed significant anelastic behavior as evidenced by stress-strain hysteresis loops, particularly in the as-sprayed coating. The elastic moduli of the coatings upon reloading were observed to increase after each subsequent 20 MPa increase in stress applied to the coating to values as high as ~ 80 GPa. This was attributed to an increase in the volume fraction of coating sustaining the load. The amount of non-recoverable strain was highest in the heat-treated coatings indicating a loss of strain tolerance of YSZ coatings during simulated service conditions.     

Residual stress distribution in different depths of TiNi/Ti2Ni-based laser clad coating prepared at different environmental temperatures

This study aimed to effectively reduce the cracking susceptibility of the laser clad coating by enhancing the environmental temperature during laser cladding, and reveal the residual stress distribution in different depths of the coating. The TiNi/Ti₂Ni-based coatings were prepared on Ti6Al4V by laser cladding at different environmental temperatures of 25, 400, 600 and 800 °C. The changes in residual stress along the depth of the coatings were investigated in detail by the nanoindentation method. Results showed that the average residual stress of 2.90 GPa in the coating prepared at 25 °C was largest. With the increase in environmental temperature, the average residual stress was reduced to 1.34 GPa (400 °C), 0.70 GPa (600 °C) and 0 GPa (800 °C). For all the coatings, the residual stress was increased with increasing the distance from the coating surface. Enhancing the environmental temperature can effectively reduce the cracking susceptibility of the coatings.     

Young’s modulus and fatigue behavior of plasma-sprayed alumina coatings

The fatigue behavior and Young’s modulus of plasma-sprayed gray alumina on low-carbon steel substrates were investigated. The investigation of the properties of composites that were defined as “coating-substrate” composites included measurements of the microhardness profile, the residual stress on the top of the coating, and the residual stress profile in the substrate. Fatigue samples were periodically loaded as a cantilever beam on a special testing machine. Failed samples were observed with a scanning electron microscope to determine the failure processes in the coating. The Young’s modulus of the coating was measured by the four-point bending method. Samples were tested both in tension and compression under low (300 N) and high (800 N) loads. The authors’ experiments revealed that the average fatigue lives of coated specimens were nearly two times longer than those of the uncoated specimens. The measurements of Young’s modulus of the coating yielded values that varied between 27 and 53 GPa, with an average value of 43 GPa. Loading in tension caused a decrease in the Young’s modulus of the coating, while loading in compression led to an increase in Young’s modulus. The increase in the lifetime of coated samples was likely due to compressive residual stresses in the substrate, originating during the spray process. The failure of the coating was due to several processes, among which the most important were splat cracking, splat debonding, and the coalescence of cracks through the voids in the coating.     

压裂管柱中陶粒对滑套球座影响

目的：防止陶粒对滑套球座产生破坏。方法利用有限元软件 LS-DYNA 对陶粒冲击滑套球座进行建模,分别改变陶粒与滑套球座表面涂层之间的摩擦系数、滑套球座涂层的厚度、陶粒的粒径、陶粒的速度和陶粒速度相对于滑套球座表面的角度,通过仿真结果观察参数变化对滑套球座表面应力的影响。结果随着陶粒和球座之间的静摩擦系数由0.1增加到0.4,球座的最大表面应力由1.67 GPa增加到2.33 GPa。随着球座表面涂层厚度由3μm增大到6μm,球座的最大表面应力由2.05 GPa减小到0.89 GPa。随着陶粒粒径由50μm增加到80μm,球座的最大表面应力由1.67 GPa增加到3.63 GPa。随着陶粒速度由24 m/s增加到96 m/s,球座的最大表面应力由0.96 GPa增加到2.42 GPa。随着陶粒和球座表面之间的夹角由15°增加到60°,球座的最大表面应力由1.67 GPa增加到4.12 GPa。结论压裂液的性能会影响陶粒和球座之间的摩擦系数,进而影响球座的表面应力大小。球座的表面涂层厚度适当增大可以降低其表面的最大应力,压裂液中陶粒的直径越大,单个陶粒对球座造成的冲击应力越大。可以通过设计使滑套球座表面与中心线的夹角尽量小,以减小球座的最大表面应力。施工排量的增大会加剧球座的破坏。     

Si对Ti-Al-Si-N涂层微观结构及性能的影响

Ti-Al-Si-N涂层是在Ti-Al-N涂层基础上发展而来的一种四元复合涂层。本文综述了Si对Ti-Al-Si-N涂层微观结构、硬度、残余应力、抗氧化性能、热稳定性能、摩擦磨损性能及切削性能的影响。分析表明:Si元素能有效细化晶粒,减少柱状晶,形成新型纳米结构,从而显著提高涂层硬度,可达39 GPa;Si的原子分数超过5%后,涂层残余应力逐渐降低;Ti-Al-Si-N涂层在1 100℃下仍具有良好的抗氧化性能;Si元素使涂层的热稳定性能有很大提高,Ti-Al-Si-N涂层1 100℃氧化后硬度无显著变化;与Ti-Al-N涂层相比,添加Si元素后涂层的摩擦系数由0.7下降至0.5;Ti-Al-Si-N涂层刀具的使用寿命与Si原子分数有很大的关系。     

交变和对钢表面有机涂层阴极剥离行为的影响

对１６Ｍｎ钢与ＣＣＳＢ钢表面环氧沥青基有机涂导以常幅交变应力与腐蚀介质共同作用下的阴极剥离行为进行了研究。结果表明,在没有外加应力条件下,涂层具有良好的界面粘附性;而在交变截荷作用的条件下,应力与局部应变集中通过影响有机涂层的介质传输与界面状态,机涂层在介质中的阴极剥离抗力显著降低,降低幅度随外加应力水平面升高。     

Nanomechanical properties of novel intermetallic coatings developed on austenitic stainless steels by siliconisation in liquid phase

Advanced nanomechanical testing has been used to evaluate mechanical properties of Ni-free Al₁₂(Fe,Cr)₃Si₂ intermetallic coatings grown on the 316 LVM steel by hot dipping in a Al-12.6 at.% Si liquid alloy for various immersion times. Despite the ultrafine-grained structure of the coating (～200 nm), the indentation size effect is more pronounced for the intermetallic coating than for the steel, which is explained by the higher geometrical necessary dislocation (GND) density of the intermetallic coating. To determine the true hardness of the coatings, the model of Nix and Gao was used. It has been shown that the hardness of the coating decreases from 6.2 GPa for the shortest time of immersion (60 s), to 3.36 GPa for the highest immersion time (600 s), which is always much higher than that for the substrate (1.82 GPa). The decrease in both hardness and GND with increasing immersion time is related to the relaxation of residual stresses, which act as a hardening factor. The net effect is an increase of the plasticity index of the coating. Young’s modulus for the intermetallic phase (146 GPa) is lower than that for the austenitic steel 316 LVM (220 GPa), which will favour the load transfer at the bone/metal interface, weakening the so-called “stress shielding effect”. Hence, the nanomechanical properties of this novel Ni-free intermetallic coating, tightly adhered to the substrate, offer a window of opportunity for orthopaedic applications.     

直流基体偏压对Al-Cr-Si-N涂层结构和力学性能的影响

采用电弧离子镀技术在不同直流偏压下沉积Al-Cr-Si-N涂层,研究基体偏压对涂层成分、微观结构和性能的影响。结果表明:Al-Cr-Si-N涂层以密排六方结构和面心立方结构的AlN相为主,随着基体负偏压增加,涂层的衍射峰整体向小角度方向偏移:涂层内残余压应力逐渐增加,最大值为-0.77 GPa;涂层硬度和摩擦系数变化不明显。当基体负偏压为-40V时,Al-Cr-Si-N涂层的特征参数H/E和H~3/E~(*2)均达最大值,分别为0.15和0.37GPa,此时涂层具有最佳的耐磨性能,摩擦系数亦最低。     

Thermal conductivity and elastic modulus evolution of thermal barrier coatings under high heat flux conditions

Laser high heat flux test approaches have been established to obtain critical properties of ceramic thermal barrier coatings (TBCs) under near-realistic temperature and thermal gradients that may be encountered in advanced engine systems. Thermal conductivity change kinetics of a thin ceramic coating were continuously monitored in real time at various test temperatures. A significant thermal conductivity increase was observed during the laser-simulated engine heat flux tests. For a 0.25 mm thick ZrO₂-8% Y₂O₃ coating system, the overall thermal conductivity increased from the initial value of 1.0 W/m K to 1.15, 1.19, and 1.5 W/m K after 30 h of testing at surface temperatures of 990, 1100, and 1320 °C, respectively, Hardness and elastic modulus gradients across a 1.5 mm thick TBC system were also determined as a function of laser testing time using the laser sintering/creep and microindentation techniques. The coating Knoop hardness values increased from the initial hardness value of 4 GPa to 5 GPa near the ceramic/bond coat interface and to 7.5 GPa at the ceramic coating surface after 120 h of testing. The ceramic surface modulus increased from an initial value of about 70 GPa to a final value of 125 GPa. The increase in thermal conductivity and the evolution of significant hardness and modulus gradients in the TBC systems are attributed to sintering-induced microporosity gradients under the laser-imposed high thermal gradient conditions. The test techniques provide a viable means for obtaining coating data for use in design, development, stress modeling, and life prediction for various TBC applications.     

中频-直流磁控溅射铝涂层微米压入特性及低温循环性能

为预防TC4钛合金紧固件与机身铝合金之间产生电偶腐蚀,采用中频-直流磁控溅射技术在钛合金表面制备铝涂层,利用SEM、EDS进行微观形貌和成分分析,采用拉伸和划痕法评价涂层结合性能,使用微米压痕法研究涂层硬度、压痕蠕变和循环力学行为,并对涂层进行低温循环性能测试。结果表明:涂层的拉伸结合强度为61.75 MPa,划痕结合力为(2.46±0.37)N,70 m N下硬度为(0.348±0.015)GPa。压痕蠕变加载时间由5 s增加到30 s,蠕变位移从87.0 nm减小至49.3 nm,保载时间由5 s增加到30 s,位移从27.8 nm增大到92.9 nm,硬度随加载及保载时间增加均下降,随循环保载时间和循环次数增加均降低。当保温时间从1 h增加到6 h,划痕形貌由耕犁状向切削状转变,边缘剥离程度加大,末端堆积增加;涂层结合力下降,硬度先升高后降低。     

铂改性铝化物涂层的热生长层内应力研究

研究了镍基高温合金热障涂层系统中铂改性铝化物粘结层在空气中非连续高温氧化生成的Al2O3层内应力状态及相应的粘结层微观结构。利用Raman光激发荧光谱技术,发现铂铝粘结层在900℃氧化初期生成了θ-和α-Al2O3,而在1100℃氧化时,表面则形成连续致密的α-Al2O3层。通过α-Al2O3的光激发荧光谱偏移量,计算得到了热障涂层中热生长层的内压应力略高于3.0GPa。铂改性铝化物涂层表面Al2O3"背脊"处的内应力相对较低,同时由于没有陶瓷层的压制,生成的Al2O3起伏较大,并发生局部的Al2O3脱落。随氧化时间延长,由于Al元素沿晶界扩散较快,导致更多的γ′-Ni3Al在粘结层晶界处形成,粘结层中基本相β-NiAl向γ′-Ni3Al转变,改变了粘结层本身的热膨胀系数,引起热生长层中内应力变化。     

飞行状态下热障涂层的受力行为

本文通过在计算机中建立航空发动机叶片的工作环境,进而模拟在飞行状态下叶片表面涂敷的陶瓷热障涂层的受力行为,获得了陶瓷涂层在热气动载荷作用下应力场分布,并得出应力场分布与涂层结构和叶片几何形状及与承受的载荷之间的关系,提出了进一步提高陶瓷热障涂层的使用寿命的途径。     

用双面氧化弯曲方法测定Al2O3膜生长应力

提出了一种测定氧化膜生长应力的双面氧化弯曲方法,经不象常规弯曲法那样为防止试样一个侧在发生氧化度制保护除层,因而可用于较高温度及较长时间的氧化情况并可测定Ａｌ２Ｏ３膜的生长应力,由于高温下合金及薄氧化膜发生蠕变,从而释放膜内应力。新方法应用于合金的蠕变数据,并采用数值计算来获得氧化膜应力值,用这种方法测定Ｆｅｃｒａｌｌｏｙ（Ｆｅ－２２Ｃｒ－５Ａｌ－０．３Ｙ）合金在１０００℃空气中氧化中形成的Ａｌ２     

NiTi-Nb原位复合材料的准线性超弹性变形EI北大核心CSCD

据文献报道,Nb纳米线增强NiTi记忆合金复合材料可展现超常的准线性超弹特性。为揭示该准线性超弹特性的产生和变形机制,通过真空感应熔炼、锻造、拔丝方法原位合成了NiTi-Nb复合材料丝材。TEM显微分析表明,Nb纳米线沿丝材轴向平行分布在纳米晶NiTi基体中。该材料在经历一次9%的预变形后会展现准线性超弹特性,其屈服强度达1.7 GPa,表观Young's模量约34 GPa,准线性超弹性应变接近5.5%。同步辐射高能X射线原位拉伸实验结果表明,准线性超弹性的产生与以下2点原因有关:(1)复合材料经历预变形后,Nb纳米线和NiTi基体间会产生耦合力,再次加载时,NiTi所受的耦合拉应力可以将局部区域应力诱发马氏体相变所需的外应力降低到零附近,并且耦合力越大,加载初期的相变速率越高,经过适当的预变形后,加载初始就能够持续发生高速率相变;(2) NiTi中耦合拉应力呈梯度分布,使相变应力-应变曲线不再是常见的“平台型”,转变为“硬化型”斜线。     

Effect of strain rate on compressive behavior of a Pd40Ni40P20 bulk metallic glass

Mechanical deformation of Pd₄₀Ni₄₀P₂₀ was characterized in compression over a wide strain rate range (3.3×10⁻⁵ to 2×10³ s⁻¹) at room temperature. The compression sample fractured with a shear plane inclined 42 degree with respect to the loading axis, in contrast to 56 degree for the case of tension. This suggests the yielding of the material deviates from the classical von Mises yield criterion, but follows the Mohr-Coulomb yield criterion. Fracture stress as well as strain was found to decrease with increasing applied strain rate. The compressive stress (1.74 GPa) was also found to be higher than the tensile fracture stress at a quasi-static strain rate. Close examination of the stress–strain curves revealed that localized shear might have occurred at a compressive stress of about 1.4 GPa, much lower than the “apparent” yield stress of 1.74 GPa. However, the stress of 1.4 GPa for shear band initiation is almost the same as the fracture stress measured at a dynamic strain rate of 5×10² s⁻¹. These results suggested that the fracture of a bulk metallic glass is sensitive to the applied loading rate.     

The axial compressive failure of titanium reinforced with silicon carbide monofilaments

Monofilament-reinforced titanium has been subjected to compressive loading, with a range of angles between the fibre axis and the loading direction. Under axial loading, the failure stress is about 4 GPa, which is well below levels predicted for kink band formation. It is proposed that compressive failure occurs under these circumstances by the crushing of individual fibres. A model is proposed for prediction of the composite strength as controlled by this mechanism. Observed strengths are consistent with monofilament crushing stresses of about 8–10 GPa. Composites were also studied after a post-consolidation heat treatment and with weak fibre–matrix interfacial bonding. In both cases, slightly higher compressive strengths were recorded than for the standard material. These increases are attributed to an enhanced matrix yield stress and to a higher monofilament compressive strength, respectively. Under off-axis loading, strengths fell from about 4 GPa at low misalignment angles to just above 1 GPa at an angle of 16°. A transition occurs between fibre crushing at low angles and kink band formation at higher angles. The transition range is around 3–4°, which is consistent with model predictions. Microstructural studies confirmed that the expected failure modes were operative in these two regimes.     

激光熔覆FeCoCrNiNb高熵合金涂层组织及力学性能

采用激光熔覆技术在304不锈钢表面制备了FeCoCrNi、FeCoCrNiNb等摩尔比高熵合金熔覆层,研究了Nb元素对熔覆层组织及性能的影响。采用XRD、SEM、EDS、纳米压痕测试和干滑动摩擦磨损实验等方法,详细分析了2种高熵合金熔覆层的相组成、组织演变、纳米硬度及耐磨性能。结果表明：FeCoCrNiNb高熵合金熔覆层相组成为fcc固溶体及富Nb-Laves相。FeCoCrNiNb熔覆层的纳米硬度(H)、弹性模量(E)、H/E和H³/E²分别为6.066 GPa、231.54 GPa、0.0262和0.0042,远高于FeCoCr Ni熔覆层的3.456 GPa、209.48 GPa、0.0165和0.000 94。随着纳米硬度的增加,FeCoCrNiNb熔覆层的摩擦系数和比磨损率也随之降低,分别为0.519和2.54×10^-6mm³/(N·m)。综上所述,FeCoCrNiNb高熵合金熔覆层具有良好的纳米硬度和耐磨性。     

Influence of Substrate Material on Plain Fatigue and Fretting Fatigue Behavior of Detonation Gun Sprayed Cu-Ni-In Coating

Cu-Ni-In coating was formulated on two substrate materials—Ti-alloy (Ti-6Al-4V) and Al-alloy (AA 6063) fatigue test specimens using detonation gun (D-gun) spray process. Coating on both substrates was dense with low porosity, high hardness, and high surface roughness. Relatively higher surface compressive residual stress was present at the coating on Ti-alloy specimens. In case of the coating on Al-alloy samples, tensile residual stress was also present in some places. Uniaxial plain fatigue and fretting fatigue experiments were conducted on uncoated and coated specimens. The detrimental effect of life reduction due to fretting was relatively larger in the Al-alloy compared to the Ti-alloy. While Cu-Ni-In coating was found to be beneficial on the Ti-alloy, it was deleterious on the Al-alloy substrate under both plain fatigue and fretting fatigue loading. The results were explained in terms of differences in the values of surface hardness, surface roughness, surface residual stress, and friction stress.     

Rolling contact fatigue of post-treated WC–NiCrBSi thermal spray coatings

The aim of this experimental study was to comprehend the relative rolling contact fatigue (RCF) performance and failure modes of functional graded WC–NiCrBSi thermal spray coatings in the as-sprayed and post processed state, by means of Hot Isostatic Pressing (HIPing) and vacuum heating. Functional graded WC–NiCrBSi coatings were deposited by a JP5000 system. HIPing was carried out at two different furnace temperatures of 850 and 1200 °C, while vacuum heating was performed at the elevated temperature of 1200 °C. The rate of heating and cooling was kept constant at 4 °C/min. Rolling contact fatigue tests were conducted using a modified four ball machine under various tribological conditions of contact stress and configuration, in full film elasto hydrodynamic lubrication. Results are discussed in terms of the relative RCF performance of the as-sprayed and post-treated coatings, and also surface and sub-surface examination of rolling elements using scanning electron microscope (SEM), light microscope and surface interferometry.

Test results reveal that performance of the coating was dependant on the microstructural changes due to post-treatment. Coatings heat-treated at 1200 °C displayed superior performance in RCF testing over the as-sprayed coatings at all stress levels (2, 2.3, 2.7 GPa) with emphasis on RCF performance at lower stress load of 2 GPa, where no failure occurred. Improvement in RCF performance was attributed to the diffusion between the carbides and matrix resulting in improved strength. At higher levels of contact stress, failure was surface initiated, and was attributed to initiation and propagation of micro-cracks at the edge of rolling contact region which led to coating delamination.