铝合金圆板上碳化硅涂层热应力有限元分析

假设涂层和基体界面处于理想结合状态下,且不考虑涂层中缺陷的影响,采用有限元软件(ANSYS8.0)分析了5～30μm厚碳化硅涂层中的热变形和热应力.结果表明,在平面法线方向(z方向)上,涂层/基体系统在热应力作用下发生热屈曲,圆心处z方向热变形为0.05mm,而在边缘处2方向热变形为-0.08mm;热变形呈现轴对称的特点,其危险区域在上下表面的圆心部位,该处的热变形最大,也最容易造成该处涂层胀裂失效;对于不同直径的圆板,发生热屈曲时均存在一个类似的z方向零位移环,并且该z方向零位移环的位置与圆盘半径有关,而与涂层厚度无关;计算得出5～30μm厚碳化硅涂层中的热应力约为2.45～11.00GPa,该值远高于1mm厚4043铝合金基体中产生的热应力(24.68MPa);圆板热屈曲后拱起高度和热应力均随涂层厚度的增加而增加.     

热处理过程中SiCP/2024Al复合材料的热应力分析

为研究热处理过程中SiCP/2024Al复合材料的热应力的变化规律,及热处理工艺对SiCP/2024Al复合材料热残余应力的影响,利用Marc有限元软件对淬火和冷热循环热处理过程中的SiCP/2024Al复合材料的热应力进行了数值模拟.研究结果表明:热处理过程中,颗粒和基体的界面附近会产生很大的热应力场,并且在SiC颗粒的尖角处产生热应力集中;经淬火处理后的SiCP/2024Al复合材料的热残余应力与基体的屈服强度接近,但经过冷热循环处理后的SiCP/2024Al复合材料中的热残余应力明显降低.     

碳纳米管增强镁基复合材料热残余应力的有限元分析

为了探寻Ni层厚度对镀镍碳纳米管增强AZ91D镁基复合材料(Ni-CNTs/AZ91D)中热残余应力的影响, 在实验基础上, 建立不同Ni层厚度时Ni-CNTs/AZ91D复合材料的有限元模型, 模拟了Ni-CNTs/AZ91D复合材料中热残余应力的分布。研究发现: 在碳纳米管表面镀镍能够明显降低Ni-CNTs/AZ91D复合材料中的热残余应力。Ni-CNTs/AZ91D复合材料中, 热残余应力在Ni层厚度为6nm时最小; Ni层厚度由2nm增至6nm时, 热残余应力随着Ni层厚度的增加而减小; 当Ni层厚度超过6 nm时热残余应力随着Ni层厚度的增加而增大。复合材料中热残余应力的最大值随碳纳米管表面Ni层厚度的增加向Ni层与基体的界面移动。      

氩气流量对四面体非晶碳膜结构和摩擦性能的影响

利用自主研制的45°单弯曲阴极电弧沉积系统,通过改变Ar流量(2,5以及10 ml/min),在p型(100)硅基底上制备了四面体非晶碳膜。借助表面轮廓仪测定薄膜厚度和粗糙度变化;采用X射线光电子谱获得薄膜微结构信息,利用残余应力仪和摩擦磨损试验机测定薄膜的内应力和摩擦学性能。实验结果表明:随Ar流量增加,薄膜的沉积速率降低,表面趋于光滑;薄膜中sp3含量由2 ml/min时的68%下降至10 ml/min时的55%;薄膜应力值随Ar流量的增大而减小,在10 ml/min处取得最小值;不同Ar流量条件下所制备薄膜的摩擦系数在0.024~0.045之间,且随Ar流量增加而增大。     

弧流对超薄四面体非晶碳膜的结构和性能的影响

使用45°双弯曲磁过滤阴极真空电弧系统(FCVA)制备超薄四面体非晶碳膜(ta-C),研究了弧流对薄膜结构和性能的影响。结果表明:当弧流由40 A增加到70 A时薄膜沉积速率提高,sp3的含量先增加后减小;当弧流为60 A时薄膜sp3的含量达到最大66%,密度也达到最大(3067 kg/m3)。残余压应力随着弧流的增加呈现先增加后减小的趋势,当弧流为40 A时薄膜的残余应力最小(4 GPa)。在碳膜沉积过程中碳源粒子有填充基体凹坑和减少基体缺陷的作用,使其表面非常光滑。超薄ta-C碳膜的表面粗糙度随着弧流的增加先降低后增加,当弧流为50 A时薄膜表面粗糙度最小(0.195 nm)。     

基体温度对中频脉冲非平衡磁控溅射技术沉积类金刚石薄膜结构与性能的影响

利用中频脉冲非平衡磁控溅射技术在不同的基体温度下制备了类金刚石(DLC)薄膜,采用Raman光谱、X射线光电子能谱(XPS)、纳米压痕测试仪、椭偏仪对所制备DLC薄膜的微观结构、机械性能、光学性能进行了分析。Raman光谱和XPS结果表明,当基体温度由50℃增加到100℃时,DLC薄膜中的sp3杂化键的含量随基体温度的升高而增加,当基体温度超过100℃时,DLC薄膜中的sp3杂化键的含量随基体温度的升高而减少。纳米压痕测试表明,DLC薄膜的纳米硬度随基体温度的增加先增加而后减小,基体温度为100℃时制备的薄膜的纳米硬度最大。椭偏仪测试表明,类金刚石薄膜的折射率同样随基体温度的增加先增加而后减小,基体温度为100℃时制备的薄膜的折射率最大。以上结果说明基体温度对DLC薄膜中的sp3杂化键的含量有很大的影响,DLC薄膜的纳米硬度、折射率随薄膜中的sp3杂化键的含量的变化而变化。     

WC—Co硬质合金基体上金刚石薄膜的附着机理研究

金刚石涂层在硬质合金(WC-Co)基体上的附着力,是影响金刚石涂层刀具切削性能和使用寿命的关键因素.采用微波等离子体化学气相沉积(CVD)法在经酸浸蚀脱Co的硬质合金基体上生长金刚石薄膜.通过对金刚石膜/基界面的微观形貌和成分分析,初步认识了金刚石薄膜的附着机理:机械锁合作用对金刚石膜/基附着力有较大贡献;界面热应力和弱中间相的存在是导致金刚石膜自发剥离的主要原因.     

基于膜系设计控制薄膜残余应力的研究

残余应力大的薄膜,容易产生脱膜现象,使得薄膜失去所需功能.在激光薄膜领域,残余应力也是薄膜激光损伤阈值难以提高的原因之一.基于热收缩效应模型和弹性力学原理,从薄膜膜系着手提出了控制薄膜残余热应力的膜系设计原则,将该原则的评价函数用于薄膜膜系设计中,采用优化方法可以设计出残余热应力可接受的薄膜.     

多层薄膜的热应力研究

薄膜的应力对薄膜性能有着重要的影响.考虑了各个膜层弹性模量不同的情况,建立了多层薄膜热应力的数理模型,计算了典型多层薄膜体系中应力的分布.如果使用0级近似,每层薄膜中的热应力是由基底和膜层之间的热失配决定的,而不受其它膜层的约束;而使用一级近似,每一膜层中的热应力受其它膜层的影响.这种方法为多层薄膜应力的评价提供了依据.     

基底硬度对软薄膜弹塑特性影响的数值研究

以2种不同硬基底和相同软薄膜构成的2种软膜硬基系统为对象,利用ABAQUS软件仿真,分别研究了σr/σy=-1、0、1时纳米压痕过程中不同基底对薄膜弹塑性变形以及力学性能的影响,并以与薄膜同材料的块体试样作为参考。结果表明,同一试样的hf/hmax在σr/σy=-1时较σr/σy=0时减小,随压深的增加而近似线性增大;σr/σy=1时hf/hmax较σr/σy=0时增大,且随压深的增大轻微的线性减小,基底的弹性模量越大,hf/hmax越大。σr/σy=0时试样均出现sink-in现象,σr/σy=1时sinkin加剧而σr/σy=-1时出现pile-up,随着压深的增加,两种应力状态下的sink-in或pile-up均有所减弱;基底的弹性模量越大,hc/hmax越大。     

Preparation and mechanical properties of Al2O3 reinforced by submicrometer Co particles

Al2O3/Co composites were fabricated by vacuum hot-pressing a mixture of -Al2O3 powder and a fine cobalt powder. Submicron-sized cobalt particles were uniformly dispersed into the Al2O3 matrix, and the dispersed type was a more inter-/intragranular one with increases of cobalt content up to 40 wt% Co addition. The growth of cobalt particles occurred with increasing cobalt content. At 50 wt% Co addition, however, the growth as well as coalescence of cobalt particles occurred. The phases formed in the Al2O3/Co composites were f-Co(fcc), h-Co(hcp), -Al2O3, and a small amount of graphite. Significant improvements in bending strength (from 341 to 771 MPa) and fracture toughness (from 3.7 to 6.7 MPam1/2) of the Al2O3/40 wt% Co(23 vol% Co) composite compared to monolithic Al2O3 were achieved by dispersing submicron-sized Co particles into the Al2O3 matrix. The improvement in bending strength was attributed to the compressive thermal residual stress in the matrix Al2O3 induced by the mismatch of the coefficients of thermal expansion (CTE) between the matrix Al2O3 grains and cobalt particles during cooling from hot-pressing temperature. The fracture toughness of the composite was enhanced by crack bridging, crack deflection, and compressive thermal residual stress.     

多相复合陶瓷刀具材料残余热应力的有限元模拟

以SiC和(W,Ti)C颗粒增强Al₂O₃多相复合陶瓷刀具材料为基础,运用有限元方法详细研究了材料内部残余热应力的大小与分布形态。计算结果发现,单元模型取法、弥散相颗粒大小、分布及其含量均对多相复合陶瓷刀具材料中的残余热应力有较大影响。基体内不仅存在拉应力区,而且存在不同程度和范围的压应力区,拉、压应力区的结构形式与弥散相颗粒的分布方式密切相关。研究表明,残余热应力的存在与材料的力学性能和微观结构有着密切的关系。      

残余热应力对Al2O3/Ni金属陶瓷断裂行为和力学性能的影响

运用残余热应力理论定性地解释也残余热应力对Al2O3/Ni金属陶瓷断裂行为和力学性能的影响，Ni颗粒位于Al2O3晶内或Ni含量低时，在Al2O3-Al2O3晶界产生张应力，易发生沿晶断裂；而其位于Al2O3晶界或Ni含量高时，在Al2O3-Al2O3晶界产生压应力，易产生穿晶断裂。     

火焰喷涂Al2O3/TiO2-NiCrBSi梯度热障涂层的微观组织

采用金相显微镜,SEM,EDAX,XRD等手段研究了1Cr18Ni9Ti基体上氧乙炔火焰喷涂制备的AI2O3／TiO2-NiCrBSi梯度热障涂层的微观结构。结果表明,涂层沿厚度方向陶瓷与合金组元较均匀过渡,二者之间结合良好。涂层制备过程中,陶瓷－合金组元之间没有发生化学反应,无新相生成。当两组元含量相差较大,涂层形成以高组元为基体相,低组元为第二相弥散分布的复合结构;当两组元含量相近时,则以带状分布。     

Mechanical analysis of indentation cracking in Al2O3/ZrO2 nanostructured laminated ceramics

Residual stress is not the only driving force for indentation cracking in Al2O3/ZrO2 laminated ceramics. An additional driving force is induced by martensitic transformation in the plastic zone beneath the indenter, whereas surface residual compressive stress controls the expansion of surface cracks. Contributions of the transformation driving force and surface residual stress are not considered in the traditional indentation and indentation-strength theory. Therefore, fracture toughness value measured by the traditional methods is usually lower than the practical one in Al2O3/ZrO2 laminated ceramics. When the improved SENB (Single edge notched beam method)-indentation-fracture method from Japanese Industrial Standard (No. JIS R 1607-1990) is used to measure fracture toughness of Al2O3/ZrO2 laminated ceramics, the value is more reliable.     

涂层基体条件对梯度涂层残余应力影响研究

采用有限元法，对结构一定的Al/Ni-ZrO2梯度涂层在基体条件改变时涂层的残余应力进行了分析，结果表明，基体材料的热膨胀系数对涂层的残余应力有显著的影响，对于基体为圆柱形的涂层，其基体与涂层界面的残余应力梯度，最大轴向拉应力均随热膨胀系数的增大而线性增大，表面纯陶瓷层与次层界面残余应力梯度则随之减小，增大基体的直径和厚度，可缓和涂层残余应力，并在基体直径为36mm,厚度为20mm时各残余应力基本稳定。     

Al_2O_3对高速火焰喷涂镍基涂层抗热疲劳性能的影响

为了提高连铸结晶器的使用寿命和生产效率,利用高速火焰喷涂(HVAF)技术在铜基体上制备了镍基涂层,探讨了喷涂粉末中不同比例的Al2O3对镍基涂层抗热疲劳性能的影响及其机理.结果表明:添加50%Al2O3的镍基涂层,抗热疲劳性能得到了明显的提高;Al2O3颗粒的添加,有效地增加了涂层的压应力,提高了涂层与铜基体之间的结合强度,从而显著地提高了涂层的抗热疲劳性能.     

Residual stress development in Pb(Zr,Ti)O3/ZrO2/SiO2 stacks for piezoelectric microactuators

The residual stress of multilayers in piezoelectric microelectromechanical systems structures influences their electromechanical properties and performance. This paper describes the development of residual stress in 1.6 μm Pb(Zr_0.52,Ti_0.48)O₃ (PZT)/0.3 μm ZrO₂/0.5 μm SiO₂ stacks for microactuator applications. The residual stresses were characterized by wafer curvature or load-deflection measurements. PZT and zirconia films were deposited on 4-in. (100) silicon wafers with 0.5 μm thick thermally grown SiO₂ by sol–gel processes. After the final film deposition, the obtained residual stress of PZT, ZrO₂, and SiO₂ were 100–150, 230–270, and − 147 MPa, respectively. The average stress in the stack was  80 MPa. These residual stresses are explained in terms of the thermal expansion mismatch between the layers and the substrate. Load-deflection measurements were conducted to evaluate localized residual stresses using released circular diaphragms. The load-deflection results were consistent with the average stress value from the wafer curvature measurements. It was found that more reasonable estimates of the stack stresses could be obtained when mid-point vertical deflection data below 6 μm were used, for diaphragms 0.8–1.375 mm in diameter.     

Influence of Ti/TiN bilayered and multilayered films on the axial fatigue performance of Ti46Al8Nb alloy

The effects of Ti/TiN bi- and multilayered films on the fatigue performance of the Ti46Al8Nb alloy were investigated. Ti/TiN films with a total thickness of 1 μm were deposited on the Ti46Al8Nb alloy substrate by the hollow cathode deposition method. The samples were examined with various analytical techniques including nanoindentation, scratch test, stripping layer substrate curvature test and scanning electron microscopy. The results show that multilayered Ti/TiN films can enhance the fatigue strength of the Ti46Al8Nb alloy, whereas bilayered films have no obvious effect. Compared with the bilayer, the multilayer exhibits higher hardness, higher residual compressive stress and higher adhesion strength to the substrate. It is also demonstrated that the multilayer is responsible for retarding fatigue crack growth. All the superior properties make the hard Ti/TiN multilayer to be an effective protection coating for the enhanced fatigue strength of the brittle substrate.     

Fracture toughness of selectively reinforced Al2124 alloy: precrack tip in the aluminium alloy side

Abstract

The fracture toughness of Al2124/Al2124+SiC bimaterials is affected by thermal residual stresses, elastic/plastic mismatch, precrack tip position, and failure mechanism. When the precrack tip is in the Al2124 side, final catastrophic failure occurs when ductile fracture of the Al2124 layer between the precrack tip and the composite side takes place, followed by fracture of the composite layer. For a precrack tip 2·0 mm from the interface, K _Q(5%) values are lower than the 'Al2124 only' value due to the near crack tip tensile residual stresses and higher stress triaxiality within the Al alloy ligament. At 0·5 mm from the interface, K _Q(5%) values increase and are usually as high as the 'Al2124 only' value due to the stronger shielding of the elastic/plastic mismatch. If the precrack tip is 2·0 mm from the interface, K _crit values of the bimaterial are higher than the 'Al2124 only' value and this is deduced to be due to the elastic/plastic mismatch shielding. At 0·5 mm from the interface, K _crit values are reduced because both the near tip tensile residual stress is higher and stress triaxiality levels of the ductile ligament are higher, although the elastic/plastic mismatch shielding is also higher at this position.