钛合金TC4表面医用氧化物陶瓷涂层的残余热应力分析

采用有限元方法分析了钛合金TC4表面分别溅射沉积的4种医用陶瓷涂层Ta₂O₅、Nb₂O₅、ZrO₂和TiO₂的残余热应力分布情况,并以Ta₂O₅涂层为例,研究涂层的厚度与结构对残余热应力最大值的影响。结果表明,4种氧化物涂层的残余热应力都表现为拉应力,且应力最大值均位于涂层/基体结合界面的外边缘,其中残余热应力最大值最大的是Ta₂O₅涂层(32.2 MPa),其次是Nb₂O₅(19.7 MPa)和ZrO₂涂层(10.2 MPa),最小是TiO₂涂层(1.03 MPa)。当涂层厚度由1 μm增加到4 μm时,Ta₂O₅涂层的残余热应力最大值呈现先减小后增大的变化趋势,其中涂层厚度为2.5 μm时的残余应力最大值最小。对于不同结构的Ta     

圆钢管加工方法诱导的残余应力分布检测与分析

为了研究圆钢管加工方法诱导的纵向残余应力分布规律,该文采用盲孔法对截面规格为 φ325×8的5组15个不同强度、不同加工方法的圆钢管试件进行了测量。基于测量数据,得到了试件截面残余应力分布和拉、压残余应力的数值大小,研究了埋弧焊、高频焊和热轧三种不同加工方法对残余应力分布的影响。试验结果表明,埋弧焊对圆钢管截面纵向残余应力的影响强于高频焊,高强度焊接圆钢管的残余应力分布比较均匀,且焊缝区最大残余拉应力分布在焊缝两侧各40 mm区域内;普通强度钢管截面的最大纵向残余压应力为0.35σ_y,而Q690高强钢焊接圆钢管截面的最大纵向残余压应力为0.21σ_y,同中点截面的纵向残余应力峰值相比,起焊点和落焊点截面处的纵向残余应力峰值偏小。不同于焊接圆钢管,热轧无缝圆钢管同一截面内外表面的最大纵向残余应力数值大小相同,符号相反,其最大值为0.15σ_y。     

Si3N4/SiC层状结构陶瓷摩擦磨损性能研究

利用Falex多重样品球-三块式的摩擦磨损试验机,重点研究了单层Si3N4陶瓷,9层和5层Si3N4/SiC层状结构陶瓷在不同的外加载荷、不同的界面应力分布大小、不同的表面组成与层状结构陶瓷的摩擦磨损性能的关系.结果表明:随着外加载荷逐渐加大,材料的耐磨损性能降低,表现为达到磨损突变点的时间缩短,磨痕直径变大;界面残余压应力对层状结构陶瓷耐磨损性能的提高起着重要的作用,9层结构陶瓷的界面残余压应力高出5层结构的层状陶瓷20%左右,表现出更高的耐磨损性能;SiC Si3N4两相复合陶瓷极大地提高了材料表面的耐磨损性能,在同样外加载荷下,表现为达到磨损突变点的时间更长,磨痕直径更小.     

紫铜/Al_2O_3陶瓷/不锈钢复合结构钎焊接头残余应力研究

采用有限元数值模拟的方法研究AgCuTi钎焊紫铜/Al_2O_3陶瓷/不锈钢复合结构的形变和残余应力分布情况,并对模拟结果进行实验验证。结果表明:残余应力主要分布在接头区,并且该区形变较小。陶瓷端的残余应力对接头性能影响较大,由于线膨胀系数差异过大,不锈钢陶瓷侧易产生裂纹缺陷,接头倾向于在该区域断裂,紫铜侧陶瓷端TiO反应层的形成导致该区域裂纹的出现,降低了接头的性能。研究各应力分量对最终残余应力的贡献,结果显示环向应力和轴向应力在陶瓷端所产生的拉应力是造成接头强度降低的主要因素。接头拉剪实验表明,接头主要在靠近不锈钢侧的陶瓷端断裂,验证了模拟结果的准确性。     

WC、ZrO2 、Cr2O3 和Al2O3 陶瓷颗粒/ 镍合金复合涂层微观组织结构的分形

采用等离子喷涂工艺, 制备了WC、ZrO₂ 、Cr₂O₃ 和Al₂O₃ 陶瓷颗粒/ 镍合金复合涂层。用X 射线衍射研究了陶瓷颗粒复合涂层相的分布; 用里氏硬度计测量陶瓷颗粒/ 镍合金复合涂层的硬度; 用CSS-1110 电子万能试验机研究陶瓷颗粒复合涂层的弯曲断裂性能。对涂层金相组织结构进行二值化处理, 利用Sandbox 法对陶瓷颗粒在金属基体中的分布进行研究, 得到了不同体积分数下陶瓷颗粒复合材料涂层的分维数。结果表明,陶瓷颗粒/ 镍合金复合涂层分维数随陶瓷颗粒含量的增加而增加, 与陶瓷颗粒种类无关; 陶瓷颗粒/ 镍合金复合涂层硬度和分维数随陶瓷颗粒直径减小而增加。随着分维数的增加, 复合涂层弯曲断裂角下降。      

LD10锻造铝合金残余应力的剥层法实验研究

[摘要]采用逐层切除法测定LD10锻造铝合金试件内的残余应力大小及分布规律。测量了铝合金试件上不同点处残余应力大小及其沿深度方向的变化,较为全面的获得了残余应力的分布规律,比较了其分布特点。结果表明：LD10锻造铝合金内部的残余应力分布较为复杂,在不同部位其分布规律存在较大差异。在材料中心部位所受残余应力为外拉内压,在靠近边缘处部位所受残余应力为外压内拉。     

圆板状SiC/C功能梯度材料残余热应力特征有限元分析

功能梯度材料残余热应力的大小及分布对其性能有效发挥及长期稳定使用有着较大的负面影响,为了尽可能充分发挥材料性能,增加材料的使用寿命,需尽可能减小残余应力以及使其合理分布.本文采用ANSYS有限元分析软件对不同叠层工艺参数的等离子体第一壁候选材料--SiC/C功能梯度材料(FGM)的残余热应力进行了数值模拟,获得了使热应力有效缓和的较适宜的工艺参数,对实际研发制备目标材料也可提供一些理论参照.相关结果表明,适量增加梯度叠层数及中间梯度层厚度可逐步有效缓和残余热应力,同时,针对本文今后应用的仍以炭材料为主体的炭基陶瓷保护层复合SiC/C FGM而言,纯SiC层厚度应取较小值,而叠层成分分布指数应取0.8～1.0为宜.     

Q355钢板对接接头裂纹扩展所致焊接残余应力重分布研究

目的 定量研究裂纹扩展导致的焊接残余应力重分布效应,得到残余应力随裂纹扩展的变化规律。方法 首先采用盲孔法测试了Q355钢板对接接头的初始残余应力;其次利用线切割技术模拟了平行以及垂直于焊缝的裂纹扩展情况,并测试了裂纹扩展导致的残余应力变化量;最后根据测试数据提出了残余应力释放量Δσ与裂纹长度a之间的函数关系式,进一步得到了基于裂纹扩展的应力重分布计算公式。结果 Q355钢板对接焊的焊缝区纵向(沿焊缝方向)存在较大的残余拉应力,拉应力峰值出现在焊趾处,为屈服强度的1.13倍。焊缝区横向存在梯度较大、拉压交替变化的残余应力,压应力峰值出现在焊趾处,大小为52.6 MPa,拉应力峰值出现在距焊缝中心线17 mm处,大小为63.5 MPa。裂纹扩展能显著释放残余拉应力:裂纹沿焊缝中心扩展,横向残余拉应力峰值降低了45.8%;裂纹沿垂直于焊缝方向扩展,焊趾处的拉应力峰值降低了63.3%。结论 裂纹扩展会显著影响焊接构件的残余应力分布,根据实测数据提出的裂纹扩展应力重分布计算公式能够较好地反映残余应力重分布情况。     

新型复相陶瓷刀具材料的研制及切削可靠性研究

研制成功了国内外尚属空白的新型陶瓷刀具材料——碳化硅晶须(SiCw)增韧和碳化硅颗粒(SiCp)弥散补强Al_2O_3陶瓷刀具材料JX-2系列,其硬度为93.5～94.8HAA,抗弯强度为650～750MPa,断裂韧性为7.5～8.5MPa·m~(1/2),并且具有导热性好和成本低等优点。 对原料组分和热压烧结工艺进行了优化设计;证实了晶须和颗粒具有增韧补强的协同作用,根据能量耗散理论,建立了晶须桥联、拔出、裂纹偏转和微裂纹增韧的理论模型;详细研究了该陶瓷刀具材料的界面力学行为及其与材料力学性能的关系,研究了材料的界面作用机理;建立了Al_2O_3/SiCw/SiCp系陶瓷刀具材料界面结合强度L_f和断裂韧性K_(IC)的关系模型,据此可以实现复合陶瓷刀具材料的组分优化设计,缩短复合材料的研制时间。 深入研究了新型复相陶瓷刀具材料的切削性能及其磨损破损机理,并对刀具热磨损和热破损的机理进行了强激光热模拟;研究了该刀具材料力学性能、界面结合强度和刀具破损寿命的随机性,它们的分布规律均较好地服从威布尔分布,首次提出了用界面结合强度评价JX-2陶瓷刀具破损可靠性的新方法。     

残余拉应力的温度依赖性及其对裂纹扩展行为的影响

为研究以高膨胀系数的陶瓷为涂层,低膨胀系数的陶瓷为基体的预应力陶瓷的高温力学性能,本工作以氧化锆为涂层,氧化铝为基体,制得表层为拉应力的“三明治”结构ZrO₂-Al₂O₃(简称ZcAs)预应力陶瓷。同时选用基体与涂层截面比值相近的Al₂O₃-ZrO₂(简称AcZs)预应力陶瓷、纯ZrO₂和纯Al₂O₃陶瓷为参照样。结合不同温度下的弯曲强度测试结果及维氏压痕结果,阐明预应力的存在形式及其对裂纹扩展行为的影响,并研究预应力的温度依赖性。结果表明:ZcAs预应力陶瓷的表层受拉应力,基体受压应力;而AcZs预应力陶瓷的表层受压应力,基体受拉应力。由于拉应力能够促进裂纹扩展,而压应力能够抑制裂纹扩展,因此室温下, ZcAs的强度比纯Al₂O₃陶瓷降低13.2%,而AcZs的强度比纯ZrO₂陶瓷提高25.0%。此外,无论表层是拉应力还是压...     

梯度陶瓷喷嘴残余应力的有限元分析

为了提高喷嘴的抗冲蚀磨损能力,将梯度功能材料理论运用于喷嘴材料的设计中,改传统的均质喷嘴材料为非均质喷嘴材料,提出在梯度陶瓷喷嘴制备中将残余压应力引入喷嘴入口的设计目标.在组成分布指数一定的条件下,针对主要设计参数对梯度陶瓷喷嘴残余应力的影响进行有限元分析,探讨了梯度层厚度、临界梯度层材料组分差对SiC/(W,Ti)C单梯度陶瓷喷嘴残余热应力的影响规律,在组成分布指数取0.5时,优化SiC/(W,Ti)C梯度陶瓷喷嘴梯度层厚和临界梯度层材料组分差.结果表明,残余应力随梯度层厚h及临界梯度层SiC体积组分差的不同产生很大差异,合理设计梯度层厚h及临界梯度层SiC体积组分差可在喷嘴入口形成有效残余压应力,最佳梯度层厚为5mm,临界梯度层SiC组分差小于5%(体积分数).     

多相复合陶瓷刀具材料的设计与制备

陶瓷材料的多相复合与计算机辅助设计是２１世纪先进陶瓷材料的重要发展趋势,章采用理论与实验相结合的方法,建立了多相复合陶瓷刀具材料力学性能与材料组分之间关系的数学模型,采用计算机辅助优化设计技术求得材料的最优组分,在此基础上,利用热压技术制得一种Ａl2O3-SiC-(W,Ti),Ｃ多相复合陶瓷刀具材料,该材料具有良好的综合力学性能。     

Autofrettage of layered and functionally graded metal–ceramic composite vessels

The residual compressive stresses induced by the autofrettage process in a metal vessel are limited by metal plasticity. Here we showed that the autofrettage of layered metal–ceramic composite vessels leads to considerably higher residual compressive stresses compared to the counterpart metal vessel. To calculate the residual stresses in a composite vessel, an extension of the Variable Material Properties (X-VMP) method for materials with varying elastic and plastic properties was employed. We also investigated the autofrettage of composite vessels made of functionally graded material (FGM). The significant advantage of this configuration is in avoiding the negative effects of abrupt changes in material properties in a layered vessel – and thus, inherently, in the stress and strain distributions induced by the autofrettage process. A parametric study was carried out to obtain near-optimized distribution of ceramic particles through the vessel thickness that results in maximum residual stresses in an autofrettaged functionally graded composite vessel. Selected finite element results were also presented to establish the validity of the X-VMP method.     

等离子喷涂ZrC基涂层逐道逐层沉积残余应力模拟与实验验证

采用商用ANSYS14.5软件, 依据复合梁增层力学模型, 采用逐道逐层累积模型模拟了C/C复合材料表面等离子喷涂ZrC基涂层沉积残余应力的特征, 分析了SiC过渡层、第二相(SiC, MoSi₂)和涂层厚度对ZrC基涂层残余应力的影响, 并进行了实验验证。结果表明, SiC过渡层有效缓解了涂层与基体的热失配应力。涂层体系的应力随着涂层厚度的增加逐渐减小, 符合应力松弛和叠加规律。在涂层内部的径向应力以拉应力为主, 基体中主要为压应力, 且在界面边缘存在压应力集中的极限区域, 易使涂层产生裂纹并沿界面扩展。该模拟采用逐道逐层累积的方法更逼近实际喷涂过程, 能更准确预测涂层的残余应力。     

Zr对(Ag-Cu-Ti)-SiCp钎焊SiC陶瓷/钛合金连接层组织结构的影响

使用Ag-Cu-Ti合金粉,SiC粉和Zr粉组成的混合粉末钎料,真空无压钎焊再结晶SiC陶瓷与Ti合金,观察Zr加入前后接头连接层组织结构的变化,研究了Zr的作用．结果表明,Zr加入前,连接层主要由Ag、SiC、Cu—Ti、Ti3SiC2、和Ti-Si相组成．Zr加入后,连接层主要由SiC、Ti1-xC、Ti-Si、AgTi和AgCu4Zr相组成．Zr的加入提高了连接层中Ti的活度,使SiC颗粒表面反应层Ti3SiC2转变,生成了Ti1-zC和TiSi相;提高了Ti与SiC颗粒的反应速度,使SiC颗粒减少;促进Ti与Ag的反应,生成了AgTi．Zr的加入导致连接层流动性的改善、连接层与SiC陶瓷界面结合强度的提高和接头热应力的降低,适量Zr的加入使接头剪切强度明显提高（达23．6MPa）．     

Thermal shock behavior of nano-sized SiC particulate reinforced AlON composites

Aluminum oxynitride (AlON) has been considered as a potential ceramic material for high-performance structural and advanced refractory applications. Thermal shock resistance is a major concern and an important performance index of high-temperature ceramics. While silicon carbide (SiC) particles have been proven to improve mechanical properties of AlON ceramic, the high-temperature thermal shock behavior was unknown. The aim of this investigation was to identify the thermal shock resistance and underlying mechanisms of AlON ceramic and 8 wt% SiC–AlON composites over a temperature range between 175 °C and 275 °C. The residual strength and Young's modulus after thermal shock decreased with increasing quenching temperature and thermal shock times due to large temperature gradients and thermal stresses caused by abrupt water-quenching. A linear relationship between the residual strength and thermal shock times was observed in both pure AlON and SiC–AlON composites. The addition of nano-sized SiC particles increased both residual strength and critical temperature from 200 °C in the monolithic AlON to 225 °C in the SiC–AlON composites due to the toughening effect, the lower coefficient of thermal expansion and higher thermal conductivity of SiC. The enhancement of the thermal shock resistance in the SiC–AlON composites was directly related to the change of fracture mode from intergranular cracking along with cleavage-type fracture in the AlON to a rougher fracture surface with ridge-like characteristics, crack deflection, and crack branching in the SiC–AlON composites.     

Evolution of internal strain during plastic deformation in magnesium matrix composites

Synchrotron radiation diffraction during in situ tensile tests has been used to evaluate the internal elastic strains within the grains of magnesium alloy, AZ31, unreinforced and reinforced with 5 and 10% volume of SiC particles. Composites present initial thermal residual stresses, which are positive (tensile) in the matrix and negative (compressive) in the reinforcing particles. Internal elastic strains evolve in a similar behaviour in the unreinforced AZ31 and in both composites. However, the accumulated elastic strains are reduced in the case of the composite because a part of the applied load is borne by the ceramic particles.     

Joining of C/C composite to TC4 using SiC particle-reinforced brazing alloy

Silicon carbide particles were used as reinforcement in the Ag-26.7Cu-4.6Ti (wt.%) brazing alloy for joining C/C composite to TC4 (Ti-6Al-4V, wt.%). The mechanical properties of the brazed joints were measured by shear strength testing. The effects of the volume percentage of SiC particles on the microstructures of the brazed joints were investigated. It is shown that the maximum shear strength of the joints is 29 MPa using 15 vol.% SiC in the brazing alloy which is greater than that with Ag-26.7Cu-4.6Ti brazing alloy alone (22 MPa). Ti is reacted with SiC particles, forming Ti–Si–C compound in the particle-reinforced brazing alloy. Due to this, more SiC particles in the brazing alloy, the thickness of TiC/TiCu reaction layer near C/C composite decreases. Moreover, SiC particles added to the brazing alloy can reduce the CTE of the brazing alloy which results in lower residual stress in the C/C composite-to-metal joint. Both of the above reasons lead to the increasing of the shear strength of the brazed joints. But excessive SiC particles added to the brazing alloy lead to pores which results in poor strength of the brazed joint.     

Joining of Cf/SiC composite to Ti alloy using composite filler materials

Abstract

C_f/SiC was successfully joined to Ti alloy with Ag–Cu–Ti–W, Ag–Cu–Ti–SiC and Ag–Cu–Ti–TiC mixed powders by some suitable brazing parameters. Microstructure and shear strengths of the preformed joint were investigated. The results showed that the W particulate and reaction products can uniformly distribute in the brazing layer of the performed joint. These composite brazing layers relaxed the thermal stress of the joint effectively. These characteristics were beneficial to the joint, which had shear strengths that were significantly higher than the optimal shear strengths of the joint brazed with pure Ag–Cu–Ti at room temperature and 500°C.     

SiC_w／Al_2O_3－（Ti，W）C复相陶瓷的微观结构及其力学性能

本文对Ａｌ_２Ｏ_３（Ｔｉ，Ｗ）Ｃ和ＳｉＣｗ－Ａｌ_２Ｏ_３（Ｔｉ，Ｗ）Ｃ的力学性能进行了分析对比，研究了热压工艺、ＳｉＣ晶须含量、晶须分散效果和晶须／基体的复合情况等对Ａｌ_２Ｏ_３（Ｔｉ，Ｗ）Ｃ复相陶瓷力学性能的影响。从热膨胀系数失配角度分析和微观结构的观察证实，ＳｉＣ晶须及（Ｔｉ，Ｗ）Ｃ固溶体对改善Ａｌ_２Ｏ_３陶瓷力学性能的效果是显著的，ＳｉＣ_ｗ－Ａｌ_２Ｏ_３．（Ｔｉ，Ｗ）Ｃ陶瓷材料的增韧机制主要是裂纹偏转和裂纹桥接。