改善ZrO2喷涂层性能的过渡层研究

本文从调整ＺｒＯ２陶瓷热障层和钢基体之间的膨胀系数匹配着手，选择４Ｊ５０铁镍合金作为中间过渡层材料。结果表明：采用该中间过渡层可显著降低涂层残余应力，明显地改善陶瓷热障层的组织、强度、韧性及热震性。由此说明了残余应力直接影响喷涂层的性能；通过调节热膨胀系数匹配来降低残余应力，从而提高喷涂导性能的方法是十分有效的。     

WC颗粒增强Ni基涂层的残余应力及耐磨性能

用扫描电子显微镜(SEM)观察了等离子喷涂WC颗粒增强Ni涂层的显微结构,用X射线衍射法(XRD)测试了不同WC含量下涂层及粘结层表面残余应力,利用摩擦磨损试验机和共聚焦激光扫描显微镜研究了涂层的磨损机制。结果表明:涂层表面残余应力为压应力,且随着WC含量的增加先增大后减小,随着涂层厚度的增加而增大,厚度为1000μm时出现分层失效,热应力对粘结层残余应力的贡献最大。一定幅值的压应力有利于涂层耐磨性的提高,同载荷下磨损量仅为基体的0.135倍,涂层磨损机制主要为磨粒磨损。     

TC4钛合金表面等离子喷涂Ni基WC涂层的组织及性能分析

采用等离子喷涂技术在TC4钛合金表面制备了Ni基WC耐磨涂层,利用扫描电镜、能谱仪、显微硬度仪、摩擦磨损试验机、X射线应力仪等研究了涂层的微观组织、成分、硬度、磨损量、磨损机制及残余应力特性等。结果表明:涂层呈现典型的层状结构,与基体结合良好,面层孔隙率为4.7%。显微硬度由表及里呈梯度变化,在798～990HV0.3之间波动,同载荷下基体体积磨损量是涂层的8.9倍,基体磨损机制主要为磨粒磨损和黏着磨损,涂层磨损机制以磨粒磨损为主。涂层表面无裂纹存在,分布着压应力状态的残余应力。     

Ti-6Al-4V基体上等离子喷涂羟基磷灰石涂层的热-力耦合和残余应力

基于热弹塑性理论建立了等离子喷涂羟基磷灰石涂层的热-力耦合模型。一方面,通过引入变形对温度的影响项对经典的Fourier瞬态热传导方程进行了修正,另一方面,在考虑了温度软化效应、应变硬化效应、和应变率强化效应后,采用适用于高温、高应变率条件下的Johnson-Cook模型作为本构方程。基于上述耦合模型,采用有限元方法对涂层内的残余应力场进行了模拟,同时还模拟了基体预热温度以及涂层厚度对残余应力的影响。为了验证数值模拟的可靠性,还采用“材料去除”的实验技术测试了涂层在界面处的残余应力。结果表明：在界面边缘有明显的应力集中;适当提高基体的预热温度有利于减小残余应力;涂层的残余应力随厚度的增加而增大。     

穿孔顶头等离子喷涂涂层残余应力分析

提出采用在顶头上喷涂等离子涂层的方法来提高穿孔顶头表面性能,从而提高其使用寿命,降低生产成本。采用有限元计算软件ANSYS对等离子喷涂过程进行瞬态分析,得到穿孔顶头与涂层内部的温度分布状况,在此基础上分析顶头与涂层界面处和涂层内部的应力状态,讨论了顶头预热温度、涂层厚度、涂层材料等因素对残余应力的影响,得出合理的喷涂工艺,为提高穿孔顶头的使用寿命提供理论依据。     

自动化电弧喷涂路径对涂层残余应力的影响

喷涂路径是影响电弧喷涂层残余应力的重要因素之一.利用自行开发的自动化电弧喷涂系统设计了四种典型的喷涂路径,采用X射线残余应力测试仪测量了不同路径下制备的82B高碳钢涂层的表面残余应力分布,并利用金相显微镜和X射线衍射仪分析了涂层的组织形貌与相组成.试验显示,"环形"喷涂路径制备的涂层的残余应力分布最均匀,最大应力值最低;"平行对称"路径的情况最差.组织分析表明涂层主要由氧化物和块状马氏体组织组成.最后探讨了高碳钢涂层骤冷应力、热应力和相变应力三种因素的影响机理.     

Fe-Ni-B屏蔽涂层相组成及残余应力分布研究

采用大气等离子喷涂技术在321不锈钥表面制备了Fe70Ni27B3屏蔽涂层和Fe64Ni20B16/Ni-al梯度涂层.对两种涂层进行分层研磨后,分别采用机械抛光和电抛光处理,测试了涂层表面及内部不同厚度处的相组成和宏观残余应力.结果表明:涂层中具有中子屏蔽功能的含硼相在Fe70Ni27B3涂层中主要为Fe2B相,含有少量的Fe7B相;在Fe64Ni20816/Ni-Al梯度涂层中主要为FeB相,有少量的Fe2B相和Fe7B相.两种涂层表面的残余应力均为拉应力,沿涂层向内部的拉应力逐渐减小,至涂层/基体界面附近时转化为压应力.两种残余应力大小均不超过50 MPa,而梯度涂层由于减小了界面热失配程度以及降低了硬质铁硼相浓度,其残余应力大小在涂层厚度方向上均小于Fe70Ni27B3涂层.     

铜基体上超音速火焰喷涂镍基涂层残余应力分析

采用X射线应力分析技术和曲率法测试了在铜基体上喷制不同成分、厚度的镍基涂层以及改变基体厚度喷制的涂层的残余应力。结果表明,超音速火焰喷涂的镍基涂层残余应力均为压应力,涂层成分、厚度的变化对残余应力均有明显的影响,添加一定量的WC、控制涂层和基体厚度,可获得较大的残余压应力。     

铜基体上超音速火焰喷涂镍基涂层残余应力分析

采用X射线应力分析技术和曲率法测试了在铜基体上喷制不同成分、厚度的镍基涂层以及改变基体厚度喷制的涂层的残余应力。结果表明，超音速火焰喷涂的镍基涂层残余应力均为压应力，涂层成分、厚度的变化对残余应力均有明显的影响，添加一定量的WC、控制涂层和基体厚度，可获得较大的残余压应力。     

纳米掺杂Al2O3基等离子喷涂涂层残余应力分析

利用逐层剥离X射线衍射法,测定了纳米粒子掺杂对Al2O3 13%TiO2(AT13)等离子喷涂涂层残余应力的影响.结果证明AT13等离子喷涂涂层残余应力分布为:陶瓷涂层部分为压应力;Al/Ni过渡层由陶瓷涂层到钢基体,由压应力过渡到拉应力;在距钢基体0.05mm处现拉应力峰值.随着纳米掺杂量的增大,陶瓷涂层及Ni/Al过渡层残余应力绝对值降低,这对改善陶瓷涂层性质是十分有益的.     

Modeling and experimental verification for non-equibiaxial residual stress evaluated by Knoop indentations

Surface residual stress is usually characterized by two parameters; (1) magnitude and (2) direction of two principal residual stresses. We propose a novel way to evaluate these parameters by instrumented indentation testing (IIT) using a Knoop indenter, which has two-fold symmetry. Non-equibiaxial surface stress causes a shift from residual stress in the force-indentation depth curve of IIT that depends on the Knoop indentation in-plane angle between residual stress and long diagonal of Knoop indenter. We develop a theoretical model to evaluate surface residual stress using only experimental parameters obtained by four Knoop IITs at 45° rotated angles, by introducing mathematical definition of conversion factor, a, which ratio of normal and parallel conversion factors was known as constants (~0.34) on previous studies. We verify this model by Knoop IITs on four metallic cruciform samples in which the surface residual stress is controlled by bending. Experimental results of principal stress and direction show good agreements with applied stress and directions.     

钛合金电子束焊接应力分析的有限元模型

建立了两种钛合金平板电子束焊接应力场的数值分析模型，针对4mm厚的TC11钛合金平板试件，计算分析不同计算模型对电子束焊接残余应力的影响。结果表明厚度为4mm的平板电子束焊接接头，在焊缝及其近缝区很窄的区域内，存在着数值接近材料屈服极限的纵向残余拉应力，而表面横向残余应力则为压应力，且残余应力在厚度上也呈不均匀分布，数值计算模型应根据研究问题的特点来选取。     

不同沉积温度对纳米Ti薄膜微观结构和残余应力的影响

本实验采用纳米压痕技术利用Suresh模型和Lee模型研究了直流磁控溅射制备薄膜时,不同基底温度对Ti薄膜内部残余应力的影响,并将其计算结果与曲率法测试结果进行比较分析。同时结合原子力和XRD对薄膜表面形貌和微观结构进行了分析。研究发现：Suresh模型的计算结果与曲率法测量结果更为接近,Lee模型更适合对Ti薄膜中的应力大小进行计算。计算结果表明：金属Ti薄膜表面晶粒随基底温度的增加先增大后减小,薄膜中的残余应力则由压应力转变为拉应力。     

热源形状参数对薄板焊接残余应力和变形的影响

采用热-弹-塑性有限元方法模拟焊接残余应力和变形时,对于移动热源模型形状参数的选取,在大多数情况下大都是根据研究者的经验来确定.然而对于热源模型形状参数对焊接残余应力和变形的影响尚不十分明确.基于ABAQUS有限元软件,以高强钢SM490A单道TIG焊为例,通过建立三维有限元模型和采用双椭球体积移动热源模型,研究了热源模型形状参数对焊接残余应力和变形的影响.结果表明,热源模型形状参数对焊接残余应力影响较小,而对焊接变形,尤其是对角变形有一定程度的影响.     

Numerical and experimental study of thermally induced residual stress in the hybrid laser-GMA welding process

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser-gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.     

核用SA508-3钢特厚板焊后热处理有限元分析

为了得到SA508-3钢特厚板焊接残余应力分布及焊后热处理对残余应力分布的影响,利用有限元方法对焊接及焊后热处理进行了模拟计算,计算结果表明:焊后热处理对试板焊接应力分布趋势影响较小,但焊后热处理可以大大减小接头应力数值,其中,纵向应力最大减小幅度为72%,横向应力最大减小幅度为70%;焊接接头存在应力分布准稳定区,且接头内部残余应力水平最小,其次为接头上表面,接头下表面应力水平最大;通过残余应力测定试验与模拟结果比对,两者结果吻合度很高,说明计算模型及计算方法可靠,可以指导实际SA508-3钢特厚板焊后热处理生产.     

FEM simulation of residual stresses induced by laser shock with overlapping laser spots

The finite element method is presented to attain the numerical simulation of the residual stresses field in the material treated by laser shock processing. The distribution of residual stresses generated by a single laser shock with square and round laser spot is predicted and validated by experimental results. With the Finite Element Method （FEM） model, effects of different overlapping rates and impact sequences on the distribution of residual stresses are simulated. The results indicate that： （1） Overlapping laser shock can increase the compressive residual stresses. However, it is not effective on the growth of plastically affected depth; （2） Overlapping rate should be optimized and selected carefully for the large area treatment. Appropriate overlapping rate is beneficial to obtain a homogeneous residual stress field; （3） The impact sequence has a great effect on the residual stress field. It can greatly attenuate the phenomenon of the “residual stress hole” to obtain a homogeneous residual stress field.     

Numerical Investigation on Residual Stresses of the Safe-End/Nozzle Dissimilar Metal Welded Joint in CAP1400 Nuclear Power Plants

The residual stress evolution in a safe-end/nozzle dissimilar metal welded joint of CAP1400 nuclear power plants was investigated in the manufacturing process by finite element simulation. A finite element model, including cladding, buttering, post-weld heat treatment (PWHT) and dissimilar metal multi-pass welding, is developed based on SYSWELD software to investigate the evolution of residual stress in the aforementioned manufacturing process. The results reveal a large tensile axial residual stress, which exists at the weld zone on the inner surface, leads to a high sensitivity to stress corrosion cracking (SCC). PWHT process before dissimilar metal multi-pass welding process has a great influence on the magnitude and distribution of final axial residual stress. The risk of SCC on the inner surface of the pipe will increase if PWHT process is not taken into account. Therefore, such crucial thermal manufacturing process such as cladding, buttering and post-weld heat treatment, besides the multi-pass welding process, should be considered in the numerical model in order to accurately predict the distribution and the magnitude of the residual stress.     

MoSi2涂层残余应力和结合强度的有限元分析

目的研究残余应力对MoSi_2涂层结合强度的影响。方法基于粉末包渗法(PC)制备的MoSi_2涂层在退火前后的微观形貌和相组成,建立有限元分析模型,计算MoSi_2涂层在退火前后的残余应力。根据涂层法向和切向残余应力随涂层厚度的变化,并结合涂层在退火前后结合强度随涂层厚度的变化规律,研究残余应力对涂层结合强度的影响。结果有限元模拟结果表明,MoSi_2涂层的法向残余应力随涂层厚度的增加而减小。涂层的切向残余应力在涂层界面边缘处形成应力集中,并且最大切向残余应力随涂层厚度的增加而增大,与涂层结合强度的变化趋势相吻合。此外,退火后,MoSi_2涂层的法向残余应力几乎没有变化,但是最大切向残余应力下降了10%左右,结合强度提高了20%左右。结论粉末包渗法(PC)制备的Mo Si_2涂层的结合强度受切向残余应力的影响,涂层切向残余应力增大,导致涂层结合强度降低。退火处理能够起到有效改善涂层界面切向残余应力集中的作用,对于提高涂层结合强度有明显的效果。     

材料硬化模型对316L不锈钢焊接残余应力的影响

316L奥氏体不锈钢具有较强的应变硬化特征,建立合适的硬化模型可以更加准确地预测焊接残余应力.建立一种新型的非线性混合硬化模型,基于SYSWELD软件,采用间接耦合的三维热弹塑性有限元法模拟316L奥氏体不锈钢三道槽焊缝的残余应力.结果表明,材料的硬化模型对焊接残余应力的预测具有重要的影响,随着热循环次数的增加,硬化模型的影响越明显;与实际测量结果比较,随动硬化模型低估了焊接残余应力,等向硬化模型高估了残余应力,采用非线性混合硬化模型可以更加准确地模拟焊接残余应力.