填料增强先驱体转化法制备陶瓷涂层的研究进展

先驱体转化陶瓷法是一种原位制备陶瓷涂层的新型方法.在先驱体转化陶瓷法制备陶瓷涂层时,选择陶瓷产率较高的先驱体和添加填料是降低陶瓷涂层气孔率和收缩率的重要途径.填料在先驱体转化陶瓷法制备陶瓷涂层中起着重要作用,通过添加填料,可进一步提高陶瓷涂层的性能并扩展其功能特性.填料主要包括惰性填料、活性填料、熔融型填料和牺牲型填料4种.对比了4种填料的类型和特点,介绍了填料增强陶瓷涂层的作用机制和选取原则,综述了填料增强先驱体转化陶瓷法制备陶瓷涂层的研究现状.在裂解过程中,惰性填料的质量和体积均保持不变,可加入较高体积分数的惰性填料制备厚涂层;活性填料可与先驱体、裂解产生的小分子气体、保护气氛等反应,实现陶瓷涂层的近净成形;熔融型填料熔融后,填充到涂层空隙中,可提高涂层的致密化程度,消除基体和陶瓷涂层以及填料和先驱体之间由于热膨胀系数不匹配产生的应力;牺牲型填料分解后,形成孔状涂层,可控制陶瓷涂层中的应力,降低陶瓷涂层的有效弹性模量,增强陶瓷涂层的应变强度.针对陶瓷涂层的服役工况,选择合适的填料类型,确定填料的临界体积分数,揭示填料对陶瓷涂层组成、晶界结构、涂层致密化、裂纹缺陷及裂解反应过程的影响规律,研发新型裂解技术和工艺以控制先驱体转化为陶瓷涂层过程中产生的应力,是后续研究中需要重点关注的问题.     

Viscoelastic behavior of HDPE polymer using tensile and compressive loading

Large containers for liquids, exposed to different static loadings, are mainly made of high-density polyethylene (HDPE). The viscoelastic response of HDPE under long-term tensile and compressive creep is investigated. Monotonic experiments under tension are performed over a wide range of strain rates. In these experiments, the transition in the damage mechanisms (development and propagation of contraction in the HDPE specimen) is analyzed. The monotonic tensile behavior of the HDPE is found to be nonlinear and depends on the strain rates. It is observed that both elastic modulus and plastic flow stress present an increase with displacement speed due to the viscoelastic behavior of HDPE. A similar observation can be made for monotonic compressive tests by developing a new experimental device that ensures accurate measurement of the strain. Such a device makes use of an extensometer of compressive displacement of the specimen. In addition, the long-term behavior of HDPE is evidenced through creep and relaxation tests at an imposed range respectively of lower stresses and strains. It is shown that the normalized curves, associated with these tests, can be represented by a single curve characterizing the compressive creep compliance or relaxation stresses versus time. The linearity of the viscoelastic behavior is confirmed within the linear domain of the monotonic compressive and tensile tests.     

蓝宝石/4J33合金钎焊接头残余应力的数值模拟分析

采用有限元法和弹塑性理论,结合ANSYS15.0软件,对使用Ag-Cu-Ti8为钎料的蓝宝石/4J33合金活性钎焊接头的温度场和应力场进行了数值仿真模拟. 温度场分析得到钎焊接头不同位置降温的快慢情况,应力场分析得到蓝宝石内最大拉应力位于外侧端面,为538 MPa,并向界面延伸,通过实际拉伸试验得出接头断裂部位与模拟结果吻合,当钎料层厚度为150 μm时,径向残余应力最小,因而可以选择适当的钎缝层厚度以减少残余应力,文中的模拟计算结果能有效指导蓝宝石/4J33合金活性钎焊工艺,有利于保证实际接头强度和可靠性.     

钎料对TiC陶瓷/铸铁钎缝处剪应力的影响

采用有限元数值模拟方法研究了采用不同钎料对冷却过程中TiC陶瓷／铸铁焊缝处剪应力的影响。结果表明，无论采用Ni基钎料、Ti基钎料还是他基钎料，剪应力均主要集中在TiC陶瓷／铸铁的钎缝端点上。当采用Ni基和Ag基钎料时，剪应力的最大值出现在钎料／TiC陶瓷界而；而采用Ti基钎料时，剪应力的最大值出现在铸铁／钎料界面。当采用Ni基和Ti基钉料时，冷却到室温的钎缝最大剪应力值较大，因此接头的连接强度较低；当采用Ag基钎料时，冷却到室温的钎缝最大剪应力值较小，因此接头的连接强度较高。     

Effect of low transformation temperature weld filler metal on welding residual stress

Abstract

The effect of weld filler metal austenite to acicular ferrite transformation temperature on the residual stresses that arise during the gas metal arc welding of a low carbon steel has been examined using a finite element model. It was found that the stress levels in the weld can be tailored by the appropriate selection of the filler metal and compressive, near zero or tensile residual stresses produced. Reasonable agreement was obtained between the model and the stresses measured using neutron diffraction both in welds using conventional and low transformation temperature filler metal.     

Influence of pre-plastic deformation on thermal residual stress and yield st rength of SiCw/Al composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｅｔｏｔｈｅｄｉｆｆｅｒｅｎｃｅｏｆｃｏｅｆｆｉｃｉｅｎｔｓｏｆｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎｂｅｔｗｅｅｎｒｅｉｎｆｏｒｃｅｍｅｎｔａｎｄｔｈｅｍａｔｒｉｘｉｎＳｉＣｗ/Ａｌｃｏｍｐｏｓｉｔｅｓ,ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｉｓｎｏｔａｖｏｉｄｅｄｗｈｅｎｔｈｅｔｅｍｐｅｒａｔｕｒｅｉｓｃｈａｎｇｅｄ[1,2].Ｔｈｅｔｈｅｒｍａｌｒｅｓｉｄｕａｌｓｔｒｅｓｓｃａｎｌａｒｇｅｌｙａｆｆｅｃｔｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｃｏｍｐｏｓｉｔｅｓ,ｓ…     

焊接应力变形原理若干问题的探讨(二)

提出焊接残余应力形成和消除原理:焊接残余应力不是压缩塑性应变引起的,而是由于焊缝和近缝区金属在"力学熔点"及以下温度冷却收缩受阻产生的;消除焊接残余应力不是产生拉伸塑性应变以减少、抵消和补偿压缩塑性应变,而是将残余弹性应变转变为塑性应变;消除焊接残余应力并不是必须去除固有应变,部分去除或完全不去除固有应变也能完全消除残余应力.提出随焊后热精确控制应力变形焊接法,既可实现无应力焊接和无应力无变形焊接,也可实现适当压应力无变形焊接和较大压应力微变形焊接;并对传统方法与有限元法进行了分析比较.     

Basic alloy development of low-transformation-temperature fillers for AISI 410 martensitic stainless steel

ABSTRACT

This study discusses the effect of Ni content of low-transformation-temperature (LTT) fillers on welding residual stresses of AISI 410 plates. The plates were joined by LTT fillers with 11?wt-% Cr and varying Ni from 3 to 11?wt-%. Evaluation of varying Ni content on the martensitic transformation temperature (M_s) by dilatometric tests indicates that the M_s of LTT fillers decreases from 335°C to 67°C by increasing Ni wt-%. Residual stress measurements show the highest compressive longitudinal stress (?310?MPa) in the weld bead deposited by the LTT filler contained 7?wt-% Ni and M_s?=?202°C. This result is associated with the highest final expansion strain (0.37%) in this composition. Microstructural analyses show the presence of retained austenite by increasing the Ni more than 7?wt-%.     

INFLUENCE OF TOP TEMPERATURE OF THERMAL CYCLE ON THERMAL STRESS/STRAIN AND THERMAL FATIGUE BEHAVIOR OF PURE IRON

１．ＩｎｔｒｏｄｕｃｔｉｏｎＦｉｇ．１　ＴｈｅｒｍａｌｆａｔｉｇｕｅｔｅｓｔｍａｃｈｉｎｅｗｉｔｈＯｕｔｅｒｃｉｎｓｔｒａｉｎｔＴｈｅｄａｍａｇｅｃａｕｓｅｄｂｙｔｈｅｒｍａｌｆａｔｉｇｕｅｉｓｏｎｅｏｆｔｈｅｍａｉｎｆａｉｌｕｒｅｆｏｒｍｓｏｆｍｅｔａｌｗｏｒｋｉｎｇｐｉｅｃｅｓｕｎｄｅｒｔｈｅｔｅｍｐｅｒａｔｕｒｅｖａｒｉａｔｉｏｎｃｏｎｄｉｔｉｏｎｓ．Ａｌｏｔｏｆｔｈｅｒｍａｌｆａｔｉｇｕｅｔｅｓｔｓｃｏｎｃｅｒｎｉｎｇｔｈｅｆａｉｌｕｒｅｗｅｒｅｃｏｎｄｕｃｔｅｄｏｎｔｈｅｖａｒｉｏｕ…     

Thermomechanical stability of memory package with LOC structure

The present work attempts to determine an appropriate design of double-sided adhesive tape, which plays a significant role in defining the degree of chip surface damage in a plastic LOC (lead-on-chip) package. Various tape designs were tested to determine their effectiveness in preventing thermal stress-related damage on the chip surface during temperature cycling. The experimental results indicate that the thermomechanical stability of the IC pattern is more influenced by whether the LOC tape is employed along the chip edge than by the size of the tape covering area. Moreover, it was found that chip surface damage associated with LOC tape can be caused by normal stress applied to the chip surface vertically as well as by shear stress, which is known to cause damage. The importance of the normal stress component is verified through a 3-dimensional FEM (finite element method) simulation adopted to define the thermal stress distribution in the present LOC package. The numerical calculation shows that when the tape is designed to cover the chip corner, the magnitude of normal stress reveals a maximum value at the edge of the chip.     

The role of residual stress in neutral pH stress corrosion cracking of pipeline steels – Part II: Crack dormancy

This investigation provides a quantitative analysis of the effect of Type I residual stresses on the occurrence of pitting and stress corrosion cracking (SCC) formation in pipeline steel exposed to neutral pH aqueous environments. It has been shown that SCC generated in neutral pH environments can be readily blunted due to plastic deformation (room temperature creep) and/or extensive anodic dissolution. As a result, a high positive tensile residual stress gradient is necessary for continued growth of SCC in pipeline steels exposed to this neutral pH environment. The tensile residual stress represents a large mechanical driving force for crack nucleation and short crack growth. Active cracks may become dormant as the near-surface residual stress gradient changes, due to self-equilibration, from highly tensile to a lower tensile state or to a compressive state. The change in residual stress level can occur within 1 mm of the surface, resulting in a large proportion of dormant SCC.     

Microstructure,hardness and residual stress distribution in maraging steel gas tungsten arc weldments

Abstract

The distribution of residual stresses due to welding has been studied in maraging steel welds. Gas tungsten arc welding process was used and the effect of filler metal composition on the nature of residual stress distribution has been investigated using X-ray diffraction technique with Cr K_α radiation. Three types of filler materials were used, they include: maraging filler, austenitic stainless steel and medium alloy medium carbon steel filler metal. In the case of maraging steel weld, medium alloy medium carbon filler, the residual stress at the centre of the weld zone was more compressive while, less compressive stresses have been identified in the heat affected zone of the parent metal adjacent to the weld metal. But, in the case of austenitic stainless steel filler the residual stresses at the centre of the weld and heat affected zone were tensile. Post-weld aging treatment reduced the magnitude of stresses. The observed residual stress distribution across the weldments has been correlated with microstructure and hardness distribution across the weld.     

基于钎料层厚度优化磨抛盘磨料粒度的仿真研究

采用热弹塑性有限元方法对钎焊金刚石磨抛盘真空钎焊过程进行建模与仿真,运用ABAQUS有限元分析软件,对其钎焊后冷却过程的瞬态温度场和应力场进行模拟,得出钎料层是影响磨抛盘钎焊后应力及变形量大小的重要因素。分析不同钎料层厚度时磨抛盘钎焊后的应力及变形量,合理确定在一定基体厚度情况下,钎料层厚度的最大值为0.2mm。结合钎料层厚度与磨粒高度的合理匹配关系,在理论上确定了钎焊金刚石磨抛盘可用的最大磨料粒度为30/35目。     

Nanoscale contact plasticity of crystalline metal: Experiment and analytical investigation via atomistic and discrete dislocation models

Nanoscale incipient plastic deformation in crystalline metals occurs as the result of the collective motion of dislocations. It is known as “nanoplasticity” and is recognized as the elementary process of the macroscopic deformation. Abrupt increases in indent displacements called displacement bursts were observed in recent nanoindentation experiments; that is, the specific behavior for nanoplasticity. In the present study, experimental tests are first conducted to educe the unique nature of the nanoscale deformation. Subsequently, large-scale atomistic simulations are performed to predict the incipient plastic deformation and a new discrete dislocation model combined with the boundary element analysis is constructed to capture the collective motion of the dislocations. Our results suggest that the incipient plastic deformation requires much higher critical shear stress than the theoretical shear strength due to high compressive stress distribution beneath the indenter, and that the displacement burst is induced by surface rearrangement corresponding to hundreds of dislocation dipoles.     

Laser Patterning Pretreatment before Thermal Spraying: A Technique to Adapt and Control the Surface Topography to Thermomechanical Loading and Materials

Coating characteristics are highly dependent on substrate preparation and spray parameters. Hence, the surface must be adapted mechanically and physicochemically to favor coating–substrate adhesion. Conventional surface preparation methods such as grit blasting are limited by surface embrittlement and produce large plastic deformations throughout the surface, resulting in compressive stress and potential cracks. Among all such methods, laser patterning is suitable to prepare the surface of sensitive materials. No embedded grit particles can be observed, and high-quality coatings are obtained. Finally, laser surface patterning adapts the impacted surface, creating large anchoring area. Optimized surface topographies can then be elaborated according to the material as well as the application. The objective of this study is to compare the adhesive bond strength between two surface preparation methods, namely grit blasting and laser surface patterning, for two material couples used in aerospace applications: 2017 aluminum alloy and AISI 304L stainless steel coated with NiAl and YSZ, respectively. Laser patterning significantly increases adherence values for similar contact area due to mixed-mode (cohesive and adhesive) failure. The coating is locked in the pattern.     

Plastic deformation and residual stresses in amorphous silica pillars under uniaxial loading

We have carried out uniaxial compression of micron-scale amorphous silica pillars. We have measured load–displacement curves and observed the morphology of the pillars after unloading, providing strong evidence for large plastic deformations. Minor cracking is also observed, with a well-defined pattern. We find that the van Mises stress in compression is comparable to the intrinsic tensile strength of silica. Precise analysis of the deformation of the pillars has been carried out by finite element modeling (FEM) using the constitutive equation determined previously (G. Kermouche et al., Acta Materialia, 56 (2008) 3222), which quantitatively takes into account densification, shear flow and strain hardening. The residual stress distribution we predict by FEM matches the observed crack pattern well. Finally the calculated stress fields in pillar compression and cone indentation are compared. We propose an interpretation of the contrasts in terms of confinement.     

Finite element modelling of brazed residual stress and its influence factor analysis for stainless steel plate-fin structure

This paper presents a finite element modelling of brazed residual stress in a stainless steel plate-fin structure applied to recuperators in microturbines. The effects of nine influence factors on residual stress are investigated. The results show that the brazed joint creates large residual stresses due to the mechanical properties mismatching between base metal and filler metal. Strength in the middle joint is affected mainly by longitudinal stress. The residual stress gradient around the interface between base metal and filler metal is very large, which can have a great effect on interface strength. The material mismatching, brazing gap, pressure loading, fin pitch, fin thickness, fin height and plate thickness significantly affect the residual stress distribution, while the brazing temperature and the number of fin layers have little impact on residual stress. This work provides a reference for optimizing the brazing procedure and decreasing the residual stress for stainless steel plate-fin structures.     

Failure characteristics of three-body model composed of rock and coal with different strength and stiffness

Four different types of three-body model composed of rock and coal with different strength and stiffness were established in order to study the failure characteristics of compound model such as roof-coal-floor. Through stress analysis of the element with variable strength and stiffness extracted from the strong-weak interface, the tri-axial compressive strength of the weak body and strong body near the interface as well as the areas away from the contact surface was found. Then, on the basis of three-dimensional fast Lagrangian method of continua and strain softening constitutive model composed of Coulomb-Mohr shear failure with tensile cut-off, stress and strain relationship of the four three-body combined models were analyzed under different confining pressures by numerical simulation. Finally, the different features of local shear zones and plastic failure areas of the four different models and their development trend with increasing confining pressure were discussed. The results show that additional stresses are derived due to the lateral deformation constraints near the strong-weak interface area, which results in the strength increasing in weak body and strength decreasing in strong body. The weakly consolidated soft rock and coal cementation exhibit significant strain softening behavior and bear compound tension-shear failure under uni-axial compression. With the increase of confining pressure, the tensile failure disappears from the model, and the failure type of composed model changes to local shear failure with different number of shearing bands and plastic failure zones. This work shows important guiding significance for the mechanism study of seismic, rock burst, and coal bump.     

Modification of residual stress in Al-[AlBO]_w/Al compound plate

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｍｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓｔａｋｅａｄｖａｎｔａｇｅｓｏｆｈｉｇｈｅｒｓｐｅｃｉｆｉｃｓｔｒｅｎｇｔｈ ,ｈｉｇｈｅｒｓｐｅｃｉｆｉｃｍｏｄｕｌｅ,ｌｏｗ ｅｒｔｈｅｒｍａｌｃｏｅｆｆｉｃｉｅｎｔｏｆｅｘｐａｎｓｉｏｎｅｔｃ[1 ,2 ] ,ｒｅｓｕｌｔｉｎｇｉｎａｔｙｐｉｃａｌｅｎｇｉｎｅｅｒｉｎｇｍａｔｅｒｉａｌｗｉｔｈｇｏｏｄｐｒｏｓｐｅｃｔｓ.Ｄｕｅｔｏｔｈｅｈｉｇｈｃｏｓｔ,ｔｈｅａｐｐｌｉｃａｔｉｏｎａｎｄｐｏｐｕｌａｒｉｚａ ｔｉｏｎｏｆｔｈｅｃｏ…     

基于Python的Abaqus二次开发在高温合金GH3039激光冲击强化中的应用

目的 提高高温合金GH3039激光冲击强化仿真建模的效率。方法 利用Python脚本语言对Abaqus进行二次开发,利用插件对高温合金GH3039激光冲击强化过程进行仿真分析。采用侧倾固定Ψ法,通过实验测量激光冲击强化后的残余应力,并对仿真结果进行验证,分析不同激光工艺参数作用下高温合金GH3039表面和深度方向残余应力的分布规律。结果 仿真插件界面简洁,操作性强,结果准确。在其他参数不变的情况下,残余压应力受到光斑尺寸的影响较大。相较于光斑直径为4、2 mm,在光斑直径为6 mm时,其中心位置残余压应力分别提高了4.3%、53%。随着光斑尺寸的增大,表面残余压应力增大,且变化梯度减小,深度方向的残余压应力增大。随着激光能量的增加,表面残余压应力增大,且变化梯度增大,残余压应力峰值位于中心区域附近,在激光能量为6、7、8 J时,残余压应力层的平均厚度分别为0.55、0.67、0.82 mm,深度方向残余压应力层增厚。随着冲击次数的增加,冲击区域表面残余压应力平均值高于单次冲击,且波动梯度增大,冲击1、2、3次后残余压应力层的平均厚度分别为0.55、0.71、0.85 mm,深度方向残余压应力层深度增大。结论 利用Python脚本语言对ABAQUS进行二次开发,提高了仿真建模的效率,可为快速预测不同激光工艺参数下高温合金GH3039残余应力的分布规律提供参考。