多元梯度自润滑陶瓷刀具材料的研制

针对均质自润滑陶瓷刀具材料不能合理兼顾减摩性能及耐磨性能的难题,运用功能梯度材料的设计思想研制出一种梯度自润滑陶瓷刀具材料。这种新型自润滑刀具材料的特征是固体润滑剂由其表层向内层梯度减少,并且材料表层存在残余压应力。提出多元梯度材料的组成分布模型,按该模型得出的组分梯度设计结果,采用粉末叠层铺填与真空热压烧结工艺制备Al2O3/TiC/CaF2梯度自润滑陶瓷刀具材料。该梯度自润滑陶瓷刀具材料的显微结构呈现出与组成分布一致的梯度变化,表层形成了残余压应力,其抗弯强度、硬度和断裂韧度分别比相应的均质材料提高了21%、16%和5.9%。材料强度的提高主要是由于CaF2由表层到中间层梯度减少,硬度和断裂韧度的提高归因于材料表层的残余压应力。以Al2O3/TiC/CaF2梯度自润滑陶瓷刀具和相应的均质自润滑陶瓷刀具对45钢进行干切削试验,结果表明,梯度刀具的耐磨性能优于均质刀具。     

梯度功能陶瓷刀具的切削性能研究

梯度功能陶瓷刀具材料是一种新型的刀具材料 ,合理的梯度设计能够有效地改善刀具的切削性能。切削试验表明 ,刀具表面层较高的导热系数和残余应力是提高切削性能的关键     

梯度功能陶瓷刀具切削应力场的有限元分析

梯度功能陶瓷刀具的切削性能与梯度的分布形式直接相关。本文首次建立了梯度功能陶瓷刀具的切削模型,并通过对不同梯度分布的陶瓷刀具在相同切削载荷下的切削应力场有限元分析,得出了最优化的梯度分布指数。     

梯度功能陶瓷刀具切削应力场的有限元分析

本文首次建立了梯度功能陶瓷刀具的切削模型,并通过对不同梯度分布的陶瓷刀具有相同切削载荷下的切削应力场有限元分析,得出了最优化的梯度分布指数。     

高速切削用陶瓷刀具多尺度设计理论与切削可靠性研究

正本文针对研制过程存在的盲目性和实验量大的弊端,提出了复合陶瓷刀具材料的多尺度设计理论,揭示了复合材料宏观性能和其微观组织之间的定量关系;研制成功了多尺度颗粒复合陶瓷刀具材料,并对刀具材料的烧结工艺、微观组织、增韧补强机理、室温和高温力学性能、动态疲劳性能、切削性能和切削可靠性进行了系统研究。提出了复合陶瓷刀具材料的多尺度设计理论。建立了刀具材料抗弯强度预测模型、残余应力力学模型、纳米颗粒最优含     

陶瓷刀具在大型薄壁加工件中的应用

分析优质合金钢的薄壁件质量不合格的原因,结合难加工材料的高速切削机理,改进工艺流程,提出利用陶瓷刀具实现大型薄壁件高速切削的可行性,澄清了利用陶瓷刀具加工的几个误区,并对切削过程中的注意事项及切削参数的选择提出一些建议。     

高速切削GH2132涂层刀具表面及次表面性能演变研究

高速切削过程中,涂层刀具表面性能及次表面残余应力的变化会直接影响刀具的切削性能。采用PVD-TiAlN硬质合金涂层刀具进行高速车削GH2132高温合金试验,研究刀具表面性能在切削过程中的变化规律,并用拉曼光谱法测量了刀具不同磨损阶段的涂层次表面残余应力分布。结果表明,刀具在完整寿命期间内,表面残余压应力和表面显微硬度均呈先增大后减小的趋势。刀具从未磨损到稳定磨损阶段中期,涂层截面残余应力均为残余压应力占主体且沿深度方向逐渐增大,但切削至稳定磨损阶段后期时,涂层在靠近基体位置出现残余压应力减小的现象。在稳定磨损阶段前期,刀具有最佳的表面性能及最大的次表面压应力,此时刀具切削性能最佳,刀具磨损缓慢。     

基于梯度结构的Al2O3/ZrO2陶瓷刀具材料的制备及其力学性能

采用真空热压烧结方式制备了Al₂O₃/ZrO₂梯度复合陶瓷刀具材料,并对ZrO₂含量及梯度结构层厚比进行了优化。层厚比为2.0的AZE20梯度复合陶瓷刀具材料维氏硬度为(18.7±0.33) GPa,抗弯强度为(937±28.5) MPa,断裂韧性为(8.2±0.32) MPa·m^1/2,相比最佳ZrO₂含量的均质复合陶瓷刀具材料AZ20,维氏硬度、抗弯强度和断裂韧性分别增加了22%、37.8%和43.8%。梯度结构的设计使表层形成残余压应力,晶粒得到一定程度的细化,更多的ZrO₂晶粒因残余压应力尺寸稳定在t相ZrO₂晶粒尺寸。在复合材料断口形貌中发现,其断裂方式为表层穿晶断裂和中间层沿晶断裂的结合,这种混合断裂方式使刀具整体力学性能得到提高。     

梯度功能陶瓷刀具切削淬硬钢的研究

在国内首先研制成功梯度功能陶瓷刀具材料FG-1，并研究了该刀具车削淬硬工具钢T10A的切削性能及耐磨性。结果表明，FG－1具备优异的物理力学性能：在低速切削条件下，FG－1与普通陶瓷刀具LT55及SG－4的耐磨性相差不大；而随着切削速度的提高，FG-1的性能明显优于LT55和SG－4刀具。其原因是刀具材料成分的梯度组成发挥了缓解热应力的作用。     

LY12硬铝合金高速切削加工残余应力的研究

对LY12硬铝合金在高速切削加工过程中出现的高度非线性问题,采用有限元软件心US对切削过程进行仿真,得到了高速切削加工过程中的残余应力分布。讨论了高速切削加工过程中影响残余应力分布的几个关键因素：切削速度、背吃刀量、刀尖圆角半径,从而为以后获得基于残余应力的刀具参数优化方案提供了依据。     

对称型梯度功能陶瓷材料的非定常热应力

采用摄动法推导出对称型梯度功能材料平板的一维非定常温度场及非定常热应力场的解析表达式，对Ａｌ２Ｏ３／（Ｗ，Ｔｉ）Ｃ系对称型梯度功能陶瓷平板表面冷却及加热过程中的非定常温度场及非定常热应力场进行了计算。讨论了提高陶瓷刀具材料抗热震性的方法即采用梯度功能陶瓷刀具材料，并结合断续车削试验进行了验证。     

磨料喷射喷嘴的应力分析及FGM模型设计

分析表明磨料喷射加工中喷嘴承受的应力在喷嘴入口最大、出口次之、中间区域相对较小。试验显示喷嘴的冲蚀磨损在喷嘴入口最严重、出口次之、中间区域相对较小。试验结果与应力分析结果一致,得出磨料喷射加工中喷嘴入口、出口处承受的高拉应力是造成其冲蚀磨损严重的主要原因的结论。针对提高均质陶瓷材料喷嘴抗冲蚀磨损能力的力度有限,提出运用梯度功能材料(Function gradient material,FGM)理论于喷嘴材料的设计和制造中,研发新型非均质的陶瓷喷嘴材料,将梯度功能陶瓷喷嘴制备中产生的残余压应力引入喷嘴入口、出口,使其减缓磨料喷射加工中喷嘴承受的拉应力,以提高喷嘴抗冲蚀磨损能力。结合喷嘴的冲蚀磨损特点、结构特点及陶瓷喷嘴材料制备工艺性等,建立了梯度陶瓷喷嘴物理模型和成分分布模型。根据本模型设计结果,研制出梯度 SiC／(W,Ti)C陶瓷喷嘴。结果表明,相同条件下制各的梯度SiC／(W,Ti)C陶瓷喷嘴的抗冲蚀磨损能力高于非梯度 SiC／(W,Ti)C陶瓷喷嘴。     

纳米复合陶瓷残余热应力的有限元模拟

基于对纳米复合陶瓷微观结构的观察和分析所建立的微观结构模型,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。计算结果表明,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,利用微观结构模型进行的残余应力分析可以反映第二相颗粒大小、含量和分布对残余应力的影响,热残余应力的大小和分布与材料的微观结构有着密切的关系。     

Cutting performance and wear mechanisms of Sialon–Si3N4 graded nano-composite ceramic cutting tools

Sialon–Si₃N₄ graded nano-composite ceramic tool materials were fabricated by using hot-pressing technique. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The cutting performance and wear mechanisms of the graded tools were investigated via turning of Inconel 718 alloy in comparison with common reference tools. The surface roughness of the finish hard turning of Inconel 718 and the microstructures of the chips were also examined. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that graded structure in Sialon–Si₃N₄ graded ceramic tool materials can induce residual compressive stresses in the surface layer during fabrication process. Tool lifetime of graded ceramic tool was higher than that of the common reference tool. The longer tool life of the graded nano-composite ceramic tool was attributed to its synergistic strengthening and toughening mechanisms induced by the optimum graded compositional structure of the tool and the addition of nano-sized particles. Wear mechanisms identified in the machining tests involved adhesive wear and abrasive wear. The mechanisms responsible for the higher tool life were determined to be the formation of compressive residual stress in the surface layer of the graded tools, which led to an increase in the resistance to fracture.     

功能梯度Al2O3涂层残余热应力分析

Al2O3/316L功能梯度材料是一种聚变反应堆第一壁的候选材料。为避免制备过程中因材料之间热物理性能差别产生的热应力过大造成材料的失效,须对梯度材料进行合理的热应力缓和设计。运用有限元软件,分析成分分布指数、梯度涂层厚度和梯度层数目等参数对Al2O3/316L功能梯度材料残余热应力的影响。分析结果表明：体积分布指数p=1.0时所受热应力最小,涂层承受压应力作用;梯度层数为9时热应力缓和效果最好;梯度层厚度不宜过大;将非功能梯度材料与优化后的功能梯度材料的残余热应力进行比,结果显示：功能梯度材料缓和热应力效果十分显著。最后利用等离子喷涂方法制备了梯度涂层测试涂层残余应力,并与有限元结果进行对比,以验证模拟的准确性。     

一种功能梯度材料活塞的材料梯度方程选择

应用复合材料热性能理论,采用有限元分析软件AD INA分析具有不同参数的材料梯度方程的陶瓷纤维梯度增强活塞的温度分布和应力分布。结果表明:陶瓷纤维梯度层可以明显改变活塞温度分布,缓和由于热膨胀系数不匹配,在陶瓷纤维增强层与活塞本体交界处产生的应力。并根据计算结果选出最优的材料梯度方程。     

Experimental investigation of residual stress distribution in pre-stress cutting

This paper presents an analysis and experimental study on the formation and distribution of machined surface residual stress in pre-stress cutting. In the first component of the paper, the mechanical and thermal effect on residual stress is analysed. The results show that machined harden layer and cutting heat transfer conditions are crucial to form residual stress in a machined surface. Residual stress has three kinds of distributions in different mechanical and thermal conditions: tensile stress, compressive stress and tensile–compressive stress. If pre-stress is applied, it would facilitate residual compressive stress in the machined surface effectively; its action is analysed with an experimental study. The experiment is carried out by hardened 40Cr alloy steel turning with different tool rounds and pre-stress loading; the results obtained in this study indicate that the tool round would redound to generate residual compressive stress in the machined surface and affect the residual stress distribution significantly, whilst pre-stress load can affect the magnitude of residual stress actively, but does not for its distribution. It is found that the experimental results of residual stress distribution are consistent with the theoretical analysis.     

Analysis of transient temperature and residual thermal stresses in friction stir welding of aluminum alloy 6061-T6 via numerical simulation

Residual stress is lower in friction stir welding (FSW) compared with other melting weldment processes. This is due to being solid-state process in its nature. There are several advantages in utilizing stir welding process. Lower fluctuation and shrinkage in weldment metal-enhanced mechanical characteristics, less defects, and ability to weld certain metals otherwise impractical by other welding processes are to name just a few of these advantages. These have caused an ever increasing attention by the concerned to the process of FSW. In this investigation, three-dimensional numerical simulation of friction stir welding was concerned to study the impact of tool moving speed in relation with heat distribution as well as residual stress. Simulation was composed of two stages. Firstly, thermal behavior of the piece while undergoing the welding process was studied. Heat is generated due to the friction between tool and the piece being welded. In the second stage, attained thermal behavior of the piece from previous stage is considered as inlet heat of an elasto-plastic, thermo-mechanical model for the prediction of residual stress. Also, in the second stage, tool is eliminated and residual stress distribution is found after complete cooling of the piece and disassembly of the clamp. Material characteristic are introduced into the proposed model as temperature-dependent parameters. Obtained residual indicate that heat distribution along thickness varies and is asymmetrical enormously. Moreover, longitudinal residual stress in the weld which increases as speed of process and tool movement ascends. In the prediction of results of residual stress, only heat impact was studied. This was recognized as the main element causing minor difference in results obtained for simulation in comparison with that of actual experiment.     

复相陶瓷刀具材料的物化相容性分析

物理和化学相容性问题是复相陶瓷刀具材料设计中的重要内容之一。本文在所建立的化学相容性计算模型基础上 ,利用计算机编程计算并分析了各种可能的复相陶瓷刀具材料组分系统的化学相容性问题。定性分析了复相陶瓷刀具材料的物理相容性 ,认为各组分材料的热膨胀系数和弹性模量的最优匹配 ,是获得同时具有较高的抗弯强度和断裂韧性的复相陶瓷刀具材料的必要条件之一。     

Design and simulation of thermal residual stresses of coatings on WC-Co cemented carbide cutting tool substrate

Large thermal residual stresses in coatings during the coating deposition process may easily lead to coating delamination of coated carbide tools in machining. In order to reduce the possibility of coating delamination during the tool failure process, a theoretical method was proposed and a numerical method was constructed for the coating design of WC-Co cemented carbide cutting tools. The thermal residual stresses of multi-layered coatings were analytically modeled based on equivalent parameters of coating properties, and the stress distribution of coatings are simulated by Finite element method (FEM). The theoretically calculated results and the FEM simulated results were verified and in good agreement with the experimental test results. The effects of coating thickness, tool substrate, coating type and interlayer were investigated by the proposed geometric and FEM model. Based on the evaluations of matchability of tool substrate and tool coatings, the basic principles of tool coating design were proposed. This provides theoretical basis for the selection and design of coatings of cutting tools in high-speed machining.