仿生非光滑表面对对磨副的损伤机理研究

利用激光处理技术在灰铸铁表面加工了4种具有非光滑形态的试样,对比研究非光滑形态对对磨副的影响规律。结果表明:非光滑表面对对磨副的损伤机理与光滑试样不同,为非光滑表面凸起对对磨副的微观切削作用。非光滑表面对磨副的磨损质量均远大于未处理试样的对磨副,以对磨副磨损质量为评价指标,条状、环状、点状和网状对对磨副的损伤作用依次减小,损伤最小的网状对磨副其质量损失仅为等面积比下的条状对磨副的55.66%,在相同的单元体面积比和几乎相同的显微硬度条件下,通过调整单元体的形态可以有效地减轻对对磨副的损伤作用。这是由于不同形态的非光滑表面在磨损过程中的载荷分配机制不同。     

合金镀层对钢冷—热疲劳性能的影响

定性和定量地研究了５种合金镀层对Ａ３钢冷－热疲劳性能的影响，结果表明，其中Ｃｏ－Ｗ镀层的冷－热疲劳抗力最高，Ｎ１－Ｐ，Ｎ１－Ｗ镀层的冷－热疲劳抗力最低，而Ｎ１－Ｃｏ－Ｐ，Ｃｏ－Ｗ－Ｐ居中。     

仿生非光滑表面磨损机理的试验研究

为研究具有不同仿生非光滑表面特征试件的磨损机理,通过加工几种具有非光滑表面形态特征的圆形45#钢试件,利用正交试验方法设计耐磨性试验方案,在国产MM200型摩擦磨损试验机上进行试验.试验结果表明,在相同试验条件下,时间、负荷、速度、形态和分布对耐磨性均有影响,并且耐磨性按照凹坑、凸包、波纹、鳞片形态递减;通过分析磨损后非光滑形态表面的形貌及磨屑的图像,得出非光滑表面形态的磨损机理是磨料磨损,并且其磨损机制是微观切削.     

激光处理非光滑凹坑表面耐磨试验的均匀设计研究

本文采用试验优化技术中的均匀设计方法，实施了影响凹坑非光滑表面耐磨性的多因素复杂试验。通过用统计分析软件SPSS（Statistical Package for the Social Sicence)处理试验数据，得出了激光处理仿生非光滑凹坑表面耐磨的多因素回归方程，发现速度、负荷、时间的凹坑圆周方向的距离对耐磨性有显著影响，凹坑轴向之间的距离对耐磨性影响不大。     

合金镀层对钢冷－热疲劳性能的影响

定性和定量地研究了５种合金镀层对Ａ３钢冷－热疲劳性能的影响。结果表明，其中Ｃｏ－Ｗ镀层的冷－热疲劳抗力最高，Ｎｉ－Ｐ、Ｎｉ－Ｗ镀层的冷－热疲劳抗力最低，而Ｎ_ｉ－Ｃｏ－Ｐ、Ｃｏ－Ｗ－Ｐ居中。     

激光熔覆仿生非光滑表面磨粒磨损性能的研究EI北大核心CSCD

以鲨鱼盾鳞表面非光滑形态为模型,制备了由镍基合金粉末熔覆层和45钢基体构成的起伏型、平面型仿生非光滑试样,并进行磨粒磨损实验和磨痕观察,分析磨损机理。结果表明:平面型涂层耐磨性明显优于起伏型涂层;设计和制备耐磨性良好涂层的判据是几何硬化率(GHR)不小于50%。起伏型涂层的磨损机理:硬化带表面自身非光滑磨损机制与磨头对硬化带的冲击磨损机制共同作用。平面型涂层的磨损机理:硬化带表面自身非光滑磨损机制与表面几何形貌非光滑磨损机制相结合。     

仿生技术在化工通风机降噪上的应用

本文从工程仿生学的角度出发,以降低煤矿通风机噪声、提高风量和效率为目标,将生物非光滑表面形态应用到风机叶片表面设计上。探索对叶片表面进行非光滑处理（即表面改形）从而提高降噪性的机理,解决化工企业所面临的风机噪声污染问题。     

GH34钢的热—机械疲劳性能和等温低周疲劳性能

本文研究了珠光体耐热钢GH34的热—机械疲劳性能。热—机械疲劳试验在最大应变与最高温度同相位和逆相位两种情况下进行。控制波形为三角波,频率为0.008Hz,温度范围为200(?)550℃。GH34在淬火+高温回火状态下,经受热—机械循环,表现出循环软化的特性。热—机械疲劳时的循环应变硬化指数,大于上限温度的等温循环应变硬化指数。同相位和逆相位热—机械疲劳抗力相差不大,但都稍高于550℃等温循环时的疲劳抗力。用550℃等温低周疲劳寿命代替200(?)550℃的热—机械疲劳寿命是可行的,且结果偏于安全。     

表面冶金复合材料残余应力产生及对热疲劳性能影响

本文通过对基体及焊层材料线膨胀系数及焊层表面应力的测试，阐述了热喷焊层残余应力产生的原因主要与第一、二次冷却过程有关，表面冷却速度是影响焊层表面应力的关键因素，分析了表面应力对焊层热疲劳性能的影响，焊层表面残余压应力对焊层抗热疲劳性有利。     

Thermal fatigue resistance of a monocrystalline alloy

Specific features of thermal fatigue fracture of a monocrystalline alloy used in manufacturing of rotor blades of gas-turbine units are investigated. The dependences of the number of cycles to failure on the crystallographic orientation of the material, maximum temperature in a cycle, temperature range, and stress concentration are established. The effects of the pores and processes of recrystallization on the degree of thermal fatigue damage are analyzed. __________ Translated from Problemy Prochnosti, No. 5, pp. 54–71, September–October, 2008.     

Thermal fatigue behavior of squeeze cast, discontinuous alumina-silicate fiber-reinforced aluminum alloy (A356) composite

Microstructural damage mechanisms owing to thermal cycling and isothermal exposure at elevated temperature are studied for a short alumina-silicate fiber-reinforced aluminum alloy (A356) composite produced by pressure casting. The tensile strength of the metal matrix composite is found to degrade considerably in each case. An X-ray double-crystal diffraction method is employed to study the mechanisms of recovery in the matrix. The fractal dimension of the X-ray “rocking curves” for individual grains in the composite reflects the substructure formation owing to the rearrangement of dislocations into subdomain walls. Recovery by polygonization is more pronounced in the case of thermal cycling than for equivalent isothermal exposure. The residual stresses in the matrix that provide the fiber clamping force undergo more relaxation in the case of isothermal exposure. The two competing damage mechanisms, thermally activated recovery by polygonization and relaxation of clamping stresses in the matrix, result in identical strength degradation (25%) for both thermal cycling and isothermal exposure.     

The fatigue threshold, surface condition and fatigue limit of steel wire

To test the hypothesis that fatigue cracks in drawn, pearlitic steel wire propagate from pre-existing surface defects which can be treated as cracks, the fatigue limits of five different wires have been statistically determined. The fatigue thresholds were measured using a new AC potential drop method and the initial defect depths then calculated using the equation a_o=1π(ΔK_th/2σ_e)² and compared with observed values.

For higher strength steel wires (σ_u>1800 MPa) the agreement was very good; for the lower strength steel wire (σ_u=1469 MPa), however, the observed values were smaller than the calculated ones. The reasons for this discrepancy are discussed. A quantitative model is developed from the hypothesis and the influence of residual tensile stresses, decarburization and polishing on the fatigue limit of drawn steel wire is assessed.     

Studies on thermal fatigue in 3Cr2W8V die steel by positron lifetime and hardness measurements

Studies on thermal fatigue in 3Cr2W8V die steel have been carried out by using positron lifetime and microhardness measurements. It is found that the mean positron lifetime and the microhardness exhibit periodic up-and-down variations with an increase in the number of fatigue cycles. The experiments indicate that in the process of thermal fatigue there are two opposing effects on variation of defects: microdeformation and dynamic recovery and recrystallization.     

Crack growth behavior at thermal fatigue of H13 tool steel processed by laser surface melting

Biomimetic specimens with striation-shape and diamond-shape morphologies were obtained by laser surface melting on an H13 die steel surface in quenched and tempered state using Nd:YAG laser. The thermal fatigue resistance behavior of the specimens with man-made crack sources was measured. For a set of number of thermal fatigue cycles, the two biomimetic specimens demonstrated decelerated crack growth that indicated better fatigue resistance as compared to the untreated one. The microstructures of the laser melting zone were finer than those of the untreated H13 specimen, and the microhardness of the former was higher than that of the latter after same number of thermal fatigue cycles.     

微观组织对贝氏体钢疲劳裂纹扩展行为的影响

为了研究组织对疲劳裂纹扩展行为的影响,对3种不同贝氏体组织钢进行了疲劳裂纹扩展实验,并采用SEM和EBSD等方法对裂纹进行了分析.结果表明,板条贝氏体组织在近门槛区和稳定扩展区阻碍裂纹扩展的能力最强,具有最小的裂纹扩展速率.板条贝氏体组织中的大角度晶界使裂纹更容易发生偏折,导致断口表面粗糙度增加,裂纹扩展受到较强的粗糙度诱导裂纹闭合效应的作用.随着ΔK的增大,塑性诱导裂纹闭合效应取代粗糙度诱导裂纹闭合效应开始占据主导作用,是板条贝氏体组织中裂纹扩展速率对ΔK的变化较敏感的原因.     

Gigacycle fatigue behavior of a high chromium alloyed cold work tool steel

The influence of carbides and the effect of surface residual stresses (RS), resulting from heat treatment or from the grinding/polishing process, on the fatigue behavior in the gigacycle regime of ingot metallurgy produced D2 type tool steel was examined. RS were found to be responsible for the occurrence of two failure modes: Internal cracks initiating at large primary carbides (clusters) were observed in the cycle number range of 10⁵–10⁶, while in the gigacycle regime near-surface cracks originating at primary carbides caused failure, which was related to degradation of the RS by cyclic loading. Simple models were employed estimating the RS degradation process and the local fatigue strength along the specimen cross section as a function of active RS. In absence of considerable RS predominantly near-surface crack initiation was obtained.     

High temperature mechanical properties and surface fatigue behavior improving of steel alloy via laser shock peening

Laser shock peening was carried out to reveal the effects on ASTM: 410L 00C_r12 microstructures and fatigue resistance in the temperature range 25–600 °C. The new conception of pinning effect was proposed to explain the improvements at the high temperature. Residual stress was measured by X-ray diffraction with sin²ψ method, a high temperature extensometer was utilized to measure the strain and control the strain signal. The grain and precipitated phase evolutionary process were observed by scanning electron microscopy. These results show that a deep layer of compressive residual stress is developed by laser shock peening, and ultimately the isothermal stress-controlled fatigue behavior is enhanced significantly. The formation of high density dislocation structure and the pinning effect at the high temperature, which induces a stronger surface, lower residual stress relaxation and more stable dislocation arrangement. The results have profound guiding significance for fatigue strengthening mechanism of components at the elevated temperature.