超音速微粒轰击诱导表面纳米化对TC11钛合金组织和力学性能的影响

采用超音速微粒轰击(SFPB)表面纳米化技术,在TC11钛合金表层构筑了一定层深的梯度纳米结构,研究了SFPB气体压力对TC11钛合金微观组织和力学性能的影响。结果表明,在低气体压力(0.5 MPa)下,形成了25 μm厚的严重塑性变形层,表层晶粒细化至纳米量级(17.7 nm)。随着气体压力的增大,表层纳米晶尺寸降低,严重塑性变形(SPD)层增大,在高气体压力(1.5 MPa)下,表层纳米晶尺寸和严重塑性变形层深度分别为9.4 nm和51 μm。随着SFPB气体压力的增大,表层显微硬度及硬化层深度逐渐增加,屈服强度、抗拉强度显著增加,而伸长率变化不大,断口形貌从典型的韧性断裂向韧-脆性混合断裂转变。      

乙醇对TC4钛合金超高周疲劳性能的影响

利用超声疲劳试验方法分别对室温下医用酒精(体积分数75%)中浸泡5min、医用酒精浸泡5min后再在生理盐水中浸泡24h、直接在生理盐水中浸泡24h、分析纯乙醇(体积分数99.9%)中浸泡6h、医用酒精中浸泡6h等处理条件下退火态Ti6Al4V(TC4)钛合金的超高周疲劳性能进行了研究,并利用扫描电子显微镜(SEM)观察疲劳断面形貌,分析了TC4钛合金的疲劳断裂特性。结果表明:在104~109周次范围内,经医用酒精处理后TC4钛合金的S-N曲线呈现一次阶梯下降型,而未用医用酒精处理的TC4钛合金的S-N曲线呈现缓慢下降型;在300~700 MPa应力范围内,医用酒精浸泡过的TC4钛合金试样疲劳寿命快速下降;医用酒精处理后的TC4钛合金的超高周疲劳断裂全部从表面发生、断面较光滑且瞬断区面积占比极小,不同于未接触医用酒精的TC4钛合金试样的穿晶塑性断裂。     

激光冲击强化对300M钢微观组织和力学性能的影响

采用激光冲击强化(LSP)技术在300M钢表层制备梯度纳米结构,并借助三维表面形貌仪、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、纳米压痕仪及拉伸试验机对300M钢不同脉冲能量LSP处理后的微观组织演变和力学性能变化进行表征。结果表明,300M钢经LSP处理后表层形成梯度纳米结构,随着脉冲能量的增加,表层晶粒尺寸从15 nm(3J)细化至10 nm(7J)左右,晶粒出现非晶化;同时,次表层组织中形成了大量位错缠结及形变孪晶等亚结构缺陷,且随着脉冲能量的增加位错密度急剧增高,同时形变孪晶数量也随之增多。LSP后300M钢表层纳米压痕硬度得到显著提高,且随着脉冲能量的增加而增加;强度和塑性得到一定程度的改善,断口形貌由典型的韧性断裂转变为韧-脆混合型断裂。      

发动机用TC17合金喷丸+微弧氧化涂层组织和疲劳性分析北大核心CSCD

通过实验研究了TC17钛合金的喷丸处理效果,利用微弧氧化方法来达到纳米晶过渡层组织结构重构的过程。通过实验测试的方式研究不同工艺涂层微观组织,硬度以及疲劳性能。研究结果表明:形成许多火山型微孔,孔洞尺寸也存在明显差异。对合金实施喷丸处理能够获得厚度更大微弧氧化层,引起了晶粒的明显细化,得到更加致密的组织结构。经过喷丸处理后,硬度为463HV0.1,表现为硬度提高。对不同深度区域的组织硬度进行对比发现,从表面过渡到基体中的范围内硬度呈现不断减小的变化趋势。当试样表面经喷丸处理后疲劳寿命可以达到15361周次,相对处理前的试样疲劳寿命延长了15%左右。对试样表面实施喷丸处理将会导致表面组织中产生众多疲劳源并进一步迁移到基体内,疲劳源范围也持续缩小,涂层表面存在众多微孔。     

超音速微粒轰击45钢表面纳米化的研究

采用超音速微粒轰击技术(SFPB)对由铁素体和珠光体组成的45钢进行表面纳米化处理,在材料表面制备了纳米结构表层,利用X射线衍射、扫描电镜、透射电镜等分析技术研究了表面纳米结构层不同深度的微观组织结构特征.研究表明:经SFPB处理后,材料表层发生了严重的塑性变形,形成了由铁素体和渗碳体组成的纳米结构层;随着处理时间的增加纳米结构层的厚度由几微米增加到15 μm(晶粒尺寸＜100 nm);在材料的最表层形成了晶粒尺寸约15 nm的具有随机取向的等轴晶,纳米晶粒尺寸随着距表面距离的增加增大;在距表面约为15 μm处,存在平均晶粒尺寸约100 nm的等轴晶和具有相近尺寸的胞状结构;在约30 μm处,大量的高密度位错墙分别将铁素体相和珠光体相分割成尺寸在200～500 nm的胞状结构.分析表明45钢表面纳米化主要是位错运动的结果.     

发动机用TC17合金喷丸+微弧氧化涂层组织和疲劳性分析

通过实验研究了TC17钛合金的喷丸处理效果,利用微弧氧化方法来达到纳米晶过渡层组织结构重构的过程。通过实验测试的方式研究不同工艺涂层微观组织,硬度以及疲劳性能。研究结果表明:形成许多火山型微孔,孔洞尺寸也存在明显差异。对合金实施喷丸处理能够获得厚度更大微弧氧化层,引起了晶粒的明显细化,得到更加致密的组织结构。经过喷丸处理后,硬度为463HV0.1,表现为硬度提高。对不同深度区域的组织硬度进行对比发现,从表面过渡到基体中的范围内硬度呈现不断减小的变化趋势。当试样表面经喷丸处理后疲劳寿命可以达到15361周次,相对处理前的试样疲劳寿命延长了15%左右。对试样表面实施喷丸处理将会导致表面组织中产生众多疲劳源并进一步迁移到基体内,疲劳源范围也持续缩小,涂层表面存在众多微孔。     

显微组织对TC18钛合金应力控制低周疲劳性能的影响

研究了片状和网篮两种典型组织对TC18钛合金不同应力振幅下低周疲劳寿命的影响.结果表明:TC18钛合金低周疲劳寿命对显微组织的变化不敏感.在相同的应力振幅下,双态组织和片状组织的疲劳寿命基本相当.TC18钛合金的低周疲劳寿命N取决于加载的应力振幅,σmax与N之间呈对数关系,相关系数达0.99以上.     

S135钻杆钢的拉扭复合加载疲劳行为

采用疲劳实验和回归分析相结合的方法,研究了S135钻杆钢在拉扭复合加载条件下的疲劳行为,并对疲劳断口进行了微观分析。结果表明:当τa/σeq=0.7时,由拉扭应力幅对应的当量应力表示的疲劳寿命公式可很好地描述S135钻杆钢的拉扭疲劳寿命规律;疲劳断口由疲劳源区、疲劳裂纹稳定扩展区和快速瞬断区组成,疲劳裂纹从试样表面萌生,并向试样内部扩展,且常为多疲劳源,不同疲劳源断口的连接和复合加载形成所谓的"屋脊"状特征;拉扭疲劳断裂试样裂纹源区的微观断口特征为明显的河流花样,裂纹扩展区的微观断口特征为疲劳条带与涟波状花样。     

超音速微粒轰击38CrSi钢表面纳米化的研究

采用超音速微粒轰击技术(Supersonic Fine Particles Bombarding,SFPB)对调质态合金钢38CrSi进行表面纳米化处理;利用X射线衍射、扫描电镜、透射电镜等分析技术研究不同工艺条件下表面纳米化层的微观组织结构特征.结果表明:经SFPB处理后,材料表层组织严重细化,并形成了纳米结构层(晶粒尺寸＜100nm),随处理时间的延长,最表面纳米晶的尺寸变化不大,纳米结构层的厚度有所增加;当处理时间为240s时,在最表面层形成了平均晶粒尺寸约为16nm的具有随机取向的等轴纳米晶.纳米结构层的晶粒尺寸随着距表面距离的增加而增大.在距表面约25μm处,存在着大量的由位错线和高密度的位错缠结分割的胞块,尺寸为80～100nm;分析表明位错运动是表面纳米化的主要原因.     

拉-拉疲劳载荷下钛合金湿喷丸的残余应力松弛及再次喷丸工艺EI北大核心CSCD

采用湿法喷丸强化工艺(wet shot-peening)对TC4钛合金表面进行处理,研究高、低周的拉-拉疲劳过程中合金残余应力松弛规律,探讨再次喷丸工艺(re-shot-peening,RSP)对疲劳寿命的影响。结果表明:在拉应力载荷状态下,残余压应力依然发生松弛现象。疲劳载荷水平对喷丸TC4钛合金残余压应力场(CRSF)的松弛速率、松弛程度和松弛范围具有重要影响。高周疲劳(HCF)过程中残余应力松弛主要发生在近表层0~30μm,松弛速率较慢。低周疲劳(LCF)过程中残余应力松弛发生在0~80μm,范围更大,速率更快。RSP周期对于TC4钛合金的疲劳寿命也具有较大影响。在25%和50%初始喷丸疲劳寿命进行RSP处理会显著提高疲劳寿命,而在75%初始喷丸疲劳寿命处进行RSP处理对于疲劳寿命基本没有影响。此外,RSP的强化效果与疲劳载荷水平相关,对于高周疲劳寿命提高明显。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.