EB-PVD热障涂层的表观压痕尺寸效应

采用Knoop压痕法评价沉积于镍基单晶高温合金基体上的EB—PVD热障涂层的显微硬度。测试结果表明，热障涂层系统的显微硬度存在压痕尺寸效应，即表观显微硬度随施压载荷的增加而显著降低。用弹／塑性模型Knoop压痕能量平衡对表观压痕尺寸效应进行分析，并从实验测试结果分析得出与载荷无关的显微硬度值。     

纳米改性Ti(C,N)基金属陶瓷的渗硼处理

真空烧结制备了纳米改性的Ti(C,N)基金属陶瓷,并对其进行了固体粉末渗硼处理。研究了渗硼处理对不同金属相的纳米TiN改性的Ti(C,N)基金属陶瓷组织与性能的影响。光学显微照片表明,材料的表面形成一层渗硼层;X射线对材料的物相分析表明,试样表面的渗硼层为TiB2、MoB、Ni3B、NiB、CoB等硼化物;硬度测试结果表明,试样的表面显微硬度大大提高。试验结果表明,不同金属相含量的Ti(C,N)基金属陶瓷均具有可渗硼性。     

C2H2/N2流量对反应等离子喷涂TiCN涂层影响的研究

以不同流量的C2H2与N2作为反应气体，通过反应等离子喷涂的方法制备TiCN涂层。并对涂层中物相、组织形貌和显微硬度进行比较与分析。实验结果表明，以C2H2气体流量为0．25m3／h喷涂时。所得涂层的组织致密，硬度较高；以C2H2N2流量比为1：1进行喷涂时，涂层中的氧化物含量较少，但组织致密性较差，硬度降低。     

球形压痕法评价(Ti,Nb)N膜层断裂性能

采用球形压痕试验，在高速钢基体上对电弧离子镀工艺沉积制备的(TixNb)N膜层断裂性能进行评价。在600N载荷下，在压痕的周围只产生径向裂纹；统计分析压痕周围产生的裂纹，采用裂纹密度函数β，对膜层的断裂性能进行了分析。结果表明：(TixNb)N均质膜层在显微硬度提高的同时，裂纹密度β增加，膜层的脆性增大，断裂韧度下降。TixNb1-xN梯度膜具有较高膜层显微硬度，仍然具有较好的断裂韧度，预渗氮处理的膜层裂纹密度较小，膜层的断裂韧度最好。采用裂纹密度函数卢统计分析，通过对(TixNb)N膜层压痕试验，可以很好的定量和半定量地比较膜层的断裂性能。     

Mo含量对CrMoAlN薄膜微观结构和摩擦磨损性能的影响

采用非平衡磁控溅射离子镀技术在M2工具钢和单晶Si表面沉积多元CrMoAlN纳米多层薄膜.利用EDS,SEM,XRD,XPS,纳米压痕仪和销盘磨损试验仪研究Mo含量对CrMoAlN薄膜成分、表面和截面形貌、相结构、化学价态、显微硬度和摩擦性能的影响.结果表明,不同Mo含量的CrMoAlN薄膜均为fcc结构,Mo代替了Cr Al N晶格中部分Cr或Al的位置,形成了以fcc-Cr N相为基础的CrMoAlN置换固溶体.随着Mo含量提高,CrMoAlN薄膜表面颗粒尺寸明显减小,截面柱状晶结构逐渐消失.CrMoAlN薄膜的显微硬度和弹性模量随着Mo含量的增加而提高,摩擦系数和磨损率随着Mo含量的提高而降低.Mo含量为19.47%(原子分数)时,显微硬度与弹性模量均达到最大值29.70 GPa和427.53 GPa,摩擦系数和磨损率达到最小值0.271和1.2×10-16m3/(N·m).     

不同基体的TiCN膜层组织与性能研究

研究了离子氮化对CrWMn冷作模具钢TiCN膜层组织与性能的影响,使用OM、XRD、SEM、EDS、台阶仪、划痕仪等方法对薄膜形貌、硬度、结合强度、粗糙度、摩擦性能等进行了研究。结果表明,未经离子氮化的TiCN膜层主要含Fe、Ti(C,N)等物相,呈现(111)面择优生长,显微硬度为364 HV_(100),膜层结合强度不高,表面不平整,耐磨性较差。离子氮化后,TiCN膜层表面颗粒细小,致密度提高;膜层主要含Fe、Fe_3N、Fe_4N等物相,呈现(111)面择优生长,显微硬度为635 HV_(100),膜层结合强度高,表面更光滑、平整,耐磨性较好。经过离子氮化的膜层结合强度高,表面光滑,耐磨性能较好。     

Co添加对17Ni-(10NiO-NiFe_2O_4)金属陶瓷的致密化及力学性能的影响

为了改善17Ni-(10NiO-NiFe2O4)金属陶瓷惰性阳极中金属相的分布,在原料中添加不同含量的Co,以Co-Ni取代纯Ni作为金属相,采用真空烧结方法制备17(x Co-Ni)-(10NiO-NiF e2O4)金属陶瓷,并研究Co添加量对金属陶瓷物相组成、显微组织、致密度及力学性能的影响。结果表明:烧结样品主要由Co-Ni、Ni Fe2O4、Ni O组成,部分Co与陶瓷基体反应生成CoO与Fe2O3。添加适量Co可以改善金属相在陶瓷相的分布和形貌,使团聚孤立的金属相分布均匀,且部分球状金属相变为长条状金属相;同时,添加适量Co还可以促进烧结,提高试样的致密度。适量Co的添加还能降低晶粒尺寸,大幅提高金属陶瓷材料强度与韧性。当Co质量分数为金属相的20%时,金属陶瓷的综合性能最好,致密度、抗弯强度、断裂韧性及硬度分别达到96.87%、163.65 MPa、8.38 MPa/m1/2和820.81HV。     

金属材料显微硬度压痕尺寸效应分析及其试验研究

利用显微硬度计和扫描电镜分别对电工纯铁DT4A、镍铍高弹合金97NiBe、化学镀镍层3种金属材料样品进行显微维氏硬度测试实验。绘制试验载荷与压痕对角线尺寸关系曲线,分析各曲线的拟合公式,建立模型。应用材料力学理论对模型进行深入分析,确定各参量的物理含义。根据各物理参量的含义,对微纳米尺度下出现硬度压痕尺寸效应现象的原因进行解释。结果表明,金属材料的显微维氏硬度表现出了显著的硬度压痕尺寸效应,用修正后的模型P0=a_1d+a_2d~2和HV_(micro)=0.189 1×(a_1/d+a_2)可以描述和解释硬度压痕尺寸效应现象。未修正模型中,a_0参数的物理含义是为了能准确反映设备试验力误差的物理量;a_1参数的物理含义是与样品的弹性模量、接触刚度、显微硬度和宏观硬度有关的物理量;a_2参数的物理含义是试验加载过程中压头压入试样表面产生塑性变形需要的压应力,其值近似等于5.288倍的宏观维氏硬度。金属材料显微维氏硬度压痕表面的接触刚度变化是其在微纳米尺度下存在压痕尺寸效应的主要原因。推导出的显微维氏硬度压痕表面的接触刚度计算模型为S=7Ed-7a1。     

纳米压痕法分析ECAP变形工业纯钛的力学性能

采用等径弯曲通道变形(Equal Channel Angular Pressing,ECAP)技术制备了不同晶粒尺寸的超细晶工业纯钛,通过纳米压痕测试技术对ECAP变形工业纯钛的力学性能进行研究,讨论了加载应变速率和晶粒尺寸对工业纯钛硬度测试结果的影响,进一步分析了ECAP变形工业纯钛的应变硬化能力和残余应力。结果表明:随着加载应变速率的增大和晶粒尺寸的减小,工业纯钛的硬度值增加。硬度-位移曲线表现出具有硬化效应的压痕尺寸效应(Indentation Size Effect,ISE)。纳米压痕形貌表明:ECAP变形工业纯钛的应变硬化能力降低,存在残余压应力。     

沉积气压对杂化离子镀TiCN薄膜结构和性能的影响

TiCN薄膜在刀模具领域有着广泛的应用前景,但它的结构和性能往往随制备工艺参数的不同而有较大差异。为了研究沉积气压对杂化离子镀TiCN薄膜结构和性能的影响,找到合适的Ar和N2分压比以优化工艺参数,采用杂化离子镀技术在高速钢、硅片以及不锈钢片表面制备TiCN薄膜,通过改变沉积过程中Ar和N2的分压获得不同的薄膜。用X射线衍射仪、扫描电子显微镜、维氏硬度计、摩擦磨损仪、XP-2台阶仪对薄膜的物相结构、表面形貌、显微硬度、摩擦因数和沉积速率进行表征。结果表明:TiCN膜层择优生长方向主要表现为TiCN相的(111)晶面;试验中保持Ar分压为0.1Pa不变,增加N2分压,即沉积气压增大,薄膜的显微硬度先升高再降低,对应摩擦因数先降低再升高,沉积速率不断减小最终趋于平缓,而表面形貌受沉积气压变化的影响很小。     

影响显微硬度测量的压痕尺寸效应

叙述压痕尺寸效应对显微硬度测量值的影响,推导出不同负荷下测得的显微硬度换算成标准负荷下显微硬度的公式,并用纯银样品进行验证。结果表明公式的应用显著提高了显微硬度测量的准确度,改善了显微硬度测量中可比性差的状况。     

An application of universal hardness test to metal powder particles

Powder metallurgy is a “net shape” components producing technology from metal powders by compaction with following sintering processes. For today actual trends of powder metallurgy are associated with modern powder grades, alloyed by elements with high affinity to oxygen (Cr, Mn, Si, etc.). Contamination of powder particles by oxides and/or other secondary phases have a negative effect on their compressibility and sinterability. The geometry properties of powders give integral information about powder quality. Evaluation of yield strength and/or rather the strain hardening exponent, characterizing the mechanical properties on the level of individual particles, really is not possible. One of available approaches could be measurement of the microhardness of particles. The contribution deals with the evaluation of the microhardness of powder particles and specification of the factors affecting measured values. Using standard Vickers microhardness HV0.01 measurements for two different powders the results obtained showed large scattering from the average. This gave no possibility to identify the influence of alloying and particle matrix purity on microhardness. Problem was solved utilizing instrumented indentation test using NanoIndenter XP. This is usable technique for estimation of microhardness of powder particle matrix and gives possibility to recognize differences between different size fractions of particles. Based on the obtained results it was concluded, that absolute results of indentation hardness and indentation modulus are strongly affected by mounting resin type. Utilizing DSI method and mounting resin of proper hardness enabled to evaluate the microhardness of powders with different alloying element content. Influence of particles purity/size on powder microhardness was established as well. Indentation hardness and indentation modulus for sintered materials are in good agreement with the data for corresponding bulk materials. Obtained results confirm that universal hardness test is valuable instrument for evaluating of sintered materials properties.     

Preparation,characterization and electrochemical properties of boron-doped diamond films on Nb substrates

A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing (9.8 N load). The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H₂SO₄solution and KFe(CN)₆ redox system compared with other doping level electrodes.     

Some observations on hardness measurements of particulate-reinforced 6061 aluminum metal matrix composites

Hardness measurements on a series of particulate- reinforced metal matrix composites in a solution treated and T- 6 condition were carried out using a Vickers microhardness tester at 25-, 50-, 100-, 200-, 300-, and 500-g indenter loads and a Vickers macrohardness tester at an indenter load of 5 kg. It appears that the presence of the particles makes a contribution to the hardness measurement, the degree of which depends on the size and distribution of the particles, and also the indentation load. Although some trends are observed, there is no predictable effect of the material and test parameter on the hardness values.     

Vickers Microhardness Study of Nonlinear Optical Single Crystals of Doped and Undoped S-Benzyl Isothiouronium Chloride

The Vickers microhardness of the doped and undoped S-benzyl isothiouronium chloride single crystals was investigated using a Vickers microhardness tester at room temperature. It was observed that, up to an applied load of 15 g, the hardness of the crystals increases with an increase in load, and thereafter it is practically independent of the indentation load. Efforts are made to improve the hardness of S-benzyl isothiouronium chloride crystal by doping. It was found that all doped crystals possess greater hardness than the undoped crystals.     

Determining microhardness and elastic modulus of plasma-sprayed Cr3C2–NiCr coatings using Knoop indentation testing

In this paper, the microhardness and elastic moduli of plasma-sprayed Cr₃C₂–NiCr coatings were measured using the Knoop indentation technique, and the effects of coating process, measurement directions and indenter loads were investigated. The measured data sets were then statistically analyzed employing the Weibull distribution to assess their variability within the coatings. It was found that the measured Knoop hardness and elastic moduli of the coatings were related to microstructure and displayed highly anisotropic behavior of the coatings. In particular, the Knoop hardness, when measured with the major diagonal of the indenter parallel to the interlamellar boundaries of the coatings, was obviously lower than that done where the major diagonal was vertical to the boundaries for an identical indenter load. The measured elastic modulus data exhibited much more scatter than those of the corresponding Knoop hardness. Because it depends on the applied indenter load and it contains systematical error, the Knoop indentation test is not practicable to measure the elastic modulus of thermal sprayed coatings when the major diagonal of the indenter is parallel to the interlamellar boundaries. The results are mainly explained in terms of interlamellar boundary sliding caused by the indenter loads.     

A new look at the influences of load, grain size and grain boundaries on the room temperature hardness of ceramics

The measured load (size) effect on the hardness is modelled assuming that for the extension of the plastically deformed zone, growth and multiplication of pre-existing elements of plasticity are more effective than the generation of new dislocations and twins in the virgin material around. This idea also explains the decreasing load effect at smaller grain sizes. Therefore, microhardness approaches must not be used to investigate grain size effects in ceramic microstructures. The comparison of the real grain size effect in sintered Al₂O₃ with the indentation size (load) effect in sapphire single crystals (shown to simulate the grain size effect in polycrystals but avoiding the influence of grain boundaries) reveals an important contribution of the grain boundaries to the permanent deformation at the indentation site at room temperature even for coarser microstructures and rules out the chances for a strong hardness increase in oxide ceramics at grain sizes < 100 nm. However, first results indicate a possibly different behavior in binder-free carbides where the covalent character of interface bonding may reduce the degree of grain boundary deformation at room temperature as it is known to reduce the microplastic deformability of the crystal lattice.     

基于原子力显微镜的薄膜原位压痕力学性能研究

基于原子力显微镜(AFM)和扫描电子显微镜(SEM)建立了一套原位纳米压痕测试系统。该系统可以实现控制带有金刚石(Cube corner)压头的AFM微悬臂梁对样品进行压入实验,并得到载荷-位移曲线,同时可以对压痕过程进行原位SEM实时观察。发展了一种基于AFM微悬臂梁加载和原位SEM压痕图像分析的力学性能测试方法,通过测量压入最大载荷和原位SEM测量压痕残余面积得到塑性薄膜的硬度和弹性模量。利用此方法对磁控溅射硅衬底上纳米晶银薄膜进行了压痕实验,并与Nanoindenter G200型纳米压痕仪实验进行对比研究。结果表明,原位AFM压痕方法具有高的载荷和位移分辨率,可以实现纳牛至微牛级的压痕实验,通过测量压痕面积得到塑性薄膜的硬度值,减小了使用Oliver-pharr方法中软膜硬基底上凸起(Pile-up)效应的影响,计算结果也具有好的测试精度和可靠性。