定向凝固多晶硅在微纳尺度下的力学性能研究

采用纳米压痕测试系统测试了定向凝固多晶硅沿晶体生长方向横/纵截面的硬度与弹性模量,分析了其受组织各向异性影响的变化规律。使用连续刚度方法借助玻氏压头采集压痕开裂前的硬度与弹性模量,并测量压痕开裂后裂纹尖端到压痕中心点的距离,一次性计算出材料的断裂韧性,避免了开裂对硬度以及弹性模量的影响。结果表明:横截面(110)面的硬度与弹性模量均低于纵截面(111)面,但断裂韧性呈现相反趋势。借助3D原位扫描功能扫描压痕裂纹的三维形貌,发现裂纹主要由剪切滑移台阶所形成。拟合不同载荷下的裂纹长度以及压痕尺寸得出临界压痕尺寸,该值与运用理论推导得出的临界压痕尺寸的结果一致。     

快速生长KDP晶体的显微硬度测试研究

对快速生长KDP晶体（001）、（101）、（100）面分别进行压痕法显微硬度测试,实验表明KDP晶体的显微硬度具有明显的各向异性,（001）、（101）、（100）面的显微硬度分别为187、156.7、151.3kg/mm2;晶体各晶面的显微硬度呈现出显著的压痕尺寸效应,即硬度随载荷的增大而减小。实验发现,当载荷较小,在5～25g时,压痕区没有出现明显的裂纹;随着载荷的增大,在25～200g时,裂纹以辐射状扩展,压痕边缘处形成崩碎状脆裂。确定以25g作为KDP晶体显微硬度测试的最佳载荷,此载荷下所测得的硬度为其显微硬度。     

基于EBSD方法测定单晶Cu纳米压痕的各向异性实验

为研究单晶Cu材料的各向异性力学特性,针对单晶连铸技术制备的单晶Cu,采用电子背散射衍射(EBSD)法对其3个不同晶粒的晶面进行定向,利用原位纳米压痕仪在不同晶面进行不同压入载荷的纳米压痕实验.通过EBSD分析,发现用单晶连铸技术制备的单晶Cu在拉拔方向上具有较强的择优取向,单个晶粒较大,且晶粒内部没有(亚)晶界存在.纳米压痕实验结果表明单晶Cu样件在各种压痕载荷下的约化模量为50 GPa～120GPa,材料的晶体取向对纳米压痕载荷-位移曲线和约化模量有很大影响,面(032)比面(119)和面(041)有更大的约化模量.不同载荷下,硬度值在0.8 GPa左右变动,晶体取向对硬度的影响较小.实验所得单晶Cu各晶面约化模量与采用金属弹性力学理论计算所得数值吻合较好.     

单晶氮化镓纳米压痕与划痕实验

为分析单晶氮化镓的微观变形机理,使用纳米压痕仪对单晶氮化镓进行压痕与划痕实验.结果表明单晶氮化镓压痕过程存在弹塑转变过程即"pop-in"现象,分析得出此现象是由材料的位错萌生和扩展导致,压痕周围产生凸起现象导致计算硬度和弹性模量偏大,通过模型修正得到更真实的硬度和弹性模量数据.单晶氮化镓的变载划痕过程发生弹塑转变和脆塑转变,弹塑变形阶段深度-位移曲线波动平稳,表面光滑;而脆性阶段曲线波动幅度较大,表面产生侧向裂纹且朝着划痕方向45°对称分布.得到弹塑转变的临界载荷为389 mN,脆塑转变临界载荷为1227 mN,因此单晶氮化镓塑性加工区域应在389～1227 mN之间,该区域内易加工出光滑表面.通过不同载荷划痕实验,发现划痕压头所受的切削力和摩擦系数随划痕载荷的增大而增大,因此氮化镓加工时应选择合理的加工载荷.     

压痕法评价钛铌合金表面(TiNb)C强化层显微硬度及断裂韧性

采用压痕法研究了钛铌合金表面(TiNb)C强化层内层状组织对显微硬度的影响，在有效测试载荷的作用下，测量大量压痕的尺寸及裂纹长度，再利用经验公式，对断裂韧性进行计算。结果表明：随着测试载荷的增加，在垂直表面方向，“硬壳-软底”结构导致的基底效应逐渐显著，有效测试载荷为2 N,L-Ⅱ层的平均硬度为2 594.13 HV;在垂直横截面方向，强化层厚度导致的边缘效应逐渐显著，有效测试载荷为1 N,L-Ⅲ层的平均硬度为2 334.88 HV;L-Ⅱ层具有较大的颗粒尺寸，其硬度和断裂韧性均优于L-Ⅲ层。     

半导体材料二次离子质谱定量分析中的基体效应

通过对Wilson等人由实验得出的Si，Ge，GaAs，GaP，InP，CdHgTe半导体和SiO2，Si3N4等绝缘基体中70多种注入元素相对灵敏度因子（RSF）值的综合分析，定义logFRS－Ii直线斜率为基体效应因子。发现基体效应因子值随基体平均原子序数的增加而增大，随基体平均电负性值的增大而减小，随基体氧化物生成热的增加而减小。应用本文提出的二次正离子发射理论分析式较好地解释了这些实验现象，并对影响基体效应的其他因素进行了进一步的讨论。     

微纳米尺度单晶铜各向异性纳米力学分析

采用纳米压痕测量仪对<100>、<110>、<111>不同取向的单晶铜进行了微纳米尺度纳米压痕试验,并对其硬度、约化弹性模量及卸载过程形貌等进行了对比分析.结果表明:在微纳米尺度下,不同取向单晶铜硬度值存在明显的尺寸效应,当压入深度小于30 nm时,单晶铜的硬度值随着压入深度的增加而增大,随后随着压入深度的增加而逐渐减小至0.8 GPa左右.<110>取向单晶铜的约化弹性模量值最大,<111>取向次之,<100>取向最小;<100>、<110>、<111>取向单晶铜的卸载表面均出现明显的堆积现象,其中<110>取向单晶铜出现明显的二维对称堆积形貌,<100>取向单晶铜的弹性恢复位移最大,而<110>取向单晶铜的弹性恢复位移最小.     

改性非晶和纳米晶FINEMET合金的显微硬度研究

本文研究了用元素W部分替代典型FINEMET合金中Nb和Fe的新型合金Fe73.3Cu1 Nb1 .5W1 .7Si1 3.5B9,在淬火态和不同退火温度及保温时间下 ,结合不同载荷大小和加载时间测试合金带芯部的显微硬度。随着纳米晶化的进行 ,自由体积缺陷含量和纳米晶晶界比例的变化会显著影响Fe73.3Cu1 Nb1 .5W1 .7Si1 3.5B9合金的显微硬度 ;合金在非晶态下有一定的压痕尺寸效应 ,而经过 4 5 0℃和 6 0 0℃退火 1h ,压痕尺寸效应消失 ;在 5 5 0℃退火温度下 ,在 0 .1kgf～ 0 .2kgf之间压痕尺寸效应不明显 ;合金的显微硬度变化趋势不符合超塑性波动公式。     

KDP晶体单点金刚石切削加工表层力学性能的研究

压痕和刻划实验是测量材料弹性、塑性和断裂行为的最简单方法,磷酸二氢钾(简称KDP)作为优质的非线性光学材料,常用作光学频率转换器件和电光开关元件,一般采用单点金刚石削的方法加工此类零件.为了深入了解KDP晶体单点金刚石切削加工表层力学性能的变化规律,本文对KDP晶体单点金刚石切削加工表层力学性能指标如硬度H、断裂韧性Kc和残余应力σr方面的有关问题进行深入研究,并通过对KDP晶体(001)面不同晶向上的硬度检测,系统分析了KDP晶体加工表面晶向对材料硬度、断裂韧性和残余应力的影响,研究结果表明:KDP晶体的同一晶面的不同晶向硬度和断裂韧性具有强烈的各向异性.     

SPS快速烧结制备纳米结构Ti5Si3-TiC复合材料

采用金属钛和碳化硅为初始原料,采用放电等离子体快速烧结(SPS)技术制备了致密纳米结构的Ti5Si3-TiC复合材料.借助XRD、SEM和TEM考察了复合材料的相组成和显微结构,利用压痕法测定了其室温显微硬度和断裂韧性.结果表明利用SPS技术可在1260℃,保温8 min条件下使金属钛和碳化硅同步完成反应、烧结、致密化,生成Ti5Si3-TiC复合材料,并且晶粒细小,其中TiC晶粒尺寸＜200nm.     

Evaluation of the fracture toughness of Nb-40Al-8Cr-1W-1Y-0.05B intermetallic material by indentation techniques

The fracture toughness of an Nb-40Al-8Cr-1W-1Y-0.05B intermetallic material was evaluated by indentation techniques at room temperature. Two widely used indentation methods, crack size measurement and indent strength, yielded excellent agreement with a conventional fracture toughness technique using straight-through precracked specimens, despite the occasional formation of poorly configured cracks. However, the modified indentation technique, using dummy indent flaws, resulted in a low fracture toughness compared to that evaluated by the other methods. The material did not exhibit rising R-curve behaviour, as evaluated from the indentation strength data. These results indicate that indentation fracture principles are applicable to this brittle intermetallic material without modification of the residual contact stress term originally calibrated for ceramic materials.     

The effect of indentation-induced cracking on the apparent microhardness

The phenomenon of apparent microhardness increase with increasing applied indentation test load, the reverse indentation size effect (RISE), was addressed from the viewpoint of indentation-induced cracking. The apparent microhardness when the cracking occurs was found to be related to the applied indentation test load as P ^5/3. Previously published results on single crystals of silicon, GaAs, GaP and InP, which differ by a factor of four, all fall on the same line when analysed through this concept. It is concluded that the RISE is a result of the specimen cracking during the indentation.     

Preparation and characterization of bioactive monolayer and functionally graded coatings

Hydroxyapatite powders were made by reacting orthophosphoric acid with calcium hydroxide and dense bioactive coatings were subsequently produced by the plasma spray technique. Three types of hydroxyapatite (flame spheroidized) monolayer coatings and three types of functionally graded coatings were manufactured. It was found that average microhardness values of monolayer coatings decreased as the indentation load increased. The relationship between indentation load and indent diagonal length observed Meyer's law. Microhardness and fracture toughness of coatings were affected by characteristics of feedstock powders for plasma spraying. The indentation fracture toughness of coatings could be significantly increased by incorporating a toughening phase. ©1999 Kluwer Academic Publishers     

用于测量陶瓷断裂韧性的Vickers和Knoop压痕裂纹技术

采用 Vickers 压痕裂纹测量法或 Knoop 压痕～强度法等压痕技术进行了陶瓷的断裂韧性测量。反应烧结 Si_3N_4,热压 Si_3N_4和 SiC 等结构陶瓷用于研究显微结构非均质性和热残余应力对断裂韧性值的影响。人工水晶用于研究晶体学取向和断裂韧性之间的关系。研究发现,Knoop 压痕～强度法比 Vickers 压痕裂纹测量法更适合于非等轴晶系的晶体断裂韧性测量。其原因是 Knoop 压痕的主裂纹和缺口试样的裂纹都沿着同样的晶面扩展,而 Vickers 径向裂纹对却须沿着相互正交的晶面扩展,仅其中的一个晶面与缺口试样的裂纹扩展面一致。在 Vickers 压痕裂纹技术的基础上,用以计算 K_(1c)值不含弹性模量 E 项的 Evans 式(21),似乎能显示出显微结构对 K_(1c)值的影响;含有弹性模量 E 项的 Evans 式(22),似乎能反映出残余热应力对 K_(?)值的影响。所有上述的陶瓷材料,除了反应烧结 Si_3N_4,其压痕和裂纹关系 a~2～C~(3/2)的线性回归相关系数都相当,甚至>0.99。这表明了 Vickers 压痕技术在测定陶瓷的断裂韧性方面具有一定的实用性。     

Theory and application of microindentation in studies of glide and cracking in single crystals of elemental and compound semiconductors

The microhardness of Si (MP 1688 K), GaP (1623 K), GaAs (1510 K) and InP (1327 K) single crystals was determined by indentation (Vicker's hardness, VHN) of low-index facets at loads of 5–100g at 296–673 K, complementing earlier work on Ge and InSb. In the brittle range, extending up to about 0.35 T _melt (K), cracking occurred preferentially along the diagonals of the indentations, and was observed at all loads, with the possible exception of the lowest (5 g) in the case of InP at 289 K. At higher temperatures the relative orientations of crack and slip traces on the crystal surface, as observed by SEM, suggested that cracks nucleated preferentially at the slip-band intersection, as was also noted by Hirsch et al. (Phil. Mag. 3 (1985) 759) in GaAs above 600 K. As earlier in Ge, the VHN was found to depend on the load, L, as L ^p , and on the indentation diameter, d, as dⁿ, with p = 1/2 and n = 2, as required by the model of indentation plasticity of Banerjee and Feltham [4, 5], but higher p and n values were found if chipping at the indentation edges was evident. The effect was related to the resulting decrease in indentation diameter due to the work lost, through chipping, by the indenter. Above about 0.35 T _melt (K), relaxation of the dislocation structures entails a decrease of p and n; both parameters tend to zero as T T _melt. Shear and tensile stresses seem to co-operate in the process of plastic deformation, the role of normal stresses, acting across slip planes, predominating in the brittle range.     

Cracking due to multiple indentations in silicon: effect of indentation spacing and relative orientations

The issue of multiple cracks in materials and their interaction is central in understanding the overall fracture behavior of materials. In the case of materials used in the microelectronics industry, indentation cracking has been extensively used for the measurement of fracture toughness due to its small sample size requirements as well as a relatively good correlation with values obtained from traditional fracture mechanics tests. The majority of these studies have focused on the fracture behavior of a single indent. The present study was aimed at understanding the effect of interaction between the cracks generated on Si from a pair of sequential indents as well as a set of four sequential indents placed at the corners of a square. The distance between the indents was varied from a level comparable to the crack size to a level where interaction could be ignored. This paper discusses the changes in the nature as well as the sizes of cracks due to interaction between the stress fields of the indents.     

Strength and sharp contact fracture of silicon

The fracture strength of Si is considered in the context of yield and reliability of microelectronic and microelectromechanical (MEMS) devices. An overview of Si fracture, including the strength of Si wafers, dice and MEMS elements, highlights the importance of understanding sharp contact flaws, with their attendant residual stress fields, lateral cracks and strength-limiting half-penny cracks in advanced Si device manufacturing. Techniques using controlled indentation flaws, including measurements of hardness, crack lengths, crack propagation under applied stress, and inert and reactive strengths, are applied in an extensive new experimental study of intrinsic, n- and p-type {100} and {110} Si single crystals and polycrystalline Si, addressing many of the issues discussed in the overview. The new results are directly applicable in interpreting the strengths of ground or diced Si wafer surfaces and provide a foundation for studying the strengths of MEMS elements, for which the strength-controlling flaws are less well-defined. Although the indentation fracture behavior of Si is shown to be quite anisotropic, the extensive lateral cracking greatly affects crack lengths and strengths, obscuring the underlying single crystal fracture anisotropy. No effects of doping on fracture are observed. Strength decreases in water and air suggest that Si is susceptible to reactive attack by moisture, although the effect is mild and extremely rapid. Strength increases of indented components after buffered HF etching are shown to be due to reactive attack of the contact impression, leading to residual stress relief.     

Influence of residual stresses and interfacial shear strength on matrix properties in fibre-reinforced ceramic matrix composites

Zircon matrix composites, uniaxially reinforced with a variety of SiC fibres were fabricated in order to create composites with different interfacial properties. Interfacial properties were varied by changing the nature of fibre coatings. The effect of changes in interfacial shear strength on important matrix properties, such as hardness and fracture toughness, was studied on a micro-scale using the microindentation technique. In addition, the relative orientation of the indented cracks with respect to the fibres was varied to investigate the existence of anisotropic behaviour of the matrix. The results indicated that the crack growth in the matrix was influenced by the presence of residual radial and axial stresses, such that relatively higher crack lengths were seen in certain directions in the matrix with respect to other directions. This asymmetric nature of the crack formation upon indentation was the reason for the observed anisotropic fracture toughness of the matrix. The residual stresses also led to anisotropic hardness and a critical load for crack initiation in the matrix.     

Instrumented and Vickers Indentation for the Characterization of Stiffness,Hardness and Toughness of Zirconia Toughened Al_2O_3 and SiC Armor

Instrumented and Vickers indentation testing and microstructure analysis were used to investigate zirconia toughened alumina(ZTA) and silicon carbide(SiC).Several equations were studied to relate the Vickers indentation hardness,Young's modulus and crack behavior to the fracture toughness.The fracture in SiC is unstable and occurs primarily by cleavage leading to a relatively low toughness of 3 MPa m~(1/2),which may be inappropriate for multi-hit capability.ZTA absorbs energy by plastic deformation,pore collapse,crack deviation and crack bridging and exhibits time dependent creep.With a relatively high toughness around 6.6 MPa m~(1/2),ZTA is promising for multi-hit capability.The higher accuracy of mediar equations in calculating the indentation fracture toughness and the relatively high c/a ratios above 2.5suggest median type cracking for both SiC and ZTA.The Young's modulus of both ceramics was most accurately measured at lower indentation loads of about 0.5 kgf,while more accurate hardness and fracture toughness values were obtained at intermediate and at higher indentation loads beyond 5 kgf respectively.A strong indentation size effect(ISE) was observed in both materials.The load independent hardness of SiC is 2563 HV,putting it far above the standard armor hardness requirement of 1500 HV that is barely met by ZTA.     

Fracture analysis of cobalt-bonded tungsten carbide composites

Specimens of WC-Co were indented to measure the resulting crack size and unindented samples were fractured in three-point flexure to obtain strength and to measure characteristic features on the fracture surface. Fracture toughness was determined using indentation techniques and compared to those determined using fractography. We show that principles of fracture mechanics can be applied to WC-Co composites and can be used to analyse the fracture process.The fracture surfaces were examined by scanning electron microscopy and optical microscopy. Characteristic features observed in glasses, single crystals and polycrystalline materials known as mirror, mist, hackle and crack branching were identified for these composites. We discuss the importance of fracture surface analysis in determining the fracture origins and in the failure analysis of WC-Co composites.