共价晶体硬度的微观理论

基于共价固体硬度正比于单位面积上每根化学键对压头的阻抗之和的假设．提出了估计极性共价固体硬度的微观理论。计算了新近合成的立方尖晶石结构Si3N4的理论硬度，计算值与最近报道的实验值吻合。最后．预测了高密度C3N4异构体的理论硬度。     

Na~+对KDP晶体热膨胀及硬度的影响

Na+是KDP原料中一种常见的杂质离子,采用"点籽晶"快速生长法生长了一系列掺杂Na+的KDP晶体,研究了不同掺杂浓度下Na+对KDP晶体热膨胀及硬度的影响。实验表明,随着Na+掺杂浓度的增大,KDP晶体Z向热膨胀系数逐步增大;KDP晶体(001)面的显微硬度整体大于(100)面的硬度,随着Na+掺杂浓度升高,KDP晶体各晶面硬度显著降低。     

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。     

金属Cu纳米晶体的显微硬度及微结构研究

为了研究自悬浮-模压法制备的纳米金属晶体材料的有关性能及微观结构特征,采用自悬浮定向流技术制备出纳米Cu粉,经过常温模压得到金属Cu纳米晶体材料,测试了样品的室温显微硬度,并探讨了不同的压制工艺对金属Cu纳米晶体材料显微硬度的影响;利用X射线衍射谱和正电子湮没技术分别分析了纳米Cu晶体的平均晶粒尺寸和其内部的孔隙状态.研究结果表明:金属Cu纳米晶体的平均晶粒尺寸为25 nm,显微硬度随压制工艺而变化,达1.55～1.90GPa,为粗晶Cu的3～4倍;材料内部缺陷大部分为单空位和空位簇,微孔隙的数量很少.     

纳米晶体材料的Hall—Petch关系

本文综述了纳米晶体材料力学性能如屈服应力，显微硬度的研究，尤其是偏离正常Ｈａｌｌ－Ｐｅｔｃｈ关系的现象及几种解释这种反常效应的模型，分析表明：纳米晶体材料的强度或硬度取决于材料的界面缺陷结构，界面过剩能与过剩体积。     

晶体弹塑性接触的微观机制

用分子动力学和金属固体的镶嵌原子模型研究了ｆｃｃ晶体Ｃｕ探针－基体微观接触的加载卸载规律、系统能量特性、基体微观应力场分布以及塑性失稳的缺陷形成机制。计算结果显示，在表面开始接触时，存在不稳定的突然粘着接触（ｊｕｍｐ－ｔｏ－ｃｏｎｔａｃｔ）。在压入状态（ｉｎｄｅｎｔａｔｉｏｎ）晶体的原子应力分布与宏观Ｈｅｒｔｚ理论的应力场相似。对弹性卸载，探针－基体分离的粘着拉应力接近Ｇｒｉｆｆｉｔｈ理论断裂强度     

显微硬度测量误差对硬度值的影响

前言:测量误差是显微硬度试验误差的主要来源.虽然新技术的应用,使商售的硬度计能够全自动测量,克服了固有的弊端,但仍有大量的硬度计需手摇目测.因此,仍有必要简述压痕d的测量对硬度值的影响,以供从事该项工作的人员参考.     

基于微观结构的WC-Co硬质合金硬度预报模型

采用"随机法"构建了考虑WC-Co硬质合金的Co相体积分数、晶粒平均粒径分布、晶粒形心分布以及晶粒取向角分布的微观结构模型,结合显微压痕实验的有限元模拟,提出一种基于材料微观结构的硬度预报模型。结果表明:"随机法"构建的微观结构模型较好地反映了材料的真实细观结构特征;材料的硬度受微观结构的影响较大,其中以Co相体积分数和晶粒平均粒径分布最为显著。模拟结果与实验结果吻合较好,从而证明了提出的模型能够准确地预报WC-Co硬质合金的硬度。     

摩擦喷射电沉积钴的微观形貌和硬度

本试验在不同的工艺参数下,分别用常规喷射电沉积以及摩擦喷射电沉积技术在石墨基底上制备钴沉积层,并对样件进行硬度检测以及微观形貌观察。结果表明,两种试验条件下,沉积层硬度随电流密度的增加均呈先增后减趋势并随着阴极转速的增大而增高,摩擦条件下的沉积层硬度相对更高(最大硬度值为581HV)。此外,硬质粒子机械摩擦工艺下的晶粒的沉积堆叠过程发生了改变,表层由岛状突起变为均匀沉积。     

硬度值的修正

综合了有关硬度值修正的内容,并增加了按硬度计检定证书修正硬度值的内容,可 硬度试验人员参考。     

Intrinsic hardness of covalent crystals: a unified multiparametric framework

Journal of Materials Science - Bond resistance, bond strength and electronegativity models have been widely utilized for predicting intrinsic hardness of novel covalent materials. Although these...     

Correlation between hardness and elastic moduli of the covalent crystals

From a statistical manner, we collected and correlated experimental bulk (B), shear (G), Young’s modulus (E), and ductility (G/B) with Vickers hardness (H_v) for a number of covalent materials and fitted quantitative and simple H_v–G and H_v–E relationships. Using these experimental formulas and our first-principles calculations, we further predicted the microhardness of some novel potential hard/superhard covalent compounds (BC₂N, AlMgB₁₄, TiO₂, ReC, and PtN₂). It was found that none of them are superhard materials (H_v ? 40 GPa) except BC₂N. The present empirical formula builds up a bridge between Vickers hardness and first-principles calculations that is useful to evaluate and design promising hard/superhard materials.     

Microscopic models of hardness

Recent developments in the field of microscopic hardness models have been reviewed. In these models, the theoretical hardness is described as a function of the bond density and bond strength. The bond strength may be characterized by energy gap, reference potential, electron-holding energy or Gibbs free energy, and different expressions of bond strength may lead to different hardness models. In particular, the hardness model based on the chemical bond theory of complex crystals has been introduced in detail. The examples of the hardness calculations of typical crystals, such as spinel Si₃N₄, stishovite SiO₂, B₁₂O₂, ReB₂, OsB₂, RuB₂, and PtN₂, are presented. These microscopic models of hardness would play an important role in search for new hard materials.     

The hardness anisotropy of ADP crystals

Ammonium dihydrogen orthophosphate (ADP) crystals undergo plastic deformation on the (100) plane by slip along the [011] direction. Vickers hardness tests have been carried out on the (100) face of the crystal for different orientations of the indentor. The observed anisotropy is explained on the basis of crossed slip bands. The shape of the impressions for different orientations of the indentor reveals the non-cubic structure of the plane. The four densely packed faces of the crystal contain sixteen active slip systems.     

Systematic hardness studies on lithium niobate crystals

In view of discrepancies in the available information on the hardness of lithium niobate, a systematic study of the hardness has been carried out. Measurements have been made on two pure lithium niobate crystals with different growth origins, and a Fe-doped sample. The problem of load variation of hardness is examined in detail. The true hardness of LiNbO₃ is found to be 630 ± 30 kg/mm². The Fe-doped crystal has a larger hardness of 750 ± 50 kg/mm².     

Knoop hardness studies on anthracene single crystals

Knoop microhardness studies were carried out on anthracene single crystals. The hardness vs load plot shows two peaks, one at 5g and another at 17·5 g having hardness values 13·0 kg/mm² and 11·4 kg/mm² respectively. The present observation shows that the dislocations split into partials.     

Towards the theory of hardness of materials

Recent studies have shown that hardness, a complex property, can be calculated using very simple approaches or even analytical formulae. These form the basis for evaluating controversial experimental results (as we illustrate for TiO₂-cotunnite) and enable a systematic search for novel hard materials, for instance, using global optimization algorithms (as we show on the example of SiO₂ polymorphs).     

Vickers microindentation hardness studies of β-Sn single crystals

The Vickers microindentation hardness anisotropy profile and load dependence of apparent hardness of white tin (β-Sn) single crystals having different growth directions were investigated. Indentation experiments were carried out on the (001) crystallographic plane at indentation test loads ranging from 10 to 50 mN. Examinations reveal that the degree of the hardness anisotropy decreases with increasing indentation test load. Also, the materials examined exhibit significant peak load dependence (i.e., indentation size effect (ISE)). The traditional Meyer's law, proportional specimen resistance (PSR) model and modified PSR (MPSR) model, were used to analyze the load dependence of the hardness. While Meyer's law can not provide any useful information about the observed ISE, the load-independent hardness (i.e., H_PSR and H_MPSR) values can be estimated for different crystallographic directions, using the PSR and MPSR models. Briefly, for microindentation hardness determinations of β-Sn single crystals, the MPSR model is found to be more effective than the PSR model.