深过冷条件下Co_7Mo_6金属间化合物的枝晶生长和维氏硬度研究

采用电磁悬浮和自由落体两种实验技术对二元Co-50%Mo过共晶合金中初生Co_7Mo_6金属间化合物的生长机理和维氏硬度进行了系统研究.电磁悬浮实验中,合金熔体获得的最大过冷度为203 K(0.12T_L),初生Co_7Mo_6枝晶生长速度与过冷度之间呈现幂函数关系.随着过冷度的增大,初生枝晶中Co元素含量单调递增,枝晶尺寸明显减小,并且其维氏硬度逐渐升高.在自由落体状态下,随着液滴直径的减小,合金熔体的过冷度和冷却速率均增大.当液滴直径减小到392μm以下时,初生Co_7Mo_6枝晶从小平面向非小平面形态进行转变.实验发现,深过冷条件下Co_7Mo_6化合物发生了显著的溶质截留效应,其维氏硬度与Co元素分布和形貌特征密切相关.     

几种FeNi基非晶态合金退火期间显微硬度与结构变化关系

本文通过测量几种非晶态合金在退火期间的显微硬度、探讨了在弛豫和晶化过程中硬度是如何反应结构变化的。     

Composite Microhardness of Quartz — Al Structures

The microhardness-depth profiles of as-obtained and annealed quartz (INFstrate)-Al (film) structures have been investigated. A layer of constant hardness has been detected beneath the initial interface. This is supposed to result from incorporation of aluminium atoms into the surface layer of the INFstrate, reduction of SiO₂ and diffusion of the atoms of a certain element during the processes of preparing and rapid thermal annealing of the structures.     

Effect of Various Impurities on the Hardness of NaCl Crystals

The hardness of NaCl crystal in the presence of mono, divalent and polyvalent ions were measured. Measurements were made in the indentation load range from 5 x 10^‐3 to 20 x 10^‐3 N. The measured data showed that there is an indentation size effect. Classical Meyer's law was used for the characterization of crystal hardness f NaCl. The Meyer index was found to be smaller than 2 indicating brittle material characteristic. The PRS model was also used for the determination of the load‐independent microhardness value. It was found that the crystal hardness of NaCl is chancing depending on the type of impurity and the concentration.     

Microhardness of 6H-SiC Epitaxial Layers Grown by Sublimation

Knoop microhardness of 6H-SiC layers grown by sublimation epitaxy was investigated. The microhardness-load curves for all of the samples were measured and then used to extract the load-independent microhardness values. The relationships of these values to the growth time and growth rate were studied. The microhardness-depth profiles indicated that the layer/substrate interface region had a microhardness value that differed significantly from that of both the epi-layer and the substrate.     

Review: Indentation size effect,indentation cracks and microhardness measurement of brittle crystalline solids – some basic concepts and trends

Indentation size effect, indentation cracks and microhardness measurement of some brittle crystals are reviewed against the background of the existing concepts of indentation deformation of crystalline solids. Several approaches reported in the literature devoted to relationships between applied indentation test load P and indentation diagonal length d are applied to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds. Using typical examples of normal and reverse ISE it is shown that the indentation induced cracking model does not give load‐independent hardness and the final expression describing the experimental data for various compounds is essentially another form of the Meyer law. Analysis of experiment data on crack lengths and indentation diagonals for different indentation loads suggests that the origin of ISE is associated with the processes of formation of indentation cracks following the general concepts of fracture mechanics. The load‐independent hardness H₀ may be determined reliably from plots of P /d against d of the proportional resistance model or of H_V against 1/d as predicted by strain gradient plasticity theories. It was found that the load‐independent hardness of depends on crystal orientation and state of the indented surface. Finally, some comments on determination of fracture toughness and brittle index of crystals are made. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology – Property Correlations of PP Materials by Means of Microhardness

The present work deals with the influence of crystallization temperature, cooling rate and annealing conditions on microhardness, indentation modulus and creep behaviour of ethylene/propylene (E/P) random copolymers with 4, 6 and 8 mol% ethylene as well as α- and β-spherulites in a homopolymer and an E/P random copolymer. The materials are unnucleated, the formation of β-spherulites occurs sporadically. Additionally the indentation creep behaviour of α- and β-nucleated PP is investigated. A nearly linear correlation between hardness as well as indentation modulus and crystallintity of the E/P copolymers can be proved. An increasing cooling rate leads to decreasing hardness and modulus values due to the hindered crystallization. For the investigation of the α- and β-phases different crystallization and annealing temperatures are used. Independent of these conditions, microhardness and modulus determined by indentation testing are lower for the β-phase in both materials. Increasing crystallization temperature and annealing lead to an increasing hardness and modulus in both phases. However, an effective annealing effect takes place only at short times and elevated temperatures above 100 °C. The increasing of microhardness and modulus is correlated with an increasing in lamellae thicknesses. Additionally, indentation creep experiments were carried out on nucleated materials that show the stronger creep tendency of the β-phase PP and the stronger influence of annealing on this phase.