超高频连续感应钎焊金刚石界面特征

提出超高频连续感应钎焊工艺方法,采用Ag-Cu-Ti合金钎焊金刚石磨粒与大尺寸钢基体.通过扫描电子显微镜(SEM)和X射线能谱仪(EDX)对钎焊后的试样界面微观结构以及金刚石磨粒表面生成物形貌特征进行观察和分析.结果表明,超高频连续感应钎焊实现了金刚石、钎料、基体三者之间的连接,钎焊后的钎料层组织晶粒细小,局部区域可见到枝晶状组织.金刚石与钎料层界面存在Ti元素与C元素的反应层,在金刚石磨粒表面生成点状TiC晶体,其直径均100 nm以下,且在金刚石表面呈离散分布.与真空炉中钎焊工艺相比,该界面结构更有利于钎料层对金刚石磨粒的连接把持.     

Cu-32Mn-8Ti预合金粉末与金刚石颗粒的界面反应

采用自制Cu-32Mn-8Ti预合金粉末为粘合剂,在低真空钎焊条件下制备了金刚石复合材料.利用扫描电镜、能谱仪、X射线衍射仪等研究预合金粉末与金刚石颗粒界面反应.结果表明,在试验条件下,胎体中的Ti原子向金刚石表面扩散,形成约为3～5μm的扩散层,并与金刚石颗粒表面的C发生化学反应生成TiC,呈非连续层片状分布于金刚石颗粒表面,实现了金刚石颗粒与金属的化学键结合.     

金刚石磨粒/Cu-Sn-Ti合金/金属胎体复合节块界面微结构

采用铜锡钛(Cu-Sn-Ti)合金钎料分别利用两种常规钎焊方法进行金刚石磨粒预钎焊处理试验并制备复合节块.通过静压强度试验测试了预钎焊磨粒的静压强度,通过三点抗弯试验测试了复合节块的强度,并使用扫描电镜、能谱仪、X型射线衍射仪分析预钎焊金刚石磨粒和复合节块断口的微结构.结果表明:真空炉中预钎焊后金刚石磨粒表面形貌较好,Cu-Sn-Ti合金钎料与金刚石在预钎焊过程中发生了界面元素扩散,形成化学结合界面,Cu-Sn-Ti合金钎料对金刚石的热损伤较小;预钎焊金刚石磨粒的体积浓度为10; ～40;时复合节块抗弯强度达到791MPa以上,高于常规金刚石节块强度;预钎焊金刚石磨粒与金属胎体在烧结过程中发生了界面元素扩散,形成冶金结合,复合节块界面结合强度高.     

Ag-Cu-Ti/TiC复合钎料钎焊细粒度金刚石的研究

在Ag-Cu-Ti合金中加入一定量的TiC颗粒制成复合钎料,进行细粒度金刚石磨粒与45钢基体的真空钎焊实验.运用三维视频显微镜、扫描电镜和X射线衍射仪分析TiC颗粒、Ag-Cu-Ti合金和金刚石磨粒之间的结合界面.结果表明:TiC颗粒能有效降低试验工艺下Ag-Cu-Ti合金在基体表面的流动性和结晶时产生的隆起,复合钎料在基体表面分布更趋平整,有利于细粒度金刚石钎焊等高性的控制;适量TiC颗粒在结合剂层中的均匀分布,能显著细化结合剂层的显微组织;复合钎料中添加TiC颗粒在实现细粒度金刚石磨粒与钢基体钎焊连接的同时,有效抑制了钎料合金对细粒度金刚石磨粒过度浸润所造成切削刃的包裹,保证了细粒度金刚石磨粒良好的出露.     

基于钎料粒度匹配机理的Ni-Cr合金钎焊金刚石的研究

为解决钎焊金刚石工艺中钎料层厚度均匀性难以控制以及钎料用量与磨粒匹配困难的问题,建立了金刚石磨粒与钎料合理钎焊的几何模型,得到了具有理想钎焊效果的金刚石与钎料粒度匹配公式.运用匹配公式进行了钎焊金刚石新工艺实验,采用粒度为60目的球状颗粒Ni-Cr合金钎料对30目、50目、80目金刚石进行真空钎焊.利用扫描电子显微镜(SEM)、X射线能谱仪(EDS)分析金刚石钎焊微观形貌及焊接界面,结果表明:金刚石与Ni-Cr合金钎料界面有新碳化物生成,保证了钎焊性;30目与50目金刚石出露较好,表面无包覆;50目金刚石磨粒被良好包埋,且对金刚石有较好的爬升效果,平均包埋高度约为金刚石粒度的30;.     

双辉等离子体表面冶金金属化CVD金刚石自支撑膜研究

采用双辉等离子表面冶金技术,在金刚石自支撑膜表面制备了W金属层.借助扫描电子显微镜(SEM)、能谱仪(EDS)和X-射线衍射仪(XRD)等分别对金属化后的金刚石膜的微观形貌、元素分布及物相组成进行了表征与分析;并通过测试Ag-Cu钎焊的金刚石膜-硬质合金刀片样品的剪切强度,评价金属层与金刚石膜的结合强度.实验结果表明:所制备的W金属层连续、致密,由大量纳米尺度的颗粒状团聚物构成;在金属层与金刚石界面一定深度区域内,存在W和C元素的相互扩散,并且反应生成了WC、W2C等金属碳化物颗粒,表明金属层与金刚石膜之间已形成了牢固的化学键合.     

Cu-Sn-Cr真空钎焊金刚石界面微结构分析

为降低钎焊金刚石的热损伤和制造成本,开发了一种适于钎焊金刚石的混合金属粉Cu-Sn-Cr作为钎料,并对金刚石磨粒进行了钎焊实验.采用SEM、EDS及XRD对金刚石焊后界面微结构进行了分析.结果表明:适合钎焊金刚石的活性成分为Cu76Sn19Cr5,该钎料能够实现金刚石的高强度连接.在金刚石与钎料界面处有碳化物生成,钎料组织主要由α-Cu固溶体、Cu41Sn11.金刚石焊后形貌完整,表面基本光滑,表面生成了连续片状Cr7C3.     

金刚石与金属(或合金)的结合界面分析

本文从晶体结构方面说明了金刚石化学性质稳定的原因,介绍了提高金刚石工具性能所采用的三种常用方法:金刚石表面金属化、金属基体改性和工艺改变方法.这三种方法起作用的机理可解释为由于强碳化物元素的加入,使得内界面张力系数的降低和发生晶界反应.从而改善了界面结合.另外,本文还介绍了当前金刚石工具的研究主要集中于微量合金元素特别是稀土元素的加入,这可改善金刚石工具综合性能.     

表层富钴无立方相梯度硬质合金的制备及性能研究

对通过真空液相烧结方法制备而成的表层富钴功能梯度WC-TiN-VC-Cr2 C3-Co硬质合金进行研究.借助扫描电镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)等手段,分析其断面的微观组织;并对合金表面和芯部的硬度与断裂韧性进行测试.结果表明:样品在真空下烧结,由于表面TiN的分解,并且Ti元素与N元素之间具有强烈的热力学耦合效应,导致Ti由表向里扩散,Co由内向外移动,进而获得梯度硬质合金,其中表层是厚度大约为20 μm的富钴无立方相层,使得该合金的表面断裂韧性高达21.5 MPa·m1/2.     

玻璃料对铜基金属结合剂性能及结构的影响

采用粉末冶金法向铜基金属结合剂中引入玻璃料,结合材料电子万能试验机、洛氏硬度仪、SEM等检测方法,研究了玻璃料加入对铜基金属结合剂及金刚石磨具的影响.结果表明,随着玻璃料含量的增加,铜基结合剂的抗折强度和抗冲击强度呈下降的趋势,其硬度呈逐渐上升趋势,硬脆相的引入提高了铜基金属结合剂的自锐性;玻璃相和金属相之间结合紧密,两相之间化学元素在界面处发生相互扩散;玻璃料的加入使结合剂对磨料的包裹更加紧密,大大提高了结合剂对金刚石的把持力,有利于增加金刚石磨具寿命及加工效率.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.