DENSIFICATION PROCESSES IN THE TUNGSTEN CARBIDE-COBALT SYSTEM

Abstract

The tungsten carbide-cobalt system is one in which the carbide matrix phase is to some extent soluble in the cobalt binder and which readily sinters to give 100% density. The characteristics of this system have been examined by determination of densification curves and metallographic examination and compared with a previous investigation on the behaviour of the insoluble tungsten carbide-copper system.

It is found that the good densification characteristics of tungsten carbide-cobalt are due to the initial solution of the carbide by the cobalt. The cobalt diffuses in the solid state into interfaces between carbide particles and as the temperature increases dissolves carbide from the adjacent particle surfaces. Forces arising from minimization of surface energy then act to bring about close packing of the carbide. By this means 100% density is achieved with 8 wt.-%, or more, of cobalt. With between 5 and 8 wt.-% cobalt 100% density is obtained by initial solution followed by a few minutes further sintering during which a solution/reprecipitation mechanism is operative.

If sintering is prolonged, a rigid carbide network is formed and this then determines the contraction of the compact on cooling. Even when 100% density is attained at sintering temperature the cobalt contracts on solidification and cannot fill the intervening space between the carbide particles, so that shrinkage-pipe-porosity forms.

Porosity seals off from the surrounding atmosphere when ～90% density has been reached. If the gas entrapped is insoluble, then the pores shrink until the balance is attained between the surface energy and the excess pressure in the pores and this results in a porosity level of the order of 0·2%     

液相烧结高比重合金早期固相烧结阶段的致密化机理

研究了PIM(粉末注射成形)的拉伸棒和传统粉末;台金P/M拉伸样的高比重合金的致密化。结果表明,在液相温度1465℃以下,1400℃烧结2h之后,合金的致密度大于90％,相对线缩率大于72.5％。高比重合金在固态烧结时,发生大部分的致密化。选用PIM和P/M两种试样的目的是为了说明压坯的孔隙度对致密化的影响。重点讨论和提出了固相烧结阶段致密化的可能机理。     

METAL FLOW AND DENSIFICATION IN THE DIE-FORGING OF POROUS PREFORMS

Abstract

Preforms of Ni-Mo alloy steel have been deformed at 1130°C in lubricated closed dies, the ratio D₀/D, where D₀ is the die diameter and D the initial preform diameter, being varied between 1·0 and 1·37. Both the high-speed Petro-Forge and a crank press were used, and parameters such as forging load, energy, and density during the forging operation were measured.

The stages by which densification proceeds are considered, together with their influence on preform design.     

重量法测定钨铜合金中钨的质量分数

采用酸溶解试料,用重量法测定钨铜合金中钨的质量分数,滤液中残余的少量钨采用电感耦合等离子体原子发射光谱法（ICP-AES）测定.实验证明该方法具有较高的回收率和精密度,可用于生产实践中.     

高密度钨合金材料设计知识库系统的开发

以高密度钨合金材料为例，建立了一个材料设计知识库系统，包括一个通用的推理机、知识库、解释系统及知识库管理系统，可以根据用户需求协调和控制知识子库、推理机等相关部分完成知识管理、使用与推理的全过程，使研究人员在材料使用、设计时能够方便地进行查询、优化，合理选择材料或得到材料设计方案。选择可视化逻辑程序设计语言Visual Prolog开发，整个系统在Windows环境运行，具有良好的人机交互界面，方便易用。     

浮选柱在钨钼浮选中的应用

介绍了浮选柱在洛阳栾川钼业集团股份有限公司的试验和使用效果,将浮选柱应用于钼的粗选和精选,提高了钼精矿的品位和回收率,达到了节能降耗的目的;在白钨矿粗选中使用效果明显.实践证明,浮选柱在有色金属选矿上有广阔的应用前景.     

Ti-Mg系复合材料的致密化及其梯度材料的制备

在625℃-30 MPa-2 h条件下,通过Ti和Mg发生固溶反应获得了Ti-Mg系梯度材料。该梯度材料厚度为1.25 mm,沿厚度方向的密度从3.416×103kg/m3到1.740×103kg/m3准连续变化。用EPMA+EDS和TEM观察了材料的显微结构和成分分布,证实了该材料具有组成梯度化和组分准连续变化的特性。     

近十年高密度钨合金的研究进展

本文概述了高密度钨合金在材质、制备工艺等方面的研究进展,对今后高密度合金的发展作出了展望。     

EFFECTS OF PARTICLE SIZE ON THE SINTERING KINETICS IN TUNGSTEN POWDER

Abstract

An experimental study has been made of the effects of initial particle size on sintering kinetics in tungsten powder within the temperature range 1100–1500°C. Particle size, compacting pressure, sintering time and temperature all influence the rate of sintering. Isothermal changes in density and volume have been measured. The results indicate grain-boundary diffusion as the mechanism principally responsible for material transport in the case of particle sizes <4 μ Surface diffusion appears to bethe mechanism of material transport in compacts with particle sizes of 14– 16 μ The temperature-dependence of the rate of sintering is characterized by activation energies of 101± 2 and 72± 2 kcal/mole for fine particles (< 4 μ) and coarse particles (14–16 μ), respectively.     

赣州钨业崛起的原因和发展战略探讨

研究了近年来赣州钨冶炼业崛起的历史轨迹和原因，提出了新一轮钨业发展的建议。     

钨铜复合材料致密化问题和方法

在常规溶渗、烧结条件下金属钨和铜之间互不溶解,浸润特性能差,使两种粉末复合的致密化过程进行相对困难。阐述了如何提高该系统致密化过程和速度,弱化致密化条件,获得均匀弥散且两相分别连续分布的组织结构,并实现对成分和尺寸的准确控制。结合各类应用的性能要求,对钨铜复合材料致密化的各种方法进行分析和讨论,试图为选择高性能钨铜复合材料加工方法提供依据。     

高线精轧机碳化钨辊环失效原因探讨

分析了高线厂精轧机引起辊环失效的现象和原因，提出了生产过程中应注意的中项。     

DEFORMATION AND DENSIFICATION DURING THE ROLLING OF METAL POWDERS

Abstract

The deformation of particles and the general process of densification during the roll-compacting of strip from metal powder have been determined by photomicrographic and QTM studies. Observations were made on the expansion of the compacted strip after it had passed the plane joining the roll axes. The effect was related to elastic recovery of the material and the expansion of gases entrapped in the pores between the particles.

The production of satisfactory green strip was found to be restricted to a range of thicknesses obtained between certain maximum and minimum roll gaps. These limits were related to roll pressure and strip density. It was also restricted by a maximum rolling speed that was governed by powder flow to the compaction zone.

Density variations that occurred across the width and through the thickness of green strip were also determined.     

DEFORMATION AND DENSIFICATION OF POROUS PREFORMS IN HOT FORGING

Abstract

Observations are reported on plane-strain upsetting, between unlubricated flat punches, of powder preforms of varying density at 1160°C (1435 K). Macroscopic deformation behaviour is characterized by the pressure/strain relationship and by the ratio of lateral to vertical flow. Increased preform porosity affects lateral flow similarly to increased friction in forging of dense material.

Densification is studied as a function of strain and pressure. Lower preform density requires not only larger strains but also higher pressures for a given final density.

The density distribution in typical forgings is charted by means of hardness measurements. Zones of incomplete densification are revealed where local pressure was reduced by lack of constraint, or where strain was impeded by friction effects.     

国内外铬矿炼钢工艺综述

本文综述了国内外铬矿炼钢工艺的发展概况。并对我国实际生产工艺及其经济效益进行了分析,指明了进一步研究开发该工艺的途径和方法。     

PDA记录诊断在轧机主传动系统中的应用

随着企业发展和技术的更新,轧机主传动数据的采集和监控需求越来越来大,常规手段显得很复杂,已经不能满足技术发展的需要.PDA系统采集轧机主传动的运行参数和数据,对现场设备状态进行实时监测和数据记录,更加有利于设备的维护和故障诊断.     

液—固掺杂垂熔钨坯中改性元素的行为

对传统粉末冶金方法(液—固混合制成掺杂钨粉,经过压制、烧结、旋锻、拉拔等工序)制成的钨坯和钨丝,用扫描电子显微镜进行了断面及磨面分析。结果发现:在晶界孔穴内,元素Si和Al的含量丰富;在晶内孔穴内,除元素Si、Al外,还富集了元素K。只用钾泡理论解释改性元素改善高温钨丝的抗下垂性能是不够的,应以分子筛理论和SiO_2-Al_2O_3系统相图予以补充。     

湘钢转炉控制系统

介绍了湘钢转炉区基础自动化系统功能，论述了新炉S7系统同老转炉TI系统之间通信的问题及解决方案，讨论了大型自动化系统硬，软件设计的思路和方法。     

用钨钼矿生产高速钢工艺方法的比较分析

对白钨矿和钼焙砂的还原机理进行了研究，并分析比较了用白钨矿和钼焙砂合金生产高速钢的3种工艺，认为双联法是最有前途的。