Hipping after sintering of titanium diboride cermets

Abstract

A new fabrication route, an alternative to glass encapsulated hipping (GEHIP), has been developed to produce dense TiB₂ cermets. Key points of this technique, based on hipping after vacuum sintering (VS + HIP), are the use of Ni₃ (Al,Ti) as binder phase and the selection of the proper amount of additions. The main advantage of VS + HIP with respect to GEHIP is the simplification of the sintering procedure which avoids the glass encapsulation step that makes it more adaptable for industrial use. Successful application of VS + HIP requires a minimum binder content about 10 vol.-% below which a significant hardness reduction is observed owing to the presence of residual porosity as compared with GEHIP. The materials produced by this technique combine low density and high stiffness with high hardness and toughness values, thus giving a set of properties especially attractive for applications where inertial loads are responsible for failure.     

Influence of sintering conditions on some properties of metal-aluminum oxide cermets

Summary A study was made of the sintering and properties of materials in the system corundum-metal. It was confirmed that the density of these cermets is influenced by the difference between the sintering temperatures of their oxide and metal constituents. The addition of MgO to the Al₂0₃ was found to have a beneficial effect on sintering in the system corundum-tungsten (molybdenum).Translated from Poroshkovaya Metallurgiya, No. 6 (66), pp. 34–40, June, 1968.     

真空微波烧结制备TiCN基金属陶瓷

采用高能球磨法,制备了TiCN超细粉末,并以TiCN、WC、Co、Ni、Mo2C等为原料,通过真空微波快速烧结制备了TiCN基金属陶瓷,探讨了坯料压制压力对烧结材料致密化和显微结构的影响。结果表明:高能球磨法能制备亚微米级的TiCN超细粉末;通过真空微波快速烧结可制备颗粒在1μm以下的TiCN基金属陶瓷材料;不同的压力压制成形的坯料,经微波烧结后,其性能存在差异,压制压力在300MPa时,材料的相对密度和硬度最好。     

细晶Ti(C,N)金属陶瓷烧结技术与性能研究进展

对当前细晶Ti(C,N)金属陶瓷烧结技术的研究成果进行了总结,分析了不同烧结方法对其组织性能的影响,总结了烧结技术特点,并展望了细晶Ti(C,N)金属陶瓷的发展方向。     

Some features of the sintering of niobium carbide

Summary A study was made of the sintering of niobium carbide in electric furnaces. It is shown that niobium carbide parts can be sintered at relatively low temperatures (2400–2500°C) if activating additions are used.An addition of ammonium chloride activates sintering by creating a defective structure, which results in a considerable intensification of the diffusion and bulk viscous flow processes. The experimental data are used for calculating the coefficients of diffusion of niobium in niobium carbide with and without an ammonium chloride addition.The activation energies of the diffusion and sintering processes are calculated. The similarity of these energies is an indication that a diffusion-viscous flow mechanism is responsible for the sintering of refractory carbides.     

Effect of sintering temperature on the microstructure and mechanical properties of Ti(C, N)-based cermets

Ti(C, N)-based cermets are produced by vacuum sintering at 1420, 1430, and 1440°C. The effect of sintering temperature on the microstructure and properties of Ti(C, N)-based cermets is studied. The microstructure and fracture morphology are investigated with a scanning electron microscope; mechanical properties such as transverse rupture strength and hardness are measured. The results show that, with increasing sintering temperature, the microstructure of cermets became uniform, and the rim phase structure is gradually completed. When the sintering temperature reaches 1440 °C, the rim phase becomes thicker and more brittle, grains start growing, and the mechanical properties decrease, indicating that a sintering temperature of 1440°C is too high.     

Some characteristic features of the sintering of binary systems

Conclusions The main process controlling the magnitude and sign of the volume changes experienced by compacts from powders of binary systems during sintering is alloy formation by the mechanism of diffusional mixing of components. The character of the volume changes of compacts is determined by the direction of migration of atoms in the course of heterodiffusion, which in turn depends on the structure of the constitution diagram of the system being sintered. A diffusional flux of atoms migrating toward particles of the main component of a compact causes its growth or hinders its shrinkage. Preferential diffusion toward alloying addition particles stimulates shrinkage provided that at the same time the bulk of excess vacancies in the particles of the main component are annihilated on dislocations. The sign of the volume change of a compact does not depend on the state of aggregation of its alloying addition. However, its passage into the liquid state intensifies alloy formation and the resultant volume change. The so-called particle regrouping mechanism, which is usually linked with the appearance of a liquid phase in a compact, cannot be reconciled with the compact growth phenomenon, since its ope ration would be expected to prevent this phenomenon rather than promote it.Published to stimulate discussion.Translated from Poroshkovaya Metallurgiya, No. 7(211), pp. 62–69, July, 1980.     

配加预处理脱硫灰对铁矿烧结基础特性的影响

 半干法脱硫灰堆弃处理占用土地且容易造成二次污染,将脱硫灰预处理后替代CaO熔剂配入烧结有望充分利用其中的熔剂组分,实现脱硫灰在钢铁企业的闭路资源化利用。研究了脱硫灰配加焦粉加热分解特性及替代CaO熔剂配加对铁矿粉烧结基础特性的影响。结果表明,配加1%焦粉可以有效提高脱硫灰分解率,减少CaSO₄的生成。随着预处理脱硫灰替代CaO比例的增加,铁矿粉同化温度和黏结相强度呈现先增加后减小的趋势;液相流动性呈现单调增加趋势,当替代比超过40%时,液相流动性形成了流动性很大的“假象”;黏结相微观结构表明,替代比例小于40%时,有利于烧结试样中铁酸钙的生成;综合考虑,最佳的替代比例应小于40%。     

准颗粒中烧结用燃料燃烧特性

为探究准颗粒中烧结用燃料燃烧特性及相关因素的影响,采用拉曼光谱和TG-DTG法对烧结现场所用无烟煤和焦粉的碳素结构和燃烧特性进行了检测,并建立了能够准确描述准颗粒中燃料燃烧过程的反应-扩散混合控制方程。同时利用非等温热重法探究了粒径和氧气体积分数对准颗粒燃料燃烧特性的影响。实验表明,焦粉中缺少了无烟煤拥有的含氢侧链,使得无烟煤的燃烧性能明显优于焦粉。低温条件下,燃烧速率、着火稳定性和燃烧性能都随着燃料粒径的减小而增大,但会在粒径小于0.1 mm时达到峰值;而反应气体中的氧气体积分数与燃料燃烧速率呈明显的线性关系。     

基于烧结基础特性的新评价方法指导烧结配矿

 对国外10种常见的铁矿粉进行了研究,着重测试其烧结基础特性。考虑到以往烧结基础特性的评价指标忽视过程信息,使用模拟烧结过程中的单个因素指标对烧结基础特性指标进行定量描述的特点, 采用了一种全新的评价指标,该指标包含了烧结的过程信息,因此能较全面地对毅星粉的烧结基础特性进行评价。根据新方法对不同配矿方案的烧结杯试验结果进行预测,烧结杯试验结果证明了该预测的有效性,试验结果认为,巴卡粉与毅星粉在小比例配比条件下可进行互替。