THE HIGH-TEMPERATURE PROPERTIES OF CERAMICS AND CERMETS

Abstract

It has been recognized for some time that, with progressive increase in the working temperature of gas turbines, metallic alloys may no longer be adequate for rotor or stator blading. The use of more refractory but more brittle materials, i.e. ceramics and ceramic-metal mixtures (cermets) has been suggested. The paper is concerned with the evaluation of the major properties involved, viz. creep strength, fatigue strength, resistance to thermal fatigue (i.e. to repeated thermal shocks), oxidation-resistance, and impact-resistance. The materials evaluated include oxides, oxide–metal cermets, carbides, carbide-metal cermets, molybdenum disilicide, and silicon nitride. The equipment for determining the effects of alternating and steady mechanical stresses up to 1200° C. is described. The relative merits of the test materials are discussed. It is concluded that the resistance to thermal fatigue and to impact of the ceramics and cermets is inferior to that of metallic alloys in current use.     

THE PREPARATION AND SOME PROPERTIES OF CHROMIC OXIDE-CHROMIUM CERMETS.

Abstract

Compacts of chromium oxide/chromium mixtures have been sintered in vacuum at temperatures up to 1600°C to produce cermets. Two types of chromium powder were used—an electrolytic and an aluminothermic powder. The effect of chromium content and of sintering temperature on the sintered density and microstructure has been studied and supplemented by tests of hardness and compressive strength.

Considerable densification was achieved by additions of chromium in the range 1–50 wt.-%, with the optimum content at 5–10%. Compressive strengths < 10 tons/in² were attained over a wide range of composition.     

THE FABRICATION AND PROPERTIES OF URANIUM OXIDE–IRON CERMETS

Abstract

Cermets of iron–uranium dioxide, containing up to 30 vol.-% UO₂ have been rolled to rod. Although the cores rolled centrally along the length, the core was distorted in section owing to stiffening of the core relative to the sheath as the temperature dropped during rolling. The UO₂ particles were fragmented during rolling and formed as “stringers” along the direction of rolling, seriously weakening the structure transversely.

By extrusion at 1200° C., cermets containing up to 50 vol.-% UO₂ were satisfactorily fabricated. The extrusion pressure increased sharply above 35 vol.-% of ceramic and when large reductions in area were taken. The extrusion characteristics do not conform to isotropic plastic extrusion nor to a pure viscosity effect; the influence of the dispersed particles on metal flow is explained by a strong interference effect between particles and the metal during flow. The properties of the extruded rods were good; the core density was 90–95% of theoretical, decreasing slightly with increasing ceramic content; there were no obvious directional properties in the core, nor was the ceramic fragmented as in rolling. The characteristic “tail-end defect” of the extrusions was partly corrected by using shaped sealing plugs.     

不同掺杂试剂的钼镧板材力学性能分析

通过对自制硝酸镧和外购分析纯硝酸镧作为掺杂试剂,分别在二氧化钼中进行喷雾掺杂,还原得到钼粉,经过压制、烧结出板坯,对轧制得到的板材进行高温力学性能分析。结果表明,采用外购硝酸镧进行掺杂得到的板材具有较好的高温力学性能。     

TiC基金属陶瓷的性能与发展

概述了TiC基金属陶瓷的发展过程和研究现状，指出了粘结相成分对TiC基金属陶瓷的显微组织和力学性能的影响，以及提高TiC基金属陶瓷材料性能的途径。     

THE MECHANICAL PROPERTIES OF SINTERED LOW-ALLOY STEELS

Abstract

An unacceptable degree of scatter in the values obtained in tensile tests of sintered parts may occur if their elongation does not exceed a few percent. To ensure the required elongation, the composition of the material selected must correspond to that of alloys made by melting which exhibit a certain minimum elongation in the forged and annealed condition. This minimum is a function of the density of the sintered compact and a knowledge of its value can be of assistance in choosing the correct composition. Values of Young’s modulus, Poisson’s ratio, and impact-resistance are also given as a function of density.     

ZrO2/Si3N4颗粒增强MoSi2基复合材料的显微组织和力学性能

采用放电等离子烧结法(SPS)制备了不同体积分数的MoSi2及其复合材料,研究了复合材料的显微组织和力学性能.结果表明:10%ZrO2/20%Si3N4/MoSi2复合材料的致密度、显微硬度、抗压强度、断裂韧性分别为92.3%、15.17 GPa、2105 MPa、6.61 MPa·m1/2.与20%ZrO2/MoSi2复合材料相比,断裂韧性下降2.9%,显微硬度和抗压强度分别提高了22.8%,13.4%;与20%Si3N4/MoSi2复合材料相比,断裂韧性提高了5.3%,显微硬度和抗压强度相近;经500℃氧化300 h,氧化增重与ZrO2和Si3N4单独增强的相近,均是纯MoSi2的1/10左右,抗氧化效果显著.     

THE PREPARATION AND SOME PROPERTIES OF CHROMIC OXIDE-CHROMIUM CERMETS MADE BY PARTIAL REDUCTION OF THE OXIDE

Abstract

Compacts of chromic oxide/carbon mixtures have been sintered in vacuum to produce oxide-metal cermets. The effect of carbon addition, type of carbon, purity of oxide, compacting pressure, and sintering temperature on the green and sintered density has been studied, and this has been supplemented by tests of hardness and compressive strength.

Considerable densification can be attained by a small addition of carbon to the powder mixture, and this is accompanied by an increase in compressive strength to 20 tons/in², compared with 3 tons/in² for the pure oxide sintered to the same temperature.     

A COMPARISON OF THE MECHANICAL PROPERTIES OF SOME POWDER-FORGED AND WROUGHT STEELS

Abstract

The tensile, impact, and fatigue properties of a range of powder-forged steels have been examined. A relationship has been found between the content of non-metallic inclusions and the fatigue performance. The properties of powder-forged steels at 900 N/mm² strength were compared with those of En16 wrought steel at the same level. The properties of wrought steel are demonstrably extremely variable, depending on the degree of hot work imparted during processing and on the relationship of the test-piece axis to the principal direction of working. The properties of powder-forged steel lie between the highest and lowest that can be expected in wrought steel; comparisons between the two types of material can be made only after careful consideration of their specific characteristics. Powder-forged steels were shown to be capable of developing useful properties over wide ranges of composition.     

三元硼化物强化相粉末高速钢的研制

用反应硼化烧结法在1192℃下真空烧结,成功制备出高耐磨的粉末高速钢与三元硼化物陶瓷的复合材料。分析表明：材料主要是由三元硼化物基硬质相和高速钢基体组成,硬质颗粒与基体界面结合良好,分散均匀,摩擦磨损试验表明此种材料具有优异的耐磨性。     

THE MECHANICAL PROPERTIES OF HOT-RECOMPACTED IRON-NICKEL SINTERED ALLOYS

Abstract

Powder-metallurgy components which are to withstand high dynamic stress are frequently required to possess both high strength and great toughness. This combination of properties can best be achieved by increasing the density of the sintered component and one method of doing so is bot pressing.

This paper deals with the mechanical properties of sintered iron–nickel alloys produced by hot compacting in six stages, as follows:

(1) Preparation of the powder mix.

(2) Production of compacts under a pressure of 8 Mp/cm²

(3) Heating the compacts to 1000°C (1275 K).

(4) Re-pressing the hot compacts in a die heated to 300°C (575 K).

(5) Cooling in air.

(6) Sintering at optimum temperature and time under optimum furnace conditions.

The investigation covered the dependence of tensile strength, elongation at fracture, and Brinell hardness of alloys with Ni contents of 1–10% on the sintering temperature and time, on the furnace conditions, and on raw-material variables.

It was found that Fe–Ni powder-metallurgy parts with a maximum tensile strength of ～60 kp/cm² could be produced. The Brinell hardness reached 190 kp/mm² with 10% Ni content. Elongation at fracture was in the region of 45% with 1% Ni and remained comparatively satisfactory even with high Ni contents if very pure raw materials were used. Powder-metallurgy materials with a tensile strength of 60 kp/cm² and an elongation at fracture of 17% can be obtained by the process.     

THE MECHANICAL PROPERTIES OF SOME SINTERED MARAGING STEELS

Abstract

Maraging steels based on 18 and 12% nickel, and containing cobalt, molybdenum, silicon, copper, chromium, titanium, and aluminium in various proportions, were prepared in sintered form under varied processing conditions. The mechanical properties of the steels have been examined with particular reference to the effects of: (1) composition; (2) degree of shrinkage; (3) atmosphere, time, and temperature of sintering; and (4) compacting pressure. The influence of the type of iron-powder base was also studied.

The results demonstrate the possibility of producing, in the sintered and maraged condition and with only slight shrinkage on sintering, tensile strengths of the order of 95–110 kgf mm^?2 (60–70 tonf in^?2). Two compositions appear promising for further development as high-strength materials, and another to provide enhanced ductility. In all cases impact properties are similar to those characteristic of conventional sintered steels.     

粉末冶金制备原位自生钛基复合材料的显微组织和力学性能研究

利用Ti与B4C、C、LaB6之间的化学反应,采用粉末冶金工艺制备了原位自生钛基复合材料(TiB+TiC+La2O3)/Ti-6Al-4V;通过X射线衍射仪和光学显微镜,分析了材料的物相组成、显微组织及增强体的微观形貌;测试了材料的室温和高温力学性能,并分析了断裂机理.结果表明:增强体总体分布均匀,但局部有团聚现象,形状和尺寸多样;粉末冶金制备Ti-6Al-4V的抗拉强度高于铸造工艺制备的材料,增强体的原位合成使复合材料的室温和高温性能与基体相比明显提高;室温时,体积较大的增强体的断裂是复合材料失效的主要原因,高温下则主要是增强体和界面的脱粘导致材料失效.     

使用VAI-Q Strip 系统首次实现热轧带钢力学性能的全面控制

VAI-Q Strip（热轧带钢综合质量系统）是一种独特的计算机辅助质量控制系统，已在奥钢联林茨钢厂7机架热带轧机上成功实施。在1997年中期以来的稳定面连续的运行中，系统的预测功能在卷取后立即对带钢力学性能进行准确的在线预测。目前，系统的功能已扩展到可对带钢质量参数进行全自动在线控制，并且自2000年1月以来已在林茨厂热带轧机上成功运行。     

EVALUATION OF THE MECHANICAL PROPERTIES OF SINTERED LOW-ALLOY STEEL COMPONENTS

Abstract

When adopting low-alloy sintered steel components instead of traditional machined steel parts, it is misleading to attempt a direct comparison of the mechanical properties of the two products. Instead it is preferable to consider in each case the service conditions to which the parts are to be subjected and then to devise suitable mechanical tests under simplified loading conditions. The paper describes certain case histories illustrating this point and discusses briefly the definition of low-alloy “sintered steel”.     

铁基金属玻璃的热磁特性

本文利用振动样品磁强计、霍普金松效应、差热分析与双臂电桥等实验方法较系统地研究了类金属硼含量对Fe_(92-X)Cr_8B_x金属玻璃的饱和磁矩(σs)、Curie温度(T_c)、晶化温度(T_(cr)),室温电阻率(ρ)与(B-T)曲线等特性的影响规律。结果表明,Fe_(92-X)Cr_8B_X金属玻璃的(σs)、T_c与ρ在15≤x≤23范围内均随类金属硼含量的增加而呈现出线性增大的变化规律,而T_(cr)却无明显变化,Fe_(92-X)Cr_8B_X的磁感应强度(B)随测量温度(T)的升高呈现出线性缓慢降低的变化规律,其降低的幅度是随类金属硼含量的减少而逐渐增大。该成果对开发新型热磁开关等功能材料具有实用价值。     

热处理对30CrMnSiNi2A钢力学性能的影响

研究了热处理对30CrMnSiNi2A钢性能的影响，试验结果表明，该钢的最佳热处理制度为890℃或900℃保温20－45min油冷，然后260－300℃回火2．5h，经该热处理制度处理的钢具有较好的强度和韧性配合。在350－550℃温度区间回火时，该钢出现了明显的回火脆性，冲击韧性的降低是片状渗碳体的析出造成的。600℃以上回火时马氏体边界的渗碳体开始聚集和球化，钢的韧性和塑性提高。     

低碳锰铌钢的工艺制度与组织性能的关系

对低碳锰铌钢的控制轧制和加速冷却工艺制度进行了实验研究,得出终轧温度为７８０±１０℃、终冷温度为６７０±１０℃、冷却速度为１０℃／ｓ的控轧控冷工艺,同时给出加大冷却速度对提高钢屈服强度和抗拉强度的定量影响数据。     

残余奥氏体对TRIP钢机械性能的影响

简要介绍了TRIP(transformation induced plasticity, 相变诱导塑性)钢中残余奥氏体的形成及其微观组织形貌,综合阐述了残余奥氏体对TRIP钢性能的影响,并由此提出对TRIP钢进一步改善的途径.     

THE FABRICATION AND PROPERTIES OF CHROMIUM–ALUMINA AND MOLYBDENUM–CHROMIUM–ALUMINA CERMETS

Abstract

After a brief review of the literature, various methods for preparing chromium–alumina and molybdenum–chromium–alumina cermets are described. The properties of such materials are discussed and an indication is given of their possible applications.