THE FORMING OF HOLLOW SHAPES IN BERYLLIUM BY LOOSE SINTERING AND HOT PRESSING

Abstract

Two methods for forming shaped bodies in beryllium by powder metallurgy are described and compared. The requirements for uniform densification during hot pressing are discussed, and it is concluded that a double-pressing method is essential if thin-walled hemispherical shapes are required.     

THE INFLUENCE OF PRESSURE,TEMPERATURE, AND TIME ON THE HOT PRESSING OF COMMERCIAL BERYLLIUM POWDER

Abstract

For a particular batch of Brush Super-Pure – 200-mesh beryllium powder the hot-pressability (defined as the length of a standard compact of < 98% theoretical density), increased: (1) continuously with pressure over the range 0–1·25 ton/in² for compacts pressed for 1 h at 1100°C;(2) with temperature from 1000°C to a maximum at 1150°C when pressed for 1 h under 1 ton/in²; and (3) to a lesser extent with time over the range 10–120 min when pressed at 1050°C under 0·25 ton/in² and at 1100°C under 1·0 ton/in². Differences in hot-pressability between various batches of the same powder were small compared with the effects of temperature and pressure.

Compaction during hot pressing occurs in two stages: first, collapse of the powder column causing bulk powder flow; followed, secondly, by sintering of particles forced into close contact. The latter is accompanied by a diminution in both the number of pores and their average size and is associated with grain growth, particularly above 1100°C; after pressing at 1200°C any remaining porosity assumes a thermally stable, spherical configuration.     

热轧带钢头部飞翘原因分析及对策

针对攀钢1450mm半连续式热轧带钢的生产情况，对带钢头部飞翘的原因进行了分析，并提出了相应的对策。     

THEORIES OF HOT PRESSING

Abstract

A survey has been carried out of the literature on hot-pressing theories and models. Theories as to the mechanism governing the process may be divided into two principal groups:

(1) Mathematical representation of densification. Equations have been derived for mechanisms controlled by plastic or viscous flow. Also equations of a purely empirical nature have been advanced. In this group there is a trend towards a hyperbolic hot-pressing equation, which, according to tests, is valid for metals and metallic compounds over wide temperature ranges.

(2) Theories asserting that the densification process is controlled by various processes, e.g. particle gliding, fragmentation, plastic flow, and volume diffusion. No complete mathematical formula has been proposed on this basis to describe the entire hot-pressing process.     

HOT PRESSING OF METALLIe CARBIDES

Abstract

A survey is presented of published work on the hot pressing of metallic carbides. On the basis of a comparison of the apparatus described in the literature, hot-pressing equipment has been built, designed for vacuum sintering using resistance heating, a combination that has many advantages.

Nine metallic carbides from Groups IV, V, and VI of the Periodic Table were hot pressed to high densities, as well as mixed carbides and carbides of varying carbon content. Compacting details are summarized, together with data covering lattice parameters and microhardness.

The purity of the metallic carbides has great significance as regards the sintering mechanism. This is demonstrated both by theory and experiment.     

HOT PRESSING OF CERAMIC POWDERS

Abstract

The processes involved in the production of dense ceramics from powder materials by the simultaneous effect of pressure and heat at temperatures above 1500°C are outlined. The factors leading to the choice of this method of fabrication, and the general principles involved in hot pressing, are first dealt with, and the advantages and disadvantages of the process are then discussed. Current techniques are described and their limitations considered. Examples of typical applications are given, and possible lines of future development are indicated.     

THE RELATIONSHIP BETWEEN POWDER PROPERTIES AND THE PRESSING AND SINTERING BEHAVIOUR OF BERYLLIUM

Abstract

The paper surveys the existing routes available for the preparation of beryllium powders, and comments on the effect of certain properties, such as particle-size distribution, on the compaction of powders by different techniques. It is emphasized that particle size, degree of oxidation, and overall purity are interdependent variables, and that little attempt has so far been made to study their effects separately.     

热压工艺参数对纳米SiC—Al2O3／TiC新型陶瓷刀具材料力学性？…

研究了压力、热压温度和保温时间等工艺因素对纳米ＳｉＣ－Ａｌ２Ｏ３／ＴｉＣ系新型陶瓷刀具材料的抗弯强度、韧性和硬度的影响。结果表明,对于纳米ＳｉＣ－Ａｌ２Ｏ３／ＴｉＣ系陶瓷复合材料,在压力为３０ＭＰａ热压温度为１７００℃,保温时间为６０ｍｉｎ时,材料的性能最好。     

SiC—TiC复相陶瓷的热等静压改性

本文通过对具有不同烧结密度的热压SiC—TiC复相陶瓷在氮气氛中进行热等静压后处理,从理论上(依据热力学数据)分析了闭合SiC—TiC复相陶瓷开孔孔隙的可能性,并用实验予以证实;同时,还研究和讨论了热等静压后处理工艺对陶瓷烧结体某些物理和力学性能(密度、强度和断裂韧性)以及氧化行为的影响。实验结果表明:SiC和TiC在高的氮气压力和温度下,可以分别氮化成Si_3N_4和TiN;对于预烧结相对密度约为95％的热压SiC—TiC复相陶瓷,在200MPa氮气压力下于1850℃氮化1小时后,室温强度由345MPa提高到686MPa,断裂韧性高达7.9MPa·m~(1/2),其抗氧化性能也有明显改善。     

碳化硼的低温热压

研究了B₄C的热压工艺及Al₂O₃对热压B₄C烧结性能的影响。结果表明,采用1.0μm左右的B₄C粉,添加Al₂O₃作为烧结助剂,在1750℃、35MPa热压条件下可获得烧结致密体。而制造纯B₄C材料的热压温度需高于2100℃,才能使坯体致密。添加5%~30%Al₂O₃可明显降低B₄C材料的热压温度,但随Al₂O₃含量的增加,这种作用不很明显,反而使材料的硬度降低。当Al₂O₃含量为5%~10%(Wt)时,材料的硬度(HRA96.5)与纯B₄C热压材料的硬度(HRA97.0)接近。     

热轧带钢侧弯的形成机理及主要影响因素的分析

板带轧制过程中因受某些因素影响会形成侧弯，本文分析侧弯形成的机理，并详细探讨其主要的影响因素。     

TiB2-Ni金属陶瓷热压烧结工艺的研究

本文采用正交试验和方差分析的方法研究了热压烧结温度、压力、时间对TiB2-Ni材料性能的影响.找出了在本实验条件下的最佳工艺参数.     

热压工艺参数对纳米SiC-Al2O3/TiC新型陶瓷刀具材料力学性能的影响

研究了压力、热压温度和保温时间等工艺因素对纳米SiC Al2 O3/TiC系新型陶瓷刀具材料的抗弯强度、断裂韧性和硬度的影响。结果表明 ,对于纳米SiC Al2 O3/TiC系陶瓷复合材料 ,在压力为 30MPa ,热压温度为 170 0℃ ,保温时间为 60min时 ,材料的性能最好     

热等静压过程中粉末高温合金坯料几何尺寸及相对密度的演化规律

根据孔隙材料及致密体的塑性变形理论,揭示了热等静压过程中粉末体及其包套的几何尺寸和相对密度的演化规律。在此基础上,提出了粉末体在圆柱形包套内均匀致密的判据,对包套尺寸的确定具有指导意义。应用本文提出的方法分析ＦＧＨ９５粉末高温合金热等静压过程,理论分析结果与试验数据吻合。     

提高粉末制品压制精度的机构设计

本文介绍了一种可有效提高粉末制品压制精度的机构设计方案。它采用机械定位机构与液压缸结构有机结合,组成一套完整的液压缸可调式行程刚性定位系统。通过该系统的调整,能方便的实现液压机主液压缸、下拉缸行程的高精度可靠定位。解决了由于液压控制精度差而引起的压坯高度尺寸偏差大等技术问题。并就其结构图论述了该系统的工作原理,展望了其应用前景。     

高速钢粉末低压热压的研究

采用电脑测控法研究了高速钢粉末低压热压过程中的致密化现象,随热压温度由1215℃升高至1238℃时,有效屈服应力由3～4MPa降至2～3MPa以下。在1220～1230℃和4 5MPa压力下制备了Mo系高速钢剃齿刀,相对密度达到99 85%,碳化物的粒度为3～7μm。与普通高速钢刀具相比,低压热压法制备的M4粉末高速钢剃齿刀寿命明显提高,减少残余孔隙度对改善刀具的疲劳寿命是很重要的。充用利用材料在高温下,特别是在接近固相线温度时的屈服现象,可以实现在低压下的粉末材料致密化,其压力比热等静压低一个数量级,这可能是一条较为经济的技术途径。     

SOME CHARACTERISTICS OF NICKEL-THORIA ALLOYS PREPARED BY HOT PRESSING IN CARBON DIES

Abstract

Fully dense nickel-thoria alloys, varying in ThO₂ content from 1·0 to 3·0 vol.-%, have been prepared by a powder-metallurgical method. The structures of the as-pressed alloys were examined and some of their mechanical properties measured. The effect on the yielding behaviour of the alloys of substituting MgO for ThO₂, and of varying the grain size of the matrix, has also been studied. An initial discontinuous yield is observed for as-pressed alloys and a strain-ageing effect for both as-pressed alloys and worked material. Decarburization has no influence on the initial discontinuous yield, but removes the strain-ageing effect. The strain-ageing behaviour of the alloys has been investigated and the interaction of carbon with dislocations demonstrated.     

热等静压冷却速度对粉末冶金高温合金组织及性能的影响

设计了热等静压机冷速的模拟实验。采用两种冷速研究了热等静压(HIP)对粉末高温合金γ′相形貌、尺寸及性能的影响。结果表明,由于HIP冷速低,析出的γ′相尺寸大,在冷却过程中γ′相发生了分裂,γ′相形貌发展成八瓣状、八瓣树枝状和树枝状;冷速越低,γ′相形貌趋向长成树枝状。两种冷速HIP处理的试样经热处理后,γ′相尺寸和形貌发生了改变,由于热处理冷速快,γ′相变为较为规则的细小方形,组织基本相同,力学性能几乎无差别。