摘要:

AbstractIt is well known that some interaction takes place between the two components when mixtures of cobalt and tungsten carbide are milled. To gain a further insight into this phenomenon, the milling process has been studied by means of the electron microscope and by the BET and X-ray methods.During the milling of cobalt powder the number of stacking faults and the amount of the hexagonal phase both increase. On milling 80:20 tungsten carbide/cobalt mixtures increasing agglomeration of cobalt and fine tungsten carbide particles was found with rise in milling intensity. The larger tungsten carbide particles appeared to have a smooth surface. However, if the cobalt was dissolved in hydrochloric acid, the true surface of the tungsten carbide particles was revealed. This became rougher with increasing milling intensity. From this it can be concluded that, during milling, cobalt settles between the surface irregularities.The variation in distribution of the cobalt that results from different milling conditions leads to a difference in sintering behaviour. A dilatometric study has been made of this aspect.The original particle size of the cobalt used for hard-metal mixtures does not affect the properties of the sintered product, if the mixtures are milled very intensively.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.001

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe relative shrinkage in the radial and in the axial directions of both conventionally pressed copper powder compacts and of loose copper powder aggregates has been determined. Irregular-shaped electrolytic copper powder and flake copper powder were used. The structures of the green and of the sintered compacts and aggregates were examined metallographically. The results led to the tentative conclusion that the theories previously advanced to explain the differences in the axial and radial shrinkage of compacts and aggregates are not correct. The pores of green and sintered compacts of irregular copper powder are not necessarily disc- or lens-shaped, but rather equiaxed, and the observed difference in shrinkage cannot be attributed to the shape of the pores. On the other hand, the ratio of axial to radial shrinkage of irregular-shaped powder and of flake powder aggregates is nearly the same, in spite of the fact that the pores in the flake powder aggregates are much larger in the radial than in the axial direction. The possibility that forces other than surface-tension forces have an influence upon shrinkage behaviour is discussed.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.002

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe preparation of alloys of beryllium and magnesium containing up to 20 wt.-% magnesium is described. Dense bodies may be prepared by infiltration of beryllium skeletons with molten magnesium or by liquid-phase sintering of cold-compacted mixed elemental powders. Such alloys consist of the appropriate element together with the compound MgBe13, usually present as a continuous intergranular phase.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.003

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractDetermination of particle density by the displacement method, with different liquid media, can be used to assess the size distribution of micropores in powder particles. Certain errors and assumptions are involved.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.004

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractIrregularly shaped powders of aluminium, 90:10 bronze, 302B stainless steel, electrolytic copper, titanium, molybdenum, and tungsten carbide were converted into spherically shaped powders by dropping the powders through vertical furnaces. Several types of furnaces were built and used. The operating temperatures extended from 1650 to 3000°C, depending on the material being spheroidized, and the protective atmosphere was argon, helium, or hydrogen. The finished powders had excellent sphericity and density.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.005

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe operating characteristics of an induction-coupled plasma torch are described. Preliminary observations are given on its use for the spheroidization of chromium, alumina, molybdenum, magnesia, tantalum, and tungsten powders.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.006

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe technique of hot pressing and the factors to be considered in designing suitable equipment are discussed. Examples are quoted of three main classes of materials: (a) unbonded hard materials, (b) materials containing a small amount of a cementing phase or impurity affecting densification, and (c) materials containing an appreciable amount of a cementing phase. Current theories concerning the mechanism of densification during hot pressing are discussed.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.007

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe porosity of hydrogen-sintered bodies composed of molybdenum disilicide and alumina has been studied as a function of alumina content and grain size. It is found that oxidation-resistant bodies can be made if the grain size of the constituents is∼10μor less, although the bodies are fairly weak.In addition, samples were sintered in dissociated ammonia and compared with those sintered in hydrogen. It became apparent that samples sintered in dissociated ammonia underwent a particularly severe form of attack when exposed to air at high temperatures. This is attributed to the formation, during sintering, of Si3N4, a phase which decomposes at high temperature in air when enclosed in the cermet bodies.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.008

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractDense self-bonded silicon carbide, prepared by impregnating with silicon pressed mixtures of silicon carbide and graphite, has been improved by attention to grading and composition. Treatment at 2000°C for½h has given a much greater degree of self-bonding. Porous self-bonded silicon carbide with a dense surface has also been prepared.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.009

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor

摘要:

AbstractThe preparation of uranium mono carbide bodies containing∼1% open porosity and with a density of∼12·4 g/c.c. by cold compacting and sintering uranium/graphite mixtures is described. The effect of iron additions in producing a liquid phase during sintering has been studied, and it is shown that the addition of 10 wt.-% UFe2to the stoichiometric mixture of uranium and graphite raises the sintered density to∼13·1 g/c.c. and reduces the open porosity to∼0·5%. The mechanism of carbide formation and densification in the presence of a liquid phase is discussed.

ISSN:0032-5899    

DOI:10.1179/pom.1961.4.8.010

出版商:Taylor&Francis    

年代:1961

数据来源: Taylor