High-temperature hardness tests

Fiq. 60,—High Temperature Hardness Tests (600 Kg.) on Duralumin quenched from 475°. 

Fig. 726.—High-temperature Hardness Tests (500 Kg.) on Aluminium Bronze, Type I —...

A series of mechanical property determinations was made to determine the reproducibility and spread of the tests results when materials of various levels of crystallinity were tested at cryogenic temperatures. It was found that there was a definite correlation between the crystallinity (as determined by the hardness test) of the samples and their low-temperature mechanical properties. As an example, samples of relatively low crystallinity were much stronger and more ductile at cryogenic temperatures than the highly crystalline samples. As a result of these determinations, it was found that a reasonably accurate set of low-temperature mechanical properties could be assigned to any fluoroplastic by performing this simple non-destructive room temperature hardness test. 

Reply bv the Authors We were not able to measure high temperature hardness (bulk or matrix) of the examined composite. Therefore we did not make any attempt to determine the K value. Abrasion tests were carried out at different temperatures under a constant test load on abrasive grains having a certain grain size. These testing conditions gave appropriate results to compare the effect of test temperature and composition on the abrasion resistance of the examined composites. 

Nis] Mechanical tests High-temperature hardness... 

Rockwell hardness testing has been extended to both low and high temperature regimes usually by enclosing the sample and part of the machine in an environmental chamber and using extensions for the anvil and indenter. 

The hardness of carbides can only be deterrnined by micro methods because of britdeness, the usual macro tests caimot be used. Neither can the extremely high melting points of the carbides be readily deterrnined by the usual methods. In the so-called Priani hole method, a small hoUow rod is placed between two electrodes and heated by direct current until a Hquid drop appears in the cavity. The temperature is determined pyrometricaHy. When high temperature tungsten tube furnaces are used, the melting point can readily be estimated by the Seger-type cone method. The sample may also be fused in a KroU arc furnace and the solidification temperature determined. 

Laboratory tests and experience during use have demonstrated that the nylons have extremely good abrasion resistance. This may be further improved by addition of external lubricants and by processing under conditions which develop a highly crystalline hard surface e.g. by use of hot injection moulds and by annealing in a non-oxidising fluid at an elevated temperature (150-200°C for nylon 66). 

It is hardly surprising that the preparation of surfaces of plain specimens for stress-corrosion tests can sometimes exert a marked influence upon results. Heat treatments carried out on specimens after their preparation is otherwise completed can produce barely perceptible changes in surface composition, e.g. decarburisation of steels or dezincification of brasses, that promote quite dramatic changes in stress-corrosion resistance. Similarly, oxide films, especially if formed at high temperatures during heat treatment or working, may influence results, especially through their effects upon the corrosion potential. 

The oxidation of ethylene in the high temperature region has recently been studied by Harding and Norrish (24). The object of this work was to test the hypothesis that formaldehyde plays an important part in the oxidation of ethylene just as it docs in that of methane. The experimental results may be summarized as follows ... 

FIGURE 15.13 Hydrolytic stability of potting compounds. Materials showing rapid loss of hardness in this test soften similarly after 2 to 4 years in high-temperature, high-humidity climate zones.35... 

In the other casts, cylindrical bars were made for hardness tests at high temperatures. These were carried out, using a 10 mm. ball and loads of 500 and 1000 kg. 

The results of the hardness tests at high temperatures are shown in Eig. 31. 

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