Interdiffusion in iron compact and nickel, cobalt, chromium, molybdenum or tungsten compact system under hot-pressing has been investigated and the results obtained are as follows. Width of diffusion band between the compacts increases as hot-pressing temperature increases in any system. The systems can be classified into the following two groups based on the rate of width-increase. One is the iron-nickel and the iron-cobalt systems in which the width of diffusion band is large under hot-pressing at 1000°C-1200°C, but small under hot-pressing at 1300°C-1400°C as compared with other systems. The other is the iron-chromium, the iron-molybdenum and the iron-tungsten systems in which the width of diffusion band is small under hot-pressing at 1200°C, but remarkably large under hot-pressing temperature at 1300°C-1400°C because intermetallic compounds generate as diffusion proceeds.

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In order to elucidate the effect of residual pores and anomalously large WC particles on fracture properties of cemented carbides at elevated temperatures, the bend tests were carried out on WC-10% Co alloys with these defects of various sizes. The results obtained are as follows. (1) The influence of the residual pores on the fracture properties gradually vanishes with the rise of temperature, especially above 700°C. At high temperatures near 1000°C, even when the size of the residual pores exceeds 100μ, transverse rupture strength (refered to as T. R. S.) becomes to be unaffected with the existence of such defects. (2) With the rise of temperature, the mode of fracture at the fracture origin of the alloy containing anomalously large WC particles changes from a transgranular to intergranular type. This change of fracture mode occurs in the temperature range of 400 to 800°C depending on the defect size. (3) With decrease of strain rate, the transition temperature at which the residual pores have no effect on T. R. S., shifts to the lower temperature.

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In this paper, the wear behavior of MgO single crystals sliding on steel (S15C) at sliding speeds of 10-50 m/s has been described. It was found that two states, which were transient and steady states, were observed in this wear. When the sliding speed was below 20 m/s, two states of the wear appeared, while there was only a steady state of wear at 50m/s. These changes in the wear behavior are due to the transfer of MgO fragments and the oxidation of steel surface caused by the temperature rising at the interface of sliding as it is supposed from the observations of steel surface.
At the speed up to 50 m/s, the generation of thin film was observed on both the wear surfaces of MgO and steel. This result suggests that the solid state diffusion between MgO and oxidized iron caused by mechanochemical reaction occurred in the interface.

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