Dislocation structures inside the cleared dislocation channels in rapid-cooled and tensile-deformed aluminum single crystals were investigated by using transmission electron microscope (TEM). The present study especially focused on the dislocation structures at their early formation stage. In their very beginning stage, arrays of prismatic dislocation loops of the primary slip system were essentially formed elongating along ½ 1 2 1 direction and each prismatic loop stacked to ½ 1 0 1. With the progress of plastic deformation, the number of the prismatic loops composing the array increased and produced tangled structures with dislocations of the primary coplanar slip system. The tangled structures may act as strong obstacles against the following primary dislocations and become a triggering factor for the creation of the cell structure.

A dispersion of precipitates introduces a threshold stress which opposes deformation. The effect of precipitate shape on dispersion strengthening at elevated temperature has been examined. Three kinds of Mod.9Cr-1 Mo steels without Nb(C.N), with spherical Nb(C.N) and with complex Nb(C.N)+V(N.C) "V-wing" were designed to havethe same microstructures except for the shapeof precipitates. Thethreshold stresses were measuredby tensile and creep tests at 600'C. Two sorts of effects have been observed. The first is that complex precipitates restrain dislocation from climbing even in a condition in which dislocation climbs over a spherical precipitate. Mobile dislocations are considerably trapped at the concavity of the V-wings during deformation. The second effect is that the probability of dislocation trapping at V-wing is larger than that at spherical Nb(C. N). Thesetrapping effects play important roles in the strengthening effect of precipitate.

The plasma nitriding of tool steel under atmospheric-pressure was performed using a dielectric barrier discharge method, resulting in the formation of a uniform nitrided layer. In this study, the tribology properties of the nitrided layer generated by atmospheric-pressure plasma nitriding were investigated. The results showed that the surface hardness of the tool steel nitrided by the atmospheric-pressure plasma method were increased by more than twofold compared with that of the core material. The surface hardness and the thickness of the nitrided layer were uniform, with values of 1300 HV and 30 m, respectively. In addition, the wear rate of the sample nitrided by the atmospheric-pressure plasma method was decreased by more than 25 times compared with that of the untreated sample. Only the emission of the N 2 second positive system and Ar were detected by the optical emission spectroscopic observation of the generated plasma. For this reason, we consider that the nitriding of this research caused by the dissociation of nonexcited N 2 , NH 3 , NH 2 , and NH etc. on the sample like a gas nitriding.

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