together with the surface layer of the substrate acts as an efficient solid lubricant in the device–metal system. The fact that such a lubricant can work under the increasing strength of the workpiece seems most significant. The possibility of surface softening due to the deposited film in metal working with a superhard contact action of the device is of enormous value for the engineering. This concerns not only rolling, stamping, drawing, and extruding, but also cutting, milling, drilling, etc. In addition, the surface softening of one of the partners of the contact pair can aid in solving many problems in tribology (friction and wear). Oxide films might find extensive and diversified application in metal working. When the yield strength is reduced, especially in difficult-to-extrude alloys, energy requirements in metal working may be considerably reduced. The feasibility of reducing temperature and strain load goes along with this. The increment in plasticity makes it possible to attain deeper deformation in high-strength and low-ductility alloys, as well as an increment in the ultimate strain, which is usually controlled by work hardening and requires in-process anneals. The main conclusion from our tests and studies, which is very important in practice, is that the optimal effect of coatings in tube drawing, as assessed by the reduction in the drawing force, can reach 40–70% depending on the alloy and drawing conditions. Other achievements are high surface quality, structural homogeneity, and a set of mechanical properties. In particular, the scatter in the mechanical properties of coated tubes after drawing under the optimal conditions is reduced several times. When drawing small-diameter thin-walled tubes, comparative tests of the efficiency of deposited oxide films were made on instrumental steel filaments. Pieces of stainless steel and a chrome–nickel alloy were drawn. The following control parameters were used: drawing force, chemical composition of the die surface, and state of the die surface as observed under a scanning electron microscope. Drawing with and without lubricants was performed, and various deposited oxide films were tested. This study showed the following results. The general trend of the effect caused by films on the drawing force during unlubricated drawing fits the following pattern (regarding the reduction in the effect, all other conditions being equal): amorphous oxide films >> crystalline oxide films, multilayered films > single-layer films, films on the tube and die > films on the die. In addition, the drawing force versus film thickness relationship has the trend plotted in Fig. 4 and is characteristic of all film materials tested. The largest reduction in the drawing force on the die for various films ranges between 5 and 30%. It was concluded that, if the film is applied only to the tool, a softening effect, like that produced by the film on the workpiece, is observed. However, in this case, surface softening of a work or cut metal is 30–50% lower. Fig.4: The effect of thickness of the deposited film on the drawing force The general trend in the effect caused by films on the drawing force during lubricated drawing with organic lubricants (regarding the weakening of the effect, all other conditions being equal) depends strongly on the lubricant and film structure. Characteristically, all other conditions being equal, the drawing force varies as a function of film thickness as plotted in Fig. 4. The strongest effect is achieved in the case where films are applied to both the tube and the die. In contrast to dry drawing, the crystal and layered structure of the film are weaker factors in this case. We concluded that with liquid lubricants the ability of the film to retain the lubricant is of primary importance. In tests, the initial reduction of the
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