PSI - Issue 20

Yakovleva S.P. et al. / Procedia Structural Integrity 20 (2019) 190–197

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Yakovleva S.P. et al. / Structural Integrity Procedia 00 (2019) 000–000

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The wear resistance of DMC samples was determined on a SMC-2 friction machine. Also for comparison, an analysis of the wear resistance of industrial diamond dressers of similar sizes, the weight group of diamonds 500/400 carats, volume fraction of diamond raw materials is 5% (about 2.5 times higher than in experimental DMC). The tests were carried out at a rubbing about the grinding wheel of electrocorundum. Weight wear after passing equal intervals of the friction path was determined. 3. Main results and discussion 3.1. The structure of DMC, obtained using explosive compaction The diamond-metal briquettes obtained by explosive pressing are a fairly monolithic material (Fig. 1, b, с ) and are characterized by a high degree of plastic compaction; the relative density varies from 0.77 to 0.98. Plastic compaction ensures the consolidation of powder particles and the mechanical fixing of diamond grains. As seen in fig. 1, c, the powder matrix fits tightly to the diamond, there are no noticeable microvoids and gaps at the diamond matrix interface, that favors mechanical adhesion. In comparison with microhardness of initial components, microhardness of pressed samples components is either kept close to initial (for powder P2) or increased by 1.2-1.7 times (in the case of powder P1). The structure of the matrix before and after heat treatment is a mixture of solid non-deformed particles of P2 powder in a framing of densely pressed particles of P1 powder (Fig. 1, c, d). The increase in the content of the component P1 reduces the porosity of the composite; with an increase in the charge power, the porosity decreases insignificantly. In other words, the main factor affecting the density of briquettes is the content of easily deformable powder. The combination of the explosive compaction with subsequent heat treatment makes it possible to increase the microhardness of both components. This is due to the high energy activity of the powder material formed by shock waves, which accelerates diffusion processes and promotes strong interaction of carbon atoms with lattice defects during heating. As a result, there is a redistribution of carbon to form fine carbides. These processes increase the microhardness of the matrix components, and the hardening of the “soft” component occurs more intensively; its microhardness increases 2 ... 3 times. On the combination the levels of hardening of both components, the pressing mode with D 2 = 50 mm was considered the most appropriate. Thus, the hardening effect observed during heating of iron-carbon alloys treated with explosion was used to create DMC as shown by Yakovleva et al. (2001), Makharova et al. (2015). The proposed approach allows to differentially adjust the strength of the matrix components to increase its hardness while maintaining a certain plasticity. The diamond particles recovered from briquettes pressed by the explosion are grains of various sizes and shapes and consist of single crystals, their fragments and polycrystals. No signs of ovalization and well-developed cutting edges are good for abrasive properties of the composites. The use of binding materials with high hardness and the reducing the duration of thermal effects on diamond particles allowed to keep close to the original level the indicators of an average grain size, proportion of grains of main fraction and static strength of the diamond component which decreased on 4%, 1% and 10% respectively as obtained by Makharova et al. (2015). This is the reason to use explosive pressing for the manufacture of diamond-abrasive composites, as in traditional methods of sintering the reduction of these characteristics reaches 30% or more. As is known, the properties of composite materials consisting of matrix phases and functional fillers are determined not only by the characteristics of these main components, but to a large extent by the structure and strength of the formed interfacial boundaries as shown by Balasubramanian (2014), Gusev et al. (2006). The basic principle of improving the properties of composites is to create strong chemical bonds between the matrix and the filler. Accordingly, the solution of the problem of increasing the diamond retention is associated with a directional influence on the conditions of the diamond-matrix boundaries formation to improve both components of adhesive 3.2. The effect of explosive compaction on the characteristics of diamond particles 3.3. Diamond-matrix interface zone