Influence of Ti and B powder mixing modes on mixture properties and SHS composite microstructure

The paper studies the influence of mixing modes for titanium and boron powder mixtures with the 81.5 % Ti + 18.5 % B composition in a ball mill on the process characteristics of mixtures, combustion parameters, and microstructure of SHS composites. It is shown that the dependence of the electrical resistivity on the density of charge compacts for the composition under study can be used as a criterion for mixing quality, mixture uniformity. It is noted that an increase in the grinding media mass includes the mechanism of mechanical activation (MA) of mixtures. Dependences of the burning speed and temperature on density were obtained for all the mixtures under study. Burning speeds for mixtures subjected to mechanical activation (М_ch/М_ball = 1 : 7; 1 : 12) and without it (М_ch/М_ball = 1 : 4) differ significantly. Mechanically activated mixtures feature by differences in burning speeds depending on the charge compact thickness. Thin compacts burn at a higher speed. The burning speed of mixtures without MA (in case of smaller grinding media masses) does not depend on the compact thickness. Maximum burning temperatures of all the mixtures studied have insignificant differences depending on the density, mixing time and grinding media mass. There was also no any effect of the compact thickness on the burning temperature observed. The structure of SHS composites depends on mixing modes. The finely dispersed structure of composites with titanium diboride grains (less than 1 μm) and a titanium-based binder phase can be obtained only from MA mixtures. Alloys with a structure consisting mainly of elongated titanium monoboride grains (up to 40 μm) and a binder phase of a solid solution of boron in titanium were synthesized of the mixtures for which mechanical activation processes are not essential.

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