Hard alloy production by SHS compaction in an open die

Abstract

The paper investigates the possibility of carrying out SHS for the Ti (81.5 wt.%) + B (18.5 wt.%) composition in the air followed by pressing combustion products in an open steel die with walls limiting their radial flow under tough heat dissipation conditions without the use of an intermediate loose medium of the heat insulator. Modes of reaction powder mixture preparation for synthesis were optimized. Such process characteristics as bulk density, compaction, elastic aftereffect were determined for initial powders and reaction mixtures, and the strength of compactions was estimated. It is shown that there is a relationship between the strength of charge compacts, combustion rate and changes in their volume after combustion in the air under intensive gas liberation during combustion. The optimal charge compact density was found equal to 0.75 corresponding to the maximum combustion rate without charge emissions with a minimum change in volume. As a result of the optimization, the possibility of effective and safe conduct synthesis process without the use of an intermediate loose medium of the heat insulator is shown. Hard-alloy plates with a diameter of 60 mm and a thickness of 11 mm were obtained in the open steel die under SHS compaction conditions. The structure of the resulting hard alloy is unique with a porosity of less than 0.5 %. It consists of titanium diboride (~60 wt.%) and titanium-based binder phase (~ 40 wt.%). Such a structure obtained as a result of accelerated cooling can be defined as nonequilibrium, since the main phase for the studied composition should be titanium monoboride (TiB) in accordance with the Ti–B state diagram. The microhardness of the fabricated hard alloy is HV = 18000 MPa.