The Influence of Activating Co and Ni Additions on the Mechanisms of Reaction and Diffusion Interaction During Sintering of PV-N55Т45 TiNi-Based Powders

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An investigation of the influence of reaction- and diffusion-induced interactions in the system of PV-N55Т45 TiNi-based powders and activating Co and Ni additions during sintering on special characteristics of microstructure and structural-phase compositions of porous TiNi-based alloys are investigated aimed at designing porous-monolithic structures. Using the method of liquid-phase sintering of TiNi-based powder, porous specimens with activating Co and Ni additions are manufactured with the concentrations of the latter being 0.5, 1.0, 1.5 and 2.0 at.%. It is found out that the activating action of Co is more moderate compared to that of Ni. A calculation of the heat released in the course of the chemical reaction as a result of introduction of activating additions demonstrates that the values of –∆H for manufacturing porous alloys with additions of Co and Ni are 28 and 52 kJ/mol, respectively. It is established that all specimens under study contain the following phases: austenitic B2, martensitic B19′, Ti₂Ni, ₂(О, N, С) and Ti3Ni4. Moreover, in the material with additions of Ni a TiNi₃ phase is observed. Due to an introduction of a monolithic plate into the sintered powder mixture it is possible to compensate for the heat sink at the concentration of the activating Co addition 1.5 at.%. This allows manufacturing porous-monolithic structures based on the TiNi alloy with a high quality of fusion between the porous and monolithic parts.