The Effect of Cobalt on the Deformation Behaviour of a Porous TiNi-Based Alloy Obtained by Sintering

Abstract

This research investigates the effect of cobalt on the deformation behaviour of a porous TiNi-based alloy that was obtained by sintering. Porous TiNi-based alloys with cobalt additives, accounting for 0–2 at. % and with a pitch of 0.5, were obtained. The structural-phase state of the porous material was researched by X-ray structural analysis. The effect of different amounts of Co (used as an alloying additive) on the deformation behaviour was investigated by tensile to fracture. The fractograms of fracture of the experimental samples were analysed using scanning electron microscopy. For the first time, the present research shows a diagram of the deformation of a porous TiNi-based alloy that was obtained by sintering under tensile. The stages of deformation were described according to the physical nature of the processes taking place. The effect of the cobalt-alloying additive on the change in the critical stress of martensitic shear was investigated. It was found that the behaviour of the concentration dependency of stress at concentrations under 1.5 at. % Co was determined by an increase in the stress in the TiNi solid solution. This phenomenon is attributed to the arrangement of Co atoms on the Ti sublattice, as well as an increase in the fraction of the B19′ phase in the matrix. The steep rise of the developed forces on the concentration dependency of the martensitic shear stress at 2 at. % Co is presumably attributed to the precipitation hardening of austenite due to the precipitation of finely dispersed coherent Ti3Ni4 phase following the decrease of fraction of martensite. An analysis of fractograms showed that as more cobalt was added, areas of fracture with traces of martensite plates of the B19′ phase started to prevail. At 2 at. % Co these plates fill almost the entire area of the fracture. The research findings presented in this work are of great importance, since they can be used to achieve the set of physical and mechanical properties required for the development of biocompatible materials for implantology.

Experimental Research for the Establishment of the Optimal Forging and Heat Treatment Technical Parameters for Special Purpose Forged Semi-Finishes

“…The method used to highlight the austenitic grain is the method of controlled oxidation and is done as follows: A flat face of the sample must be sanded, and the rest must show no signs of oxidation [ 9 , 13 ]; The sample is placed in the oven with the surface sanded up and is kept for 1 h at the austenite temperature provided for each quality of material; then open the oven door and leave the sample in its door for about 10–15 s for oxidation, then place the iron in water; In the case of significant oxidation, the oxide adhering to the polished surface is easily removed by grinding with fine sandpaper, after which the sample is attacked with Villella reagent (1 g picric acid, 5 mL hydrochloric acid, 100 mL ethyl alcohol) [ 14 , 15 , 16 , 17 , 18 , 19 ] …”

“…In the case of significant oxidation, the oxide adhering to the polished surface is easily removed by grinding with fine sandpaper, after which the sample is attacked with Villella reagent (1 g picric acid, 5 mL hydrochloric acid, 100 mL ethyl alcohol) [ 14 , 15 , 16 , 17 , 18 , 19 ]…”

“…Its versatility, durability, and resistance make it a popular choice for various fields: railway, machine building, naval, extractive, and chemical industries [ 15 , 16 , 17 , 18 , 19 ].…”

Structure and Properties of Metal-Matrix Composites Based on an Inconel 625–TiB2 System Fabricated by Additive Manufacturing

“…The obtained composite powders were used as raw stock in additive deposition systems. In research work [27], it was shown that the structure of the materials obtained by direct laser deposition inherits the structure of the particles of the SHS powders. Titanium nitride particles are evenly distributed in the intermetallic CrNi matrix.…”

Mechanical Properties and Microstructural Evolution of TiNi-Based Intermetallic Alloy with Nb Addition

“…The addition of Nb as a doping element has attracted particular attention due to its effects in enhancing the yield strength through the formation of ultrafine grains, good corrosion resistance at high temperature, and high dislocation density [24][25][26]. Co-addition is also beneficial in improving the solid solution strengthening effect and magnetic hysteresis, thereby improving the thermal coupling performance and oxidation resistance [27]. During the forming process and application, the TiNi alloy will suffer differential strain rate deformation, so it is necessary to investigate the strain rate effect on the TiNi alloy.…”