Microstructure and Mechanical Properties of NiTi-Based Eutectic Shape Memory Alloy Produced via Selective Laser Melting In-Situ Alloying by Nb

This paper presents the results of selective laser melting (SLM) process of a nitinol-based NiTiNb shape memory alloy. The eutectic alloy Ni45Ti45Nb10 with a shape memory effect was obtained by SLM in-situ alloying using a powder mixture of NiTi and Nb powder particles. Samples with a high relative density (>99%) were obtained using optimized process parameters. Microstructure, phase composition, tensile properties, as well as martensitic phase transformations temperatures of the produced alloy were investigated in as-fabricated and heat-treated conditions. The NiTiNb alloy fabricated using the SLM in-situ alloying featured the microstructure consisting of the NiTi matrix, fine NiTi+β-Nb eutectics, as well as residual unmelted Nb particles. The mechanical tests showed that the obtained alloy has a yield strength up to 436 MPa and the tensile strength up to 706 MPa. At the same time, in-situ alloying with Nb allowed increasing the hysteresis of martensitic transformation as compared to the alloy without Nb addition from 22 to 50 °C with an increase in Af temperature from −5 to 22 °C.

MODELING THE ACCUMULATION OF DAMAGES AND THE FAILURE OF CERAMIC COMPOSITES Al2O3-ZrO2, OBTAINED BY ADDITIVE TECHNOLOGIES, UNDER HIGH-SPEED LOADING

Functional ceramic composite materials are widely used in industry due to their high strength, hardness, high operating temperature, and chemical inertness. Among the most famous types of functional ceramics are the ceramic composites based on the Al2O3-20% ZrO2 system. In this work, the effect of the loading rate on the crack resistance is studied as well as the effect of the crack resistance of ceramic composites Al2O3-20% t-ZrO2 with a mass content of submicron tZrO2 particles on the high-speed compression of model specimens in shock waves and on the high-speed tension in the region of interaction of unloading waves. It is established that nonlinear effects of the mechanical behavior of ceramic composites ZrO2-Al2O3 with a transformationhardened matrix obtained by additive technologies are manifested at shock loading amplitudes close to or exceeding the Hugoniot elastic limit. Nonlinear effects under intense dynamic impacts on the considered composites are associated with the processes of self-organization of deformation regimes at a mesoscopic level, as well as with the occurrence of martensitic phase transformations in the matrix volumes, which are adjacent to strengthening particles. The modeling approach presented in this work can be used to determine the dynamic characteristics of ceramic composites up to shock loads of 1000 m/s.