Mechanical Properties of NiTi-Based Foam with High Porosity for Implant Applications

Abstract

In order to better understand NiTi-based shape memory alloy foams for implant applications, Ni 40 Ti 50 Cu 10 foams were heat treated and then deformed under incremental and cyclic compression loading. After heat treatment, the microstructure consists of a (Ni,Cu)Ti matrix with small (Ni,Cu) 4 Ti 3 precipitates and a large Ti 2 (Ni,Cu) secondary phase. The heat-treated Ni 40 Ti 50 Cu 10 foam exhibits a two-step transformation, involving B19 0 ? B19 and B19 ? B2 on heating and B2 ? B19 and B19 ? B19 0 on cooling, respectively. One Ni 40 Ti 50 Cu 10 foam was compression loaded for 10 cycles at each subsequent strain level, i.e., 1, 2, 3, 4, 5, and 6 % strain. In each set of compressive stress-strain loops, the maximum stress level decreases due to plastic damage accumulation and/or retention of transformed martensite. Cross-sectional images from micro-computed tomography were collected during compression loading, which shows very uniform deformation without severe structural damage even up to 5 % strain. Localized deformation is visible at 6 % strain.

Mechanical response of mesoporous amorphous NiTi alloy to external deformations

“…To generate the homogeneous amorphous sample without pores, a liquid melt at the temperature T = 3500 K has been isobarically cooled with the rate 10 13 K/s to a state with the temperature T = 300 K at the pressure p = 1 atm. The generated amorphous sample has the density ρ 0 6.17 g/cm 3 that is close to the density of crystalline NiTi, 6.45 g/cm 3 , at the same temperature [44]. Note that the glass transition temperature T g of titanium nickelide estimated by T. Rouxel and Y. Yokoyama is ∼ 750 K [45].…”

“…After ultrafast cooling, each sample has been aged at the state with the temperature T = 300 K and the pressure p = 1 atm over the time 1 ns. Amorphous samples prepared in this way have the different densities ρ 5.71, 5.24, 4.87, 4.5 and 4.01 g/cm 3 . These values of the density ρ are much lower than the density ρ 0 of the homogeneous amorphous system.…”

“…Amorphous metal foams based on Ni and Ti exhibit unique physical and mechanical properties, among which are low specific weight, low stiffness, high corrosion resistance and good biocompatibility [1,2,3,4,5,6]. These properties depend primarily on size and geometry of the pores as well as on the stability of an amorphous matrix [7,8,9,10].…”