Mechanical Properties of Highly Porous NiTi Alloys

Abstract

Highly porous NiTi alloys with pseudoelastic properties are attractive candidates for biomedical implants, energy absorbers, or damping elements. Recently, a new method was developed for net-shape manufacturing of such alloys combining metal injection molding with the application of suitable space-holder materials. A comprehensive study of mechanical properties was conducted on samples with a porosity of 51% and a pore size in the range of 300-500 lm. At low deformations <6%, fully pronounced pseudoelasticity was found. Even at higher strains, a shape recovery of maximum 6% took place, on which the onset of irreversible plastic deformation was superposed. Results of static compression tests were also used to calculate the energy-absorbing capacity. Fatigue of porous NiTi was investigated by cyclic loading up to 230,000 stress reversals. The failure mechanisms responsible for a reduction of shape recovery after an increased number of load cycles are discussed.

In Search of the Optimal Conditions to Process Shape Memory Alloys (NiTi) Using Fused Filament Fabrication (FFF)

“…Therefore, in a H 2 environmental atmosphere, the best parameter set for the sintering thermal cycle is a maximum temperature of 1165 °C, holding time of 5 h, and heating and cooling rates from 0.1 to 10 K min −1 . Other sintering studies on NiTi applied high sintering temperatures and holding times from 5 [ 13 , 15 , 28 ] to 10 h [ 13 , 17 , 30 ], depending on the size and geometry of the specimens.…”

Metals for bone implants. Part 1. Powder metallurgy and implant rendering

“…While Guaxin et al [131] use the conventional MIM process for the production of porous NiTi from elemental powder, Bram et al [132,133] and Köhl et al [134][135][136] adopted the space-holder technique to create highly porous NiTi with large pore sizes and good structural and functional properties by MIM from pre-alloyed powder (see Figure 7). This procedure starts with creating a feedstock of NiTi powder, NaCl space-holders and a binder system (amide wax and polyethylene wax) by means of mixing in a heated kneader.…”

Review and perspectives: shape memory alloy composite systems

“…9a and b, respectively. The mechanical properties of NiTi foams was extensively investigated and characterized by Bram et al [70] who considered a 51% porous specimen produced via metal injection molding and some representative properties of different porous SMAs are given in Table 8. Dense SMA Matrix Materials -The effect of small concentrations of various reinforcement on a NiTi matrix has been studied.…”