Study of titanium nickelide based alloy structure effect on biological environment corrosion resistance

The effect of volume fraction and size of Ti4Ni2Ox particles on pitting, crevice, and fretting corrosion processes is studied by testing implanted elements of titanium nickelide based alloys as part of spinal pedicle screw devices in a 0.9% NaCl solution, tested elements being produced from ingots melted by various technologies (vacuum induction melting; combined skull melting with subsequent vacuum-arc remelting). It is shown that the vacuum induction melting method, which provides higher purity of the resulting material, in particular with respect to oxygen, and reduces the Ti4Ni2Ox volume fraction, is preferable for increasing titanium nickelide based alloy corrosion resistance in a biological environment. It is established that a reduction in volume fraction (and size, dmax) of Ti4Ni2Ox particles from 5.1 +/- 1.2 vol.% (dmax = 10 mu m) to 3.5 +/- 0.7 vol.% (dmax = 7 mu m) results in the pitting potential increasing from 552 +/- 70 to 854 +/- 123 mV and the fretting corrosion current decreasing from 11 +/- 2.7 to 6.7 +/- 2.8 mu A. At the same time, the content of Ni ions in a test corrosion medium after crevice and fretting corrosion studies decreases from 84 +/- 6 to 64 +/- 5 and from 74 +/- 6 to 57 +/- 4 mu g/liter, while the area of corrosion sites decreases by 1.3 and 1.8 times respectively. It is shown that a further reduction in Ti4Ni2Ox particle volume fraction down to 1.2 +/- 0.2 vol.% (dmax = 5 mu m) does not have a significant effect on corrosion resistance indices.