Selective leaching and surface properties of TiNiFe shape-memory alloys

Abstract

This study investigated the selective leaching and surface characteristics of Ti50Ni50-xFex (x = 1, 2, and 3) shape-memory alloys using inductively coupled plasma-mass spectrometry, X-ray diffractometry, electrochemical tests and X-ray photoelectron spectroscopy. According to our results, the concentrations of Ni and Fe ions selectively leached from each specimen were considerably higher than that of Ti ions. Electrochemical tests revealed a gradual deterioration in the corrosion resistance of the Ti50Ni50-xFex SMAs as the Fe content in the alloys was increased. X-ray photoelectron-spectroscopy results indicate that the surface of each specimen is primarily made up of a passive TiO2 film. NiO and Fe2O3 oxides, which also formed on the surfaces of the Ti50Ni50-xFex SMAs, caused a deterioration of the uniformity, undermining the protective effect of the TiO2 films, resulting in a highly selective leaching of the Ni and Fe ions. The Ti50Ni50-xFex SMAs exhibit a number of favourable properties compared to the other SMAs; however, high concentrations of selectively leached Ni and Fe ions may pose a risk in biomedical applications, particularly when used as implant materials. Keywords: TiNiFe shape-memory alloys, biomaterials, selective leaching, corrosion, X-ray photoelectron spectroscopy V {tudiji je prou~evano selektivno izpiranje in zna~ilnosti povr{ine zlitine s spominom Ti50Ni50-xFex (x = 1, 2, in 3), z uporabo masne spektrometrije z induktivno sklopljeno plazmo, rentgensko difrakcijo, elektrokemijskimi preizkusi in rentgensko fotoelektronsko spektroskopijo. Rezultati ka`ejo, da je bila koncentracija selektivno izpranih Ni in Fe ionov iz vsakega vzorca veliko ve~ja kot pa Ti ionov. Elektrokemijski preizkusi so pokazali postopno zmanj{anje korozijske odpornosti Ti50Ni50-xFex SMA, ko je vsebvnost Fe v zlitinah nara{~ala. Rezultati rentgenske fotoelektronske spektroskopije ka`ejo, da je povr{ina vseh vzorcev predvsem sestavljena iz pasivnih TiO2 plasti. NiO in Fe2O3 oksidi, ki so tudi nastali na povr{ini Ti50Ni50-xFex SMAs, poslab{ajo enotnost in ogro`ajo varovalno plast iz TiO2 prevlek, kar ima za posledico bolj selektivno izpiranje ionov Ni in Fe. Ti50Ni50-xFex SMAs vsebuje {tevilne ugodne lastnosti v primerjavi z drugimi SMA; vendar pa velika koncentracija selektivno izpranih Ni in Fe ionov lahko predstavlja tveganje pri biomedicinski uporabi, posebno pri implantiranih materialih. Klju~ne besede: TiNiFe zlitine s spominom, biomateriali, selektivno izpiranje, korozija, rentgenska fotoelektronska spektroskopija

Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

“…Moreover, the i corr values for the Cu12.5Al4Ni, Cu13.0Al4Ni, and Cu13.5Al 4Ni SMAs were calculated as (9.31 « 0.489) © 10 ¹6 , (8.54 « 0.468) © 10 ¹6 , and (12.2 « 0.796) © 10 ¹6 A/cm 2 , respectively. Compared with our previous studies, 18,19) the E corr values for the CuXAl4Ni SMAs (approximately ¹0.2 V) are slightly higher than those of the Ti 50 Ni 50 (approximately ¹0.496 V), Ti 50 Ni 50¹x Cu x (from ¹0.330 to ¹0.416 V), and Ti 50 Ni 50¹x Fe x (from ¹0.379 to ¹0.433 V) SMAs. However, the i corr values for the CuXAl4Ni SMAs (approximately 10 © 10 ¹6 A/cm 2 ) are also higher than those of the Ti 50 Ni 50 (approximately 7.57 © 10 ¹7 A/cm 2 ), Ti 50 Ni 50¹x Cu x (from 2.43 © 10 ¹7 to 4.13 © 10 ¹7 A/cm 2 ), and Ti 50 Ni 50¹x Fe x (from 3.27 © 10 ¹7 to 5.52 © 10 ¹6 A/cm 2 ) SMAs.…”

“…5 also reveals that the selective leaching rate of Ni ions from the CuXAl4Ni SMAs is much higher than those of Cu and Al ions, even though the weight percentage of Ni atoms is only approximately 4 wt.%, which is much lower than those of Cu and Al atoms in the CuXAl4Ni SMAs. Compared with our previous studies, 18,19) the concentrations of the Ni ions selectively leached from the CuXAl4Ni SMAs (approximately 600 ppb after 90 days) are much higher than that of the Ti 50 Ni 50 SMA (approximately 25 ppb after 30 days), but are much lower than those of the Ti 50 Ni 50¹x Cu x (approximately 2500 ppb after 30 days) and Ti 50 Ni 50¹x Fe x (above 1500 ppb after 80 days) SMAs. Moreover, the concentrations of the Cu ions selectively leached from the CuXAl4Ni SMAs (approximately 200 ppb after 90 days) are also much lower than that of the Ti 50 Ni 45 Cu 5 SMA (above 800 ppb after 30 days), even though the weight percentage of Cu atoms is above 80% for the CuXAl4Ni SMAs.…”

“…Unfortunately, the concentrations of Ni ions selectively leached from the Ti 50 Ni 50¹x Cu x SMAs (approximately 2500 ppb after 30 days) and the Ti 50 Ni 50¹x Fe x SMAs (above 1500 ppb after 80 days) were simultaneously significantly increased. 18,19) This is because the uniformity and protection of the highly passive TiO From the results of this study, the selective leaching property of the CuXAl4Ni SMAs are not as good as that of the Ti 50 Ni 50 SMA, but are still far superior to those of the Ti 50 Ni 50¹x Cu x and Ti 50 Ni 50¹x Fe x SMAs. Moreover, the Cu XAl4Ni SMAs also possess the advantages of low cost, good workability, exceptional electrical and thermal conductivities, and easily obtainable wide range of martensitic transformation temperatures by precise adjustment of the chemical compositions of the CuXAl4Ni SMAs.…”

“…5, we can conclude that the surfaces of the Cu13.5Al4Ni SMA were dominantly composed of Cu 2 O and Al 2 O 3 oxide layers. The NiO oxide layer, which was normally observed on the surface of TiNi-based SMAs, 18,19) was not observed on the surface of the CuXAl4Ni SMAs.…”

“…Gil et al 1517) studied the Ni release behaviors of TiNi orthodontic archwires and reported that the titanium oxide on their surface significantly improves the corrosion resistance and decreases the Ni ion release of the alloys. Chang et al 18,19) reported that TiNiCu and TiNiFe SMAs exhibited higher selective leaching rates of Ni ions compared to that of TiNi SMA.…”