Corrosion Resistant Titanium Alloys For Medical Tools and Implants
Manana Mikaberidze1, Corby Anderson2, Bill Gleason2
George Gordeziani1, Eteri Gozalishvili1, Lia Akhvlediani1, Dali Ramazashvili1
1
Tavadze Institute of Metallurgy and Materials Science, Tbilisi ,Republic of Georgia
2
Center for Advanced Mineral and Metallurgical Processing,
Montana Tech, Butte, Montana, USA
Summary
New corrosion resistant Ti-8Ni-Cr system alloys with increased hardness and strength have been developed for medical
tools and implants. The development was made based on study of chromium influence on the phase constituents,
microstructure, mechanical properties, corrosion resistance and electrochemical characteristics of Ti-8Ni alloy.
Optimum condition of thermal treatment, providing high strength, hardness and corrosion resistance of alloys has been
defined – quenching from 9500C with content of chromium in alloys 1 – 3% (by addition of Yttrium in quantity 0,001
– 0,01 mass%). The cause is that alloys after quenching from 9500C have structure of transformed β-solid solution and
contain ω-phase, which is micro dispersive during concentration of chromium up to 1-3%.
On the base of studying of the phase equilibrium by microstructural, x-ray investigations and differential thermal
analysis of Ti-8Ni-Cr system alloys polythermal sections of phase diagram of this system have been constructed, which
is in complete accordance with the phase diagram formed by thermodynamic calculations.
Study of mechanical properties of Ti-8Ni-(0-3)Cr quenching alloys show, that chromium increases the tensile strength
(1000MPa) and hardness (48 HRC) and slightly influences on plastic properties of the Ti-8Ni alloy. Tensile strength of
titanium commercial alloys: Ti-6Al-4V and Ti-5Al-3Sn do not exceed 900 MPA.
Corrosion tests in medium containing human body: blood, physiological solution, gastric juice, tissue liquid and also
corrosion testing according to the following regime: cleaning+disinfection+sterilization in aggressive solutions with
addition of hydrogen peroxide reveal high corrosion resistance of Ti-8Ni-(0-3)Cr alloys, without the changing of
surface. After 20 cycles corrosion losses of the commercial titanium alloys are ~ one order more than the losses of new
alloys.
Study of toxic properties of alloys Ti-8Ni-(1-3)Cr during their implantation in muscles and abdominal cavity of
animals show, that they do not cause local irritative actions on different tissues, they do not suppress local tissue
reactions and do not have any toxic effects during short or long term implantation conditions.
High corrosion resistance of alloy Ti-8Ni-1Cr is established also by the modeling and prediction of corrosion behavior
in the physiological solution at the temperature 37oC with using of electrochemical investigations, spectral analysis,
regression and variance analysis of the mathematical statistics.
Alloys Ti-8Ni-(1-3)%Cr are recommended for manufacturing high-strength medical tools of multiply usage and
surgical implants.
Application of new alloys will allow improving functional properties and increase quality, reliability, service life of
medical tools and implants.
Introduction
The purpose of the present paper is the development of new corrosion resistant Ti-Ni-Cr system alloys with increased
strength and hardness by investigating phase equilibrium and structural transformations, mechanical properties and
corrosion resistance in medical solutions.
Last years are characterized by fast development of medical engineering. For maintenance of the newest methods of
operations in vascular and neural surgery, ophthalmology, traumatology and other areas of medicine the new
instruments, modern sets of microsurgical tools and implants are created. The most important question in creation of
medical tools is not only their constructive design, but also selection of such materials, which considerably will raise
their quality, reliability, service life and will improve their functional properties. For the increase of wear and corrosion
resistance, and also functional properties of medical tools and implants, the microsurgical tools with hardened working
surfaces are developed.[ 1 - 4]
The high strength, low weight, outstanding corrosion resistance possessed by titanium and titanium alloys have led to a
wide and diversified range of successful applications which demand high levels of reliable performance in surgery and
medicine as well as in aerospace, automotive, chemical plant, power generation, oil and gas extraction, sports, and
other major industries. More than 1000 tones of titanium devices of every description and function are implanted in
patients worldwide every year. Requirements for joint replacement continue to grow. Light, strong and totally
biocompatible, titanium is one of few materials that naturally match the requirements for implantation in the human
body.
However, most of commercial titanium alloys have low hardness and insufficient corrosion resistance in aggressive
washing and sterilizing media. In this connection, the development of new titanium alloys with high mechanical
properties together with corrosion resistance represents significant interest, both for manufacturing medical tools and
implants and for coating them with the purpose of their hardening.
The basic way of creation of high-strength, corrosion resistant titanium alloys at the present stage is a complex alloying
of solid solutions. The choice of rational structures of alloys is based on theoretical assessment, phase diagram and
"structure - property" investigations for various alloying elements.
The most cost saving elements raising hardness of titanium based binary alloys are iron, chrome, manganese, copper,
aluminum, silicon etc., however they considerably lower corrosion resistance of titanium. At alloying with
molybdenum, tantalum, cobalt, nickel, germanium, niobium the high corrosion resistance is achieved only at rather
high concentration of these elements.
For medical tools, where the high-strength, hardness and corrosion resistance is required, the development of
metastable β titanium alloys can be expedient. They can be created by complex alloying by elements, such, as: chrome,
nickel, manganese, molybdenum, vanadium etc., which form with titanium substitutional solid solutions, stabilize β
phase and expand its area on phase diagrams. Simultaneously, the chosen elements should raise or not influence
corrosion resistance of titanium. The alloys with metastable β structure can be strengthened with the help of dispersion
hardening by submicroscopic precipitates.
Titanium alloys with α and (α+β) containing up to 2% β stabilizing elements are used for tools, details and designs,
which are not requiring high durability and hardness. Wider application finds titanium alloys with (α+β) structure.
They have much greater strength than the α-alloys, have more bend plasticity, can be forged, rolled and stamped more
easily than alloys with α and β structure. Mass manufacture of these alloys is rather simple.
Titanium and its alloys such as: unalloyed titanium (ASTM F1341, F67), Ti-6Al-4V (ASTM F620), Ti-4Al-3Mo-V,
Ti-5Al-3Sn, Ti-3Al-1,5Mn etc. are used for manufacturing some medical tools like mirrors, wound wideners, nails for
osseointegration, tracheametric tubes, needle holders, eye and wire fixation tweezers, heart valves and other
microtools. [5 - 14 ]
In the literature there are no data on the behavior of ternary titanium based Ti-Ni- Cr system alloys in medium, that
contains human body: blood, physiological solution, gastric juice, tissue liquid and also washing, disinfection and
sterilization solutions for medical tools; the influence of above mentioned alloying elements on corrosion and
mechanical properties of titanium is not investigated; data is scarce about phase equilibrium in titanium rich
multicomponent alloys.
The development of new corrosion resistant titanium alloys with increased mechanical properties and their application
in medical engineering will allow to improve functional properties and to increase quality, reliability, service life of
medical tools and consequently it will have significant social impact.
Technical approach
Smelting of the Ti-8Ni-Cr system alloys have been carried out in arc vacuum furnace of the MIFI type with the
unexpended tungsten electrode in the atmosphere of argon. Working mixture loaded into a water-cooled copper
crucible. Titanium sponge, nickel, and chromium were used as working mixture materials. Regime of melting was –
200-300 A, at 50V. For achieving the homogeneity of composition four and five times remelting was used. The control
of chemical composition was carried out by comparative weighing of the received ingots. Difference in the weigh
composed not more than 0,5%/ The received rods were cut on 10 mm size pieces, which were placed into the special
device, intended for getting the cylindrical ingots with 4,6 and 10 mm diameters.
Thermal treatment of alloys has been carried out according to the following regimes: quenching from temperatures
9500in the water.
The structure of the received samples was studied by optical (“Noplot-21”) microscopy methods together with x-ray
analyses. Mechanical properties of alloys were carried out by measurements of hardness, tensile strength, elongation
and cross-section reduction by using the standard methods.
For the estimation of corrosion resistance of alloys gravimetric method was used together with visual control.
Corrosion resistance of titanium alloys in media containing the human body: blood, physiological solution (0,9%
NaCl), gastric juice (1% HCl) and tissue liquid, as well as in solutions used for disinfections, washing and sterilization
of medical instruments have been studied. 3 types of sterilization were used: 1. Chemical sterilization in 6% solution of
hydrogen peroxide (during 3 hours, at 500C); 2. Sterilization in air-drying chamber (at 1800C, 45 min); 3. Vapor
sterilization autoclave (at 1150C, 1,5 ATM, 30 min.). Washing solution of 0,5% hydrogen peroxide was used as
cleaning solution means. Disinfection was done in boiling distilled water during 45 minutes with addition of cooling to
the room temperature [ 15].
Electrochemical investigations on potentiostats have been carried out in NaCl, HCl and NaOH solutions.
Potentiodynamic curves E-lgi of alloys have been constructed.
Corrosion currents were defined graphically according to proposed by us method: stationary potential was adjusted to
the electrode, anodic and cathodic polarized curves E-lgi with the amplitude of 80-100 (mV) were got and their linear
section in 26-75 mV diapason were extrapolationed on the shown potential; corrosion rate K (g/m2hr) was calculated
according to the well-known formula K = Ai/zF, where A is atomic weight, g/mol (for titanium A=47,9 g/mol), zvalency, F – Faraday number – 26,8 A·hr/mol, I – current density A/m2.
Thermodynamic study and theoretical calculation of phase diagram of Ti-8Ni-Cr system alloys were carried out by
using “Thermo-Calc” Software [16 - 25].
Investigation of toxic properties of new titanium alloys Ti – 8Ni-(1-3)Cr was carried out during their short and long
term implantations into the muscles and abdominal cavity of animals [26].
Short Term Implantation
After cleaning, disinfection and sterilization in 70% Ethanol solution 5 disks of test samples (Ф10 mm, thickness – 1
mm) were implanted aseptically into the muscles of rats and mice using hypodermic needle and Nembutal narcosis (for
rats 40 mg/kg and 80 mg/kg for mice). Similarly 5 equal size of negative control rubber dicks were implanted. There
were 5 animals in each experimental and controlled group. The animals were maintained for 10 days and sacrificed.
Tissues around the implant site were harvested and examined macroscopically. (visual control) the implants sites were
also excised, placed in formalin and processed for microscopia, pathological evaluation
Long Term Implantation
After cleaning, chloroform disinfection and sterilization 5 disks of test samples were implanted aseptically into the
abdominal cavity of rats and mice. Similarly 5 disks of negative control rubber were implanted. The animals were
maintained for 60 days and sacrificed. There were 5 animals in each experimental and controlled group. Animals were
weighed for 10, 20, 40 and 60 days. During this period their general condition was controlled.
Tissues around the implant site were harvested and examined by visual control and microscopically. Visual control of
abdominal cavity has been made too.
Results
Alloys of Ti-Ni-Cr system have been melted with constant content of Nickel- 8% and variable content of Chromium 010%, by the addition of Yttrium in Quantity 0,001-0,01%. Thermal treatment of alloys has been carried out according
to regime: quenching from temperatures: 9500, 8000, 7000 and 6000 C in the water. Microstructure of alloys has been
studied is casting condition and after quenching.
Characteristic microstructure of alloys in casting condition consists of primary crystallized grains of β-solid solution
with tracks of dendrite structure.
After quenching from 9500C all alloys of this section show the structure of transformed β-solid solution.
In the table 1. results of X-ray phase analysis of alloys are represented, as it is seen the solid solution on the basis of
hexagonic closepacking structure of α-titanium, β-phase on the basis of cubic sizecentrid structures of titanium and
intermetallic compounds Ti2Ni and TiCr2 have been received on X-ray photographs. In alloys with 0-3% of chromium
there was β phase after 8000C quenching, but because of unstableness of β-solid solution during quenching on X-ray
photograph of these alloys of lines has been received, answering to hexagonic closepacking structure - α′.
After 9500C quenching all alloys showed β+ω structure.
Table 1.
Results of x-ray phase analysis of Ti-Ni-Cr alloys
№
Alloys
1
2
3
4
5
6
7
8
Ti-8Ni
Ti-8Ni-0,1Cr
Ti-8Ni-0,5Cr
Ti-8Ni-1Cr
Ti-8Ni-3Cr
Ti-8Ni-5Cr
Ti-8Ni-8Cr
Ti-8Ni-10Cr
Phase content of alloys after quenching from
temperatures
9500
8000
6000
β+ω
α′+ Ti2Ni
β+ω
α′+ Ti2Ni
α+ Ti2Ni
β+ω
α′+ Ti2Ni
α+ Ti2Ni
β+ω
α′+ Ti2Ni
α+ Ti2Ni
β+ω
α′+ Ti2Ni
β+ω
α+ Ti2Ni+TiCr2
β-ω
β+ Ti2Ni
α+ Ti2Ni+TiCr2
β-ω
β+ Ti2Ni
α+ Ti2Ni+TiCr2
Influence of chromium on the hardness of the alloys Ti-Ni-Cr system after quenching from the temperatures: 9500,
8000, 7000 and 6000C is presented in the Figure 1. As shown in diagrams, alloys of this type after quenching from
6000C is characterized with low value of hardness that is connected with dilution of matrix by alloying elements. The
highest value of hardness of quenching from 9500 and 8000 alloys is connected with decomposition of β-phase in
quenching conditions from these temperatures. After quenching from 9500C all alloys have β+ω structure; at the same
time in alloys, containing 1-3% of chromium, formed ω-phase is microdispersive causing their high hardness.
.Corrosion resistance of Ti-Ni-Cr system alloys was studied out in 10% solutions of hydrochloric acid (HCl), sodium
chloride (NaCl) and sodium hydroxide (NaOH) in cast condition and after quenching from temperatures: 9500, 8000
and 6000C.
Studying of kinetics of corrosion rate of alloys showed, that maximum corrosion losses were observed in alloys after
100-hour tests. The results of corrosion tests are given in Figures 2-4.
As it is seen in quenching from 9500 and 8000C alloys, chromium up to 3% does not influence on corrosion rate of Ti8%Ni alloy in all examined solutions. Further increase of chromium causes insignificant rise of corrosion rate in NaCl
and NaOH solutions, but it increases corrosion rate of Ti-8%Ni alloy 6 times more in solution of HCl.
It should be mentioned that pH solutions does not change after tests.
Corrosion rate of casting alloys and after quenching from 6000C is rather higher, though the character of curves is the
same as in quenching from 9500 and 8000C alloys – with increasing content of chromium from 3 to 10% corrosion rate
increases in all solutions, especially in solution of HCl.
High corrosion resistance of quenching from 9500 alloys is caused by the fact that the structure of these alloys consists
of β-solid solution or contains intermetallic compound Ti2Ni.
In alloys after quenching from 6000C chromium abruptly increases corrosion losses of Ti-8%Ni alloy, that is caused by
increasing of quantity of not stability in these solutions compound TiCr2.
Results of chemical analysis after testing of alloys in all solutions are according to their corrosion resistance. In
solutions NaCl and NaOH quantity of moving ions of titanium, nickel and chromium are insignificant. After tests in
HCl maximum quantity of moving into solution ions is observed in quenched alloys from 6000C. With increase of
chromium content, quantity of moving ions of Ni and Cr are 0,001 g/l and 0,005 g/l accordingly. Quantity of moving
into solution ions of Ti increases from 0,004 to 0,03 g/l.
Optimum regime of thermal treatment of alloys, guaranteeing high strength, hardness and corrosion resistance has been
defined – quenching from 9500C, and content of chromium in alloys up to 1-3%.
Mechanical properties of quenching from 9500C alloys Ti-8Ni-(0-3) Cr are given on Fig.5-.6. As shown on Figures
chromium increases hardness and tensile strength, and slightly influences on plastic properties of Ti-8Ni alloy.
Studying of Ti-8Ni-3Cr alloy surface and distribution of alloying elements on the characteristic x-ray emission TiKα,
NiKα and CrKα were carried out on the electro microanalizer, Cameca, Microsonde MS46. Surface of alloy Ti-8Ni-3Cr
and element distribution are shown on the figure 7. As it is visible the elements – titanium, chromium and nickel are
proportionally distributed on the surface of Ti-8Ni-3Cr alloy.
Corrosion resistance of Ti-8Ni-(0-3)Cr alloys have been studied in medium that contains the human body: blood,
physiological solution (0,9% NaCl), gastric juice (1% HCl) and tissue liquid.
In conserved blood in physiological solution and tissue liquid after 100 hour tests, corrosion rate of all alloys,
containing about 3% chromium did not exceed 0,0002 g/m2hr.
After the researches, blood test shown that the blood formula does not change (eozinophils 0,5-5%, limphocytes 2030%, monocytes – 10%, leicocytes 5000/l, neitrophils - within norm).
In the 1% solution of HCl chromium influences slightly to 1%, and further changes from the worse corrosion resistance
of alloys and constitutes 0,05 g/m2hr after 100 hour tests.
Fig. 5. Influence of chromium on the tensile strength and hardness of the alloy Ti-8Ni.
Fig. 6. Influence of chromium on the elongation and cross-section reduction of the Ti-8Ni
alloy
Fig. 7. The surface of Ti-8Ni-3Cr alloy (a)and element distribution in the characteristic,
X-ray emissions: b - Crkα, c-Nikα, d - Tikα
Phase transformation of Ti-8Ni-Cr system alloys has been determined with help of differential thermal analysis.
On the base of microstructural, X-ray investigations and differential thermal analysis of Ti-8Ni-Cr system alloys the
polythermal sections of phase diagram of this system have been constructed. Fig. 8.
All alloys of this section are crystallized as the β solid solutions on the base of titanium. On the section there are: β,
β+Ti2Ni , α+β+Ti2Ni , α+Ti2Ni and α+Ti2Ni +TiCr2 phase areas. By a method of the differential thermal analysis it is
established, that alloys of the studied section undergo phase transformations in the solid state, connected with the
transformations in the binary systems: Ti-Ni and Ti-Cr. Obtained temperatures of transformations are shown on the
polythermal section of the Ti-8Ni-Cr system alloys phase diagram. In process of increase of chromium concentration
(from 0 up to 10%) in alloys, the transition temperature β → β+Ti2Ni is reduced from 8600C to 8000C. The
temperature of transition β+Ti2Ni → α+β+Ti2Ni in process of increase of concentration of chromium in alloys from 0
up to 10% decreases from 7600 up to 7000C. The alloys containing from 0,5 up to 10% chromium at the temperature
6500C undergo eutectoid transportation β → α+Ti2Ni+TiCr2. Compound TiCr2 will be in the alloys with >0,3%
chromium concentration.
Thermodynamic study of alloys of system Ti-8Ni-Cr was carried out. Polythermal sections of phase equilibrium
diagrams of Ti-8Ni-Cr system alloys, which have been constructed by our calculations, are given on the figure 9.
For the purpose of checking the accuracy of calculated values of theoretical (Fig.9) and the experimental (Fig..8)
diagrams of Ti-8Ni-Cr system alloys have been compared with each other.
On the diagram, that has been constructed by our calculations), all the formed phases completely coincide with phases,
which are represented on the experimental diagram. Temperature -concentration sections are completely given as well
and they coincide with the data determined experimentally. Hence, it can be concluded that the diagram constructed by
five-member coefficients of binary interaction is sufficiently exact and coincide with the experimentally obtained
diagram.[ 27]
a
b
Fig. 9. Polythermal sections of the phase equilibrium diagrams of :
(a)_ (0-100)Ti-8Ni-(0-10)Cr and (b) _ (0-100)Ti-8Ni-(0-100)Cr system alloys
Corrosion testing of the Ti-8Ni-(0-3)-Cr alloys has been carried out according to the following regime:
cleaning+desinfection+sterilization.
Washing solution with 0,5% hydrogen peroxide was used as cleaning solution means. Desinfection was done in boiling
distilled water during 45 minutes with addition of cooling to the room temperature. Three types of sterilization were
used: 1.Sterilization in air-drying chamber (at 1800C, 45 min) 2. Vapor sterilization autoclave (at 1150C, 1,5 ATM, 30
min) and 3,6% H2O2 (500C, 3hr).
For comparing titanium standard alloys have been studied, they are used nowadays in medical technique. The results
after 20 cycle tests according to the regime: cleaning + desinfection + sterilization are given on the table 2. As it is seen
corrosion losses of alloys Ti-Ni-Cr increase insignificantly, though all alloys have high corrosion resistance. For alloy
with 1% Cr Δm/s=0.0035 g/m2 after 20 cycles. Corrosion losses of the known alloys are ~one orders more than the
losses of Ti-Ni-Cr alloys. Visual control of alloys showed that known alloys withstand 10 cycle of cleaning without
surface changing. Further the surface condition changes, spots of oxide tint appear; the surface of Ti-8Ni-(0-3) Cr
alloys does not change after 20 cycles.
Table 2.
Corrosion loses, Δm/s (g/m2), of alloys after 20 cycle of cleaning,
desinfections and sterilization
TYPES OF STERILIZATION
Chemical, in
in air drying chamber vapor sterilization
ALLOYS
autoclave (at 1150C; 1,5 6% H2O2; 500C,
(at 1800C, 45 min)
ATM, 30 min)
3 hr
Ti – 8Ni
0,001
0,002
0,0202
Ti – 8Ni – 0,5Cr
0,002
0,002
0,0251
Ti – 8Ni – 1Cr
0,002
0,0025
0,0354
Ti – 8Ni – 2Cr
0,003
0,004
0,0541
Ti – 8Ni – 3Cr
0,003
0,005
0,0851
Pure titanium
0,17
0,21
0,2312
Ti – 4Al –2Mn
0,21
0,158
0,2508
Ti – 6Al – 4V
0,37
0,315
0,4509
Ti – 5Al – 3Mo – 2V
0,50
0,52
0,6123
Ti – 5Al – 3Sn
0,41
0,32
0,4822
Electrochemical investigations of alloys have been carried out in 0,9% NaCl, 1% HCl and 1% NaOH solutions.
Potentiodynamic curves E-lgi of Ti-Ni-Cr alloys are given on the figures 10 - 12. As the analysis of the curves show,
alloys in all solutions are characterized with a passive field and overpassivation; with raise of chromium content anodic
currents increase in all solutions.
Corrosion currents were defined graphically, according to proposed by us method: stationary potential was adjusted to
the electrode, anodic and cathodic polarized curves E-lgi with the amplitude of 80-100 (mv) were got and their linear
section in 25-75 mv diapason were extrapolationed on the shown potential; corrosion rate K (g/m2hr) was calculated
according to the well – known formula K=A/ZF, where A is atomic weight, g/mol (for titanium A=47,9 g/mol), Z –
valency, F – Faradey number – 26,8 Ahr/mol, i – current density A/m2.Stationary potentials, (E, V) corrosion currents
(icor, μA/sm2) and corrosion rates (K, g/m2hr) of the Ti-Ni-Cr alloys have been calculated according to the formula are
shown on the table 3..
Table 3.
Stationary potentials (E,V), Corrosion currents (icor, μA/sm2) and corrosion
rate (K, g/m2 hr) of Ti-8Ni-Cr system quenching alloys.
SOLUTIONS
0.9% NaCl
1% HCl
ALLOYS
Cleaning
solution
+0,5%H2O2
1% NaOH
K,
Ecor,
icor,
K,
K,
icor,
icor,
E ,V
E ,V
V μA/sm2 g/m2 hr cor
μA/sm2 g/m2 hr cor
μA/sm2 g/m2 hr
Ti-8Ni
Ti-8Ni-0.5Cr 0,3
Ti-8Ni-1Cr 0,3
Ti-8Ni-3Cr 0,23
2,28
2,09
2,68
0,010
0,009
0,012
0,06
0,12
0,19
1,07
0,35
0,85
0,005
0,002
0,004
-0,08
0,01
-0,24
2,29
2,4
4,17
0,01
0,011
0,019
Ecor
icor
-0,4
-0,25
-0,6
-0,65
-0,6
-0,58
-0,55
-0,5
Calculated values of alloy corrosion rates are in complete accordance with values of corrosion rates got by the
gravimetrical tests.
Fig. 10. Potentiodynamic curves Ti-8Ni-Cr alloys in 0,9% solution NaCl
1. Ti-8Ni-0,5Cr; 2. Ti-8Ni-1Cr; 3. Ti-8Ni-3Cr.
Fig.11. Potentiodynamic curves Ti-8Ni-Cr alloys in 1% solution HCl
1. Ti-8Ni-0,5Cr; 2. Ti-8Ni-1Cr; 3. Ti-8Ni-3Cr.
Fig.12. Potentiodynamic curves Ti-8Ni-Cr alloys in 1% solution NaOH
1. Ti-8Ni-0,5Cr; 2. Ti-8Ni-1Cr; 3. Ti-8Ni-3Cr.
Study of toxic properties of new titanium alloys
Among requirements, resulting from adopted conditions implants from the new alloys, the most significant is
biocompatibility in a human body’s organism. Surgical implants closely adjoin with organism tissues during their
exploitation; they are blood – washed and washed by tissue- liquids.
That is why it is inadmissible that unhealthy for an organism combinations extract on the surface of these implants.
Thus it is very important to study of toxicity of surgical implants during their implantation period.
Investigation of toxic properties of new titanium alloys: Ti-8Ni-1Cr, Ti-8Ni-2Cr and Ti-8Ni-3Cr was carried out during
their short and long term implantations into the animals muscles and abdominal cavity.
Results of Short Term Implantation
Tissues around the implanted Ti-Ni-Cr alloys and rubber samples were harvested and examined for inflammation
hemorrhage, necrosis and discoloration macroscopically the macroscopic (visual control) observation showed neither
sign of inflammation no encapsulation, hemorrhage, necrosis or discoloration.
The Microscopic research of extracted tissues showed that histological picture in the case of implanted titanium alloys
and rubber implantation is identical the microscopic evaluation did not reveal any increase in biological reaction as
compared with the control rubber disks.
Toxicity rating for the implanted titanium alloys samples at the end of 10 days time period was – 0,18, indicating no
toxicity according to ISO 10993-6. 0-indicates normal tissues and 0,5-for very slight reaction.
Thus new titanium alloys samples do not prevent the development of the normal reactions of connective tissue and
consequently have not render local toxic action on the tissue elements.
Results of Long Term Implantation
The general state of animals during all time of observation was not characterized with any symptoms of intoxication:
animals were mobile, willingly ate forage, behavioral reactions – excitability, reactivity, tearfulness, spontaneous
activity – did not change. That specifies absence of oppression of the central nervous system and activity vegetative
ganglions. The average weight of rats bodies in the beginning of experience has made 155 g, the subsequent weighing
for 60 days after operation has shown increase in weight at 15%. The same weight increasing has been observed in the
group of mice.
On opening the abdominal cavity investigation of tissues, harvested around the implant samples should no sign of
cavity irritations, inflammation, hemorrhage, necrosis or discoloration.
Only one rat had a thin purulent capsule around its heterogeneous body and its cavity appeared to be hyperemized, it
might be the result of the infection obtained during the implantation process (operation).
The microscopic evaluation did not reveal any increase in biological reaction. Histological picture in both cases of
titanium alloys samples and rubber disks implantation are practically identical. Toxicity rating for the implant samples
was 0,2, indicating no toxicity according to ISO 10993-6.
Thus, alloys Ti-8Ni-(1-3)Cr do not cause the phenomena of local irritation at contact with the peritoneum and internal
organs of animals, located in abdominal cavity and they do not cause the phenomena of general intoxication, which
might arise in the case of the resorptive action of the material of alloys.
New alloys do not render local irritation on different tissues of animals, do not suppress local tissue reactions and do
not render any toxic action during the long implantation conditions.
Consequently using of new Ti-8Ni-(1-3)Cr alloys for manufacturing of surgical implants is rather actual nowadays.
Conclusions
New corrosion resistant Ti-8Ni-Cr system alloys with increased hardness and strength have been developed for medical
tools of multiply usage and implants. The development was made based on study of chromium influence on the phase
constituents, microstructure, mechanical properties, corrosion resistance and electrochemical characteristics of Ti-8Ni
alloy.
Chromium increases the hardness of the alloys Ti-Ni-Cr system after quenching. The highest value of hardness of
quenching from 9500 and 8000 alloys is connected with decomposition of β-phase in quenching conditions from these
temperatures. After quenching from 9500C all alloys have β+ω structure; at the same time in alloys, containing 1-3% of
chromium, formed ω-phase is microdispersive causing their high hardness.
Optimum condition of thermal treatment, providing high strength, hardness and corrosion resistance of alloys has been
defined – quenching from 9500C with content of chromium in alloys 1 – 3% (by addition of Yttrium in quantity 0,001
– 0,01 mass%).
On the base of studying of the phase equilibrium by microstructural, x-ray investigations and differential thermal
analysis of Ti-8Ni-Cr system alloys polythermal sections of phase diagram of this system have been constructed. Based
on thermodynamic study and theoretical calculations of phase equilibrium by the Maxwell rule and with using iteration
procedures of Newton, phase equilibrium diagrams of Ti-8Ni-Cr system alloys have been formed too.
Comparison of the theoretical and experimental diagram of Ti-8Ni-Cr system alloys showed, that all the formed phases
on the diagram, that have been constructed by our calculations, completely coincide with the phases, which are
represented on the experimental diagram. This fact is of definite interest as from theoretical so practical point of view.
Study of mechanical properties of Ti-8Ni-(0-3)Cr quenching alloys show, that chromium increases the tensile strength
(1000MPa) and hardness (48 HRC) and slightly influences on plastic properties of the Ti-8Ni alloy. Tensile strength of
titanium commercial alloys: Ti-6Al-4V and Ti-5Al-3Sn do not exceed 900 MPA.
Investigation of Ti-8Ni-3Cr alloy surface and distribution of alloying elements on the characteristic x-ray emission
TiKα, NiKα and CrKα were carried out on the electro microanalizer, Cameca, Microsonde MS46. and showed that the
elements – titanium, chromium and nickel are proportionally distributed on the surface of Ti-8Ni-3Cr alloy.
Corrosion tests in medium containing human body: blood, physiological solution, gastric juice,tissue liquid reveal high
corrosion resistance, after 100 hour tests corrosion rate of all alloys, containing about 3% chromium did not exceed
0,0002 g/m2hr. Corrosion testing of the Ti-8Ni-(0-3)Cr according to the following regime:
cleaning+disinfection+sterilization in aggressive solutions with addition of hydrogen peroxide showed also high
corrosion resistance of Ti-8Ni-(0-3)Cr alloys, without the changing of surface. After 20 cycles corrosion losses of the
commercial titanium alloys are ~ one order more than the losses of new alloys. Visual control of alloys showed that
known alloys withstand 10 cycle of cleaning without surface changing. Further the surface condition changes, spots of
oxide tint appear; the surface of Ti-8Ni-(0-3) Cr alloys does not change after 20 cycles.
Study of toxic properties of alloys Ti-8Ni-(1-3)Cr during their implantation in muscles and abdominal cavity of
animals show, that they do not cause local irritative actions on different tissues, they do not suppress local tissue
reactions and do not have any toxic effects during short or long term implantation conditions.
Of the assumption of results we can give following conclusion - Alloys Ti-8Ni-(1 -3 )%Cr have higher corrosion
resistance, strength and hardness in comparison with commercial titanium alloys, used nowadays in medical technique.
Alloys Ti-8Ni-(1 -3 )%Cr are recommended for manufacturing high-strength medical tools of multiply usage, surgical
implants and also for hardening working surface of surgical tools.
Application of new alloys will allow improving functional properties and increase quality, reliability, service life of
medical tools and implants.
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Corrosion Resistant Alloys for Medical Tools and
Implants
Manana Mikaberidze1, Corby Anderson2, Bill Gleason2,
Eteri Gozalishvili1, Lia Akhvlediani1, Dali Ramazashvili1
1 Tavadze Institute of Metallurgy and Materials Science,
Tbilisi, Republic of Georgia
2 Center
C t for
f Ad
Advanced
d Mineral
Mi
l and
d Metallurgical
M t ll i l Processing
P
i
Montana Tech, Butte, Montana
Corrosion Resistant Alloys for Medical Tools and
Implants
The p
pace of development
p
in medical
engineering is increasing every year.
New operational methods in
ophthalmology, traumatology, vascular
and neural surgery as well as other areas
require new instruments
Microsurgical tools and implants to match
these needs must be designed.
Corrosion Resistant Alloys for Medical Tools and
Implants
Titanium and titanium alloys:
low weight
hi h strength
high
t
th
outstanding
corrosion resistance
naturally match the requirements for
implantation in the human body.
Corrosion Resistant Alloys for Medical Tools and
Implants
Because off these
h
properties Ti and
d its alloys
ll
have been used in a wide and diverse range of
applications which demand high levels of
reliable performance in surgery and medicine
More than 1000 tones of titanium
devices are implanted in patients
worldwide every year.
Corrosion Resistant Alloys for Medical Tools and
Implants
However, most of commercial titanium
alloys have low hardness and insufficient
corrosion resistance in aggressive washing
and sterilizing media
y
New titanium alloys
development holds
substantial promise
Manufacturing
g medical tools and implants
p
For coating applications.
Corrosion Resistant Alloys for Medical Tools and
Implants
Conventional methods of production
Complex alloying of solid solutions
Alloy structures are based on
theoretical assessment, phase
diagram and "structure - property"
investigations
Corrosion Resistant Alloys for Medical Tools and
Implants
α Alloys (HCP)
Designs such as tools and detail-work which
do not require high durability and hardness
β Alloys (BCC @ 1621° F)
High-strength, hardness and corrosion resistance
α+β alloys
Greater strength and better bend plasticity
Easier to forge, roll and stamp
Corrosion Resistant Alloys for Medical Tools and
Implants
Aluminum
Chrome
Nickel
Manganese
Molybdenum
Vanadium
(ASTM F1341, F67)
Ti-6Al-4V (ASTM F620)
Ti-4Al-3Mo-V
Ti-5Al-3Sn
Ti
5Al 3Sn
Ti-3Al-1.5Mn
Form substitutional solid solutions,
stabilize β phase and expand its
area on phase diagrams
Corrosion Resistant Alloys for Medical Tools and
Implants
This investigation deals with a different
alloy system
Ti-8Ni-Cr (0.1-20)
Corrosion Resistant Alloys for Medical Tools and
Implants
Vacuum arc furnace with
tungsten electrode in an argon
atmosphere
Titanium sponge, nickel,
and chromium in a watercooled copper crucible
4-5 re-melts to homogenize
Cast pieces were then
quenched in the water
Corrosion Resistant Alloys for Medical Tools and
Implants
Samples were then analyzed
Microstructure
X ray analysis
X-ray
Corrosion properties including biological
systems (short
( h
term/long
/l
term))
Electrochemical
Theoretical thermodynamic
calculations (Thermo-Calc)
Corrosion Resistant Alloys for Medical Tools and
Implants
Phase Results
•№
•Alloys
•Phase content of alloys after quenching
from temperatures
9500
•950
•800
8000
•600
6000
•1
•Ti-8Ni
•β+ω
•α′+ Ti2Ni
•-
•2
•Ti-8Ni-0,1Cr
β+ω
α′+ Ti2Ni
•α+ Ti2Ni
•3
•Ti-8Ni-0,5Cr
β+ω
α′+ Ti2Ni
α+ Ti2Ni
•4
•Ti-8Ni-1Cr
β+ω
α′+ Ti2Ni
α+ Ti2Ni
•5
•Ti-8Ni-3Cr
β+ω
α′+ Ti2Ni
•-
•6
•Ti-8Ni-5Cr
β+ω
•-
α+ Ti2Ni+TiCr2
•7
•Ti-8Ni-8Cr
i 8 i 8C
β
β-ω
β Tii2Nii
β+
α+ Tii2Ni+TiCr
i iC 2
•8
•Ti-8Ni-10Cr
β-ω
β+ Ti2Ni
α+ Ti2Ni+TiCr2
Corrosion Resistant Alloys for Medical Tools and
Implants
Phase Results
Experimental phase diagram
Theoretical phase diagram
Corrosion Resistant Alloys for Medical Tools and
Implants Quenching Results
Hardness
Corrosion Resistant Alloys for Medical Tools and
Implants Quenching
Q
hi
Results
R
lt
Corrosion
IIn 10% HCl
HCl,
various quenching
rates
In 10% NaCl,
various quenching
rates
Corrosion Resistant Alloys for Medical Tools and
Implants Results
R
lt
Corrosion
In conserved blood-based corrosion tests
(blood and tissue liquid),
liquid) 100 hour tests of 3%
Cr alloys, the corrosion rate did not exceed
0.0002 g/m2hg
Post-test blood analysis also
showed no change to the blood
used for testing
testing.
Corrosion Resistant Alloys for Medical Tools and
Implants
R
Results
lt
Potentiodynamic curves E-lgi of Ti-Ni-Cr alloys
In 1% NaOH,
various Cr content
Fig.11. Potentiodynamic curves Ti-8Ni-Cr alloys in 1%
olution HCl
,
; 2. Ti-8Ni-1Cr;; 3. Ti-8Ni-3Cr.
1. Ti-8Ni-0,5Cr;
In 1% HCl, various
Cr content
Fig.12. Potentiodynamic curves Ti-8Ni-Cr alloys in 1%
solution NaOH
1. Ti-8Ni-0,5Cr; 2. Ti-8Ni-1Cr; 3. Ti-8Ni-3Cr.
Corrosion Resistant Alloys for Medical Tools and
Implants Cr
C content
t t Results
R
lt
Elongation &
Cross section
reduction
Tensile Strength &
Hardness
Corrosion Resistant Alloys for Medical Tools and
Implants
Biocompatibility Results
Short term implantation results showed no sign of
p
, hemorrhage,
g ,
inflammation no encapsulation,
necrosis or discoloration. ISO 10993-6 toxicity
results showed very little toxicity (0.18).
Long
g term implantation
p
results showed no sign
g of
cavity irritations, inflammation, hemorrhage, necrosis
or discoloration. ISO 10993-6 toxicity results showed
very little toxicity (0
(0.2).
2)
Corrosion Resistant Alloys for Medical Tools and
Implants
Conclusions
Comparison of the theoretical and
experimental phase diagrams for Ti
Ti8Ni-Cr system alloys showed, that the
theoretical phases coincide with the
experimental phases.
Corrosion Resistant Alloys for Medical Tools and
Implants
Conclusions
After
f
quenching
h
from
f
950°C allll
alloys have β+α structure
1-3% chromium alloys,
y , form
microdispersed α -phase resulting in higher
hardness of quenched alloys
Ti, Cr and Ni are proportionally distributed
Ti
on the surface of Ti-8Ni-3Cr alloy
Corrosion Resistant Alloys for Medical Tools and
Implants
Conclusions
For Ti-8Ni-Cr
Ti 8Ni Cr alloys the optimum
thermal treatment for high strength,
hardness and corrosion resistance:
1 – 3% Cr alloys
(Supplemented by 0.001%
– 0.01% Yttrium))
Quenching from
950°C
Corrosion Resistant Alloys for Medical Tools and
Implants
Conclusions
Corrosion tests in media containing blood,
physiological solution, gastric juice and tissue
liquid result in lower corrosion rates than
currently used Ti alloys.
The alloys have low toxicity in both
short term and long term studies.
Corrosion Resistant Alloys for Medical Tools and
Implants
Conclusions
Ti-8Ni-Cr system
y
alloys
y with
increased hardness and strength are
not onlyy suitable for medical tools
and implants but are improvements
on currentlyy used materials.