Thermal treatment influence on micro hardness titanium alloy biomaterials.

Catana, Dorin ; Scarneciu, Ioan ; Popescu, Rodica 等

1. INTRODUCTION

Human desire for ameliorating his health state, affected by diseases or accidents has imposed the idea of the use in well determined conditions, of some artificially produced parts which are made of naturals or artificial materials. It appeared two alternatives even by the time of the first substitution assays:

--dead or alive tissues and organs transplantation;

--parts, devices or systems made of natural or artificial material implants.

Present implants advantages are: functionality, availability and the capacity of reproduction. Implants major disadvantages are determined by nature, way of synthesis and materials different features used in relation with alive tissues. Implant materials lack two important characteristics of the alive tissues:

--the capacity of modifying its structure and features depending on the solicitations that they support (for example: mechanical charging for the osseous tissue or the blood flow for the blood-vessels);

--auto-annealing capacity.

Hip articulation has as main physiological functions: the mechanical loads transmission between pelvis and femur, as well as the relative movement between the system's two parts, osteo articular. Hip articulation (cox-femoral) is a spherical type articulation, with tree degree of movement facility: flexion-extension, abduction-adduction and internal-external rotation. This articulation is greased with synovial fluid, synovial cartilage--fluid combination carrying out the diminution friction coefficients. Total replacement of the joint is made by using prosthesis with its main purpose of taking over the biomechanical function of natural joint.

2. THEORETICAL CONSIDERATIONS

The biomaterials are synthetic materials used for the parts, devices and artificial systems carrying out, with the object of replace and/or take over, totally or partially, the function of an alive tissue for a limited or unlimited time. For the manufacture of some articulation prothesis components, the metallic biomaterials must have:

--an elasticity module as similar as possible, to that of the long bone;

--good fatigue resistance and lastingness;

--wear and electrochemical corrosion resistance as advanced as possible.

The metallic materials that can be used for the hip articulations replacement are: stainless steels, Co- Cr alloys and titan alloys (Catana, 2002).

From all these presented metallic materials, the titanium and its alloys are considered to be the most biocompatible, with the best corrosion resistance in the human organism average and with the most powerful relation between the implant and the surrounding osseous tissue. The alloys for the implants are described in table 1 (Wusinczky et al., 2007).

Titanium base alloys used for implants were subject of quenching thermal treatment followed by artificial ageing. The thermal treatments have been carried out in argon atmosphere.

Thermal treatments differentiated by the heating temperature, cooling temperature and cooling average. Cooling time has been 1 hour for all the tests (Wusinczky & Popescu, 2005).

To accentuate the metallurgical processing influence on the micro hardness used as mechanic features modification indicator, there have been carried out measurements of this, for all the materials with titan base taken to be studied, respectively, for all the metallurgical materials applied to these.

In the case of the Ti-6Al-4V alloy (Popescu et al., 2005) the applied thermal treatment has been the placing into the solution with the following parameters (micro hardness evolution is described in figure 1):

TC1--heating at 950--970[degrees]C water cooling;

TC2--heating at 950--970[degrees]C furnace cooling;

TC3--heating at 850--870[degrees]C water cooling;

TC4--heating at 850--870[degrees]C furnace cooling.

Maintaining time has been for 1 hour and, after the hardening, followed an ageing, its parameters being: 2 hours of heating at 700-710[degrees]C followed by air cooling.

For Ti-6Al-7Nb alloy the placing in solution hardening has been performed in the following parameters:

TC1--heating at 920--940 [degrees]C water cooling;

TC2--heating at 920--940[degrees]C furnace cooling;

TC3--heating at 820--840[degrees]C water cooling;

TC4--heating at 570--580[degrees]C furnace cooling.

The ageing parameters were: heating at 570--580[degrees]C, 2 hours maintenance, followed by cooling.

Alloy micro hardness evolution is described in figure 2.

For Ti-5Al-2.5Fe alloy the placing in hardening solution has been performed in the following parameters:

TC1--heating at 1010--1030[degrees]C water cooling;

TC2--heating at 1010--1030[degrees]C furnace cooling;

TC3--heating at 900--920[degrees]C water cooling;

TC4--heating at 900--920[degrees]C furnace cooling.

Ageing parameters were: heating at 555--545[degrees]C, 2 hours maintenance, followed by airy cooling. Alloy micro hardness evolution is described in figure 3 (Wusinczky et al. 2005).

The last alloy studied is Ti-6Al-2Nb-1Ta-1Mo which has in composition thallium and molybdenum, two essential chemical elements for implants. For this alloy the placing in hardening solution has been performed in the following parameters:

TC1--heating at 1020--1040[degrees]C water cooling;

TC2--heating at 1020--1040[degrees]C furnace cooling;

TC3--heating at 920--940[degrees]C water cooling;

TC4--heating at 920--940[degrees]C furnace cooling.

Ageing parameters were: heating at 595--605[degrees]C, 2 hours maintenance, followed by airy cooling. Alloy micro hardness evolution is described in figure 4. To be used in medicine, the presented treatments have been completed with an anodization thermal treatment and a thermochemical in electrolytic plasma in order to make the alloys biocompatible.

3. CONCLUSIONS

For titanium base biocompatible materials the application of adequate hardening thermal treatments will determine the improvement of micro hardness which is essential when these materials are used for joint prosthesis. For Ti6Al14V alloy, the TC1 treatment permits the attainment of the highest hardness. For the Ti6Al7Nb alloy the entire TC1 treatment is that which determine the wearing resistance. Also, the hardness is increased, especially, due to the cooling increased speed values, more than due to maintenance at placing in solution hardening different temperatures. Ti5Al2.5Fe and Ti6Al2Nb1Ta1Mo alloys have a similar behavior with the prior presented alloys at the TC1 treatment. In order to have a significant increasing of titanium alloys micro hardness the recommended placing in solution thermal treatment is that one coded TC1. The researches will be completed with corrosion and biocompatibility tests in order to determine which one is the best solution for thermal treatment. When all test results will be available, finally will be established which thermal treatments will increase the micro hardness of studied titanium alloys and implicitly the best one to produce the prostheses.

4. REFERENCES

Catana, D. (2002). Advanced Materials Processing, Lux Libris, ISBN 973-9428-73-8, Brasov

Popescu, R.; Catana, D. & Wusinczky, D. (2005). Optimal parameters experimentally set for the temper heat treatment with laser beam applied to steel C120, Proceedings of International Conference on Materials Science and Engineering, pp. 125-128, ISBN 973-635-454-7, University Transylvania, 02.2005, University Transylvania, Brasov

Wusinczky, D. & Popescu, R. (2005). New material used in the medical area, Proceedings of International Conference on Materials Science and Engineering, pp. 181-184, ISBN 973-635-454-7, University Transylvania, 02.2005, University Transylvania, Brasov

Wusinczky, E.; Wusinczky, D. & Popescu, R. (2005). Hip joint implants, Bulletin of Polytechnic Institute of Jassy, Vol. LIII, No. 4, 05.2007, pp. 333-338, ISSN 1453-1690

Wusinczky, D.; Wusinczky, E. & Popescu, R. (2007). Titan based biomaterials behaviour used in joint replacements, Bulletin of Polytechnic Institute of Jassy, Vol. LIII, No. 4, 05.2007, pp. 339-344, ISSN 1453-1690

Tab 1. Main alloying elements for titanium implant alloys.

Alloy Chemical composition [%]
type
 Al V Fe Nb

Ti6Al4V 5.5-6.5 3.5-4.5 0.25 --
Ti6Al7Nb 5.5-6.5 -- 0.25 6.5-7.5
Ti5Al2.5Fe 4.5-5.5 -- 2-3 --
Ti6Al2Nb1Ta1Mo 5.5-6.5 -- -- 2

Fig. 1 Average micro hardness value for Ti-6A1-4V alloy.

TAV-TC1 246,8
TAV-TC2 204,8
TAV-TC3 228,9
TAV-TC4 222,9

Note: Table made from bar graph.

Fig. 2 Average micro hardness value for Ti-6A1-7Nb alloy.

TAV-TC1 244,2
TAV-TC2 191,9
TAV-TC3 228,8
TAV-TC4 194,11

Note: Table made from bar graph.

Fig. 3 Average micro hardness value for Ti-5A1-2.5Fe alloy.

TAV-TC1 264,43
TAV-TC2 206,36
TAV-TC3 191,6
TAV-TC4 215,9

Note: Table made from bar graph.

Fig. 4 Average micro hardness value for Ti-6A1-2Nb-1Ta-1 Mo alloy.

TAV-TC1 248,36
TAV-TC2 188,74
TAV-TC3 243,12
TAV-TC4 200,5

Note: Table made from bar graph.