FR2565603A1 - PROTHETIC ALLOY OF THE FE-CR-AL TYPE FOR MEDICAL TREATMENT AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

THE INVENTION RELATES TO A PROTHETIC ALLOY OF THE FE-CR-AL TYPE FOR MEDICAL TREATMENT WHICH IS ESSENTIALLY CONSTITUTED, BY WEIGHT, OF: 20 TO 32 CHROME, 0.5 TO 5.0 ALUMINUM, 0.5 TO 4, 0 OF MOLYBDENE, 0.05 TO 0.5 OF M (OR M REPRESENTS AT LEAST ONE ELEMENT CHOSEN BETWEEN ZIRCONIUM AND HAFNIUM), THE REMAINDER CONSISTING OF MAINLY IRON. THE ALLOY FEATURES AN OXIDE FILM ON ITS SURFACE, THE FILM IS MAINLY CONSISTING OF ALPHA-ALO. APPLICATION TO ORTHOPEDIC SURGERY AND DENTAL SURGERY.

Description

265656-03

  The present invention relates to a prosthetic alloy

  Fe-Cr-Al type tick for medical treatment. The alloy of the invention is useful as a prosthetic material for medical treatment such as orthopedic surgery or dental surgery. It is necessary that a prosthetic material for orthopedic surgery has the following properties:

  1) the prosthetic material must be tested in accordance with the

  solution and absorption; 2) the material must have very good resistance to corrosion;

  (3) the material must have very good mechanical strength

  maintain and maintain this property for a long period of time;

  4) the material must be non-toxic and non-irritating; this is

  is a fundamental problem that should not only

  be considered as a direct and local problem but also

  as a general problem; and) the material must have good biological compatibility

  with the living body tissue that surrounds it. Other-

  In other words, the material must be very good in terms of its

  adaptation to the tissue or its affinity with the

  living body. If the prosthetic material presents only

  does not weak biological compatibility with the tissue, it is formed in the living body, in contact with the prosthetic material, a fibrous tissue that isolates the material and it

  forbidden to come into contact with the living body and he

  is the connection between matter and the living body

  becomes cowardly which gives rise to various defects.

  Fe-Ni-Cr austenitic stainless steel

  is conventionally used as a prosthetic material.

  This stainless steel has very good properties

  but suffers from the unsolved problem that poses

  his affinity with a living body. In addition, stainless steel

  sometimes lacks resistance to cracking by

  stress corrosion, pitting corrosion resistance

  resistance to corrosion by cracking, and

  very corrosion resistance properties, so that

  the use of stainless steel is restricted to a

  the period of time. In addition, a problem is posed by the harmful effects on the human body of metal ions

  dissolved, especially nickel or other ions.

  In recent years, a test of

  the use of a ceramic material has been attempted. Such a ma-

  It has many advantages because it presents

  It has a very good corrosion resistance, remains stable in a living body in the long term, is non-toxic to the body and has a high biological compatibility with it. But its big disadvantage is that it lacks mechanical resistance, including resistance to

sagging.

  In view of the situation described above, the

  deresse carried out extensive research and finally

  developed a new prosthetic alloy with

  simultaneously, the superior mechanical properties of the

  stainless steel, the very good biological compatibility with

  the human body of a ceramic material, as well as a large

  resistance to corrosion, and has developed a process

  manufacturing of this prosthetic alloy.

  Thus, the alloy according to the present invention is a prosthetic alloy of the Fe-Cr-Al type intended to be

  used in a medical treatment, the alloy being essen-

  made up of 20 to 32% by weight of chromium, 0,5

  to 5.0% by weight of aluminum, 0.5 to 4.0% by weight of molyb-

  dene, 0.05 to 0.5% by weight of M (where M represents at least one element selected from zirconium and hafnium, this definition being applicable thereafter), and iron which

is the rest of the alloy.

  Since the alloy of the invention contains aluminum and M in appropriate amounts, it forms

  at the surface an oxide film mainly composed of

  pha-A1203, which is dense and very good adhesion, by heating in air or oxygen. This oxide film has a very good property of biological compatibility with a living body and has a very good resistance to corrosion. In addition, the prosthetic alloy of the invention is not inferior in practical application to AISI 316 L conventionally used as a prosthetic material for living bodies, nor to the Fe-30 Cr-Mo type alloy. which is a base alloy of the alloy of the invention, and

  its mechanical strength is sufficient for it to be

read as a prosthetic material

  In the appended drawing, the single figure is a

  representing a relationship of the mass contributed by oxidation and the thickness of the oxide film with respect to

  heat treatment of the alloy of the invention.

  A detailed description will be given below

  about the content and function of the elements that

  contains the prosthetic alloy of the invention.

  1) Chromium: 20 to 32% by Weight Chromium is, as a constituent for the formation of a passivation film, an essential element

  for the improvement of the resistance to corrosion. The re

  corrosion resistance increases with the increase of the

  amount of chromium. But since the alloy is

  weakened by the simultaneous presence of elements

  such as aluminum, molybdenum, the upper limit of

  the chromium content is 32% by weight of the alloy

  thetic. The alloy of the invention can find applications

  cations as an in vivo prosthesis whose service life

  vice extends over a short period of about two to three months. In this case, the corrosion resistance criterion that is required of the alloy is tempered to a certain extent, but it is required that the corrosion resistance be greater than that of a ferrite type stainless steel of great size. purity containing at least 18% chromium, so that the lower limit of the chromium content of

the alloy is 20% by weight.

2) Aluminum: 0.5 to 5.0% by weight

  Aluminum is, in the invention, an important element

  with regard to the formation of an oxide film, but for the improvement of the corrosion resistance of the alloy of the invention, it is necessary to add to

  less than 1.5%, preferably about 3%, by weight of molyb-

  not. And because of this addition of molybdenum, the content

  aluminum is limited to a maximum of 5.0% by weight.

  On the other hand, if the aluminum content is

  the amount of alpha-A1203 produced by heat treatment

  is reduced and the amount of Cr 2 O 3 is increased. If the proportion of Cr203 is increased, the limit between

  two types of oxide are enlarged and the result is a frag-

  the oxide film present on the surface of the alloy, which alters the function of the alloy. Thus, when the heat treatment is carried out in an oxygen atmosphere, an aluminum content greater than or equal to

  about 2% by weight. Also, when the heat treatment

  If the material is made by adjusting the atmosphere to a pressure lower than the atmospheric pressure, it is possible to bring the lower limit of the aluminum content to 0.5% by weight. When the upper limit of

  the aluminum content exceeds 5%, the toughness and the

  Shaping study of the alloy decreases.

  3) Molybdenum: 0.5 to 4.0% by weight

  Molybdenum has a pronounced effect in improving

  improvement of corrosion resistance, especially corrosion resistance by stitching and resistance

  crack corrosion, and a quantity of molybdenum

  no greater than or equal to 0.5% by weight is necessary to obtain this effect. On the other hand, increasing the amount of molybdenum tends to decrease the toughness and,

  addition, to promote an alteration, in particular of

  shaping titanium, in the simultaneous presence of chromium and aluminum. For this reason, the upper limit of

  the molybdenum content is set at 4.0% by weight.

  4) M (o M represents at least one chosen element

  from zirconium and hafnium): 0.05 to 0.5% by weight.

  In the prosthetic material of the invention, M is

  filter in the oxide film consisting mainly of

  pha-A1203 and gives a great tenacity to the oxide film

  which is initially very brittle, and it has an

  nity with oxygen somewhat larger than that of

  aluminum, so that the film is oxidized inside-

  by forming fine oxide particles and improving

  thus the adhesion of the oxidized film on the surface to the alloy core.

  ge. However, when the M content is increased, the mixing ratio of M in the film is increased, which not only

  makes the film less dense but also has decisive effects

  favorable to the corrosion resistance of the core of

  bonding, cold and hot workability, and

  on the tenacity of the alloy. Therefore, the upper limit

  The M content is 0.5% by weight. In return

  when the M content is too low, the alloy obtains

  can not give tenacity to the film, nor a maximum of

  dermal, so that the lower limit of the content of

M is set at 0.05% by weight.

) Other constituents.

  Silicon causes embrittlement of the alloy

  and, during the heat treatment, the silicon is oxidized to SiO 2 which is incorporated in the alpha-Al 2 O 3 film. In

  Consequently, it is desirable to lower the

  licium at a value less than or equal to 0.3% by weight.

  Carbon and nitrogen can easily react with chromium

  me during heat treatment by forming a chromic compound. This chromium compound has a strong tendency to form at the boundary of the grains of the alloy and causes a reduction in the density of chromium near the limit and induces a corrosion of the grain boundary. Furthermore,

  the carbon also has the effect of being transformed into oxy-

  of gaseous carbon and carbon dioxide that break the

  alpha-A1203 film. As a consequence of what is described

  above, it is desirable to set the carbon content of the alloy to a value of 0.008% or less in

  weight and nitrogen content at a lower or equal

  0.015% by weight. Since phosphorus and sulfur also affect the toughness of steel, it is desirable that

  to fix their respective contents at a lower value than

  less than 0.025% by weight 6) The remainder being essentially iron The alloy having a composition in the above ranges retains a ferrite structure even by

  heating (1100 - 1300 C) which will be described later.

  The method of manufacturing the prosthetic alloy

  that the invention is not subject to particular limits.

  res but gives the possibility of manufacturing, by conventional methods, an alloy having a composition located in the ranges described above, namely by vacuum melting and,

  if necessary, by melting in a non-oxidizing atmosphere.

  The alloy of the invention, after having been heat treated, is used as a prosthetic material. This heat treatment produces an oxide film, this film consisting mainly of alpha-Al 2 O 3 having a dense structure and a very good adhesion to the alloy core. The

  heat treatment is carried out in the air or in the oxygen

  normally at atmospheric pressure, at a temperature of

  1100 to 1300 C. However, when the Al content of the alloy is of the order of 0.5 to 2% by weight, it is

  desirable to perform the heat treatment at a pres-

  below atmospheric pressure.

  It is only necessary to make a choice of

  time period of approximately 0.5 to 30 hours for the treatment

  temperature, depending on the required thickness of the oxide film. Incidentally, the composition of the oxide film is, for example, 90 mol% of alpha-Al 2 O 3, 5 mol% of

  ZrO 2, 3 mole% Fe 2 O 3 and 2 mole% Cr 2 O 3.

  The prosthetic alloy of the invention has a

  very good biological compatibility with the living body and-

  high resistance to corrosion thanks to the oxide film

  produced by heat treatment. In addition, the nucleus of

  binding itself also has resistance to

  superior erosion. The prosthetic alloy of the present invention

  also feels mechanical properties sufficient for practical use as a prosthetic material. Thus, the alloy of the invention satisfies the required conditions

  of the prosthetic material and can be effectively used.

  The prosthetic alloy of the invention will now be described in the following about some of its

embodiments.

Example 1

  A vacuum alloy is produced by vacuum melting

  Fe-Cr-Al type tick having the composition indicated on the

Table 1.

TABLE 1

  Elements Cr Alh Mol Zr Sil C N O Fe% by weight 30 3,212,0 0,2 0,15 0,004 0,007 0,001 Rest

2 O 01 0.00411

  The alloy is heat treated in oxygen to form an oxide film. The attached diagram shows the

  relationship of the mass contributed by oxidation and the thickness

  the film produced compared to the heat treatment.

  An examination of the cross-sectional structure of the oxide film shows that the boundary between the alloy core and the surface of the oxide film follows a complicated path that enters the core

  alloy and the layer to which a very good

  do not stick. The same results are achieved by the treatment

heat to air.

  i) Mechanical properties Table 2 indicates the mechanical properties that

  present the alloy of the invention before heat treatment

  than. By way of comparison, the mechanical properties of AISI 316 L, conventionally used as an in vivo prosthetic material, are also indicated in the table. Tensile strength and elongation are tested in accordance with

  Japanese standard JIS-Z-2201 and the hardness is tested against

in accordance with JIS-Z-2244.

TABLE 2

  5. Example 1 AISI 316 L Density (g / cm2) 7.3 8.0 Magnetic Magnetic Magnetic Non-Magnetic Performance Tensile Strength (kg / cm2) 65 63 Hardness (Vickers) 250 170 Elongation (%) 15 49 results shown in Table 2

  that the alloy of the invention has a mechanical strength

  that of the same order of magnitude as that of conventional products

c.

  Table 3 shows the variations in properties

  the alloy undergoes heat treatment

  only in air at a temperature of 1250 OC.

TABLE 3

  Heating time Tensile strength Hardness Elongation (h) (kg / cm2) (Vickers) (%)

1 60 230 15

3 58 220 10

55,220 10

20 51 210 10

  The results shown in the Table show

  3 that the prolongation of the heating time leads to

  variations in the mechanical properties of the alloy and

  does not bring disruption in practical use.

  ii) Corrosion resistance test

  Experience shows that the alloy has a good

  resistance to corrosion in the state where it is coated with an oxide film by heat treatment. That is to say, no corrosion or wear is observed by a corrosion resistance test on the criteria indicated.

  in Tables 4 and 5 below.

  We are here in the case where the oxide film of

  the alloy of the invention is damaged by a mechanical impulse

  canic or screw fixation and o the alloy core is exposed to the corroding medium of a living body. We make a

  study on the corrosion of the alloy core. All of

  on board, a test (of resistance to corrosion by cracking) is carried out on the alloy of Example 1 before heat treatment. Thus, a flat test piece is immersed in a 10% FeCl 3 aqueous solution, a 5 mm glass rod.

  diameter being placed on the test piece, and we observe

  after 24 hours the corrosion of the test piece under the

  glass rod. The results are shown in Table 4.

TABLE 4

  Liquid temperature (C) 20 40 50 60 | Example 1 O O O x I AISI 316 L x x __

  O: No corrosion is observed by cracking.

  x: There is significant corrosion cracking. 0: There are traces of corrosion by

cracking.

  Table 5 shows the results of

  knowledge of alkali resistance, intergranular corrosion resistance, acid resistance, and stress corrosion resistance.

  performed in accordance with JIS-G-0573.

1.0

TABLE 5

  Example 1 AISI 316 L Alkali Resistance 1) 0.05 g / m2h 3.39 g / m2h Corrosion Resistance 2) Intergranular 0.36 g / m2h 0.24 g / m2h Resistance to acids 3) 0.005 g / m2h 180 g / m2h Resistance to cracking 4) by stress corrosion more than 100h less than 10E 1) Weight loss after immersion of the test piece in a boiling aqueous solution of 50% NaOH + NaCl

6% for 48 hours.

  2) Weight loss after immersion of the test piece in a boiling aqueous solution of 65% HNO2 for

48 hours.

  3) Weight loss after immersion of the test piece in a boiling aqueous HCl solution at 1 Z

48 hours.

  4) Time required to initiate corrosion cracking

  under tension after immersion of a folded sample

  In a boiling aqueous solution of 48% MgCl 2.

  In addition, a test is conducted on the

  the test piece placed in physiological saline (3% NaCl) and found that the elution of

  Fe, Cr and Al are each less than 1 ppm / 200 cm 2 / liter

  12 days at 20 C and that when the piezo-

  this test is immersed in a boiling liquid for hours, the elution of Fe is 2 ppm and that of the others

is less than 1 ppm.

  The results above show that the alloy of the invention is superior in corrosion resistance to conventional alloys even when it is in a situation where it is prevented from forming

  an oxide film by heat treatment.

It

  It has also been found that resistance to

  erosion of the alloy core after heat treatment is as important as before heat treatment. For example,

  after heating the alloy of Example 1 to 1250 C

  After 5 hours in the open, the oxide film is completely sintered and the results are then carried out according to the criteria of Tables 4 and 5. There is no difference between the results obtained and those shown on

Tables 4 and 5.

Example 2

  The same test as that of Table 1 of Example 1 is carried out on the alloy in which the zirconium has been

replaced by hafnium.

  The mass provided by oxidation during the execution

  heat treatment on the alloy of Example 2

  is smaller than that of Example 1. For example, when

  that the alloy is heated at 1200 C for 20 hours, the mas-

  brought about by oxidation is about 1 mg / cm2. The adhéren-

  this of this oxide film is very good, to the same extent

* than that found in Example 1.

  In addition, tests are carried out on the mechanical properties and the corrosion resistance of

  the alloy, in the same manner as in Example 1, to obtain

  from the alloy containing Hf, the practical results

  identical to those found in Example 1.

  Animal experiment results.

  Test plates each 20mm in length, 7mm in width and 1mm in thickness are prepared.

  of the alloy of the invention and, by way of example,

  tif, of AISI 316 L. The plates are grafted on the surface of the tibia of adult rabbits. The results show that, with the oxide-forming alloy of the invention, the membrane of

  Intermediate connective tissue between the plate and the bone is

  becomes sluggish over time so that it becomes difficult to observe with an ordinary light microscope in four to six weeks. Also, we observe the development

256560-3

  of an osteoid substance around the grafted plaque

  oxidized face. On the surface of the plate are attached

  cartilage and osteids, and the amount of tissue

  Xé also increases and the fabric becomes denser

  sure that the duration of the transplant is prolonged. The amount of fabric attached to the surface of AISI 316 L is less than that of

  fabric attached to the bare surface of the alloy of the invention. AT-

  by heat treatment, the alloy of the invention is ab-

  solubility in the test of a harmful dissolution of the ions

  in a living body and does not, however, pose any

  problem from the point of view of the mechanical resistance of the

terials.

R EV END I C AT I 0 N S

  1 - Prosthetic alloy of the Fe-Cr-Al type for treating

  medical device, characterized in that it consists essentially of, by weight, 20 to 32% of chromium, 0.5 to 5.0% of aluminum, 0.5 to 4.0% of molybdenum, 0.05 at 0.5% of M (where M represents at least one element selected from

zirconium and haf-

  nium), the remainder consisting mainly of iron and in that it has an oxide film on the surface, said film consisting mainly of alpha-Al 2 O 3.

  2 - Prosthetic alloy of the Fe-Cr-Al type for treatment

  medical device, characterized in that it consists essentially of, by weight of: at 32% of chromium, 0.5 to 5.0% of aluminum, 0.5 to 4.0% of molybdenum, 0.05 to 0.5% of M (where M represents at least one element selected from zirconium and hafnium), 0.3% of silicon, 0.008% of carbon, 0.015% of nitrogen, the balance consisting mainly of iron, and in that it comprises on the surface an oxide film,

  said film consisting mainly of alpha-A1203.

  3 - Fe-Cr-Al type prosthetic alloy for medical treatment according to claim 2, characterized in that it comprises, by weight: 0.025% of phosphorus, and

0.025% sulfur.

  4 - Process for manufacturing a prosthetic alloy

  only of the Fe-Cr-Al type, characterized in that it comprises the steps of: manufacturing an alloy consisting essentially of

  20 to 32% of chromium, 0.5 to 5.0% of aluminum,

  0.5 to 4.0% of molybdenum, 0.05 to 0.5% of M (where M represents at least one element selected from zirconium and hafnium), the remainder consisting mainly of iron; and heat treating said alloy in air or in

  oxygen at a temperature of 1100 C to 1300 C to form

  sea an oxide film on the surface of the alloy, said film

  consisting mainly of alpha-A1203.

  - Process according to claim 4, characterized in that, when said alloy contains 0.5 to 2.0% by weight of aluminum, the manufacture is done at a pressure

  less than atmospheric pressure.

  6 - Process according to claim 4 or 5, characterized

  in that the heating time of said heat treatment

is 0.5 to 30 hours.