FR2806421A1 - POROUS INTERMETALLIC ALLOY - Google Patents

Abstract

The invention relates to the production of intermetallic alloys of the Ti-X or Ti-XX type with open and controlled macroporosity and microporosity, both in pore size and porosity rate, intended for the realization of various industrial applications in whether the presence of titanium is necessary such as prostheses, filter elements, storage of hydrogen or isotope of hydrogen, or the titanium-X combination makes it possible to obtain elements having all or part of the characteristics of shape memory alloys.

Description

The interest of titanium is well known for the production of prostheses

  intended for restorative surgery or dental implantology. Different configurations of the devices used have been implemented to increase the surface area of titanium likely to be affected by osteogenesis. This is how reliefs or cavities are created by machining to both increase the free surface of titanium and allow penetration of osteoblasts. Increasing the speed of consolidation, improving its durability and reliability can be effectively achieved by

the addition of porous elements.

  The consolidation of prostheses requires that the osteogenesis mechanisms by formation and penetration of osteoblasts be improved by the presence of elements with open double porosity: a macroscopic porosity between 100 and 400 micrometers, and, a microscopic porosity less than 10 micrometers, with an overall porosity rate of between 20 and 50%. In addition the formation of connective tissue

  intervenes for pores of 50 micrometers.

  Likewise, the advantage of titanium is well known in the industrial field for absorbing hydrogen in large quantities and for desorbing it under the effect of temperature? The increase in the quantities of hydrogen absorbed by a given volume of titanium is directly proportional to the exchange surface, therefore to the open surface of titanium,

  considerably increased when the material has an open porosity.

  The subject of the invention is a process for obtaining and forming by reactive sintering of an intermetallic alloy with open porosity of the Ti-X or Ti-XX type from elementary powders of the various constituents of the alloy and capable of to be related to

  massive elements of the same composition.

  Depending on the material X selected, the alloys can also be of the shape memory type and therefore have all or part of the properties inherent in these alloys such as. actual shape memory, superelasticity and damping of shocks and vibrations. Various methods for developing porous intermetallic materials by powder metallurgy are currently well used. These include: - plasma projection which does not allow open porosity, - cold compression and sintering with

  pre-alloyed powders which do not allow double porosity to be obtained.

  The production of solid intermetallic materials can advantageously be obtained by powder metallurgy and reactive sintering as described by Yves BIGAY in patent N 95 07283 "Process for reactive sintering of intermetallic materials". On the other hand, it should be noted that the process described leads to materials whose porosity rate is less than 10% and therefore comparable to massive products which makes them unusable in osteosynthesis. The process thus described

  is based on six clearly identified stages: 1 - mixing of the elementary powders, 2 -

  compression of the mixture to obtain a compacted powders, 3 - placement of

  the element obtained in a thick sheath resistant to pressure and heat, 4 -

  reactive sintering to obtain the intermetallic compound, 5 hot densification, 6 -

sheath removal.

  The PCT filed by Victor GJUNTER and published on July 15, 1999 under the number WO 99/34845 specifies the conditions necessary for initiating the reactive sintering reaction, which is moreover known, but gives no indication of the

  measures to be taken to obtain an alloy whose porosity can be controlled.

  The objective of the present invention is to provide a reactive sintering process for obtaining intermetallic materials with open macroporosity and microporosity and the porosity characteristics of which can be controlled. For applications in the medical field, the materials thus obtained must also have mechanical and biocompatibility characteristics such that their use in the production of prostheses can provide patients with guarantees of integration and

  durability superior to those obtained with currently known porous materials.

  These objectives are obtained in accordance with the process described below: a) choice of powders as to the nature of the base materials (Ti, Ni, AI, etc.) and as to their particle size, b) preparation of the mixture of powders elementary metal in the proportions desired for the characteristics of the desired alloy, c) compression of the powder mixture to obtain a "compact" of elementary powders capable of being shaped, d) reactive sintering operation after placement of the "compacted" in a metal sheath (steel, titanium, and their alloys) resistant to temperature and pressure, the internal dimensions of which have been defined to allow the alloy to expand during the said operation,

e) elimination of cladding.

  When producing the "compacted", massive alloying elements of the same kind can be integrated therein so as either to improve the mechanical strength of the porous device thus produced, or then to allow it to be mechanically secured with other structural components. or functional of the porous part. An additional heat treatment applied between steps d and e above at a temperature higher than that of reactive sintering will ensure diffusion between the porous element and

the massive element.

  The granulometry of the elementary powders, their state of compaction and the clearance between the sheath and the compacted element allow the desired porosity to be obtained in terms of

porosity and pore size.

  The sheath can be made waterproof in order to have an atmosphere defined by the nature of the

treated materials.

  During step d, to avoid any diffusion between the "compacted" and the sheath during reactive sintering, a barrier, compressible or not, can be placed between the "compacted" and the sheath. Its design will be such that it allows the expansion of the "compacted" during reactive sintering. Similarly to avoid oxidation of the alloy, it

  it will be possible to create a vacuum inside it.

  Example 1: The preparation of a piece of porous Ti-Ni intermetallic material weighing 1000 g for medical and surgical use in which prosthetic elements will then be produced will proceed as follows: 1. Weighing of the elementary powders of titanium and nickel, 2. Turbulent mixture for 1 hour, 3. Uniaxial compression in a cylindrical mold with an inside diameter of 50 mm and a length of 200 mm, 4. Sheathing of the "compacted" with mild steel with a diameter inside 50 + X mm and 200 + Y mm long internally coated with a layer of alumina, 5. Reactive sintering by bringing the assembly to 1000 ° C. for 2 hours in order to obtain the reaction Ti + Ni = TiNi ,

  6. Removal of the sheath by turning then chemical pickling.

  Example 2: Preparation of a solid TiNi rod covered with 1000 g of porous TiNi: 1. Weighing of elementary powders of titanium and nickel, 2. Turbulent mixing for 1 hour, 3. Uniaxial compression around a rod of Solid TiNi of 2 mm in diameter in a cylindrical mold with 6 mm inside diameter and 10 mm long, 4. Sheathing of the "compacted" with mild steel with an inside diameter of 10 + X mm and 200 + Y mm long each of the elements being coated internally with a layer of alumina, 5. Reactive sintering by bringing the assembly to 1000 o C for 2 hours in order to obtain the reaction Ti + Ni = TiNi, 6. Heat diffusion treatment between the porous TiNi and the solid TiNi rod at a temperature higher than that of reactive sintering such as 1200 o C.

  7. Removal of the sheath by turning then chemical pickling.

Claims (10)

  1. Process for the preparation by reactive sintering of porous intermetallic materials comprising the succession of the following stages: choice of powders and preparation of the mixture of elementary powders in the appropriate proportions, - compression of the mixture to obtain a compacted element, - sheathing of the compacted element, - treatment of the sheathed product by reactive sintering under conditions allowing a porous intermetallic alloy to be obtained, - elimination of the sheath.   2. Method according to claim 1 characterized in that the elementary powders are chosen so that the alloy obtained is biocompatible for medical applications, or, any for other fields of application, 3. Method according to claim 1 characterized in that the particle size of the elementary powders, their state of compaction and the clearance between the sheath and the compacted element allow the desired porosity to be obtained in porosity rate and in pore dimensions, 4. Method according to claim 1 characterized in that a compressible or non-compressible diffusion barrier is interposed between the compacted element and the sheath, 5. Method according to claim 1 characterized in that the sheath can be made waterproof in order to have an atmosphere defined by the nature of the materials treated, 6. Method according to claim 1 characterized in that the compacted and sheathed element is placed in an oven making it possible to reach, as a function of the constituent materials, the temperatures necessary for reactive sintering, 7. Method according to claim 1 characterized in that the sheath is removed by machining and / or chemical attack, 8. Method according to claim 1 characterized in that a solid element of the same nature as the porous element produced by any method, is incorporated into the porous element during compaction, 9. Method according to claim 8 characterized in that a complementary heat treatment at a temperature higher than that of reactive sintering is applied before removal of the sheath to increase the diffusion between the solid element and the porous element, 10. Method according to claim 1 characterized in that the powders used are arbitrary as long as they are chosen to allow the production of a porous intermetallic material intended for applications not requiring biocompatibility. ----------------