EP3181710A1 - Alliage comprenant du cr, du ni, du mo et du co pour une utilisation dans des dispositifs médicaux - Google Patents

Alliage comprenant du cr, du ni, du mo et du co pour une utilisation dans des dispositifs médicaux Download PDF

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Publication number
EP3181710A1
EP3181710A1 EP15201407.2A EP15201407A EP3181710A1 EP 3181710 A1 EP3181710 A1 EP 3181710A1 EP 15201407 A EP15201407 A EP 15201407A EP 3181710 A1 EP3181710 A1 EP 3181710A1
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European Patent Office
Prior art keywords
alloy
range
wire
content
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Prior art date
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EP15201407.2A
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German (de)
English (en)
Inventor
René RICHTER
Jörg-Martin GEBERT
Heiko Specht
Francis E. Sczerzenie
Radhakrishnan M. Manjeri
Weimin Yin
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Heraeus Medevio & Co Kg GmbH
Resonetics Smart Materials Inc
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Heraeus Deutschland GmbH and Co KG
SAES Smart Materials Inc
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Priority to EP15201407.2A priority Critical patent/EP3181710A1/fr
Publication of EP3181710A1 publication Critical patent/EP3181710A1/fr
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/07—Alloys based on nickel or cobalt based on cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon

Definitions

  • the invention generally relates to an alloy comprising Cr, Ni, Mo and Co, preferably with tightly controlled levels of impurities.
  • the invention further relates to a process for the preparation of an alloy, an alloy obtainable therefrom, a lead, and the use of a lead in medical devices, preferably pacemakers.
  • Cardiac Pacemakers, Implantable Cardioverter Defibrillation Devices and Cardiac Resynchronisation Devices are applications where reliability is particularly important, especially in terms of resistance to physical fatigue and to chemical corrosion. Invasive surgery is required to implant a pacemaker into the body or remove or replace parts, and it is highly desirable for the individual components of the pacemaker to have a long working life in order to reduce the requirement for surgical intervention. Furthermore, it is desirable for the working life to have a low variance. In a heart pacemaker, one component which is exposed to a particularly high amount of stress during normal operation is the so called lead which connects the implantable pulse generator to the heart tissue.
  • a flexible lead is required in order to connect the implantable pulse generator to the heart tissue without imposing undue physical stress on the heart and the lead flexes during normal operation, typically repetitively with a frequency on the order of that of a human heart beat.
  • a high resistance to fatigue is therefore required in the lead in order to withstand frequent physical stress over a long period of time.
  • a high resistance of the lead to corrosion is important not only in terms of the lifetime of the component, but also in terms of reducing toxicity to the body.
  • WO 2005026399 A1 discusses an approach to improving the properties of an alloy by reducing the content of titanium nitride and mixed metal carbonitride.
  • the invention is generally based on the object of overcoming at least one of the problems encountered in the state of the art in relation to alloys.
  • the invention is further based on the object of providing an alloy having improved properties.
  • One object of the invention is to provide an alloy which has improved resistance to physical fatigue, preferably also having a high corrosion resistance. Another object is to provide an alloy which can be drawn into a thin wire, preferably less than about 50 ⁇ m.
  • a further object of the invention is to provide a method for the preparation of an alloy having improved properties, preferably an improved resistance to physical fatigue, preferably also having a high corrosion resistance, preferably also which can be drawn into a thin wire, more preferably less than about 50 ⁇ m.
  • One object of the invention is to provide a wire having comparable tensile properties to known wire, but for which the proportion of outlying failures in fatigue resistance is reduced.
  • Preferred alloys according to the invention comprise two or more elements, preferably as a solid mixture, preferably with an enthalpy of mixing of the constituent elements of less than about 10 KJ/mol, preferably less than about 5 KJ/mol, more preferably less than about 1 KJ/mol.
  • Preferred alloys comprise Cr, Ni, Mo and Co as major constituents, preferably with at least about 95 wt. %, more preferably at least about 99 wt. %, further more preferably at least about 99.9 wt. %, more preferably at least about 99.95 wt. % of the alloy being Cr, Ni, Mo and Co.
  • a composition of the alloy is preferred which improves favourable properties of the alloy, in particular resistance to fatigue and/or corrosion resistance, preferably both.
  • the properties of the alloy prefferably be improved by limiting the content of impurities or limiting the content of a combination of different impurities, preferably according the embodiments of the invention.
  • the alloy contains less than about 0.01 %, preferably less than about 0.005 %, more preferably less than about 0.001 % inclusions.
  • the % of inclusions is preferably determined using the microscopic inspection method given in the test methods. Content of inclusions as % is there determined as the proportion of the cross sectional area of the sample surface made up of inclusions.
  • the alloy comprises a low, preferably a zero concentration of inorganic non-metallic solid inclusions, more preferably of inorganic oxide inclusions.
  • Inorganic oxides in this context can refer to metal oxides, non-metal oxides and metalloid-oxides.
  • the alloy comprises a low, preferably a zero concentration of inclusions comprising one or more selected from the group consisting of: Si, Al, Ti, Zr and B; preferably selected form the group consisting of: Si Ti, and Al.
  • one or more treating material(s) is/are contacted with the mixture of the process in order to remove oxygen from the mixture of the process, preferably by incorporation of the oxygen into a dross and removal of the dross.
  • Preferred treating materials in this context comprise one or more selected from the list consisting of: Al, Mg, Ca and Ce; preferably in the form of an element and/or in the form of an alloy, wherein the alloy preferably contains a further metal being selected from group consisting of Cr, Ni, Mo and Co or at least two thereof, preferably Ni.
  • the skilled person may vary the proportions of starting materials employed in the preparation process.
  • the proportions of the starting materials might not be equal to the proportions of constituents of the product, due to net loss or gain during the preparation process.
  • the process for the preparation of the alloy preferably comprises the following steps:
  • the process comprises two or more vacuum induction melting steps. In another embodiment of the invention, the process comprises two or more vacuum melting steps. In another embodiment of the invention, the process comprises two or more vacuum induction melting steps and two or more vacuum arc melting steps.
  • the process further comprises one or more of the following steps:
  • the process comprises a combination of the above steps selected from the list consisting of: c), d), e), f), g), c)+d), c)+e), c)+f), c)+g), d)+e), d)+f), d)+g), e)+f), e)+g), f)+g), c)+d)+e), c)+d)+f), c)+d)+g), c)+e)+f), c)+e)+g), c)+f)+g), d)+e)+f), d)+e)+g), d)+f)+g), e)+f)+g), d)+f)+g), e)+f)+g), d)+e)+f)+g), d)+e)+f)+g), d)+e)+f)+g), d)+e)+f)+g), d)+e
  • one or more of the steps c)-g) is carried out two or more times.
  • a material is heated by inducing an electric current in the material, preferably by electromagnetic induction.
  • the pressure in the vacuum induction melting step is preferably below about 0.1 mbar, more preferably below about 0.01 mbar, most preferably below about 0.001 mbar.
  • the vacuum induction melt step is preferably carried out in an oven, preferably with a low leak rate, preferably below about 0.1 mbar ⁇ l/s, more preferably below about 0.01 mbar ⁇ l/s, most preferably below about 0.001 mbar ⁇ l/s.
  • the leak rate is preferably tested before the vacuum induction melting step by evacuating the oven, closing the valves of the oven, and measuring the rate of increase of pressure in the oven.
  • the vacuum induction melting step is carried out in an inert atmosphere, preferably argon, preferably an atmosphere comprising at least about 90 wt. %, more preferably at least about 99 wt. %, most preferably at least about 99.9 wt. % of inert gas, preferably argon.
  • the oven is evacuated and inert gas, preferably argon, introduced into the oven before melting.
  • the pressure in the vacuum induction melting step is in the range from about 1 to about 200 mbar, preferably in the arrange from about 10 to about 150 mbar, most preferably in the range from about 20 to about 100 mbar.
  • a material is heated by passing an electrical current through the material, preferably with an electrical power in the range from about 300 to about 1200 W/kg, more preferably in the range from about 400 to about 1000 W/kg, most preferably in the range from about 450 to about 900 W/kg, based on the mass of material heated.
  • the pressure in the vacuum arc melting step is preferably below about 0.1 mbar, more preferably below about 0.01 mbar, most preferably below about 0.001 mbar.
  • the vacuum arc melt step is preferably carried out in an oven, preferably with a low leak rate, preferably below about 0.1 mbar ⁇ l/s, more preferably below about 0.05 mbar ⁇ l/s, most preferably below about 0.01 mbar ⁇ l/s.
  • the leak rate is preferably tested before the vacuum arc melting step by evacuating the oven, closing the valves of the oven, and measuring the rate of increase of pressure in the oven.
  • the vacuum arc melting step is carried out in an inert atmosphere, preferably argon, preferably an atmosphere comprising at least about 90 wt. %, more preferably at least about 99 wt. %, most preferably at least about 99.9 wt.
  • the oven is evacuated and inert gas, preferably argon, introduced into the oven before melting.
  • the pressure in the vacuum arc melting step is in the range from about 0.001 to about 0.2 bar, preferably in the range from about 0.01 to about 0.15 bar, most preferably in the range from about 0.05 to about 0.1 bar.
  • Homogenisation steps according to the invention preferably allow reduction of inhomogeneity in a material, preferably by heating. In preferred homogenisation steps according to the invention, a material is heated to a temperature which is below its melting temperature, preferably below its incipient melting temperature.
  • the material be homogenised for a duration in the range from about 10 min. to about 20 hours, more preferably in the range from about 3 hours to about 10 hours, most preferably in the range from about 5 hours to about 8 hours.
  • Homogenisation is preferably carried out in a vacuum or in a gaseous atmosphere, preferably in a gaseous atmosphere. It is preferred that the homogenisation step be carried out close to atmospheric pressure, preferably in the range from about 0.5 to about 1.5 bar, more preferably in the range from about 0.8 to about 1.2 bar, most preferably in the range from about 0.9 to about 1.1 bar. In one preferred embodiment, the homogenisation step is carried out in air.
  • the porosity or grain size or both of a material are reduced, preferably at elevated temperatures, preferably below the melting point of the material, preferably with the application of compressive force.
  • Compressive forces may be applied locally or in a delocalised manner, preferably by one or more selected from the group consisting of: rolling, pressing, beating and turning.
  • rolling is preferred.
  • the material to be cogged has a mass above about 10 kg, preferably above about 20 kg, more preferably above about 30 kg, beating or turning is preferred. It is preferred that the smallest dimension of the material is reduced during the cogging process.
  • Preferred finish roll steps according to the invention reduce the smallest dimension of the material, preferably by passing the material through one or more pairs of rolls, preferably below the melting point of the material, more preferably below its incipient melting point.
  • the finish roll step reduces the porosity or grain size of the material, preferably both.
  • Straightening preferably reduces the physical curvature of the material, preferably so as to facilitate further grinding or machining steps.
  • Straightening is preferably carried out by applying compressive force.
  • the straightening step is preferably carried out below the melting point of the material, more preferably below its incipient melting point.
  • the process comprises a hot straightening step.
  • the process comprises a cold straightening step, preferably carried out at around ambient temperature. Cold straightening is preferably carried out at a temperature in the range from about 10 to about 100 °C, more preferably in the range from about 15 to about 80 °C, most preferably in the range from about 20 to about 50 °C.
  • a coated or cladded wire which comprises a wire core and a shell.
  • the shell might be coated or cladded onto the core wire.
  • a preferred lead according to the invention comprises at least one proximal connector, at least one distal electrode and a flexible elongated conductor that is electrically connecting the electrode(s) to the connector(s).
  • the elongated conductor is a coiled wire or a cable and comprises the alloy according to the invention.
  • a wire comprising an alloy according to the invention, preferably having a thickness in the range from about 10 to about 50 ⁇ m, preferably in the range from about 15 to about 35 ⁇ m.
  • the wire further comprises silver metal.
  • the lead comprises a silver core and an alloy according to the invention, preferably present as a shell surrounding the silver core.
  • a lead comprising one or more wires according to the invention, preferably grouped into two or more cables, each cable comprising two or more wires according to the invention.
  • the cables have a thickness in the range from about 0.05 to about 0.5 mm, preferably in the range from about 0.1 to 0.4 mm.
  • a contribution to achieving at least one of the above mentioned problems is made by a medical device, preferably a pacemaker, comprising a lead according to the invention.
  • a preferred pacemaker comprises:
  • the pacemaker comprises one or more pulsers.
  • the pacemaker comprises one or more energy cells, preferably one or more electrical cells.
  • a preferred process for the preparation of a wire according to the invention comprises the steps:
  • the Ag content of the wire obtainable by the process is in the range from about 15 to about 50 wt. %, preferably in the range from about 17.5 to about 45.7 wt. %, more preferably in the range from about 28.7 to about 37.7 wt. %, based on the total weight of the wire.
  • the diameter of the wire obtainable by the process is in the range from about 5 to about 50 ⁇ m, preferably in the range from about 15 to about 35 ⁇ m.
  • the filling degree of silver in the wire obtainable by the process is in the range from about 15 % to about 41 %, preferably in the range from about 20 % to about 35 %, more preferably in the range from about 23 % to about 33 %.
  • FIG. 1 shows schematically a lead having a cable bundle 140, which comprises cables 100.
  • the cables 100 each comprise 7 wires 10.
  • Each wire comprises a first region 20 and a further region 30, wherein the first region 20 is interior to the region 30 along the length of the lead 140.
  • the first region 20 is 41 area % of the cross sectional area the wire 10 and the further region is 59 area % of the cross sectional area of the wire 10, in each case based on the total cross sectional area of the wire 10.
  • the first region 20 is silver.
  • the further region 30 is an alloy according to the invention.
  • the cable bundle 140 comprises 7 cables 100, each cable 100 comprising 7 wires 10. The invention is not limited to this arrangement. In particular, other arrangements of wires 10 in cables 100 and/or other arrangements of cable bundles 140 in leads are conceivable.
  • Figure 2 shows schematically an apparatus for measuring fatigue resistance.
  • FIG. 3 shows schematically a pacemaker 50 with a pulse generator 70, and a lead 140 comprising an electrode 60.
  • the lead 140 connects the pulse generator 70 and the heart tissue via the electrode 60.
  • Figure 4 shows a cross sectional image of a wire of material according to example 2 (comparative) as observed by backscattered electron imaging according to the test method. A dark inclusion is indicated with an arrow.
  • Figure 5 shows a cross sectional image of a wire of material according to example 2 (comparative) as observed by backscattered electron imaging according to the test method.
  • Figure 5 shows the same image as figure 4 , but at higher magnification. A dark inclusion is indicated with the reference mark #A1.
  • Figure 6 shows an analysis of elemental composition by energy dispersive x-ray spectroscopy according to the fracture surface analysis test method of the surface of an inclusion in a wire of material according to example 2 (comparative).
  • the surface analysed is the inclusion indicated as #A1 in figure 5 .
  • the analysis shows the presence of Al and Mg impurities and also of entities with a Cr-O bond.
  • Figure 7 shows a cross sectional image of a wire of material according to example 2 (comparative) as observed by backscattered electron imaging according to the test method. A dark inclusion is indicated with the reference mark #A1.
  • Figure 8 shows a cross sectional image of a wire of material according to example 2 (comparative) as observed by backscattered electron imaging according to the test method.
  • the surface shown in figure 8 is taken from the same slice as that of figure 7 .
  • Figure 9 shows a cross sectional image of a wire of material according to example 2a (comparative) with an Ag core, as observed by backscattered electron imaging according to the test method. A dark inclusion is indicated with an arrow.
  • Figure 10 shows a cross sectional image of a wire of material according to example 2a (comparative) with an Ag core, as observed by backscattered electron imaging according to the test method.
  • Figure 10 shows the same image as figure 9 , but at higher magnification. A dark inclusion is indicated with the reference mark #A2.
  • Figure 11 shows an analysis of elemental composition by energy dispersive x-ray spectroscopy according to the fracture surface analysis test method of the surface of an inclusion in a wire of material according to example 2a (comparative) with an Ag core.
  • the surface analysed is the inclusion indicated as #A2 in figure 10 .
  • the analysis shows the presence of Al impurities and also of entities with a Cr-O bond.
  • Figure 12 shows a plot of fatigue results for a wire of material according to example 1 (inventive) and a wire of material according to example 2 (comparative).
  • 1 inventive
  • results are shown for 2 lots, lot A as represented by a solid circle and lot B as represented by a solid triangle.
  • 2 comparativative
  • results are shown for 2 lots, lot C as represented by a hollow square and lot D as represented by a hollow diamond.
  • the number of cycles before failure is shown as dependent on the stress amplitude applied in the test. Outliers which performed poorly are indicated with arrows.
  • Figure 13 shows a plot of fatigue results for a wire of material according to example 1a (inventive) with an Ag core and a wire of material according to example 2a (comparative) with an Ag core.
  • 1a inventive
  • results are shown for 3 lots, lot E as represented by a solid circle, lot F as represented by a solid triangle and lot G as represented by a solid square.
  • lot H as represented by a hollow square
  • lot J as represented by a hollow diamond
  • lot K as represented by a cross.
  • the number of cycles before failure is shown as dependent on the stress amplitude applied in the test. Outliers which performed poorly are indicated with arrows.
  • the leak rate of the furnace chamber is measured using the following procedure:
  • Rotating beam fatigue testing was carried out using Valley Instruments model # 100 test machine ( Figure 2 ) according to Valley Instruments Wire Fatigue Tester Model # 100 user manual (Valley Instruments (Division of Positool Technologies, Inc.), Brunswick, Ohio, USA. Fatigue Tester Model 100 Manual).
  • the equipment consists of a synchronous motor rotating at 3600 rpm.
  • For each test of a wire specimen a sample having a predefined length is fixed in a custom fine-wire collet at one end, looped through a complete 180 degree turn and is placed at the other end in a low-friction bushing in which it is free to rotate.
  • the synchronous motor of the test device is directly clocked by a counter where the number of cycles is shown in a LCD-display.
  • the fatigue testers are equipped with a sensor to detect the wire fracture which automatically stops the timer, means the display of the timer shows the number of cycles until failure. If no fracture occurs within 100 Million cycles, the test is stopped.
  • the machine set-up involves calculating the desired sample length and center distance using the modulus of elasticity of the material and equations developed by Valley Instruments Company (user manual).
  • Inclusions are defined as internal flaws or contaminations (such as nitrides or oxides) within the billet or rod from which the wire or tube is produced.
  • the transverse inclusion size is defined as the largest dimension of an internal flaw measured on transverse cross-sections of the billet, rod or wire.
  • the longitudinal inclusion size is defined as the largest dimension of an internal flaw measured on longitudinal cross-sections of the billet, rod or wire.
  • a cross-section diametral line is defined as any line within the cross-section having a length equal to or greater than 95% of the true cross-section diameter.
  • the billet, rod or wire is to be sectioned at each end so that there are an equal number of cross sections sampled at the one end as there are samples at the other end (number of samples taken from each end shall differ by no more than one).
  • the total number of cross sections samples depends on the diameter of the billet, rod or wire and is specified in Table 1.
  • the length of each cross section is to be less than its diameter.
  • a cross-section diametral line is defined as any line within the cross-section having a length equal to or greater than 95% of the true cross-section diameter. Angular separation between two diametral lines on a cross- section shall be a minimum of 60 degrees.
  • the number of images and the number of diametral lines depends on the diameter of the billet, rod or wire and is specified in Table 1. The total number of images is shown in Table 1 and was calculated based on the number of images per sample and the number of samples.
  • Each of the images is to be inspected to detect the presence of inclusions or strings of inclusions that exceed a size of 3.0 ⁇ m in their largest dimension.
  • the image inspection may be accomplished either by manual examination or by automated scanning.
  • Table 1 cross section diameter of billet, rod or wire Number of diametral lines per section (no requirement for tube samples) Number of images per section Number of cross-sections Total images per lot equal to or greater than [mm] but no greater than [mm] transverse longitudinal transverse longitudinal 2.54 3.80 5 40 12 12 480 480 3.81 5.71 3 40 12 12 480 480 5.72 11.42 2 40 12 12 480 480 11.43 13.96 1 40 12 12 480 480 13.97 17.14 1 48 10 10 480 480 17.15 21.58 1 60 8 8 480 480 21.59 27.93 1 80 6 6 480 480 27.94 33.01 1 96 5 5 480 480 33.02 43.17 1 120 4 4 480 480 43.18 57.14 1 160 3 3 480 480
  • the test method to analyse fracture surfaces of fatigue tested samples was Scanning electron microscopy (SEM).
  • SEM Scanning electron microscopy
  • a Zeiss Ultra 55 Gemini was used for the sample analysis of the present invention and comparative samples. Two imaging modes were used to analyse and illustrate the tested samples.
  • Energy-dispersive X-ray spectroscopy (EDS, EDX) was used for the elemental analysis of features (inclusions/particles) found on the fatigue resistance test samples. A high-energy beam of electrons is focused onto the location of the sample being analysed. This leads to the emission of characteristic X-rays which allows the elemental composition of the feature (inclusions/particles) to be measured.
  • Figures 6 and 11 show EDX scans.
  • the MP35N heats were VIM-VAR melted, to minimize the impurity content and to obtain a sound ingot with good chemical uniformity and metallurgical properties.
  • the chemistry of representative heats: Heat 1, Heat 2 and Heat 3 are listed in Table 3.
  • the table also provides the chemistry of a VIM-VAR melted, commercially available MP35N alloy and for reference the chemical requirements per ASTM F562-13, a standard specification for wrought MP35N alloy.
  • the major constituents of MP35N alloy are Co, Ni, Cr and Mo.
  • the new alloy heats were melted in 2 steps.
  • the first melting step was Vacuum Induction Melting (VIM).
  • the VIM furnace consists of a water cooled vacuum melt chamber, an oxide ceramic crucible held in a cylindrical induction heating coil inside the melt chamber, an AC electric power supply, a vacuum pumping system, a raw material adding chamber and a cylindrical metal mold held below and offset from the crucible-induction coil assembly.
  • the vacuum melt chamber, raw material adding chamber and vacuum pumping system are separated by isolation valves.
  • the induction heating coil is water cooled. Electric current from the power supply passes through the induction heating coil creating a magnetic field inside the furnace. The magnetic field induces eddy currents inside the raw materials causing Joule heating. Joule heating raises the temperature of the raw materials to above their melting point.
  • the magnetic field mixes the liquid raw materials to make a homogeneous alloy.
  • the crucible is tilted to pour the liquid alloy from the crucible into the mold.
  • the alloy cools to a solid in the mold under vacuum and is removed from the furnace.
  • the alloy ingot is removed from the mold and it is prepared for re-melting.
  • 136 kilograms of elemental raw materials were placed in the furnace in proportions calculated to make the aim chemistry.
  • the VIM furnace was closed and pumped down to ⁇ 0.00001 bar.
  • a leak-up rate was measured after reaching the desired vacuum pressure level to ensure a vacuum tight furnace.
  • the leak-up rate was ⁇ 0.00001 bar/min. Electric power was applied to the induction heating coil.
  • the VAR furnace consists of water cooled vacuum chamber, a 203.2 mm diameter water cooled copper crucible, a direct current electric power supply, a vacuum pumping system, isolation valves and a computer based electrical system to monitor and control the application of current to the electrode inside the vacuum chamber.
  • the furnace was pumped down to ⁇ 0.000006 bar before carrying out the leak-up rate test. A leak rate of ⁇ 0.000006 bar /min was obtained.
  • the electrode was moved to a close proximity to the bottom of the crucible. Electric power was applied at a level to cause an electric arc to be struck between the crucible bottom and the alloy electrode. The electric arc causes the electrode to melt and drip into the bottom of the crucible creating a liquid metal pool that solidifies as the arc moves away from the molten pool. The process was continued at a controlled rate until the electrode was consumed. The power was turned off and the ingot was cooled under vacuum. The ingot was removed from the furnace for processing to product.
  • the as-cast ingot was charged into a gas-fired front opening box furnace with ambient air atmosphere.
  • the furnace was preset to a temperature of 815°C.
  • the ingot was held for additional 4 hours prior to raising the furnace temperature.
  • the ingot was then heated to 1177°C at a heating rate of 200 K per hour.
  • the ingot was held for 7 hours at 1177°C for homogenization.
  • the ingot was hot rolled from 203 mm to 137 mm round cornered square (RCS) billet using a 559 mm diameter Morgenshammer Mill operating at ambient temperature.
  • RCS round cornered square
  • the Morgenshammer Mill is a manually operated tilt table mill with 3 high rolls allowing heavy bar to be rolled alternately between the bottom and middle roll and the top and middle roll. After hot rolling the RCS billet was air cooled, abrasively ground by hand to remove surface imperfections and cut to square the ends.
  • the billet was reheated and hot rolled to 51 mm RCS at 1177°C on the 559 mm Morgenshammer Mill.
  • the RCS was cut to shorter lengths of final rolling on a hand operated 406 mm diameter Morgenshammer Mill with 3 high rolls. All bar manipulation on this mill is done by hand at floor level.
  • the RCS was reheated at 1177°C and rolled to 33.4 mm round bars and air cooled to ambient temperature.
  • the rolled bars were then reheated to 1038°C and held for 30 minutes for hot rotary straightening. After straightening, the bars were air cooled to room temperature.
  • the bars were rough centerless ground, ultrasonic tested for voids and then centerless ground to final size.
  • the grinded bars were gun-drilled to produce hollows for subsequent tube drawing. Tubes were filled with Ag-rods and cold-drawn using diamond dies and mineral oil. For a final wire diameter of 127 ⁇ m, the last intermediate annealing was carried out at a wire diameter of 157.5 ⁇ m at 900 - 950 °C in Argon atmosphere. From the last intermediate annealing until the final diameter of the wire, 35% cold-work were applied. Three wire lots were manufactured having UTS values of 1456, 1469 and 1474 MPa. For bare wire, the bars were further hot-rolled to 0.2 inch outer diameter followed by cold-drawing.
  • the last intermediate annealing was carried out at a wire diameter of 122 ⁇ m at 1100 °C in Argon atmosphere to apply 30% cold-work to the final size.
  • Two wire lots were manufactured having UTS values of 1870 and 1875 MPa.
  • the wires of inventive example 1 (Lots A & B) and the cladded wires of inventive example 1a (Lots E, F & G) were made using the alloy of Heat 1 in table 3.
  • the wires of comparative example 2 (lots C & D) and the cladded wires of comparative example 2a (lots H, J & K) were made from the alloy of the commercial heat in table 3 obtained from Fort Wayne Metals, Inc., USA under the trade name 35 NLT ® .
  • the processed alloy was also obtainable from SAES Smart Materials, Inc. Alloys for the further examples were acquired from SAES Smart Materials, Inc. Table 3 Element Heat 1 Heat 2 Heat 3 Commercial Heat ASTM F-562-13 Wt. % Wt. % Wt. % Wt. % Wt. % Wt. % Wt.
  • the microscopic inspection for microcleanliness of the inventive alloy (example 1 and example 1a with an Ag core) and of the comparative alloy (example 2 and example 2a with an Ag core) was carried out according to the procedure and test method described above.
  • 4 rods with an outer diameter of 31.75 mm 5 transverse and 5 longitudinal sections were taken according to table 1 and metallographically prepared.
  • the metallographically prepared sections were examined in the as-polished condition by scanning electron microscopy (SEM) using backscattered electron imaging (BEI).
  • SEM scanning electron microscopy
  • BEI backscattered electron imaging
  • the brightness of sample features is proportional to the atomic weight of the elements constituting those features.
  • present inclusions consisting of heavier elements than the surrounding matrix material appear brighter than the matrix material.
  • Inclusions consisting of lighter elements than the surrounding matrix material appear darker than the matrix material.
  • nonmetallic inclusions e.g. oxide or nitride inclusions
  • these ceramic inclusions appear darker than the surrounding matrix material. Images were acquired at a magnification of 500X along a diametral line extending across the entire bar. Analysis of features darker and brighter than the background was conducted on the images using image analysis software to determine the maximum dimension for each detected feature. The largest dimension and area were recorded for each individual feature. The inclusions were categorized by largest dimension into 1 ⁇ m groups up to 14 ⁇ m. The total area of the dark and bright features was also calculated. Inclusions greater than 14 ⁇ m were also counted. Features smaller than 3.0 ⁇ m were not included in the measurements.
  • Results of the inclusion analysis of example 1 are shown in tables 4-6.
  • Results of the inclusion analysis of example 2 are shown in tables 7-10.
  • Image fields showing typical dark (ceramic) inclusions are shown in Figures 4,5 , 7-10 .
  • the total area of dark inclusions found is 478 ⁇ m 2 (409 ⁇ m 2 in longitudinal direction and 69 ⁇ m 2 in transverse direction).
  • the total area of dark inclusions found is only 218 ⁇ m 2 (121 ⁇ m 2 in longitudinal direction and 97 ⁇ m 2 in transverse direction). So the amount of dark inclusions (Percent of total area) in example 1 (inventive) is only 4.8 ppm (0.00048 %) while in example 2 (comparative) the amount of dark inclusions is 11 ppm (0.0011 %). In terms of inclusions (micro-cleanliness) this means that example 1 (inventive) is more than 2 times cleaner than example 2 (comparative).
  • Example 2 wire lot C sample C25 tested at an applied stress of 700 MPa broke after only 71,790 cycles and sample C31 tested at an applied stress of 520 MPa broke after only 145,260 cycles.
  • Sample C26 tested at an applied stress of 700 MPa broke after 47,547,540 cycles and sample C29 tested at an applied stress of 700 MPa broke after 41,282,990 cycles.
  • sample D27 tested at an applied stress of 700 MPa broke after only 549,227 cycles and sample D35 tested at an applied stress of 520 MPa broke after only 2,689,952 cycles.
  • SEM-images of sample C25 shows an inclusion at the fracture surface.
  • high peaks for Aluminium, Magnesium, Chromium and Oxygen were found. This mixed-oxide inclusion was identified as the crack initiation point for the early failure of this sample.
  • An SEM-image of sample D35 also shows an inclusion at the fracture surface.
  • Example 1a/Ag28% wire Three lots of example 1a/Ag28% wire (diameter 127 ⁇ m) were also tested against three lots of example 2a wire (same diameter - 127 ⁇ m). All six wire lots have comparable mechanical properties (UTS of 1456 - 1475 MPa). Table 13 - Example 1a + 28 wt. % Ag (inventive) Example 2a + 28 wt. % Ag (comparative) Batch Lot E Lot F Lot G LotH Lot J ( Fig. 10 & 11 ) Lot K UTS [MPa] 1456 1469 1474 1460 1462 1475 YM [GPa] 121 121 122 121 122 122 Elongation [%] 2.2 2.3 2.3 2.1 2.0 2.3
  • SEM-images of sample J23 show an inclusion at the fracture surface.
  • high peaks for Aluminium, Magnesium, Chromium and Oxygen were found. This mixed-oxide inclusion was identified as the crack initiation point for the early failure of this sample.
  • SEM investigations of samples H24, J18 and K24 also showed oxide-inclusions at the fracture surface which were identified causing the early failure.
  • the same elements show high peaks in EDX analysis for these three samples.
  • Table 14 Example 1a + 28 wt. % Ag

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EP15201407.2A 2015-12-18 2015-12-18 Alliage comprenant du cr, du ni, du mo et du co pour une utilisation dans des dispositifs médicaux Pending EP3181710A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050051243A1 (en) 2003-09-05 2005-03-10 Forbes Jones Robin M. Cobalt-nickel-chromium-molybdenum alloys with reduced level of titanium nitride inclusions
US7015392B1 (en) * 2003-05-28 2006-03-21 Accellent, Inc. High torsional ductility wire and methods of making the same
US20100075168A1 (en) * 2008-09-19 2010-03-25 Fort Wayne Metals Research Products Corporation Fatigue damage resistant wire and method of production thereof

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7015392B1 (en) * 2003-05-28 2006-03-21 Accellent, Inc. High torsional ductility wire and methods of making the same
US20050051243A1 (en) 2003-09-05 2005-03-10 Forbes Jones Robin M. Cobalt-nickel-chromium-molybdenum alloys with reduced level of titanium nitride inclusions
WO2005026399A1 (fr) 2003-09-05 2005-03-24 Ati Properties, Inc. Alliages de cobalt-nickel-chrome-molybdene presentant un taux reduit d'inclusions de nitrure de titane
US20100075168A1 (en) * 2008-09-19 2010-03-25 Fort Wayne Metals Research Products Corporation Fatigue damage resistant wire and method of production thereof

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