JP2005126767A - Method for surface treatment of titanium material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for increasing the hardness of a desired fine area of a titanium material by selectively performing surface treatment thereof. <P>SOLUTION: In a surface treatment method, a desired fine area of a titanium material is covered by nitride by applying arc discharge with weak discharge energy to the area while blowing gaseous nitrogen thereto at predetermined flow rate. The flow rate of gaseous nitrogen is preferably 2.5-30 liter/minute. In this method, gaseous nitrogen is preferably blown to the fine area for 0.3-3.0 milli-seconds before applying the arc discharge thereto, and for 0.3-9.9 milli-seconds after applying the arc discharge. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to a method of surface treating a titanium material. More specifically, the present invention relates to a method for selectively surface-treating desired fine regions of a titanium material.

  Titanium is a material that has various excellent chemical and physical properties such as light weight and excellent corrosion resistance and biocompatibility, but has a drawback of poor wear resistance. Therefore, it is desired to improve the wear resistance by increasing the hardness in order to meet the use under severe conditions such as use in the sliding portion. Conventionally, as a method for increasing the hardness of titanium, a method of adding an alloy metal such as aluminum or vanadium to titanium is known.

  On the other hand, gas nitriding, laser nitriding, ion implantation method and the like are known as nitride coating methods for metal surfaces, but disadvantages of these methods (long processing time, high processing temperature, high cost, The present inventors have proposed a nitriding method using arc surface melting in a nitrogen atmosphere as a method with a simple processing time, low cost, and good adhesion. (See Non-Patent Document 1).

Arita Univ., Kiyotaka Matsuura, Masayuki Kudo: Functionally Graded Material Proceedings 2002, edited by the Unexplored Science and Technology Association, 2003, pp. 37-41

  The above-described conventional method for increasing the hardness of titanium has a hardness of only about 400 Hv, and is still not satisfactory for applications that require hardness such as sliding portions. On the other hand, even in applications where hardness is required, when the location where hardness is required is a small part rather than the entire object, such as a surgical knife or an artificial joint, There are also many sliding parts in artificial joints. Therefore, it is required to increase the hardness of a desired fine region of the titanium material.

  The present invention has been devised in view of such a current situation, and an object of the present invention is to provide a method for increasing the hardness by selectively surface-treating a desired fine region of a titanium material.

In the experiment described in Non-Patent Document 1 described above, it was confirmed that a TiN layer, a (TiN + Ti ₂ N + αTi) layer, and an αTi layer were formed sequentially from the surface with respect to a pure titanium material. We succeeded in increasing the hardness to about 1500 Hv. The present invention is based on the research results described in Non-Patent Document 1, and created a method for selectively surface-treating a desired fine region (that is, coating with nitride).

  In order to selectively coat desired fine regions with nitride, it is necessary to precisely control the position and size of the melted portion on the treated surface of the titanium material. The present inventors have found that a fine coating of nitride can be formed by reducing the discharge energy during the surface treatment.

  The method for selectively surface-treating a desired fine region of the titanium material according to claim 1 of the present invention is to perform arc discharge with weak discharge energy while blowing a predetermined flow rate of nitrogen gas to the fine region, It is characterized by forming a nitride coating.

  The surface treatment method according to claim 2 of the present invention is characterized in that, in the method of claim 1, the flow rate is 2.5 liters / minute to 30 liters / minute.

  The surface treatment method according to claim 3 of the present application is the method according to claim 1 or 2, wherein nitrogen gas is blown into the fine region for 0.3 to 3.0 milliseconds before performing the arc discharge. It is characterized by.

  A surface treatment method according to a fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein after the arc discharge is performed, nitrogen gas is supplied to the fine region from 0.3 milliseconds to 9 milliseconds. .9 milliseconds of spraying.

  According to the method of the present invention, the width and depth of the melted portion can be reduced to several tens to several hundreds of μm, so that a desired fine region of the titanium material can be selectively (up to about 1500 Hv). It can be cured. The method of the present invention can be used, for example, to harden the blade portion of a surgical knife, the sliding portion of an artificial joint, or the like.

  Next, a method for surface-treating a titanium material according to a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a state in which surface treatment is performed by the method of the present invention. In FIG. 1, reference numeral 10 indicates a torch portion, and reference numeral 12 indicates a tungsten electrode. The torch part 10 is provided with a nitrogen gas supply port 10a.

  First, the torch portion 10 is brought close to a fine region to be surface-treated of an electrically grounded titanium material, and a predetermined flow rate of nitrogen gas is blown from the nitrogen gas supply port 10a of the torch portion 10 to the fine region. Arc discharge is performed with high discharge energy.

  The flow rate of nitrogen gas blown to the fine region is preferably about 2.5 liters / minute to about 30 liters / minute. When the flow rate of nitrogen gas is about 2.5 liters / minute or less, it becomes difficult to form a nitride coating.

  The discharge energy of arc discharge is represented by the product of voltage, current and time. In order to weaken the discharge energy, the discharge current may be weakened and the discharge time may be shortened with the applied voltage being constant. In this embodiment, with the applied voltage being 200 volts, the discharge current is varied between 1 ampere and 30 amperes, and the discharge time is turned on / off at intervals of 0.5 milliseconds to 180 milliseconds. Repeated. Further, the discharge current can be repeatedly varied between the high current and the low current (the maximum number of repetitions: 99 times) within these discharge times. In this case, the range in which the high current can be taken is 1 ampere to 30 amperes, and the range in which the low current can be taken is 50% to 99% of the high current.

  As described above, by shortening the discharge time and repeatedly lowering the discharge current within the discharge time, arc discharge with weak discharge energy becomes possible, and thereby the nitride coating is applied to the fine region. Can be formed.

  In addition, before performing arc discharge, it is preferable to blow nitrogen gas into the fine region for about 0.3 milliseconds to about 3.0 milliseconds. As a result, the arc can be stabilized. Moreover, it is preferable to blow nitrogen gas on the fine region for about 0.3 milliseconds to about 9.9 milliseconds after the arc discharge. Thereby, oxidation prevention of the heating part of a titanium member can be aimed at.

  When the torch portion 10 is brought close to the fine region, the distance between the tungsten electrode 12 and the titanium material is preferably about 0.2 mm to about 0.5 mm.

  Next, a 3D-Micro Welder apparatus (three-dimensional microwelding apparatus) used when carrying out the method of the present invention will be briefly described. The 3D-Micro Welder apparatus is an apparatus developed by the present inventors, and a patent application has already been filed (Japanese Patent Application No. 2003-69281). In the 3D-Micro Welder apparatus, the principle of arc generation itself is substantially the same as that of the conventional TIG welder, but the discharge energy can be set very small compared to the conventional TIG welder, It is characterized in that the electrode position can be freely controlled.

  2A is a schematic longitudinal sectional view of the 3D-Micro Welder device, and FIG. 2B is a view taken along line 2b-2b in FIG. 2A. 2A and 2B, a 3D-Micro Welder apparatus generally indicated by reference numeral 500 includes a modeling section 520 serving as a central portion of the apparatus 500 and a driving section disposed below the modeling section 520. 530, an elevating section 540 disposed on the back of the modeling section 520, an exhaust section 510 disposed above the modeling section 520, and a control section 550 disposed below the driving section 530 and the lifting section 540. ing. Each section and part of the device 500 is surrounded by a panel-like member 501.

  The modeling section 520 accommodates the torch unit 10, and the torch unit 10 is configured to be movable in the vertical direction (Z direction) by each mechanism provided in the elevating section 540 described later. A modeling table 521 configured to be able to move to an arbitrary position in the horizontal direction (X direction and Y direction) is provided below the torch portion 10 of the modeling section 520. A CCD camera 522 is disposed in front of the torch unit 10 in order to obtain information such as confirmation of the operating state of the torch unit 10 and remote adjustment of an electric arc.

  The drive section 530 is provided with an electric motor 531 and a horizontal drive device 532 for moving the modeling table 521 to an arbitrary position in the horizontal direction (X direction and Y direction). The modeling section 520 and the drive section 530 are partitioned by a panel-like member 501 except for the movable range of the modeling table 521.

  An elevator 541 is accommodated in the elevator section 540, and a support beam 544 fixed to the elevator 541 is connected to the torch unit 10. The elevator 541 is connected to the electric motor 542 via the piston 543, and is configured to move the torch unit 10 to an arbitrary position in the vertical direction by controlling the rotation direction and the rotation amount of the electric motor 542. Has been.

  The exhaust portion 510 is provided with an axial exhaust fan 511 so as to penetrate the panel-like member 501 that partitions the modeling section 520. The exhaust part 510 guides the exhaust from the exhaust duct 505 to the outside. In addition, the arrow in Fig.2 (a) shows the direction of exhaust_gas | exhaustion.

  The control section 550 accommodates a programmable controller unit 551, a wire harness unit 552, a collective terminal block 553, and a power supply cable 554.

  Coordinate (X, Y, Z) data of the fine region to be subjected to the surface treatment, data on the discharge time, etc. are stored in advance in the storage device of the programmable controller unit 551, and the electric motors 531 and 542 are based on these data. Is driven by sending a signal to arc discharge in a fine region. The accuracy of coordinates in the 3D-Micro Welder apparatus 500 is 0.1 micrometers, and the accuracy of the discharge time is 0.5 milliseconds. The apparatus 500 controls the discharge position, the moving speed thereof, the discharge current, and the discharge time to form a nitride coating on the fine region.

  Next, an experiment conducted to verify that a nitride coating can be formed even by arc discharge with weak discharge energy will be described. In the experiment, a tungsten electrode (diameter: about 1 mm) was placed above a disc-shaped pure titanium sample (diameter: 10 mm, height: 3 mm) using the 3D-MicroWelder apparatus described above, and arc discharge was performed. The current conditions and discharge time during the experiment were controlled by a computer and were 6 to 24 amps and 91 ms. The flow rate of nitrogen gas was 2.5 liters / minute. The distance between the tungsten electrode and the pure titanium sample was 0.4 mm to 2 mm, the discharge position interval was 0.1 mm to 1 mm, and the discharge time interval was 3 seconds. In the experiment, structural observation, concentration analysis, XRD analysis, and hardness test were performed on the sample thus subjected to arc discharge.

  When the appearance of the sample subjected to arc discharge under conditions of a discharge current of 12 amperes and a discharge time of 1 cycle was observed, traces of a discharge (diameter of about 0.9 mm) showing a golden color were observed on the surface of the sample. Next, when a structure in a longitudinal section perpendicular to the treated surface of the sample was observed, dendrites were observed. Thereby, it can be seen that the region once melted despite the weak discharge energy. The shape of the melting region was a hemisphere with a maximum depth of about 140 μm, and the melting mark was formed so that the center was raised. In addition, the dendrite grew linearly from the surface toward the bottom of the molten region.

  Subsequently, in order to confirm that it was titanium nitride that was generated in the coating layer, concentration analysis was performed with an EPMA (microscopic X-ray analyzer) in the depth direction of the sample. The result is as shown in FIG. In the graph of FIG. 3, the horizontal axis represents the distance from the sample surface, the vertical axis represents the concentration, the diamond points indicate the titanium concentration, and the rectangular points indicate the nitrogen concentration. From the graph of FIG. 3, it can be seen that nitrogen penetrates into the sample, and the ratio of titanium and nitrogen on the outermost surface of the sample is about 1: 1 in atomic ratio. From this result and the XRD analysis result, it was found that TiN was formed near the outermost surface of the sample. Further, it was found that the concentration of nitrogen decreased with increasing distance from the surface of the sample, and nitrogen penetrated to about 140 μm despite a low voltage of 12 amperes, 91 milliseconds, and a short time.

  Subsequently, a micro Vickers hardness test was performed in order to confirm how nitriding affects the hardness. The result is as shown in FIG. In the graph of FIG. 4, the horizontal axis represents the distance from the sample surface, and the vertical axis represents the Vickers hardness. The Vickers hardness in the vicinity of the outermost surface of the sample was about 1800, and a hardness substantially equivalent to that obtained when a conventional TIG welder was used was obtained. The hardness decreased as it proceeded in the depth direction from the sample surface, and the hardness in the vicinity of the bottom of the melted portion was approximately the same as that of the untreated sample. From this test, it was found that a cured layer of about 100 μm can be formed.

  The above experiments confirmed the formation of a nitride coating having a width of the order of mm and a thickness of the order of μm on the pure titanium sample, and proved the effectiveness of the method of the present invention.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say, it is something.

It is the schematic which showed the state which is implementing surface treatment by the method of this invention. FIG. 2 (a) is a longitudinal sectional view of a 3D-MicroWelder apparatus used for carrying out the method of the present invention, and FIG. 2 (b) is a view taken along line 2b-2b in FIG. 2 (a). It is. It is the graph which showed the result of the concentration analysis by EPMA with respect to the depth direction of the sample obtained by the experiment conducted in order to demonstrate the effectiveness of the method of this invention. It is the graph which showed the result of the hardness test in the depth direction of the sample obtained by the experiment conducted in order to demonstrate the effectiveness of the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Torch part 10a Nitrogen gas supply port 12 Tungsten electrode 500 3D-Micro Welder apparatus 510 Exhaust part 520 Modeling section 530 Drive section 540 Elevating section 550 Control section

Claims (4)

A method of selectively surface-treating a desired fine region of a titanium material,
A method of forming a nitride coating by performing arc discharge with weak discharge energy while blowing a predetermined flow rate of nitrogen gas to the fine region. The method according to claim 1, wherein the flow rate is from 2.5 liters / minute to 30 liters / minute. 3. The method according to claim 1, wherein nitrogen gas is blown into the fine region for 0.3 to 3.0 milliseconds before performing the arc discharge. The method according to any one of claims 1 to 3, wherein after the arc discharge, nitrogen gas is blown into the fine region for 0.3 milliseconds to 9.9 milliseconds.

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