JP5191298B2 - Method for producing wear-resistant metal body - Google Patents

Description

  The present invention relates to a method for producing a wear-resistant metal body obtained by modifying the surface of a cemented carbide.

For example, when manufacturing an exhaust gas purification filter using ceramics mainly composed of silicon carbide (SiC), a raw material mainly composed of silicon carbide is extruded through a mold.
The mold used for the extrusion molding is made of a cemented carbide having excellent wear resistance, but the hardness of the silicon carbide particles is extremely high, and the HV hardness is about 2500, and the HV hardness of the mold. It is higher than about 1800.
Therefore, there is a problem that the inner wall of the slit for molding the ceramic raw material in the mold is worn early by repeating the extrusion molding.

  Regarding the wear mechanism of such a cemented carbide, it has been reported that tungsten carbide (WC) particles constituting the cemented carbide fall off due to the flow of silicon carbide (non-patent). Reference 1). That is, as shown in FIGS. 15A and 15B, in the cemented carbide 2 in which the tungsten carbide particles 21 are bonded by the binding phase 22 made of cobalt (Co), the tungsten carbide particles 21 exposed on the surface thereof are exposed. As the SiC particles 5 collide, the tungsten carbide particles 21 gradually fall off. Thereby, the wear of the cemented carbide 2 proceeds.

Therefore, in order to prevent the tungsten carbide particles 21 from falling off, a technique for firmly bonding the tungsten carbide particles 21 on the surface of the cemented carbide 2 is desired.
In this regard, it has been reported that the WC-Cu system exhibits stronger resistance to wear than the WC-Co system, and the resistance to wear increases by 30 to 60% (Non-Patent Document 2).

Shuichi Ishikawa et al., “Construction of a database for friction and wear in mold materials”, Proceedings of Mold Engineer Conference 2004, No. 211 June 2004 p. 132-133 "Wear-Resistant WC Composite Hard Coating by Brazing" by J. Bao, JW Newkirk, S. Bao, "Wear-Resistant WC Composite Hard Coating by Brazing" "Journal of Materials, Engineering and Performance, Vol. 13 (4) (Volume 13 (4)), August 2004 (August 2004) p.385-388.

  Therefore, there has been a demand for a wear-resistant metal body having improved wear resistance by forming a modified surface layer made of WC-Cu on the surface thereof as a cemented carbide used in the above-described mold. Further, such a wear-resistant metal body is not only limited to a mold, but also a cemented carbide metal body in various fields where wear is a problem.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a method for producing a wear-resistant metal body having excellent wear resistance.

The present invention includes an etching step of forming an etched surface obtained by etching a surface of a cemented carbide formed by bonding tungsten carbide particles with a binder phase with an acid to remove a part of the binder phase;
Thereafter, copper is gasified by irradiating a copper target disposed with the cemented carbide in the chamber with an electron beam, and the gasified copper is liquefied on the etching surface to impregnate the grain boundaries of the tungsten carbide particles. By performing the impregnation step,
A method for producing a wear-resistant metal body is characterized in that a modified surface layer in which the tungsten carbide particles are bonded by copper is formed on the surface of the cemented carbide (Claim 1).

Next, the effects of the present invention will be described.
The manufacturing method of the wear-resistant metal body includes the copper impregnation step, gasifies copper and supplies it to the etching surface, and liquefies the gasified copper on the etching surface to form grain boundaries of the tungsten carbide particles. Impregnate. That is, the gasified copper enters the fine grain boundary between the tungsten carbide particles formed on the etched surface, and the copper liquefied on the etched surface further impregnates the fine grain boundary of the tungsten carbide particle by capillary action. To go.

  That is, it can be seen from the following Non-Patent Documents 3 and 4 that the equilibrium contact angle between the molten oxygen-free copper and the tungsten carbide base material is 0 ° (± 5 °) under certain conditions. As described above, copper is almost completely wetted with the surface of the tungsten carbide particles, and the grain boundaries are impregnated.

<Non-Patent Document 3> G. Kaptay, E. Bader and L. Bolyan, “Interfacial Forces and Energy in Manufacturing Metal Matrix Composites” (Interfacial Forces and Energies Relevant to Production of Metal Matrix Composites ”, Materials Science Forum, Vols. 329-330 (2000), p.151-156
<Non-Patent Document 4>"ON Wetability and Bonding of Cobalt Phase Bonded Tungsten Carbide by Liquid Copper" by ON Verezub, L. Zoltai, and G. Kaptay Source: e-journal with ISSN 1586-0140, Vol. 4, No. 1 (Vol. 4 No. 1 Nov. 2003)

Then, as the copper solidifies, a modified surface layer in which the tungsten carbide particles are bonded by copper can be formed on the surface of the cemented carbide.
As described above, the modified surface layer is excellent in wear resistance. For example, even when a ceramic raw material mainly composed of silicon carbide passes through the slit repeatedly, wear due to the ceramic raw material can be suppressed.

  As described above, according to the present invention, a method for producing a wear-resistant metal body having excellent wear resistance can be provided.

In the present invention (Claim 1), the wear-resistant metal body is, for example, a mold for molding an exhaust gas purification filter made of ceramics mainly composed of silicon carbide, a mold for pultruding a steel radial, or the like. In addition to these various molds, it can be used as various metal bodies made of cemented carbide that requires chipping resistance, wear resistance, and corrosion resistance.
Further, the modified surface layer may be formed on the entire surface of the cemented carbide or a part thereof.
Moreover, as said binder phase, cobalt (Co) and nickel (Ni) can be used, for example.

Further, it is preferable that a buffer plate for relaxing the energy of the electron beam irradiated to the cemented carbide is disposed between the electron beam irradiation source and the cemented carbide.
In this case, it is possible to prevent the electron beam from being directly irradiated onto the cemented carbide and to reduce the impact on the cemented carbide. Thereby, the possibility of damaging the cemented carbide can be prevented.

Moreover, it is preferable to remove the oxide adhering to the tungsten carbide particles by treating the etching surface with an alkali solution after the etching step and before the copper impregnation step. .
In this case, the wettability of the copper impregnated in the copper impregnation step with respect to the tungsten carbide particles can be ensured, and the bonding strength of the tungsten carbide particles with copper can be sufficiently ensured. Therefore, the tungsten carbide particles can be more reliably prevented from falling off and the wear resistance of the wear resistant metal body can be improved.

Moreover, it is preferable that the removal depth of the said binder phase in the said etching process is more than the average particle diameter of the said tungsten carbide particle (Claim 4).
In this case, the modified surface layer is sufficiently formed, and the wear resistance can be effectively improved.
When the removal depth is less than the average particle diameter of the tungsten carbide particles, the thickness of the modified surface layer becomes insufficient, and it may be difficult to obtain sufficient wear resistance.
For example, if the average particle diameter of the tungsten carbide particles is about 1 μm, the removal depth of the binder phase is preferably 1 μm or more. In this case, the removal depth is preferably 10 μm or less. That is, when the average particle diameter of the tungsten carbide particles is about 1 μm, if the removal depth exceeds 10 μm, the tungsten carbide particles may fall off the surface of the cemented carbide in the handling after the etching step. There is.

Example 1
A method for producing a wear-resistant metal body according to an embodiment of the present invention will be described with reference to FIGS.
In this example, a method of manufacturing a wear-resistant metal body used as a mold 1 (FIG. 5) for extruding an exhaust gas purification filter made of ceramics mainly composed of silicon carbide will be described.

  First, as shown in FIG. 2, a cemented carbide 2 formed by bonding tungsten carbide particles 21 with a bonding phase 22 made of cobalt is prepared. Then, by cutting the cemented carbide 2, as shown in FIGS. 5 and 6, the slit 11 for forming the partition wall of the exhaust gas purification filter and the raw material mainly composed of silicon carbide are supplied to the slit 11. A supply hole 12 is formed.

  Thus, the following etching process and copper impregnation process are performed on the cemented carbide 2 processed into the shape of the mold 1.

  In the etching step, at least the inner surface 111 of the slit 11 is etched with acid to form an etched surface 112 from which a part of the binder phase 22 is removed as shown in FIG.

In the copper impregnation step, as shown in FIG. 7, the copper target 316 disposed with the cemented carbide 2 in the chamber 314 is irradiated with an electron beam 301 to gasify the copper, and the gasified copper is etched. It is liquefied on the surface 112 and impregnated in the grain boundaries of the tungsten carbide particles 21.
Thereby, as shown in FIG. 1, the modified surface layer 113 in which the tungsten carbide particles 21 are bonded by the copper 23 is formed on the inner surface 111 of the slit 11.

Below, the manufacturing method of the abrasion-resistant metal body actually performed is demonstrated concretely.
As shown in FIG. 2, the cemented carbide 2 is formed by bonding tungsten carbide particles 21 with a bonding phase 22 made of cobalt. In the etching step, the surface including the inner surface 111 of the slit 11 provided in the cemented carbide 2 was etched.
A strong acid was used as the etchant. As the strong acid, a product obtained by diluting Fuji Aceclean (registered trademark) FE-17 of Fuji Acetylene Kogyo Co., Ltd. with pure water so that the weight ratio with pure water was 1: 3 was used. . The composition of Fujiseclean FE-17 is HNO ₃ : HF: H ₂ O = 53.8: 8.0: 38.2 in weight ratio.
By immersing the cemented carbide 2 in this etching solution for 400 seconds while applying ultrasonic waves, pickling was performed to form an etching surface 112. Thereafter, it was washed with pure water and dried.
After this drying, as shown in FIG. 9, when the cross section of the etching surface 112 was observed with SEM (scanning electron microscope), the removal depth of the binder phase 22 was 5 to 7 μm.

Next, the etching surface 112 of the cemented carbide 2 was surface-treated with an alkaline solution. That is, the cemented carbide was immersed in an alkaline solution for 60 minutes while applying ultrasonic waves. As the alkaline solution, Murakami's reagent was used as it was without being diluted. The composition of Murakami's reagent is 10% by weight potassium hydroxide (KOH) + 10% by weight potassium ferricyanide (K ₃ [Fe (CN) ₆ ]) + balance water (H ₂ O).
Thereafter, it was washed with pure water and dried.

The surface treatment of the etching surface 112 with the alkaline solution is for removing the thin oxide film 211 formed on the surface of the tungsten carbide particles 21 as shown in FIG. That is, an oxide film 211 made of WO ₃ or the like may be formed on the exposed surface of the tungsten carbide particles 21. Therefore, the oxide film 211 is removed to improve the wettability and adhesion between the copper 23 and the tungsten carbide particles 21 to be impregnated later.

  When the etching surface 112 was observed by EDS after alkali washing and drying, it was confirmed that the oxygen component was sufficiently reduced. Further, when the etched surface 112 was observed with an SEM as shown in FIG. 10, the tungsten carbide particles 21 were not removed. Further, as a result of observation with a magnifying glass, there was no problem in the dimensional tolerance of the cemented carbide 2.

Next, a copper impregnation step was performed. That is, the cemented carbide 2 after acid cleaning and alkali cleaning was loaded into the electron beam irradiation apparatus 3 shown in FIG.
The electron beam irradiation apparatus 3 includes a turntable 33 on which the cemented carbide 2 is placed in a chamber 314, and an irradiation source 30 of an electron beam 301 disposed above the turntable 33. The chamber 314 is connected to a pump 315 for evacuating the chamber 314.

The irradiation source 30 includes a gas introduction part 35 for introducing argon gas, a magnet 312 for exciting the introduced argon gas molecules, and a hollow anode 36 and a hollow cathode 37 for conveying the excited argon molecules to the plasma generation part. A plasma generation unit 38 that converts argon molecules into plasma, a grid 39 that accelerates electrons in the plasma in the plasma generation unit 38 toward the copper target 316, and a drift tube that conveys the electron beam 301 toward the copper target 316. 311. In the plasma generator 38, argon molecules are turned into plasma by a pulsed magnetic field generated by the magnet coil 313 disposed around the plasma generator 38.
The bundle of electron beams 301 that has passed through the grid 39 is converged toward the copper target 316 by the magnetic field of the magnet coil 323 disposed below the chamber 314. 7 indicates a power source for applying a voltage to the hollow anode 36, the hollow cathode 37, the grid 39, and the drift tube 311.

The copper impregnation step was performed using such an electron beam irradiation apparatus 3.
First, a receiving plate 317 made of graphite is disposed on the upper surface of the turntable 33, a copper target 316 is disposed on the upper surface of the receiving plate 317, and the cemented carbide 2 is disposed thereon. As the copper target 316, a copper foil having a thickness of 0.05 mm was used. As shown in FIG. 8, the copper target 316 has a size corresponding to the region where the slit 11 and the supply hole 12 are formed in the cemented carbide 2 and is disposed so as to correspond to the region. That is, the copper target 316 was disposed below the formation region of the supply hole 12.
In addition, a buffer plate 319 made of graphite is disposed above the cemented carbide 2 via a spacer 318.

In this state, the inside of the chamber 314 is evacuated to about 10 ⁻³ Pa, and then the pulsed electron beam 301 is directed from the irradiation source 30 toward the copper target 316 while rotating the turntable 33 at 15 rpm. Irradiated. The electron beam 301 was irradiated with 10,000 pulses at a beam current value of 100 A, an acceleration voltage of 20 kV, a pulse width of 200 μs, and a frequency of 10 Hz. At this time, the irradiation time was 16 minutes and 40 seconds, and the average required power was 4 kW.

As described above, by irradiating the copper target 316 with the electron beam 301, the copper of the copper target 316 is gasified, and the gasified copper passes through the supply hole 12 in the cemented carbide 2 and the inner surface 111 of the slit 11. To reach. The gasified copper is liquefied on the etching surface 112 formed on the inner surface 111 and impregnated in the grain boundaries of the tungsten carbide particles 21.
Thereby, the modified surface layer 113 in which the tungsten carbide particles 21 were bonded by the copper 23 as shown in FIG. 1 was formed on the inner surface 111 of the slit 11.

  After the electron beam irradiation, the cross section of the modified surface layer 113 was observed with an SEM as shown in FIG. 11. As a result, the portion from which the binder phase 22 made of cobalt was removed was almost completely filled with copper 23, and the pores were Not observed. Moreover, the copper 23 in the modified surface layer 113 was deposited not only at the grain boundaries of the tungsten carbide particles 21 but also from the surface S where the tungsten carbide particles 21 exist to the outside by a thickness of 0.3 to 0.5 μm.

Next, the function and effect of this example will be described.
The manufacturing method of the mold includes the copper impregnation step, gasifies copper and supplies it to the etching surface 112, and liquefies the gasified copper on the etching surface 112 to impregnate the grain boundaries of the tungsten carbide particles 21. Let That is, the gasified copper enters the fine grain boundary between the tungsten carbide particles 21 formed on the etching surface 112, and the copper liquefied on the etching surface 112 is further refined by the capillary phenomenon. Impregnate into. As the copper solidifies, a modified surface layer 113 in which tungsten carbide particles 21 are bonded by copper 23 is formed on the surface of the cemented carbide 2, that is, at least the inner surface 111 of the slit 11, as shown in FIG. can do.

Such a modified surface layer 113 is excellent in wear resistance as described above. Therefore, even when a ceramic raw material mainly composed of silicon carbide passes through the slit 11 repeatedly, wear caused by the ceramic raw material can be suppressed, and the long-life mold 1 can be obtained.
Further, as shown in FIG. 8, since the buffer plate 319 is disposed between the irradiation source 33 of the electron beam 301 and the cemented carbide 2, the electron beam 301 is prevented from being directly irradiated onto the cemented carbide 2, The impact on the cemented carbide 2 can be reduced. Thereby, the possibility of damaging the cemented carbide 2 can be prevented.

  Further, after the etching step and before the copper impregnation step, the etching surface 112 is treated with an alkaline solution to remove oxide (oxide film 211) attached to the tungsten carbide particles 21. Thereby, the wettability with respect to the tungsten carbide particle 21 of the copper 23 impregnated in the said copper impregnation process can be ensured, and the bond strength of the tungsten carbide particle 21 by the copper 23 can fully be ensured. Therefore, the tungsten carbide particles 21 can be more reliably prevented from falling off and the wear resistance of the mold 1 can be improved.

  Moreover, since the removal depth of the binder phase 22 in the etching step is 5 to 7 μm, the modified surface layer 113 is sufficiently formed, and the wear resistance can be effectively improved.

  As described above, according to this example, it is possible to provide a method for manufacturing a wear-resistant metal body having excellent wear resistance.

(Example 2)
In this example, as shown in FIGS. 12 to 14, a friction / wear test of the cemented carbide 2 was performed in order to confirm the effect of the present invention.
First, the modified surface layer 113 was formed on the surface of the cemented carbide 2 in the same manner as in Example 1. At this time, the cemented carbide 2 is not the mold 1 shown in Example 1, but a plate-like test body 41 having a flat surface 411 as shown in FIG. 12, and the modified surface layer 113 is formed on the surface 411. (FIG. 1) was formed. This sample is designated as Sample 1.
On the other hand, for comparison, a cemented carbide plate-like body (test body 41) made of the same material was prepared, and sample 2 was prepared in which no modified surface layer was formed.

For these specimens 41 (Sample 1 and Sample 2), the friction coefficient was measured using a HEIDON (trademark of Shinto Kagaku Co., Ltd.) wear and friction tester, and the wear resistance was evaluated.
A test method using the wear / friction tester will be described with reference to an image diagram shown in FIG. As shown in the figure, an indenter ball 42 made of silicon carbide having a diameter of 10 mm is pressed against the surface 411 of the test body 41 with a load of 100 g (0.98 N) (arrow F), and linearly slid by a distance of 6 mm. Move (arrow M). At this time, the indenter sphere 42 does not rotate but always abuts the test body 41 at the same position on the spherical surface. This sliding was performed 1000 times and the friction coefficient was measured.

  FIG. 13 shows the measurement results of the friction coefficient in Sample 1 and Sample 2. In the figure, the curve L1 represents the result of the sample 1, and the curve L2 represents the result of the sample 2. Here, the friction coefficients at the time of 5 reciprocations, 50 reciprocations, 100 reciprocations, 500 reciprocations, and 1000 reciprocations are plotted, and these are connected by curves L1 and L2, respectively. The friction coefficient at each time point means the average of the friction coefficients for five consecutive reciprocations up to that time point. That is, for example, the friction coefficient at the time of 5 reciprocations means the average friction coefficient of the first reciprocation to the fifth reciprocation, and the friction coefficient at the time of 500 reciprocations is the average of the 446 reciprocations to 500 reciprocations. It means the coefficient of friction.

  As can be seen from FIG. 13, the coefficient of friction of each sample gradually increases as the number of sliding increases. However, the friction coefficient (L1) of sample 1 is greatly reduced as compared to the friction coefficient (L2) of sample 2. That is, the sample 1 using the present invention has a low coefficient of friction against silicon carbide, and therefore has low resistance and is difficult to wear.

  Further, after the indenter sphere 42 was slid back and forth 1000 times, and further after 20000 slid back and forth, the wear marks of the indenter sphere 42 were observed. Here, the wear mark of the indenter sphere 42 was observed instead of the wear mark of the test body 41 because the hardness of the cemented carbide is high and it is difficult to observe the wear state. This is because the degree of wear of the test body 41 is indirectly evaluated by the marks. That is, the larger the wear trace of the indenter sphere 42, the stronger the test body 41 is against the indenter sphere 42. The degree of wear is smaller, and conversely, the smaller the wear trace of the indenter sphere 42 is, the smaller the wear of the indenter sphere 42 is. Therefore, the test body 41 is weak, and the degree of wear is large.

  FIG. 14 shows an SEM photograph of the wear scar of the indenter sphere 42 obtained by this test. (A) of the figure is the wear scar of the indenter sphere that was slid back and forth 1000 times on the sample 1, (B) is the wear track of the indenter sphere that was slid 20,000 times back and forth on the sample 1, and (C) is the sample 2 (D) shows the wear scar of the indenter sphere that was slid back and forth 20000 times, respectively. Moreover, in each figure, the comparatively white substantially circular shaped part represents a wear trace.

As can be seen from the figure, both Sample 1 and Sample 2 surely have larger wear marks at the time of 20000 reciprocation than at the time of 1000 reciprocation. However, the wear scar diameter of the indenter sphere 42 used for the sample 2 is 170 μm at the time of 1000 reciprocations and 320 μm at the time of 20000 reciprocations, whereas the diameter of the wear scars of the indenter sphere 42 used for the sample 1 is 320 μm. Was as large as 240 μm at 1000 round trips and 530 μm at 20000 round trips. That is, at the time of 20000 reciprocation, the diameter of the wear scar of the indenter sphere 42 used for the sample 1 which is an invention product is 2.75 times the diameter of the wear scar of the indenter sphere 42 used for the sample 2 which is a comparative product. It was big.
From this result, it can be seen that the wear strength of the sample 1 is sufficiently larger than the wear strength of the sample 2, and according to the present invention, it can be seen that a mold having excellent wear strength can be obtained.

  In addition, in the said Example 1, although demonstrated about the manufacturing method of the metal mold | die for shape | molding an exhaust gas purification filter, the abrasion-resistant metal body obtained by the manufacturing method of this invention is not limited to this, for example, steel radial. In addition to various molds such as a mold for pultrusion molding, it can be used as various metal bodies made of cemented carbide that requires chipping resistance, wear resistance, and corrosion resistance.

Sectional drawing of the modified surface layer vicinity of the cemented carbide in Example 1. FIG. Sectional drawing of surface layer vicinity of the cemented carbide alloy in Example 1. FIG. Sectional drawing of the cemented carbide near the etching surface after the etching process in Example 1. FIG. 2 is a cross-sectional view of tungsten carbide particles on which an oxide film is formed in Example 1. FIG. Sectional drawing of the cemented carbide alloy (metal mold | die) in Example 1. FIG. Sectional drawing of the slit and supply hole which were formed in the cemented carbide alloy (metal mold | die) in Example 1. FIG. 1 is an explanatory diagram of an electron beam irradiation apparatus in Embodiment 1. FIG. Explanatory drawing of the cemented carbide and the peripheral member with which the electron beam irradiation apparatus in Example 1 was loaded. The SEM photograph substituted for drawing which shows the cross section of the etching surface vicinity after the etching by the acid in Example 1. FIG. The SEM photograph substituted for drawing in Example 1 showing the etched surface after alkali treatment. The SEM photograph substituted for drawing which shows the section near the modification surface layer after the copper impregnation process in Example 1. Explanatory drawing explaining the method of an abrasion and a friction test in Example 2. FIG. The diagram which shows the measurement result of the friction coefficient in Example 2. FIG. In Example 2, (A) Abrasion trace of indenter sphere slid 1000 times on sample 1, (B) Abrasion trace of indenter sphere slid 20,000 times on sample 1, (C) 1000 reciprocation slide on sample 2 The drawing substitute SEM photograph which shows the wear trace of the moved indenter ball | bowl, and (D) the wear trace of the indenter ball | bowl which slid to 20000 reciprocatingly, respectively. Explanatory drawing explaining the mechanism of the abrasion of the surface of the cemented carbide by silicon carbide.

Explanation of symbols

1 Mold (Abrasion resistant metal)
DESCRIPTION OF SYMBOLS 11 Slit 111 Inner surface 112 Etching surface 113 Modified surface layer 12 Supply hole 2 Cemented carbide 21 Tungsten carbide particle 22 Bonded phase 23 Copper

Claims (4)

An etching step of etching the surface of the cemented carbide formed by bonding tungsten carbide particles with a binder phase with an acid to form an etched surface by removing a part of the binder phase;
Thereafter, copper is gasified by irradiating a copper target disposed with the cemented carbide in the chamber with an electron beam, and the gasified copper is liquefied on the etching surface to impregnate the grain boundaries of the tungsten carbide particles. By performing the impregnation step,
A method for producing a wear-resistant metal body, comprising forming a modified surface layer in which the tungsten carbide particles are bonded by copper on the surface of the cemented carbide.   The buffer plate for relaxing energy of the electron beam irradiated to the cemented carbide is disposed between the electron beam irradiation source and the cemented carbide according to claim 1. A method for producing a worn metal body.   3. The oxide attached to the tungsten carbide particles is removed by treating the etched surface with an alkaline solution after the etching step and before the copper impregnation step. A method for producing a wear-resistant metal body.   The method for producing a wear-resistant metal body according to any one of claims 1 to 3, wherein a removal depth of the binder phase in the etching step is equal to or greater than an average particle diameter of the tungsten carbide particles.