Friction material, vibration type actuator, optical device, and electronic device

Abstract

To provide a friction material that retains frictional force even under high-humidity conditions while exhibiting high wear resistance.SOLUTION: A friction material comprises a stainless steel-based sintered body having pores, the friction material comprising a nitride phase containing an iron nitride and present on a surface of the friction material, and an interior phase present inside the friction material and adjacent to the nitride phase, the interior phase comprising an austenite phase and a martensite phase, the content of the austenite phase in the interior phase being 75 vol.% or more and 99 vol.% or less, and the Vickers hardness of the interior phase being 300 HV0.1 or more and 600 HV0.1 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a friction material, a vibration type actuator, an optical device, and an electronic device.

Background Art

[0002] There is known a vibration type actuator that relatively moves a vibrating body and a contact body by bringing a vibrating body provided with an electro-mechanical energy conversion element and the contact body into pressure contact, exciting a predetermined vibration in the vibrating body, and applying a frictional driving force from the vibrating body to the contact body. The vibrating body is composed of an elastic body joined with piezoelectric bodies, and the vibration generated by applying a voltage to the piezoelectric bodies is transmitted to the contact body through the elastic body. As described above, since the driving force of the vibration type actuator depends on the frictional force acting between the elastic body and the contact body, the contact body is required to function as a friction material. On the other hand, when the vibration type actuator is left in a high humidity environment, moisture may be adsorbed on the surfaces of the elastic body and the contact body, and the frictional force may decrease.

[0003] Further, in a general vibration type actuator, the elastic body has a protrusion, and the tip of the protrusion is in contact with the contact body. Since a frictional force acts between the elastic body and the contact body, the surface of the contact body gradually wears during driving. The formation of deep wear marks on the contact body surface is not desirable from the viewpoint of maintaining braking performance. Therefore, a contact body having high wear resistance is required for applications that require high braking accuracy.

[0004] Patent Document 1 discloses a technique of using a stainless steel sintered body impregnated with resin as a contact body. Patent Document 1 also describes using a quenched martensitic stainless steel material or an austenitic stainless steel material having a nitride phase formed on the surface as the stainless steel sintered body.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] Here, when assuming longer-term use or when the pressure for bringing the vibrating body into contact with the contacting body is higher, etc., a contacting body having even higher wear resistance is required.

[0007] One object of the present invention is to provide a friction material that maintains frictional force even in a high-humidity environment and has high wear resistance. Another object of the present invention is to provide a vibration type actuator, an optical device, and an electronic device including a friction material that maintains frictional force even in a high-humidity environment and has high wear resistance. Another object of the present invention is to provide a method for manufacturing a friction material that maintains frictional force even in a high-humidity environment and has high wear resistance.

MEANS FOR SOLVING THE PROBLEMS

[0008] The above object is achieved by the following present invention. That is, according to the present invention, there is provided a friction material including a stainless steel sintered body having pores, the friction material having a nitride phase containing an iron nitride compound and present on the surface of the friction material, and an internal phase present inside the friction material and adjacent to the nitride phase, the internal phase including an austenite phase and a martensite phase, the content of the austenite phase in the internal phase being 75 vol% or more and 99 vol% or less, and the Vickers hardness of the internal phase being 300 HV0.1 or more and 600 HV0.1 or less.

[0009] Further, according to the present invention, there is provided a friction material including a stainless sintered body having pores, the friction material having a nitride phase containing an iron nitride compound and present on the surface of the friction material, and an internal phase present inside the stainless sintered body and adjacent to the nitride phase, the internal phase including an austenite phase and a martensite phase, the content of the martensite phase in the internal phase being 1.0 vol% or more and 25 vol% or less, and the Vickers hardness of the internal phase being 300 HV0.1 or more and 600 HV0.1 or less.

[0010] Further, according to the present invention, there is provided a method for manufacturing a friction material including a step of obtaining a sintered body by pressure molding a raw material powder containing stainless powder and then firing the pressure-molded raw material powder, and a nitriding treatment step of forming a nitride phase on the surface of the sintered body, the friction material having a nitride phase containing an iron nitride compound and present on the surface of the friction material, and an internal phase present inside the friction material and adjacent to the nitride phase, the internal phase including an austenite phase and a martensite phase, the content of the austenite phase in the internal phase being 75 vol% or more and 99 vol% or less, and the Vickers hardness of the internal phase being 300 HV0.1 or more and 600 HV0.1 or less.

[0011] Further, according to the present invention, there is provided a method for manufacturing a friction material including a step of obtaining a sintered body by pressure molding a raw material powder containing stainless powder and then firing the pressure-molded raw material powder, and a nitriding treatment step of forming a nitride phase on the surface of the sintered body, the friction material having a nitride phase containing an iron nitride compound and present on the surface of the friction material, and an internal phase present inside the stainless sintered body and adjacent to the nitride phase, the internal phase including an austenite phase and a martensite phase, the content of the martensite phase in the internal phase being 1.0 vol% or more and 25 vol% or less, and the Vickers hardness of the internal phase being 300 HV0.1 or more and 600 HV0.1 or less.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a friction material that maintains frictional force even in a high-humidity environment and has high wear resistance. Further, according to the present invention, it is possible to provide a vibration type actuator, an optical device, and an electronic device including a friction material that maintains frictional force even in a high-humidity environment and has high wear resistance. Further, according to the present invention, it is possible to provide a method for manufacturing a friction material that maintains frictional force even in a high-humidity environment and has high wear resistance.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0014] The inventors of the present invention studied a method for manufacturing a friction material that maintains frictional force even in a high-humidity environment. In the study, it was found that the martensite-based material described in Patent Document 1 has a Vickers hardness that remains at about 600 HV to 800 HV even when it is high. That is, it was found that conventional friction materials do not have sufficient wear resistance in ultra-long-term use or in driving in a state where a vibrating body and a driven body are in contact with a high pressing force.

[0015] On the other hand, in the austenitic material with a nitride phase formed as described in Patent Document 1, although the surface hardness is sufficiently high at 1000 HV or more, the hardness of the internal phase where the nitride phase is not formed is extremely low. Therefore, it has been found that when going through various processing steps and transportation steps, surface defects are likely to occur due to contact between parts or contact with a transportation container or processing jig.

[0016] As a result of further investigation, it has been found that when the amount of austenite phase is small and the hardness is excessive, the wear amount increases significantly. This is considered to be due to local fracture occurring on the surface embrittled by the formation of the nitride phase. That is, in order to ensure the wear resistance as a friction material, it is necessary not to cause such fracture, and as a result of intensive investigation, it has been found that it is important to increase the toughness of the internal phase.

[0017] From such a viewpoint, it has been found that by including an austenite phase having toughness at a certain value or more and setting the hardness at a certain value or less, the wear resistance of the friction material can be improved. Specifically, the content ratio of the austenite phase in the internal phase is 75 vol% or more and 99 vol% or less, and the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less, whereby a friction material having high wear resistance can be provided.

[0018] Hereinafter, the present invention will be described in more detail by giving preferred embodiments.

[0019] [First Embodiment] [Sintering Process] First, the process of manufacturing a sintered body, which is the base material of the friction material, will be described. In the friction material of the present embodiment, from the viewpoint of improving the corrosion resistance in a high humidity environment, it is preferable to use stainless steel powder containing 10.5 wt% or more of Cr (chromium) as the raw material of the sintered body. That is, it is preferable to use a stainless steel sintered body as the sintered body. Further, it is more preferable that the chromium content in the stainless steel sintered body is 16 wt% or less.

[0020] As described above, since a sintered body composed only of an austenite phase has low hardness and surface defects, it is desirable to select martensitic stainless steel powder as a raw material for the sintered body. In order to appropriately control the ratio of the martensite phase and the austenite phase contained in the sintered body, it is necessary to appropriately select the process conditions of the sintering and heat treatment processes described later.

[0021] From the viewpoint of hardness adjustment, a mixed powder mixed with carbon powder may be used as a raw material for the sintered body. However, when an excessive amount of carbon powder is mixed, the free carbon powder provides a lubricating action and reduces the frictional force. Therefore, the addition amount of carbon powder is limited to 2 wt%.

[0022] A molding die (mold) of a desired shape is prepared according to the application, the raw material powder is filled into the molding die, and a molded body is produced by pressure molding. The obtained molded body is fired at a predetermined temperature and time to produce a sintered body.

[0023] FIG. 1 shows a surface schematic diagram of the friction material according to the present embodiment. In the friction material 1, gaps generated when the stainless steel raw material particles 2 are bonded remain as pores 3. Further, if necessary, a part of the pores 3 may be made to contain resin by an impregnation process described later. From the viewpoint of ensuring wear resistance, the volume ratio occupied by the pores 3, that is, the porosity of the stainless steel sintered body, is preferably 15% or less. Also, from the viewpoint of improving the frictional force in a high humidity environment, the porosity is preferably 3% or more.

[0024] FIG. 2 shows a cross-sectional image diagram of the friction material according to the first embodiment. The friction material 1 has a nitride phase 21 containing a nitride (nitrogen compound of iron) on the surface, and an internal phase 22 adjacent to the nitride phase. Note that FIG. 2 does not show the whole of the friction material according to the present embodiment, and a part thereof is omitted.

[0025] The structure and mechanical properties of the sintered body greatly affect the structure and mechanical properties of the internal phases in the finished product after nitriding treatment described later, and they are directly related to the effects of the invention. Factors such as the amount of carbon powder mixed in the manufacturing process up to the sintering process, the sintering temperature, and the cooling rate greatly affect the volume ratio and hardness of the martensite phase and austenite phase of the sintered body to be produced. In order to obtain a sintered body having martensite phase and austenite phase with a volume ratio within the preferable range described later, it is necessary to appropriately select the above factors.

[0026] Specifically, when manufacturing the sintered body is completed only by the sintering process of sintering the molded body without performing post-processes such as heat treatment or sub-zero treatment, it is preferable to perform the sintering process at a temperature of 1150°C or higher.

[0027] Also, post-treatment may be performed after the sintering process from the viewpoint of more precisely controlling hardness and toughness. Specifically, after performing sub-zero treatment at a temperature of -100°C or lower for 1 minute or more after the sintering process, it is preferable to perform heat treatment at a temperature of 1150°C or higher. As another example, it is preferable to perform sub-zero treatment at a temperature of -100°C or lower for less than 1 minute after the sintering process and then not perform heat treatment.

[0028] Note that the sintering process and heat treatment are more preferably performed at 1300°C or lower from the viewpoint of controlling the porosity within a suitable range. In the sintering process, it is also possible to adjust the porosity of the sintered body by the molding pressure and sintering temperature. For the evaluation of porosity, the Archimedes method, the gas replacement method, and the method calculated from dimensions and weight are effective.

[0029] (Nitriding treatment process) Next, the nitriding treatment will be described. The nitriding treatment method in this embodiment is not limited, and it can be processed by any of the commonly used ion nitriding treatment, radical nitriding treatment, gas nitriding treatment, gas soft nitriding treatment, salt bath nitriding treatment, etc. Among them, ion nitriding treatment can form a relatively thick nitride phase, and it is a very effective method when a part of the surface layer is removed by finishing polishing described later. In any method, by controlling the temperature and treatment time in the nitriding treatment, a nitride phase with a desired thickness and hardness can be formed. Also, similarly depending on the material selected, since the thickness and hardness of the nitride phase are affected, it is desirable to experimentally determine appropriate treatment conditions.

[0030] The nitride phase formed by the nitriding treatment contains a nitrogen compound of iron. Also, as a nitrogen compound of iron, the nitride phase contains either one of the ε-phase (Fe 2-3 N) and the γ'-phase (Fe4N), or a mixed phase of the ε-phase (Fe 2-3 N) and the γ'-phase (Fe4N).

[0031] Specifically, the Vickers hardness of the nitride phase is preferably 1000 HV0.1 or more, and the thickness of the nitride phase in the finished friction material is preferably 1.0 μm or more. When performing surface grinding or polishing as a subsequent process, it is desirable to determine the target nitride phase thickness in the nitriding treatment in consideration of the removal amounts of these.

[0032] When flatness is required for the parts, it is preferable to perform grinding or polishing to remove warping and distortion generated after sintering to ensure flatness, and then perform the nitriding treatment. If a flattening process is performed after the nitriding treatment, more nitride layers will be removed, so a longer treatment time is required to ensure the thickness of the final nitride layer. As described above, by performing the nitriding treatment after flattening, the minimum required treatment time can be selected.

[0033] (Resin impregnation process) Next, the resin impregnation process will be described. By using the sintered body as a base material, the frictional force in a high-humidity environment can be increased. However, by containing resin in the pores, an even higher frictional force can be obtained. From such a perspective, resin impregnation is not necessarily required in the present invention, but a friction material having a higher frictional force in a high-humidity environment can be obtained. As the resin impregnation process, for example, a general vacuum impregnation treatment can be used.

[0034] The vacuum impregnation treatment is performed, for example, according to the following procedure. One or more sintered bodies are placed in a vacuum chamber, evacuated to below atmospheric pressure to remove air and adsorbed moisture in the pores of the sintered body, and then a resin material as an impregnating material is introduced into the chamber. As the resin material to be impregnated, resins of various material systems such as acrylic, epoxy, silicone, phenolic, and polyester are used, and the components are appropriately adjusted to have a low viscosity at room temperature for easy impregnation.

[0035] To promote impregnation deeper inside, after pressurizing to a pressure above atmospheric pressure, the chamber is opened, the resin on the surface is removed by centrifugation or wiping, and then the impregnated resin is cured by heating. The heat treatment uses appropriate means according to the resin material to be selected, but simply, methods such as immersing in hot water at a temperature of 80°C or higher or treating at a desired temperature using an oven can be used. By using such a vacuum chamber, more resin can be impregnated deeper inside. Note that the resin impregnation process in this embodiment is not limited to the above, and for example, a method of applying an appropriate amount of impregnated resin material to the friction surface, heating to lower the viscosity, and using gravity for impregnation may also be used.

[0036] (Finishing and Polishing Process) When used for applications that require high braking performance, such as the driven body of a vibration type actuator, it is also possible to perform polishing to reduce the surface roughness of the sliding surface. Examples of polishing means include polishing using fixed abrasive grains, polishing using loose abrasive grains, and barrel polishing. However, caution is required because if the polishing abrasive grains are too large, polishing marks with a large period will be formed on the surface, the pores generated by sintering will be crushed, and the impregnated resin will not be exposed on the surface, resulting in insufficient achievement of the effects of the present invention. When it is not necessary to reduce the surface roughness depending on the application, post-processing is not always required.

[0037] (Characteristics of the friction material) The friction material produced in this way has a nitride phase formed on its surface and an internal phase formed adjacent to the nitride phase inside. The nitride phase, as a nitrogen compound of iron, contains either one of the ε-phase (Fe 2-3 N) and the γ'-phase (Fe4N), or a mixed phase of the ε-phase (Fe 2-3 N) and the γ'-phase (Fe4N).

[0038] The internal phase contains an austenite phase and a martensite phase. The content ratio of the austenite phase in the internal phase is preferably 75 vol% or more and 99 vol% or less, and more preferably 75 vol% or more and 97 vol% or less. In other words, the content ratio of the martensite phase in the internal phase is preferably 1.0 vol% or more and 25 vol% or less, and more preferably 3.0 vol% or more and 25 vol% or less. Furthermore, the Vickers hardness of the internal phase is preferably 300 HV0.1 or more and 600 HV0.1 or less, and more preferably 390 HV0.1 or more and 580 HV0.1 or less.

[0039] By suppressing the austenite content in the internal phase and increasing the hardness, surface defects caused by collisions between the above-mentioned parts can be suppressed. On the other hand, when the austenite content is low and the hardness is excessive, it has been found that the wear amount increases significantly. This is considered to be due to local fracture occurring on the surface embrittled by the formation of nitride phases. That is, in order to ensure the wear resistance of the friction material, it is necessary not to cause such fractures. As a result of intensive studies, it has been found that it is important to increase the toughness of the internal phase for this purpose. From such a perspective, in order to improve the wear resistance of the friction material, it is necessary that the sintered body contains an austenite phase having toughness at a certain ratio or more and the hardness of the sintered body is below a certain value.

[0040] In order to control the structure and hardness of the internal phase, mainly the sintering process or the subsequent heat treatment process is important. However, since the nitriding treatment process is also exposed to a thermal environment exceeding 400°C, in some cases, organizational changes occur due to the annealing effect. From such a perspective, it is desirable to produce a sintered body that does not cause significant organizational changes even in the nitriding treatment. In that case, the austenite phase ratio and hardness obtained by sintering or heat treatment are directly inherited by the internal phase. When changes in the nitriding treatment cannot be avoided, it is possible to obtain the same effect of the invention by determining the austenite phase ratio and hardness to be achieved at the time of the sintered body based on the tendency of the changes.

[0041] (Analysis of friction material) For the quantitative evaluation of the crystal phase, a method using magnetic induction such as a ferrite meter can be used. Thereby, the volume ratio occupied by the martensite phase, which is a ferromagnetic body, in the sample can be measured. When the crystal phase generated after sintering or heat treatment consists only of the austenite phase and the martensite phase, the portion other than the measured martensite phase can be evaluated as the austenite phase content ratio.

[0042] When carbides or the like are included, it is necessary to separately evaluate their content ratios. In this case, quantification by X-ray diffraction or methods such as analyzing the sample cross-section using an electron microscope equipped with an energy dispersive X-ray analyzer (EDX) and quantifying the carbide phase present in the observation image by image processing are effective. Also, since sintered materials contain many pores, it is necessary to determine the ratio contained in the net stainless steel material excluding them. For example, if the measured value by the magnetic induction method is 40% and the total porosity of the sintered body is 10%, the martensite ratio based on 90% excluding pores, that is, 40 / 90 = 44.4% is the martensite ratio to be determined. And when the sample consists only of the austenite phase and the martensite phase, 100 - 44.4 = 55.6% is the content ratio of the austenite phase to be evaluated.

[0043] When evaluating the internal phase after the nitride phase is formed, accurate evaluation is possible by breaking the sample to check the thickness of the nitride phase from the fracture surface and evaluating after removing the nitride phase on the sample surface by polishing or the like. However, when the thickness of the nitride phase is extremely small compared to the thickness of the sample, such considerations are not always necessary. That is, in the method using magnetic induction, since the depth to be measured is deep and evaluation of the interior is possible, when the ratio of the thickness of the nitride phase to the thickness of the sample is as small as the measurement error, there is no problem in obtaining the austenite phase ratio of the internal phase by measurement including the nitride phase.

[0044] Hardness can be measured using a commercially available micro-Vickers hardness tester, and in the case of a sintered sample, it is desirable to select and evaluate a region where there are no pores. The surface hardness corresponding to the nitride phase can be obtained by measuring the sample surface, while the internal phase hardness is measured by measuring the fracture surface of the broken sample or by measuring the surface after removing the nitride phase by polishing or the like.

[0045] In this way, the obtained friction material can be used as a contact member of the vibration type actuator as shown in Fig. 2. The vibrating body 5 includes a substantially rectangular and flat elastic body 5a as a base material, and a substantially flat piezoelectric element 5b which is an example of an electro-mechanical energy conversion element and is joined to one surface of the elastic body 5a by an adhesive. The elastic body 5a has two protrusions 5c on the surface opposite to the surface adhered to the piezoelectric element 5b, and the tips of the protrusions 5c contact the contact surface of the contact member 4.

[0046] The contact member 4 is in pressure contact with the vibrating body 5 by a pressurizing means (not shown). By applying a voltage to the piezoelectric element 5b so as to generate an elliptical motion in the protrusions 5c, the contact member 4 and the vibrating body 5 can be relatively moved in the driving direction of the arrow in Fig. 3. By using the friction material according to the present embodiment as the contact member, a vibration type actuator having a high driving thrust and high wear resistance can be obtained even in a high humidity environment.

[0047] [Second Embodiment] Next, as an example of an optical device and an electronic device to which the vibration type actuator using the contact member 1 described above is applied, an imaging device and an industrial robot will be described.

[0048] Fig. 6 is a top view showing a schematic configuration of an imaging device 700 (device) which is an example of an optical device. The imaging device 700 includes a camera body 730 equipped with an imaging element 710 and a power button 720. Further, the imaging device 700 includes a lens barrel 740 which includes a lens group (not shown) and a vibration type actuator. The driving of the lens group which is an example of an optical element is performed by the vibration type actuator. The lens barrel 740 is replaceable as an interchangeable lens, and a lens barrel 740 suitable for the imaging object can be attached to the camera body 730.

[0049] As the vibration type actuator, the vibration type actuator described with reference to FIG. 3 can be used. Although the driving of the lens by the vibration type actuator is considered suitable for driving the lens for autofocus, it is not limited to this, and it is considered that the lens for zoom can also be driven by the same configuration. Further, the vibration type actuator can also be used for driving the imaging element and for driving the lens or the imaging element during shake correction.

[0050] FIG. 7 is a perspective view showing a schematic configuration of a robot 100 (device) equipped with a vibration type actuator 1 which is an example of an electronic device, and here, a horizontal articulated robot which is a type of industrial robot is illustrated.

[0051] The robot 100 has, as members, an arm joint portion 111 and a hand portion 112. The arm joint portion 111 connects two arms so that the angle at which the two arms 120 intersect can be changed. The hand portion 112 has an arm 120, a gripping portion 121 attached to one end of the arm 120, and a hand joint portion 122 connecting the arm 120 and the gripping portion 121. The vibration type actuator is built into the arm joint portion 111 and the gripping portion 121, and performs angle adjustment and rotational movement of the arm 120 and the hand joint portion.

[0052] Note that, for bending of the arm joint portion 111 and the gripping operation of the hand portion 112, a vibration type actuator having a TN characteristic (a drooping characteristic showing the relationship between load torque and rotational speed) with a low rotational speed and high torque is preferably used.

[0053] As described above, the present invention has been described in detail based on its preferred embodiments, but the present invention is not limited to these specific embodiments, and various forms within the scope not departing from the gist of this invention are also included in the present invention. For example, as a device capable of driving a flat contact body in an arbitrary direction within its plane, an XY stage can be cited.

[0054] [Examples and Comparative Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples in any way as long as the gist thereof is not exceeded. The Examples and Comparative Examples shown below are examples of contact bodies in a vibration type actuator, but the present invention is not limited to these examples and can be applied to other friction materials as well.

[0055] (Method for manufacturing the sintered body of Example 1) In Example 1, as the stainless steel raw material powder, a mixed powder in which a predetermined amount of carbon powder was mixed with SUS410L powder at 1 wt% or less was used. The SUS410L powder is a JIS standard product (C: 0.15 wt% or less, Cr: 11.5 wt% - 13.0 wt%, Si: 0.5 wt% or less, Mn: 1 wt% or less, P: 0.04 wt% or less, S: 0.03 wt% or less, the balance being Fe). The raw material powder was put into a superhard mold having a cavity shape of 40 mm × 5 mm and compression molded until it reached a predetermined plate thickness. The obtained molded body was fired at 1220°C for 30 minutes, and then a sintered body was produced by flowing nitrogen gas and rapidly cooling it.

[0056] (Method for manufacturing the sintered body of Example 2) In Example 2, a sintered body was produced in the same manner as in Example 1 except that the sintering temperature was changed to 1150°C and the firing process was performed.

[0057] (Method for manufacturing the sintered body of Example 3) In Example 3, a sintered body was produced in the same manner as in Example 1 except that the sintering temperature was changed to 1100°C and the firing process was performed, and then the sintered body was immersed in liquid nitrogen for 30 minutes as a sub-zero treatment and heat-treated at 1220°C for 30 minutes. After the heat treatment, the sintered body was rapidly cooled with nitrogen gas.

[0058] (Method for manufacturing the sintered body of Example 4) In Example 4, a sintered body was produced in the same manner as in Example 3 except that the heat treatment temperature was changed to 1150°C.

[0059] (Method for manufacturing the sintered body of Example 5) In Example 5, a sintered body was produced in the same manner as in Example 3, except that the heat treatment temperature was changed to 1260°C.

[0060] (Method for producing the sintered body of Example 6) In Example 6, a sintered body was produced in the same manner as in Example 1, except that the sintering temperature was changed to 1240°C and the firing process was performed.

[0061] (Method for producing the sintered body of Example 7) In Example 7, a sintered body was produced in the same manner as in Example 1, except that after the firing process, the sintered body was immersed in liquid nitrogen for 1 second as sub-zero treatment.

[0062] (Method for producing the sintered body of Comparative Example 1) In Comparative Example 1, a sintered body was produced in the same manner as in Example 1, except that SUS304 powder without mixed carbon was used as the stainless steel raw material powder. The SUS304 powder is a JIS standard product (C: 0.08 wt% or less, Cr: 18 wt% - 20 wt%, Ni: 8 wt% - 10.5 wt%, Si: 1 wt% or less, Mn: 2 wt% or less, P: 0.045 wt% or less, S: 0.03 wt% or less, the balance being Fe).

[0063] (Method for producing the sintered body of Comparative Example 2) In Comparative Example 2, a sintered body was produced in the same manner as in Comparative Example 1, except that the sintering temperature was changed to 1200°C.

[0064] (Method for producing the sintered body of Comparative Example 3) In Comparative Example 3, a sintered body was produced in the same manner as in Example 1, except that the sintering temperature was changed to 1100°C and the firing process was performed, and then the sintered body was immersed in liquid nitrogen for 30 minutes as sub-zero treatment.

[0065] (Method for producing the sintered body of Comparative Example 4) In Comparative Example 4, a sintered body was produced in the same manner as in Comparative Example 3, except that after the sub-zero treatment, a heat treatment was performed at 1100°C for 30 minutes.

[0066] (Method for producing the sintered body of Comparative Example 5) In Comparative Example 5, a sintered body was produced in the same manner as in Comparative Example 1, except that the sintering temperature was changed to 1150°C.

[0067] (Method for producing the sintered body of Comparative Example 6) In Comparative Example 6, a sintered body was produced in the same manner as in Example 1, except that after the firing process, the sintered body was immersed in liquid nitrogen for 1 minute as a sub-zero treatment.

[0068] Barrel polishing was performed on the sintered bodies obtained by the production methods according to the above-described Examples 1 to 7 and Comparative Examples 1 to 6 for deburring. Table 1 shows the production conditions of each Example and Comparative Example.

[0069] Here, before moving to the next process, measurement of density, hardness, martensite ratio, and identification of crystal phases by X-ray diffraction were performed. The density was measured by the Archimedes method, and the relative density was obtained by dividing the measured density by the theoretical density, and the porosity was calculated by subtracting the relative density from 100%. The hardness was measured using a micro-Vickers hardness tester HMV-2 manufactured by Shimadzu Corporation. Specifically, an area without pores on the surface of the sintered body was used as the measurement point, and the hardness was measured with a pressing load of 0.98 N.

[0070] The martensite ratio of the sintered body was measured by the magnetic induction method using a FISCHERSCOPE manufactured by Fischer Instruments. As described above, since the ratio obtained as the measured value is based on the total volume including pores, it was converted to a volume basis excluding the porosity. The X-ray diffraction measurement was carried out using an X-ray diffractometer Ultima4 manufactured by Rigaku Corporation, using Cu as the target, with an output of 40 kV - 40 mA, and X-ray diffraction measurement was performed in the range of 2θ from 35° to 60°.

[0071] In the obtained spectrum, only the peak derived from the α' structure indicating the martensite phase and the peak derived from the γ structure indicating the austenite phase were detected, and it was confirmed that both were composed of the martensite phase and the austenite phase. Thus, the volume ratio of the austenite phase was determined by subtracting the martensite phase ratio from 100%. The evaluation results of these sintered compacts in the examples and comparative examples are shown in Table 1.

[0072]

Table 1

[0073] Since warping occurred during sintering, polishing was carried out using a #1200 SiC abrasive grain polishing sheet until the warping became 0.1 mm or less, and then ion nitriding treatment was performed. Specifically, in a chamber into which nitrogen gas was introduced, glow discharge was generated under a predetermined pressure, and nitride ions were formed by colliding nitrogen ions with the sample surface.

[0074] Subsequently, an impregnation treatment with a silicone-based resin was performed to increase the frictional force in a high-humidity environment. The sintered compact was placed in a metal mesh cage and put into a vacuum chamber, the lid was closed, and the inside of the chamber was depressurized to a pressure of 1 kPa or less. After depressurization, an impregnating agent in an amount sufficient to fully immerse the metal mesh cage was introduced from the pipe connected to the chamber. Then, the inside of the chamber was pressurized, and when the pressure rose to 0.5 MPa, it was left for about 10 minutes, the chamber was opened to the atmosphere, the sintered compact was taken out, the surface was wiped with a wipe, and then it was put into an oven at 100°C or higher and 150°C or lower to cure the impregnated resin and left.

[0075] Finally, in order to reduce the surface roughness, a load of 600 g was applied to one sintered compact using 3-μm diamond abrasive grains, and lapping polishing was performed for 10 minutes.

[0076] After completion, a surface layer destruction test was carried out from the viewpoints of surface observation, surface hardness measurement, and wear resistance. In the surface observation, the presence or absence of defects was confirmed visually and by microscope. The surface hardness was measured by the same method as the evaluation after sintering. The surface layer destruction test was carried out using the evaluation apparatus shown in Fig. 3. Using an ultrasonic cutter manufactured by Honda Denko Co., Ltd., ultrasonic vibration was applied at a frequency of 40 kHz for 1 minute in a state where a load of 150 g was applied to the sample surface in contact.

[0077] The ultrasonic cutter 6 is connected to the upper surface part 8 via a spring 7 while being fixed to the fixture 9, and the fixture 9 is connected to the movable linear guide 10. The ultrasonic cutter 5 is provided with a rod 11 having a spherical tip with a radius of 2 mm made of SUS420J2, and the tip of the rod 11 is brought into contact with the sample 12 by the linear guide 10. The sample 12 is placed on the electronic balance 13, and the contact load is adjusted so that the load becomes 150 g with this electronic balance 13. In this way, the observation of the indentation formed on the sample surface and the measurement of the indentation depth were performed.

[0078] The indentation depth was measured using a scanning white light interference microscope manufactured by Hitachi High-Technologies Corporation, and the depth at the deepest part of the indentation was evaluated as the indentation depth. Table 2 shows these evaluation results for each example and comparative example.

[0079] After the above evaluation, the thickness of the nitride phase, the hardness of the internal phase, and the content of the martensite phase in the internal phase were measured. When measuring the thickness of the nitride phase, the sample was cut approximately in half, and after polishing the fracture surface, it was observed with a microscope. The nitride phase formed on the surface layer can be visually recognized with a different color from the internal phase, and the distance from the boundary part where the color changes to the surface layer was measured from the observation image to evaluate the nitride phase thickness. These measurement results are shown in Table 2.

[0080] Since the maximum nitride phase thickness in all the examples and comparative examples was 22 μm, after removing the nitride layer by polishing the surface by about 0.1 mm, the evaluation of the internal phase was carried out. The hardness of the internal phase was measured in the same manner as after sintering and on the nitride layer surface, and for the evaluation of the austenite phase content, the martensite phase content was measured in the same manner as the evaluation of the sintered body, and then the austenite phase content was calculated.

[0081] The results obtained in each example and comparative example are shown in Table 2. Since there were no significant changes in the hardness of the internal phase and the austenite phase content compared to the results in the sintered body, and the amount of change was equivalent to the measurement error in each case, it can be inferred that the microstructural changes in the internal phase during the nitriding treatment were extremely small.

[0082] From the results shown in Table 2, in Examples 1 to 7, the Vickers hardness of the internal phase was in the range of 300 HV0.1 or more and 600 HV0.1 or less, and the austenite phase content of the internal phase was in the range of 75 vol% or more and 99 vol% or less. In Examples 1 to 7, the Vickers hardness of the surface layer corresponding to the nitride phase was as high as 1000 HV0.1 or more, and no fracture marks were observed in the surface fracture test. Also, no particularly large defects were found on the surface of the finished products of Examples 1 to 7.

[0083] On the other hand, in Comparative Example 1 and Comparative Example 2, it was confirmed that indentations were formed on the surface at a certain rate, and thus the subsequent evaluation was not carried out. This was presumably due to insufficient hardness, which occurred when the parts came into contact with each other or with the surrounding materials during the barrel polishing process after sintering or during transfer between processes.

[0084] Also, in Comparative Examples 3 to 6, the hardness of the internal phase exceeded 600 HV0.1, and the austenite phase content of the internal phase was below 75 vol% in all cases. Although the Vickers hardness of the surface was high, in the surface fracture test, fracture marks, i.e., locally deep gouged areas accompanied by cracks, were observed. Also, correspondingly, the depth of the indentations caused by ultrasonic vibration was also deeper compared to Examples 1 to 7.

[0085] From the above results, it was confirmed that the friction materials according to each example can provide a friction material including a stainless steel sintered body having high surface hardness, fracture strength, and excellent wear resistance. That is, by controlling the Vickers hardness of the internal phase within the range of 300 HV0.1 or more and 600 HV0.1 or less, and the content of the austenite phase of the internal phase within the range of 75 vol% or more and 99 vol% or less, a friction material having high surface hardness, fracture strength, and wear resistance can be provided.

[0086] In addition, friction force evaluations were performed in all examples and comparative examples except Comparative Example 1 and Comparative Example 2. It was carried out in the form shown in FIG. 4 using a friction and wear tester manufactured by Resca Co., Ltd. A friction material 16 fixed to the movable stage 15 with screws was installed, and the pin material 18 was brought into contact with the friction material 16 while a load was applied by the weight 17, and the friction force was measured by the load sensor 20 while reciprocally driving the stage within a range of 10 mm.

[0087] As the pin material 18, a round bar with a diameter of 2 mm of SUS420J2 was used, and it was brought into contact in a state where the angle was adjusted using a level so that the arm 19 was horizontal. The mass of the weight used was 150 g. First, as a running-in sliding, sliding was performed under the above conditions at a moving speed of 20 mm / s and a reciprocating number of 5000 times, and then the friction force in the dry state was measured at a moving speed of 1 mm / s. Among the measured friction forces for 10 mm, the average value of the friction forces from the position 2 mm to the position 8 mm from the start position where the measured value was relatively stable was calculated, and the friction coefficient was calculated based on that average value. Then, the friction material and the pin material were left in a constant temperature and humidity chamber at 60°C and 90% for 20 hours, and immediately after being taken out from the constant temperature and humidity chamber, the pin material and the friction material were installed again, and the friction force was measured and the friction coefficient was calculated under the same conditions as in the dry state. As a result, it was confirmed that all of them maintained a high friction force with a friction coefficient of 0.4.

[0088]

Table 2

[0089] The disclosure of this embodiment includes the following configurations and methods.

[0090] (Configuration 1) A friction material comprising a stainless steel sintered body having pores, wherein the friction material has a nitride phase present on the surface of the friction material and containing an iron nitride compound, and an internal phase present inside the friction material and adjacent to the nitride phase, the internal phase includes an austenite phase and a martensite phase, and the content of the austenite phase in the internal phase is 75 vol% or more and 99 vol% or less, and the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less. A friction material characterized by this.

[0091] (Configuration 2) The friction material according to Configuration 1, characterized in that resin is present in at least a part of the inside of the pores.

[0092] (Configuration 3) The friction material according to Configuration 2, characterized in that the resin includes a silicone-based resin.

[0093] (Configuration 4) The friction material according to any one of Configurations 1 to 3, characterized in that the porosity of the stainless steel sintered body is 15% or less.

[0094] (Configuration 5) The friction material according to any one of Configurations 1 to 4, characterized in that the chromium content in the stainless steel sintered body is 16 wt% or less.

[0095] (Configuration 6) The nitride phase is, as the iron nitride compound, either one of an ε phase (Fe 2-3 N) and a γ' phase (Fe4N), or a mixed phase of an ε phase (Fe 2-3 N) and a γ' phase (Fe4N) and the friction material according to any one of Configurations 1 to 5 is characterized by including this.

[0096] (Configuration 7) The friction material according to any one of Configurations 1 to 6, wherein the thickness of the nitride phase in the friction material is 1.0 μm or more.

[0097] (Configuration 8) The friction material according to any one of Configurations 1 to 7, wherein the Vickers hardness of the internal phase is 390 HV0.1 or more and 580 HV0.1 or less.

[0098] (Configuration 9) The friction material according to any one of Configurations 1 to 8, wherein the content of the austenite phase in the internal phase is 75 vol% or more and 97 vol% or less.

[0099] (Configuration 10) A friction material including a stainless sintered body having pores, The friction material has a nitride phase containing an iron nitride compound and present on the surface of the friction material, and an internal phase present inside the stainless sintered body and adjacent to the nitride phase, The internal phase includes an austenite phase and a martensite phase, and the content of the martensite phase in the internal phase is 1.0 vol% or more and 25 vol% or less, The friction material is characterized in that the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less.

[0100] (Configuration 11) A vibrating body having an electro-mechanical energy conversion element and an elastic body, A contact body including the friction material according to any one of Configurations 1 to 10, The contact body is in contact with the surface of the elastic body at a contact surface, A vibration type actuator characterized in that the vibrating body and the contact body relatively move due to the vibration of the vibrating body.

[0101] (Configuration 12) The vibration type actuator according to Configuration 11, An optical device comprising at least one of an optical element and an imaging element driven by the vibration type actuator.

[0102] (Configuration 13) A member, An electronic device comprising the vibration type actuator according to Configuration 11 for driving the member.

[0103] (Method 1) A step of obtaining a sintered body by pressure molding a raw material powder containing stainless steel powder and then firing the pressure molded raw material powder; A nitriding treatment step of forming a nitride phase on the surface of the sintered body; A method for manufacturing a friction material including: The friction material contains an iron nitride compound and has a nitride phase present on the surface of the friction material and an internal phase present inside the friction material and adjacent to the nitride phase; The internal phase includes an austenite phase and a martensite phase, and the content of the austenite phase in the internal phase is 75 vol% or more and 99 vol% or less; A method for manufacturing a friction material, characterized in that the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less.

[0104] (Method 2) A step of obtaining a sintered body by pressure molding a raw material powder containing stainless steel powder and then firing the pressure molded raw material powder; A nitriding treatment step of forming a nitride phase on the surface of the sintered body; A method for manufacturing a friction material including: The friction material contains an iron nitride compound and has a nitride phase present on the surface of the friction material and an internal phase present inside the stainless steel sintered body and adjacent to the nitride phase; The internal phase includes an austenite phase and a martensite phase, and the content of the martensite phase in the internal phase is 1.0 vol% or more and 25 vol% or less; A method for manufacturing a friction material, characterized in that the Vickers hardness of the inner phase is 300 HV0.1 or more and 600 HV0.1 or less.

Explanation of symbols

[0105] 1 Friction material 2 Stainless steel particles 3 Void 4 Contact body (friction material) 5 Vibrator 5a Elastic body 5b Piezoelectric element 5c Protrusion

Claims

1. A friction material comprising a stainless steel sintered body having voids, wherein the friction material contains a nitrogen compound of iron and has a nitride phase present on the surface of the friction material and an internal phase present inside the friction material and adjacent to the nitride phase, the internal phase contains an austenite phase and a martensite phase, and the content of the austenite phase in the internal phase is 75 vol% or more and 99 vol% or less, and the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less. A friction material characterized by this.

2. The friction material according to claim 1, characterized in that resin is present in at least a part of the inside of the voids.

3. The friction material according to claim 2, characterized in that the resin contains a silicone-based resin.

4. The friction material according to claim 1, characterized in that the porosity of the stainless steel sintered body is 15% or less.

5. The friction material according to claim 1, characterized in that the chromium content in the stainless steel sintered body is 16 wt% or less.

6. The nitride phase is, as the nitrogen compound of iron, either the ε phase (Fe ２－３ N) or the γ' phase (Fe ４ N), or a mixed phase of the ε phase (Fe ２－３ N) and the γ' phase (Fe ４ N) The friction material according to claim 1, characterized by containing this.

7. In the friction material, the thickness of the nitride phase is 1.0 μm or more. The friction material according to claim 1, characterized by this.

8. The friction material according to claim 1, characterized in that the Vickers hardness of the internal phase is 390 HV0.1 or more and 580 HV0.1 or less.

9. The friction material according to claim 1, wherein the content of the austenite phase in the internal phase is 75 vol% or more and 97 vol% or less.

10. A friction material including a stainless steel sintered body having pores, The friction material includes a nitride phase present on the surface of the friction material and containing an iron nitride compound, and an internal phase present inside the stainless steel sintered body and adjacent to the nitride phase, The internal phase includes an austenite phase and a martensite phase, and the content of the martensite phase in the internal phase is 1.0 vol% or more and 25 vol% or less, The friction material is characterized in that the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less.

11. A vibrating body having an electro-mechanical energy conversion element and an elastic body, A contact body including the friction material according to any one of claims 1 to 10, wherein The contact body is in contact with the surface of the elastic body at a contact surface, A vibration type actuator, characterized in that the vibrating body and the contact body relatively move due to the vibration of the vibrating body.

12. The vibration type actuator according to claim 11, and An optical device, characterized by including at least one of an optical element or an imaging element driven by the vibration type actuator.

13. A member, and An electronic device, characterized by including the vibration type actuator according to claim 11 for driving the member.

14. A step of obtaining a sintered body by pressure molding a raw material powder containing stainless steel powder and then firing the pressure molded raw material powder, A nitriding treatment step of forming a nitride phase on the surface of the sintered body, A method for manufacturing a friction material, including: The friction material has a nitride phase containing a nitrogen compound of iron and present on the surface of the friction material, and an internal phase present inside the friction material and adjacent to the nitride phase. The internal phase includes an austenite phase and a martensite phase, and the content of the austenite phase in the internal phase is 75 vol% or more and 99 vol% or less. A method for manufacturing a friction material, characterized in that the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less.

15. A step of obtaining a sintered body by pressure molding a raw material powder containing stainless steel powder and then firing the pressure-molded raw material powder. A nitriding treatment step of forming a nitride phase on the surface of the sintered body. A method for manufacturing a friction material, including: The friction material has a nitride phase containing a nitrogen compound of iron and present on the surface of the friction material, and an internal phase present inside the stainless steel sintered body and adjacent to the nitride phase. The internal phase includes an austenite phase and a martensite phase, and the content of the martensite phase in the internal phase is 1.0 vol% or more and 25 vol% or less. A method for manufacturing a friction material, characterized in that the Vickers hardness of the internal phase is 300 HV0.1 or more and 600 HV0.1 or less.

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