WO2016087045A1

WO2016087045A1 - Spherically shaped wear part

Info

Publication number: WO2016087045A1
Application number: PCT/EP2015/002446
Authority: WO
Inventors: Claudio BERTALAN; Eric SCHOUVELLER; Alexandre VOS
Original assignee: Ceratizit Luxembourg S.A.R.L.
Priority date: 2014-12-05
Filing date: 2015-12-03
Publication date: 2016-06-09
Also published as: AT14387U1

Abstract

A spherically shaped wear part made from a cermet material is provided. The cermet material is a Ti(C, N)-based cermet comprising hard Ti(C_y, N_z) grains, with y > 0, z ≥ 0 and y + z ≤ 1, embedded in a ductile binder phase formed by a Ni-base alloy, a Co-base alloy, or a Fe-base alloy. The Ti(C, N) grains have a mean grain size in the range between 0.2 μrm and 3.0 μrm.

Description

SPHERICALLY SHAPED WEAR PART

The present invention relates to a spherically shaped wear part made from a Ti(C, N) based cermet material.

Spherically shaped wear parts made from very resistant material are used in several different applications. For example, such spherically shaped wear parts are employed as pen-balls in ball pens. DE 14 61 656 A describes a wear-resistant ball as a writing ball for a ball pen. A writing ball made of a cermet material is described, which cermet material can e.g. be formed by a TiC-based cermet having a composition of 4 wt.-% Cr, 4 wt.-% Co, 12 wt.-% Ni and rest TiC, or by a TaC-based cermet having a composition of 2 wt.-% Cr, 2 wt.-% Co, 6 wt.-% Ni and rest TaC.

Cermets are materials formed by at least one hard phase forming the main constituent embedded in a ductile metallic binder phase which usually is formed by a base alloy of Co, Ni, or Fe. Base alloy of a metal means that this metal forms the main constituent in wt.-% of the alloy. The hard phase is in most cases formed by metal carbides, in particular by carbides of the elements in groups IV to VI of the periodic table of the elements. For example, one common cermet material is mainly composed of TiC grains embedded in a Ni-binder phase or Ni-Co-binder phase. Where the present specification refers to a specific chemical composition, the chemical composition can preferably be assessed by EDX analysis (Energy Dispersion X-Ray Analysis) as is well- known in this technical field.

It is an object of the present invention to provide a spherically shaped wear part having increased hardness and corrosion resistance. According to one aspect, it is an object to provide an improved pen-ball for a ball pen.

The object is solved by a spherically shaped wear part according to claim 1. Further developments are specified in the dependent claims. The spherically shaped wear part is made from a cermet material which is a Ti(C, N)-based cermet comprising hard Ti(C_y, N_z) grains, with y > 0, z≥ 0 and y + z < 1 , embedded in a ductile binder phase formed by a Ni-base alloy, a Co-base alloy, or a Fe-base alloy. The Ti(C_y, N_z) grains have a mean grain size in the range between 0.2 pm and 3.0 μητι.

The mean grain size of the Ti(C_y, N_z) grains is determined based on EBSD (electron back scattering diffraction). The method grain size determination is e.g. defined in ASTM E2627-10. A Ti(C, N)-based cermet is a material in which hard particles consisting predominantly of Ti(C_y, N_z)-particles are embedded in a ductile binder phase of Co, Ni, Fe or a base alloy of these. Base alloy of a metal means that this metal forms the main constituent of that alloy. In such cermets, the weight fraction of hard particles is significantly larger than the weight fraction of the binder phase. In the preferred case of z > 0, or even more preferred z > 0.1 , the Ti(C_y, N_z)-particles in such a Ti(C, N)-based cermet comprise a core-rim structure in which the core is formed by Ti(C_y, N_z), with y > 0, z > 0 and y + z≤ 1 , (preferably y > 0.4 and z > 0.4) and the surrounding rim has a more complex structure of a solid solution (Ti_a, Me_b)C_yN_z, with a, b, y, z each > 0 and y + z < 1 and Me being one or more other metals. For example, Me can be one or more of W, Mo, V, Ta, Nb, Mn, Y, Zr, Hf and Cr.

The Ti(C, N)-based cermet with Ti(C_y, N_z) grains having a small mean grain size in the range between 0.2 pm and 3.0 pm results in a particular high hardness of the spherically shaped wear part. Further, a particularly high corrosion resistance is achieved. Preferably the mean grain size can be in the range between 0.5 pm and 0.8 pm (i.e. in the submicron range). These features are particularly suitable for an application in pen-balls for ball pens. However, the particularly advantageous feature combination is also well suited for other applications, such as a wear ball for a bearing, a ball for a ball valve, a ball for ballizing (a manufacturing process involving balls to induce a plastic

deformation), a ball for shot peening, a ball for milling, a ball for gauging and metering, a ball for a bandsaw or circular saw application (i.e. a ball applied to a band saw or circular saw and then ground to provide at least one cutting edge), a ball as a sensor component, a ball as a component of an inertial navigation system, a ball in steering mechanisms, a ball for drills (i.e. a ball which is applied to a drill body and then ground to provide at least one cutting edge), and a ball for electrical contact. According to a further development, the cermet material has a Ti content

> 40 wt.-%. Such a high Ti content achieves both particularly high hardness and particularly high corrosion resistance. Preferably, the Ti content of the cermet material is > 50 wt.-%, more preferably in a range between 50 wt.-% and 75 wt.-%.

According to a further development, cermet material comprises at least one of Mo and W in a total amount between 1.5 wt.-% and 30 wt.-% of the cermet material. Preferably, most of the Mo and/or W is present as Mo₂C grains or WC grains, respectively, distributed in the binder phase and some of the Mo and/or W is incorporated in the (Ti_a, Me_b)C_yN_z rim of the Ti(C_y, N_z) grains. The given range of Mo content results in particularly advantageous tradeoff between high hardness and high corrosion resistance, on the one hand, and still good fracture toughness, at the other hand. This goal is in particular achieved with a

Mo content in the range between 6.5 wt.-% and 10 wt.-%.

According to a preferred realization, the cermet material comprises Cr in an amount between 0.5 wt.-% and 10 wt.-% of the cermet material. In this case, an even increased corrosion resistance is achieved. Preferably, the Cr content is in the range between 3 wt.-% and 5 wt.-% of the cermet material. Preferably, at least some of the Cr is solved in the ductile binder phase.

According to a further development, the cermet material comprises at least one of Re and Ru in a total amount between 0.1 wt.-% and 1 wt.-% of the cermet material. An addition of Re and/or Ru in such an amount leads to improved oxidation resistance and corrosion resistance. Preferably, the Re and/or Ru is partly dissolved in the ductile binder phase and partly incorporated in the (Ti_a, Me_b)CyN_z rim of the Ti(C_y, N_z) grains. Preferably, the cermet material comprises a binder phase content in the range between 1 wt.-% and 20 wt.-%. In particular in this range, a good tradeoff between hardness and fracture toughness is achieved. Still more preferably, the binder phase content is in the range between 6 wt.-% and 10 wt.-%.

According to a preferred realization, the binder phase is formed by a Ni-base alloy. The binder phase can have a Ni content of more than 50 wt.-% of the binder phase. In addition, the binder phase can in particularly also comprise Co and lower contents of other metals. In particular, the binder phase can also comprise dissolved Cr and/or Re.

According to a particularly preferred realization, the spherically shaped wear part is a pen-ball for a ball pen. Due to the achieved high hardness and high corrosion resistance, the described Ti(C, N)-based cermet material is

particularly suited for application as a pen-ball for a ball pen.

The object is solved by the use of the described spherically shaped wear part as a pen-ball for a ball pen. Further developments and advantages of the invention will become obvious from the following description of an embodiment with reference to the enclosed figures.

In the figures:

Fig. 1 : is a schematic representation of a spherically shaped wear part according to an embodiment;

Fig. 2: is an SEM image of a first Ti(C, N)-based cermet material

according to a first example; and

Fig. 3: is an SEM image of a second Ti(C, N)-based cermet material according to a second example with the same composition but having a smaller average grain size,

Fig. 4: is a graphical representation of corrosion tests in a buffered

solution pH3. Fig. 5: is an SEM image of the conventional material after the corrosion test according to Fig. 4.

Fig. 6: is an SEM image of the Ti(C, N)-based cermet material according to the embodiment after the corrosion test.

Fig. 7: is an SEM image of the conventional material after a corrosion test in a buffered solution pH8.

Fig. 8: is an SEM image of the Ti(C, N)-based cermet material according to the embodiment after a corresponding corrosion test in the buffered solution pH8.

Fig. 9: is a graphical representation of the corrosion test in the buffered solution pH8.

An embodiment of the present invention will be described in the following with reference to Fig. 1. The spherically shaped wear part 1 according to the embodiment is specifically formed by a pen-ball which is suited and intended for use in a ball pen.

The wear part 1 according to the embodiment is produced in a powder metallurgy production process from base materials in powder form. In the powder metallurgy production process, the base materials are mixed in the required ratios and then pressed to green compacts having at least roughly spherical shape, as is well-known for a person skilled in the field of pen-ball manufacturing. Further, the green compacts are subjected to a sintering process in order to form substantially dense intermediate products still having only roughly spherical shape. Subsequently, the thus formed intermediate products are ground to the final spherical shape in a grinding process which is also well known to a person skilled in the technical field of pen-ball

manufacturing. The wear part 1 according to the embodiment is formed from a Ti(C, N)-based cermet comprising Ti(C_y, N_z) grains, with y > 0, z > 0 and y + z≤ 1 , embedded in a ductile binder phase formed by a metal or metal alloy. The ductile binder phase is made from a Ni base alloy, a Co base alloy, a Fe base alloy or a combination thereof. According to one realization, the binder phase is substantially composed of Ni or of Ni and Co and comprises only slight amounts of other metals. Preferably, the total amount of other metals is less than

20 wt.-% of the binder phase. As can be seen in Fig. 2 for a Ti(C, N)-based cermet according to a first example and in Fig. 3 for a Ti(C, N)-based cermet according to a second example, the Ti(C_y, N_z) grains are distributed in the binder phase and are each composed of a core substantially consisting of Ti(C_y, N_z), with y > 0, z > 0 and y + z≤ 1 , which core is surrounded by a rim consisting of (Ti_a, Me_b)C_yN_z, with a, b, y, z each > 0 and y + z≤ 1. The Ti(C_y, N_z) grains comprise a grain size in the range from 0.2 pm to 3.0 pm, in the specific examples in the sub-micron range, i.e. a mean grain size in the range between 0.5 pm and 0.8 pm.

EXAMPLES

FIRST EXAMPLE

According to a first example (corresponding to Fig. 2), a spherically shaped wear part 1 to be used as a pen-ball was produced in a powder metallurgy production process as follows.

In a first step, Ti(C, N) particle powder was blended with Ni powder, Cr3C₂ powder, M02C powder and a slight amount of Re powder with the following weight percentages. 8 wt.-% of Ni powder having a mean particle size in the range 0.3-5.0 pm, in the specific realization 2.2-2.8 pm, was blended with

8 wt.-% M0₂C powder having a mean particle size in the range from 0.3-3 pm, in the specific realization 1.0-1.7 pm, 4.85 wt.-% Cr₃C₂ powder having a mean particle size in the range from 0.3-5.0 pm, in the specific realization 1.0-2.0 pm, 0.02 wt.-% of Re powder having a mean particle size in the range 0.5-10.0 pm, in the specific realization 3.0-4.6 pm, and the remaining wt.-% of Ti(C_y, N_z) particle powder having a mean particle size in the range from 0.5-5.0 pm, in the specific realization 1.1-1.6 pm. The TiC_yN_z particles in the Ti(C_y, N_z) particle powder had a carbon content y in the range 0.45-0.50 and a nitrogen content z in the range 0.45-0.55. It should be noted that instead of Cr₃C_2> for example chromium nitride or chromium carbonitride could also be used in corresponding amounts.

The blend of the powders was produced by milling the powders in an attritor mill for 15 hours in a milling medium comprising alcohol.

The thus produced blend was spray-dried and subsequently compacted to green parts having substantially spherical shape in appropriate dies well-known in the technical field of pen-ball production. The green parts were thereafter sintered under nitrogen atmosphere at 1450 °C with 2 hours dwelling time in order to produce dense parts having substantially spherical shape.

After cooling down, the produced dense parts were ground by means of double- face grinding to spherically shaped wear parts 1 having a diameter in the range 0.5-1.0 mm.

SECOND EXAMPLE

According to a second example (corresponding to Fig. 3), a spherically shaped wear part 1 to be used as a pen-ball was produced in a powder metallurgy production process similar to the production process described with regard to the first example. However, instead of the Ti(C_y, N_z) particle powder used for the first example, a Ti(C_y, N_z) particle powder having a smaller average particle size in the range 0.7-1.0 pm was used. As a consequence, the Ti(C, N)-based cermet according to the second example has a substantially smaller resulting average grain size, as can be seen in Fig. 3.

TEST

Spherically shaped wear parts 1 according to the first and second examples were tested with regard to hardness and corrosion resistance. It was found that high hardness and high corrosion resistance were achieved.

Corrosion tests were performed in which the spherically shaped wear part 1 according to the first example was compared to a corresponding spherically shaped wear part made from a conventional grade CTF08R by CERATIZIT® comprising WC with an average grain size in the range 0.8-1.3 μιη as the main constituent of the hard phase embedded in a binder phase comprising Ni as the main constituent, with an overall Ni-content in the grade of 4.0 wt.-%. The corrosion tests were performed in an electrochemical corrosion cell

Radiometer type CEC/TH using buffered solutions pH3 and pH8. The voltage was increased from -800 mV to 1000 mV at a rate of 20 mV/min. In such a test set-up, the measured current density increases with the quantity of ions in the buffered solution which have been corroded from the materials tested. The higher the current density, the more severe is the corrosion.

As can be seen in Fig. 4 for the buffered solution pH3, the spherically shaped wear part 1 according to the example showed considerably less corrosion as compared to the conventional spherically shaped wear part. This can also be seen in comparing the SEM-images in Fig. 5 (for the conventional spherically shaped wear part) and Fig. 6 (for the spherically shaped wear part according to the example) after the corrosion tests.

Corresponding results were found for the buffered solution pH8, as can be seen in Figs. 7, 8 and 9.

Claims

Spherically shaped wear part made from a cermet material, the cermet material being a Ti(C N)-based cermet comprising hard Ti(C_y, N_z) grains, with y > 0, z > 0 and y + z < 1 , embedded in a ductile binder phase formed by a Ni-base alloy, a Co-base alloy, or a Fe-base alloy, the Ti(C_y, N_z) grains having a mean grain size in the range between 0.2 pm and 3.0 pm.

Spherically shaped wear part according to claim 1 , wherein z > 0, preferably z > 0.1.

3. Spherically shaped wear part according to any one of claims 1 and 2, wherein the cermet material has a Ti content > 40 wt.-%. 4. Spherically shaped wear part according any one of the preceding claims, wherein the cermet material comprises Mo and/or W in an amount between 1.5 wt.-% and 30 wt.-% of the cermet material, preferably between 6.5 wt.-% and 10 wt.-%.

Spherically shaped wear part according to any one of the preceding claims, wherein the cermet material comprises Cr in an amount between 0.5 wt.-% and 10 wt.-% of the cermet material, preferably between 3 wt.-% and 5 wt.-% of the cermet material.

Spherically shaped wear part according to any one of the preceding claims, wherein the cermet material comprises Re and/or Ru in an amount between 0.01 wt.-% and 1 wt.-% of the cermet material.

Spherically shaped wear part according to any one of the preceding claims, wherein the cermet material comprises a binder phase content in the range between 5 wt.-% and 12 wt.-%, preferably between 6 wt.-% and 10 wt.-%.

8. Spherically shaped wear part according to any one of the preceding claims wherein the binder phase is formed by a Ni-base alloy, a Co-base alloy or a Ni-Co base alloy. 9. Spherically shaped wear part according to any one of the preceding claims wherein the wear part is one of a pen-ball for a ball pen, a wear ball for a bearing, a ball for a ball valve, a ball for ballizing, a ball for shot peening, a ball for milling, a ball for gauging and metering, a ball for a bandsaw or circular saw application, a ball as a sensor component, a ball as a component of an inertial navigation system, a ball in steering mechanisms, a ball for drills, and a ball for electrical contact.

10. Spherically shaped wear part according to any one of the preceding

claims, wherein the wear part is a pen-ball for a ball pen.

1 1. Use of a spherically shaped wear part according to any one of the

preceding claims as a pen-ball in a ball pen.