CEMENTED CARBIDE COMPOSITIONS AND APPLICATIONS THEREOF

Description

FIELD

The present application relates to grade powder compositions and associated sintered cemented carbide compositions comprising solid solution carbides of lanthanum and yttrium.

BACKGROUND

In cemented carbides for metal cutting purposes, the quality of a cemented carbide is often determined by its high temperature properties. Hardness of cemented carbides can be reduced dramatically with increasing temperatures with simultaneous increases in scaling and degradative diffusion processes. Additionally, deformation properties of sintered cemented carbides can change substantially at high temperatures. A basic WC—Co cemented carbide, for example, will feature only about one third of its hardness at 800° C. compared to hardness at room temperature. Additions of TiC and (Ta,Nb)C to the WC—Co cemented carbide can increase hot hardness, but losses in hardness may still exceed fifty percent. Moreover, tantalum is an expensive additive that can significantly increase the cost of cemented carbide compositions.

Mechanical properties of cemented carbides are also affected by high temperatures encountered during carbide sintering conditions. Grain growth, for example, is very difficult avoid during sintering and hot isostatic pressing (HIPping) of green compacts. As is well known, excessive grain growth can negatively impact bending strength of the sintered cemented carbide. Therefore, specific metal carbides are added to the green compact as grain growth inhibitors.

The complexity of process sequences in cemented carbide manufacture is still further increased in that both tungsten from the tungsten carbide and metals of the grain growth inhibitors diffuse into the binder phase to form a solid solution. Since the solubility of these metals in the binder increases with temperature, the maximum dissolved concentration at a particular temperature can be exceeded, whereby excessive amounts precipitate out of the binder phase or deposit on the surface of the WC grains. Such deposition, however, impairs wetting of the grains with the binder metal which can compromise mechanical properties of the cemented carbide composition.

SUMMARY

In view of the foregoing considerations, new grade powders and associated cemented carbide compositions are needed that balance both performance and economic priorities. In one aspect, a powder composition described herein comprises particles of a solid solution carbide comprising lanthanum (La) and yttrium (Y), metallic binder phase comprising at least one metal for the iron group, and a balance of tungsten carbide particles. In some embodiments, the solid solution carbide further comprises an oxygen content. Additionally, the powder composition, in some embodiments, further comprises cubic carbide particles and/or additional solid solution carbide particles, the additional solid solution carbide particles comprising two or more transition metals selected from Groups 4-6 of the Periodic Table.

In another aspect, sintered cemented carbide compositions are described herein. In some embodiments, a sintered cemented carbide composition comprises at least one solid solution carbide phase comprising lanthanum (La) and yttrium (Y), a metallic binder phase, and a balance of tungsten carbide. The sintered cemented carbide composition, in some embodiments, has a hardness of at least 1300 HV30. As with the powder compositions described herein, the sintered cemented carbide can further comprise cubic carbides and/or additional solid solution carbide phases, the additional solid solution carbide phases comprising two or more transition metals selected from Groups 4-6 of the Periodic Table.

These and other embodiments are further described in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray diffractogram of a powder composition according to some embodiments described herein.

FIGS. 2A-2C provide metallographic images of a sintered cemented carbide composition described herein according to some embodiments.

FIGS. 3A-3C provide metallographic images of a comparative sintered cemented carbide composition.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by reference to the following detailed description and examples and their previous and following descriptions. Elements, apparatus and methods described herein, however, are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.

I. Powder Compositions for Sintered Cemented Carbide Production

Powder compositions and the associated sintered cemented carbide compositions produced from such powders are described herein. The powder compositions comprise particles of a solid solution carbide of La and Y. In some embodiments, the La, Y solid solution carbide is of the formula (La, Y)C₂. As described further herein, the La, Y solid solution carbide particles can be employed to at least partially replace tantalum (Ta) content in powder compositions for the production of sintered cemented carbides. For example, the La, Y solid solution carbide particles can at least partially replace TaC particles and/or solid solution carbide particles comprising Ta, such as TaNbC. Such replacement can significantly reduce the cost of powder compositions while maintaining desirable performance properties of sintered cemented carbide compositions produced from such powders. La and Y can be present in the powder compositions in any desired amount consistent with the objectives described herein. In some embodiments, La and Y are each present in an amount of 0.1 to 5 weight percent or 0.5 to 3 weight percent of the powder composition. Additionally, a value of (Y/La) in the solid solution particle can range from 0.5 to 2, in some embodiments. The value of (Y/La), in some embodiments, can be greater than 1, such as 1.1 to 2.

The La, Y solid solution carbide particles, in some embodiments can further comprise an oxygen content. Oxygen content of the solid solution particles, for example, can range from 0.01 to 3 weight percent. Oxygen can be introduced in the La, Y solid solution carbide particles during milling and/or other processing of the particles prior to incorporation of the particles into sintered cemented carbide compositions.

Powder compositions described herein can further comprise solid solution carbide particles in addition to the La, Y solid solution carbide particles. The additional solid solution carbide particles include two or more transition metals selected form Groups 4-6 of the Periodic Table. Suitable solid solution particles can comprise (Ti,W)C, (Ta,Nb)C, or mixtures thereof. Additional solid solution particles can be present in the powder composition in any desired amount consistent with the objectives described herein. In some embodiments, additional solid solution carbide particles are present in a total amount of 0.5 to 15 weight percent or 1 to 10 weight percent of the powder composition.

Powder compositions described herein can further comprise cubic carbide particles, wherein the cubic carbide particles comprise a transition metal selected from Groups 4-6 of the Periodic Table. Cubic carbide particles can be employed to control grain growth and promote grain refinement during production of sintered cemented carbide articles from the powder compositions. Cubic carbides for use in powder compositions described herein can include vanadium carbide, chromium carbide, titanium carbide, zirconium carbide, molybdenum carbide, and mixtures thereof. Cubic carbide particles can be present in the powder composition in any desired amount consistent with the objectives described herein. In some embodiments, cubic carbide particles are present in a total amount of 0.5 to 10 weight percent or 1 to 5 weight percent of the powder composition.

Powder compositions described herein also comprise a metallic binder phase comprising at least one metal from the iron group. The metallic binder phase can be dispersed throughout the powder composition and coat particular components, including the La, Y solid solution carbide particles, additional solid solution particles, cubic carbide particles, and tungsten carbide particles. The metallic binder phase can be present in any desired amount. The metallic binder phase can generally be present in an amount of 1 weight percent to 30 weight percent of the powder composition. Metallic binder phase may also be present in the powder composition in an amount selected from Table I.

TABLE I
Metallic Binder Phase (wt. %)

	1-20
	5-20
	3-15
	8-12

Tungsten carbide (WC) particles provide the balance of powder compositions described herein. The individual particle components including the La, Y solid solution carbide particles, additional solid solution particles, and/or cubic carbide particles can be combined with WC particles and milled to provide the powder compositions. FIG. 1 is an XRD of a powder composition according to some embodiments described herein. WC and various solid solutions phases including La, Y solid solution are identified in the XRD.

II. Sintered Cemented Carbide Compositions

In another aspect, sintered cemented carbide compositions are described herein. In some embodiments, a sintered cemented carbide composition comprises at least one solid solution carbide phase comprising La and Y, a metallic binder phase, and a balance of tungsten carbide. The solid solution phase comprising La and Y can further include an oxygen content as described herein. In some embodiments, La and Y are each present in an amount of 0.1 to 5 weight percent or 0.5 to 3 weight percent of the sintered cemented carbide composition. Additionally, a value of (Y/La) in the solid solution phase can range from 0.5 to 2, in some embodiments. The value of (Y/La), in some embodiments, can be greater than 1, such as 1.1 to 2. Further, a value for (La+Y)/Ta in the sintered cemented carbide composition can range from 0.1 to 10 or 0.3 to 5, in some embodiments.

The solid solution phase carbide phase of La and Y can be employed to at least partially replace Ta carbide phases, including TaC and (Ta,Nb)C, in the sintered cemented carbide compositions without concomitant losses in performance. In some embodiments, the La, Y solid solution carbide phase completely replaces Ta carbide phases such that the sintered cemented carbide composition does not comprise Ta beyond impurity levels/limits. In some embodiments, the sintered cemented carbide composition has a hardness of at least 1300 HV30. Hardness of the sintered cemented carbide composition, for example, can be 1300-1450 HV. Hardness values are determined according to ASTM E384-17, Standard Test Method for Microindentation Hardness for Materials.

Sintered cemented carbide compositions described herein, in some embodiments, exhibit magnetic saturation of 80% to 100% or 90% to 98%. Magnetic saturation values recited herein are based on magnetic component(s) of the metallic binder phase and are determined according to ASTM B 886-12, “Standard Test Method for Determination of Magnetic Saturation (MS) of Cemented Carbides,” ASTM International. As known to one of skill in the art, magnetic saturation values may be converted from percentages to μTm³/kg or other comparable units based on comparison to a nominally pure Co binder phase. For example, see Roebuck, B. Magnetic Moment (Saturation) Measurements on Hardmetals, Int. J. Refractory Metals & Hard Materials, 14 (1996) 419-424. Additionally, sintered cemented carbide compositions described herein can be free of eta phase and/or other lower carbides, such as W₂C. Sintered cemented carbide compositions described herein, in some embodiments, exhibit a coercivity of at least 135 Oe. The sintered cemented carbide compositions can have a coercivity of 135-170 Oe, in some embodiments. Coercivity is measured according to ASTM B887-12, Standard Test Method for Determination of Coercivity of Cemented Carbides.

As the sintered cemented carbide compositions are formed from the powder compositions described in Section I hereinabove, the sintered cemented carbide compositions can further comprise additional solid solution carbide phases and/or cubic carbide phases having chemical identities and amounts provided in Section I.

Sintered cemented carbide compositions described herein can be prepared by providing the powder composition described in Section I above and milling the powder composition in a ball mill or attrition mill with the optional addition of sintering aids. The powder composition is formed into a green article, and the green article is vacuumed sintered or sintered-hot isostatic press (HIP) at a temperature ranging from 1350° C. to 1560° C. for a time period sufficient to produce the sintered cemented carbide of desired density and microstructure. (La, Y)C₂ particles of the powder compositions described in Section I above are produced via carburization of lanthanum oxide and yttrium oxide particles. La₂O₃ and Y₂O₃ particles can be milled with a carbon source, such as graphite, prior to the carburization process. Milling is conducted for a time period sufficient to place the carbon in intimate contact with the La₂O₃ and Y₂O₃ particles. Carburization can be administered at 2000° C. and 750-850 L/hr of H₂ for a time period sufficient to produce the (La, Y)C₂ particles.

Sintered cemented carbides described herein can be employed in various applications including, but not limited to, cutting tools. In some embodiments, sintered cemented carbide compositions are formed into cutting inserts, such as indexable milling inserts and interrupted cutting inserts. The sintered cemented carbide compositions can also be formed into rotary cutting tools including drills and endmills of various geometries. In some embodiments, sintered cemented carbide articles having composition and properties described herein are coated with one or more refractory materials by PVD and/or CVD. In some embodiments, the refractory coating comprises one or more metallic elements selected from aluminum and metallic elements of Groups IVB, VB and VIB of the Periodic Table and one or more non-metallic elements selected from Groups IIIA, IVA, VA and VIA of the Periodic Table. For example, the refractory coating can comprise one or more carbides, nitrides, carbonitrides, oxides or borides of one or more metallic elements selected from aluminum and Groups IVB, VB and VIB of the Periodic Table. Additionally, the coating can be single-layer or multi-layer.

These and other embodiments are further illustrated by the following non-limiting examples.

Example 1—Sintered Cemented Carbide Articles

A non-limiting example of a powder composition having composition and properties described herein was provided according to Table 2.

TABLE 2
Inventive Powder Composition

	Component	Amount (wt. %)

	WC	75.4
	(W, Ti)C	9.2
	NbC	0.94
	(Ta, Nb)C 40/60	1.80
	(La, Y)C2O 40/60	1.16
	Co binder	11.5
	Total	100.0

A comparative prior powder composition was provided according to Table 3.

TABLE 3
Comparative Powder Composition

	Component	Amount (wt. %)

	WC	73.8
	(W, Ti)C	9.2
	NbC	1.9
	(Ta, Nb)C 90/10	3.6
	(La, Y)C2O 40/60	—
	Co binder	11.5
	Total	100

As provided in Tables 2 and 3, approximately 50 percent of the (Ta,Nb)C in the Comparative powder composition was replaced by (La, Y)C₂O in volume fraction of the Inventive powder composition.

The powder compositions of Tables 2 and 3 were pressed into green milling inserts having the ANSI geometry TPKN22. The green milling inserts were subsequently vacuum sintered at peak temperature of 1440° C. and a time period of 50 minutes to provide sintered cemented carbide turning inserts for metal cutting testing. Metallography was performed on the inserts formed of the sintered Inventive powder composition of Table 2 and the sintered Comparative powder composition of Table 3. FIGS. 2A-2C provide metallographic images of the Inventive sintered cemented carbide composition, and FIGS. 3A-3C provide metallographic images of the Comparative sintered cemented carbide composition. As evidenced in the figures, partial replacement of (Ta,Nb)C with (La, Y)C₂O did not result in discernable morphological changes. Table 4 provides test results of hardness, magnetic saturation, and coercivity of the Inventive and Comparative sintered cemented carbide cutting inserts.

TABLE 4
Testing Results

		Magnetic
Sample	Hardness (HV30)	Saturation (%)	Coercivity (Oe)
Inventive	1375	96.4	138.8
Comparative	1415	80.5	162.9

The Inventive and Comparative turning inserts were subjected to metal cutting testing under the following conditions:

• • Machine: FJV 3-axis machining center
  • Tool Holding: HSK-63A-Shell mill adaptor
  • Cutter Description: M40 Dia 80 cutter
  • Test Material: Steel 4340
  • Hardness: 220-240 BHN
  • Block Size: 300 mm×150 mm

The Inventive and Comparative turning inserts were in an uncoated condition, and cutting time was recorded until the turning inserts reached a maximum wear of 0.3 mm. The results of the metal cutting are provided in Tables 5 and 6.

TABLE 5*
Metal Cutting Results

Test	Inventive (minutes)	Comparative (minutes)

1	11.17	7.80
2	11.17	13.40
3	9.31	5.08
Average	10.55	8.76
Percent Improvement	20.4	—
*Cutting Speed - 90 m/min at 2 mm depth of cut

TABLE 6*
Metal Cutting Results

Test	Inventive (minutes)	Comparative (minutes)

1	9.10	5.66
2	9.18	5.96
Average	9.14	5.81
Percent Improvement	57.3	—
*Cutting Speed - 200 m/min at 3 mm depth of cut

As provided in Tables 5 and 6, the Inventive turning inserts provided substantial gains in cutting lifetimes.

Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.