Patent Application
20140262537
Cutting elements as disclosed herein comprises a diamond wear surface and a substrate material that has been specially engineered to prolong cutting element service life.
Cutting elements, such as those used with bits for drilling subterranean formations known in the art comprises a diamond surface layer coated on a carbide substrate. The diamond surface layer is used to provide improved wear and abrasion resistance, relative to the substrate, and the substrate is used to provide an attachment structure to a machine tool, e.g., such as a drill bit or the like.
Such known cutting elements have a diamond layer or diamond table formed from polycrystalline diamond and make use of a carbide substrate such as WC—Co. While the diamond layer operates to provide improved wear and abrasion resistance to the cutter, the diamond layer is known to have a coefficient of thermal expansion that is much lower than that of the underlying substrate. Accordingly, high residual stress along the interface between diamond table and substrate generates during the formation of the cutting element. The high residual stress area is a weak link of the cutting element, which may cause delamination during a drilling operation when an extra load is applied to the cutting element, thereby reducing the effective service life of the cutting element.
Attempts to improve the service life of such cutting elements have included using an increased thickness diamond layer. However, while this approach provides a further increase in strength to the cutting element, it also leads to an increase in thermal mismatch between the diamond layer and the substrate, thereby further increasing the residual stress.
It is, therefore, desired that a cutting element be developed in a manner having an improved degree of strength while also having an improved service life when compared to conventional cutting elements. It is further desired that such cutting element be capable of being manufactured in a manner that uses known processes and materials, and that does not add significantly to the cost or time for manufacturing.
Cutting elements as disclosed herein comprise a body and a polycrystalline diamond table disposed on the body and forming a wear surface of the cutting element. In an example, the polycrystalline diamond table has a thickness of greater than about 2 mm. The body is formed from a material comprising WC—Co, and is specially developed to provide an improved degree of strength and improved service life when compared to conventional cutting element bodies as used with such polycrystalline diamond tables.
Specifically, cutting elements as disclosed herein have a body comprising a Co content of equal to or less than about 10 weight percent based on the total weight of the WC—Co, a coefficient of thermal expansion that is less than about 5×10−6/° C., a Palmqvist toughness greater than about 180 kg/mm, and a hardness equal to or greater than about 88 HRA. In an example, the WC has an average particle size of between about 2 to 5 micrometers, the Co content is in the range of from about 7 to 9 weight percent, the coefficient of thermal expansion is in the range of from about 4 to 5×10−6/° C., the Palmqvist toughness is in the range of from about 200 to 300 kg/mm, and the hardness is in the range of from about 88 to 90 HRA.
Cutting elements as disclosed herein may have an interface between the body and polycrystalline diamond table that is smooth or that is nonsmooth, e.g., characterized by one or more surface features that operate to provide an improved mechanically attachment between the body and the polycrystalline diamond table. That cutting element may comprise one or more layers of material interposed between the substrate and polycrystalline diamond table.
Cutting elements as disclosed herein may be configured in the form of diamond enhanced inserts or PCD shear cutters for attachment with bits for mining or drilling, wherein such bits may include one or more rotary cones and/or one or more fixed blades, depending on the particular end-use application.
These and other features and advantages of cutting elements as disclosed herein will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Cutting elements as disclosed herein comprise a body or substrate having a relatively thick diamond table formed from polycrystalline diamond (PCD) coated as a working or wear surface of the cutting element. The body or substrate is specially engineered to accommodate the relatively thick diamond layer and provide combined properties of thermal expansion, toughness, and hardness that operate to increase the operational service life of the cutting element.
The cutting element 10 illustrated in
The cutting element may comprise a diamond table provided in the form of a single layer or multiple layers, and in an example the diamond table is formed from PCD.
The PCD used to form the diamond table comprises a material microstructure made up of a matrix phase of bonded-together diamond grains with a second phase. In an example, the second phase comprises a catalyst material that is used to form the PCD at high pressure/high temperature (HPHT) conditions. The catalyst materials include conventional catalyst materials such as those selected from Group VIII of the CAS version of the Periodic Table. The second phase may also include the particles of carbide of a metal, such as W, Nb, Ti, Ta and the like. In an example, the PCD may have a diamond volume content in of from about 80 to 99, from about 88 to 98, and from about 90 to 96 percent based on the total volume of the materials used to form the PCD. In an example, the PCD may have a catalyst volume content in the range of from about 1 to 20, from about 2 to 12, and from about 4 to 10 percent based on the total volume of the materials used to form the PCD. In an example, the PCD has a diamond volume content of above about 95 percent by volume, and a catalyst content of less than about 5 percent by volume.
While the cutting element examples illustrated in
In an example, the cutting elements as disclosed herein have a relatively thick diamond table. In an example, the diamond table has a thickness greater than about 2 mm, greater than about 2.5 mm, and greater than about 5 mm. In an example, the diamond table thickness is between about 2 to 10 mm, and between about 2.5 to 5 mm. In an example, the diamond table thickness is approximately 3.8 mm. A feature of cutting elements having such an increased diamond table thickness, when compared to that of conventional cutting elements, is that the increased diamond thickness operates to provide the cutting element with an improved degree of wear resistance, abrasion resistance, and fracture resistance for use in certain demanding end-use applications.
The cutting element body or substrate is specially engineered to provide an improved degree of thermal compatibility or matching with the relatively thick diamond table to avoiding undesired delamination, while also providing improved properties of toughness, strength and hardness to provide a service consistent with that of the diamond table.
In an example, the body is formed from WC—Co having a coefficient of thermal expansion (CTE) that is less than about 5×10−6/° C. In an example, the WC—Co may have a CTE in the range of from about 4 to 5×10−6/° C., and in the range of from about 4.5 to 5×10−6/° C. In an example embodiment, the WC—Co is engineered having a CTE of approximately 4.75×10−6/° C. The CTE was measured according to ASTM E228.
In an example, the desired CTE is achieved by controlling the amount of Co or Co content in the WC—Co. In an example, it is desired that the Co content in the WC—Co be equal to or less than about 10 weight percent, based on the total weight of the WC—Co. The Co content may be in the range of from about 7 to 10 percent by weight, and in the range of from about 7 to 9 percent by weight. In an example, WC—Co is engineered having a Co content of approximately 8 percent by weight.
The WC—Co as disclosed herein is engineered having a particular WC particle or grain size for the purpose of gaining good strength and reducing or eliminating major eruptions that may occur within the body during the process of forming and bonding the diamond table to the substrate. During the HPHT process of forming and bonding the diamond table, major eruptions within the WC—Co material microstructure initiating at the interface with the diamond table may occur if the WC particle size is too large and/or if there is too large an amount of Co. The presence of such major eruptions operates to disrupt the otherwise homogeneous microstructure of the diamond table, which may operate as stress concentration sites and weaken the bond at the interface attaching the diamond table to the substrate. It has been discovered that by controlling the size of the WC particles, along with Co content, used to form the substrate that such major eruptions may be minimized or avoided.
In an example, the WC—Co used to form cutting elements as disclosed herein has an average WC particle size of less than about 6 micrometers, between about 1 to 5 micrometers, and between about 2 to 5 micrometers. WC particle size is measured by the mean lineal intercept method. In this method, the average grain size is measured based on two dimensional images on which lines are drawn across the images horizontally and average grain size is measures from the intersections and determined by:
NWC/WC—number of intersections between the WC-WC boundary and the measuring line per unit length of measuring line
NWC/Co—number of intersections between the WC—Co boundary and the measuring line per unit length of measuring line
The WC—Co used to form cutting elements as disclosed herein has a toughness that is engineered to complement the enhanced strength provided by the relatively thicker diamond table, e.g., by enhancing substrate impact strength and avoiding substrate breakage. In an example, the WC—Co is engineered having a toughness as measured by a Palmqvist toughness number greater than about 180 kg/mm, in the range from about 200 to 300 kg/mm, in the range of from about 210 to 270 kg/mm. In an example, the WC—Co has a Palmqvist toughness of approximately 230 kg/mm. This toughness value is achieved as a result of both WC—Co grain size and Co content. Accordingly, WC—Co materials having the WC—Co grain size and Co content as disclosed herein in addition to avoiding unwanted major eruptions operate to provide the desired Palmqvist toughness value.
Palmqvist toughness is a toughness value obtained from measuring crack lengths at the corners of a Vickers hardness indentation. For example, a Vickers hardness indentation is first made in a composite material using an applied load P, such as a 150 kgf, and the lengths in mm of the cracks which extend from each corner of the indentation are measured, wherein l1, l2, l3, and l4 represents the length of the crack at each corner, respectively. From these values a Palmqvist toughness value, W, can be calculated as W=P/(l1+l2+l3+l4).
WC—Co useful for forming cutting elements as disclosed herein has a hardness that provides a desired level of wear resistance for use with the cutting element. In an example, the WC—Co material has a hardness of equal or greater than about 88 HRA, in the range of from about 88 to 90 HRA. In an example, the WC—Co has a hardness of approximately 89 HRA. The Rockwell A hardness was determined according to ASTM B294.
In summary, example WC—Co materials as disclosed herein when used to form constructions comprising relatively thick diamond tables display improved performance, such as less tendency of cracking and/or delamination during end-use applications (e.g., during drilling operation).
Cutting elements as disclosed herein may be formed according to the same methods used to form conventional cutting elements comprising a body or substrate and a diamond table or layer coated or otherwise disposed on the substrate. In an example, the substrate and diamond table may be formed during a single HPHT process or may be formed during separate processes, e.g., wherein the substrate is formed first and then a diamond table formed and attached to the substrate during a different HPHT process. In an example, the substrate is formed first by conventional process, and the diamond table is formed and bonded to the preformed substrate during an HPHT process.
Cutting elements as disclosed herein may be used in a number of different applications, such as tools for mining, cutting, machining, milling and construction applications, wherein properties of wear resistance, abrasion resistance, toughness, and mechanical strength, and/or reduced thermal residual stress, e.g., caused by mismatched CTE, are highly desired. Cutting elements as disclosed herein are particularly well suited for use in machine tools and drill and mining bits such as PDC or fixed blade bits, roller cone rock bits, percussion or hammer bits and the like used in subterranean drilling applications. Accordingly, it is to be understood that the cutting elements illustrated in
Other modifications and variations of cutting elements as disclosed herein will be apparent to those skilled in the art. It is, therefore, to be understood that within the scope of the appended claims, cutting elements may be practiced otherwise than as specifically described.
