Dual grade carbide substrate for earth-boring drill bit cutting elements, drill bits so equipped, and methods

An earth-boring drill bit, comprising:

• at least one substrate secured thereto and including:
• an erosion-resistant and abrasion-resistant outer shell including a cavity open to a single end thereof, said cavity extending into a substantial majority of said outer shell, said outer shell defining an exterior surface of said at least one substrate other than a cavity opening;
• and
• a core configured to fit within said cavity, comprising a carbide, and having a greater ductility that said outer shell, said core being configured and located within the cavity to absorb impact upon a cutting table positioned directly over an end of said core.

An earth-boring drill bit, comprising:

• a bit body;
• and
• at least one cutting element secured to said bit body, said at least one cutting element comprising:
• a substrate including an erosion-resistant and abrasion-resistant base including a substantially centrally located, close-ended cavity opened to a cutting end of the base, said close-ended cavity extending into a substantial majority of said base, said base defining an exterior surface of said substrate other than a cavity opening, said close-ended cavity receiving a substantially complementarily-shaped core therewithin, said core comprising a carbide and having a greater toughness than a material of said base;
• and
• a superabrasive cutting table disposed directly over said core, proximate said cutting end of said base, said core being configured and located within said cavity to absorb impact upon said cutting table.

A method of fabricating a substrate, comprising:

• forming a first mixture of a matrix material and a binder into an erosion-resistant and abrasion-resistant outer shell including an open cavity therein continuous with one end of said outer shell, said open cavity extending into a substantial majority of said outer shell, said outer shell defining an exterior surface of the substrate other than a cavity opening;
• forming a second mixture of carbide and a binder into a core exhibiting greater ductility than said outer shell, complementary in shape to said open cavity and configured to be insertable therein;
• assembling said outer shell and said core such that said core is configured and located within said cavity to absorb impact upon a cutting table positioned directly over and end of said core;
• and
• securing said outer shell and said core to one another.

A method of fabricating a substrate, comprising:

• disposing a first mixture of a matrix material, a binder, and an adhesive material within a cavity of a mold to form an erosion-resistant and abrasion-resistant base of the substrate, said base having a cavity formed therein, said base defining an exterior surface of the substrate other than a cavity opening;
• disposing a second mixture of a matrix material, a binder, and an adhesive material within another cavity of another mold to form a core exhibiting greater ductility than the base of the substrate;
• assembling said base and said core, said core extending into a substantial majority of said base, said core being configured and located within said cavity to absorb impact upon a cutting table positioned directly over an end of said core;
• and
• securing said base and said core to one another.

A method of fabricating a substrate, comprising:

• forming an erosion-resistant and abrasion-resistant outer shell of the substrate from a first mixture comprising a matrix material and a binder material, said outer shell having a cavity formed therein that extends a majority of a distance into said outer shell, said outer shell also defining an outer surface of the substrate other than a cavity opening;
• disposing a second mixture comprising a matrix material and a binder material within the cavity of said outer shell to form a core exhibiting greater ductility than the outer shell, said core being configured and located within said cavity to absorb impact upon a cutting table positioned directly over an end of said core;
• and
• securing said outer shell to said core.