Thermally stable polycrystalline compacts for reduced spalling earth-boring tools including such compacts, and related methods

An earth-boring tool, comprising:

• a tool body;
• and
• a plurality of cutting elements attached to the tool body, wherein at least one cutting element of the plurality of cutting elements comprises a generally planar polycrystalline compact, the polycrystalline compact including:
• a body of inter-bonded grains of hard material having a first major surface defining a front cutting face of the polycrystalline compact, a second major surface on an opposing back side of the body, at least one lateral side surface extending between the first major surface and the second major surface, and a central axis extending through a center of the body and generally perpendicular to the first major surface and the second major surface, the hard material comprising diamond or cubic boron nitride;
• and
• an interstitial material;
• and
• wherein a first volume of the polycrystalline compact is at least substantially free of the interstitial material such that voids exist in interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume, a second volume of the polycrystalline compact includes the interstitial material in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume, and an interface between the first volume and the second volume is located and oriented such that at least one crack originating proximate a point of contact between the polycrystalline compact and a subterranean formation near the at least one lateral side surface of the body and propagating along the interface generally toward the central axis will propagate generally toward the second major surface of the body at an acute angle or angles to each of the first major surface and the second major surface.

A method of forming a generally planar polycrystalline compact, comprising:

• using a high-temperature/high-pressure (HTHP) sintering process to form a body of inter-bonded grains of hard material having a first major surface defining a front cutting face of the polycrystalline compact, a second major surface on an opposing back side of the body, at least one lateral side surface extending between the first major surface and the second major surface, and a central axis extending through a center of the body and generally perpendicular to the first major surface and the second major surface, the hard material comprising diamond or cubic boron nitride, using the high-temperature/high-pressure (HTHP) sintering process including catalyzing the formation of inter-granular bonds between the inter-bonded grains of hard material using a catalyst, the catalyst forming an interstitial material in the body of inter-bonded grains of hard material;
• and
• removing the interstitial material from interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume and leaving the interstitial material in interstitial spaces between surfaces of the inter-bonded grains of hard material within the second volume such that the first volume is at least substantially free of the interstitial material and voids exist in the interstitial spaces between surfaces of the inter-bonded grains of hard material within the first volume, and forming an interface between the first volume and the second volume configured, located and oriented such that at least one crack originating proximate a point of contact between the polycrystalline compact and a subterranean formation near the at least one lateral side surface of the body and propagating along the interface generally toward the central axis will propagate generally toward the second major surface at an acute angle or angles to each of the first major surface and the second major surface.