A superhard polycrystalline construction comprises a body of polycrystalline superhard material comprising a structure comprising superhard material, the structure having porosity greater than 20% by volume and up to around 80% by volume. A method of forming such a superhard polycrystalline construction comprises forming a skeleton structure of a first material having a plurality of voids, at least partially filling some or all of the voids with a second material to form a pre-sinter assembly, and treating the pre-sinter assembly to sinter together grains of superhard material to form a body of polycrystalline superhard material comprising a first region of superhard grains, and an interpenetrating second region; the second region being formed of the other of the first or second material that does not comprise the superhard grains; the superhard grains forming a sintered structure having a porosity greater than 20% by volume and up to around 80% by volume.

There is provided a vitrified bond super-abrasive grinding wheel including: a core; and a super-abrasive grain layer provided on the core, wherein the super-abrasive grain layer includes a plurality of super-abrasive grains and a vitrified bond that joins the plurality of super-abrasive grains, and the vitrified bond has a plurality of bond bridges located between the plurality of super-abrasive grains to join the plurality of super-abrasive grains, not less than 80% of the plurality of super-abrasive grains are joined to the super-abrasive grains adjacent thereto by the bond bridges, and not less than 90% of the plurality of bond bridges in a cross section of the super-abrasive grain layer have a thickness equal to or smaller than an average grain size of the super-abrasive grains, and have a length greater than the thickness.

To provide an alumina sintered body, abrasive grains, and a grinding wheel having high hardness and excellent wear resistance. An alumina sintered body comprising: an inner layer comprising alumina crystal grains; and an outer layer covering at least a part of the inner layer from outside, having a higher content of an alkaline earth metal than the inner layer, and comprising alumina crystal grains, wherein the content of the alkaline earth metal in the outer layer is 1.0 to 30.0 mass % in terms of oxide, the alumina sintered body being free from silicon except unavoidable impurities.

To provide an alumina sintered body, abrasive grains, and a grinding wheel having high hardness and excellent wear resistance. An alumina sintered body comprising: an inner layer comprising alumina crystal grains; and an outer layer covering at least a part of the inner layer from outside, having a higher content of an alkaline earth metal than the inner layer, and comprising alumina crystal grains, wherein the content of the alkaline earth metal in the outer layer is 1.0 to 30.0 mass % in terms of oxide, the alumina sintered body being free from silicon except unavoidable impurities.

An abrasive article including a body having a bond material extending throughout the body and including at least 8 wt % aluminum oxide (Al.sub.2O.sub.3) for a total weight of the bond material, and also including unagglomerated abrasive particles including silicon carbide (SiC) contained within the bond material and present in an amount of greater than 30 vol % for a total volume of the body.

An abrasive article including a body having a bond material extending throughout the body and including at least 8 wt % aluminum oxide (Al.sub.2O.sub.3) for a total weight of the bond material, and also including unagglomerated abrasive particles including silicon carbide (SiC) contained within the bond material and present in an amount of greater than 30 vol % for a total volume of the body.

A sintered vitrified superfinishing grindstone is provided which is a sintered product which is obtained by compression molding of a mixed powder of: a sinterable vitrified binder composed of a powder of a borosilicate glass composition; hard abrasive grains; and soft abrasive grains; and which includes bonded portions formed by necking due to heat compression, between particles of the powder of the borosilicate glass composition which are in contact with each other; and wherein the sinterable vitrified binder contains from 94 to 100% by mass of a powder composed of a low-melting-point borosilicate glass composition containing from 35 to 55% by mole of SiO.sub.2; from 3 to 5% by mole of Al.sub.2O.sub.3; from 10 to 35% by mole of B.sub.2O.sub.3; and from 25 to 30% by mole of R.sub.2O+RO.

A sintered vitrified superfinishing grindstone is provided which is a sintered product which is obtained by compression molding of a mixed powder of: a sinterable vitrified binder composed of a powder of a borosilicate glass composition; hard abrasive grains; and soft abrasive grains; and which includes bonded portions formed by necking due to heat compression, between particles of the powder of the borosilicate glass composition which are in contact with each other; and wherein the sinterable vitrified binder contains from 94 to 100% by mass of a powder composed of a low-melting-point borosilicate glass composition containing from 35 to 55% by mole of SiO.sub.2; from 3 to 5% by mole of Al.sub.2O.sub.3; from 10 to 35% by mole of B.sub.2O.sub.3; and from 25 to 30% by mole of R.sub.2O+RO.

To provide an alumina sintered body, abrasive grains, and a grinding wheel having high hardness and excellent wear resistance. An alumina sintered body comprising: an inner layer comprising alumina crystal grains; and an outer layer covering at least a part of the inner layer from outside, having a higher content of an alkaline earth metal than the inner layer, and comprising alumina crystal grains, wherein the content of the alkaline earth metal in the outer layer is 1.0 to 30.0 mass % in terms of oxide, the alumina sintered body being free from silicon except unavoidable impurities.

To provide an alumina sintered body, abrasive grains, and a grinding wheel having high hardness and excellent wear resistance. An alumina sintered body comprising: an inner layer comprising alumina crystal grains; and an outer layer covering at least a part of the inner layer from outside, having a higher content of an alkaline earth metal than the inner layer, and comprising alumina crystal grains, wherein the content of the alkaline earth metal in the outer layer is 1.0 to 30.0 mass % in terms of oxide, the alumina sintered body being free from silicon except unavoidable impurities.