A cutting tool comprises a substrate and a coating that coats the substrate, the coating including an α-alumina layer provided on the substrate, the α-alumina layer including crystal grains of α-alumina, the α-alumina layer including a lower portion and an upper portion, the upper portion being occupied in area at a ratio of 50% or more by crystal grains of α-alumina having a (006) plane with a normal thereto having a direction within ±15° with respect to a direction of the normal to the second interface, the lower portion being occupied in area at a ratio of 50% or more by crystal grains of α-alumina having a (110) plane with a normal thereto having a direction within ±15° with respect to the direction of the normal to the second interface, the α-alumina layer having a thickness of 3 μm or more and 20 μm or less.

A cutting tool comprises a rake face and a flank face, the cutting tool being composed of a substrate made of a cubic boron nitride sintered material and a coating provided on the substrate, the coating including a MAlN layer, the MAlN layer including crystal grains of M.sub.xAl.sub.1-xN in the cubic crystal system, n.sub.F<n.sub.R being satisfied, where n.sub.F represents a number of voids per 100 μm in length of the MAlN layer on the flank face in a cross section of the MAlN layer, and n.sub.R represents a number of voids per 100 μm in length of the MAlN layer on the rake face in a cross section of the MAlN layer, n.sub.D being 3 or less, where n.sub.D represents a number of droplets per 100 μm in length of the MAlN layer on the flank face in a cross section of the MAlN layer.

A surface-coated cutting tool with a hard coating layer exhibits excellent chipping resistance and wear resistance in a high-speed cutting process. The surface-coated cutting tool comprises a lower layer consisting of a titanium compound layer and an upper layer consisting of an aluminum oxide layer deposited on a surface of a tool substrate constituted of a tungsten carbide-based cemented carbide as a hard coating layer. In the upper layer, a (006) plane texture coefficient TC(006) is 1.8 or more, a ratio I(104)/I(110) of a peak intensity I(104) of an (104) plane to a peak intensity I(110) of an (110) plane is in a range of 0.5 to 2.0, and furthermore, an absolute value of a residual stress in the aluminum oxide layer is 100 MPa or less.

A coated cutting tool has a substrate and a coating layer. At least one layer of the coating layer is a coarse grain layer with an average layer thickness of 0.2 to 10 μm and an average grain diameter in excess of 200 nm measured at the direction parallel to the interface of the coating layer. A composition of the layer is represented by (Al.sub.aTi.sub.bM.sub.c)X, wherein M represents at least one of Zr, Hf, V, Nb, Ta, Cr, Mo, W, Y, B and Si, X represents at least one of C, N and O, and a, b and c represents atomic ratios of Al, Ti and M relative to one another such that 0.30≦a≦0.65, 0.35≦0.70, 0≦c≦0.20 and a+b+c=1.

A method of producing a boron nitride polycrystal includes: a first step of obtaining a thermally treated powder by thermally treating a powder of a high pressure phase boron nitride at more than or equal to 1300° C.; and a second step of obtaining a boron nitride polycrystal by sintering the thermally treated powder under a condition of 8 to 20 GPa and 1200 to 2300° C.

A coated cutting tool includes a substrate and a coating layer formed onto the surface of the substrate. The coating layer contains an outermost layer. The outermost layer contains NbN. The NbN contains cubic NbN and hexagonal NbN. When a peak intensity at a (200) plane of cubic NbN is made I.sub.c, a peak intensity at a (101) plane of the hexagonal NbN is made I.sub.h1, and a sum of peak intensities at a (103) plane and a (110) plane of the hexagonal NbN is made I.sub.h2 in X-ray diffraction analysis, a ratio [I.sub.h1/(I.sub.h1+I.sub.c)] of I.sub.h1 based on a sum of I.sub.c and I.sub.h1 is 0.5 or more and less than 1.0, and a ratio [I.sub.h1/(I.sub.h1+I.sub.h2)] of I.sub.h1 based on a sum of I.sub.h1 and I.sub.h2 is 0.5 or more and 1.0 or less.

A coated cutting tool has a substrate and a coating layer formed onto a surface of the substrate. The coating layer contains a hard layer of a composition represented by (Ti.sub.xM.sub.1-x)N, wherein M represents at least one kind of an element selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, Si and Y, and x represents an atomic ratio of a Ti element based on a sum of the Ti element and an M element, and satisfies 0.45≦x≦0.9. Also, an average grain size of grains constituting the hard layer is 200 nm or more and 600 nm or less, and the grains of the hard layer satisfy predetermined conditions.

A hard material which, when used as a material of a sintered material, makes it possible to obtain a sintered material with excellent abrasion resistance, a sintered material, a cutting tool including the sintered material, a method for manufacturing the hard material and a method for manufacturing the sintered material are provided. The hard material contains aluminum, nitrogen, and at least one element selected from the group consisting of titanium, chromium, and silicon, and has a cubic rock salt structure.

A sialon sintered body and a cutting insert each having thermal shock resistance and VB wear resistance. The sialon sintered body and the cutting insert contain β-sialon and 21R-sialon and exhibit an X-ray diffraction peak intensity ratio R[(I.sub.21R/I.sub.A)×100] of 5% or greater and smaller than 30%, wherein I.sub.A represents the sum of the peak intensities of the sialon species, and I.sub.21R represents the peak intensity of 21R-sialon, the ratio being calculated from the peak intensities of the sialon species obtained by using X-ray diffractometry.

In one aspect, coatings are described herein employing composite architectures providing high aluminum content and high hardness for various cutting applications. For example, a coated cutting tool comprises a substrate and a coating comprising a refractory layer deposited by physical vapor deposition adhered to the substrate, the refractory layer comprising a plurality of sublayer groups, a sublayer group comprising a titanium aluminum nitride sublayer and an adjacent composite sublayer comprising alternating nanolayers of titanium silicon nitride and titanium aluminum nitride.