A coated cutting tool comprising: a substrate and a coating layer, wherein the coating layer includes a lower layer and an upper layer; the lower layer includes one or two or more specific Ti compound layers; the upper layer includes an α-type Al.sub.2O.sub.3 layer; an average thickness of the lower layer is 2.0 μm to 15.0 μm; an average thickness of the upper layer is 3.5 μm to 15.0 μm; in the upper layer, a ratio of a length of Σ3 grain boundaries to a total length of 100% of a total grain boundary is more than 50% and 80% or less, and a ratio of the length of Σ3 grain boundaries to a total length of 100% of CSL grain boundaries is 70% or more; and in the upper layer, a texture coefficient TC(0,0,12) of the α-type Al.sub.2O.sub.3 layer is 8.0 or more and 8.9 or less.

Provided is a ceramic sintered body having high wear resistance and chipping resistance. Also provided are an insert, a cutting tool and a friction stir welding tool, each of which uses such a high-performance ceramic sintered body. The ceramic sintered body includes Al.sub.2O.sub.3 (alumina), WC (tungsten carbide) and ZrO.sub.2 (zirconia), wherein Zr (zirconium) element is present at either one or both of: (1) a grain boundary between crystal grains of the Al.sub.2O.sub.3; and (2) a grain boundary of crystal grains of the Al.sub.2O and crystal grains of the WC, wherein the ceramic sintered body contains 55.0 to 97.5 vol % of the WC, 0.1 to 18.0 vol % of the ZrO.sub.2, and the balance being the Al.sub.2O.sub.3, and wherein the ZrO.sub.2 is in a phase of tetragonal structure (T) or a mixed phase of tetragonal structure (T) and monoclinic structure (M).

A method of providing a self-healing coating includes providing substrate, applying a layer of an aluminum-containing MAX phase material and another material to the substrate. The method includes exposing the layer to a temperature greater than 2000° F. to form alpha aluminum.

A method of providing a self-healing coating includes providing substrate, applying a layer of an aluminum-containing MAX phase material and another material to the substrate. The method includes exposing the layer to a temperature greater than 2000° F. to form alpha aluminum.

A cutting tool comprising a base material and a coating, wherein the coating includes a first layer having a multilayer structure in which a first unit layer and a second unit layer are alternately stacked; a thickness of the first unit layer is 2 to 50 nm; a thickness of the second unit layer is 2 to 50 nm; a thickness of the first layer is 1.0 m or more and 20 m or less, the first unit layer is composed of Ti.sub.aAl.sub.bB.sub.cN, and the second unit layer is composed of Ti.sub.dAl.sub.eB.sub.fN, wherein 0.49a0.70, 0.190.40, 0.10<c0.20, a+b+c=1.00, 0.39d0.60, 0.29e0.50, 0.10<f0.20, d+e+f=1.00, 0.05ad0.20, and 0.05eb0.20 are satisfied, and a percentage of the number of atoms of titanium to the total number of atoms of titanium, aluminum and boron is 45% or more in the first layer.

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 MAIN layer, the MAIN 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 m in length of the MAIN layer on the flank face in a cross section of the MAIN layer, and n.sub.R represents a number of voids per 100 m in length of the MAIN layer on the rake face in a cross section of the MAIN layer, n.sub.D being 3 or less, where n.sub.D represents a number of droplets per 100 m in length of the MAIN layer on the flank face in a cross section of the MAIN layer.

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 MAIN layer, the MAIN 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 m in length of the MAIN layer on the flank face in a cross section of the MAIN layer, and n.sub.R represents a number of voids per 100 m in length of the MAIN layer on the rake face in a cross section of the MAIN layer, n.sub.D being 3 or less, where n.sub.D represents a number of droplets per 100 m in length of the MAIN layer on the flank face in a cross section of the MAIN layer.

Ground surface comprising a substrate (110) having a Young's modulus of between 100 and 1000 GPa, and in which the ground surface has, on a working surface (120), a Vickers hardness of between 1300 and 10 000 kgf/mm.sup.2, and/or a surface coating forming the working surface, in which the surface coating contains amorphous carbon and/or titanium nitride and/or chromium nitride and/or tungsten carbide.

A coated cutting tool, comprising: a substrate made of a cubic boron nitride-containing sintered body; and a coating layer formed on the substrate, wherein the cubic boron nitride-containing sintered body includes 65 volume % or more and 85 volume % or less of cubic boron nitride, and 15 volume % or more and 35 volume % or less of a binder phase; the cubic boron nitride is in a form of particles, the particles having an average particle size from 1.5 m or more to 4.0 m or less; the coating layer includes a lower layer, and an upper layer formed on the lower layer; the lower layer contains particles each having a composition represented by (Ti.sub.1-xAl.sub.x)N; the lower layer has an average thickness from 0.1 m or more to 1.0 m or less; the particles forming the lower layer have an average particle size from 0.01 m or more to 0.05 m or less; the upper layer contains particles each having a composition represented by (Ti.sub.1-yAl.sub.y)(C.sub.1-zN.sub.z); and the upper layer has an average thickness from 1.0 m or more to 5.0 m or less.

A coated cutting tool, comprising: a substrate made of a cubic boron nitride-containing sintered body; and a coating layer formed on the substrate, wherein the cubic boron nitride-containing sintered body includes 65 volume % or more and 85 volume % or less of cubic boron nitride, and 15 volume % or more and 35 volume % or less of a binder phase; the cubic boron nitride is in a form of particles, the particles having an average particle size from 1.5 m or more to 4.0 m or less; the coating layer includes a lower layer, and an upper layer formed on the lower layer; the lower layer contains particles each having a composition represented by (Ti.sub.1-xAl.sub.x)N; the lower layer has an average thickness from 0.1 m or more to 1.0 m or less; the particles forming the lower layer have an average particle size from 0.01 m or more to 0.05 m or less; the upper layer contains particles each having a composition represented by (Ti.sub.1-yAl.sub.y)(C.sub.1-zN.sub.z); and the upper layer has an average thickness from 1.0 m or more to 5.0 m or less.