Coated cemented carbide endmill

Abstract

The present invention relates to a cemented carbide endmilling tool particularly useful for semifinishing and finishing machining of hardened steels of HRC above 46, comprising a substrate and a wear resistant coating. The substrate, a, comprises from about 90 to about 94 wt % WC in a binder phase of Co also containing Cr in such an amount that the Cr/Co weight ratio is from about 0.05 to about 0.18. The wear resistant coating, b, is from about 1.8 to about 9.5 μm thick, and comprises a first layer, c, of a hard and wear resistant refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti having a thickness of from about 1.0 to about 4.5 μm and an atomic fraction of Al to Me of from about 1.20 to about 1.50, a second layer, d, of hard and wear resistant refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti, having a thickness of from about 0.5 to about 4.5 μm, and an atomic fraction of Al to Me of 1.30-1.70, and in between the first layer (c) and the second layer (d), a from about 0.05 to about 1.0 μm thick low-Al layer, e, the thickness being less than about 0.95 times the thickness of thinnest of the first and the second layer, of an AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti and an atomic fraction of Al to Me of from about 0 to about 0.3.

1 . Cemented carbide endmilling tool comprising a substrate and a wear resistant coating wherein:
 the substrate (a) comprises from about 90 to about 94 wt % WC in a binder phase of Co also containing Cr in such an amount that the Cr/Co weight ratio is 0.05-0.18, and   the wear resistant coating (b) is from about 1.8 to about 9.5 μm thick comprising:   a first layer (c) of a hard and wear resistant refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti having a thickness of from about 1.0 to about 4.5 μm and an atomic fraction of Al to Me of from about 1.20 to about 1.50,   a second layer (d) of hard and wear resistant refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti having a thickness of from about 0.5 to about 4.5 μm, and an atomic fraction of Al to Me of from about 1.30 to about 1.70, and   in between the first and the second layer, a from about 0.05 to about 1.0 μm thick low-Al layer (e), the thickness of layer (e) being less than about 0.95 times the thickness of thinnest of the first layer (c) and the second layer (d), of an AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti and an atomic fraction of Al to Me of from about 0 to about 0.3.   
     
     
         2 . Cemented carbide endmilling tool of  claim 1 , wherein the Cr/Co ratio of the binder phase is from about 0.06 to about 0.16. 
     
     
         3 . Cemented carbide endmilling tool of  claim 1 , wherein the first layer and the second layer both have crystallites of the cubic rock salt structure with a grain size less than about 50 nm. 
     
     
         4 . Cemented carbide endmilling tool of  claim 1 , wherein the low-Al layer (e) has a crystallite grain size larger than about 40 nm perpendicular to the growth direction and larger than about 100 nm parallel to the growth direction. 
     
     
         5 . Cemented carbide endmilling tool of  claim 1 , wherein the first layer (c) has a residual compressive stress more than about 1000 MPa and that the second layer (d) has a residual compressive stress more than about 1000 MPa. 
     
     
         6 . Cemented carbide endmilling tool of  claim 1 , wherein the low-Al layer (e) has a residual stress of an absolute value less than 600 MPa, being compressive or tensile. 
     
     
         7 . Cemented carbide endmilling tool of  claim 1 , wherein the substrate comprises from about 91 to about 93 wt-% WC and the Cr/Co weight ratio of the substrate is from about 0.06 to about 0.16, the wear resistant coating is from about 2.5 to about 6.0 μm thick, the Me of the said first layer (c) is Ti, said first layer (c) having a thickness of from about 2 to about 3 μm and an atomic fraction of Al to Me of from about 1.30 to about 1.40. 
     
     
         8 . Cemented carbide endmilling tool of  claim 7 , wherein in said second layer (d), Me is Ti and said second layer (d) has a thickness of from about 1.0 to about 2.0 μm and an atomic fraction of Al to Me is from about 1.50 to about 1.6. 
     
     
         9 . Cemented carbide endmilling tool of  claim 8 , wherein the thickness of said low-Al layer (e) is from about 0.1 to about 0.7 μm, the thickness being less than about 0.8 times the thickness of the thinnest of the first layer (c) and second layer (d), Me of said low-Al layer (e) is Ti and the atomic fraction of Al to Me is from zero to about 0.05. 
     
     
         10 . Cemented carbide endmilling tool of  claim 7 , wherein the Cr/Co ratio of the substrate is from about 0.07 to about 0.14, the thickness of the low-Al layer (e) is less than about 0.5 times the thickness of the thinnest of the first layer (c) and second layer (d). 
     
     
         11 . Cemented carbide endmilling tool of  claim 1 , wherein the low-Al layer (e) is MeN. 
     
     
         12 . Cemented carbide endmilling tool of  claim 3 , wherein the grain size of said crystallite of said first layer (c) and second layer (d) is less than about 40 μm. 
     
     
         13 . Cemented carbide endmilling tool of  claim 4 , wherein the grain size of said crystallite of said low-Al layer (e) is less than about 50 nm. 
     
     
         14 . Cemented carbide endmilling tool of  claim 5 , wherein the first layer (c) and second layer (d) each have a residual compressive stress from about 1800 to about 3500 MPa. 
     
     
         15 . Cemented carbide endmilling tool of  claim 6 , wherein the low-Al layer (e) has a residual stress of an absolute value less than about 300 MPa. 
     
     
         16 . Cemented carbide endmilling tool of  claim 15 , wherein the low-Al layer (e) has a residual stress of an absolute value less than about 80 MPa. 
     
     
         17 . Method of making a cemented carbide endmilling comprising the following steps:
 providing a cemented carbide endmill blank with a composition comprising from about 90 to about 94 wt % WC in a binder phase of Co also containing Cr in such an amount that the Cr/Co weight ratio is from about 0.05 to about 0.18,   wet milling submicron powders of tungsten carbide cobalt, at least one of Cr 3 C 2 , Cr 23 C 6  and Cr 7 C 3  to obtain a slurry,   drying the slurry to obtain a powder,   pressing the powder into rods,   sintering the rods in vacuum or in nitrogen, and   optionally performing an isostatic gas pressure step during sintering temperature or at the final stage of sintering,   grinding the rods cylindrical to h6 tolerance,   grinding flutes using diamond wheels with emulsion cutting fluid,   depositing whilst maintaining a partial pressure of nitrogen in the recipient, and using the appropriate selection of active evaporation sources and rates,   a wear resistant coating (b) from about 1.8 to about 9.5 μm thick, comprising:   a first layer (c) of a hard and wear resistant refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti having a thickness of from about 1.0 to about 4.5 μm and an atomic fraction of Al to Me of from about 1.20 to about 1.50 with process parameters:   arc current from about 50 to about 200 A in the equipment, N 2 -pressure from about 5 to about 50 μbar and deposition temperature from about 400 to about 700° C. and a substrate bias of from about −150 to about −300V,
 a second layer (d) of hard and wear resistant refractory PVD AlMe nitride or carbonitride where Me is Zr, V, Nb, Cr or Ti, having a thickness of from about 0.5 to about 4.5 μm and an atomic fraction of Al to Me of from about 1.30 to about 1.70 with process parameters: arc current from about 50 to about 200 A in the equipment, N 2 -pressure from about 5 to about 50 μbar, and deposition temperature from about 400 to about 700° C. and a substrate bias of about −50 to about −140 V, and 
   in between the first and the second layers, a from about 0.05 to about 1.0 μm thick low-Al layer (e) at a temperature from about 400 to about 700° C., the substrate bias from about −30 to about 150 V and the arc current from about 80 to about 210 A.   
     
     
         18 . Method of making a cemented carbide endmilling tool of  claim 17 , further comprising:
 the substrate comprises from about 91 to about 93 wt-% WC and the Cr/Co weight ratio of the substrate is from about 0.06 to about 0.16, the wear resistant coating is from about 2.5 to about 6.0 μm thick, the Me of the said first layer (c) is Ti, said first layer (c) having a thickness of from about 2 to about 3 μm and an atomic fraction of Al to Me of from about 1.30 to about 1.40;   in said second layer (d), Me is Ti and said second layer (d) has a thickness of from about 1.0 to about 2.0 μm and an atomic fraction of Al to Me is from about 1.50 to about 1.6, and   the thickness of said low-Al layer (e) is from about 0.1 to about 0.7 μm, the thickness being less than about 0.8 times the thickness of the thinnest of the first layer (c) and second layer (d), Me of said low-Al layer (e) is Ti and the atomic fraction of Al to Me is from zero to about 0.5.   
     
     
         19 . Method of making a cemented carbide endmilling tool of  claim 17 , further comprising the Cr/Co ratio of the substrate is from about 0.07 to about 0.14, the thickness of the low-Al layer (e) is less than about 0.5 times the thickness of the thinnest of the first layer (c) and second layer (d). 
     
     
         20 . Method of making a cemented carbide endmilling tool of  claim 17 , further comprising the low-Al layer (e) is MeN. 
     
     
         21 . Method of making a cemented carbide endmilling tool of  claim 17 , wherein the process parameters for depositing said first layer (c) are arc current from about 120 to about 160 A, N z -pressure 7 to about 20 μbar, deposition temperature of from about 550 to about 650° C. and a substrate bias of from about −170 to about −230 V. 
     
     
         22 . Method of making a cemented carbide endmilling tool of  claim 17 , wherein the process parameters for depositing said second layer (d) are arc current from about 120 to about 160 A, N z -pressure 7 to about 20 μbar, deposition temperature of from about 550 to about 650° C. and a substrate bias of from about −80 to about −120 V. 
     
     
         23 . Method of making a cemented carbide endmilling tool of  claim 17 , wherein the process parameters for depositing said low-Al layer (e) are arc current from about 140 to about 190 A, N z -pressure 7 to about 20 μbar, deposition temperature of from about 550 to about 650° C. and a substrate bias of from about −70 to about −120 V.