CERAMIC COMPOSITIONS

Abstract: Ceramic compositions with mechanical properties, namely, wear resistance and transverse rupture strength, far exceeding that of conventional ceramic materials have been prepared. Said compositions comprise aluminum oxide and titanium carbonitride with or without metal phases. Articles made of such compositions can be used efficiently in such areas as metal cutting and other wear resistance applications.

Description: CERA IC COMPOSITIONS Technical Field The present invention relates to ceramic compositions with superior mechanical properties of wear resistance and transverse rupture strength. The ceramic compositions of the present invention comprise aluminum oxide and titanium carbonitride with or without metal phases. Background Art Although ceramic materials, especially alumina, have been used in many wear applications, their use has been severely limited due to their brittle nature or lack of toughness. Consequently, in applications where both wear resistance and toughness are needed, tungsten carbide and other complex carbides have been the materials of choice. Numerous efforts have been made to improve the toughness of ceramic oxides while retaining their inherent wear resistant character, but such efforts have met with only limited success. The combination of alumina with titanium carbide is one such example. It is commonly believed that oxides will, in general, exhibit higher wear resistance than the corresponding carbides or pure metals probably due to their chemical stability resulting from their more negative standard free energy of formation. This is especially evident when the materials are used in wear applications such as in metal cutting in which relatively high interface temperatures are generated thereby making diffusion of atoms across the interface a rate-controlling step for the wear process. According to this theory, the overall wear resistance ranking of ceramic materials in metal cutting is, in general, in the order of oxides, nitrides, and finally, carbides with their correspondingly lower negative free energy of formation. Yates, U.S. Patent 3,409,419 which is directed to ceramic compositions consisting of essential nitrides bonded with iron, cobalt, or nickel and wherein up to fifty percent of the essential nitride can be substituted with a carbide provided that the carbide cannot reduce the nitride content below 20 volume percent is another attempt to provide wear resistant compounds with exceptional properties. Disclosure of Invention The present invention provides ceramic compositions having improved toughness properties without materially affecting the inherent wear resistance characteristics thereof. This is achieved by adding an intermediate nitride phase to the alumina-titanium carbide compositions. It was found that in so doing, the titanium carbide and titanium nitride form a solid solution in the hot forming step thereby resulting in an alumina-titanium carbonitride composition of increased strength and wear resistance. The ceramic compositions of the present invention comprise 10-90 weight percent alumina and 90-10 weight percent titanium carbonitride, viz. c + n ≥. -- 50 ' wherein c is titanium carbide and n is titanium nitride and wherein said carbonitride includes 0-30 weight percent of a metal phase comprised of Group IVB or Iron group elements including Mo or combinations thereof. Articles made of such compositions are especially effective in applications where both wear resistance and toughness are required such as in metal cutting operations. Detailed Description Recent trends and more demanding conditions both in metal cutting operations and other wear applications have created the need for materials which are more wear resistant and tougher than conventional ceramic materials. As hereinabove noted, pure alumina cutting tools have been used in only limited cases such as in simple turning due to their lack of toughness. The highest strength hot pressed alumina may have a transverse rupture strength of about 7000 kg/cm 2 . Alumina-TiC cutting tools were more recently introduced and have successfully overcome some of the difficulties encountered with pure alumina tools. The transverse rupture strength of alumina-TiC materials is about 8400 kg/cm 2 . While it is common for both metallic and ceramic materials that any gain in toughness, measured by transverse rupture strength of the material is accompanied by some sacrifice in wear resistance such as measured by turning tests, the compositions of the present invention have average transverse rupture strengths above such alumina-TiC compositions and also possess generally improved wear resistance properties. The following specific examples are intended to illustrate more clearly the nature of the present invention. Example 1 A 700 gram mixture of alumina having an average particle size of 0.65 micron, titanium carbide powder having an average particle size of 3-5 micron, titanium nitride powders having an average particle size of 1 micron, and molybdenum powders having an average particle size of 1 micron, in a weight ratio of 10 percent, 41 percent, 40 percent, 4.5 percent and 4.5 percent, respectively, was ball milled in Soltrol for 40 hours. The milled powder mixture was vacuum dried at 240°C for 14 hours and subsequently hot pressed at 1550°C for 7 minutes under a presure of 280 kg/cm 2 . The resulting hot pressed parts had a density of 5.31 g/cc and a Rockwell A (R, ) hardness of 94. Cutting tool inserts having a geometry of 12.7 mm x 12.7 mm x 4.75 mm have been fabricated from hot pressed blanks. These tools have been used, in machining tests, to turn 4142 alloy steel tube of Rockwell hardness ■ BU of R Q 52-58. The results, given in Table 1, represent th surface speed of the work material at which the tool brok in this machining test where the surface speed was increased at an increment of 25.4 surface cm per minute (scps), two minutes at each increment starting from 50.8 scps. Samples of transverse rupture test of geometry, 1,7 in x 1.7 m x 19 mm, were also made and tested in 3-point bending tests. The results are given in Table 1. Examples 2-16 In these Examples, ceramic compositions were pr duced as 700 gram mixtures with the indicated components in the proportions shown in Table 1, following the procedure of Example 1 and tested in the same manner hereinbefore set forth. O.V. Vfeight Percent of Components Hot Transverse Ex. Pressing Hardness Density Machining* Rupture No. AI2O3 TiC TiN Ni Mo Condition ( ) (g/cc***) Test (scps) Strength(kg/ 14 80.0 14.0 6.0 0 0 1650°C 93.5 4.18 228.6 13,090 15 90.0 5.0 4.5 0.25 0.25 1650°C 94.0 4.14 228.6 9,310 16 70.0 30.0 0 0 0 1650°C 93.5 4.23 228.6 8,680 17 10.0 20.0 61.0 4.5 4.5 1550°C 94.0 5.38 254 8,610 18 50.0 14.25 33.25 1.25 1.25 1650°C 93.0 4.65 266.7 6,370 19 70.0 7.5 22.5 0 0 1650°C 94.0 4.35 254 7,000 The numbers represent the surface speed of the work material at which the tool broke in a machining test where the surface speed was increased at an increment of 25.4 scps for 2 minutes at each increment. Example 16 is directed to a conventional composition of alumina-TiC for comparison with the compositions of the present invention, alumina-titanium carbonitride composition where the titanium nitride is the major phase, i.e., C + n £ 0-50, where c represents titanium carbide and n represents titanium nitride. Example 17 should be compared with Examples 1 and 2 where only the ratios of titanium carbide and titanium nitride have been changed leaving the alumina and metal phase constant. One can see similar differences by comparing Example 18 to Example 6 and also comparing Example 19 to Example 12. Examination of Table I will show that the compositions of the present invention are significantly tougher than pure alumina materials and are generally superior to the alumina-titanium carbide composition of Example 14 in either machining tests and/or transverse rupture strength, Furthermore, it can be seen that having titanium carbide as the major phase of the titanium carbonitride generally gives superior results to compositions where titanium nitride is the major component. In addition to the machining tests described previously, a comparative wear machining test was conducted for the compositions of Example 10 and Example 16. In this test, SNG 432 tools were used to turn 4142 steel having a Rockwell C hardness of 57 at 101.6 surface cm per sec, 0.38 mm DOC (Depth of Cut) and a feed rate of 0.254 mm per revolution for 30 minutes. The uniform flank wear of the tools was read every two minutes. The results are given in Table 2. TABLE 2 Results of Wear Machining Test Test Conditions: 101.6 scps 0.38 mm DOC 0.254 mm/revolution orkpiece: 4142 steel R 57 Time (min.) Sample 10 12 14 17 20 25 Example 16 0.10 0.10 0.15 0.15 0.15 0.25 0.25 0.30 0.35 0.35 Example 10 0.025 0.05 0.05 0.07 0.07 0.07 0.10 0.10 0.10 0.10 The numbers represent the amount of flank wear in mm. after each time period. As can be seen in Table 2, the compositions of the present invention show greater wear resistance than currently commercially available compositions. BU EΛ

Claims: WHAT IS CLAIMED IS: ~ 10 ~ 1. Ceramic composition having superior mechanical properties of wear resistance and transverse rupture strength comprising about 10 to 90 weight percent aluminum oxide and about 90 to 10 weight percent titanium carbonitride, the major phase of said carbonitride com¬ prising titanium carbide, said carbonitride including up to 30 weight percent of a metal phase comprised of group IVB or Iron group elements including molybdenum or combination thereof. 2. Ceramic composition according to claim 1 wherein the metal phase comprises nickel and molybdenum. 3. Ceramic composition according to claim 1 comprising 30 weight percent alumina, 49 weight percent titanium carbide and 21 weight percent titanium nitride, said ceramic composition having a transverse rupture strength of 11,130 kg/cm 2 . 4. Ceramic composition according to claim 1 comprising 10 weight percent alumina, 61 weight percent titanium carbide, 20 weight percent titanium nitride, 4.5 weight percent nickel and 4.5 weight percent molybdenum, said ceramic composition having a transverse rupture strength of 17,500 kg/cm 2 . 5. Ceramic composition according to claim 1 comprising 68.7 weight alumina, 22.2 weight percent titanium carbide, 7.5 weight percent titanium nitride, 0.8 weight percent nickel and 0.8 weight percent molybdenum, said ceramic composition having a transverse rupture strength of 9660 kg/cm 2 . OM

Inventors: LEE S
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1980
Main classification: C04B35
IPC codes: C04B35, C22C29