DE102007055711A1 - Material based on silicon aluminum oxynitride used in ceramic cutting tools contains a hafnium-containing grain boundary phase a dispersion phase containing globular particles made from carbides and/or nitrides - Google Patents

Abstract

Material based on silicon aluminum oxynitride (SiAlON) contains alpha /beta -SiAlON with 5-50 wt.%, preferably 5-30 wt.% a/(alpha +beta )RE-alpha -SiAlON (where RE = yttrium, scandium, lutetium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium or ytterbium), 95-50 wt.%, preferably 95-70 wt.% b/(alpha +beta )beta -SiAlON, a hafnium-containing amorphous or partially crystalline grain boundary phase and a dispersion phase containing globular particles with an average particle size of 0.4-10 mu m and made from silicon carbide, titanium nitride, titanium carbide, carbides and/or nitrides of group IVb, Vb and VIb elements. Independent claims are also included for the following: (1) Method for the production of a material based on silicon aluminum oxynitride; and (2) Sintered body made from the above material.

Description

SiAlON materials Due to their high wear resistance, they are suitable for machining metallic surfaces Materials, preferably cast iron. In particular, alpha / beta SiAlONs own a cheap one Combination of hardness and toughness. In addition to the mechanical properties at room temperature are for the application as a ceramic cutting material also the properties at temperatures around 800 ° C decisive up to 1000 ° C. An economical production of SiAlONen, however, is only possible by using sintering aids. These simplify though the compression of the material, however, remain after cooling as predominantly vitreous grain boundary phase in the product. The softening of this grain boundary phase determines the mechanical and chemical properties of the material at elevated Temperatures. When machining metallic materials is the Wear predominantly by mechanical abrasion and additionally by chemical reactions caused. A high wear resistance So can only be achieved if hardness, toughness and chemical resistance stay high even at the application temperatures. The crowd and Therefore, composition of the glassy grain boundary phase has a key feature in terms of wear.

improved High temperature properties can in principle, by using a smaller amount of sintering additives be achieved. this leads to to less grain boundary phase in the product, thereby softening At high temperatures the influence on the material properties is lower. Because conventional Cutting materials already have very small amounts of additive, is a further reduction because of the then deteriorating sintering properties hardly possible, in particular, when economic gas pressure sintering is applied shall be.

The hardness of SiAlON materials at higher temperatures can also be increased by the addition of hard particles such as SiC, such as from the WO 2005/016847 A1 is known.

In the EP 0 479 485 A1 describes how a SiC-reinforced beta-SiAlON material can be more easily compacted by the addition of 1 to 60% by mass HfO ₂ , without the additional HfO ₂ addition adversely affecting the high-temperature properties. The HfO ₂ forms a liquid phase during sintering, which promotes the compression, but after the sintering process is present as a "disperse phase".

In the US 5,200,374 A It is described that upon addition of HfO ₂ after sintering, a Hf oxide phase having a defect fluorite structure is formed, in which trivalent ions such as rare earth elements are incorporated.

Also in other publications as in the EP 0 227 471 A2 and the EP 0 792 854 A2 describes how HfO ₂ or a similar additive can be added to achieve a sufficient final density in a difficult to compact material. In any case, however, as in particular from the EP 0 479 485 A2 a minimum quantity of 1% by mass of HfO _{2 is} considered necessary in order to achieve a noticeable improvement in the compaction behavior.

task The present invention is a wear resistant SiAlON material to provide, despite low levels of Sintering aids, especially Hf, instead of the complex hot pressing (HP) or hot isostatic Pressing (HIP) also by the more economical gas pressure sintering can be compressed.

At the material according to the invention On the basis of SiAlONen already a lesser Hf addition is sufficient as with conventional SiAlON materials to good sintering properties and improved wear resistance to achieve during machining. The material according to the invention is used at temperatures of 1750 to 2000 ° C sintered. It can be compressed by gas pressure sintering to> 99% theoretical density.

The α / β-SiAlON material according to the invention contains 5 to 50% by mass, preferably 5 to 30% by mass% α / (α + β) RE-α-SiAlON, where RE is at least one cation from Y, Sc, Lu, La , Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Mg or Ca, preferably at least one cation of Y, Sc, Lu, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and additionally at least one cation of Mg or Ca, and 95 to 50% by mass, preferably 95 to 70% by mass β / (α + β) β-SiAlON and an Hf-containing amorphous or partially crystalline grain boundary phase with a share of the total material of less than 10% by volume. The Hf content of the sintered material is 0.2 to 1.0 mass%, preferably 0.3 to 0.8 mass%, particularly preferably 0.4 to 0.6 mass%. The dispersion phase contains globular particles with average particle sizes of 0.2 to 15 μm before zugt 0.4 to 10 microns of at least one hard material of SiC, TiN, TiC, Ti (C, N), carbides and / or nitrides of the elements of groups IVb, Vb and VIb of the Periodic Table (PSE) and scandium carbide and / or Scandiumoxicarbid or mixtures of the listed hard materials, which are contained in a proportion of 5 to 30% by volume, preferably 7.5 to 20% by volume, particularly preferably 10 to 15% by volume in the sintered body.

The raw material mixture of the α / β-SiAlON-SiC material contains the components Si ₃ N ₄ , Al ₂ O ₃ , AlN, MgO, Y ₂ O ₃ , HfO ₂ and SiC, the proportion of SiC being 5 to 30% by volume, preferably 7.5 to 20% by volume, particularly preferably 10 to 15% by volume, the proportion of HfO _{2 is} 0.2 to 1.0% by mass, preferably 0.3 to 0.9% by mass, particularly preferably 0.4 to 0 , 8 mass%, the total additive content 6.0 to 10.0, preferably 6.5 to 9.0, particularly preferably 7.0 to 8.5 and the atomic% ratio of Y to Mg 7.0 to 10.0, preferably 7.5 to 9.0, particularly preferably 8.0 to 8.5.

HfO ₂ has a low solubility in the melt phase of the other sintering additives, which depends on the composition of the starting mixture. Upon cooling, the dissolved Hf partially precipitates as a finely divided crystalline Hf phase in the grain boundary phase. The addition of a small amount of Hf oxide thus increases the amount of melt phase during the sintering process, but does not lead to more glassy grain boundary phase in the product. Thus, there is a possibility to reduce the amount of other sintering additives without deteriorating the sinterability. Excess HfO ₂ , which can not dissolve in the liquid phase, can be converted by sintering through a N ₂ -rich atmosphere into dispersed Hf nitrides.

Only by the addition of HfO ₂ at the same time slightly reduced amount of other additives, a significant improvement in the wear behavior can be found, as demonstrated by means of embodiments (see Table 2). In contrast, addition of more than 1% by mass of HfO ₂ deteriorates the material properties, as shown by examples. The simultaneous use of sintering additives with different cations, such as Y and Mg of the embodiments, in addition to the Hf additive, the sintering behavior positively. However, it is believed that even with raw material blends with only one cation, an additional Hf addition causes the benefits described.

Instead of being an oxide, the Hf can also be introduced in other forms as an organic or inorganic compound. If the Hf is introduced as a pulverulent compound, for example as HfO ₂ , the size of the powder particles should be only a few μm. If the powder particles are too coarse, they dissolve only slowly during sintering and thus hardly contribute to increasing the liquid phase, which does not improve the sintering properties.

To can sinter with conventional X-ray Analysis methods, such as XRD, no or only very weak ones Signs for the presence of a crystalline Hf oxide phase can be detected since their contents are too low, i. less than about 1 mass%. Depending on the sintering conditions however, small amounts of Hf oxinitride or Hf nitride phases are detected, at high Hf levels even in the SEM as disperse particles about 0.5 μm Diameter are visible.

Except SiC All other hard material particles are possible with the other Components of the material according to the invention do not react. However, the size of the added hard particles is to be observed. If these are too small, less than 0.2 μm, because of the big Powder surface a lot Glass phase needed for wetting, which is missing during sintering. Are the hard particles too coarse, about in the range of over 15 microns, takes place a sintering obstruction.

Reference to exemplary embodiments, the invention is explained in detail. Three groups of materials were formed, which are listed in Tables 1 and 2 below. From the respective materials sintered bodies were produced in the form of cutting tools. The effect of adding HfO ₂ to Y-Mg-alpha / beta-SiAlON materials of different composition on sintering behavior and wear during cutting was compared.

To produce a SiAlON material according to the invention of the embodiments, fine or finely ground Si ₃ N ₄ powder with a particle size of D50 ≤ 1 microns and with a specific surface ≥ 10 m ² / g and SiC as a hard material particles with a particle size of D50 about 0.6 microns with the addition of the other powdery raw materials and known binder mixed and pressed axially.

To Debinding was done by sintering. The embodiments were all by gas pressure sintering at 1930 ° C and a gas pressure of 100 bar. The holding time was three hours.

• (1) Entspricht der Menge von AlN + Al₂O₃+ MgO + Y2O₃ + HfO₂, den Stoffen, die beim Sintern die flüssige Phase bilden (Oxid-Verunreinigung des Si₃N₄ oder AlN bleiben unberücksichtigt).
• Das Masse%-Verhältnis zwischen Al₂O₃ und MgO beträgt stets 2,53.

Eigenschaften Werkstoff Gruppe Nr: Dichte [% th.] Alpha-SiAlON [Masse-%] (2) Harte [HV10] Zähigkeit K_IC [MPam^1/2] Verschleiß bzgl. Referenz A 1 (Ref. 99,8 42 1782 6,3 1 A 2 99,8 38 1697 5,9 –^*) A 3 99,7 19 1582 6,3 –^*) B 4 (Ref.) 99,8 25 2053 6,3 1 B 5 99,8 33 1897 5,8 1,06 B 6 99,8 41 1893 6,1 1,03 C 7 (Ref.) >99,8 30 1746 6,3 1 C 8 >99,8 17 1707 5,8 0,96 C 9 >99,8 20 1758 6,0 0,94 C 10 >99,8 20 –^*) –^*) –^*) C 11 >99,8 18 1744 5,8 0,81 C 12 88 –^*) –^*) –^*) –^*) Tabelle 2: Ausführungsbeispiele: Eigenschaften

• *) nicht bestimmt
• (2) Im gesinterten Bauteil; Anteil von alpha-SiAlON, bezogen auf die Gesamtmenge von alpha- und beta–SiAlON, d.h. α/(α + β) in Masse%.

The material was used to produce cutting tools with which Zerspantests were carried out on brake discs made of the material GG15. The brake disks were turned off at a cutting speed of vc = 1000 m / min, a feed of f = 0.50 mm / rev, a cutting depth of ap = 2.0 mm and a setting angle of α = 85 °. raw material mixture Grupe No: Si ₃ N ₄ [mass%] AlN [mass%] Atom% ratio Y: Mg Total additive content [% by mass] (1) Hf [mass%] SiC [vol.%] A 1 (Ref.) 89.5 5.00 7.5 10.5 - - A 2 88.5 5.00 7.5 11.5 0.85 - A 3 85.5 5.00 7.5 14.5 3.39 - B 4 (Ref.) 66.0 4.14 9.0 9.3 - 25 B 5 65.0 4.14 9.0 10.3 0.85 25 B 6 65.3 4.14 9.0 10.0 0.42 25 C 7 (Ref.) 80.8 4.14 9.0 9.3 - 10 C 8th 81.1 4.14 8.5 9.0 0.85 10 C 9 81.3 4.14 8.3 8.8 0.76 10 C 10 81.7 4.14 8.3 8.4 0.69 10 C 11 82.4 4.14 8.2 7.7 0.58 10 C 12 83.2 4.14 9.2 6.9 0.46 10 Table 1: Exemplary embodiments: data of the raw material mixture

• (1) Corresponds to the amount of AlN + Al ₂ O ₃ + Y 2 O ₃ + MgO + HfO _2, the substances which form the liquid phase during sintering (Me oxide contamination of the Si ₃ N ₄ or AlN disregarded).
• The mass% ratio between Al ₂ O ₃ and MgO is always 2.53.

Properties Material group No: Density [% th.] Alpha-SiAlON [% by mass] (2) Hard [HV10] Toughness K _IC [MPam ^1/2 ] Wear with reference A 1 (Ref. 99.8 42 1782 6.3 1 A 2 99.8 38 1697 5.9 - ^*) A 3 99.7 19 1582 6.3 - ^*) B 4 (Ref.) 99.8 25 2053 6.3 1 B 5 99.8 33 1897 5.8 1.06 B 6 99.8 41 1893 6.1 1.03 C 7 (Ref.) > 99.8 30 1746 6.3 1 C 8th > 99.8 17 1707 5.8 0.96 C 9 > 99.8 20 1758 6.0 0.94 C 10 > 99.8 20 - ^*) - ^*) - ^*) C 11 > 99.8 18 1744 5.8 0.81 C 12 88 - ^*) - ^*) - ^*) - ^*) Table 2: Exemplary embodiments: Properties

• *) not determined
• (2) in the sintered component; Amount of alpha-SiAlON, based on the total amount of alpha and beta SiAlON, ie α / (α + β) in mass%.

Group A (Nos. 1 to 3):

Influence of adding HfO ₂ to an α / β-SiAlON composition: The hardness decreases, the toughness is not significantly changed. Zerspantests were not performed because of the low hardness. An additional addition of Hf to a conventional SiAlON composition thus worsens the hardness, which would directly affect a higher wear during machining.

Group B (Nos. 4 to 6):

The influence of the addition of HfO ₂ to a SiC-containing α / β-SiAlON: Here, despite the high SiC content, the hardness also drops markedly. The wear on the Hf-free composition is increased. The sinterability of the highly hard-containing SiAlONs is not significantly improved by the low Hf addition.

Group C (Nos. 7 to 12):

The influence of the addition of HfO ₂ to a SiC-containing SiAlON, in which the total additive, ie the sum of all melt-forming additives of the raw material mixture, despite additional HfO ₂ addition is not increased: The conventional Sinteradditiv amount is reduced and as compensation HfO ₂ is added, which, as described above, increases the amount of the liquid phase during sintering, but crystallized on cooling and causes a high-temperature stable grain boundary phase. The compensation amount of HfO ₂ may even be lower than the reduced amount of the remaining sintering additives. The hardness is not significantly affected, but the wear is reduced. The better wear behavior is in this case caused by the lower content of amorphous grain boundary phase, which causes a better hot hardness and lower chemical reactions with the material of the workpiece.

Claims (11)

Material based on SiAlONs, containing an α / β-SiAlON material with 5 to 50% by mass, preferably 5 to 30% by mass% α / (α + β) RE-α-SiAlON, where RE is for at least one cation of Y, Sc, Lu, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Mg or Ca, preferably at least one Cation of Y, Sc, Lu, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, He, Tm, Yb and in addition at least one cation of Mg or Ca, and 95 to 50% by mass, preferably 95 to 70 mass% β / (α + β) β-SiAlON and a Hf-containing amorphous or semi-crystalline grain boundary phase with a share of the total material of less than 10% by volume, the Hf content of the sintered material 0.2 to 1.0% by mass, preferably 0.3 to 0.8% by mass, more preferably 0.4 to 0.6 mass% and a dispersion phase consisting of globular particles with middle Particle sizes of 0.2 to 15 μm, preferably 0.4 to 10 microns of at least one hard material of SiC, TiN, TiC, Ti (C, N), carbides and / or nitrides of elements of Groups IVb, Vb and VIb of the Periodic Table (PSE) and scandium carbide and / or scandium oxycarbide or mixtures from the listed Hard materials in an amount of 5 to 30% by volume, preferably 7.5 to 20% by volume, more preferably 10 to 15% by volume in the sintered body are. Material according to claim 1, characterized in that the raw material mixture of the α / β-SiAlON-SiC material contains the components Si ₃ N ₄ , Al ₂ O ₃ , AlN, MgO, Y ₂ O ₃ , HfO ₂ and SiC, wherein the Content of SiC 5 to 30% by volume, preferably 7.5 to 20% by volume, particularly preferably 10 to 15% by volume, the proportion of HfO ₂ 0.2 to 1.0% by weight, preferably 0.3 to 0.9 mass %, particularly preferably 0.4 to 0.8% by weight, the total additive content 6.0 to 10.0, preferably 6.5 to 9.0, particularly preferably 7.0 to 8.5 and the atom% Ratio of Y to Mg is 7.0 to 10.0, preferably 7.5 to 9.0, particularly preferably 8.0 to 8.5. Material according to claim 2, characterized in that the Si ₃ N ₄ powder has a specific surface area of ≥ 10 m ² / g. Material according to one of claims 1 to 3, characterized the hard material particles have a particle size between 0.2 μm and 15 μm. Material according to claim 4, characterized in that that the grain size of added SiC at 0.6 μm lies. Material according to one of claims 1 to 5, characterized that the theoretical density is greater than 99% is. Sintered body, made of a material according to one of claims 1 to 6, characterized in that it is a cutting tool. Process for producing a material on the Basis of SiAlONs containing an α / β-SiAlON material with 5 to 50% mass%, preferably 5 to 30% mass% α / (α + β) RE-α-SiAlON, where RE is at least a cation of Y, Sc, Lu, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Mg or Ca, preferably at least one cation Y, Sc, Lu, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and additionally at least one cation of Mg or Ca, and 95 to 50% by mass, preferably 95 to 70 mass% α / (α + β) β-SiAlON and a Hf-containing amorphous or partially crystalline grain boundary phase with a share of the total material of less than 10% by volume, the Hf content of the sintered material 0.2 to 1.0 mass%, preferably 0.3 to 0.8% by mass, more preferably 0.4 to 0.6% by mass, and one Dispersion phase, consisting of globular particles with medium Particle sizes of 0.2 to 15 μm, preferably from 0.4 to 10 microns at least one hard material of SiC, TiN, TiC, Ti (C, N), carbides and / or Nitrides of elements of Groups IVb, Vb and VIb of the Periodic Table (PSE) as well as scandium carbide and / or scandium oxycarbide or mixtures from the listed Hard materials in an amount of 5 to 30% by volume, preferably 7.5 to 20% by volume, more preferably 10 to 15% by volume in the sintered body are by axial pressing a binder-containing pressed granules at 140 to 200 MPa, debinding at temperatures adjusted to the binder and then Sintering, optionally pressure sintering or HIP, at temperatures between 1750 ° C and 2000 ° C. A method according to claim 8, characterized in that a raw material mixture of the α / β-SiAlON-SiC material of the composition α / β-SiAlON and α / (α + β) RE-α-SiAlON from the components Si ₃ N ₄ , Al ₂ O ₃ , AlN, MgO, Y ₂ O ₃ , HfO ₂ and hard material particles of SiC, TiN, TiC, Ti (C, N), carbides and / or nitrides of the elements of Groups IVb, Vb and VIb of the Periodic Table (PSE) and Scandiumcarbid and / or Scandiumoxicarbid or mixtures of the listed hard materials in a particle size of 0.2 .mu.m to 15 .mu.m with a proportion of 5 to 30% by volume, preferably 7.5 to 20% by volume, particularly preferably 10 to 15% by volume a proportion of HfO ₂ of 0.2 to 1.0% by mass, preferably 0.3 to 0.9% by mass, particularly preferably 0.4 to 0.8% by mass, is prepared, wherein the total additive content of 6 , 0 to 10.0, preferably 6.5 to 9.0, particularly preferably 7.0 to 8.5 and the atomic% ratio of Y to Mg 7.0 to 10.0, preferably 7.5 to 9, 0, more preferably 8.0 to 8.5 and the Si ₃ N ₄ powder has a particle size of D50 ≤ 1 microns and a specific surface ≥ 10 m ² / g. Method according to claim 8 or 9, characterized that gas pressure sintering at 1930 ° C and 100 bar gas pressure in a holding time of 3 hours. Sintered body, manufactured according to a method according to one of claims 8 to 10, characterized in that it is a cutting tool.