EP2850041A1 - Céramiques de nitrure de silicium à résistance à l'usure améliorée et leur procédé de production - Google Patents

Céramiques de nitrure de silicium à résistance à l'usure améliorée et leur procédé de production

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Publication number
EP2850041A1
EP2850041A1 EP13724567.6A EP13724567A EP2850041A1 EP 2850041 A1 EP2850041 A1 EP 2850041A1 EP 13724567 A EP13724567 A EP 13724567A EP 2850041 A1 EP2850041 A1 EP 2850041A1
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EP
European Patent Office
Prior art keywords
sintering
silicon nitride
mgo
sintered
mol
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13724567.6A
Other languages
German (de)
English (en)
Inventor
Prof. Hasan MANDAL
Prof. Ferhat KARA
Prof. Servet TURAN
Prof. Alpagut KARA
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MDA Ileri Teknoloji Seramikleri Sanayi Ticaret Ltd STi
Original Assignee
MDA Ileri Teknoloji Seramikleri Sanayi Ticaret Ltd STi
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Application filed by MDA Ileri Teknoloji Seramikleri Sanayi Ticaret Ltd STi filed Critical MDA Ileri Teknoloji Seramikleri Sanayi Ticaret Ltd STi
Priority to EP13724567.6A priority Critical patent/EP2850041A1/fr
Publication of EP2850041A1 publication Critical patent/EP2850041A1/fr
Withdrawn legal-status Critical Current

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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
    • C04B35/593—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by pressure sintering
    • C04B35/5935—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by pressure sintering obtained by gas pressure sintering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23B—TURNING; BORING
    • B23B2226/00—Materials of tools or workpieces not comprising a metal
    • B23B2226/18—Ceramic
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    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
    • C04B2235/3206—Magnesium oxides or oxide-forming salts thereof
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3224—Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
    • C04B2235/3225—Yttrium oxide or oxide-forming salts thereof
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    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3231—Refractory metal oxides, their mixed metal oxides, or oxide-forming salts thereof
    • C04B2235/3244—Zirconium oxides, zirconates, hafnium oxides, hafnates, or oxide-forming salts thereof
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    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/34—Non-metal oxides, non-metal mixed oxides, or salts thereof that form the non-metal oxides upon heating, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3418—Silicon oxide, silicic acids, or oxide forming salts thereof, e.g. silica sol, fused silica, silica fume, cristobalite, quartz or flint
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    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
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    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/66—Specific sintering techniques, e.g. centrifugal sintering
    • C04B2235/661—Multi-step sintering
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    • C04B2235/74—Physical characteristics
    • C04B2235/76—Crystal structural characteristics, e.g. symmetry
    • C04B2235/767—Hexagonal symmetry, e.g. beta-Si3N4, beta-Sialon, alpha-SiC or hexa-ferrites
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/80—Phases present in the sintered or melt-cast ceramic products other than the main phase
    • C04B2235/81—Materials characterised by the absence of phases other than the main phase, i.e. single phase materials
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/80—Phases present in the sintered or melt-cast ceramic products other than the main phase
    • C04B2235/85—Intergranular or grain boundary phases

Definitions

  • Silicon nitride ceramics with improved wear resistance and production method therefore
  • the invention concerns silicon nitride ceramics, which especially can be produced by adding only the slightest amounts of sintering additives, resulting in ceramic bodies comprising very little grain boundary phase.
  • the invention further concerns a method for producing such Si3N 4 ceramics.
  • Si3N ceramics have been used e.g. as cutting tools for many years. They are commonly produced by liquid phase sintering. Sintering additives generally used in the range of 2 to 15 Vol%, form a liquid phase during sintering and remain in the microstructure of the sintered body as a secondary phase either in the amorphous state or partially/fully crystalline. The amount of secondary phase, its composition and crystallinity severely affects the cutting performance.
  • temperatures at the cutting tip in excess of 800°C are common. Temperatures at the contact between the insert and the work piece can be even higher. Secondary phase oxidizes at these temperatures and causes wear. This effect is especially prominent during cutting operations where notch wear due to increased oxidation attack occurs.
  • Sintering additives to be used according to EP 2 138 252 A1 are Mg and rare earth elements Re (Y, La, Ce, Er, Dy, Yb), wherein Mg in terms of MgO is 1 .0 to 7.0 mol%, and the content of Re in terms of an oxide thereof is 0.4 to 1 .0 mol%, and the total content of Mg and Re is from 1 .7 to less than 7.5 mol% in the sintered body, respectively.
  • sufficient sinter activity is not achievable if the content of the sintering additives is less than 1 .7 mol%. If the content of sintering additives is in excess of 7.5 mol% unnecessary high amounts of secondary phase build in the ceramic which is undesired since high amounts of secondary phase reduce wear resistance.
  • the object of the invention is to provide Si3N ceramics with improved wear resistance, especially with respect to oxidation processes at high temperatures as well as a method for producing such a Si3N ceramics.
  • a further object of the invention is to provide ceramic inserts for cutting tools with an improved wear resistance and especially an improved notch wear resistance.
  • this object is achieved by a method for producing a sintered silicon nitride body according to claim 1 and a sintered silicon nitride body according to claim 8.
  • the method for producing a sintered silicon nitride body comprises the mixing of a Si3N powder with sintering additives, wherein the sum of the added sintering additives is between 1 .1 and 1 .5 wt% with respect to the mass of the entire mixture, and wherein the sintering additives comprise at least an oxide of at least one rare earth element with an atomic number greater than 62 in an amount between 0.6 and 0.8 wt%.
  • a sintered silicon nitride body according to the invention comprises Si3N grains and a basically amorphous grain boundary phase, consisting of 80-95 mol% SiO 2 .
  • amorphous grain boundary is avoided and crystalline grain boundary phase is aimed at since the crystalline grain boundary phase exhibits a clearly better wear resistance.
  • the inventors found that the state is less important than the composition of the grain boundary phase as long as low amounts are assured.
  • a good oxidation resistance is achieved if the grain boundary phase contains as low amounts as possible in MgO and in Yb2O3, i.e. the MgO-rich crystalline phase MgYbSi2O 5 N should be as low as possible.
  • the inventors further found out that a grain boundary phase low in MgO-rich crystalline phase can be achieved if high amounts of S1O2 prevail.
  • the amount of sintering additives added to the mixture for producing the sintered body is below 1 .5 wt% but above 1 .1 wt% with respect to the mass of the entire mixture which surprisingly was found to be sufficient to achieve sintering.
  • this minimal amount of sintering additives that accumulates in the grain boundary phase of the sintered product reduces the vulnerability of the product to wear.
  • the resistivity of the sintered Si3N body to oxidation attack at elevated temperatures is enhanced due to its SiO2-rich grain boundary phase composition, giving rise to an extraordinary notch wear resistance.
  • a product as claimed can advantageously be used as cutting tool, especially as an insert for a cutting tool, e.g. for cast iron machining or for use in automotive production in general .
  • the rare earth element added as sintering additive is Yb2O3.
  • Yb 3+ is oxidized to Yb 4+ and meanwhile more oxygen can be provided to the liquid phase which in turn can reduce the viscosity of the liquid phase.
  • sintering is enhanced.
  • MgO and/or ZrO2 are used as sintering additives.
  • MgO lowers the melting temperature and viscosity of the liquid phase which forms during sintering and helps to ease densification. It was found that the addition of ZrO2, even in minimal amounts, allows for the production of very dense ceramics. Relative densities in excess of 99% can be realized when ZrO2 is added as sintering additive. It is believed that the presence of ZrO 2 reduces the volatilizing tendency of the sintering additives, particularly MgO, before sintering and thus, is aiding densification. Without ZrO 2 relative densities in excess of 99 % cannot be achieved even if much higher than the claimed amounts of sintering additives are added, compare e.g. example 1 and comparative example 2 of Tab. 1 .
  • MgO is added in an amount between 0.4 and 0.5 wt% and/or ZrO 2 is added in an amount between 0.15 and 0.25 wt% with respect to the mass of the entire mixture.
  • a sintered silicon nitride body of the mixture described above preferably is produced by gas pressure sintering and subsequent heat treatment of the sintered body.
  • the gas pressure sintering comprises the steps: a) pre-sintering at 1700 to 1800°C and at 1 to 5.5 bar in nitrogen gas atmosphere for 0.5 to 1 .5 hours,
  • step a) substantial densification takes place reducing the porosity and surface area of the compact. This prevents/reduces the loss of the sintering additives which would otherwise take place by going straight up to the sintering temperature.
  • step b1 pore closure due to solution precipitation occurs.
  • step b2) sintering is continued under high pressure leading to final pore elimination.
  • the subsequent heat treatment step comprises heat treating the sintered silicon nitride body at 1700 to 1800°C at 1 bar to 100 bar in nitrogen gas atmosphere for 2-5 hours.
  • the chemistry of the amorphous grain boundary phase changes, especially near the surface of the sintered silicon nitride body.
  • the heat treatment reduces the MgO content and enhances S1O2 content of the amorphous phase.
  • Silica rich glasses improve the oxidation resistance of the ceramics.
  • the oxidation resistance of Si3N bodies is governed by the chemistry of its oxide scale which in turn depends on the composition of the grain boundary phase. If the oxide scale has a very low viscosity at oxidation temperatures then oxidation resistance is low, since the material oxidizes quickly due to high oxygen diffusivity through the scale. MgO reacts with S1O2 and forms a low viscosity glass, thus making the body vulnerable to oxidation attack. However, certain amounts of MgO are necessary to form dense sintered bodies.
  • the inventors realized that amounts of sintering additives above 1 .5 wt% result in the forming of YbMgSi2O 5 N regions within the generally amorphous grain boundary phase. These regions reduce the oxidation resistance of the material by providing MgO to the oxide scale.
  • MgO rich, mostly crystalline, regions are avoided by generally using low amounts of sintering additives (not only MgO but the sum of sintering additives) and further reducing the amount of MgO by the post sintering step of heat treatment and at the same time enhancing the relative content of SiO2-rich amorphous intergranular phase.
  • MgO content is preferably less than 10 mol% within intergranular phases.
  • a sintered silicon nitride body according to the invention comprises Si3N grains and a basically amorphous grain boundary phase, preferably containing on average 80 to 95 mol% amorphous S1O2. Due to the high silica content the claimed Si3N body displays exceptional high wear resistance.
  • the sintered body according to one embodiment of the invention has a relative density of at least 99%. Relative densities that high can advantageously be produced if ZrO2 as sintering additive is used. Due to the strength of Si3N ceramics as well as the extraordinary wear resistance of the ceramics according to the invention it can advantageously be used as a cutting tool, especially as insert of a cutting tool, e.g. for cast iron machining or for use in automotive production.
  • Fig. 1 scanning electron microscopy micrograph of oxide scale thickness of heat treated Si3N 4 ceramic body of example 2;
  • Fig. 2 scanning electron microscopy micrograph of oxide scale thickness of heat treated Si3N ceramic body of example 1 .
  • Table 1 shows one example, example 1 , which is composed according to the invention, i.e. less than 1 .5 wt% of the entire mixture consist of sintering additives, wherein the sintering additives comprise at least an oxide of at least one rare earth element with an atomic number greater than 62 in an amount between 0.6 and 0.8 wt%.
  • the mixture comprises Si3N powder and Yb2O3 as an oxide of a rare earth element with an atomic number greater than 62 as well as ZrO2 and MgO as further sintering additives.
  • the comparative examples 2 to 4 in general comprise the same sintering additives but in different amounts or not all of them, see Tab. 1 .
  • the S1O2 content of the ceramic material results from the use of SN E10 as Si3N source (SN E10: Si3N powder from UBE Industries, Tokyo, Japan). This powder contains intrinsically 2.74 wt% S1O2 (1 .3 wt% O2) on the surfaces of Si3N particles.
  • Example 1 and comparative example 2 achieved 99% of the theoretical density, i.e. a complete densification, whereas comparative examples 3 and 4 were not readily densified and showed only 93% and 95% of the theoretical density, respectively.
  • microstructure of the sintered surface of example 1 contained -Si3N grains and only amorphous grain boundary phase.
  • the amorphous grain boundary phase contained elements of Si, Mg, Yb, O.
  • Microanalysis carried out by Transmission Electron Microscopy (TEM) showed that some pockets with grain boundary phase were extremely rich in silica with average compositions of:
  • the sintered surface microstructure of comparative example 2 contained -Si 3 N grains and both, crystalline (YbMgSi 2 O 5 N, the presence of which was verified by X- Ray Diffraction) and amorphous grain boundary phase.
  • Microanalysis (TEM) showed that the secondary phase located in grain boundary phase containing pockets contained generally two different chemistries with respect to the amount of SiO 2 , MgO and Yb 2 O 3 :
  • composition amorphous phase containing 1 -7 mol% MgO, 3-20 mol% Yb 2 O 3 and 78-91 mol% SiO 2 .
  • ZrO 2 was mainly observed to form zircon precipitates (ZrO 2 SiO 2 ) and only less than 0.5% ZrO 2 was present in the amorphous grain boundary phase containing pockets.
  • comparative example 2 exhibits very good relative density values, oxidation resistance is much lower than the one of example 1 , compare Figs. 1 and 2. This is attributed to the higher content of sinter additives (2,7 wt%) and especially the high content of Yb 2 O 3 , 2,0 wt%.
  • Comparative example 3 contained less than 1 .1 wt% sintering additives with respect to the mass of the entire mixture. Density determination revealed only 93% relative density, implying that the amount of sintering additives was not sufficient to allow for complete densification. Comparative example 4 contained no Zr0 2 as sintering additive at all but more than 5 wt% sintering additives in total. Although comparably high amounts of sintering additives were used, nevertheless, densification was incomplete and only 95% relative density of the sintered body was achieved.
  • Figures 1 and 2 both show scanning electron microscopy (SEM) micrographs of silicon nitride bodies referenced as example 1 and comparative example 2 which were subjected to oxidation in static air at 1400°C for 10 hours.
  • SEM scanning electron microscopy
  • Fig. 1 comparative example 2 is displayed.
  • On the left side of the micrograph a zone of 20 ⁇ thickness with a different texture can be observed. This zone developed due to oxidation attack at the surface of the ceramic body.
  • Figure 2 shows a SEM picture of a ceramic Si3N body according example 1 which was oxidized under the same conditions as the body illustrated in Fig. 1 .
  • the surface under oxidation attack is located at the right side.
  • the zone which depicts a different texture due to the oxidation attack comprises only approximately 5 ⁇ and hence, is 4 times smaller than the one in Fig. 1 .
  • the depth to which the ceramic body according to the invention shows oxidation is four times smaller than the depth of a ceramic body which was sintered with 2.7 wt% of sintering additives
  • Example 2 Higher oxidation resistance of example 1 was attributed to the predominance of the silica rich amorphous phase and the absence of MgO-rich secondary phase at the grain boundary phase containing pockets. MgO causes the formation of a low viscosity glassy phase during oxidation through which oxygen diffuses easily which is what happened in Example 2.
  • Comparative example 2 contains some pockets with amorphous grain boundary phase with more or less same amount of MgO as example 1 .
  • comparative example 2 also has pockets with intergranular phase containing 24 mol% MgO, comprising crystalline YbMgSi 2 O 5 N regions. These regions reduce the oxidation resistance of the material by providing MgO to the oxide scale. According to the invention, such highly MgO containing (crystalline) regions are avoided and thus, enhanced oxidation resistance is obtained.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Ceramic Products (AREA)

Abstract

L'invention concerne des céramiques de nitrure de silicium, qui peuvent notamment être produites par simple ajout de petites quantités d'additifs de frittage, résultant en des corps céramiques comprenant très peu de phase de joint de grain. L'invention concerne également un procédé de production de telles céramiques Si3N4.
EP13724567.6A 2012-05-16 2013-05-16 Céramiques de nitrure de silicium à résistance à l'usure améliorée et leur procédé de production Withdrawn EP2850041A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP13724567.6A EP2850041A1 (fr) 2012-05-16 2013-05-16 Céramiques de nitrure de silicium à résistance à l'usure améliorée et leur procédé de production

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
EP12168174 2012-05-16
EP12179514 2012-08-07
EP12182818 2012-09-03
PCT/EP2013/060197 WO2013171324A1 (fr) 2012-05-16 2013-05-16 Céramiques de nitrure de silicium à résistance à l'usure améliorée et leur procédé de production
EP13724567.6A EP2850041A1 (fr) 2012-05-16 2013-05-16 Céramiques de nitrure de silicium à résistance à l'usure améliorée et leur procédé de production

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EP2850041A1 true EP2850041A1 (fr) 2015-03-25

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CN107151144A (zh) * 2017-05-27 2017-09-12 陈国生 一种铝合金低压铸造用氮化硅配件新材料及其制备方法
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