SE451195B - CERAMIC MATERIAL BASED ON SILICON NITRID - Google Patents

Description

»W 10 15 20 25 30 35 451 195 the system. Characteristic of these materials is that they in addition of the refractory carbide or nitride consists of a crystalline phase of silicon nitride or beta'-sialon and possibly another phase containing a large part of the sintering aids such as yttrium oxide and which may be amorphous. * According to the invention, it has surprisingly been found that properties cutting operations can in some cases significantly reduce improved in a material substantially based on silicon nitride, refractory carbide / nitride phase and a phase containing sintering aids on the silicon nitride-based component as in this case är-sialon exists in two crystalline modifications namely alpha 'and beta'.

Alpha 'is a hexagonal phase of the general formula Mx (Si, Al) 12 (O, N) 16 where M = Li, Ca, Y or other lanthanides and where x i 2.

Beta 'is a hexagonal phase of the general formula si6_zA1zozN8_z where 0 <z <4.2.

The presence of alpha 'phase increases the hardness measured at room temperature but also has a beneficial effect on the resistance to plastic deformation (see below) why it is likely that the hardness also increased in a favorable direction. Plastic deformation of cutting the edge occurs under conditions where it is exposed to high luck ie at high cutting speed and large feed. The place-- The deformation leads to crack initiation in the cutting edge and as the cracks grow, cutting fractures are obtained. This type of cracking formation has been described in, among others, Met. Tech. lQ (l983): December, pp. 482-9 (Bhattacharyya et al, Wear mechanisms of Syalon ceramics tools when machining nickelbase materials). It has surprisingly, the presence of alpha'-sialon has been shown to be significant increases the ability of the material to withstand plastic deformation through higher cutting speed and cutting feed can be used without ~ risk of catastrophic crime. 10 15 20 25 30 451 195 The property improvement manifests itself primarily in the resistance against egg chips so-called chipping is significantly increased in some pickling material. This advantage has above all been observed in some heat-resistant nickel-based materials due to the prevailing high cutting temperatures. The same phenomenon occurs however, also in other working materials when some are exceeded values of cutting speed and feed. The present invention therefore refers to a material which is characterized in that it contains a sialon-type alpha 'phase and a sialon-type beta' phase and another intergranular phase which is usually glass species but can also consist of crystalline phases in addition to it refractory hard material phase consisting of carbides, nitrides or carbonitrides of the metals of Group IVB, VB and / or VIB in the periodic table.

Coexistence of the alpha 'and beta' phases is possible in some material compositions and has been described by, among others, H.K. Park et al i "Alpha '~ sialon ceramics", Science of Ceramics, Vol.10, p 251-256, H. Hausner (Ed), and further in the Swedish patent the application 83009282. The said application thus deals with ceramic cutting materials of silicon aluminum oxynitride comprising an alpha 'phase of Si-Al-O-N and a beta' phase of Si-Al-O-N and a glassy phase. However, the known material does not contain any refractory carbide, nitride or carbonitride.

The material properties specific to the invention are apparent from the following description. Presence of a refractory phase aims to improve the abrasion resistance properties and it is present in the material in the form of a fine-discrete phase. In the subsequent In the following description, titanium nitride is used as the refractory phase as it is a common hard substance but it is obvious similar property improvements can be obtained with types of refractory hair substances such as carbides, nitrides or carbonitrides or mixtures thereof of the metals titanium, tantalum, chromium, molybdenum, niobium, zirconium, hafnium and tungsten.

The presence of oxygen in the refractory hard substances has not been shown be disadvantageous, but may, on the contrary, affect the sintering in same direction. From a manufacturing point of view, the nitrides are 10 15 20 25 30 35 451. 195 HRS _ pull as they allow pressureless sintering to a tight sinter body. With the use of carbides, sintering often can not carried out without pressure.

The presence of sialon of alpha 'and beta' phases are achieved by regulating the input raw materials in such a way that a smaller amount of alumina and silica dioxide as well as a larger amount of aluminum nitride and surface mite elLæ: nwt- / âlæšmëâfäïoânimêlrudâåren. Presence of alpha 'sialon leads to increased hardness without appreciable deterioration of the flexural strength.

In the preparation of the above product, the sintering aids preferably yttrium oxide but similar results can obtained with one or more oxides of eg strontium, cerium, lanthanum and the other elements of the lanthanum series; The use of yttrium as a sintering aid gives rise to an intergranular phase which is predominantly vitreous but may also include other phases such as YAG (a cubic phase with formula Y3Al5O12), Y-N-alpha-wollastonite (a monoclinic phase with the formula YSiO2N), YAM (monoclinic with the formula Y4Al2O9) and N ~ YAM (monoclinic phase of the formula Y4Si2O7N2).

The product described in the invention consists of several phases and can be prepared as described below.

Silicon nitride, aluminum nitride, alumina and silica, where the oxides may consist of impurities in the nitrides are brought reacting with an oxide of at least one of the elements yttrium, scandium, cerium, lanthanum or other metals of lanthanide series whereby obtained with suitable material compositions two phases of the sialon type namely a hexagonal first phase (beta 'phase) which satisfies the general formula Si6_zAlzOzN8_z there 0l.5) a decrease in the toughness behavior is obtained while at low z-values the material composition can be difficult to seal without print. The lower limit of z is suitably selected on such 10 15 20 25 30 35 5 '451 195 way that sintering without pressure becomes possible. The exact wonder the limit of z at which pressureless sealant is still present possible is difficult to determine, as this may depend on the nature of the constituent refractory phases. So has the material compositions with eg titanium nitride as refractory hardener proved to be possible to sinter without pressure at such low z-values as 0.1 which is not possible without this additive.

The refractory hard materials can therefore, in addition to the combination a high wear resistance contribute to an efficient closure during sintering. The exact nature of this processes are not known, but they certainly play a role in the refraction the carbides and nitrides contained in the pollutants a certain role in this context.

The second phase of the sialon type (alpha 'phase) which is also hexa- gonal satisfies the general formula Mx (Si, Al) 12 (0, N) 16 where M may, for example, be one or more of the elements lithium, cium, yttrium or other lanthanides and 0.l In addition to the formation of alpha 'phase, these metals also a glass phase in the sintered product. This glass phase has proved necessary to be able to carry out waterproofing without print. If the amount of glass phase in the sintered product is high can it causes a deterioration of the high temperature properties. Multi- however, the glass phase can be reduced by slightly less yttrium oxide additive (or equivalent additive of other compounds) or by heat treatment in which part of the glass is transferred to crystalline form such as YAM, YAG, N-YAM or Y-N-alpha- wollastonit. The refractory hard material phase which consists of bites, nitrides or carbonitrides of titanium, niobium, tantalum, vanadium, chromium, molybdenum, tungsten, hafnium and / or zirconium is added in the form of a fine-grained powder raw material to give a homogeneous dispersion in the above-mentioned matrix.

The amount of the constituent raw materials is selected in such a way that the sintered structure contains 5 ~ 60 vol% of a refractory hard phase containing one or more carbides or nitrides of the aforementioned refractory metals in a matrix consisting of 10 to 70% by volume of a sialon-type alpha 'phase, 10 15 20 25 30 35 o 451 195 6 90% by volume of a sialon-type beta 'phase and a glassy phase constituting 0.1 - 20% by volume which may be partially crystalline.

In general, the matrix contains no more than 40% of the alpha 'phase.

Furthermore, the content of intergranular phase in the matrix is normally highest 15 vol%. The sintered structure usually contains no more than 45 vol% hard material phase, which, as previously mentioned, is advantageously made of nitrides, preferably titanium nitride.

The described material structure can of course be obtained on other than as described above. So, for example, describes the US U.S. Pat. No. 4,27,4,16 uses silicon aluminum oxynitrides of polytype instead of aluminum nitride in the production of beta 'type sialon.

Example 1 A mixture consisting of 85% Si3N4, (of which about 2% is constituted of SiO2) 1.5% Al2 O3, 7% AlN, (of which 2-3% Al2O3) and 6.5% YZO3 and constituting 85% of the total composition The mixture was mixed with 15% TiN, ground in propanol, dried, pressed into specimens and sintered in a nitrogen atmosphere at 1775 OC. X-ray analysis showed strong reflections of alpha ' and beta 'sialon and medium reflex of TiN. The material showed a very fine-grained and evenly distributed TiN phase together with alpha '+ beta' phase with a certain proportion of glass phase ( clear microporosity could be discerned.

Example 2 Composition as above but the sialon composition was 70% of total weight. 30% TiN accounted for the remainder. Sintering was performed at 1790 OC in nitrogen for 1 hour. Smooth and fine-grained structure obtained with low microporosity. Density 3.55 g / cm3. X-ray diffraction measurements gave strong reflections of TiN and beta sialon and medium reflex of alpha'-sialon. Hardness 1550 HV1. p 10 15 30 .35 451 195 Example 3 62% Si3N4 (containing about 2% SiO2) was mixed with 15% TiN, 16% of self-made polyphase of type 2L (approx formula SiAl6O2N6, containing about 5% AlN), 5% YZO3 and 2% Al2O3 and melted in a vibrating slurry filled with propanol, with an additional 1.2% AIZO3 (calculated on dried powder) without pressing agent) was added by grinding the grinding body material. The powder was dried, pressed into test rods, concentrated des p s s as in example l ie at 1775 OC. A dense and even structure was obtained with a density of 3.32 g / cm 3 and a hardness of ca 1560 HV1. Insignificant microporosity was obtained. X-ray examination search yielded strong reflexes of alpha 'and beta' sialon and medium reflex of TíN.

Example 4 Materials prepared according to Examples 1 and 2 were tested in a turning operation in steel SS 2541 - 03 whereby the and pit wear, VB (mm) and KT (/ um), respectively, as a function of engagement time T (min). As reference material in the test two commercially available materials were used namely Sandvik CC680 (Sialon) and Sandvik CC650 (Al2O3 + 30% by weight Ti (N, C)). The test was performed with the following insert geometry and cutting data: Cutting geometry: ISO SNGN 120416, reinforcement phase 0.2 mm x 200 Cutting speed: 100 m / min Feed rate: 0.36 mm / rev Cutting depth: 2.0 mm The wear is reported in Figures 1 and 2 as an average of two sample with Fig. 1 showing the phase wear and Fig. 2 the wear as a function of the engagement time. In Figs. 1 and 2, when the different curves have the following materials: l - CC680, 2 - Ex 1, 3 - Ex. 2 and 4 - CC650. 10 15 20 ü 451 195 Furthermore, the toughness behavior was tested in a specially designed cast specimen where the cutting material was subjected to strong mechanical and thermal shock loads.

Cutting geometry: ISO SNGN 120416, reinforcement phase 0.2 mm x 200 Cutting speed: 300 m / min Feed rate: 0.50 mm / rev Cutting depth: 3.0 mm The service life is limited in this test of cutting fractures. Average- life expectancy, which can be obtained from the accumulated the frequency in Fig. 3 (designations according to Figs. 1 and 2), is determined from 15 samples. It was for the tested variants: CC680 7.93 min Ex 1 4.87 min Ex 2 6.00 min CC650 1.20 min As shown by the technological test of durability and toughness behavior, materials according to the invention are characterized by that it has succeeded in combining the superior wear resistance of the based ceramics with the superior toughness behavior of silicon nitride-based ceramics. According to Figures 1 and 2 correspond wear image best with the oxide-based material while the toughness behavior of Figure 3 best conforms to it silicon nitride-based material. Material according to the invention therefore has a much wider range of applications than until known ceramic cutting materials. : (1

Claims (5)

10 15 20 25 30 35 451 195 Patent claims Ceramic material based on silicon nitride and comprising a first component I consisting of, in volume percentage, 10 ~ 70% alpha 'phase of the formula Mx (Si, Al) 12 (0, N) 16, where M is one or more of Li, Ca, Y or other lanthanides and 0.l Si6_ZAlzOzN8_z, where 0 granular phase containing sintering aids such as an antioxidant of M, preferably yttrium oxide, is characterized in that the sintered structure of the ceramic material additionally contains, in volume 5 - 60% a refractory hard phase of carbides, nitrides and / or carbonitrides of Ti, Nb, Ta, V, Cr, Mo, W, Hf And / percent, of a second component II consisting of or Zr, the first component I contains a maximum of 40% by volume of the alpha 'phase and a maximum of 15% by volume of the intergranular phase. _ ,. ,,., _, -_, .._.- n1 .., \ .._ ,,, .. _. ..... _ _ ...__ ......... v- .. n .. _ ._ _ .. s -......, .-.