WO2000008234A1

WO2000008234A1 - Multilayer composite wear resistant coating

Info

Publication number: WO2000008234A1
Application number: PCT/RU1998/000255
Authority: WO
Inventors: Alexei Anatolievich Vereschaka; Anatoly Konstantinovich Pchelintsev; Anatoly Stepanovich Vereschaka; Viktor Sergeevich Sinitsin; Sergei Sergeevich Lastochkin; Valery Fedorovich Lapin; Alexandr Igorevich Dodonov
Original assignee: Alexei Anatolievich Vereschaka; Pchelintsev Anatoly Konstantin; Anatoly Stepanovich Vereschaka; Viktor Sergeevich Sinitsin; Sergei Sergeevich Lastochkin; Valery Fedorovich Lapin; Alexandr Igorevich Dodonov
Priority date: 1998-08-05
Filing date: 1998-08-05
Publication date: 2000-02-17
Also published as: RU2198243C2

Abstract

The present invention relates to the method of the modification of various article surface properties and, in particular, to the multilayer composite wear resistant coating designed mainly for the cutting and die tools. The suggested multilayer coating comprises adhesive and strengthening underlayers, transition and alternating layers of refractory metal compounds. The strengthening layer is of a solid solution type, the adhesive layer contains an element of the substrate as well as of the transition layer. The first of the alternating layers contains Al. This coating allows to increase durability and reliability of cutting and die tools.

Description

MULTILAYER COMPOSITE WEAR RESISTANT COATING

Field of Invention

The present invention relates to the method of the directed modification of various article sur ace properties and, in particular, to the wear resistant coatings for the cutting and die tools mainly as well for as the rubbing parts which can be produced by ion plasma methods. Such coatings can be used in the machine - building industry as well as in the metalworking industry.

Prior Art

The multilayer wear resistant coatings applied on the machine articles or carbide cutting tools are well-known (Patent application of France No 257 6668 , 1987).

The coating is deposited under high temperatures and it includes the zirconium, chromium, titanium, tantalum, nickel layers with the subsequent deposition of nitride layers from the underlayer elements. The shortcoming of the above wear resistant coating is a high temperature of the coating synthesis which does not allow to obtain the coatings for the article material made of semithermostable and thermostable tool and constructional steels having tempering temperature considerably below coating synthesis temperature; besides, the relatively high adhesive activity and low strength of the coating there is a probability of its intensive destruction, especially under the high thermomechanical loads during the exploitation of articles with this kind of coating. The most close technical solution is a multilayer composite coating for cutting and die tools ( Patent of Russian Federation No 2096518 , 1997); according to that, one of the alternating layers has refractory metal compounds of Periodic Table Groups IV, V or IV, VI and another one includes refractory metal compounds of Groups IV, V or VI with a 1 -10 mm layer thickness.

The shortcoming of the known technical solution is a relatively low article wear resistance of this coating under the influence of higher operational thermomechanical stresses, especially if they have a cyclic nature, due to high tendency of the coating to the intensive micro - and/or macrodestruction in the contact areas of the cutting and die tools. The above mentioned phenomenon is caused by the presence of only refractory metal compounds of Periodic Table Groups IV, V or VI in the bottom layer, not providing enough adhesion strength between the materials of the coating bottom layer and article material, especially if the value of the isobaric potential of the reaction between them is positive under the temperatures of the synthesis and coating performance. Besides, there is a high probability of the formation of the critical tensile stresses on the "coating- article" separation boundaries due to a considerable difference between their physical - mechanical and thermal -physical properties which can lead to the total coating destruction (delamination) on the "coating-article" separation boundaries. The coating intensive destruction can also be caused by the loss of the cutting tool form stability occurring as a result of more intensive reduction of contact length compared with the normal loads reduction which results in the contact stress increase as well as the shift of maximum temperature profiles to the cutting edges which leads to the article material microcreeping phenomenon directly under the coating and, as a result, to the destruction of the brittle coating. Furthermore, due to the appearance of "edge effects" related to the formation of destructional critical stresses in the radius areas of tool cutting edges with too big difference in the coefficients of the coating and the article materials heat conduction as well as with a non-optimal relation of coating thickness and the radius value of edge roundness there is a probability of the total coating separation in these areas.

The above mentioned fundamental shortcoming can be excluded by the application of the multilayer composite coating on the article providing more favourable combination of crystal - chemical, physical - mechanical and thermal - physical properties of the coating layers and article material as well as by the introduction of strengthening (thermostabilization) underlayer directly under the coating thereby blocking the article material microcreeping under high operational thermomechanical stresses. The article with the suggested structure of the multilayer composite coating will resist longer to the macro- and microdestruction as a result of increased durability of the coating functioning that reduces the thermomechanical loads on the article material and the latter creates more favourable working conditions for the coating due to the better resistance to the microcreeping and plastic deformation.

Essence of Invention

The present invention object is to increase operational characteristics of articles and, in particular, their durability (tool life) as well as the functioning reliability factors - the time between failures with a given probability.

The present method offers to achieve the object through the use of multilayer composite wear resistant coatings applied on different article working surfaces. The coating comprises an adhesive underlayer , transition and alternating layers of refractory metal compounds. The coating is distinguished in that the adhesive underlayer comprises, at least, one element from the article material composition and/or its compound and one element from the coating transition layer composition and/or its compound; the transition layer includes the refractory metal compounds of Groups IV, V or VI or their combinations; the first alternating layer, includes the combination of refractory metal compounds of Groups IV and/or V and/or VI alloyed with aluminium, the other one comprises refractory metal compounds of Groups IV, V or VI or their combinations.

The multilayer composite wear resistant coating includes alternating layers 1 , 2 and transition layer 3, adhesive and strengthening underlayers 4, 5 applied on the article material 6 ( Fig. 1 ).

Composite adhesive underlayer 4 having crystal - chemical structure similar to that of article material and transition coating layer provides a strong adhesive bond between them. In this case due to a sophisticated compound composition it has a high degree of thermodynamic stability and its physicomechanical and thermophysical properties differ only slightly from respective properties of strengthening underlayer 5, article material 6 and coating adhesive layer 3. In the process of the formation of adhesive underlayer 4 having the maximum crystal - chemical compatibility with the article material the probability of critical tensile stress formation on the "coating-article" separation boundaries is sharply reduced which increases the coating destruction resistance due to the delamination. Furthermore, the crystal - chemical compatibility of adhesive layer 4, transition layer 3 and alternating functional layers 1 , 2 of the coating main sources generating dislocations and other defects get weaker which set up a barrier on the way of microcracks and dislocation movement.

The refractory metal compounds of Groups IV and/or V and/or VI alloyed with aluminium are introduced in the composition of alternating layer 2 directly adjacent to transition layer 3 to increase hardness and thermodynamical stability with an optimal combination of strength and hardness and to reduce physical-chemical activity of the coating with respect to the external medium 7 (counterbody for rubbing parts or the machined material for cutting and die tools). The aluminium introduction into the composition of the functional layer leads to the formation of the multi - component compounds of transition metals of Groups IV - VI with the aluminium, the increase of the static weight of atoms with the stable electronic configuration (SWASC) of sp³ and s²p⁶ type, providing higher hardness and stiffness for the crystal lattice as well as an extraordinary high degree of wear resistance. The formation of special properties in one of coating alternating layers 2 (functional layer) allows not only to increase article wear resistance, but also to provide its high operational reliability, owing to barrier functions, preventing heat flow into the article and reducing intensity of interdiffusive processes between crystal - chemical structures of the machined and tool (article) materials.

The introduction of more plastic layer 1 which has a high thermodynamic stability under the influence of operational thermomechanical stresses reduces the risk of the destruction of hard, wear-resistant but relatively brittle layer 2 . The alloyage of metal compounds of Groups IV and V with metals of Group VI leads to the formation of heterophasic structures and reduces even more physical - chemical activity of layer 1 in respect to external medium 7.

At last, the introduction of strengthening underlayer 5 between the coating and article material to increase its stiffness, microcreeping resistance, thermoplastic deformation assists to increase the coating durability and article operational efficiency as well. The strengthening layer can be formed by means of additional ion influence on the surface structures of article material (for example, by means of nitriding stimulated by an electric discharge).

The composite multilayer wear resistant coating consists of adhesive underlayer 4, transition layer 3 and alternating layers 1 , 2, strengthening adhesive underlayer 5, including compound multicomponent system and their combination has a higher degree of wear resistance and strength, low physical - chemical activity with respect to external medium 7 in the combination with high characteristics of thermostability, corrosion resistance, adhesive strength in relation to article material 6 and cohesion strength between coating layers 1 ,2,3,4. These characteristics are obtaned only in the joined operation of layers 1 -4 under the various conditions of the article functioning with the suggested multilayer wear resistant coating. Strengthening underlayer 5 contributes to the more stable article material operation under the influence of the operational thermomechanic stresses, reduces its tendency to high temperature creeping and to the loss of the formstability, therefore, assists to reduce the risk of brittle destruction of the multilayer composite coating.

The article maximum efficiency with the suggested coating is provided only with an optimal thickness of the multilayer composite coating which depends on the roundness radius value of tool cutting edges and the kind of technological cutting operation . It is equal to 0.1 -0.7 of the above mentioned value for the uninterrupted cutting operations (turning, drilling etc.). The total coating thickness is reduced 20-40% for interrupted cutting operations (milling, shaping etc.). The tool efficiency also depends on the thickness ratio of the strengthening underlayer and the coating. The maximum tool efficiency, used for uninterrupted cutting operations is provided within the range of 5-10 of the total coating thickness and it is reduced 10-20% for interrupted cutting operations.

The suggested multilayer composite wear resistant coating assists to increase the tool resistance to various types of wear : corrosion-oxidative, adhesive-fatigue and diffusive which is a main source of tools durability and reliability increase. In particular, cutting and die tools have an increased time between failures (tool life) with a high probability of faultless operation, especially in the process of interrupted contact while cutting hardmachining material as well as when it is necessary to resharpen tools along one of working tool surfaces in the operation period. Furthermore, the use of cutting or die tools with the suggested coating which has a very low physical-chemical activity in relation to the machined material considerably increases the machining quality and accuracy parameters due to the reduction of tool tendency to build up edge formation, reduction of friction and shear stresses directly in the surface forming area of the machined article.

The suggested technical solution is as follows.

The cutting tools with thoroughly prepared (active) surfaces cleaned from the impurities are positioned in the chamber of the vacuum -arc installation. The installation is equipped with three evaporators, which can operate simultaneously as a special gas mixer which permits to introduce into the chamber up to three gases at a time with a strict control of their quantity which provides the possibility to synthesise various refractory metal compounds (carbides, nitrides, carbonitrides, oxides etc.) as well as the device permitting to eject the electrons directly into the chamber vacuum space to carry out the process of tool thermal activation. The tool rotation velocity in the chamber during the process of article cleaning and the coating synthesis on their active surfaces is 2.5 - 50 rpm. The technological synthesis process of multilayer composite coatings is carried out as follows.

Version 1 . The multilayer composite wear resistant coating is deposited on MC 131 cemented carbide inserts (5% TiC, 85%WC, 10%Co) with shape 031 1 (Russia GOST 19042-80, shape SNUN according to ISO standard) after their stay in the chamber of the ion-vacuum installation. Three cathodes made of titanium, chrome and aluminium are set up. Further, the formation of the coating adhesive underlayer, transition and alternating layers takes place with bias voltage within the range of 0.8-1.0 kW in the cleaning and thermal activation processes and 0.15-0.2 kW in the synthesis processes. The surface cleaning and thermoactivation are carried out at 10^"3 Pa and the deposition of the adhesive underlayer and coating layers take place under reaction gas (nitrogen) pressure within 10 "¹ - 10'² Pa with arc current of 80-120 A. The process is carried out at 700 °C .

The adhesive underlayer is formed during the operation of two evaporators, i.e. titanium and chrome; the formation of the transition layer takes place with the evaporation of titanium and chrome and with nitrogen feed. The formation of the first alternating layer takes place when three evaporators (titanium, chrome, aluminium) are activated and nitrogen is supplied. The second alternating layer is formed on the activation of the titanium evaporator and nitrogen feed. In this case the thickness of the coating and the adhesive underlayer depends on the type of a technological cutting operation, the machined material, geometric parameters and the form of tool cutting surface. For the given case the total coating thickness is 2-12 μm with the adhesive underlayer thickness about 0.8 μm and with roundness radius value of insert cutting edges within the range of 30 μm.

Version 2. The coating is synthesized on the BKI O-XO carbide inserts (2%CrC, 88%WC, 10%Co) of the same shape as in version No 1. Three cathodes of zirconium, niobium and aluminium are positioned. The formation of the strengthening underlayer is carried out as follows. After chamber preliminary evacuation down to the p=10"² Pa pressure the neutral gas (e.g. argon) is introduced up to the pressure of 2 x 10"¹ Pa, then the carbide insert thermoactivation is performed by means of the electron beam ejected from the plasma of dependant gas discharge up to the temperature of 600-650 °C with the 0.01 A/sm² density of the electron current-. Then the insert precleaning is carried out with bias voltage of 0.8-1 .2 kW, current density of 0.05-0.1 1 A/sm² and cleaning time of 3-7 min. In this case the insert temperature is increased up to 700-720 °C. Then, the formation of the strendthening underlayer takes place with the voltage of 0.2-0.3 kW and nitrogen pressure of 1 -3 Pa for 20-60 min.

Further, the technological process is carried out as in version No 1 . The adhesive underlayer is formed by means of two evaporates - zirconium and niobium, the transition layer - on evaporation of zirconium and niobium and the nitrogen feed; the first alternating layer is formed on the activation of three evaporators (zirconium, niobium and aluminium), the second alternating layer is formed when the zirconium evaporator works and nitrogen is supplied.

The total thickness of the coating is 2-12 μm, the adhesive underlayer thickness is about 0.3-0.8 μm and the strengthening underlayer thickness is about 10 - 100 μm for the inserts with the roundness radius of 20-30 μm.

Version 3. The coating is deposited on 0 6 mm drills, made of HSS P6M5 (6%W, 5%Mo) with geometric parameters α=1 1°, ψ=55°, 2φ=1 18°. Three cathodes of zirconium, chrome and aluminium are set up. The strengthening layer formation process is carried out as follows. After the chamber preliminary evacuation to the pressure of Pa = 5.0 x 10"² Pa the neutral gas (e.g. argon) is introduced into the vacuum chamber with the pressure of 1 *10^_1 - 3^χ10-¹ Pa and the thermoactivation of drills is carried out by means of the electron beam ejected from the plasma of dependant gas discharge up to the temperature 420 - 480 °C with the following values of the technological process parameters: electron current density - 0.01 A/sm²; the pressure in the vacuum chamber - 0.5-10 Pa; bias potential of the tool - from 40 V; the thermoactivation time - 10-12 min. The technological process of the multilayer composite coating formation is performed similar to version No 1 , but the temperature of the coating cleaning and synthesis is reduced down to 480°.

The adhesive underlayer is formed by means of two evaporators - titanium and chrome; the transition layer is formed in the process of the evaporation of titanium, chrome and nitrogen feed. The first alternating layer is formed on the activation of the evaporators - titanium and aluminium, and nitrogen feed; the second alternating layer is formed when titanium evaporates and nitrogen is supplied. For the drills having the 5-6 μm roundness radius the total coating thickness is 2.0-3.5 μm with the 0.5 μm and 15- 35 μm thickness of adhesive and strengthening underlayer respectively.

Then the coated cutting tools were tested to determine their main efficiency factors, i.e. the tool life mean value and tool life deviation coefficient.

The tests were carried out while turning the 45 HB 180 steel (V- 200 m/min; S= 0.3 mm/ in; t= 1.0 mm) by means of tools equipped with MC131 inserts having control and suggested coatings ; while turning XH77TUP chrome - nickel alloy (V=30 m/min: S = 0.15 mm/rev: t=1 mm) by means of tools equipped with BK10-XOM indexable inserts with the control and suggested coatings on the 16K20 machine-tool as well as while drilling in the 40X HB 200 steel by P6M5 HSS drills having the control and suggested coatings on the 2H135 machine-tool (V = 30 m/min: S = 0.3 rev/min: I = 30 mm); in the process of symmetrical face milling the 40X HB 200 steel by the tools equipped with BK10-XOM inserts with the control coating and suggested coatings on the 6G55 horizontal milling machine (V = 170 m/min: B= 140 mm: t = 2 mm: S = 0.3 mm/tooth). In the process of testing tools with the suggested and control coatings the periodical measuring of tool wear along the contact surfaces depending on the cutting path length was carried out by means of the MBC-2 tool microscope. The limit value of 0.5 mm clearing face wear land was taken as a tool life criteria according to which the time between failures was evaluated on the graph h₃=f(τ). The statistical processing of the obtained data was performed for the evaluation of tool life arithmetic mean value and its deviation coefficient. The tool life increasing coefficient was evaluated as a tool life ratio with the given wear criteria for the tools with the suggested and control coatings (in accordance with the prototype description) and uncoated tools.

The results of the comparative tool life tests are given in the table.

The comparative analysis of the data given in the table shows that the life of tools with the suggested multilayer composite coating was 2.5 - 3.0 times longer than the tool life with the control coating of the prototype and the tool life deviation coefficient is reduced 20% on the average which, demonstrates the achievement of the invention object.

Table. Test results

*tuming milling drilling

Claims

1. The multilayer composite wear resistant coating applied on the different article working surfaces having an adhesive underlayer, transition and alternating layers of refractory metal compounds distinguished in that the adhesive underlayer comprises, at least, one element from the article material composition and/or its compound and one element from the coating transition layer composition and/or its compound; the transition layer includes the refractory metal compounds of Groups IV, V or VI or their combinations; the first alternating layer includes the combinations of refractory metal compounds of Groups IV and/or V and/or VI alloyed with aluminium, the other one has refractory metal compounds of Groups IV, V or VI or their combinations.

2. The coating as claimed in claim 1 , distinguished in that the active metals from the Ti and/or Zr and/or V and/or Cr and/or Al series reduced from the oxides in the hydrogen medium amounting to 5-30 % mass, are additionally incorporated into the adhesive underlayer.

3. The coating as claimed in claim 1 , distinguished in that the total coating thickness is 0.1 -0.7 of the roundness radius of the cutting edge of the tools used for uninterrupted cutting operations and is reduced 20 - 40 % for the tools used for interrupted cutting operations.

4. The coating as claimed in claim 1 , distinguished in that the strengthening layer is introduced between the coating and tool material, the strengthening layer thickness being 5-10 of the total coating thickness for the tools used for uninterrupted cutting operations and being reduced 10-20 % for tools used for interrupted cutting operations.