Compositions: ceramic – Ceramic compositions – Refractory
Patent
1982-10-28
1984-03-13
Poer, James
Compositions: ceramic
Ceramic compositions
Refractory
501 97, C04B 3558
Patent
active
044368305
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the metal working and, more specifically, to a coating for metal-cutting tools.
BACKGROUND OF THE INVENTION
Known in the art is a titanium nitride-based coating for a metal-cutting tool (cf. e.g., H. F. Bunshan et al. Thin solid films, 1977, 45, No. 3, pp. 453-462).
Tools with coating of titanium nitride show a high abrasion-resistance in machining of workpieces of structural steels which exceeds by 5-7 times that of tools without coating.
However, in machining, by means of a tool with coating of titanium nitride, parts made of stainless steels and refractory alloys wear-resistance of such tools is but insufficient. The reason therefor resides in a high degree of an adhesion interaction of the coating with the machined workpiece which occurs at the contact surfaces of the tool during cutting. As a result, temperature in the cutting zone is increased and mechanical strength of the coating is substantially reduced at the account of the effect produced by water vapours and oxygen.
SUMMARY OF THE INVENTION
The present invention is directed to the provision of a coating for metal-cutting tools having such a composition which would ensure a high wear-resistance of the tool provided with such coating in machining of workpiece made of stainless steels and refractory alloys.
Said object is accomplished by that the coating for metal-cutting tools consisting of titanium nitride, according to the present invention, additionally contains either chromium nitride in an amount of from 10 to 30% or taken in combination and uniformly distributed over the coating volume aluminium nitride in an amount of from 3 to 18% by weight, molybdenum nitride in an amount of from 2 to 8% by weight, chromium nitride in an amount of 2 to 10% by weight and silicon nitride in an amount of from 0.5 to 10% by weight.
The bicomponent coating consisting of nitrides of chromium and titanium is somewhat less expensive in manufacture, whereas the multi-component coating ensures a high wear-resistance for a wider range of machinable materials.
Both embodiments of the coating according to the present invention, while being applied onto the metal-cutting tool, improve its wear-resistance in machining of stainless steels and refractory alloys by 4-6 times as compared to a known coating based on titanium nitride.
In machining of stainless steels and refractory alloys chromium nitride in the coating consisting of titanium nitride and chromium nitride acts as a barrier hindering active adhesion processes on contact areas of the tool thus increasing its wear-resistance. Furthermore, partial oxidation of boron nitride occurring at high temperature developing during the cutting process results in the formation of thermodynamically stable chromium oxides which still more reduce the adhesion-fatigue wear of the tool.
In the use of a coating consisting of nitrides of titanium, aluminium, molybdenum, chromium and silicon in the above-mentioned ratio, said nitrides ensure a high microhardness of the coating and, owing to their uniform distribution within the volume, all enter into operation simultaneously. As the temperature in the cutting zone is increased, the resulting abrasion products and the superficial layer of the coating containing nitrides of aluminium, molybdenum are subjected to oxidation with air oxygen and water vapours to oxides. The resulting aluminium oxide lowers the adhesive interaction of the tool with the machined material and decreases the chemical activity of the coating. The molybdenum oxide formed in the course of cutting possesses lubricating properties and contributes to a redeced friction coefficient and, consequently, lowered temperature in the cutting zone. As the temperature is increased, chromium nitride starts to decompose with the formation of a stable oxide creating an electrical barrier hindering the redistribution of the current carriers. The converted nitrides protect titanium and silicon nitrides from losing their mechanical strength which nitrides are responsibl
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patent: 3108887 (1963-10-01), Lenie et al.
patent: 3251698 (1966-05-01), Colton
patent: 3544486 (1970-12-01), Passmore
patent: 3649314 (1972-03-01), James
patent: 3679442 (1972-07-01), Bergna
Andreev Anatoly A.
Gavrilko Igor V.
Gavrilov Alexei G.
Padalka Valentin G.
Sinelschikov Andrei K.
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