Coating processes – Direct application of electrical – magnetic – wave – or... – Ion plating or implantation
Reexamination Certificate
1999-07-21
2001-03-13
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Ion plating or implantation
C427S531000, C427S528000, C427S566000, C427S255380, C427S255394
Reexamination Certificate
active
06200649
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides a controllable process for forming titanium boronitride coatings on large or small workpieces using ion beam assisted deposition. The process may be relatively easily scaled up for commercial use.
BACKGROUND OF THE INVENTION
Titanium nitride (TiN) has been widely used for wear-resistant coatings, e.g. on cutting tools, for many years. More recently, a mixed titanium aluminum nitride has provided improved performance on drills, and at least one group has reported superior hardnesses and wear life using deposited coatings of titanium boronitride (Ti—B—N).
The methods described to date for depositing titanium boronitride coatings are dual target magnetron sputtering processes, in which two targets are sputtered with an argon-nitrogen plasma. The two sputter targets are (1) titanium, and (2) titanium diboride. The properties of the resulting titanium boronitride coatings depend strongly upon the chemical composition of the coating formed. The best coating properties are obtained when the coating comprises particles having a small grain size, because this imparts hardness, and when the coating has a boron content of about 20 atomic % or less in relation to the titanium content, and a nitrogen content of about 40 atomic % or less in relation to the titanium content. The Vickers hardness number reported for the titanium boronitride coatings formed using dual target magnetron sputtering was 6800 HVN. The abrasive wear resistance reported for the same coatings was nine times better than that of TiN.
Unfortunately, magnetron sputtering involves so many process variables that it is difficult to exercise a great degree of control over the chemical composition of the resulting titanium boronitride coating. The process variables which may affect the chemical composition of a coating produced by dual target magnetron sputtering include: (1) the position of the workpiece relative to the two sputter targets; (2) the argon flow rate; (3) the nitrogen flow rate; (4) the power deposited in the plasma discharge; and, (5) the bias voltage used. In addition to the large number of process variables that can affect the chemical composition of the resulting coating, dual target magnetron sputtering suffers from the disadvantage that it cannot readily be used to coat large components because the distance between the sputter targets and the workpiece cannot be greater than about twelve inches.
A process is needed which can be used to coat large scale components, and which provides more control over the chemical composition of the resulting titanium boronitride coating.
SUMMARY OF THE INVENTION
The present invention provides a method for producing a titanium boronitride coating comprising: exposing a substrate to a vacuum, depositing onto the substrate an amount of titanium; substantially simultaneously exposing the substrate to a source comprising boron and nitrogen; and, substantially simultaneously bombarding the substrate with an energetic beam of ions under conditions effective to form a first quantity of titanium-boron bonds and a second quantity of titanium-nitrogen bonds effective to produce a titanium boronitride coating on said substrate having a hardness of at least about 5000 kg/mm
2
.
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Padgett Marianne
Paula D. Morris & Associates P.C.
Southwest Research Institute
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