Formation of hard coatings on cutting edges

A method for making a cutting edge which comprises the steps of:

• a. selecting a cutting edge substrate having a cross-sectional shape up to a distance of forty micrometers from the extreme edge which is defined by the equation:
• w.ltoreq.ad.sup.n
• where w is the tip width in .mu.m of the cutting edge at distance d from the ultimate tip, a is a factor of proportionality of greater than 0 and up to about 1, and n is an exponent having a value in the range of 0.65 to 0.75.
• b. coating the selected cutting edge substrate with a material which is harder than the material of the substrate coating edge by a vapor deposition or sputtering process at a pressure of less than about 10.sup.-3 m bar, said coating step optionally including the presence of gaseous or vaporized molecules of another element or compound of another element, and
• c. simultaneously subjecting the selected cutting edge substrate to ion bombardment with ions of sufficient mass and energy to cause sputter removal of the deposited material at a rate which is less than the rate of deposition to provide a cutting edge formed of the deposited material and having a cross-sectional geometry defined by the equations:
• ##EQU3## where w, d, a and n have the above-stated meanings, m is the ratio of the yield strength of the deposited coated material to that of the substrate material, and f is between about 0.2 .mu.m to about 0.3 .mu.m, said edge having an ultimate tip radius of less than 500 .ANG., and where the aspect ratio of the coating is between about 4.5 to about 6.8.