Diamond Turned Super Alloy Mandrel for Slump Forming X-Ray Observatory (IXO) Mirrors

Diamond turning is proven to be able to quickly produce highly aspheric grazing incidence optical contours to visible wavelength tolerances with extremely smooth surfaces. Super alloys with exceptional dimensional stability and strength under cyclic high temperatures have been developed for gas turbine engines. The thermal expansion can be in the range of the expansion of the borosilicate glasses used for X-Ray mirrors. This proposal utilizes an existing manufacturing learning curve to develop a reliable material and manufacturing process for glass slumping mandrels. This development process will involve the following investigations and development goals : -develop electroless nickel plating processes for super alloys, -ultra precision machining and polishability of super alloys. -diamond turning of electroless nickel before and after the slumping heat cycle. -heat treatment for dimensional stability under thermal cycling. -evaluation of oxidation of directly polished super alloys. -evaluation of oxidation of polished electroless nickel. Heat treatment and plating processes will be evaluated by producing a number of flat test mirror samples which will be measured optically before and after the glass slumping process to evaluate contour distortion, oxidation resistance, increase in surface roughness, and diamond machineability of the electroless nickel plating. A test slumping mandrel will be designed for fabrication in a Phase II SBIR.

With current technology, the cost to fabricate and the time to produce large mirrors is one of the limiting factors for many missions. A major emphasis in achieving a successful IXO is reducing the cost of the grazing incidence mirrors. Diamond turning is proven to be able to quickly produce highly aspheric grazing incidence optical contours to visible wavelength tolerances with extremely smooth surfaces. Because diamond turning can produce mandrels with extremely repeatable contour accuracy, the process allows manufacture of mandrels which can be adjusted in dimension to compensate for the thermal expansion of the borosilicate glass and the mandrel so that the curvature of the slumped glass can be adjusted. Any number of slumping mandrels can be produced with exactly the same contour with repeatability of approximately 1/100 wave visible light. This uniformity and rapidity of production of a relatively low cost mandrel will be enabling technology for IXO mirror fabrication.

Diamond turned electroless nickel plated mirrors are in wide use in commercial and military applications. Molds for injection and compression molding of plastic and glass optics and other products utilize diamond turned electroless nickel plated molds. Electroless nickel plated mirrors are used for synchrotron light source installations around the world. Mandrels for slump forming of x-ray mirror optical segments will lower costs to the point of enabling large space borne x-ray optical instruments.

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