Patent Publication Number: US-2002000269-A1

Title: Architectural titanium

Description:
[0001] This application claims the benefit of priority under 35 U.S.C. §119(e) to provisional application number 60/214,384, filed Jun. 28, 2000. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The invention is a method of thermally treating titanium, titanium alloys and titanium composites to produce an aesthetically attractive speckled surface and articles made therefrom.  
       DESCRIPTION OF THE RELATED ART  
       [0003] Titanium and titanium alloy sheet are finding increasing application in building and architectural construction. Selected newly designed office buildings and museums are sometimes clad with titanium sheet. Further enhancement of the appearance over conventional titanium would offer a highly desirable characteristic of added value.  
       [0004] Titanium and its alloys microstructually exist in two phases. The alpha phase has a close packed hexagonal structure while the beta phase has a body centered cubic structure. Heating this material to above approximately 180° F. (the exact temperature will depend on the composition of the titanium alloy) produces beta (body centered cubic) structure which on cooling undergoes transformation to the alpha/beta (hexagonal closed pack) structure.  
       [0005] The Inventors have found that repeated heating and cooling of these materials or heating for longer times in vacuum at temperatures well over the beta transformation (heating typically at 220° F.) causes the grain size to grow larger. The average diameter of the grain size can thus be made to vary from 0.5 mm for one or two cycles or short times to 25 mm or larger as additional thermal cycles or longer times are employed. These large grains produce an attractive sparkled texture to the titanium sheet.  
       [0006] The thermal treatments can also be applied to fabricated components of titanium that include watch cases, computer containers and telephone components such as cell phone bodies. The attractive “bright speckled” titanium can be used as processed or can be further anodized by conventional technology to produce a variety of colors while still retaining the speckled titanium surface.  
       SUMMARY OF THE INVENTION  
       [0007] Accordingly, the present invention is directed to a thermally treated sheet product or components of titanium and its alloys with an architecturally and aesthetically desirable surface finish. In addition, the resulting titanium sheet product may exhibit beneficial mechanical and wear properties normally associated with titanium and its alloys. Therefore, the attractive finish of the thermally treated sheet product or components resulting from the inventive process can be used in articles such as computer cases, watch cases, cell phones and as automotive interior and exterior trim. 
     
    
    
     [0008] It is understood that both the forgoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.  
     [0009] The inventors have discovered that the cyclic thermally treated titanium components result in an attractive article with a speckled grained surface. To produce small speckled grains treatment comprises only 1 or 2 cycles or heating above the beta transformation temperature for short times are determined to be sufficient. Where large speckled grains are desired, additional cycles or higher temperature and longer times can be applied until the preferred grain size for the particular article is achieved.  
     [0010] Preferably, each thermal cycle in performed in vacuum and comprises a heating rate, a maximum temperature, holding at the maximum temperature for a controlled interval of time, followed by a controlled cooling rate. To control the actual grain size achieved, thermal cycling (number of cycles), maximum temperature, and the holding time interval at the maximum temperature are varied.  
     [0011] Articles which can be made according to the inventive process include, but are not limited to cases for watches or computers, components (or sheets) for building structures, articles such as automotive trim, and accessories such as doorknobs, bathroom fixtures and other household components.