In a patent that was spotted recently, it detailed methods where sapphire glass could very well see action. The patent is known as “Attachment Techniques”, where it begins by explaining the difficulty in attaching sapphire to other materials. “Sapphire, for example, may be particularly difficult to mechanically couple with other materials. Specifically, machining sapphire may be difficult due to its crystalline structure, hardness and strength. Further, sapphire may have a high level of stiffness relative to other materials, as well as a relatively low level of thermal expansion. As such, conventional adhesive attachment techniques may not be effective or lasting. That is, mechanical strain on the adhesive bond resulting from the difference in the thermal expansion and stiffness of the materials eventually causes failure of the bond.”
Apple intends to get around this particular obstacle by creating an aperture within a sapphire substrate, followed by filling up the aperture with an attachment material, before mechanically joining that with a different part thanks to the attachment material.