Asymmetric chemical strengthening

1. A glass article, comprising:

a chemically strengthened central portion;

a chemically strengthened peripheral portion surrounding the central portion and including a bend defining a curved first front surface and a curved first rear surface of the peripheral portion;

a first chemically strengthened zone within the peripheral portion and having a first asymmetric stress pattern extending from the curved first front surface to the curved first rear surface of the peripheral portion; and

a second chemically strengthened zone within the central portion having a second asymmetric stress pattern extending from a second front surface to a second rear surface of the central portion, the second asymmetric stress pattern defining:

a front compressive stress layer having a uniform depth across the second chemically strengthened zone;

a rear compressive stress layer having a depth less than the uniform depth of the front compressive stress layer; and

an imbalance of compressive stress between the front compressive stress layer and the rear compressive stress layer, the imbalance of compressive stress counteracted by the chemically strengthened peripheral portion to produce a substantially flat second front surface and a substantially flat second rear surface.

2. The glass article of claim 1 , wherein:

the first asymmetric stress pattern defines:

a first front compressive stress layer having a first depth from the curved first front surface of the peripheral portion; and

a first rear compressive stress layer having a second depth, less than the first depth, from the curved first rear surface of the peripheral portion;

the front compressive stress layer of the second asymmetric stress pattern is a second front compressive stress layer and the uniform depth is a third depth from the substantially flat second front surface of the central portion; and

the rear compressive stress layer of the second asymmetric stress pattern is a second rear compressive stress layer and the depth of the second rear compressive stress layer is a fourth depth from the substantially flat second rear surface of the central portion.

3. The glass article of claim 2 , further comprising one or more ion-diffusion barrier coatings.

4. The glass article of claim 3 , wherein one of the one or more ion-diffusion barrier coatings is provided along the substantially flat second rear surface of the central portion.

5. The glass article of claim 1 , wherein the curved first front surface is convex and the curved first rear surface is concave.

6. A method, comprising:

asymmetrically strengthening a glass article to include an asymmetric distribution of compressive stress comprising:

chemically strengthening a peripheral portion of the glass article including chemically strengthening a first zone including a bend located along the peripheral portion of the glass article and defining a curved front surface and a curved back surface, thereby creating a first stress pattern extending through a first thickness of the glass article at the bend; and

chemically strengthening a central portion of the glass article including chemically strengthening a second zone corresponding to the central portion of the glass article, thereby creating a second stress pattern extending through a second thickness of the glass article in the second zone, the second stress pattern defining a front compressive stress layer having a uniform depth across the second zone, a back compressive stress layer, and an imbalance of compressive stress between the front compressive stress layer and the back compressive stress layer; wherein:

the first stress pattern is asymmetric along the first thickness and the second stress pattern is asymmetric along the second thickness;

the back compressive stress layer has a depth less than the uniform depth of the front compressive stress layer;

the first stress pattern and the second stress pattern differ;

the chemically strengthened peripheral portion counteracts the imbalance of compressive stress in the second zone and front and rear surfaces of the second zone are substantially flat; and

the glass article is for use in a portable electronic device.

7. The method of claim 6 , wherein the bend is localized to the first zone and a back surface of the bend defines a concave shape.

8. The method of claim 6 , further comprising pre-heating a portion of the glass article prior to the operations of chemically strengthening the first zone and chemically strengthening the second zone, thereby increasing a density of the pre-heated portion from a first density to a second density greater than the first density.

9. The method of claim 6 , further comprising:

locally heating one or more of the first zone and the second zone during the operations of chemically strengthening the first zone and chemically strengthening the second zone thereby facilitating the operation of asymmetrically strengthening the glass article; and

quenching the glass article.

10. The method of claim 6 , further comprising:

operatively attaching a layer of a material to the glass article, wherein:

the second zone resists deformation from the asymmetric distribution of compressive stress.

11. The method of claim 10 , wherein:

the material is transparent.

12. The method of claim 10 , wherein:

the glass article is a cover glass; and

the portable electronic device is a mobile phone.

13. The method of claim 12 , wherein

the operations of chemically strengthening the first zone and chemically strengthening the second zone each comprise exchanging ions in the glass article with potassium ions.

14. A cover glass, comprising:

a first chemically strengthened zone within a chemically strengthened peripheral portion of the cover glass, the peripheral portion including a bend formed in the cover glass and the first chemically strengthened zone having a first stress pattern extending through a first thickness of the cover glass from a curved first front surface to a curved first rear surface, the first stress pattern asymmetric along the first thickness; and

a second chemically strengthened zone within a chemically strengthened central portion of the cover glass, the second chemically strengthened zone having a second stress pattern extending through a second thickness of the cover glass from a substantially flat second front surface to a substantially flat second rear surface, the second stress pattern asymmetric along the second thickness, and defining:

a front compressive stress layer having a uniform depth across the second chemically strengthened zone and a rear compressive stress layer having a depth less than the uniform depths; and

an imbalance of compressive stress between the front compressive stress layer and the rear compressive stress layer, the imbalance of compressive stress counteracted by the chemically strengthened peripheral portion to produce the substantially flat second front surface and the substantially flat second rear surface;

wherein the first stress pattern and the second stress pattern differ.

15. The cover glass of claim 14 , wherein the front compressive stress layer of the first chemically strengthened zone of the cover glass is deeper than the rear compressive stress layer of the second chemically strengthened zone of the cover glass.

16. The cover glass of claim 14 , wherein the first chemically strengthened zone has a greater amount of chemical strengthening than the second chemically strengthened zone.

17. The cover glass of claim 14 , wherein:

the bend is localized to the peripheral portion; and

a rear surface of the bend defines a concave shape.

18. The cover glass of claim 17 , wherein the bend surrounds the central portion of the cover glass.

19. The cover glass of claim 14 , wherein the second stress pattern further defines a tensile stress region having a maximum tensile stress positioned between a midpoint and a rear surface of the central portion.

20. The cover glass of claim 14 , wherein the peripheral portion abuts the central portion.