Differential densification strengthening of glass-ceramics

• US 3,931,438 A
• Filed: 11/07/1973
• Issued: 01/06/1976
• Est. Priority Date: 11/08/1971
• Status: Expired due to Term

• Current Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Original Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Inventors: Beall, George H., Chyung, Kenneth
• Primary Examiner(s): Lesmes, George F.
• Assistant Examiner(s): McDonald, Alan T.
• Application Number:
  US05/413,544
• Time in Patent Office: 790 Days
• Field of Search: 161/193, 161/192, 161/164, 156/84, 156/85, 156/86, 65/33, 65/30, 428/218, 428/426, 428/428, 428/212
• US Class Current: 428/218
• CPC Class Codes: C03B 17/02 Forming molten glass coated with coloured layers; Forming molten glass of different compositions or layers; Forming molten glass comprising reinforcements or inserts
• CPC Class Codes: C03B 27/012 by heat treatment, e.g. for crystallisation; Heat treatment of glass products before tempering by cooling C03B27/008, C03B27/016 take precedence
• CPC Class Codes: C03B 32/02 Thermal crystallisation, e.g. for crystallising glass bodies into glass-ceramic articles C03B27/012 takes precedence
• CPC Class Codes: C03C 10/00 Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
• CPC Class Codes: C03C 10/0027 containing SiO2, Al2O3, Li2O as main constituents
• CPC Class Codes: C03C 17/02 with glass C03C17/34, C03C17/44 take precedence
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/24992 Density or compression of components

Abstract

A strengthened glass-ceramic laminated article having a compressively-stressed surface layer substantially enveloping a tensilely-stressed core portion, produced by choosing the core and surface layer compositions such that the core undergoes a net positive differential densification with respect to the surface layer as the result of phase transformations occurring in the laminated article during crystallization in situ. Such an article offers significant advantages over glass and glass-ceramic articles strengthened by prior art methods, including improved mechanical stability, thermal shock resistance, and, most importantly, excellent high temperature strength retention.

Claims

1. A strengthened laminated glass-ceramic article comprising a glass-ceramic core portion and a compressively-stressed glass-ceramic surface layer laminated to and substantially enveloping said core portion, wherein

a. the difference in thermal expansion coefficient between the core and surface layer glass-ceramics is less than about 5 ×

10^-7 /°

C.;

b. the glass-ceramic core portion is formed of a composition having at a selected crystallization temperature a density D_ci prior to crystallization in situ and a density D_cf subsequent thereto;

c. the compressively-stressed glass-ceramic surface layer is formed of a composition having at said crystallization temperature a density D_si prior to crystallization in situ and a density D_sf subsequent thereto; and

wherein

d. the values of the densities D_ci, D_cf, D_si, and D_sf are such that the present value of the densification differential (D) as defined by the expression;

##EQU3## is positive.

2. A strengthened laminated glass-ceramic article according to claim 1 wherein D has a value in the range of about 0.5-20%.

3. A strengthened laminated glass-ceramic article according to claim 2 wherein D has a value in the range of about 1-5%.

4. A strengthened laminated glass-ceramic article according to claim 2 wherein the core and compressively-stressed surface layer glass-ceramics are composed of Li₂ O--Al₂ O₃ --SiO₂ compositions wherein the principal crystal phases are selected from the group consisting of beta-quartz and beta-spodumene solid solutions.