Glass-based articles including a stress profile comprising two regions, and methods of making

Abstract

Glass-based article including a first surface and a second surface opposing the first surface defining a thickness (t), and a stress profile are disclosed having a thickness (t) of about 3 millimeters or less, and wherein all points of the stress profile between a thickness range from about 0·t up to 0.3·t and from greater than 0.7·t, comprise a tangent with a slope that is less than about −0.1 MPa/micrometers or greater than about 0.1 MPa/micrometers. Also disclosed are glass-based articles having a thickness (t) in a range of 0.1 mm and 2 mm; and wherein at least one point of the stress profile in a first thickness range from about 0·t up to 0.020·t and greater than 0.98·t comprises a tangent with a slope of from about −200 MPa/micrometer to about −25 MPa/micrometer or about 25 MPa/micrometer to about 200 MPa/micrometer, and wherein all points of the stress profile in a second thickness range from about 0.035·t and less than 0.965·t comprise a tangent with a slope of from about −15 MPa/micrometer to about 15 MPa/micrometer.

What is claimed is: 
     
         1 . A method of chemically strengthening a glass-based substrate comprising a first major surface, a second major surface, an average thickness t extending perpendicularly between the first and second major surfaces, and an edge extending between the first and second major surfaces, the method comprising:
 performing a first IOX step by holding the glass-based substrate for a first period of time in a first bath comprising a mixture of sodium and potassium ions;   performing a second IOX step, after the first IOX step, by holding the glass-based substrate for a second period of time in a second bath comprising a mixture of sodium and potassium ions to form a stress profile in the glass-based substrate, the stress profile having a compressive stress region and a central tension region, wherein the stress profile extends along the thickness (t) according to a mathematical formula that is a function of the thickness;   wherein at least one point of the mathematical formula for stress profile in a first thickness range from about 0·t up to 0.020·t and greater than 0.98·t comprises a tangent with a slope of from about −200 MPa/micrometer to about −25 MPa/micrometer or about 25 MPa/micrometer to about 200 MPa/micrometer,   wherein all points of the mathematical formula for stress profile in a second thickness range from about 0.035·t and less than 0.965·t comprise a tangent with a slope of from about −15 MPa/micrometer to about 15 MPa/micrometer, wherein the mathematical formula for stress profile along the span of the second thickness range forms a power-law function having a power exponent, wherein the power exponent is from about 1.2 to about 3.2,   wherein maximum compressive stress is from about 200 MPa to about 1100 MPa, and   wherein the stress profile comprises a depth of compression ranging from about 0.1·t to 0.25·t,   the second bath has a molar ratio of Na: K that is 3-10 times smaller than the Na:K molar ratio of the first bath.   
     
     
         2 . The method of  claim 1 , wherein the maximum compressive stress of the glass-based article after the second IOX step is 600 MPa or more, the depth of compression is greater than or equal to 0.14·t, and further comprising a maximum central tension that is less than or equal to 80 MPa. 
     
     
         3 . The method of  claim 2 , wherein both steps of ion exchange are completed in a bath comprising both a Na-containing salt and a K-containing salt, wherein the ratio of Na ions to K ions in the first bath is from 2.5 to 800 times higher than the ratio of Na ions to K ions in the second bath. 
     
     
         4 . The method of  claim 2 , the second bath has a molar ratio of Na to K that is from 0.03 to 0.4. 
     
     
         5 . The method of  claim 2 , an effective diffusion time of the second IOX step is from 1/20 to ½ that of the first step. 
     
     
         6 . The method of  claim 2 , a depth-of-layer sp  is: (i) from 0.5 to 1.5% of the thickness when the thickness is from 1 to 1.3 mm; (ii) from 0.6 to 2% of thickness when the thickness is from 0.8 to 1 mm; (iii) from 0.7 to 2.5% of the thickness when the thickness is from 0.65 to 0.8 mm; (iv) from 0.9 to 3% of the thickness when the thickness is from 0.5 to 0.65 mm; and (v) from 1 to 3% when the thickness is from 0.3 to 0.5 mm. 
     
     
         7 . The method of  claim 2 , wherein the mathematical formula in the central tension region comprises a power-law function having a power exponent, wherein the power exponent from 1 to 3.4. 
     
     
         8 . The method of  claim 2 , wherein at least one of:
 (i) the Knoop Scratch Lateral Cracking Threshold of the strengthened glass-based substrate is greater than 10N and is less than 16N;   (ii) the strengthened glass-based substrate has a survival rate of 40% to 100%, when impacted on one of the first and second major surfaces with a force of 400N or more according to the surface Impact Threshold Test with 180 grit abrasive; and   (iii) the strengthened glass-based substrate can survive an edge-impact of from more than 300N to less than 500N, or an edge-impact of from more than 0.68 J to less than 1.58 J according to the edge Impact Threshold Test with 30 grit abrasive.   
     
     
         9 . The method of  claim 2 , wherein the thickness t is less than or equal to 1 mm.