Glass-ceramic articles having reduced surface defects and ion-exchange methods for making same

A method for ion-exchanging glass-ceramic substrates, the method comprising:

• a first contacting step comprising contacting a first glass-ceramic substrate with a molten salt bath comprising a lithium ion buffer and at least one of NaNO3 and KNO3, whereby (1) lithium ions diffuse from the first glass-ceramic substrate into the molten salt bath to provide a first dissolved lithium ion concentration, and (2) at least one of sodium and potassium ions diffuse from the molten salt bath into the first glass-ceramic substrate, thereby forming a first glass-ceramic article;
• a pH adjusting step comprising adding a pH modifier to the molten salt bath that adjusts a pH of the molten salt bath;
• a lithium ion scavenging step comprising contacting a lithium ion scavenger with the molten salt bath that, in conjunction with the lithium ion buffer, adjusts the first dissolved lithium ion concentration, wherein the lithium ion scavenger comprises a sodium-containing glass-based material having a different composition than the first glass-ceramic substrate;
• wherein the pH adjusting and lithium ion scavenging steps (1) take place simultaneously or sequentially in any order, and (2) in combination provide a regenerated molten salt bath having a pH of 9-11 and a second dissolved lithium ion concentration of 115-250 ppm based on 100 wt. % of a sum total of NaNO3 and KNO3, if present;
• and
• a second contacting step comprising contacting a second glass-ceramic substrate with the regenerated molten salt bath, whereby (1) lithium ions diffuse from the second glass-ceramic substrate into the regenerated molten salt bath, and (2) at least one of sodium and potassium ions diffuse from the regenerated molten salt bath into the second glass-ceramic substrate, thereby forming a second glass-ceramic article.

A glass-ceramic article, comprising:

• first and second primary surfaces, the first primary surface comprising a textured region, a void having an edge, or both the textured region and the void having the edge;
• a first compressive stress layer extending from the first primary surface to a first depth of compression (DOC1) and a second compressive stress layer extending from the second primary surface to a second depth of compression (DOC2);
• a central tension region extending from DOC1 to DOC2;
• and
• at least one region that satisfies Equation 1:
• ❘
• "\[LeftBracketingBar]"
• (
• Ca
• n
• -
• Ca
• n
• ±
• 1
• )
• Ca
• n
• ❘
• "\[RightBracketingBar]"
• ×
• 100
• >
• 15
• ⁢
• %
• ;
• (
• Equation
• ⁢
• 1
• )
• wherein Can is an average normalized intensity of calcium in a first 50 nm region, Can±1 is an average normalized intensity of calcium in a second 50 nm region immediately adjacent to the first 50 nm region, both the first and second 50 nm regions are within a depth of 25 nm to 5000 nm from the first primary surface, and both Can and Can±1 are measured by SIMS analysis;
• wherein at least one of the textured region and the edge, if present, is substantially free of line defects;
• and
• wherein at least one of the textured region and the edge, if present, is substantially free of a low index layer.