Timothy M. Gross

Dr. Timothy M Gross is the Director of Inorganic Materials at Corning Incorporated, Corning, NY. He is responsible for leading a research and development team focused on building deep technical understanding of inorganic materials to enable invention and optimization of new glasses and ceramics.

Tim has a PhD in Materials Engineering from Rensselaer Polytechnic Institute, an MS in Materials Science and Engineering from Rochester Institute of Technology, and a BS in Ceramic Engineering from Alfred University. Tim joined Corning in 2008 and has established himself as an expert in both fracture mechanics and glass formulation. Tim’s early work focused on mechanics of ion-exchangeable glass and resulted in invention of several iterations of Corning® Gorilla® Glass. Tim also served as the research lead of the Corning® Bendable Glass program where he defined the solution space for use of ultra-thin, bendable glass in mobile electronic devices. Tim’s work on automotive glass resulted in several innovations including Fusion5® damage-resistant windshield glass. Tim also invented Guardiant® antimicrobial glass-ceramic that kills ≥ 99.9% of bacteria and viruses while maintaining long term efficacy. For his technical achievements at Corning, Tim was given the title of Research Fellow in 2017. Tim has 153 granted United States patents and 34 peer-reviewed publications. He has won numerous Corning internal awards including the 2012 Stookey Award for outstanding exploratory research and the outstanding external publication award in both 2019 and 2022. Tim is a member of the American Ceramic Society and American Chemical Society. His current areas of research include high ionic conductivity glass-ceramics and glasses with hydration-induced stress profiles.

Abstract: Discovery of strong and damage-resistant glasses through indentation studies

The response of glass to indentation provides considerable information regarding modes of deformation and propensity towards cracking. Learning to tailor the observed glass response through composition design has resulted in several key discoveries including numerous versions of Corning® Gorilla® Glass, Corning® Fusion5® (break resistant windshield glass), and glasses with hydration-induced compressive stress profiles.
In between normal glasses that deform with a considerable volume displacing shear component and anomalous glasses that deform primarily by densification, a third type of glass, defined as intermediate, was shown to deform with less subsurface damage while also displaying high indentation crack resistance. By designing ion-exchangeable compositions with intermediate deformation behavior, Vickers cracking threshold values exceeding 30 kilograms force were observed for the first time. This discovery paved the way for multiple generations of Corning® Gorilla® Glass. To fully understand the significance and utility of this breakthrough, an investigation of damage from various contact geometries was conducted to mimic all possible real-world events. While intermediate glass provides an advantage against a significant population of contact types, the damage resistance advantage is no longer present under ultra-sharp contact. This understanding led to another directional change for Gorilla® Glass. With the knowledge that there is no defense against ultra-sharp contact, glasses were then designed to contain this inevitable type of damage within ultra-deep compressive layers. These glasses maintained the inherent damage resistance, resulting in glasses that could protect against all contact types.

Understanding sharp contact deformation continues to evolve. It was recently shown that the amount of densification vs. shear is inadequate to predict the crack resistance of intermediate glasses. The way in which volume is displaced via shearing is critical, with high shear band density resulting in improved crack resistance. On the anomalous end of the deformation spectrum, another unique and useful sub-category has also been recently defined. A small composition space that produces large ring cracks has been discovered and commercialized as Corning® Fusion5® windshield glass. The large ring crack provides a barrier to the extension of the radial cracks that result in windshield failure.
Lastly, indentation studies on glasses designed specifically to enable high water diffusion resulted in a surprising observation of high stored strain energy at failure. Subsequent stress analyses revealed a significant stress profile induced by hydration. Mechanical analyses showed that these glasses with hydration-induced stress profiles offer strength and damage resistance comparable to ion-exchanged glass. This alternative to ion-exchange provides a highly sustainable strengthening solution with lower carbon footprint, less waste byproduct, and ease of recycling.