Distinguished Alumni Colloquium: Dr. Adam Pilchak, Characterizing and modeling abnormal grain growth in beta-annealed titanium alloys

Abstract

Owing to an exceptional balance of strength, fatigue performance, corrosion resistance, and density, alpha+beta titanium alloys are often used in flight-critical airframe components. These alloys are typically used in the beta-annealed condition with 1~2 mm prior beta grains filled with colonies approximately half that size which offers increased toughness and reduce fatigue crack growth rates over alpha+beta forged products. Despite years of experience and a seemingly simple heat treatment, there have been sporadic observations of abnormally large grains (~10 mm) in structural titanium forgings produced by a range of suppliers who sourced billet from a range of producers. Investigation of typical process controls and material variables (e.g. preform geometries, furnace temps, time in furnace, composition, forging reduction, etc.) yield no explanation for the anomaly. In fact, there are cases when one of two identical forgings with mults cut from the same billet and produced back-to-back on the same shift exhibit abnormal gran growth (AGG)!

This talk will describe efforts to understand the fundamental mechanisms leading to AGG in beta-annealed titanium alloys by exploring the early stages of beta recrystallization in Ti-6Al-4V sheet. Alpha-phase crystal orientation maps (COMs) were measured on a series of samples subjected to short soak times above the beta transus (10 to 750 sec.) and cooled to room temperature. The date were reconstructed to obtain the beta-phase COMs. The results showed that the initially weak (001)[110] (“rotated cube”) texture was strengthened during heating into the beta phase field that resulted in a dominant texture component comprised of low angle subgrain boundaries and a very small population of {221}<114>-oriented grains (twin related to the rotated cube). A small population of subgrains were highly misoriented relative to the average orientation and hence had higher energy and increased mobility compared to the low angle boundaries in the majority of the microstructure. These subgrains were the nuclei for metadynamic recrystallization of the beta phase when they became mobile after dissolution of the primary alpha phase. This texture is well known to form during plane strain compression deformation, which is a typical deformation path for structural Ti alloy components. Hence, additional investigations were performed on side-pressed Ti-6Al-4V bars to investigate the relationship between initial microstructure, total strain, average strain-rate, peak temperature achieved during forging, and heating rate into the beta phase field during beta-annealing on the propensity to form abnormally large grains. Continuum finite element and crystal plasticity models were used to assess local thermomechanical histories in AGG-prone and AGG-devoid locations while Monte Carlo calculations were used to explore the effect of texture on AGG. The talk will conclude with a discussion of implications on the production of components. 

Bio

Dr. Adam Pilchak is a senior research materials engineer in the Metals Branch in the Air Force Research Laboratory’s Materials and Manufacturing Directorate where he performs basic and applied research both inhouse and in collobration with external partners in the aerospace supply chain. He has broad research interests that include quantitative characterization of microstructure and its application to understanding and modeling processing-structure-property relationships in existing and emerging aerospace alloy systems. Dr. Pilchak is internationally recognized for his work on the dwell fatigue response of titanium alloys that includes processing, development of destructive and nondestructive characterization methods, failure analysis, microstructure-informed risk analysis, and probabilistic fatigue lifetime prediction. In addition to his research, Dr. Pilchak also highly values transition of research to industry and serves as Technical Monitor for Metals Affordability Initative Programs valued at $20M and as Program Manager for the AF “Spin for Life” Program valued at $8M assessing state of the art microstructure-based models for dwell fatigue at TRL6 via component spin pit testing.

EDUCATION

2005 B.S. Materials Science and Engineering, Michigan State University, East Lansing, Michigan

2008 M.S. Materials Science and Engineering, The Ohio State University, Columbus, Ohio

2008 Ph.D. Materials Science and Engineering, The Ohio State University, Columbus, Ohio

CAREER CHRONOLOGY

1. 2005 – 2006, Undergraduate Research Engineer, Dept. Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan
2. 2006 – 2009, Graduate Research Associate, Dept. of Materials Science and Engineering, The Ohio State University, Columbus, Ohio
3. 2009 –  2010, Research Scientist, Universal Technology Corporation, worked onsite in the Metals Branch, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio
4. 2011 – 2014, Materials Research Engineer, Metals Branch, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio
5. 2014 – 2015, Acting Research Lead and Materials Research Engineer, Metals Branch, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio
6. 2015 – 2017, Research Lead and Senior Materials Research Engineer, Metals Branch, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio
7. 2018 – present, Senior Materials Research Engineer, Metals Branch, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio

HONORS AND AWARDS

• Presidential Early Career Award in Science and Engineering (PECASE), 2017.
• Director’s Award, AFRL/RX, 2017
• Jacquet Lucas Award, International Metallographic Contest, M&M 2016 (Best Poster)
• Air Force Early Career Award, AFRL/AFOSR, 2015
• Robert T. Schwartz Award (for sustained support managing risk to the fleet), AFRL/RX, 2014
• First Recipient of Robert W. Cahn Prize (Best Paper) Journal of Materials Science, 2012
• Champion H. Mathewson, TMS, 2012 (Best Paper)
• Engineering Expertise Award (for turbine engine blade sustainment), AFRL/RX, 2012
• Director’s Junior Workforce Award Finalist, AFRL/RX, 2012
• Henry Marion Howe Medal, ASM International, 2011 (Best Paper)
• Henry Marion Howe Medal, ASM International, 2009 (Best Paper)
• Six-time recipient of Editor’s Choice for Open Access, Met. Trans. A, 2008 – present
• Best Poster, Surface Modification Division, Ti-2007: 11th International Conference on Titanium, Kyoto, Japan, 2007