Session: Poster Session

Paper Number: 162930

Developing a Micro-Hardness Database for Nonstandard Thin-Walled Metallic Parts and Coatings 

Hardness is a physical characteristic that defines the ability of a material to resist local plastic deformation. Hardness measurements can aid in numerous different applications, but at Technetics Group, they are generally utilized for assessing quality control of seals and metals that have undergone specific heat treatments. Existing standards specify load force, indenter, and hold time based on surface area and condition of material under test. ASTM E384 outlines microhardness standard preparation, test procedures, and potential sources of error for specified indenter heads based on test purpose and specimen type. The parts processed at Technetics Group typically have small diameters, thin material thickness, and unique surfaces requiring loads less than 1 kilogram force (kgf). With these limitations the data collected cannot be related to most external databases or existing standards. This work therefore establishes a set of data comparable to specific samples used for making metallic seals, and for base material evaluation and quality verification.  

This testing used a Duramin-40 M3 to indent samples with a Vickers indenter under 500-gram force (gf) and a 12 second hold. The creation of a database was made by producing consistent values of hardness for very thin samples. Procedural guidelines dictated a minimum distance away from other indent interfaces (2.5 times the length of Vickers diagonal). Mounted cross-sections with minimal surface imperfections were indented multiple times. The hardness values were recorded, and the process was redone if the geometry of the resulting diamond-shaped indent was noted to be skewed in post-test review.  

The hardness database consists of two datasets, one containing manufactured parts of specified dimensions and the other with uniform material coupons. Manufactured parts included various types of metallic seals, including Helicoflex ® (spring energized metal seals), O-rings, E-rings, and C-rings. To ensure accuracy, each seal liner, jacket, and spring (as applicable) were examined. Material types were considered during data acquisition, as were the various dimensions that could have influenced the measured hardness values (e.g., spring wire diameter, material strip/bar width, material thickness, spring coil diameter, final seal outer diameter (OD), material tube OD). The coupon database accounted for materials selection, nominal thickness, and any heat treatment if applicable. A seal jacket and seal spring both made of Alloy 600 showed a difference in hardness values, with the spring measuring a higher hardness value than the jacket. This highlights a possible difference in heat treatment or manufacturing cold work influence. This data also validates product functionality with a sturdier spring being more favorable to provide a reaction force at the sealing interface, and the lower hardness value of the jacket suggesting increased ductility for better sealing capabilities. Additionally, when comparing results of a seal jacket, seal liner, and annealed coupon, all made of Stainless Steel 316L, the anneal treated coupon showed an expected decrease in hardness compared to the manufactured counterparts. 

Published data is typically documented using macro-hardness standards, such as Rockwell indenters, to validate the bulk properties of materials. However, micro-hardness values can vary due to procedural differences and measurement techniques. The International Nickel Company’s published hardness value for Inconel ® 718 is HRC 45. When converted to Vickers hardness, this is approximately 446 HV, which is 17% higher than the hardness value measured and recorded in the micro-hardness database. Therefore, published macro-hardness values may not be directly applicable to the manufactured parts and test purposes at Technetics Group. Currently, the database is limited to common materials under ambient conditions. Future work will adapt this database to include further sample variations and investigate similar parameters at elevated temperatures. 

Presenting Author: Becca Jones Technetics Group

Presenting Author Biography: Becca Jones is currently a Research Lab Engineer Intern at Technetics Group. She is currently pursuing a Bachelor of Science in Mechanical Engineering at University of South Carolina. In her free time, she enjoys ceramics and playing card games.

Authors:

Becca Jones Technetics Group
Erin Volpe Technetics Group
Jonathan Kweder Technetics Group