Hardness Standardization and Measurements

Summary

• As the U.S. National Metrology Institute (NMI), our objective is to standardize and improve hardness and coating thickness measurement both in the U.S. and internationally.

Description

DESCRIPTION
Purpose:
Provide measurement traceability for the Knoop, Rockwell, and Vickers hardness scales and for coating thickness measurements that are based on magnetic methods. 

Goals:
Harmonization of hardness and coating thickness testing protocols, in pursuit of reduction of measurement uncertainty through extensive participation and leadership of international comparisons and related efforts
Expanding NIST’s realization of hardness scales and increasing the associated international collaborations and key comparisons
Providing analysis and consultation to customers / stakeholders
Support the development of the documentary standards covering the associated test methods 

Challenges:
Transferring the Rockwell C and N scale realization to the new Primary Hardness Standardization Machine
Approach:

• Used standards certified by another NMI to perform acceptance measurements for accepting the machine (focused on the scales that we offer SRMs).
• Used NIST SRM blocks for a comprehensive comparison between the new and the legacy machine.

Outcome:    

• Commissioned the new machine Fall 2019. 

Future:        

• As part of certification of new SRMs, NIST SRMs are being remeasured, along with measuring the controls and new candidate SRMs.
• Plan to expand hardness scales for which we offer traceability, through a Measurement Assurance Program.

Support Standard Development Organizations (SDOs). Influence of test cycle parameters must be determined before a hardness definition can be developed. Currently, only the Rockwell C and N scales have been standardized and formal key comparisons performed between NMIs.

Approach:    

• In collaboration with guest researchers from other NMIs, determine the influence of the test cycle parameters. 

Outcome:    

• Sensitivity coefficients have been calculated and submitted for international recognition. 
• Development of new CCM-WGH Rockwell hardness scale definitions. 

Future:    

• Expand on this work for additional hardness scales.

Specific requirements in ISO hardness standards may differ from the corresponding ASTM requirements. This can lead to conflict during international transactions
Approach:    

• Serve as convener or US technical expert within an ISO Working Groups. 

Outcome:    

• U.S. served as Convener of the Working Groups for the last revisions of the ISO Knoop, Rockwell, and Vickers standards.

Future:        

• The ISO Rockwell hardness standard documents will undergo additional revisions over the next 3 years.

Graceful termination of the Coating Thickness verification service (~2 years)
Approach:    

• Partner with Office of Reference Materials on the dissemination of the project’s termination notice (the production termination notice posted since 2012).
• Increase leadership role in the ASTM Committee that owns jurisdiction over the applicable test methods.

Outcome:    

• Leadership role in associated ASTM Committee guiding through transition.

Future:      

• Termination of the verification service.
• Serve as Technical Contact for the related ASTM documentary standards due for reapproval.