Investigators: F. S. Biancaniello, R. J. Schaefer, S. D. Ridder, R. D. Jiggetts, U. R. Kattner M. E. Williams, F. W. Gayle and J. S. Adams

Technical Description:

Advanced powder metallurgy processing methods are being evaluated to determine the effect of process measurements and control on high performance materials. The current studies in this area are an outgrowth of a highly successful NIST/Industry Consortium project where intelligent processing (measuring and modeling) techniques were applied to production of rapidly-solidified alloy powder by controlled atomization. Homogeneity advantages provided by rapid solidification are being used to produce improved standard reference materials. Effects of rapid solidification on powder size, grain size, and properties of nitrogenated stainless steel are being evaluated and kinetic and thermodynamic models are being investigated to explain, predict, and optimize these rapid solidification effects. The measurements and process models being developed will provide guidelines for designers of industrial processes. Property measurements include hardness, ultimate tensile strength, yield strength, elongation, pitting potential, resistance to crevice corrosion, and stress corrosion cracking.

Technical Objectives:

• Provide industry with measurements, predictive models and methodologies needed to apply the processes investigated in this project to advanced alloys.

• Develop techniques to prepare improved standard reference materials.

• Apply phase diagram information and kinetic models to develop methods for predicting solubility and phase stability in alloys. Develop guidelines for eliminating the tendency to form undesirable intermetallic phases.

• Investigate possible synergism between ultra fine grain size and solute strengthening effects in providing improved mechanical and corrosion properties. Develop an improved method of measuring these grain sizes.

• Apply powder metallurgy models to aid in studies of powder consolidation by hot isostatic pressing (HIP) at temperatures greatly reduced from those normally used.

Anticipated Outcome:

• Availability of more homogeneous standard reference materials.

• Development of improved measurements and process models for producing alloys with greatly improved properties.

• Identification and modeling of new and improved processing methods so that industry can more efficiently produce advanced alloys.

• Development of guidelines for achieving powder consolidation by hot isostatic pressing at much lower temperatures than those normally used, thus improving alloy properties and reducing costs.

Accomplishments for FY95:

• Developed methods for producing iron-and nickel-based standard reference materials with greatly improved homogeneity.

• Applied process models, kinetic measurements, and phase diagram data to establish methods for predicting nitrogen solubility and phase stability in atomized and consolidated stainless steel alloys. Validated predictive models by producing stainless steel alloys with enhanced phase stability at high nitrogen contents.

• Combined nanostructure research with atomization to produce nitrogenated stainless steel test samples with grain sizes as small as 72 nm, as determined by x-ray diffraction, and very high tensile strength, estimated at 2137 Mpa (310 ksi) from Vickers hardness measurements. Developed method for correcting systematic errors in x-ray diffraction measurements of grain sizes in these materials.

• As an outgrowth of a project on powder consolidation done in cooperation with the auto industry, showed that use of nanostructure steels allowed HIP consolidation at 700 ^oC, a 400 ^oC-500 ^oC reduction from current industrial powder metallurgy practice.

Impacts and Technical Highlights:

• Melt practice developed at NIST for atomization applications is currently being incorporated by industrial producers into their metals processing.

• Nitrogenated stainless steel test specimens produced at NIST by atomization and HIP consolidation showed excellent properties for use as extremity and body armor in a test report by Sandia National Laboratories. Similar material is currently being evaluated by the U.S. Army for tank and armored personnel carrier armor.

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Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister