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INTELLIGENT PROCESSING OF MATERIALS
Research activities in the Intelligent Processing of Materials (IPM) Program investigate the
conversion of materials into value added products using model-based control of processing
variables. The central elements of IPM are (1) process understanding expressed in terms of an
advanced process model, (2) sensors capable of monitoring the condition of the processed
material, not just its environment, (3) accurate thermophysical properties as needed for input
to the process model, and (4) a model-based sensing and control strategy to achieve the desired
characteristics in the finished product.
Many advanced materials have microstructures, and hence properties, which are highly
sensitive to the conditions under which they are produced. While it is possible to construct
process models on the basis of empirical correlations between processing conditions and
microstructures, such models will be unable to account for conditions or material compositions
which lie outside the range of the empirical data. If, instead, the models are based on a detailed
analysis of the development of material microstructure during processing, the models can be
applied to a very wide range of compositions and processing conditions.
In the Metallurgy Division, a large IPM effort has been devoted to work with the aircraft
engine industry under the NIST-led Consortium on Casting of Aerospace Alloys. Members of
this Consortium include the leading aircraft engine manufacturers (GE Aircraft Engines and
United Technologies - Pratt & Whitney), their suppliers of high-quality castings (Howmet
Corp. and PCC Airfoils) and the producer (UES, Inc.) of ProCASTTM software for the modeling of casting, as well as several
universities. This Consortium's activity is closely coordinated with that of the DARPA-
sponsored Investment Casting Cooperative Arrangemant (ICCA), which has also promoted the
use of modeling to improve casting quality. The Casting Consortium activity includes four
porjects in the Metallurgy Division, described below, as well as a project on X-ray Diffraction
Sensing of Solid-Liquid Interfaces in the Materials Reliability Division and a project on Low-
sulfur Standards for Superalloys in the Analytical Chemistry Division of the Chemical Science
and Technology Laboratory. Each of these projects is closely coordinated with the activities of
one or more of the industrial members of the Consortium. The central goal of the Consortium's
activities is to greatly increase the capacity of modeling software to predict critical
microstructural features of aerospace castings, and to make this enhanced capacity available to
the industrial users by incorporating it into the ProCASTTM software.
The fifth Metallurgy Divison IPM project develops magnetic sensor technology which can be
used on-line for measurement of mechanical properties of sheet steel. By detecting variations
in the mechanical properties of the steel without the need for actual mechanical tests, such
sensors can provide warning of possible formability problems.
Project Title: SOLIDIFICATION PATH MODELING FOR CASTING OF MULTICOMPONENT AEROSPACE ALLOYS
Investigators: W. J. Boettinger, U. R. Kattner, S. R. Coriell and A.
Davydov
Objectives:
The objective of this project is to provide simulations and predictive models that aerospace
companies can apply to optimize the quality of superalloy investment castings and reduce reject
rates.
Technical Description:
This project provides a method to predict the fraction solid (and heat content) vs.
temperature relationship for multicomponent superalloys. This information is necessary for
accurate macroscopic heat flow modeling of castings used to determine soundness. The
information and solidification models produced in this project also predict the identity and
volume fraction of all phases present in the casting microstructure. For ease of application, the
solidification models are provided in a form compatible with software used by the aerospace
industry. A combination of multicomponent phase diagram calculations with a kinetic analysis
of solidification microsegregation is being applied to superalloys to predict the phases that will
form, and these predictive models are being implemented into a commercial software code for
castings as part of the NIST Consortium on Casting of Aerospace Alloys.
Planned Outcome:
This project will result in the availability of a thermodynamic data base for Ni-base superalloys, which can be used for the calculation of phase equilibrium information required for the solidification models. These will be coupled with solidification kinetic models for multicomponent superalloys to treat the dendritic aspects of solidification. To make these models available to industrial users, they will be integrated into commercial casting software.
The data bases and models produced by this project are planned to provide a comprehensive
system that industry can use for design of aerospace castings. Availability of alloy phase
diagram and solidification path information, especially in commercial software used by the
aerospace industry, aids in casting design and promotes manufacturing efficiency. Improved
quality of simulation of investment castings by industry will provide more reliable prediction of
casting defects and reduce casting reject rates, thus reducing manufacturing costs.
External Collaborations:
The phase diagram data are being developed in collaboration with the University of
Wisconsin-Madison and the University of Florida. Integration of the models into commercial
software is being carried out in collaboration with UES, Inc. Howmet Corp. has interacted
strongly on the choice of important alloy systems and evaluation of the output from the models.
Data generated by this project has served as input to models of macrosegregation and fluid flow
processes being developed at the Universities of Arizona and Iowa.
Accomplishments:
As part of the Consortium on Casting of Aerospace Alloys, NIST developed phase diagram
subroutines that are being used within commercial casting simulation software. These sub-
routines have been modified to predict the enthalpy vs. temperature relation during
solidification and to utilize existing commercial thermodynamic databases for Al, Fe, Ti and Ni-
base alloys. An additional thermodynamic database for Ni-base superalloys that contain
elements such as Ta and Re is also being constructed. Such a data base is required to treat
single-crystal alloys now favored by industry for blades and vanes in aero- and land-based
turbines. This work combines NIST, University of Florida, and University of Wisconsin-Madison
research. Current progress includes a treatment of the elements Ni-Al-Cr-Ta-Re. Next year
the elements Ti, Co, W, Mo, Nb, and Hf will be added to the data base. Use of these data bases is
reducing the quantity of alloy specific data that a simulation software user must either find or
guess in order to model a casting.
Outputs:
Publications:
M.C. Schneider, J.P. Gu, C. Beckermann, W. J. Boettinger and U.R. Kattner,"Modeling of
Micro-Macrosegregation and Freckle Formation in Single-Crystal Nickel-Base Superalloy
Directional Solidification," Met. Mat. Trans. A, 28A 1517-1531.
D. K. Banerjee, M. T. Samonds, U. R. Kattner and W. J. Boettinger,"Coupling of Phase
Diagram Calculations for Multicomponent Alloys with Solidification Micromodels in Casting
Simulation Software," Solidification Processing, 1997, edited by J. Beach and H.
Jones, Department of Engineering Materials, University of Sheffield, UK 1997, p.354.
F. Zhang, S.L. Chen, Y.A. Chang and U.R. Kattner,"A Thermodynamic Description of the Ti-Al
System," Intermetallics, submitted Nov. 1996.
I. Ansara, T.G. Chart, A. Fernandez Guillermet, F.H. Hayes, U.R. Kattner, D.G. Pettifor,
N.Saunders, and K. Zeng,"Thermodynamic Modelling of Selected Topologically Closed-Packed
Intermetallic Compounds," CALPHAD, submitted June 1997.
Poster:
U.R. Kattner, "Phase Diagram Activities in the Metallurgy Division of NIST", CALPHAD
XXVI, Palm Coast, FL, May 1997.
Presentations:
W. J. Boettinger, "Overview of Modeling the Solidification of Cast Alloys," at the Institute
for Theoretical Physics Workshop, Quantitative Methods in Materials Research,
University of California at Santa Barbara, Jan.27, 1997.
W. J. Boettinger, "Multicomponent Alloy Solidification," Annual Meeting, Consortium on
Casting of Aerospace Alloys, NIST, April 21, 1997.
W. J. Boettinger, "Modeling of Superalloy Investment Castings: NIST - Industry
Consortium", April American Physical Society Meeting, Washington, DC, April 21, 1997.
W. J. Boettinger, "Coupling of Phase Diagram Calculations for Multicomponent Alloys with
Solidification Micromodels in Casting Simulation Software", CALPHAD '97, Palm Coast, FL,
May 14, 1997.
Project Title: GENERATION OF GRAIN DEFECTS NEAR CORNERS AND EDGES IN
CASTINGS
Investigators: R. J. Schaefer, R. E. Napolitano, W. J. Boettinger, D. R.
Black (Ceramics Division) and M. D. Vaudin (Ceramics Division)
Objectives:
This project seeks to provide the aerospace casting industry with understanding and
quantitative models which can be used to minimize the occurrence of grain defects in single
crystal superalloy castings. By identifying the thermal conditions which cause these defects to
form, the project will make it possible to identify likely sites of defect formation in computer
simulations of the casting, and modify the design without requiring a long series of test
castings.
Technical Description:
Single crystal superalloy castings enable aircraft turbine engines and, more recently, industrial gas turbines (IGTs), to operate at higher temperatures and thus at higher efficiency. Defects such as stray grains or regions of crystallographic misalignment degrade the high- temperature performance of superalloys and thus cause a high reject rate in these castings, which because of their critical applications are subject to extremely detailed inspection. Models which are capable of predicting when and where these defects form will enable the industry to decrease the lead time on newly designed parts, reduce the costs associated with high reject rates, and produce a viable yield of much larger single crystal components for IGT applications. This project analyzes the defect structure in single crystal superalloys and develops models to describe their formation.
Several different mechanisms, such as nucleation of new crystals, fragmentation of dendrites, and convective flow effects, can lead to the formation of grain defects. An importamt part of this project is analysis of the detailed geometry and crystallography of the defects, using techniques such as synchrotron X-ray topography and analysis of electron back- scattering patterns (EBSP). This information helps to identify the mechanism responsible for formation of the individual defects, and thus the thermal conditions which lead to defect formation.
Single crystal growth of superalloys occurs by propagation and branching of dendritic
crystals along specific crystallographic axes. In order to determine the thermal conditions
which prevail at the time a crystal reaches a specific point in the casting, it is not sufficient to
simply follow the spreading of the liquidus isotherm. One must determine the actual path by
which the branching dendrite reached that point. When combined with a model for the growth
kinetics of the dendrite tips and an analysis of the thermal field in the casting, the growth path
information can be used to predict the undercooling ahead of the dendrite tips. The undercooling
can then be used to estimate the probability of stray grain nucleation.
Planned Outcome:
This project will result in guidelines and models which can be used by the casting industry
to predict when certain types of grain defects will form. The work will provide a method for
predicting the thermal conditions at the solidification front which result from transient growth
behavior as the dendrites propagate around corners and edges of the casting. The ability to
predict defect formation by processes such as nucleation will depend in part on the outcome of
other studies which are attempting to quantify the nucleation behavior of superalloys. The
models developed in this project will provide predictive capability beyond that which is possible
with models which are based solely on the local conditions within the casting.
External Collaborations:
This project is carried out as part of the NIST Consortium on Casting of Aerospace Alloys
and involves collaboration with most of the members of this group. NIST provided guidance to
Howmet Corp. on the design of test castings to evaluate defect formation processes, and
Howmet made the castings and supplied them to NIST and other consortium members for
evaluation. PCC Airfoils and Pratt & Whitney have provided guidance on the conditions
which lead to defect formation. NIST has collaborated with UES, Inc. on strategies for linking
growth path models to their commercial ProCASTTM
software for modeling metal casting. Howmet and the University of Wisconsin have provided
preliminary nucleation data for use with the model.
Accomplishments:
A laboratory analysis of several superalloy single-crystal test castings was conducted. The castings were produced by Howmet Corp. to study the effects of mold geometry on the development of grain defects, such as spurious grains, low angle boundaries, and freckle grains. Optical metallography and x-ray topography revealed several defect forming tendencies associated with geometric features of the castings. Spurious grains were identified in some areas where the undercooling may have become relatively high before the arrival of the solidification front. Low-angle boundaries were observed in virtually all regions of the castings and may be attributed to a number of sources. A mold wall anomaly in the expansion zone is one such example. In the bulk, most of these boundaries resulted from extended growth of a freckle grain. The complex geometry of the platform region also caused the formation of low-angle boundaries as the nonplanar growth front advanced through a tortuous growth path. These analyses provided guidance for the development of models for defect prediction.
The Growth-Path method was developed to predict when conditions in the casting will be favorable for spurious grain nucleation. This method incorporates thermal simulation results and the anisotropic growth kinetics of a dendritic front to compute the time-minimized path to any given location in a 3-dimensional casting. Experimental nucleation data or an analytical nucleation rate expression can then be used to quantify the nucleation tendency along the path. The unique feature of the method is that the complete time-temperature history is accounted for. Additionally, the computation is time-efficient, since it need only be performed for a limited number of paths, eliminating the need for slower front-tracking methods.
A lattice model for single crystal dendritic growth was also developed, to predict the
detailed features of a dendritic array as it progresses through a mold. The solid is modeled as
an interconnected array of "needles" where the tips are tracked on a square lattice. The
needles grow according to the local temperature and a specified relationship governing dendrite
tip kinetics. New tips are generated according to a branch criterion, and each branching event
results in four new tips which behave independently, according to their local conditions. The
model provides a 3-dimensional map of local primary direction, the instantaneous shape of the
growth front during solidification, a connectivity parameter for the dendritic network, a 3-D
map of undercooling at the time of solidification, and a 3-D map of nucleation tendency,
calculated in a fashion similar to that described for the Growth-Path method. Many features
observed in the test casting have been reproduced using this model.
Outputs:
Publications:
Schaefer, R. J., Black, D. R., Vaudin, M. D., Mueller, B. A., and Giamei, A. F., "Geometry
and Mechanisms of Dendrite Misalignments in Superalloy Single Crystals," pp. 37-40 in
Solidification Processing 1997, ed. J. Beech and H. Jones, University of Sheffield
(1997).
Presentations:
Schaefer, R. J., " Defect Formation Models," NIST Consortium on Casting of Aerospace
Alloys Semi-Annual Meeting, Howmet Corp., Whitehall, MI, November, 1997.
Napolitano, R. E. and Schaefer, R. J., "Defect Formation near Corners and Edges,"
ICCA/NIST Annual Program Review, NIST, April 1997.
Project Title: POROSITY IN CASTINGS
Investigators: R. J. Schaefer, W. J. Boettinger, and R. D. Jiggetts
Objectives:
This project seeks to help the metal casting industry understand the origin and effects of
porosity in aluminum die castings by characterizing the distribution and geometry of the
porosity. It also seeks to develop a predictive model for microporosity formation during
directional solidification through an analysis of the alloy solidification path and the flow of
liquid metal through the mushy zone.
Technical Description:
Porosity is a common feature of metal castings, which may or may not be harmful depending on its location, size, and connectivity. In addition to mechanical weakening of a component, porosity may cause leakage in parts intended for hydraulic applications and may cause unacceptable roughness in machined surfaces. For some applications, small pores within the interior of a part may not interfere with the part's function, and there is then no need to eliminate them. Understanding the location and geometry of porosity may thus be critical.
The major sources of porosity in cast parts are the reduction in volume which occurs when a liquid metal solidifies, the presence of gas dissolved in the molten metal, and air trapped within the metal during filling of the mold. The importance of these sources varies greatly depending on the casting method, the part geometry, and the alloy composition. In many cases it is difficult to determine which of these sources is responsible for the porosity in a given set of castings. It is also difficult to understand the true geometry of porosity because a large interconnected network of interdendritic porosity will generally appear in a polished cross section as an array of small round pores. Better understanding of the nature and geometry of porosity and better models to predict porosity formation would both help the metal casting industry control the distribution and amount of porosity and thus reduce the number of rejected parts.
This project has used experimental and theoretical tools to study porosity: the former consists of the use of hot isostatic pressing (HIP) to analyze the connectivity of pores within castings, and the latter is the use of modeling to predict microporosity by an analysis of fluid flow through the alloy mushy zone to feed solidification shrinkage.
The porosity in castings can often be closed by the HIP process in which the casting is subjected to a high pressure gas at elevated temperature. However, this is effective only if the pores themselves are not pressurized via a connection to the surface of the casting. Examination of porosity in a HIPed casting can thus give an indication of how much of the porosity is not closed and therefore is presumably connected to the surface. This method is not effective, however, if the pores themselves contain gas which prevents their closure even if not connected to the surface. In this case, a heat treatment at the same temperature used in the HIP process but without the applied pressure can cause "blistering" of the casting, in which pores close to but not connected to the surface expand to form a visible lump on the casting surface. Thus heating of the casting with and without pressure can provide a variety of information on the connectivity and gas content of the pores.
Modeling of microporosity requires and accurate description of the pressure at each point
in the liquid in the mushy zone of a casting. The pressure varies due to the fluid flow required
to feed the solidification shrinkage. A fluid flow calculation is therefore necessary. Such a
calculation requires a knowledge of the density of the liquid and solid as a function of
temperature and liquid or solid composition, a description of the solidification path
(temperature and composition of liquid and solid as a function of fraction solid) and a
description of the permeability of the mushy zone. Since this model is being developed primarily
for application to superalloys, the effects of dissolved gases are neglected. Porosity occurs
when the pressure drops below a critical negative value.
Planned Outcome:
This project provides an evaluation of HIP as a diagnostic tool in the analysis of porosity in castings, particularly as a tool for determining the connectivity of porosity to the surface, which is a critical question for castings intended for hydraulic applications. Successful application of such a tool could provide guidance to die casters in how to minimize the deleterious effects of porosity.
The project will provide a predictive tool for microporosity formation which will, for the
first time, account for the detailed effects of alloy solidification behavior and not require the
use of empirical parameters.
External Collaborations:
The experimental part of this project was carried out in collaboration with The Top Die Casting Company, recipients of an ATP award (joint venture with Allied Signal and Stahl Specialty Company) for reduction of defects in aluminum castings. Top Die provided the castings used in this study and radiographs showing where some of the major porosity was located.
The modeling of porosity is carried out in collaboration with the members of the Consortium
on Casting of Aerospace Alloys.
Accomplishments:
Metallographic analysis of die castings heated at a range of temperatures and pressures showed that most of the porosity in these castings contains gas. This, and the size and location of the pores, confirmed the conclusion of Top Die that the major source of porosity in these castings was gas trapped during filling of the die. When Top Die used an evacuated die, this source of porosity was greatly reduced, but the remaining pores still contained significant gas pressure. Nonetheless, it was still possible to conclude from the HIP experiments that clusters of micropores in the castings had typical dimensions of 250 to 500 m.
A model for microporosity formation was developed, based on flow of liquid through the
mushy zone to feed solidification shrinkage. The model calculates the mass fraction of liquid
and solid, the composition of the liquid and the average composition of the solid as functions of
the temperature. It then calculates the fluid flow and pressure drop in the mushy zone and the
fraction of porosity based on the assumption that pores form when the pressure drops to zero.
Calculations of fraction porosity as a function of temperature were carried out for a typical
superalloy composition. Using the Scheil model of solidification (complete mixing in the liquid,
no diffusion in the solid), the model predicts porosity to form more than 50C above the
temperature at which the last liquid remains. In contrast, the simpler but unrealistic lever law
of solidification predicts no porosity.
Impact:
The experiments at NIST supported Top Die Company's interpretation of the origin of porosity in their castings, on the basis of which they modified their casting practice in such a way that they greatly reduced the number of rejects.
The model for microporosity formation provides a means of predicting porosity distribution
without the need for empirical criteria containing numerical parameters which must be
evaluated for each alloy. It has predictive capability to account for the variable tendency for
porosity formation between different alloy compositions. UES, Inc. is now working to use this
model in conjunction with their commercial ProCASTTM
software for modeling investment castings.
Outputs:
Presentations:
Boettinger, W. J., "Microporosity Modeling," Annual Meeting, Consortium on Casting of
Aerospace Alloys, NIST, April, 1997.
Project Title: THERMOPYSICAL DATA FOR CASTINGS
Investigators: A. Cezairliyan, J. McClure, and D. Basak
Objectives:
The objective of this project is to obtain accurate thermophysical properties data on
selected multicomponent nickel and titanium based alloys of technological interest, primarily
those used in the aerospace industry, in support of modeling of casting processes.
Technical Description:
This project is focused on the accurate determination of selected thermophysical properties
of high temperature alloys of technological interest, particularly nickel and titanium based
superalloys, important to the NIST Consortium on Casting of Aerospace Alloys. Millisecond- and
microsecond-resolution pulse-heating techniques are used to make measurements in both solid
and liquid phases up to about 300 K above their melting region. Work focuses primarily on
measurements of selected key properties, such as enthalpy, specific heat capacity, heat of
fusion, electrical resistivity, hemispherical total emissivity, and normal spectral emissivity.
Planned Outcome:
A database will be generated for selected thermophysical properties of nickel and titanium based alloys in both solid and liquid phases near the melting region.
Demonstration, for the first time utilizing optical techniques (radiometric and
polarimetric), of the heating rate dependence of the melting behavior of an alloy will expand our
understanding of the fundamental processes involved in melting of alloys.
External Collaborations:
A titanium alloy, Ti-6242, of interest to the aerospace industry was provided by Howmet,
a leading company in casting of aerospace alloys. Discussions were held with the manufacturers
of aircraft engines, such as General Electric and Pratt and Whitney, in relation to the
properties of alloys used in aircraft engines. Measurement problems were discussed with the
members of the Space Power Institute at Auburn University in relation to thermophysical
properties of aircraft engine materials.
Accomplishments:
Definitive measurements of the properties (enthalpy, specific heat capacity, electrical resistivity, hemispherical total emissivity, and normal spectral emissivity) of a titanium alloy, Ti-6242, were made in the solid phase near the melting region. Accurate data on this alloy will be used by producers of aerospace alloy castings in modeling of casting processes.
For the first time, optics-based (radiometric and polarimetric) experiments were
conducted to study the effect of heating rate on the melting behavior of the binary alloy 53Nb-
47Ti (mass %). The heating rate ranged from 100 to 12,000 K/s. The results show that the
onset of melting of the alloy, in contrast to pure metals, depends significantly on heating rate.
Measurements designed to determine the source of the heating rate effect will continue to
include both lower and higher heating rates than those used so far in order to clarify the source
of the heating rate effect.
Impacts:
Thermophysical properties of alloys such as IN718, measured earlier in this project, are
now available to the industrial members of the Casting Consortium and have been used by them
in their simulations.
Outputs:
Publication:
Cezairliyan, A., Boettinger, W. J., Basak, D., Josell, D., and McClure, J. L., "Effect of
Heating Rate on the Melting Behavior of the Alloy 53Nb-47Ti (Mass %) in Rapid Pulse-Heating
Experiments," Int. J. Thermophys., in press.
Presentation:
Cezairliyan, A., "Thermophysical Properties of Aerospace Alloys," Annual Meeting of the
Consortium on Casting of Aerospace Alloys, Gaithersburg, Maryland, April, 1997.
Project Title: MAGNETICS FOR STEEL PROCESSING
Investigators: F. Biancaniello, G. E. Hicho, L. J. Swartzendruber, and F.
Bendec (Guest Researcher, Nuclear Research Centre, Negev, Israel)
Objectives:
The project seeks to provide U.S. industry with a scientific basis for the development of
magnetic sensors to monitor the uniformity of mechanical properties of sheet steels as they
are processed and to serve as a quality control device for the user.
Technical Description:
In the steel industry, or for that matter any industry that requires the mechanical testing
of the finished product, tensile tests are required to verify mechanical properties such as the
yield and ultimate tensile strengths. The costs for testing to industry are quite high and a rapid
and nondestructive procedure for determining these mechanical properties would result in
substantial savings. Recent work completed for the AISI has shown that magnetic sensors have
considerable potential for providing rapid and nondestructive measurement of the yield strength
of sheet steels. In this work, measurement methods for rapidly obtaining a large number of
magnetic properties were developed. Using these findings, the relationship between yield
strength and magnetic properties for a plastically deformed low carbon steel was examined.
Results indicate that the magnetic and mechanical properties of steels are closely related
because the same defects which pin magnetic domain walls also pin, for example, glide planes.
The yield strength of a low carbon steel was modified by plastic deformation and then a number
of magnetic properties, including the Barkhausen signal emission, coercive force, and relative
permeabilities were obtained. Both the yield strength and coercive field were found to be
linearly related to the square root of the plastic strain. The widths of the Barkhausen signal
emission curve and the permeability curve increased significantly as the strain, i.e., rolling
deformation, was increased, showing that the dislocation density is non-uniform on a micro
scale. Observations of the domain pattern using a high resolution colloidal contrast technique
revealed a fine intra-grain magnetic domain structure with the walls more effectively pinned in
the highly strained samples. In order to better characterize the contributions of dislocations to
both the magnetic and mechanical properties, studies are currently underway using Ferrovac E
iron.
Planned Outcome:
Upon completion of the project, a relationship similar to that of the Hall/Petch relationship
will have been developed using the magnetic measurements. In place of the grain size in the
Hall/Petch, a combination of magnetic properties obtained from a surface coil detector will be
used to obtain the yield strength without performing a mechanical property test. Of
considerable importance is the fact that such a test could be rapidly applied to large sheets of
steel to determine the uniformity of properties. Similar relationships could be developed to
obtain the ultimate tensile strength, hardness, or grain size. Being able to determine the
mechanical properties from the magnetic response will be advantageous to the steel producers
and users because costs for tensile testing will be significantly reduced and the amount of scrap
steel considerably reduced, producing savings in both costs and energy usage.
External Collaborations:
Professor Harsh D. Chopra of Dartmouth College is a co-investigator on this project. He
has performed the domain size/dislocation determination on the strained low carbon steel.
NIST has provided strained samples and Professor Chopra has used a high resolution
interference colloidal contrast technique to reveal the fine intra-grain magnetic domain
structure.
Accomplishments:
The effect of plastic strains on the magnetic and mechanical properties were determined
for a commercial ultra low carbon sheet steel. It was shown that, for plastic strains up to
10%, a linear relationship can be established between magnetic and mechanical properties.
Impact:
Our results on the effect of strain on magnetic properties of steel are being used by
Materials Innovation (a U.S. company) to help develop new materials for use in electric motors.
Outputs:
Publications:
Swartzendruber, L. J., Hicho, G. E., Chopra, H. D., Leigh, S. D., Adam, G., and Tsory, E.,
"Effect of Plastic Strain on Magnetic and Mechanical Properties of Ultralow Carbon Sheet
Steel," J. Appl. Phys. 81, 4263 (1997).
Presentations:
Swartzendruber, L. J., Hicho, G. E., and Chopra, H. D., "Relationship Between Yield Stress
and Magnetic Properties in Plastically Deformed Low Carbon Sheet Steel," Bulletin of the
American Physical Society, vol. 42, p. 563, March 1997.
Patents Granted:
Steel Hardness Measurement System and Method of Using Same
Gabe Kohn, George Hicho, and Lydon Swartzendruber
U.S. Patent No. 5,619,135 issued 4/8/97
U.S. Department of Commerce
Technology Administration
National Institute of Standards and Technology
Materials Science & Engineering Laboratory
Metallurgy Division
For further help finding information about specific NIST programs and publications,
please contact the Public Inquiries Unit, (301) 975-3058
Revised March 09, 1998