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Real-time monitoring of laser surface hardening of ferrous alloys.

Description: An infrared process monitor was used to monitor in real-time the infrared emissions during laser surface hardening of gray cast iron and 1045 steel. The signal from the monitor was correlated with the hardness and case depth of the laser-treated tracks. Test data show that a linear relationship exists between the monitor output DC level voltage and hardness up to the maximum hardness possible and also between the monitor output DC level voltage and case depth. This simple relationship of the monitor voltage signal with hardness and case depth makes it easy to monitor process hardness, case depth and quality. A calibration test on prototypic material can be used to determine at what voltage level melting occurs and the heat treating process hardness and case depth can be monitored easily by setting an upper and lower bound for the voltage signal. The monitor is also capable of tracking changes in surface quality or flatness of the part that is being treated.
Date: September 30, 1999
Creator: Xu, Z.; Leong, K. H. & Reed, C. B.
Partner: UNT Libraries Government Documents Department

Excimer laser processing of tool steel: Tribological effects of multiple pulse processing and titanium alloying

Description: Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1000 cycles, indicating wear=through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.
Date: December 1, 1995
Creator: Jervis, T.R.; Nastasi, M.; Griffin, A.J. Jr.; Zocco, T.G.; Taylor, T.N. & Foltyn, S.R.
Partner: UNT Libraries Government Documents Department

Surface Hardening by Nanoparticle Precipitation in Ni(Al,O)

Description: Ion implantation of O and Al were used to form nanometer-size precipitates of NiO or Al{sub 2}O{sub 3} in the near-surface of Ni. The yield strengths of the treated layers were determined by nanoindentation testing in conjunction with finite-element modeling. The strengths range up to {approximately}5 GPa, substantially above values for hard bearing steels. These results agree quantitatively with predictions of dispersion-hardening theory based on the precipitate microstructures observed by transmission electron microscopy. Such surface hardening by ion implantation may be beneficial for Ni components in micro-electromechanical systems.
Date: April 1, 2001
Creator: MYERS, SAMUEL M. Jr.; FOLLSTAEDT, DAVID M. & KNAPP, JAMES A.
Partner: UNT Libraries Government Documents Department

Pulsed laser surface hardening of ferrous alloys.

Description: A high power pulsed Nd:YAG laser and special optics were used to produce surface hardening on 1045 steel and gray cast iron by varying the process parameters. Unlike CO{sub 2} lasers, where absorptive coatings are required, the higher absorptivity of ferrous alloys at the Nd:YAG laser wavelength eliminates the necessity of applying a coating before processing. Metallurgical analysis of the treated tracks showed that very fine and hard martensitic microstructure (1045 steel) or inhomogeneous martensite (gray cast iron) were obtained without surface melting, giving maximum hardness of HRC 61 and HRC 40 for 1045 steel and gray cast iron respectively. The corresponding maximum case depths for both alloys at the above hardness are 0.6 mm. Gray cast iron was more difficult to harden without surface melting because of its lower melting temperature and a significantly longer time-at-temperature required to diffuse carbon atoms from the graphite flakes into the austenite matrix during laser heating. The thermal distortion was characterized in term of flatness changes after surface hardening.
Date: September 30, 1999
Creator: Xu, Z.; Reed, C. B.; Leong, K. H. & Hunter, B. V.
Partner: UNT Libraries Government Documents Department

Modeling of Ion Beam Surface Treatment

Description: Use of intense pulsed ion beams is providing a new capability for surface engineering based on rapid thermal processing of the top few microns of metal, ceramic, and glass surfaces. The Ion Beam Surface Treatment (IBEST) process is shown to produce enhancements in the hardness, corrosion, wear, and fatigue properties of surfaces by rapid melt and resolidification. We have created a new coe IBMOD that enables modeling of intense ion beam deposition and the resulting rapid thermal cycling of surfaces. This code has been used to model the effect of treatment of Al, Fe, and Ti using different ion species and pulse durations.
Date: June 1, 1996
Creator: Stinnett, R.W.; Maenchen, J.E.; Renk, T.J.; Struve, K.W. & Campbell, M.M.
Partner: UNT Libraries Government Documents Department

Examination of Compatibility of Potentially Cavitation-Resistant Modifications of Type 316LN Stainless Steel with Mercury in a Thermal Convection Loop

Description: A 316L stainless steel thermal convection loop (TCL) containing a variety of stainless steel coupons circulated mercury for 2000 h. The TCL conditions included a maximum temperature of 307 C, a maximum temperature gradient of 90 C, and a Hg velocity of about 1.4 m/min. In addition to mill-annealed/surface-ground 316LN coupons serving as the baseline material, other coupons included 316LN that was 50% cold-worked, 316LN that was given a proprietary surface hardening treatment termed ''kolsterizing,'' and Nitronic 60. The purpose of this test was to examine Hg compatibility with these modest variations of annealed 31 6LN stainless steel that are considered potential improvements over annealed 31 6LN for cavitation-erosion resistance in the Spallation Neutron Source (SNS) target containment system. The results indicated negligible weight change for each coupon type, no significant indication of attack or surface roughening, and generally no interaction with Hg.
Date: August 29, 2002
Creator: Pawel, SJ
Partner: UNT Libraries Government Documents Department

Thin-film characterization and flaw detection. Progress report No. 7, February 1, 1993--January 31, 1994

Description: Objective is to determine the elastic constants of thin films deposited on substrates, measure residual stresses, and detect and characterize defects in thin film substrate configurations. A line-focus acoustic microscope is being used to measure speed of surface acoustic waves (SAW) in thin film/substrate system. V(z) curves (record of transducer voltage output (V) with variation of distance z between acoustic lens and specimen) were calculated in terms of characteristic functions of acoustic lens and reflectance function of fluid-loaded specimen, and were compared with data for isotropic, anisotropic, and layered anisotropic materials. For thin film/substrate of known elasticity, theoretical surface acoustic wave velocities agree with measured V(z) curves for full range of wave propagation directions. Results have been obtained for homogeneous nitride films and transition-metal nitride superlattice films.
Date: November 24, 1993
Creator: Achenbach, J. D.
Partner: UNT Libraries Government Documents Department

Hard-facing with electro-spark deposition. Final report

Description: A common method to improve wear resistance of metals in rubbing contact is to increase their surface hardness. Electro-Spark Deposition is a process which uses capacitive discharge pulses of high current passing through a hard carbide electrode in contact with and scanning the metal surface to be hardened. The result is a thin, hard, adherent coating of carbide deposited with a minimum of heat influence on the substrate and a significant increase in wear life of the coated metal. Electro-Spark Deposition is similar to a micro-welding process. It is a simple, portable and inexpensive coating method, which has great potential for commercial utilization. This thesis is an in depth study of the parameters associated with the ESD process and the wear resistance of the coatings.
Date: January 1, 1983
Creator: Kees, K.P.
Partner: UNT Libraries Government Documents Department

Mechanical properties of excimer laser modified titanium surfaces

Description: Excimer laser processing enables both thermally-driven transformations and the incorporation of solutes into the surface of materials through melting and diffusional mixing. We have examined the effect of excimer laser processing on the microstructure and surface mechanical properties of titanium alloys. Changes in the surface hardness due to laser processing were studied using a Nanoindenter [trademark]. Alloying experiments using both mixing of evaporated surface layers of boron and laser gas alloying in air and in nitrogen all result in changes in the surface hardness of the material. Alloying with boron results in an amorphous surface which is somewhat harder than the as polished surface. Laser processing in air and pure nitrogen results in incorporation of oxygen and nitrogen and the development of fine ([approximately] 50 nm) precipitates of TiO and TiN respectively. Substantial increases in surface hardness result due to solution and precipitation mechanisms. The effects of alloying on the surface hardness of the materials will be discussed in terms of the concentration of the solute and microstructures observed.
Date: January 1, 1993
Creator: Jervis, T.R.; Zocco, T.G.; Hubbard, K.M. & Nastasi, M.
Partner: UNT Libraries Government Documents Department

Suppression of the uranium-hydrogen reaction using high-dose carbon implantation

Description: We have previously reported the delay and reduction of the hydriding of uranium by implantation of oxygen. The reduced hydriding was attributed to the presence of the uranium oxide layer created near room temperature. In this paper we present results for the layers formed by implantation of 80 keV C/sup +/ to a dose of 8E17 C/cm/sup 2/. The carbide layers formed were characterized by Auger electron spectroscopy, Rutherford backscattering, and glancing angle x-ray diffraction. Hydriding properties of both non-implanted and implanted uranium were measured for 76 Torr hydrogen at 130/sup 0/C. The implanted specimens had significantly longer incubation times for the start of the reaction after exposure to hydrogen and less area participating in the reaction.
Date: April 17, 1987
Creator: Musket, R.G.
Partner: UNT Libraries Government Documents Department

Ion beam surface treatment: A new capability for rapid melt and resolidification of surfaces

Description: The emerging capability to produce high average power (5--250 kW) pulsed ion beams at 0.2--2 MeV energies is enabling us to develop a new, commercial-scale thermal surface treatment technology called Ion Beam Surface Treatment (IBEST). This technique uses high energy, pulsed ({le}100 ns) ion beams to directly deposit energy in the top 2--20 micrometers of the surface of any material. Depth of treatment is controllable by varying the ion energy and species. Deposition of the energy with short pulses in a thin surface layer allows melting of the layer with relatively small energies and allows rapid cooling of the melted layer by thermal diffusion into the underlying substrate. Typical cooling rates of this process (10{sup 9}10{sup 10} K/sec) cause rapid resolidification, resulting in production of non-equilibrium microstructures (nano-crystalline and metastable phases) that have significantly improved corrosion, wear, and hardness properties. We have conducted IBEST feasibility experiments with results confirming surface hardening, nanocrystaline grain formation, metal surface polishing, controlled melt of ceramic surfaces, and surface cleaning.
Date: April 1, 1994
Creator: Stinnett, R. W.; McIntyre, D. C.; Buchheit, R. G.; Greenly, J. B. & Thompson, M. O.
Partner: UNT Libraries Government Documents Department

Friction Stir Processing for Efficient Manufacturing

Description: Friction at contacting surfaces in relative motion is a major source of parasitic energy loss in machine systems and manufacturing processes. Consequently, friction reduction usually translates to efficiency gain and reduction in energy consumption. Furthermore, friction at surfaces eventually leads to wear and failure of the components thereby compromising reliability and durability. In order to reduce friction and wear in tribological components, material surfaces are often hardened by a variety of methods, including conventional heat treatment, laser surface hardening, and thin-film coatings. While these surface treatments are effective when used in conjunction with lubrication to prevent failure, they are all energy intensive and could potentially add significant cost. A new concept for surface hardening of metallic materials and components is Friction Stir Processing (FSP). Compared to the current surface hardening technologies, FSP is more energy efficient has no emission or waste by products and may result in better tribological performance. FSP involves plunging a rotating tool to a predetermined depth (case layer thickness) and translating the FSP tool along the area to be processed. This action of the tool produces heating and severe plastic deformation of the processed area. For steel the temperature is high enough to cause phase transformation, ultimately forming hard martensitic phase. Indeed, FSP has been used for surface modification of several metals and alloys so as to homogenize the microstructure and refine the grain size, both of which led to improved fatigue and corrosion resistance. Based on the effect of FSP on near-surface layer material, it was expected to have beneficial effects on friction and wear performance of metallic materials. However, little or no knowledge existed on the impact of FSP concerning friction and wear performance the subject of the this project and final report. Specifically for steel, which is the most dominant tribological material, FSP ...
Date: January 31, 2012
Creator: Smith, Mr. Christopher B. & Ajayi, Dr. Oyelayo
Partner: UNT Libraries Government Documents Department

Low Temperature Surface Carburization of Stainless Steels

Description: Low-temperature colossal supersaturation (LTCSS) is a novel surface hardening method for carburization of austenitic stainless steels (SS) without the precipitation of carbides. The formation of carbides is kinetically suppressed, enabling extremely high or colossal carbon supersaturation. As a result, surface carbon concentrations in excess of 12 at. % are routinely achieved. This treatment increases the surface hardness by a factor of four to five, improving resistance to wear, corrosion, and fatigue, with significant retained ductility. LTCSS is a diffusional surface hardening process that provides a uniform and conformal hardened gradient surface with no risk of delamination or peeling. The treatment retains the austenitic phase and is completely non-magnetic. In addition, because parts are treated at low temperature, they do not distort or change dimensions. During this treatment, carbon diffusion proceeds into the metal at temperatures that constrain substitutional diffusion or mobility between the metal alloy elements. Though immobilized and unable to assemble to form carbides, chromium and similar alloying elements nonetheless draw enormous amounts of carbon into their interstitial spaces. The carbon in the interstitial spaces of the alloy crystals makes the surface harder than ever achieved before by more conventional heat treating or diffusion process. The carbon solid solution manifests a Vickers hardness often exceeding 1000 HV (equivalent to 70 HRC). This project objective was to extend the LTCSS treatment to other austenitic alloys, and to quantify improvements in fatigue, corrosion, and wear resistance. Highlights from the research include the following: • Extension of the applicability of the LTCSS process to a broad range of austenitic and duplex grades of steels • Demonstration of LTCSS ability for a variety of different component shapes and sizes • Detailed microstructural characterization of LTCSS-treated samples of 316L and other alloys • Thermodynamic modeling to explain the high degree of carbon solubility possible ...
Date: December 7, 2007
Creator: Collins, Sunniva R.; Heuer, Arthur H. & Sikka, Vinod K.
Partner: UNT Libraries Government Documents Department

Inside Sandia

Description: Articles in this issue include ``Molten salt corrosion testing,`` ``Pulsed ion beams for thermal surface treatment: Improved corrosion, wear, and hardness properties at low cost,`` ``Unmasking hidden armaments: Superconducting gravity sensor could find underground weapons, bunkers,`` ``Charbroiled burgers, heterocyclic amines, and cancer: Molecular modeling identifies dangerous mutagens,`` ``Revolutionary airbag offers increased safety options,`` ``EcoSys{sup TM}: an expert system for `Green Design` ``, ``Sandia, salt, and oil: Labs` diagnostics and analysis help maintain vital US oil reserve,`` and ``Automated fixture design speeds development for prototypes and production``.
Date: December 31, 1995
Partner: UNT Libraries Government Documents Department

Cluster carburizing. Progress report, June 1, 1977--May 31, 1978

Description: When aging quenched Ta-27% Hf alloys at 685/sup 0/C, excess thermal vacancies were found to condense into vacancy loops. The loops are responsible for the first age-hardening peak observed during heat treatment. In a study of binary alloys formed by two monocarbides, a miscibility gap was found in the NbC-HfC system with a critical temperature between 1100--1200/sup 0/C, while homogeneous solutions were formed by TaC-HfC down to 1000/sup 0/C. An investigation of solid phase carburizing of Ta-Hf and Nb-Hf alloys indicated that this technique results in a higher carbon activity, but slower kinetics than was obtained by gas carburizing. Work continues on improving this technique and on preparing cluster carburized specimens for study by transmission electron microscopy.
Date: February 1, 1978
Creator: Morral, J.E.
Partner: UNT Libraries Government Documents Department

Chemical reactions in the helium impurities loop. [HTGR]

Description: The Helium Impurities Loop (HIL) at Brookhaven National Laboratory has been run to study reactions between the three metals and the four major helium oxidation and reduction and on carburization of the metals. Preliminary work on hydrogen diffusion through the loop walls and on hydrogen retention in the walls is also presented. During the past year much experience has been accumulated on loop operation and instrument reliability. A small ''bench test'' loop has been built and operated to study reactions under more controlled conditions than possible in the HIL. These efforts are in preparation for more quantitative experiments that will be performed during the coming year.
Date: January 1, 1978
Creator: Epel, L.G. & Schweitzer, D.G.
Partner: UNT Libraries Government Documents Department

Cluster carburizing. Final report, June 1, 1973-May 31, 1979

Description: Three major accomplishments of the cluster carburizing program were showing that the hardness of aged and carburized materials could be controlled via the aged structure; developing a new and analytical theory of subscale formation; and characterizing the properties of Ta-Hf alloys with respect to precipitation kinetics and morphology, diffusion kinetics, age hardening, and subscale formation. The first of these verified the cluster carburizing concept, which has potential use in the development of high strength materials. The second has applications in the fields of hot corrosion, oxidation, and high temperature coatings. The third provided necessary background for this study and provided a further understanding of the behavior of refractory metals. Details about the above are contained in this final report as well as comments on the Ta-Hf, TaC-HfC and NbC-HfC phase diagrams, a comparison of hardening in the Nb-Hf and Ta-Hf system, and a discussion of possible future work.
Date: May 1, 1979
Creator: Morral, J.E.
Partner: UNT Libraries Government Documents Department

Changes in the mechanical properties of Hastelloy X when exposed to a typical gas-cooled reactor environment

Description: The helium used in a gas-cooled reactor will contain small amounts of H/sub 2/, CO, CH/sub 4/, H/sub 2/O, and N/sub 2/ which can lead to oxidation and carburization/decarburization of structural materials. Long-term creep tests were run on Hastelloy X to 30,000 h at 649 to 871/sup 0/C. It was found that extensive carburization occurred, the minimum creep rate and time to rupture were equal in air and impure helium environments, and the fracture strain was less in helium than in air. Thermal exposure in the temperature range of 538 to 871/sup 0/C resulted in the reduction of ductility in impact and tensile tests at ambient temperature, and this reduction was greater when the exposure was in impure helium rather than in air. A modified alloy with lower chromium and 2% titanium resisted carburization.
Date: January 1, 1981
Creator: McCoy, H.E. Jr.
Partner: UNT Libraries Government Documents Department

Metallographic evaluation of the reactions between boronated graphite and Fe-Ni-Cr alloys

Description: The compatibility of boronated graphite with alloy 800H and type 316 stainless steel was evaluated metallographically after exposures at 700 and 810/sup 0/C for up to 10,000 h. At 700/sup 0/C, the principal reaction with both alloys was limited oxidation. At 810/sup 0/C, three types of reactions were observed: localized reactions at sites where the B/sub 4/C particles were in contact with the alloys' surfaces, intergranular penetration (much more prevalent for alloy 800H), and carburization.
Date: January 1, 1984
Creator: Tortorelli, P.F.; Mayotte, J.R.; Henson, T.J. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Relationship between carburization and zero-applied-stress creep dilation in Alloy 800H and Hastelloy X. [HTGR]

Description: Typical HTGR candidate alloys can carburize when exposed to simulated service environments. The carbon concentration gradients so formed give rise to internal stresses which could cause dilation. Studies performed with Hastelloy X and Alloy 800H showed that dilations of up to almost 1% can occur at 1000/sup 0/C when carbon pickup is high. Dilation was normally observed only when the carbon increase was >1000 ..mu..g/cm/sup 2/ and ceased when the diffusing carbon reached the center of the specimen.
Date: January 1, 1981
Creator: Inouye, H. & Rittenhouse, P.L.
Partner: UNT Libraries Government Documents Department

Carburization-decarburization behavior of ferritic steels in a sodium environment. [LMFBR]

Description: The kinetics of the carburization-decarburization process of Fe-Cr-Mo ferritic steels in high-temperature flowing sodium have been studied in terms of (1) the equilibrium carbon activity-carbon concentration relationship for the steels, (2) the chromium and molybdenum content in the steel, and (3) the carbon concentration in sodium. Ferritic steels with chromium and molybdenum contents in the range 0.5 to 12 wt % and 0.5 to 2.5 wt %, respectively, were exposed to sodium at temperatures between 773 and 973 K. Carbon equilibration experiments were conducted using 0.05-mm-thick foils, and cylindrical specimens (6.5 mm in diameter) were used to establish the kinetics of carbon migration in the steels. The sodium exposure time varied from 3.6 to 25 Ms.
Date: April 1, 1978
Creator: Chopra, O.K.; Natesan, K. & Kassner, T.F.
Partner: UNT Libraries Government Documents Department

Influence of a simulated HTGR environment on the mechanical properties of a commercial Ni-Cr-Mo-Fe alloy (Hastelloy Alloy X)

Description: The influence of a simulated advanced-reactor helium environment, containing 500 ..mu..atm H/sub 2//50 ..mu..atm CH/sub 4//50 ..mu..atm CO/approx. 1 ..mu..atm H/sub 2/O, on the mechanical properties of two heats of Hastelloy Alloy X is discussed. Simultaneous exposures in air and controlled-impurity helium at temperatures in the range of 650/sup 0/ to 1000/sup 0/C for times of 3000 h or more were performed. A combination of tensile testing, Charpy V-notch impact toughness testing, and creep testing was used to study the effects of reactor helium/metal interactions on the mechanical behavior of this alloy. Carburization was identified as the primary corrosion phenomenon. Increasing exposure time and temperature were observed to increase the depth of carburization. The increase in carbon concentration in the carburized zone suppressed the additional formation of M/sub 6/C, which is observed in air-aged specimens, and resulted in the precipitation of M/sub 23/C/sub 6/, a chromium-rich carbide variant. The precipitation of M/sub 23/C/sub 6/ in the carburized zone occurred primarily along grain and twin boundaries; however, matrix precipitation was also observed, the degree of which depended on exposure temperature. Strength and impact toughness properties were found to be controlled primarily by thermal aging reactions, with only a small effect related to the carburization. Although tensile and creep ductilities were decreased as a result of carburization, substantial ductility remained. Variation was observed between the two heats, the finer-grained heat appearing to be weaker in the high-temperature creep tests and also possibly more susceptible to a loss of creep strength as a result of carburization.
Date: December 1, 1979
Creator: Li, C.C.; Johnson, W.R. & Thompson, L.D.
Partner: UNT Libraries Government Documents Department

Effects of methane concentration on the controlled-impurity helium corrosion behavior of selected HTGR structural materials

Description: The corrosion behavior of candidate structural alloys in a series of three simulated advanced gas-cooled reactor environments at 900/sup 0/C (1652/sup 0/F), with methane concentration varied, is discussed. The alloys investigated include three wrought alloys, Hastelloy X, Inconel 617, and Incoloy 800H; two cast superalloys, Rene 100 and IN 713; one centrifugally cast alloy, HK 40; and an oxide-dispersion-strengthened alloy, MA 754. Corrosion behavior was found to be strongly dependent upon both the alloy chemistry and the environment. Oxidation, carburization, and/or mixed behavior was observed depending upon the specific conditions. An equilibrium thermodynamics approach has been used to predict alloy behavior and explain observations relevant to the understanding of gas/metal interactions in reactor helium, which inherently contains small amounts of reactive impurity species. Carburization was identified as the primary corrosion phenomenon of concern, and detailed analyses were performed to determine the susceptibility and control of carburization reactions. The presence of alumina scales, containing small amounts of titanium, was found to be particularly effective in inhibiting carburization. Small variations in methane concentration have been shown to have a dramatic effect upon the oxidation potential and subsequent corrosion behavior of the alloy systems.
Date: December 1, 1979
Creator: Johnson, W.R. & Thompson, L.D.
Partner: UNT Libraries Government Documents Department

Carburization of austenitic alloys by gaseous impurities in helium

Description: The carburization behavior of Alloy 800H, Inconel Alloy 617 and Hastelloy Alloy X in helium containing various amounts of H/sub 2/, CO, CH/sub 4/, H/sub 2/O and CO/sub 2/ was studied. Corrosion tests were conducted in a temperature range from 649 to 1000/sup 0/C (1200 to 1832/sup 0/F) for exposure time up to 10,000 h. Four different helium environments, identified as A, B, C, and D, were investigated. Concentrations of gaseous impurities were 1500 ..mu..atm H/sub 2/, 450 ..mu..atm CO, 50 ..mu..atm CH/sub 4/ and 50 ..mu..atm H/sub 2/O for Environment A; 200 ..mu..atm H/sub 2/, 100 ..mu..atm CO, 20 ..mu..atm CH/sub 4/, 50 ..mu..atm H/sub 2/O and 5 ..mu..atm CO/sub 2/ for Environment B; 500 ..mu..atm H/sub 2/, 50 ..mu..atm CO, 50 ..mu..atm CH/sub 4/ and < 0.5 ..mu..atm H/sub 2/O for Environment C; and 500 ..mu..atm H/sub 2/, 50 ..mu..atm CO, 50 ..mu..atm CH/sub 4/ and 1.5 ..mu..atm H/sub 2/O for Environment D. Environments A and B were characteristic of high-oxygen potential, while C and D were characteristic of low-oxygen potential. The results showed that the carburization kinetics in low-oxygen potential environments (C and D) were significantly higher, approximately an order of magnitude higher at high temperatures, than those in high-oxygen potential environments (A and B) for all three alloys. Thermodynamic analyses indicated no significant differences in the thermodynamic carburization potential between low- and high-oxygen potential environments. It is thus believed that the enhanced carburization kinetics observed in the low-oxygen potential environments were related to kinetic effects. A qualitatively mechanistic model was proposed to explain the enhanced kinetics. The present results further suggest that controlling the oxygen potential of the service environment can be an effective means of reducing carburization of alloys.
Date: March 1, 1980
Creator: Lai, G.Y. & Johnson, W.R.
Partner: UNT Libraries Government Documents Department